Axiom Home Page Forums General Discussion Stereo Using M60 as Studio Monitors? (compared to Mackie)

Hi,

I am wondering how well the M60's are as studio monitors with an amp like the Anthem MCA-20 or Adcom 555? I produce electronic music and want speakers that are very detailed, uncoloured, and have a very flat response. These speakers are in line price wise to the Mackie 824's. Can anyone comment how they sound compared to the Mackie's? Sorry for the cross post but discovered I may get answers here that I may not in the technical forum. Thanks!

I don't create it, but I listen to electronica and the M60's are supremely detailed, uncolored, and flat. I'd bet they'd be perfect for your needs.

I want to bump this thread and ask if anyone is familiar with using Axiom bookshelves as nearfield monitors as well.

I have an older Cambridge Soundworks Ensemble sub/sat system that I've used in my editing suite and also wondered about the Mackies. Now that I own M60s and am very happy with them, I wonder if M2s or M3s have ever found their way into professional monitor applications?

I love my 60s, but I guess I have a tendency to think of monitors in ANY sort of ixing/Mastering suite to NOT be floorstanders based upon simple logistics of room size, listener proximity and the layout of most rooms with a console preventing good location opportunities.

I was a synth. aficionado back in the late80s & early 90s and used to have a pretty decent MIDI home studio.
The only thing I can think of that would not make the M60 an ideal reference monitor is that they are very sensitive to placement. If what you’re looking is a close reference monitor I would suggest the m22 instead (although I never heard them) or even the M3.

There was an ad on the main site a few years ago that stated that Aldo Nova used the Axiom M?? (can't remember the model) as his studio monitors.

Maybe a search or an email to the powers that be will bring this back - I am too lazy to search the site for it!!!!
I am sure Ken or Peter might do this - they LIKE having all the stuff!!!

I believe he was using the M22's. He needed to be shot for that outfit he was wearing though. What WAS he thinking????

boy, was THAT a subjective comment!!!! LOL

Subjective? Nah...I'm just not blind. Do you remember that get up? LOL!

Sure...you are attacking his choices......whatever they may have been!!!! LOL

No, I can't say I remember...I guess I have been reading to many of Jack and Ray's posts...I am fogetting everything!!!

Hey!.......................................I was gonna say something, but I forgot what it was.

Yeah............what he was about to say but completely forgot where he was!!!

Ummmm. OK.

"Thanks for the help guys" he replies while walking away and shaking his head...

Well, I mentioned the only thing that seemed to be close....did you search for it....fashion problems and all?

...and hey, you have been allowed to run with us long enough to realize we move on quickly!!!! So don;t take offense to us changing gears!!!

Anyone up for a BBQ and beer?

Mark...we answered the question and moved rapidly on to bad fashion.

I actually think M2i's or M22ti's would make better monitors than M60's, as you can sit nearer to the bookshelf speakers without harming the soundstage as badly.

Look at this and tell me I'm wrong...



btw...go here for some more info on him and his Axioms.

nice find!!!

...I see he simply looks like he is living the rock star thang'......I will cut him some slack (slacks?) as he is from Quebec - which is local to Canada.....

Thanks guys! It looks like there's LOTS to read there!

Some people (very few) can pull off the all leather thing...he's not one of them.

HA!!!!

The picture makes him look about 4 foot nuthin" as my dear ole' granpappy usta say!!! (Thanks for the quote Jack)

Yeah, it doesn't even look like he's a smoker. Somehow, smokers can more easily pull off the all leather look. Unfortunately, that also means their leather reeks of smoke.

Or a biker. Bikers can pull it off. He's way to clean cut for that look.

>>I actually think M2i's or M22ti's would make better monitors than M60's, as you can sit nearer to the bookshelf speakers without harming the soundstage as badly.

Yep. I used to have a pair of Rogers LS3/5A's (the BBC monitor speaker) and thought the M2s were comparable -- disclaimer again, this was without benefit of direct comparison 'cause I sold the Rogers years before buying the Axioms

Hey guys,

Thanks for your input. What would really help me is if I had

* Freq to SPL graphs of M22 and M60
* Imp to Freq graphs of M22 and M60
* Waterfall graphs of M22 and M60

How can I get these? I'm sure there must be measurements somewhere!

I've had the pleasure of hearing the Axioms on several occassions from trips up to Toronto and Montreal hi-fi shops. I'm trying to decide between the M22 or M60 speakers and possibly combine them with a HSU VTF-2 sub or an Axiom one.

My "studio" is a non traditional one. I am in a room that is narrow, quite long, and has a sloped ceiling. The room is 20 ft long. 10ft wide. and 10 ft high at the front going to 8 ft in the back. My setup is a portable one - Mac laptop with Logic with a controller. I have a futon in the middle of my room with a coffee table and with a 36" TV about 6ft in front of me. The floors are hardwood, walls are plaster with brick underneath, and no dicernable echo. My plan is to place the speakers 6ft in front and 3.5 ft apart with no toe-in initially.

Based on my listening tests, I thought the M60s were more natural sounding in the mid-bass than the M22's. The M22's sounded a bit compressed - like the difference between the M3's and M22's I suppose. These are my subjective opinions and I would welcome any constructive comments any of you may have on them.


By the way, there is a very good article on Sound on Sound magazine talking about the merits of using hi-fi speakers versus monitors to do production work. I've copied it below. Finally, I really need the frequency graphs for M22 and M60! Where can I get them?


MONITORS versus HI-FI SPEAKERS
For Project Studio Monitoring
Published in SOS June 2002
Print article Print article : Close window
Technique : Miscellaneous




Loudspeakers are traditionally designed for either monitor or hi-fi applications, but is there actually any difference? And just how suitable are hi-fi speakers for nearfield monitoring in the project studio? In part one this month, we examine measured responses.

Phil Ward

"Can I use my hi-fi speakers as nearfield monitors?" It's a question often asked of Sound On Sound, but it's hard to answer, unless you're the kind of person that's satisfied with the reply 'it depends'. To be a little more precise (but not a lot), it depends on the type of material you're recording, your aspirations for it, the specific hi-fi speakers you have (the term can cover a multitude of interpretations) and the recording environment you're working in.

Of course, at one level, you can use any old speakers as monitors, nearfield or otherwise, but whatever you use, you can guarantee one thing: the characteristics and idiosyncrasies of your chosen monitors will colour the sound of everything you record and mix. And if you've used speakers that demonstrate extremes, they may well leave the results of all your efforts sounding far from as intended when your music is played back on any other system.


Figure 1: The frequency response of the B&W DM303.


Figure 1b: The DM303 waterfall plot.
So monitoring is a vital part of the recording chain — but that doesn't answer the hi-fi speakers question. Even at the end of this two-part feature the answer is likely to be a shade of grey rather than black or white. But through a technical analysis and investigation of four speakers — two that carry the 'hi-fi' label and two the 'pro' — I'm going to try and discover a little about the typical differences between them. And perhaps that question won't then be quite so hard to answer.

The four quivering, apprehensive guinea-pig speakers are, in the 'hi-fi' corner, the B&W DM303 and Wharfedale Diamond 8.2, and, in the 'pro' corner, the Dynaudio BM5 and the KRK K-ROK. Both the B&W and the Wharfedale were launched recently, and both have been pretty well reviewed in the hi-fi press and very widely distributed. The Dynaudio and KRK have been established in the market for much longer (and indeed both have been reviewed in Sound On Sound before — see www.soundonsound.com/sos/1995_articles/jun95/krkkrok.html and www.soundonsound.com/sos/1996_articles/jun96/dynaudiobm5.html1996_articles/jun96/dynaudiobm5.html or SOS June '95 and '96 respectively). The longer-established nature of the 'pro' models perhaps reflects the less rapid turnover of new models in the 'pro' sector, and are, similarly, widely used products from well-respected manufacturers. In fact, there are some strong similarities between all four. They're all of similar physical size, and are all passive two-way systems. They all feature 6.5-inch bass/mid drivers and one-inch dome tweeters. And they all use reflex bass loading, a design technique used to increase the perceived amount of bass a speaker can produce (for more on this, see part one of my previous SOS article on loudspeakers in the October 2000 issue, or head for www.soundonsound.com/sos/oct00/articles/monitor.htm).

However, there's one significant difference between our guinea pigs — price. The 'hi-fi' speakers will set you back around half the cost of the 'pro' monitors. Perhaps this explains why the nearfield question comes up so regularly at SOS... ?

What Makes A Good Studio Monitor?

The archetypal studio nearfield monitor, Yamaha's NS10M, is well known to have (put politely) a 'characterful' tonal balance. The general consensus seems to be that it is uneven through the mid-range and too bright at the top (hence the commonly employed trick of hanging tissue paper over the tweeters to calm it down). So if the Yamaha's balance is questionable, what should we be looking for in the perceived tonal balance of a nearfield monitor?


Figure 2: The frequency response of the KRK K-ROK.


Figure 2b: The K-ROK waterfall plot.
In two words, we should be looking for the 'neutral average' — neither too bright nor too dull. If the aspirations we have for our work are that it should sound tonally acceptable on the widest range of systems out there, from hi-fi systems costing many thousands to AM radio (or its low-bit-rate MP3 equivalent), then the perceived tonal balance of our nearfield monitor, which will be used up close and probably with its back to the wall, should be as close to the 'population average' as possible. The same is probably true of a hi-fi speaker, because in balance terms, the hi-fi speaker is nothing but a monitor that's used a few stages down the line (ie. by the consumer of the music you're mixing).

A neutral tonal balance, however, is not the same thing as a flat axial frequency response — this is a common mistake. The perceived tonal balance of a speaker is the combination of the direct sound from the drivers and reflected sound from nearby surfaces, and, as speakers are directional devices (especially at high frequencies), a flat axial frequency response doesn't mean that a loudspeaker will necessarily sound that way. But we can work backwards, and predict generally how the axial response might look for different types of loudspeakers if they are to sound neutral. Firstly, a hi-fi speaker that's positioned perhaps four metres away from the listener and is mounted a little away from the wall on a floor stand should have a subtly different response shape compared to a nearfield monitor that's maybe one to two metres away and mounted on a wall. Where the nearfield should demonstrate a slightly up-shelved response at a few hundred Hertz combined with a slow roll-off at either frequency extreme, the hi-fi speaker, unless it has been specifically balanced for use against a wall, should probably be closer to flat.

Secondly, if a nearfield monitor is to be used in a small room, where strong reflections from the side walls will reach the ear within a few milliseconds, the shape of the horizontal off-axis response is vital too. Wild variations between on and off-axis responses are well-known to result in perceived tonal imbalances, so if the monitor is not to sound unnaturally coloured, its off-axis response should be as close to a gently down-tilted version of the axial response as possible. This is one very good reason why landscape-mounted nearfield monitors tend to be a bad idea
— the horizontal off-axis response from laterally adjacent drivers will almost certainly display major discontinuities through the region where the drivers' outputs overlap.

But, as I'm probably too fond of writing, there's more to a speaker than its simple frequency response, and there's a few other characteristics that a loudspeaker that aims for accuracy ought to possess. And while we'll concentrate this month on frequency-response issues, next month we'll look at power-handling and compression effects.

The Nearfield Monitor — A Brief History
The term 'nearfield monitor' was an invention of the early '80s. It just about predates the explosive rise of the home and project studio and was originally the term applied to auxiliary monitors that sat on the meterbridge in large commercial studios, and were supposed to reflect the sound of typical home audio or TV speakers.

One speaker originally defined the breed: the Auratone 5C. The Auratone was, and is, little more than a five-inch 'full-range' driver screwed into a small cube-shaped enclosure. It had little pretence to audio accuracy or wide bandwidth, and was simply intended to provide a reference for the likely sound of recordings when reproduced on an AM radio, or via a TV. So the Auratone was not really a 'nearfield' in the sense that we understand the term now, but it did set a precedent for auxiliary monitors, and prepared the ground for the second nearfield icon — the Yamaha NS10M.

The early '80s also saw the rise of freelance 'celebrity' engineers, and I suspect it was one or two of these, carrying a few items of favoured gear from studio to studio, that first introduced the NS10M to the world. As studios began to realise that equipping with favoured gear helped to attract the celebrities, NS10Ms began to pop up everywhere, taking up a position on the meterbridge next to the Auratones. The role of the NS10M, however, was not to mimic the low-fi performance of a TV speaker, but to offer a level of performance and sound that reflected that of a domestic hi-fi. In fact, I believe the Yamaha was derived from a domestic hi-fi product — which, in the context of the question asked at the start of this article, is perhaps significant. But the NS10M had something more going for it. Probably by accident, it displayed a pretty characterful tonal balance and this perhaps helped it become the nearfield benchmark, as material mixed on NS10Ms sounded 'wrong' on anything else. The balance of the NS10Ms also resulted in many a discussion about the exact brand of tissue paper that should be draped over the tweeter in order to dull the balance a little. So despite becoming the industry-standard nearfield monitor, the NS10 has always provoked derogatory mutterings about its sound and tonal balance. What's more, the niche it opened up was soon crowded by countless competitors.

We now live in different times. The huge studios, if not quite heading the way of the dinosaurs (there'll always be a role for recording spaces the size of tennis courts, and mixers that could do with a Burger King at the halfway point), have long been under threat from small-scale recording spaces and control rooms. And being very much smaller than of old, the typical control room now has little space for vast main monitors. These days, the nearfield has had a promotion. More often than not, it's now out on its own, the top dog.


Examining The Frequency Responses

The frequency-response measurement of each of our guinea-pig speakers shows scant evidence of subtle tailoring to suit different roles. The curves are primarily dominated by the particular strengths and weaknesses of the drivers used, the size and proportions of their front panels and the low-frequency roll-off shapes chosen. I say primarily dominated because, particularly in the design of the hi-fi speakers, there does tend to be a certain amount of balance-tweaking, engineered to help ensure that a speaker reviews well and sounds competitive in the retail environment. But there's certainly no obvious split here between 'hi-fi' and 'pro' in terms of frequency response.


Producer Spike Stent with his Yamaha NS10s and KRK 9000Bs at Olympic Studios, London.
Figures 1 to 4, which appear over the course of the next couple of pages, illustrate the on-axis and 30-degree off-axis frequency response of each of the four speakers. Figures 1b to 4b additionally show a 'waterfall' plot indicating how each speaker's response decays with time. The waterfall is a 3D representation of the speakers' response to a wide-bandwidth signal that stops instantaneously. The Y-axis is level in dB, the X-axis is frequency from 200Hz to 20kHz, and time runs from back to front on the Z-axis (measurement constraints limit the length of time window available as frequency falls). The waterfall plots therefore illustrate how good the speakers are at switching off, and the Z-axis plot for a notional 'perfect speaker' would be empty. Any signals within the plot occurring after zero time represent the decay of mechanical or acoustic resonances. This is output that the speaker adds to the intended signal, colouring the sound and effectively degrading the signal-to-noise ratio.

The curves were generated through a combination of direct acoustic measurement and, below 150Hz, prediction and synthesis from the measured electroacoustic parameters (see the box on measuring low frequencies at the end of this article for more on this subject). The vertical scale of each diagram shows sound pressure level in dB measured at a distance of one metre, and the curves are calibrated for a nominal 1W input into 8(omega). Each curve reveals some interesting characteristics of the speaker in question.

What Do The Graphs Tell Us?

Figure 1, the graph of the B&W DM303 on the previous page, is probably the tidiest basic frequency response of the four and, along with that of the Dynaudio BM5, has a shape that should be pretty well suited to nearfield use in a small control room. The response is characterised by an early but gentle bass roll-off and well controlled, wide dispersion — the tweeter is only 6dB or so down at 20kHz. The B&W also demonstrates a definite lump in its response between 4kHz and 8kHz, however. This will be audible, particularly as emphasis on sibilance and cymbals, and is in a critical region as far as balance perception is concerned. It will also tend to give the speaker an explicit, detailed kind of sound; I wonder if it may be an intentional part of the 'voicing' of a hi-fi product.


Figure 3: The frequency response of Wharfedale's Diamond 8.2.


Figure 3b: The waterfall plot for the Diamond 8.2.
The B&W's tidy frequency response is accompanied by a similarly good waterfall plot (see Figure 1b). There's very little to note which suggests that, apart from the enclosure panel resonance effects that all these speakers will display, the DM303 will make little contribution of its own to the sound. For a hi-fi speaker, the DM303 is a fine nearfield monitor — at least in terms of its frequency response.

Figure 2, the graph of the KRK K-ROK on the previous page, could hardly be more different. Two features dominate. First, the bass-response shape chosen is far more extended than that of the B&W, but it is bass extension at the expense of a resonant peak at 70Hz and consequently of transient behaviour. The K-ROK will play 70Hz for many milliseconds after a signal around that frequency has stopped. In a small control room, with the speakers positioned close to a wall, bass on the K-ROKs is likely to be significantly emphasised. Certainly, the added low-frequency bandwidth will mean that bass signals all but inaudible on the B&W will be heard, but its resonant nature is likely to result in bass-light mixes. The second interesting feature of the K-ROKs' response is a sharp notch at 750Hz — more on this in the following paragraph. The rest is relatively tidy, with good dispersion control up to 7kHz, although with a fast decay thereafter.

The KRK's waterfall plot, Figure 2b, is also quite a contrast to that of the B&W. The response notch at 750Hz is revealed as a strong and persistent resonance. The resonance is almost certainly the result of a mechanical mismatch between the bass/mid driver cone and its rubber surround, and may be audible as a distinctive mid-range character — one that we'd all be likely to try to suppress during recording or mixing. There's also more general 'hash' in the K-ROK's waterfall, suggesting a generally higher 'noise floor' and less ability to resolve low-level detail. In terms of frequency response, it's hard to see where the 'professional' K-ROK is a better nearfield monitor than the 'hi-fi' DM303.


Figure 4: The frequency response of the Dynaudio BM5.


Figure 4b: The BM5's waterfall plot.
Figure 3 (above), the plot of the Wharfedale Diamond 8.2, demonstrates another neat frequency response. However, an upper-bass to lower-mid emphasis, while not making it a bad speaker, perhaps rules out the 8.2 for monitoring duties if it likely to be positioned close to a rear wall. Speakers demonstrate an effect analogous to the proximity effect with microphones. If a speaker is positioned close to a solid boundary (for example the wall behind), its natural tendency towards omnidirectional dispersion at low frequencies and narrow dispersion at higher frequencies will mean that only lower frequencies will be reflected forward and add to the perceived output. So a speaker such as the Wharfedale that already has an emphasis below a few hundred Hertz will begin to sound tonally unbalanced. And a neutral perceived tonal balance is one of our vital criteria for a monitor. The Wharfedale also has a discontinuity in its off-axis response at 12kHz that suggests a not entirely well-behaved tweeter. Generally the 8.2's down-tilted balance would probably result in over-bright mixes.

The Wharfedale's waterfall plot has no obvious dominant problems, but is still less good than the exemplary B&W. There's evidence of some cone/surround mismatch problems around 1kHz but the energy decays quickly, and, although it's likely to add some character, it's relatively benign.

The final frequency response curve, Figure 4, is that of the Dynaudio BM5, and again there's a couple of features to note (see below). Firstly, I've included two 30-degree off-axis curves to reflect the fact that the BM5's tweeter is not placed symmetrically in the cabinet. The differences between the two off-axis curves are perhaps not as significant as they might look, as the mechanism of off-axis measurement (rotation of the speaker on a turntable) moves the tweeter either closer to or further from the microphone in addition to changing its angle. The sharp dip in the response at just over 4kHz is not a measurement artifact, however, and reveals that the integration of woofer and tweeter is less good on one side of the speaker. BM5s should be used with their tweeters facing inwards, but they are then at risk of coloration effects from tonally diverse side-wall reflections. Another feature of the BM5 is the sharp lump and dip in response between 4kHz and 5kHz. This feature, one that I've seen demonstrated by other Dynaudio bass/mid drivers, is, I suspect, a consequence of their unusual external voice-coil construction.

The response discontinuity shows up on Figure 4b, the waterfall plot of the BM5, but in contrast to the K-ROK's resonance, the energy decays very quickly, so it's likely to be reasonably benign — although not completely inaudible. The BM5 waterfall also shows some evidence of a driver problem in the 1kHz region (maybe you're getting the message that speaker designers face a continual struggle against cone/surround resonance in the 1kHz region), and this could add some audible character.

Making Low-Frequency Measurements
It is notoriously difficult to measure the low-frequency response of a loudspeaker with any accuracy. With wavelengths measured in many metres and room effects dominating, the chances of a measurement microphone capturing any truly reliable data are remote — even in an anechoic chamber. However, the electroacoustic parameters of a speaker that define its low-frequency characteristics (box volume, driver compliance, magnetic flux density, and so on) can be derived from its input impedance, then analysed in terms of classical analogue filter theory, and finally turned into a frequency-response prediction. With care in measurement and analysis, predictions can be accurate to within 0.5dB, which is far more accurate and reliable than readings taken in all but the largest anechoic chambers. The low-frequency sections of the response curves published here were generated via such a technique and then spliced at 150Hz onto directly measured frequency-response data. Although the splicing technique doesn't produce definitively accurate results, in the case of similarly dimensioned speakers like these four, it is accurate enough for valid comparison.

Conclusions

So, in terms of frequency response measurement, there's no obvious split between 'pro' and 'hi-fi' among these four speakers. In fact, if anything, they fall into two rather different groups, with the B&W and Dynaudio offering a balance appropriate for nearfield use in small rooms (coincidentally, the Dynaudio and B&W have low-frequency response shapes so similar they could almost be a pair), while the Wharfedale and KRK offer something more suited to listening at a greater distance in larger rooms. The B&W is also the best in terms of resonant behaviour.

Next month, I'll be giving the guinea pigs a harder time, by looking at some of the power-handling and compression issues that might sort the 'pro' from the 'hi-fi'. So while 'hi-fi', in the shape of the B&W, looks to have a lead at this stage, don't count any chickens just yet!
Published in SOS June 2002

Here is part 2 of that SOS article:

MONITORS versus HI-FI SPEAKERS
For Project Studio Monitoring
Published in SOS July 2002
Print article Print article : Close window
Technique : Theory + Technical


We conclude our two-part examination into whether the traditional distinction between studio monitors and hi-fI speakers is justified. This month, the power-handling and compression characteristics of our four test monitors come under scrutiny...

Phil Ward

The first instalment of our investigation into the differences between nearfield hi-fi speakers and pro monitors ended last month with the conclusion that, in terms of frequency response, there was little obvious distinction between two entry-level products from each market sector (see last month's SOS or www.soundonsound.com/sos/Jun02/articles/monitors.asp). The 'hi-fi' B&W DM303 and 'pro' Dynaudio BM5 demonstrated response characteristics that appear pretty well balanced for nearfield duties, while the 'pro' KRK K-ROK and 'hi-fi' Wharfedale Diamond 8.2 appeared less well suited. If speaker engineers were asked to look at the response curves of all four with no knowledge of the identity or intended application of the speakers, I'm pretty sure they would be unable to sort the 'hi-fi' from the 'pro' other than by guesswork.

But of course frequency-response issues are but one aspect of speaker performance, and in this second instalment of the investigation, I'm going to look at some power-handling and compression characteristics of the four speakers -- a
Figures 1 and 1a: graphs of the thermal
performance (above left) and reflex-port
compression/distortion effects (right) for
the B&W DM303.
gain with the aim of investigating the potential for the significantly less expensive hi-fi speakers to be used as nearfield monitors. If you're unfamiliar with what these terms mean with regard to speakers, don't worry too much, as I'll explain as I go along.

If we were to speculate on the power-handling characteristics that we'd want to be better on a nearfield monitor than a hi-fi speaker we'd probably focus on compression and distortion effects. We'd expect that both hi-fi and pro speakers would have good long-term reliability, but as nearfield monitors are probably more likely to be used for critical listening at relatively high levels over extended periods, we'd want them to be more accurate and consistent in that scenario.

Compression effects caused by speakers are likely to have a direct influence on how we record and mix. We all use audio compression in recording, but a monitor that adds its own level- and time-dependent dynamic and tonal aberrations is not going to be much use as a consistent reference. However, compression issues are very rarely raised by speaker manufacturers in promotional material. This is partly because a loudspeaker designed to be completely free of such effects would be significantly more expensive to manufacture than one that isn't, and partly because compression is a kind of 'stealth' distortion that very much influences our opinions about sound (and therefore decisions about how we record and mix), even though we're often not specifically aware of it happening.

Since a speaker with a higher quoted power handling might be expected to perform better in terms of compression, power handling is the one oft-quoted specification that might give us an idea how each speaker is likely to behave at high levels. However, there's probably just as much misunderstanding and confusion surrounding power handling as most other speaker specifications, so before getting onto the performance of our four potential monitors, it's probably useful to describe a little of what happens to power in a speaker, and where power-handling limits actually come from.

What Is Power Handling?

In very simple terms, you find out the power handling of a given speaker by turning up the volume till the speaker breaks. But just as frequency-response measurements can be misleading unless you know where the measurements were taken from, and with which mic, so it is with power handling. Power handling has also become a 'competitive' specification that suffers inflation from market pressures -- and manufacturers, knowing the spec is hard to pin down, often play safe and pick a nice big round number. The way power handling is specified for our four guinea-pig speakers demonstrates this nicely (see below). Each figure is specified differently and, moreover, in the context of the highly complex mechanisms at play, means very little. In fact, the specs shown below are all pretty meaningless. For example, what exactly is the spectral balance of the "unclipped programme" t
Figures 2 and 2a: graphs of the thermal
performance (above left) and reflex-port
compression/distortion effects (right) for
the KRK K-ROK.
hat B&W refer to? Or how do we define the 100W of the still-vaguer "programme" that the Wharfedale will stand? Are we talking thrash metal or a recorder quintet? And for how long? Going one stage further, KRK simply specify a maximum amplifier power. Does this mean the speaker can never be damaged by an amplifier of less than 100W? I don't think so... Only Dynaudio, in referring to a "long-term power" for the speaker while at the same time recommending an amplifier rating, hint at the true complexity of the issue -- and even then, the spec has lost all real value through simplification.

Explaining the "true complexity" of the power-handling issue and how it ties in with compression effects isn't easy, but if you have a grasp of electrical knowledge and basic physics, you shouldn't find it too heavy going, and my article on understanding how monitors work from SOS October 2000 should also help (it can be found on the SOS web site at: www.soundonsound.com/sos/oct00/articles/monitor.htm). Essentially, any loudspeaker comprising moving-coil driver units in a box will exhibit two distinct mechanisms that limit its power handling, and the limit that's reached first will be dependent on the frequency balance of the programme material, and perhaps the length of time it's been playing.

The first mechanism is thermal. The laws of physics are not kind to loudspeakers -- typically, less than one percent of the electrical energy thrown at them is converted into acoustic energy. So around 99 percent of the power an amplifier pumps into your monitors does nothing but heat things up. As the internal components of the drivers warm, thermal stresses begin to build and, if the heating continues unchecked, things will eventually smell, smoulder, break, melt or even burst into flames.

Testing to establish the point at which a driver will fail thermally, and therefore the thermal power handling, is pretty straightforward if the test signal is a nice, consistent one with a defined spectral balance, such as pink noise, or even noise 'profiled' to resemble the spectral balance of some average, imagined music (and believe it or not, there is such a thing intended to do just that -- it's called IEC 268 noise). But real music is, in test-signal terms, as far from predictable as it's possible to get. The spectral balance varies continuously, as does the instantaneous level.

So, because the variable nature of a speaker's input impedance means that power at different frequencies will have different heating effects, you can perhaps see that specifying a 'thermal power handling' that's relevant to real programme material is all but impossible. Or, to put that another way, if you're a manufacturer, you're pretty much free to think of a 'music programme' number, double it if you wish, and still remain pretty confident that nobody out there will really be able to prove you wrong. I mean, what if the music programme you decide to base your spec on is John Cage's '4 minutes 33 seconds'? What's the 'music programme' power handling if the music programme is silence ("for piano or any instrument" as Cage specifies with delicious irony)?

The second power-handling limit mechanism is predominantly mechanical, with some acoustics and fluid dynamics thrown in for good measure. Those same laws of physics that stop a moving-coil speaker from efficiently converting Volts
SPEAKER POWER HANDLING
(MANUFACTURER'S SPECIFICATION)
B&W DM303 "Maximum amplifier power 100W, 100W unclipped programme"
KRK K-ROK "100W maximum amplifier power"
Wharfedale Diamond 8.2 "100W Programme"
Dynaudio BM5 "Long-term amplifier power 100W, recommended amplifier power 200W"
into noise require that the volume of air a speaker has to move to generate a specific sound level increases as frequency falls (one major reason why woofers are big and tweeters small).

Now, it's pretty easy to calculate how much air a speaker can move -- you just multiply the area of the cone by its maximum travel. But unfortunately for loudspeaker designers, a power-handling trade-off applies here. You can have any two of the following: a speaker with good bass extension, a speaker that goes very loud, or a speaker with a relatively small bass driver. What you can't have is all three at the same time, and some pretty nasty things can happen if you try. The first problem is that well before a bass driver hits its end stops, it'll begin to produce high levels of harmonic distortion. Play a bass guitar bottom E through your monitors (but don't blame me if you damage them!) and you'll hear the tone start to get dirty as the level rises. Its pitch may even start to become more hazy as high-order harmonic distortions begin to dominate the fundamental frequency of the note.

Problems two and three are the exclusive of reflex-loaded speakers (ie. those with a port to increase the perceived amount of bass they can produce -- there's more on this in that October 2000 SOS article). These days, however, it's getting hard to find any loudspeakers that don't have such ports! Problem two is that the necessarily tiny reflex ports used in small speakers behave in a far-from-linear fashion at anything but low volume levels. There's only so much air that can be pumped through a port before it becomes noisy and a significant source of distortion.

Problem three is related; the non-linearity of the port at high levels can begin to cause the bass driver to oscillate away from its nominal zero position. Given that one end of the port terminates in a small volume of air inside a mostly enclosed box, while the other terminates in the outside world at atmospheric pressure, it's hardly surprising that it doesn't behave the same way for air moving in as it does for air moving out. Once the driver's zero position begins to drift, if it has any significant non-linearity inherent in its magnet or suspension system, the drift may be all that's needed to 'lock' the cone (potentially terminally), aga
Figures 3 and 3a: graphs of the thermal
performance (above left) and reflex-port
compression/distortion effects (right) for
the Wharfedale Diamond 8.2.SPEAKER
TEMPERATURE VOICE-COIL
SENSITIVITY DROP
inst either of its end-stops.

Maybe you can now begin to see how truly uninformative the average manufacturer's programme material power-handling spec is. If you need convincing further, I should also point out that that it's very difficult to accurately to measure the true power of a programme material signal anyway. And, of course, along with the completely unpredictable nature of musical material, you should also consider that the playback systyem you use to hear the programme material will respond in completely different ways at different frequencies!

About Loudspeaker Compression

OK, so that's how the power-handling limits are reached (and how power-handling specs can be 'invented'), but what has all that got to do with compression? Well, long before the failure limits are reached, the very same thermal and mechanical mechanisms that will eventually send a speaker to the service department are responsible for compression and distortion effects. Let's look at the thermal side again first.

As loudspeaker driver voice-coils warm, their electrical resistance increases. Primarily, this increase in electrical resistance reduces the sensitivity of the driver, by making it harder for the amplifier to push current into it. There are attack and release times associated with the mechanism too (defined by the driver's thermal time constant), just like the dynamic-range compressors we know and love. However, there are also two more subtle thermal-compression effects that don't so much affect overall volume level as they do frequency response. Firstly, a speaker's low-frequency roll-off is defined by a number of electrical and acoustic parameters, an important one of which is driver voice-coil resistance. So again, as volume increases, the low-frequency performance changes. Similarly, in passive speakers, the frequency response of the crossover filters that divide the audio spectrum between drivers is very sensitive to voice-coil resistance. So there's another mechanism that potentially changes the frequency response and the sound of a speaker as the volume level changes. I've already touched on how the dynamics of reflex ports at low frequencies can alter the overall response shape. But while these effects constitute one of the power-handling limits, their effects can begin to influence the sound of a speaker, even at relatively low volume levels. And in a monitoring situation, anything that dynamically influences the sound of the speaker without us being aware of it is an effect that we're likely (erroneously) to take into account when we record or mix. Have you ever noticed mixes that work at one volume level yet seem nothing like as good when you change the volume? It's not all down to your monitors -- your ears play cunning tricks too -- but your choice of speaker could well be part of the problem.

Tests & Measurements

Now, having got through the theory, on to the practical. If we take our four guinea-pig speakers and carry out a few measurements designed to reveal how well they behave in terms of some of these compression mechanisms, will we see any obvious differentiation between 'pro' and 'hi-fi' types? The first simple thing to check is the voltage sensitivity of each speaker. Sensitivity is a measure of a speaker's output volume level for every volt of input and it's potentially important in the context of compression effects because, all things being equal, for a given volume level, a higher sensitivity speaker should be less pr
Figures 4 and 4a: graphs of the thermal
performance (above left) and reflex-port
compression/distortion effects (right) for
the Dynaudio BM5.Thanks to Phil Knight
for the measurements and help with analysis.
one to compression -- less power needed means less dissipated as heat. However, as it turns out, there's not a great deal to choose between them. The least sensitive speaker of the four is the Wharfedale, with an 86dB output level (measured at a distance of one metre) for an input of 2.83V (2.83 Volts is nominally one Watt into an 8(omega) load). The most sensitive is the KRK, which produces 88.75dB of output under the same conditions (a surprising 3.25dB shy of the claimed 92dB). The B&W and Dynaudio sit in-between, at 88dB and 87.25dB respectively. So with all four speakers within 1.5dB of the group average, we don't have to worry too much about differences in sensitivity distorting comparisons of compression effects over comparatively large changes in level. Nevertheless, it's worth bearing in mind that the higher the baseline sensitivity, the louder the speaker will play before compression hits.

The first comparison of compression effects on the four speakers was a simple measurement of bass/mid driver voice-coil temperature rise with a noise signal of increasing level. The change in voice-coil resistance equates directly with a reduction in driver sensitivity -- ie. compression by any other name. This is quite a tough test for a small speaker. The final input level of 20V RMS is pretty loud, but it was important to drive the speakers hard in order to reveal any differences without any ambiguity.

The directly measured voice-coil temperature rise, calculated voice-coil resistance rise (from knowledge of the voice-coil winding material and its temperature coefficient of resistance), and calculated sensitivity drop over a 20dB increase in input level (from 2 to 20 Volts of IEC 268 noise) for each speaker are as shown in the panel above.

There are three points of interest here. Firstly, the KRK and Wharfedale are very similar in behaviour, suggesting that they have bass/mid driver voice-coils of similar construction -- so there's little differentiation between 'hi-fi' and 'pro' there. Secondly, the B&W DM303 shows fundamentally higher levels of thermal compression. This is most likely because the B&W has a voice-coil construction based on a polyamide former rather than the more usual aluminium. A polyamide former does have the significant advantages of being light (in terms of weight) and non-conductive, and it may well be that the use of this former significantly contributes to the B&W's exceptional frequency-response performance -- but it clearly gets hot quickly. Polyamide simply disperses heat less effectively than aluminium. Lastly, the Dynaudio suffers the least thermal compression. This is an expected result, as its voice-coil construction is very different and features a significantly more massive aluminium component that can dissipate more heat.

It's not just overall sensitivity that suffers when a voice-coil warms. A speaker's low-frequency alignment will change too, and the severity of the change will depend not only on the level of heating but the sensitivity of a specific alignment to variation in voice-coil resistance. Figures 1 to 4, shown throughout this article, display the mathematically modelled base-line low-frequency performance of each speaker, with red overlays generated by the same mathematical model with raised voice-coil resistance. The values for voice-coil temperature rise, and therefore resistance rise, were taken from the same IEC 268 noise test data, but not for the full 20V. These temperature rises correspond to 10V input.

There's actually not a great deal of difference between the way each speaker behaves in this respect -- or at least there's nothing that surprises in the context of what we already know about each one's ability to disperse heat. The B&W again suffers the most, changing from a well-judged low-frequency alignment to one with a mild 1.5dB peak at 100Hz. The KRK gets a little more resonant and loses some extension, as does the Wharfedale. The Dynaudio is again the least affected, reflecting its voice-coil's better ability to disperse heat. While these changes in response generally look pretty subtle, remember that at these frequencies they represent the speakers becoming more resonant.

Talking of resonant, the last set of measurements aimed at sorting the men from the boys looks at reflex-port compression and distortion. Figures 1a to 4a show the output of a microphone (a B&K omni measurement mic) placed directly at the port mouth of all four speakers while the speaker is driven with a sine wave at its port-tuning frequency. Using a close mic and driving the speaker at its port-tuning frequency means that the bass driver itself makes negligible contribution to the measured signal. I carried out the test for each speaker at two levels, one 18dB higher than the other (2V and 16V), but the higher levels (the red ove
RISE RESISTANCE RISE (COMPRESSION)
B&W DM303 195°C 176 percent 4.9dB
KRK K-ROK 125°C 149 percent 3.5dB
Wharfedale Diamond 8.2 120°C 147 percent 3.3dB
Dynaudio BM5 100°C 139 percent 2.9dB
rlays) in graphs 1a to 4a have been lowered by the same 18dB. If the speakers showed a complete lack of port compression, or noise and distortion increase, the two curves would overlay exactly.

The first thing to note is just how much harmonic distortion a reflex port generates, even at low levels, and even when extravagantly flared and dimpled like the B&W's (such design features are supposed to minimise the effects of the port). Harmonics all the way up to 12th-order or higher are easily identifiable. The second thing to notice is that there's significant wide-band noise between the distortion peaks -- this is the audible chuffing that ports are prone to produce. The third point of note is that the B&W and Dynaudio ports get noisier as they work harder, more so than those of the KRK and Wharfedale -- the base-line noise levels between the peaks increase more markedly. This is probably because they are tuned lower in smaller cabinets and their ports are necessarily of a smaller diameter. Compression at the port-tuning frequency (the lowest peak) can be seen on these curves -- although the result here will incorporate some thermal element that is hard to remove from the mix. The Wharfedale comes off worst in this respect, showing a 4.3dB loss, while the KRK is top dog, with a loss of only 1.8dB. The K-ROK's significantly higher tuning frequency probably helps -- although, harking back to the frequency measurements, the high-tuning frequency also results in a resonant bass characteristic.

Conclusions

So have any of these two sets of measurements revealed a fundamental difference between 'pro' and 'hi-fi' speaker types? Well, the 'pro' Dynaudio, thanks probably to its voice-coil construction, is best suited to being driven hard, and it has a well-controlled and appropriately balanced frequency response. The 'pro' KRK, through its higher sensitivity and reasonable compression performance, is also more suited to operation at high levels than either the B&W or the Wharfedale. So maybe there's a glimpse of a distinction here. But then the KRK is, in my opinion, let down by the questionable frequency-response characteristics I noted last month. The Wharfedale is pretty similar to the KRK in terms of its thermal-compression performance, but loses out through being around 3dB less sensitive. Its frequency response isn't really the stuff of a nearfield monitor either. Lastly, the B&W is not so good at elevated levels, but its exceptional frequency response performance still argues pretty strongly in its favour. In truth, there are a range of abilities across the four different designs, and it'd be a brave man to say that any group of two is obviously inappropriate.

If pressed to rank the four speakers for nearfield duties in, say, a small project studio handling a wide variety of material, I'd go for the Dynaudio first -- if I had the cash. But if I knew that really high-level monitoring was going to be a rare occurrence, I'd plump for a hi-fi speaker, the B&W, on the grounds of its response accuracy -- and I'd maybe put my savings towards a microphone. In the right environment, with the right type of material, any of these four speakers could be used successfully -- countless wonderful recordings have been made using monitors worse than anything here. So, can you use hi-fi speakers as nearfield monitors? Well, as I wrote at the start of this article, it depends...
Published in SOS July 2002

Sound On Sound, Media House, Trafalgar Way, Bar Hill, Cambridge CB3 8SQ, UK.
Email: sos@soundonsound.com | Telephone: +44 (0)1954 789888 | Fax: +44 (0)1954 789895

Here's some info on the M22ti...

M22ti graph

SP, thanks for including the Sound on Sound articles, which were very interesting. Much of the information which you're interested in is available for the M2 and M22 in the SoundStage reviews with included lab measurements from the NRC. Unfortunately, the same isn't available for the M60, but at your operating distance it appears that the M2 or M22 might be more suitable.

... and here's the same on the M80. Couldn't find M60 measurements.

Link to M80 graphs

If you want to see the corresponding reviews just do a search on this page :

List of audio reviews

What about high sound pressure levels? I plan on high volume monitoring. Do you think the M22's will hold up? I'm really hoping someone will post graphs for the M60. I'm surprised Axiom doesn't have anything they can publish.

I own a pair of M22s, and I am certain that they'd be able to blow your ears off when used as nearfield monitors. They can pretty much destroy my ears from 9 feet away.

He could be the fashion impaired son of Cat Woman.

Hi Studioproject,

Thanks for posting the articles. Axiom does have curves from the NRC as well as data from our lab at Axiom, but we do not publish them, because most consumers misinterpret curves. Indeed, even the Soundstage measurements at the National Research Council do not include the complete "family" of on-axis and off-axis curves. You really need to look at all of these to make an informed interpretation as to what the tonal balance of the speaker will be in most average rooms. I'd also comment that the Soundstage curves of the M80ti are no longer relevant.

As former editor of Sound&Vision in Canada for many years, we did all our speaker tests double-blind, following the testing protocol of anechoic measurements established by Dr. Floyd Toole, a scientist and pyscho-acoustician (past president of the Audio Engineering Society world-wide). I used to run a compression curve along with our test reports of speakers, but readers did not understand it so I removed it.

I was part of a listening panel for some sessions commissioned by CBC (the national radiio&TV network in Canada) to choose new monitoring speakers for near-field purposes and in other applications. The listening panel included recording engineers, CBC music producers, and some consumer magazine editors like myself, who had long experience with double-blind tests. Some of the highly regarded pro monitors did very poorly (including a very expensive Urei) in both measurements and listening tests.

I can tell you that the power handling of the M22ti's is generally excellent. I can't comment on the Dynaudio, Mackie, etc. because I've not been part of any controlled listening tests of those brands. Historically, British and European speakers have not had particularly good power handling compared to some Canadian and American domestic brands.

Your comments on the Yamaha NS10 were amusing. I recall going into a studio in Toronto, and seeing a pair with Kleenex tissues taped to the tweeters. The NS10 was sold in Canada as a consumer product and in tests we did, it wasn't very accurate. If memory serves, a Paradigm mini-monitor (I think it was the Paradigm 3se mini; I still have a pair) outscored it by a large margin. I recall asking the engineer why on earth he was using the NS10 as a monitor.

Finally, I do know of several M3ti's and M22s have been sold to recording studios as nearfield monitors, including Mapleshade Records.

Regards,

Hi Alan,

Thanks for your feedback. Can you at least tell me how the M60's would fare as studio monitors? In listening tests I did in Toronto, I felt the M60's sounded more neutral and open. The M22's felt compressed at the mid-bass. I noted from the Impedance curves that the port resonance is somewhere around 50hz - don't know if this had an interaction in the listening room. The amp was a Rotel and the CD Player was a Denon I believe. I also remember the M60s were just as easy to drive as the M22's

Any comments and opinions you can make about the sound characteristics of the M60 compared to the M22's you can make I would really appreciate it.

Hi,

The timbral balance of the Axiom M22ti and M60 in the midrange and highs is extremely similar (likewise the current M80ti) so much so than in immediate comparisons, conducted with a subwoofer (not at extremely high SPLs) and at listening levels of about 85 dB SPL with occasional peaks to 95 dB or so, the two speakers are virtually identical.

In stereo, without a sub, the M22ti has limited bass, usable to about 40 Hz. And of course it won't have the same power handling as the M60. But in my view it gives up nothing in terms of transparency and timbral neutrality to the M60 or M80.

With the qualifier that Axiom does not design speakers intended for the pro market, I think the M60 would make an excellent monitor. If anything, they'll be easier to drive than the M22ti's. As to compression in the mid-bass with the M22s, being a compact speaker with fewer and smaller drivers than the M60s, that would not surprise me. But compression is a fact of life in any compact speaker driven to high levels. I think the M22s are less susceptible than many others because of the dual woofers.

Re Bridgman's comments, the M2i has far more midrange and upper mid clarity and detail than the fabled Rogers LS3-5A, which I owned for many years. The Rogers, in their time, were certainly a very nice and reasonably accurate speaker, but they had a kind of swayback dip through the midrange, which made them sound quite distant on vocals and choral works. They also had terrible power handling; indeed the Kef T27 tweeter used to change shape at high power levels--it actually began to melt-- which radically altered the dispersion and high-frequency response. When it cooled down, its performance would improve.

By the way, in general I've found B&W compact speakers to be somewhat muddy and colored through the midband, not at all neutral. That is not true of the 700 series, which seem to be quite good. I've not kept up on current Wharfedale models. In years past (pre-1996) they fared rather poorly in our NRC tests.

Regards,

Hi Alan,

Thanks for your opinions. They are very useful. When you mention subwoofer, do you mean the Axiom EP500 and EP600's? I am really interested in knowing how well the EP500 performs especially in terms of neutrality and detail. Can you comment on this?

Studioproject, below is the graph of an M60 with an EP500. The EP600 would add another 4 Hz to the low end response going flat down to 16Hz. This is an excellent combination for studio use if you can live with the size of the M60s. If the size is just too large then I would suggest the M22 instead with either an EP500 or even an EP600. A subwoofer cable of reproducing the very low frequencies of the EP500 and EP600 will ensure that you know what is going on way down there in your final recording.



The distinction between pro and hi-fi speakers for studio use has really nothing to do with performance. The usual difference is the pro studio speakers tend to have built in amplifiers for ease of connection to the board. The key to proper monitors is mainly linearity. Any colouration in the speaker will affect the mix in a detrimental fashion. Certainly the items mentioned in the article you posted re compression are also factors but there is no reason to think that compression is any less likely to occur in a pro speaker versus a hi-fi speaker. It really comes down to good speakers versus bad ones no matter their classification. Coincidently enough I measured some KRKs when we were setting up one of Aldo’s studios and they were appalling. The colouration was so bad that they were hard to listen to; this would certainly make for some poor end results in the recording. Hope all this helps you out.

WOW! That looks very very good. I'm very impressed with the M60 graph. Thanks for this information. Question, how did you wire it? Did you connect the sub to a receiver sub-out or did you send the speaker outs from the amp to the sub then let the sub do the crossover to the speakers?

Ian actually posted! First time I've seen it since I've been on the boards.

Also, that graph looks incredible. Man, I want an EP500...

Studioproject; thanks for the compliment; our goal with the whole Axiom line is neutrality. This sub was wired with an XLR connector from the pre-amp to the sub and the sub x-over set to 60Hz. You could use the RCA or high level into the sub and it would work the same. The problem with a receiver sub out is that it tends to shut off in the stereo mode. This is actually a bug in the Cirrus chip but that is the chip the majority of receivers have.

Out of curiosity, Ian, can you post a graph of the current M50s? I've never seen one of those. BTW, welcome back!

kcarlile, it is great to be back. They let me out of the lab every once and awhile. Below is the M50 graph.

Interesting... a little more uneven, and a slight roll off on the high end. Is that an effect of the crossover? I have a hard time understanding why it might be related to the "missing" midrange driver. Guess I should cross the sub a little higher, too...

Thanks, Ian!

I would like to see a more recent gragh of the M80s if possible.

Oh,
Let me say put in my two cents worth about cat womans son...maybe he could be james bond on a special mission. Heck, I bet his sisters tease him about that one.

huh??

ah...he's referring to the dude in the black leather outfit on page 1.

Had me wondering for a minute as well. Our threads weave in and out of subjects so much!

ooooooohh! i see, i musta missed that one. damn, no man should EVER wear an outfit like that. i dont think even freddie mercury rocked that getup.