Axiom Home Page Forums General Discussion Technical Questions Any science behind claim swfrs reducing loads on mains?

I am curious to know if there are any frequency curves or other data that support the anecdotal claim often heard that using a powered subwoofer to handle bass "frees up" both the amp/receiver and the mains allowing better power, more dynamic headroom, and overall improved performance for receivers and mains.

Anyone know of such tests? Or does anyone (Alan/Ian?) know how one could suggest that the NRC undertake such tests? I'd love to know if you can see scientifically registered differences in speaker and/or amp/receiver performance when a powered subwoofer handles the low-bass load.

Maybe we could end up with some NRC tests like these documenting the situation. It's hard to determine in any home environment, but in a test chamber, you could test the mains with the sub receiving bass (with the sub volume turned up regular or down to nothing, depending on what you want to see), then compare results with the performance of mains that are handling the bass themselves. Seems this would put some facts behind the oft-repeated claim that for music listening, we can enhance the performance of our mains with a sub. (This is strictly a speaker performance question, not a thread questioning subwoofers.)

I know I'd like especially to see how the floor-standers benefit, if at all, from this arrangement.

And while we're at it, can anyone at Axiom share with us the frequency response curves for M60Tis? We all assume they resemble the M80 curves posted at the NRC site, but that's pretty old data and regardless, I'd like to see the M60 results. Surely Axiom has something, no?

Anyone have thoughts on this or data about subwoofers "freeing" mains?

Birdman

In reply to:

---

"frees up" both the amp/receiver and the mains allowing better power, more dynamic headroom, and overall improved performance for receivers and mains....see scientifically registered differences in speaker and/or amp/receiver performance

---

An inherent problem here is defining 'performance' and subsequently any effect on sound being perceived as 'better'.

With tower speakers set to 'small' supposedly relieving the amplifier of having the towers reproduce the low end, what logically would this accomplish?
The amp would not have to supply as much power to the tower itself?
Most likely.
But if your amp/receiver is capable of properly driving the system then what does this matter?
As has been discussed in the past, more power only means a marginal increase in SPL anyway.

As for the dynamics part, that would be interesting to see, however i personally doubt one would see any significant change in the tower response beyond the loss of its lower end frequencies on those NRC graphs UNLESS the loss of the lower end sound waves from the tower has an effect on the midrange and upper frequency sound waves which would normally interact as they are produced from near source points (the tweeter, midrange drive and lower woofer).

I would also like to see NRC measurements on the M60s if they exist. Alan must know the answer to that one.

Hi austinbirdman & chesseroo,

Some Axiom folks were at the NRC yesterday, I believe, and there may have been time to run some curves with grilles on and off (this relates to a thread on how loudspeaker frequency response is affected by leaving grilles in place). I did ask for that, and mentioned a couple of models, including the M22ti and M60ti but I'm not aware just yet which curves were run.

In any case, the answer to your question--the long version--will have to wait, because I'm just getting ready to leave for Las Vegas and the CES, as is Ian Colquhoun and several other Axiomites.

The short answer is this: it all relates to loudspeaker distortion as the woofers' voice coils are forced by loud signals to move farther out of the magnetic gap. It's a motor, remember, so when a woofer is producing substantial bass frequencies (without subwoofer assistance), its excursion--the amount of voice coil travel back and forth from its position of rest--becomes significant. In order to remain linear, you want the woofer's voice coil to remain in the portion of the speaker magnet's field where the field is linear, i.e. of equal strength. Now, as a loud, low-frequency signal forces the voice coil further "out of the gap," the cone's performance becomes non-linear, so it doesn't exactly reproduce the audio signal it is receiving. This is measured as Total Harmonic Distortion (THD), and if you scroll down and look at the NRC curves for THD&Noise at various sound levels, you'll note that with all speakers, the curve begins to climb as the frequencies get lower (and louder). On many smaller speakers, the NRC test signal is limited to 90 dB SPL, because if you try to measure the speaker at 95 dB SPL, the distortion will climb to very high levels--10% or greater. We hear this as a kind of fat, bloated bass sound (some enthusiasts even grow to like it!) and an increasing "edgy" quality as distortion climbs when SPL levels get really high.

Large floorstanding speakers will generally have much lower overall measured THD levels in the bass, typically 1% or less, than bookshelf systems because they usually have larger--and more--woofers, until you raise the SPL levels to 95 dB and much higher.

When you set your bass management to Small for the main speakers, and run a subwoofer, deep bass to the main speakers will be reduced, the woofer voice coil excursion becomes less, distortion falls, and they sound much cleaner. The sub, with a big driver and enclosure and its own amp, is better equipped to reproduce the deepest bass at lower THD levels. That way, you keep the main speakers' woofers more linear with much less THD.

Again, with smaller satellites, this is very beneficial. The sat's small woofers can operate within their ideal range and keep THD at audibly insignificant levels. It would be interesting to measure the differences and perhaps Axiom will have time to do so in the future. But loudspeaker distortion is well documented, and audible, especially with smaller bookshelf designs, and running a sub will keep the satellites THD at lower levels than would otherwise be the case.

Ian Colquhoun will have much more to say about this, as will Peter, one of our engineers. I've tried to simplify this but other factors come into play as well.

Regards,

And you said the long version would have to wait. Thanks for the explanation, Alan.

Ha, ha. And here's something I'm going to ponder on the plane, something that no-one ever talks about. Doppler distortion to other frequencies caused by the woofer cone's movement reproducing low bass frequencies. In and out, in and out. . .I'll raise this question with Ian C and some speaker engineers in Las Vegas. Hmmmm. . .

Regards,

i looked at those measurements, inersting, but a couple of them i dont understand, like the THD for one. Have fun at CES. (i know i would!)

That is a great explanation Alan which only brings more thoughts to the forefront:

1) If distortion occurs at levels >95dB (or another relatively high value) that effects the overall THD for towers, then the point of using a subwoofer as the substitution for the low end tower bass is really only applicable at higher volumes

2) If you take the idea that a subwoofer will lessen the audible distortion b/c is it better suited to reproducing this low frequency range (unless one prefers to hear bloated bass), then why bother making towers at all? Why not simply make only satellites with subwoofer additions?
I think part of this is probably answered in the first point regarding the volume at which the distortion becomes audible and to what extent.

In reply to:

---

It would be interesting to measure the differences and perhaps Axiom will have time to do so in the future. But loudspeaker distortion is well documented, and audible, especially with smaller bookshelf designs

---

3) Just how low a frequency would the cutoff for audible distortion be (if an exact point exists) and at what volumes then (e.g. 0% THD at 80dB? 1% at 90dB? etc)? (obviously a question answered only by alot of measuring of every individual speaker out there)
This may help to answer the exact point at which a user may want to switch their sub over to handle the entire low end and where to set a crossover in their receiver settings for their towers, if they are still being used in the 'large' mode and if an adjustable receiver crossover is possible.

One more thing to note, it appears that the THD for the M80s between the 100Hz -200Hz mark is virutally the same for both SPLs and just as significant as the THD hit by the lower bass around 50Hz. Just offhand most receivers would be set for a crossover of 80Hz with the towers set to small and yet the tower would still play this 100-200Hz sound range.
I find it interesting how there is significant THD in the range that the subwoofer would not be playing anyway. Forget the low bass, how about the audible distortion in the low midrange?

Whoah. Never thought of that one.

So whenever the cone is moving outward it increases the pitch of the tone it's supposed to be reproducing, and when it moves inward it decreases it.

I'm sure they could electrically compensate with some sort of feedback loop...

Alan, thanks for the quick insights -- and I do want to hear the longer version. I think I might be able to grasp this, sorta kinda, except I have no real idea what those THD charts mean, other than that THD exists and gets worse on all speakers at the low end if you crank 'em up. But beyond that, all the charts are Chinese to me, and they all look the same, from M22s to M80s to other manufacturers. We'll await your elucidation post CES.

If I'm catching your initial drift, however, it's that using a SWFR reduces the potential for distortion with satellites. Does it do anything of measurable value for large floorstanders? Or for amps/receivers, which is another part of the oft-cited claim?

Don't gamble too much. Those free drinks can cost you in the end.

Birdman

Alan wrote:

"Ha, ha. And here's something I'm going to ponder on the plane, something that no-one ever talks about. Doppler distortion to other frequencies caused by the woofer cone's movement reproducing low bass frequencies. In and out, in and out. . .I'll raise this question with Ian C and some speaker engineers in Las Vegas. Hmmmm. . ."

So, are we going to see a new line of time corrected Axiom speakers? BTW, have you ever listened to the de Capo MM's? Great $2500 speakers - time corrected, I think. It would be great if you could target the best speakers in the world, think and tweak, tweak and think, and build an Axiom competitor which fairly matches the sound but at an Axiom price!

Alan - Have a safe and enjoyable trip .

I don't think time-corrected has anything to do with doppler shift, but just the phase and "alignment" of the sound waves as they reach your ear.

Vandersteen speakers, for example, achieve time-alignment by mounting the different drivers not in a vertical plane, but slighly staggered from one another. Thiel accomplishes this by having the speaker baffle angled backward. All are still subject to this doppler shift.

On the other hand, anything that creates sound is subject to doppler shift, is it not? Take the violin for example. Vibration is created as the resined horse hair is dragged across the strings. The vibration is transmitted to the sounding board through the bridge, and then to the entire body. The vibrations are similar to -- though much more complex than -- a speaker cone in that surface of the violin oscillates back and forth.

I sometimes wonder if I really know that much less about all this stuff then some of you or if you're all just talking out your a** with some of these posts.

I guess I just have a lot of catching up to do with some of the finer details of speakers and how they work...or just get what I can out of threads like this(a good chunk of it made sense) and ignore the rest!

I don't know that it would be much more complex; after all, the speaker is reproducing those vibrations by vibrating itself. Therefore, a speaker playing violin music (a good speaker, mind you) would have to vibrate in a very complex way to even approximate the sound of the violin.

And yes, I am talking out of my ass. :-)

Hey, now. When I talk out of my a**, I usually try to make it transparent enough that it wouldn't fool anybody. Granted, I'm an acoustic engineer, but what I said above has at least a moderate grounding in reality.

No, you're not an acoustical engineer.

Hi all,

Thanks for the feedback and kind wishes re my trip to LV. pmbuko is right; Doppler stuff isn't related to the time-alignment of drivers.

The Doppler distortion results when a woofer cone is moving outward to reproduce, for example, a 40-Hz tone at the same time that it's reproducing a 100-Hz tone. The 40-Hz movement would add Doppler components (pitch shift?) to the 100-Hz tone. Is it audible? Does anyone care? Don't know; will quizz colleagues at CES.

In fact, it still amazes me that a woofer can reproduce two or more frequencies simultaneously with reasonable fidelity. Think about it: the cone is vibrating at 40 cycles per second at the same time that it's vibrating at 100 times per second. Huh? You'd think the results would be total grunge, not music.

Regards,

Hi Chess,

I forgot to say that to interpret those THD charts, you subtract the number of dB between the SPL level at the top (usually around 90 dB SPL) and the distortion curve at the bottom. So if there is 40 dB difference, or, to put it differently, if the THD curve at the bottom is 40 dB down from the upper curves, the distortion is 1% or less. If the distortion is just 20 dB below the test level, then the distortion is 10%.

As to midrange audibility, if you keep THD at 1% or less, it's generally inaudible with musical programs but audible with a fixed tone.

With music, THD distortion usually has to get well into the whole percentages to become audible or annoying. And this is even-order harmonic distortion, which is "musical" in a sense, nothing like as nasty as odd-order distortion that you can get from amplifiers.

Regards,

Alan, sounds like you're a closet fan of tube amps!

In reply to:

---

In fact, it still amazes me that a woofer can reproduce two or more frequencies simultaneously with reasonable fidelity.

---

The same thing I realized when I first started with digital audio theory on the C64 (wow, 40K of BASIC memory, with more under ROM? I can have an 8 second digital audio clip at 4000 samples per second, 4 bit resolution, holy cow!

The first time it occured to me that a 50-50 mix of two digital audio streams is a mathematical average of the two:
x=(a+b)/2
... it blew my mind... mix in 8 different signals and you should get mud, not a fine audio signal! Made me interested enough that I built a quick and dirty audio digitizer around a 0820 ADC, worked very well except the source had to be a DC walkman or similar (since I didn't build in any sort of ground isolation, it would hum like a bugger otherwise)

Bren R.

Doppler shift . Clearly, those audiophiles desiring to experience true purity of sound(at least those who hear differences in interconnects and speaker wires)would be required to use an individual speaker for each separate frequency up to at least 20,000Hz in order to avoid intermodulation effects; of course the wave form distortion of each individual frequency caused by driver excursions might still leave them unfulfilled, although a step closer to nirvana.

Oops! I forgot the the not. You can tell by my sentence structure that I meant to put that in there, right?

"Granted, I'm not an acoustic engineer."

This isn't you, is it?

hahahaha

that's great Peter, come on now John show your true self

If that is JohnK, congrats on the new speaker design!!

Are those Quads on the front page?
The new version of that is one of my dream speakers.

http://www.quad-hifi.co.uk/esl989blue.htm

Geez. Are those things for real?

And Peter, some warning about the 70s game show music that plays when you go to that page, please!

I think that music is in your head. I don't hear anything on that page.

Try turning on your computer speakers. Of course, that could wake up your wife and/or your baby.

No, Peter, it isn't me, although we're apparently of at least neighboring ethnic backgrounds and some people say "all these h.....s look alike to me". Differences that immediately jump out at me are that I'd have Rachmaninoff playing on my site, my hair's blond, and I spell better.

Some quite interesting articles there, besides the Doppler paper. John's apparently really into dipoles. I suppose that I doubt any audiophiles are enthusiastic enough to set up a 20000.0 system to avoid Doppler IM distortion.

So, what facts do we know about JohnK so far?

• He is of slavic descent -- my guess is Polish (see this post)
• He has blonde hair
• He gives tax advice on another forum (see this post)
  

What else can we squeeze out of him?

I have some Polish in my family lines.
I have yet to see anyone with blond hair.
Maybe that's because of the Ojibway genetics....or possibly the French...or Irish....

We'll figure it out someday.

Did you use to supply/courier/code/manage/Distro for DoD years ago?

Negative.