Axiom Home Page Forums General Discussion Technical Questions Frequency response & what we can hear

And what happens with room effects.

Watching my M80 fund grow is almost as fun as watching grass grow (well, ok, it is a little more fun),so I'm bored.

In my never ending quest to understand what the heck some people are talking about, I am wondering what sort of effect smaller fluctuations in frequency response, up to +-3db, have on the sound of a speaker.

This comes from a discussion on another board where the assertion was made that most speakers are mediocre (including M80s, can you believe it ) because they do not have a ruler flat frequency response and have cabinet resonance. The suggestion is that these fluctuations, along with cabinet resonance, (hopelessly) colour the sound of the speaker.

This prompted me to go back and look at the graphs for a bunch of speakers including the M80. It seems that there are some small but notable dips and rises in the curve for the M80: one dip being in the 100Hz range and a general rise above about 11kHz

When I say notable, I mean that they stand out visually on the graph, not that they are large. If I had to guess, (and I do because the graphs are not that noticable) I would say the spread between the lowest and the highest might reach 5 or 6 db.

It is also worth while to note that Debbie at Axiom suggested that the cutoff during testing of each speaker is about +- 2db.

Compare that to a speaker, Ascends I think it is, (and not very expensive at that) which appear to have a very uncommonly flat graph that looks like +-1 to 2 db.

Will such small differences between speakers noticably colour the sound?

Can/will room effects accentate those differences to noticable levels?

How does cabinet resonance fit in here and how much effect can it have?

To put this in perspective, the commentor believes that there are only a handfull of speakers ever made that meet his lofty expectations; all of them being well above my budget.

Fred, room effects(e.g. see Mark Johnson or Randy)far exceed the fluctuations in response that well-designed speakers exhibit. You try to start off with the flattest anechoic response possible, since fluctuations can possibly coincide with room effects and make the net result worse. "Ruler flat" response is typical of even modest-cost players and receivers, but doesn't exist in speakers, regardless of price.

OK, 'ruler flat' wasn't the right choice of words.

Thinking more on this, I remembered doing some reading on what spl changes we could hear and tracked it back to an audioholics article. It seems average joe listener can detect changes as low as ~1db. So, in theory, the differences we see between two speakers that both have a tolerance of +-3db over a given range could result in a noticable difference in sound.

I still wonder what the reality is.

Given the above, it is a reasonable proposition that when room effects combine with particular peaks/valleys it is likely to have a noticable effect on the sound of the speaker.

You know, if I ever win the lottery, I can keep myself amused for years on stuff like this.

room effects + variations in freq response of the speaker can yes, increase or decrease that variation derived from the speaker

consider the idea of 'bass loading' the sound in a room by placing a speaker near a wall coupled with a natural response peak like the M3 bass area (90-120Hz), as an example

Fred,

IF the speakers are carefully measured in an anechoic chamber and no "smoothing" has been applied to the resulting frequency response curve, then fluctations of 3 dB especially peaks, rather than dips, may be quite audible.

By the way, 1 decibel is defined as the smallest step upwards or downwards in SPL that we can detect, however, such tiny variations are extremely hard or virtually impossible to hear with musical programming. You can, however, hear them with pink noise test signals.

A 3-dB variation is subjectively audible as "slightly louder" (or slightly softer).

In terms of coloration, and audibility, it depends greatly on where the non-linearity occurs. Small variations in response above 10 kHz are essentially inaudible and similar variations in the bass octaves are also insignificant.

In the midrange, where most of the energy of musical instruments is concentrated, such variations are quite audible. The M80 v2s are extremely linear both on-and off-axis through the critical midrange, which explains why they are so accurate and musically transparent.

The technically untutored comments on other boards can be ignored. Some of the most neutral and transparent speakers around include the Axiom M80s, a couple from Revel,and Snell, Energy Veritas, PSB and a few others.

The accumulated data from the National Research Council program in which Axiom participated for many years has shown that it's not only the smoothness of the on-axis frequency response, but the off-axis curves that are equallly important in establishing the overall sound quality in a room--the so-called "family of curves".

Most manufacturers publish curves to which 1/3rd octave smoothing has been applied, which makes them look very nice and smooth for marketing purposes.

The quasi-anechoic room measurements conducted by many manufacturers (and published) are not nearly as precise as speaker curves measured in a large anechoic chamber. Axiom has its own large chamber, a clone of the chamber at the Research Council in Ottawa, which we previously used dating back to the 1980s.

Sometimes correcting a small glitch in the on-axis frequency response doesn't make the speaker sound better, because it will affect the off-axis curves.

Incidentally, be sure and check the M80 v2 anechoic measurements at Soundstage.com. There you'll see the full family of curves.

Hope this helps.

Regards,

Alan

Alan. Thanks for the response. I was hoping that you would weigh in.

The comments on another site that sparked this thread, were 'technically turored', but possibly misguided. Having several times tried (mostly unsuccessfully) to get some understanding of quantum physics, I have come away with an appreciation that we can measure things on an infinately smaller scale than we can ever hope to directly observe (or hear).

Thanks for the pointer to soundstage.com. I was there the other day, but did not bookmark, and could not find it in my browser history. Funny, I had looked at the curves the other day, but did not look closely at the off axis stuff and did not make much sense of it.

Looking again I can see that the M80 has very nice off axis response and compares favourably to the graphs I have seen on another site and of much more expensive B&W speakers.

Of couse, I already knew that, because my ears told me so when I auditions the M80.

The comment about people being able to hear differences of 1db in music came from an article on Audioholics by Mark Sanfilipo. Given his background I though it should be a reasonable proposition. Perhaps it is easier for someone such as Mark to hear these differences, because he has been making a living dealing with sound reproduction.

I have one other question. Would cabinet resonance show up in THD + N measurements of a speaker?

By the way, for anyone that is interested, I found a really cool site here
that does a great job of explaining sound reproduction and the things that effect what we hear.

I found the explanation on timbre particularly interesting, because I had been wondering what it is that makes some speakers sound more 'realistic' than others.

Yes it would. The microphone has no way of discriminating the sound that it's picking up.

That is exactly what I thought.

Interestingly, looking at the charts at the website Alan listed, the update from v1 (2000 measurements) to v2 (2005 measurements) on the M80 shows improvements in frequency response across the board, but particularly in the mid frequencyes 100hz - 5kHz, improvements in off axis response, and a reduction in THD + N in the mid frequencies.

Now that I have a better understanding of what those charts represent, I can conclude that the poster on the other forum was blowing (technical) smoke out his woofer port.

What did the v1 design look like? Did it have a mid between two tweets?

Fred,

I know Mark Sanfilipo and he has visited Axiom, but he has no background in the NRC research and double-blind listening program that began with Floyd Toole, past president of the Audio Engineering Society world-wide. Rather than repeat myself, you can read in detail about this program in the Axiom articles archive:

http://www.axiomaudio.com/NRC.html
http://www.axiomaudio.com/frequencyresponse.html

Cabinet resonances in well-designed speakers like the M80s are suppressed to a degree that they are not a source of audible coloration. Yes, if they were significant, they would cause measurable aberrations in the frequency response curves.

If Mark had participated, as I have, in over 25 years of editing AV magazines in Toronto and New York and doing double-blind tests of loudspeakers from Canada, the USA, England, etc., he wouldn't say: "The suggestion is that these fluctuations, along with cabinet resonance, (hopelessly) colour the sound of the speaker."

The best of modern speakers like the M80 v2s and some others are remarkably natural and uncolored, capable of thrilling musical reproduction that is extremely convincing when the source recording is of high quality.

Moreover, what is startling and gratifying about the NRC research is that realistic sound reproduction and smooth frequency response on and off-axis does not correlate with loudspeaker price. I still have data from comparisons at the NRC between some top speakers from Axiom, PSB, Energy Veritas, Snell, and Paradigm Studio Reference vs. speakers up to $7,000 per pair from B&W, Kef, Thiel, etc. that lost out in the double-blind tests to speakers that were a fraction of the prices of the "high-end" brands.

In terms of the 1-dB differences, yes, our brains and ears are indeed sensitive to such differences, which is why casual comparisons of speakers are so flawed when the playback levels of two different speakers are not adjusted so there is less than 1 dB difference. But you won't be aware of such small volume differences in casual comparisons and you'll often choose the imperceptibly louder speaker as sounding "better." It's a trick of salesmen in stores to slightly increase the volume of the models they want the customer to purchase.

Hope this helps in your understanding.

Regards,
Alan Lofft