Axiom Home Page Forums General Discussion Stereo Two curves is enough

I thought I’d chime in on which measurements matter. And it might be possible to distill goodness down to two composite curves. This is an expanded discussion of the 150+ anechoic measurements discussed in Amie’s blog:

https://www.axiomaudio.com/blog/the-family-of-curves/

First of all, it’s been known for three decades how sound coloration affects frequency response. This unattributed image has been circulated around Audio Science Review, and I haven’t found anyone in the audio field who’s refuted it’s validity yet.

https://www.dropbox.com/s/0bcbw2c7v7spqzb/1614637989068.png?dl=0

Using the audiophile press to make recommendations, particularly those that don’t use measurements nor A/B direct comparison with rival products, is audio foolery.

https://seanolive.blogspot.com/2009/04/dishonesty-of-sighted-audio-product.html

Axiom only provides three types of curves. The 2 way speakers usually have a frequency response graph (leaving us to imply that it’s an on-axis frequency response curve), and the 3 way speakers have a listening window and sound power curve. I’ve wondered why they chose to post these particular curves out of the 150+ measurements they’ve made.

These are the Axiom measurements of various models:

M5HP: https://www.axiomaudio.com/pub/media/catalog/product/m/5/m5hp-listening-window-and-sound-power.png
M60: https://www.axiomaudio.com/pub/media/catalog/product/m/6/m60_freq.gif
M80: https://www.axiomaudio.com/pub/media/catalog/product/m/8/m80_freq.gif
M100: https://www.axiomaudio.com/pub/media/catalog/product/m/1/m100_freq_graph.gif

LFR660: https://www.axiomaudio.com/pub/media/catalog/product/l/f/lfr660.jpg
LFR880: https://www.axiomaudio.com/pub/media/catalog/product/l/f/lfr880.jpg
LFR1100: https://www.axiomaudio.com/pub/media/catalog/product/l/f/lfr1100-sp-lw.jpg
LFR1100 active: https://www.axiomaudio.com/pub/media/catalog/product/l/f/lfr1100_active_graph_1.jpg

These are some competitors that have been acclaimed for both their measurements and their subjective audio performance.

JBL M2: https://www.erinsaudiocorner.com/loudspeakers/jbl_m2/
KEF Reference 1 Meta: https://www.erinsaudiocorner.com/loudspeakers/kef_reference_1_meta/
Dutch & Dutch 8C: https://www.erinsaudiocorner.com/loudspeakers/dutch_dutch_8c/
Genelec 8331a: https://www.erinsaudiocorner.com/loudspeakers/genelec_8331a/
Revel Performa F226be : https://www.erinsaudiocorner.com/loudspeakers/revel_f226be/

What they all have in common is a great listening window and gently sloping sound power curve. These curves are straight because straight means minimal colorations and resonances, and we are highly sensitive to low-Q deviations (very broad hills and dips). High-Q (sharp spikes up and down) look terrible on a frequency response graph but are psychoacoustically inaudible to us. Here are some deeply flawed (and expensive!) loudspeakers to contrast with the above. Can you say “buyer’s remorse”?

Klipsch Heresy IV: https://www.erinsaudiocorner.com/loudspeakers/klipsch_heresy_iv/
Bose 901: https://www.erinsaudiocorner.com/loudspeakers/bose_901_series_v/
McIntosh XR50: https://www.erinsaudiocorner.com/loudspeakers/mcintosh_xr50/
Wilson Audio TuneTot: https://www.audiosciencereview.com/...review-high-end-bookshelf-speaker.29219/
Magnepan LRS: https://www.audiosciencereview.com/forum/index.php?threads/magnepan-lrs-speaker-review.16068/

An example of what high-Q looks like:

IKEA Symfonisk: https://www.erinsaudiocorner.com/loudspeakers/ikea_symfonisk_lamp/

There’s a composite curve that appears to combine the listening window and sound power curve into something called the in-room response. Ideally, it should be straight and sloping slightly downward. I’m still evaluating its merits because some reviews with good looking in-room response have noted subjectivity issues if there’s deviations in the midrange and lower treble range.

Is frequency response king? If you don’t get it right, it’s hard to compensate with other redeeming qualities. Sean Olive listed some other factors that matter to perceived performance: spatial width, spaciousness, dynamics, and maximum sound pressure level:

https://seanolive.blogspot.com/2010/05/evaluating-sound-quality-of-ipod-music.html
https://seanolive.blogspot.com/2009/01/what-loudspeaker-specifications-are.html

At least there’s some agreement (for some of us) that science is a great thing in audio:

Don’t fear modern tech: https://www.audioholics.com/editorials/future-audiophiles
Why measurements matter: https://youtu.be/zrpUDuUtxPM?t=3433

The image of coloration that you shared is fabulous. I have never seen it before. I can't say I totally agree with it due to my lack of knowledge but I certainly agree with the parts I've personally experienced. I've downloaded it and will study it very carefully.

Ian has told me Axiom has both curves for all v4. He was going to ask Andrew to publish them but likely other matters took priority. I know from listening experience the M2 and M3 image and stage like the M5 and the M2, within its specified band, is more linear than the M3 and M5.

With regard to the curves Axiom publishes, the sound power is a composite of all curves using weight coefficients that Axiom has selected. You could call the sound power curve the weighted average of all curves. How Axiom selects the weights is largely what makes the "Axiom sound". We don't know how Axiom selects those weights - and they won't divulge the methodology - but it stems from experience, science and listening. I believe they've nailed the formula. Once the formula is nailed, it makes speaker engineering easier because the formula constrains or maybe informs the design. For example, if the sound power curve comes out "too lumpy" at say 200 to 300Hz, the curve weighting factors for that band won't be questioned. Rather, it will point to a deficiency in the design. The designer can then examine the mess of curves in that band to determine how the lump should be mitigated. The challenge is that to mitigate the lump, one or more lumps or dips may be introduced elsewhere. Would that be better or worse? The sound power curve for a modified design helps to answer that. If the new lumps and dips are within a specified tolerance, then the modified design is good to go. This is why for a speaker like the LFR1100, there may be thousands of curves to inform the final design. Those thousands of curves also include the curves for each driver.

The listening window and sound power are the only curves lay people need to judge how the speaker will sound in a room. The science says when these curves ride on top of each other, audio Nirvana is reached. Why? Because the direct and reflected sound fields become fused and the speakers acoustically disappear.

With regard to the slope of the curves, the science says a slope of 3dB/decade out to 15Khz or beyond will make the speakers sound natural in a room.

These two curves inform how wide and spacious the speaker will sound in room. In fact, what you listen to provided you're not sitting in the near field of a speaker is sound power.

The last factor is SPL. Ideally, we should have a family of listening window and sound power curves for various SPLs. If these two curves "deform" at higher SPLs, that spells trouble. I personally have not detected this trouble in v4. I can turn them up ridiculously loud, and they will distort, but the stage and imaging remain intact.

It's also interesting to note that some (all?) Bryston speakers have flat listening window curves. Was this done for marketing reasons or do Bryston owners have more dampened rooms that demand a flatter curve rather than the 3dB/decade attenuation I described in the last post?

BTW, the Family of Curves is not unique to audio. There are for example families of curves for flow rate vs. pump pressure for various RPMs. There are families of curves for chemical sensors. Even transistors, other semiconductors and passive components. What's unique about audio though is that the curves need to be interpreted through the lens of subjective descriptions provided by trained listeners.

I didn't see the Bryston curves, and no wonder, they buried them in the post-purchase owner's manual instead of the pre-purchase sales brochure.

A1: http://support.bryston.com/downloads/Loudspeakers/Model%20A1%20R1.0.pdf
A2: http://support.bryston.com/downloads/Loudspeakers/Model%20A2%20R1.0.pdf
A3: http://support.bryston.com/downloads/Loudspeakers/Model%20A3%20R1.0.pdf
Mini T: http://support.bryston.com/downloads/Loudspeakers/Mini-T-R1.0.pdf
Mini A: http://support.bryston.com/downloads/Loudspeakers/Mini-A-R1.0.pdf
AC1 Mini: http://support.bryston.com/downloads/Loudspeakers/Model%20AC1%20Mini%20Center%20R1.0.pdf
TC1: http://support.bryston.com/downloads/Loudspeakers/Model-TC1-R1.0.pdf
Model T: http://support.bryston.com/downloads/Loudspeakers/Model-T-R1.0.pdf
Middle T: http://support.bryston.com/downloads/Loudspeakers/Middle-T-R1.0.pdf

I think that if the lines are straight, they look good, and they play as loud as you want, then you're done. End game achieved. Looking at other loudspeakers is a waste of time.

In principal, yes. But what is the definition of "straight" and "look good"? There may be trade-offs between those two. Brystons may be "straight" but the wife doesn't like the aesthetics. So now you have to look elsewhere.

There is also the issue of how much power is required to achieve the necessary SPL. And how low you need the speaker to go.

What makes the Middle T better than an M60? A good exercise may be to look at the specs, including curves between the two, and try to identify the answer.

Those are good questions, and I don't know what the audible threshold is between one companies squiggly line and another companies less-squiggly line. It might be that spending a little more on better cabinets provides better measurements, and I certain think Bryston has the appropriate high-end look. But I don't think it's unreasonable to be satisfied with any of the well measuring speakers.

Heck, it would beat having this $11,000 CDN stinker:

https://soundstagenetwork.com/index.php?option=com_content&view=article&id=2629:nrc-measurements-bowers-wilkins-805-d4-loudspeakers&catid=77:loudspeaker-measurements&Itemid=153

Let's analyze, using published specs, if the Middle T is better than the M60v4.

1. The T goes 3Hz lower (33 vs. 36). This is assuming that the Middle T is an anechoic spec like the M60 and not in room.

2. The impedance of the T is 4 Ohms vs. 8 Ohms for the M60. Better have an amp that supports a 4 Ohm load.

3. The SPL is identical assuming the T spec is for anechoic and RMS power. Note there is no dynamic SPL given for the T. The M60 dynamic SPL can be calculated from the dynamic power and sensitivity to be 117 dB. This just means it won't melt or rip apart at that SPL.

4. The sensitivity is identical.

5. The cross-over frequencies are different. The T is 160 and 2.3KHz vs. 500 and 2 KHz for the M60. I find it really hard to believe the M60 woofer is crossed to the mid at 500Hz. I think that's a mistake. Regardless, I really have no way of knowing if crossing so high in the mid-range on the M60 detracts from the M60 compared to the T. Ditto for the tweeter.

6. The T woofer is 8" vs. the M60 6.5". This tells me nothing about performance.

7. The T cabinet encloses more volume. Likely this and the 8" woofer is why the T goes 3Hz lower.

8. The T is almost double the mass. Hmmm...might this imply less audible resonances and hence improved acoustic disappearance? Maybe.

9. Now we get to the amplitude response:
a. The T does go lower.
b. The T has a noticeable depression between 70 and 200Hz of around 4dB. I have no idea how that might affect what I hear.
c. The T listening window is flatter. Maybe that will make it brighter. I don't know.
d. Both sets of curves are well-behaved and more similar than different.

So what can I deduce from all this? Not much other than the 3Hz difference down below and beefier amp needed for the T. As for the difference in mass, there's nothing in the curves to suggest a more massive T is better.

Based on all of this, I can only conclude from the published specs, the additional money for the Middle T will not result in improved performance over the M60v4 other than the 3Hz in bass performance.

Listening may reveal more differences. But if so, where in the curves and specs are those differences reflected?

Anyone who wants to geek out on these two measurements should go to Pierre Aubert's collection of Spinorama measurements. It's an incomplete list, but you see a pattern on whom takes their R&D seriously, and the fact that good measurements are unicorns in a sea of mediocrity.

https://pierreaubert.github.io/spinorama/index.html

I would be curious to know the source of that ASR graph on sound qualities vs. frequencies. Certainly there are some truths to it, common knowledge (like the general range of human hearing), but some subjectivity on how something like upper/lower midrange is defined. Still, an interesting graph and from my experience, using the frequency response graphs and relating it to my sound preference, i know i am not a fan of big bass humps, have heard what a small bass suckout sounds like, and know that i like neutral speakers but with a small hump (or minimal rise defined as no more than around +2-3dB relative to lower frequencies) in that upper midrange-ish area which sounds more clear, detailed to me.

There is so much data out there on the topic, i'm sure there's more in publications along these lines. I try to defer away from people's blog sites unless they are known experts in the field (such as Sean Olive, Floyd Toole who have more publications than many over many years).

An interesting topic though Hamb.
Lots of searching went into this one!

Actually, it took less than an hour!

That graph shows there's only one way to make a good all-around loudspeaker, but countless ways to make a bad one. I was deeply dissatisfied with Audio Science Review and Erin's Audio Corner. Most of their data is noise, and I wanted to know what the best sounding and ranking speakers had in common that the poor sounding ones didn't.

After rewatching some of the Axiom videos, I noticed Ian and Andrew kept harping on the listening window and sound power. So I gathered up all the acclaimed reviews on those two sites to look at those two measurements. Lo and behold, every single one of them have a straight listening window and straight sloping sound power. It tells you EVERYTHING you need to know about who wins a double blind listening test. All the other stuff (on axis, step response, phase response, dispersion map, etc) is just noise.

Even going back to the early 2000's with the loudspeakers Harman used in their research papers about the state of the art (which are never mentioned, but are the Infinity Prelude MTS and IL60), and you see the same pattern.

I can still be proven wrong, but it looks like this has legs.