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Speaker/Room Measurement Witchcraftery

AndyU said:
Here’s Colloms’ review of the passive 50s.

http://atcloudspeakers.co.uk/wp-content/uploads/2018/01/Hi-Fi_Critic_SCM50PSL_WEB.pdf

And here’s one from Absolute Sound that’s just come out of the active 50 ASLTs. The reviewer bought them.

http://www.theabsolutesound.com/articles/atc-scm50-aslt-loudspeaker/
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20 000$ for scm50asl. dont think it fits this thread

S-Man said:
Rolloff at 50Hz might be your idea of "proper".

Gale 401s are significantly improved by using them with the ZRBs. You don't know what you're missing.
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in my room, I have -6db at 35hz. not perfect but good enough for me. what I mean by proper is how well it does bass (midbass/upperbass), extension notwithstanding
I wish I could hear a perfectly well integrated sub, but all the sub I have had ended up disturbing me. Im thinking of adding a 15 inch diy sub, I might do it.

so your using your diy speakers again? the Kef ls50 eventually tired you up?
 
darrenyeats said:
… E.g. 3rd harmonic distortion:
ATC 50 (passive), 85dB 100Hz 0.03%
Kii Three, 86dB 125Hz 0.35%
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And in the HFN Kii Three review a disappointing 3.4% THD at 100Hz & 90 dB 1 metre SPL.

Compared to linear (frequency and time domain) behaviour as in most of this thread, the subjective effect of non-linear behaviour is an aspect of loudspeaker measurement that is under-researched as far as I can see.

I recall reading (a while ago) two papers from Lee and Geddes (presented at an AES Convention IIRC) showing that listener subjective evaluation is not always found to correlate well with simple THD/IMD measurements. Toole agrees (but then states that the only reasonable target is zero). However maybe a good practical subjectively-correlated measure of loudspeaker non-linearity can be found.
 
Hadn't seen that review, thanks John.

Interesting that the reviewer mentions "one note bass", but that it all starts and stops on time. My findings exactly!

On the subject of distortion; I don't think DSP can improve this (but I could be wrong) and extending the bass by equalisation will increase distortion for the same SPL. The ZRB system is actually correcting the non-linearities of the drivers and results in an order of magnitude distortion reduction for the same excursion uncorrected. Hwever I doubt that this distortion is the reason for the difference in bass quality.
 
There are more things in heaven and earth, Keith, than are dreamt-of in your usual sales pitch...

Several ways such a thing can be approached. S-Man has long & previously explained on several occasions (that, to précis) he's under an NDA for key aspects.

(And yes, I'm curious myself, but can think of maybe half-a dozen ways such a thing might be approached, without trying hard; albeit also without doing enough sums to check which approaches might be worth pursuing. And just because DSP is now cheap and coding libraries free enough any idiot can nail something together like Duplo, does not mean it is a panacea.)
 
I think first you need to define what is encompassed by the term "non linearities".

Adding a sub has benefits to the mid range driver reducing distortion etc. However It can't correct phase issues, time alignment or frequency response of the other drivers and crossover. The measurements appear to confirm this conclusion.
 
martin clark said:
There are more things in heaven and earth, Keith, than are dreamt-of in your usual sales pitch...

Several ways such a thing can be approached. S-Man has long & previously explained on several occasions (that, to précis) he's under an NDA for key aspects.

(And yes, I'm curious myself, but can think of maybe half-a dozen ways such a thing might be approached, without trying hard; albeit also without doing enough sums to check which approaches might be worth pursuing. And just because DSP is now cheap and coding libraries free enough any idiot can nail something together like Duplo, does not mean it is a panacea.)
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Well give us your best shot.
Keith
 
S-Man said:
Are you actually reading any of my posts?
#236
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Post 236

it seems that the Kiis measure better than my speakers, but they don't sound as good.
In particular, there is the anomaly that the Kiis sounded mediocre when cold, but after a few hours warm up (which could be relevant/important because the amps are inside the boxes) they sounded very good.
The problem is that drive units are notoriously difficult to model (stiffness of the surround due to age, temperature, signal-history, & inductance nonlinearity etc.) and therefore DSP correction can be a hit and miss affair.

I did read this but it is a partial list of potential driver non linearities. Asking you to define what you were referring to seemed quite reasonable. BTW The output of Drive units are quite measurable and correctable.

You were talking about non linearities that your ZRB sub box can correct. I'm struggling a bit to see how it can correct those non linearity mentioned above in the speaker it's attached to. Can you explain?
 
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S-Man said:
Hadn't seen that review, thanks John.

Interesting that the reviewer mentions "one note bass", but that it all starts and stops on time. My findings exactly!

On the subject of distortion; I don't think DSP can improve this (but I could be wrong) and extending the bass by equalisation will increase distortion for the same SPL. The ZRB system is actually correcting the non-linearities of the drivers and results in an order of magnitude distortion reduction for the same excursion uncorrected. Hwever I doubt that this distortion is the reason for the difference in bass quality.
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Now, I haven't heard the Kiis so the following is a bit if speculation and please take it as such.

You talk about one note bass. There is only one explanation for that, a significant resonance in the speaker making one frequency louder and stand out. We know that the Kiis do not have this problem.

However we know that your room does. Not only louder but rings for significant lengths of time at 30, 60 and 90 Hz.

We do know that the Kiis low frequency output is very different to a conventional speaker in terms of directivity.

My view is that what you heard was a generally better behaved low frequency that made your room issue stand out further.
 
Strictly Stereo said:
That’s impressive. Can you tell me more about how you did it?
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OK back to your question. Here is a brief description. Luckily I have a dedicated theatre / listening room. About 6*4.5*2.7m size. First item was passive acoutic treatments. The reverberation time in the room was obviously high without so the aim was to bring it down as evenly as possible across the frequency range, not overdoing the absorption. Also the usual modal resonances were high too. I used products from Vicoustic.

God this forum is a PITA that you cant directly upload pictures.....

Resonant Corner traps for a general low frequency absorption- https://www.vicoustic.com/product/super-bass-extreme

SBE_zpss0smztai.png


Absorbers for the mid High frequencies - https://www.vicoustic.com/product/cinema-round-premium

Abs_zpsxzufmh3f.png


Diffuser/Absorbers which appear to be discontinued by similar in performance to this alternative model - https://www.vicoustic.com/product/wavewood

ABDIF_zpsgt00rsom.png


Diffuser for ceiling - also helped eliminate a flutter echo - https://www.vicoustic.com/product/multifuser-dc2

diff_zpsqtzb6md3.png


This got the Reverberation time down pretty much within EBU studio recommendations across the frequency range without overly treating the high frequencies

reverb_zps9yc7jerj.png


This is just one sub and no EQ. During speaker dev phase with a passive XO. Much improved modal decay time over no treatments but it is still prevalent at 30 and 60Hz.

wf%201%20sub_zpsxi6zqg8s.png


The speaker development was finished. 3 way AMT tweeter and dome mid. Sealed, fully active DSP crossover, phase linear with time alignment performed by Acourate software.

Added 4 small B&W ASW608 subs.

Atmos speakers in ceiling, theater duties with a Yamaha AV amp

DSC02644_zpseosm8jsn.jpg

DSC02648_zpsvl2gt0xq.jpg


DSC02651_zpsmkbsl7ee.jpg


DSC02652_zpsxjsygn8a.jpg


Low frequencies under control. 4 subs and a dash of EQ works. 4 subs also greatly even out the bass response around the room.

me%20wf_zpsqnd5ae9y.png


How does it sound? The overwhelming feedback I get from visitors is

"I have never heard bass this tight"
" I have never heard a soundstage as wide, deep and clear"

This is an old measurement, I seem to have mislaid the current FR measurement. Basically the final correction draws a pretty flat but sloping line from 20Hz to 24 kHz, falling 10dB.

FR_zpsw5ds5bfb.png


All reflections with the first 10ms are at least 20dB down

ref_zps7uylx7ct.png


need to work a little on the impulse response and get the subs better aligned.

TA_zpss9i2jsma.png



without measurements you have no idea where you are. Its just guesswork.

Just a final note, there are only 3 bass traps in each corner. It would have been more effective with 4 and thats what I would recommend for this model. reason it ended up 3 was that when the house was built I was a dumbass and put electrical sockets right in the way :) and couldnt fit 4 in.
 
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March Audio said:
Now, I haven't heard the Kiis so the following is a bit if speculation and please take it as such.

You talk about one note bass. There is only one explanation for that, a significant resonance in the speaker making one frequency louder and stand out. We know that the Kiis do not have this problem.

However we know that your room does. Not only louder but rings for significant lengths of time at 30, 60 and 90 Hz.

We do know that the Kiis low frequency output is very different to a conventional speaker in terms of directivity.

My view is that what you heard was a generally better behaved low frequency that made your room issue stand out further.
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Agreed, I am taking it as speculation.
 
March Audio said:
Low frequencies under control. 4 subs and a dash of EQ works. 4 subs also greatly even out the bass response around the room.

me%20wf_zpsqnd5ae9y.png


FR_zpsw5ds5bfb.png
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That's a stunning looking room, @March Audio. Can I ask the reason for the steep rise in low frequency output below 30Hz, is it a personal preference?

Hopefully when I get a bigger listening room I'll use lots more passive treatments than I'm currently able to accommodate (at the moment I have all four corners stacked bottom to top with GIK TriTraps and have four GIK 244 absorbers at first reflection points on sidewalls).

I dream of having a room large enough to be able to lower the ceiling and bring each wall in and stuff the cavities with rockwool, and then use thinner absorption panels and diffusers in the visible area of the room for a more streamlined look.

PS - I'd be interested to hear your opinion on Acoustic Fields "Activated Carbon Diaphragmatic Absorption" product? (www.acousticfields.com/product-category/sound-absorption). According to the maker it is much more effective at reducing modal frequencies than Tuned Membrane absorbers such as the GIK T40 etc. The downside is it is very heavy and expensive (though they do sell a DIY version, - basically they supply the carbon and you build the enclosure). However if the maker's claims are to be believed, it offers significantly better low frequency absorption than any other comparable passive room treatment.
 
ToTo Man said:
PS - I'd be interested to hear your opinion on Acoustic Fields "Activated Carbon Diaphragmatic Absorption" product? (www.acousticfields.com/product-category/sound-absorption). According to the maker it is much more effective at reducing modal frequencies than Tuned Membrane absorbers such as the GIK T40 etc.
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https://www.acousticfields.com/product/acda-12-activated-carbon-diaphragmatic-absorber/
"100% absorption at 50 Hz., 63% at 40 Hz". Unless it can be custom tuned to peak at the exact frequency required (I have GIK Scopus custom "T35"s for my 35 Hz mode) then I won't spring for it. Peaking at the wrong frequency will actually make bass sound weirder IMO. It's really important to measure, then tune the traps accordingly, IME.

PS:
It's MUCH harder to absorb 35Hz than 50Hz! I also have two user-tunable fridge-freezer sized HH resonators tuned to 35Hz, and they only halved the long resonance. These HH resonators absorb very narrow band, and the T35s more wide band - but both peak at the mode frequency 35Hz. After all this, I've still got the mode problem but it's mitigated enough for me.
 
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