Acoustic measurement standards for stereo listening rooms defined

Nyal Mellor · Oct 13, 2011

Some of the many questions that can be found scattered across the internet and overheard in conversations amongst audiophiles today relate to room acoustic measurements:

What are the key measurements?
How do I interpret them?
What does good look like?
How do they relate to each other?

These questions arise from the recent availability of cheap and accurate 'consumer' acoustical measurement products like XTZ Room Analyzer, Room EQ Wizard and Dayton Audio Omnimic. Whist these packages allow you to measure your room they do not provide any guidance on how to interpret the results relative to the audiophile situation of two speakers in a room.

In April of 2011 I started work on creating a set of measurement standards specific to the requirements of the two channel audiophile. Many hours of hard work have culminated in the release of the white paper Acoustic Measurement Standards for Stereo Listening Rooms, co-authored with Jeff Hedback.

This paper is recommended reading if you are interested in understanding how room acoustics can influence sound quality. It also provides clear targets for the acoustic measurements that characterize your room's performance.

Jeff and I are really interested in your thoughts and questions, so fire away

RUR · Oct 13, 2011

At last!

Read this yesterday, after Jeff posted it. Plan to re-read more carefully on the plane tomorrow, but a few early questions:

No Haas kicker?

Why use RT60 which is widely claimed to be inappropriate to small room acoustics? (same Q posted @ GS)

What software are you guys using to get ETC by frequency band? Better still, what can I reasonably use?

/Ken

Nyal Mellor · Oct 13, 2011

RUR said:
At last! Read this yesterday, after Jeff posted it. Plan to re-read more carefully on the plane tomorrow, but a few early questions:

No Haas kicker?

Why use RT60 which is widely claimed to be inappropriate to small room acoustics? (same Q posted @ GS)

What software are you guys using to get ETC by frequency band? Better still, what can I reasonably use?

/Ken

Ah the infamous Haas kicker...I'm gonna let Jeff answer that one, I know he has a lot to say on that topic....

On the subject of RT60 we do say this in the first paragraph of the paper....."Single figure T60 measurements cannot do much more in a small room than tell you whether a room is overly live or overly dead.". Looking back at things I think the revolt against single figure measurements has ended up with any decay time measurement bearing Tx being put into the not useful category. In fact Tx measurements are useful if you look at the spectrum. This is much the same line of thinking as when we say single figure ETC measurements are not particularly useful either. You have to look at the spectrum.

We used Room EQ Wizard for most of the graphs, and the latest version allows you to look at the impulse response over filtered bands. ARTA can also do this (and in a more user friendly way, which is kind of funny because most of the time ARTA is not user friendly at all)

c1ferrari · Oct 13, 2011

Excellent

I will peruse it.
Nyal -- would you mind if I asked questions about other measurement systems/apparatus?

Thank you

Nyal Mellor · Oct 13, 2011

c1ferrari said:
I will peruse it.
Nyal -- would you mind if I asked questions about other measurement systems/apparatus?
Thank you

Of course not! What questions do you have?

c1ferrari · Oct 13, 2011

Thanks!

Nyal Mellor said:
Of course not! What questions do you have?

I have an Audio Precision Portable One Dual Domain and was curious if you have ever utilized Audio Precision gear in your field of endeavor. I may upgrade to an AP System Two or a current AP box.

Also, have you any experience with HOLM Acoustic's HolmImpulse?

Looking forward with great anticipation to your commentary, experiences, and observations.

Jeff Hedback · Oct 14, 2011

Thank you both (Ken and Sam),

This has been a wonderful process that has led to results beyond original "thinking"...that can lead me to the Haas Kicker which would be an integral part of LEDE design. If you carefully read the Section B standards on reflected sounds, they don't have to conflict with LEDE...but in our opinion the shift of using ETC to study L to R spectral balance and spectral balance within each spkr would validate the device (not the amplitude of energy return or an extended ISD). I probably could go on for much longer, but that's pretty much the story we're telling.

Sam, first thank you for your kind words on Art's room (in other thread). I use HolmImpulse and it is fantastic.

As much as possible Nyal and I focused on the "what" and not the "how". We didn't want to be device-centric, speaker-centric, or platform-centric. That said, you need a clean accurate impulse response. Although there are benefits to other types of room excitations, log sine sweeps offer the most data across the board. HolmImpulse really does work with any soundcard. If you get their powered mic (or Earthworks), you can negate the USB pre and go right in/out your laptop's soundcard

Nyal Mellor · Oct 14, 2011

c1ferrari said:
I have an Audio Precision Portable One Dual Domain and was curious if you have ever utilized Audio Precision gear in your field of endeavor. I may upgrade to an AP System Two or a current AP box.

Also, have you any experience with HOLM Acoustic's HolmImpulse?

Looking forward with great anticipation to your commentary, experiences, and observations.

I did have a chat with a AP sales rep about their latest AP5x5 products. Suffice to say the conclusion was that the AP is not designed for room acoustics measurements, in particular it does not have any time based measurement functions such as cumulative spectral decays, energy time curves, etc. Here's what he said:

"it sounds like you are primarily interested in measurements for room tuning/acoustical treatment etc. That is definitely not currently within the scope of AP’s focus. Our acoustical tests are primarily aimed at measuring the response characteristics of transducers. It’s something that could certainly be added to the software as a future option, but I wouldn’t suggest our current product as a solution for that application."

c1ferrari · Oct 15, 2011

Hi Jeff

Jeff Hedback said:
Thank you both (Ken and Sam),

This has been a wonderful process that has led to results beyond original "thinking"...that can lead me to the Haas Kicker which would be an integral part of LEDE design. If you carefully read the Section B standards on reflected sounds, they don't have to conflict with LEDE...but in our opinion the shift of using ETC to study L to R spectral balance and spectral balance within each spkr would validate the device (not the amplitude of energy return or an extended ISD). I probably could go on for much longer, but that's pretty much the story we're telling.

Sam, first thank you for your kind words on Art's room (in other thread). I use HolmImpulse and it is fantastic.

As much as possible Nyal and I focused on the "what" and not the "how". We didn't want to be device-centric, speaker-centric, or platform-centric. That said, you need a clean accurate impulse response. Although there are benefits to other types of room excitations, log sine sweeps offer the most data across the board. HolmImpulse really does work with any soundcard. If you get their powered mic (or Earthworks), you can negate the USB pre and go right in/out your laptop's soundcard

You are welcome...my remarks regarding Art's room/system are well-earned

The assertion of focusing on "what" rather than "how" is well-stated.
Your comments are extremely informative

c1ferrari · Oct 15, 2011

Great stuff, Nyal

Nyal Mellor said:
I did have a chat with a AP sales rep about their latest AP5x5 products. Suffice to say the conclusion was that the AP is not designed for room acoustics measurements, in particular it does not have any time based measurement functions such as cumulative spectral decays, energy time curves, etc. Here's what he said:

"it sounds like you are primarily interested in measurements for room tuning/acoustical treatment etc. That is definitely not currently within the scope of AP’s focus. Our acoustical tests are primarily aimed at measuring the response characteristics of transducers. It’s something that could certainly be added to the software as a future option, but I wouldn’t suggest our current product as a solution for that application."

I love absorbing it...now, if only I will apply it

Presently, my T&M gear has to satisfy a variety of needs...one of which, rather importantly, is characterizing transducer behavior

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Acoustic measurement standards for stereo listening rooms defined

Nyal Mellor

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RUR

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Nyal Mellor

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c1ferrari

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Nyal Mellor

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c1ferrari

Member Sponsor & WBF Founding Member

Jeff Hedback

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Nyal Mellor

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c1ferrari

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c1ferrari

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