Acoustic measurement standards for high end audio listening rooms defined

Nyal Mellor · « **on:** 13 Oct 2011, 11:41 pm »

There have been many many threads and questions on this forums regarding acoustic measurements. Some of the questions that have been asked include:

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

These questions and more have come about because of the cool, cheap and accurate measurement products from XTZ Room Analyzer, Room EQ Wizard and Dayton Audio Omnimic. Whist these products 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 Jeff Hedback of HdAcoustics and 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 which can be downloaded from this link http://blog.acousticfrontiers.com/storage/AMS%20for%20Stereo%20List.%20Rms.pdf.

This paper is good 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!

tubamark · « **Reply #1 on:** 21 Oct 2011, 10:12 pm »

'Just saw this - Certainly is an idea that has been kicked around for a very long time. I look forward to reading it this weekend.

What I'd also like to see is a standard for the recording industry . . . It's the one HUGE variable [in the long chain that stretches from the original sound captured to the listener's ear at the other end] over which we will never have any control. It's the one (professional) part of the reproduction process that is most arbitrary and variable. There are no standards for studio monitors, mix rooms, playback levels when mastering, how much DYNAMIC COMPRESSION is reasonable, etc.

The artistry of recording is fine, have at it.

Anyhoo, rant over.

'Hope to have some feedback for you!

poseidonsvoice · « **Reply #2 on:** 21 Oct 2011, 10:57 pm »

Nyal & Jeff,

Thank you very much for the herculean effort. As soon as I am done perusing your publication, I'll fire off some thoughts/observations. Your magnanimity to this community is deeply appreciated.

Anand.

ted_b · « **Reply #3 on:** 22 Oct 2011, 12:53 am »

I am exhibit room one (Jeff did an incredible job) so I'm just geeked that I made this report.

DEV · « **Reply #4 on:** 22 Oct 2011, 01:25 am »

Quote from: Nyal Mellor on 13 Oct 2011, 11:41 pm

There have been many many threads and questions on this forums regarding acoustic measurements. Some of the questions that have been asked include:

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

These questions and more have come about because of the cool, cheap and accurate measurement products from XTZ Room Analyzer, Room EQ Wizard and Dayton Audio Omnimic. Whist these products 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 Jeff Hedback of HdAcoustics and 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 which can be downloaded from this link http://blog.acousticfrontiers.com/storage/AMS%20for%20Stereo%20List.%20Rms.pdf.

This paper is good 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!

Nyla & Jeff, first I would like to thank you for the time you spent doing this, allot of great information.

I do have some questions;

Question 1:

What did you use to do you measurements, method and locations.

I have held off for some time now building a room but now it's time.

The room will be located in a basement, large space but messed up due to poor layouts of stairs, furnace room location etc.

The space I have to work with is 18' by 22'10" with 9' 3" clearance from the bottom of floor joist to concrete slab floor.
Two exterior walls are below grade with already constructed 2" x 6" walls. The other two walls I would like to construct in a method using a 2" x 6" top and bottom plate and studs to be 2" x 4" but installed in a staggered method.

Reading your white paper I already see my measurements fall well below your recommended 9'5" - 11' ceiling height and mine will only even be less upon finish.

Question 2:

What would you recommend for construction?

The ceiling joist cavities (resilient engineered joists) are clean of cold air returns etc., I was planning on securing "Sonopan" 5/8" drywall to the underneath of the sub-floor. Then leaving a bit of space installing Roxel Save & Sound, then leaving another space and adding another layer of Roxel.

I was going to cover the entire ceiling with the Sonopan first, then install resilient channel with two sheets of 5/8" drywall, staggered joints.

Unfortunately doing this has now just lowered my ceiling space by 3" down to 9ft and I still need to finish the floor.

Thoughts so far or changes

Floor:

I was thinking of putting down either DRIcore subfloor www.DRIcore.com 7/8" thick or Barricade insulated subfloor www.ovrx.com 1 1/4” and then putting on top my finished floor.

Undecided: a) wood flooring throughout and then ad area rugs on top b) carpet with under pad c) a portion with the hardwood where speakers are and the rest with carpet.

Wall:

I was going to do the same method, Sonopan - resilient channel - 2 layers of 5/8 drywall, Roxel Safe & Sound in the joist space weaved in and out due to the staggered studs.

Before installing the 5/8' on the walls going to have it say 3/8" off the concrete and then fill with acoustic sealant, same with up close to the ceiling.

Install mentioned flooring material leaving a space around the perimeter and again calking.

Door:

2 - Safe & Sound solid core doors sealed with rubber weather stripping, there would be approx. 6" space between the two doors

Room treatment:

Undecided whom to go with but GIK is on my short list

Speakers:

MBL 101E's

Seating:

One single in front and seating behind

Lighting:

Wall sconces and possibly a couple L.E.D. ceiling but still undecided

Any guidance, thoughts would really be appreciated.

JohnR · « **Reply #5 on:** 22 Oct 2011, 02:24 am »

Nyal, what is RC20, RC30, etc, and how do you measure it?

DEV · « **Reply #6 on:** 22 Oct 2011, 11:31 am »

Nyal, sorry about that spelled your name wrong.

bpape · « **Reply #7 on:** 22 Oct 2011, 02:35 pm »

Congrats guys. Haven't had time to read thoroughly but skimming through it, it looks very interesting.

Bryan

Jeffrey Hedback · « **Reply #8 on:** 22 Oct 2011, 02:48 pm »

Thank you all for the response and I'll try to answer most of the above (surely Nyal will join in at some time soon as well).

To Tubamark: there are specific and refined standards for audio production control rooms (AES...BBC). There are also many ways to get "there" as evidenced by my peers in the studio design niche. The top level pro control rooms have reached a very high standard in the past ~20 years with implementation of much hard earned knowledge...the converse is that today's recording budgets don't allow those rooms to be used as one would hope and much recording is done in less controlled environments. There is a nice evolution growing in the project/home rooms that pros are using toward compliance to standards (like those in our paper). If the record labels can come to terms with how people are going to purchase music, the situation has hope to improve sonically. Much more could be said, but that's not a bad place to leave it for now.

DEV: your room dimensions hold great promise. I have not studied them as given, but your 9'-3" is going to be fine. As for wall construction, it is important as it is possible to have similar mass in sidewalls. Concrete on one side and drywall on the other can do "funky" things to the LF region (below ~150Hz). Also in that regard, the attachment/spacing of materials to concrete walls has its own set of variables that can be positive or limitations (in most general terms, drywall should NOT be attached with direct coupling to concrete...either a 1" air gap or high performing isolation mounts should be used...and appropriate insulation). GIK is a great option for interior panels and LED lights have come of age. I use them frequently.

JohnR: thank you for your review of the paper. RC is Room Criteria and it is used in specifying HVAC (and related) systems...NOTE: Nyal and I have already discussed a revision to RCmk11 which is the in-field measurement aspect of Room Criteria. These have to be measured with high-quality (low self-noise) measurement system. ARTA does provide for RC measurements, but you'd need the whole system (mic, pre, soundcard, etc...to be lo-noise). The point of RC is that the spectrum of low frequency rumble and high frequency hiss are accounted for. Prior use of NC as a standard did not do so.

Jeffrey Hedback · « **Reply #9 on:** 22 Oct 2011, 02:53 pm »

Thanks Bryan.

In particular we think you'll appreciate Section B "Room Reflections". This is to us is a revolutionary (maybe a bit strong huh) view on energy over time where the focus is NOT on amplitude being automatically good or bad. Instead we now focus on the symmetry of energy and the spectrum within. We were very fortunate to have intense reviews with Dr. Floyd Toole. Our result gained his approval and are doable in REW and ARTA.

Thanks for the note!

Nyal Mellor · « **Reply #10 on:** 22 Oct 2011, 04:49 pm »

Quote from: tubamark on 21 Oct 2011, 10:12 pm

'Just saw this - Certainly is an idea that has been kicked around for a very long time. I look forward to reading it this weekend.

What I'd also like to see is a standard for the recording industry . . . It's the one HUGE variable [in the long chain that stretches from the original sound captured to the listener's ear at the other end] over which we will never have any control. It's the one (professional) part of the reproduction process that is most arbitrary and variable. There are no standards for studio monitors, mix rooms, playback levels when mastering, how much DYNAMIC COMPRESSION is reasonable, etc.

The artistry of recording is fine, have at it.

Anyhoo, rant over. 'Hope to have some feedback for you!

Indeed, and Dr. Toole makes exactly the same point in his book. As Jeff points out the trend towards more recording in 'non-optimized' spaces such as home studios and elsewhere means there is almost a divergence, in one direction towards standardization at the high end, at the other a real mish mash at the low end.

What was very interesting to me, not having a background in pro audio, was how control room design has often followed the preferred monitor speakers of the day, with some paradigms such as RFZ coming about at the same time as most studios were using monitors with very poor off axis response. And infact even more interesting, from Newell's Loudspeakers book, was that from this environment which is heavily treated many speaker designers have focused less on off axis response and more on things like power handling and max SPL since the rooms in place compensated for the off axis performance.

The other thing that happened during the writing of this white paper was the realization that the design paradigm many (but not all it seems, although they did not do a great deal about shouting about it) have been following is the reduction in reflected energy by xxdB rule. Quite clearly from discussing with Dr. Toole and reviewing the research it has been known for 20 years plus that this approach is simply not deep enough to understand what is really going on. Yet it has been popularized and now is quite entrenched, in fact it is the approach that nearly all acousticians have been taught and are following even though it is not right. A bit like dipole surrounds

jhm731 · « **Reply #11 on:** 22 Oct 2011, 04:52 pm »

There's a typo on page 22, room volume is shown in sq ft.

Rob Babcock · « **Reply #12 on:** 23 Oct 2011, 05:34 am »

Gonna check out the PDF, thanks!

Rclark · « **Reply #13 on:** 23 Oct 2011, 06:00 am »

I am very thankful for this. Within a few weeks, provided I maintain my savings for my Dec Maggie mod, I want to buy an spl device, soundcard, and start looking at what needs to be done to this room.

Nyal Mellor · « **Reply #14 on:** 23 Oct 2011, 10:51 pm »

Quote from: jhm731 on 22 Oct 2011, 04:52 pm

There's a typo on page 22, room volume is shown in sq ft.

LOL, if that's the only comment you have then I am VERY happy !! (it means the rest makes so much sense and is so well explained there is simply nothing to add)

jhm731 · « **Reply #15 on:** 25 Oct 2011, 06:50 am »

Quote from: Nyal Mellor on 23 Oct 2011, 10:51 pm

LOL, if that's the only comment you have then I am VERY happy !! (it means the rest makes so much sense and is so well explained there is simply nothing to add)

I only read the part about room size. Since there was no supporting info for the data you presented, I pointed out the typo.

IMO, most of what you've presented is self serving BS.

Based on what you've presented, and the excellent free info from Bryan and others, I won't pay anything for your services.

Have fun, but don't quit your day job.

JohnR · « **Reply #16 on:** 25 Oct 2011, 10:18 am »

Quote from: jhm731 on 25 Oct 2011, 06:50 am

I only read the part about room size. Since there was no supporting info for the data you presented, I pointed out the typo.

IMO, most of what you've presented is self serving BS.

The way I read it, it is absolutely nothing of the sort. The paper simply sets up some standards, which are sorely lacking. I see no "self-serving" in it at all. Any DIYer or anyone in the business can use those standards, or discuss or challenge them, or whatever. I find it a refreshing change from the "buy my acoustic product" tone that has permeated this circle in the past. No disrespect to Bryan or any other acoustics vendor intended - but they are after all in the business of selling acoustic treatment products, whereas the paper posted by Nyal is vendor-neutral as far as I can tell. I will say however that I do not think the followup response by Jeff Hedback to my question to be very helpful.

DEV · « **Reply #17 on:** 25 Oct 2011, 10:59 am »

Quote from: JohnR on 25 Oct 2011, 10:18 am

The way I read it, it is absolutely nothing of the sort. The paper simply sets up some standards, which are sorely lacking. I see no "self-serving" in it at all. Any DIYer or anyone in the business can use those standards, or discuss or challenge them, or whatever. I find it a refreshing change from the "buy my acoustic product" tone that has permeated this circle in the past. No disrespect to Bryan or any other acoustics vendor intended - but they are after all in the business of selling acoustic treatment products, whereas the paper posted by Nyal is vendor-neutral as far as I can tell. I will say however that I do not think the followup response by Jeff Hedback to my question to be very helpful.

I have to agree with JohnR thoughts above along with adding "I also did not think the followup responce to my question posted was very helpful."

Jeffrey Hedback · « **Reply #18 on:** 25 Oct 2011, 01:20 pm »

JohnR and DEV, you are very welcome.

To jhm731, the section you refer to is one that I was the primary content generator. I would gladly discuss any questions you have. I specifically re-read that section through the lens of your statement and I fail to see your point.

JohnR's kind assessment of this paper is the intent.

And I can add that "this is my day job", I take every aspect of it seriously, I love this field and work and enjoy the rewards.

Jeffrey Hedback · « **Reply #19 on:** 25 Oct 2011, 01:44 pm »

JohnR,

No sarcasm at all, I actually misread your post. So, first I apologize for that...you are right, that would seem horribly shallow and sarcastic.

If my reply was not helpful, I'd be glad to clarify. You asked what RC was and how to measure it. if my answer left more questions, then again...I'd be glad to clarify.

I apologize for my reply and misinterpretation of yours and DEV's reply.