Need qualified room acoustician

[Jeff Hedback]

just for reference

to give a bit of perspective on NC numbers: typical residential background noise levels are 35-45dB and typical speech levels are 55-65dB. This link http://www.engineeringtoolbox.com/nc-noise-criterion-d_725.html does an excellent job of correlating NC ratings to typical dB's and types of spaces.

 

[vinylphilemag]

to give a bit of perspective on NC numbers: typical residential background noise levels are 35-45dB and typical speech levels are 55-65dB. This link http://www.engineeringtoolbox.com/nc-noise-criterion-d_725.html does an excellent job of correlating NC ratings to typical dB's and types of spaces.

Very useful! Thanks for posting that link.

 

[amirm]

Thanks Jeff. I put it in our technical library .

 

[The Bogg]

Hmmm....that's interesting that there is some agreement that a lower ETC is acceptable in a "quiet" room. I thought about this myself independently and thought it also made some sense. But Jeff Hedback's qualifier about the highs and mids is the real point (for me) b/c although my room is very quiet (as long as my wife isn't stomping around upstairs! not like she's huge or anything, 5ft nothing and 110lbs, but a stomper for sure) it is evident that the room balance is a bit "dull" with my fairly neutral speakers. I don't recall what the NC measurement was for my room but I recall Adam noted that it was quite quiet. It just means that I can't listen at really low volumes or the spectral balance is too far off for enjoyment. It's not my hearing!

I have a room within a room with kinetics isomax hangers on the ceiling. It's just like the water analogy - one leak and it changes everything. My door turned out to be a weak link also. One of the issues I have with the Rives process is that despite a lot of attention to hvac etc... the airflow and air exchange is completely inadequate for the room (3 supplies and 2 returns). In the winter with the heat on (not a dedicated hvac) and the projector running the room gets way too hot. Don't get me started about how for 5 figures you should get stuff "guaranteed" but at least the basics should be spot on. I'm not a guy looking for "perfection" but just something that is really good and would make most people happy. Didn't get that through the Rives room, although the end result after Adam's tweaking and integrating the first subs is quite good. Changing the room's acoustic signature to get that last "10%" would probably not be cost effective although it is something I still think about.

Ethan, I do get your point from the dermatology analogy, but I wouldn't fuss if it were a 50 dollar "mistake" that I had made choosing Rives - it was significantly more than that when you factor in the build cost on top of the service cost. But if I took off your wart and didn't give you what you paid for then I would've redone it for free - I've taken off "extra" skin tags at no charge and the pleased patient usually tells friends which leads to more business yada yada...

 

[The Bogg]

Maybe I'm just a softy, but I recently assisted a client in Germany (a recording/mix/post suite) who had hired a designer and was left with a horrible result. I offered an agreement, once I had a good understanding of his factors, of 50% to engage the process and 50% on success (and we defined what the exact acoustical goals were).

Guarantees are tough to offer, but real expectations aren't. I always want to feel that the "trust exchange" is an equal relationship between myself and my clients.

As for markers, some of this is relative to the background noise level. If the room is has low noise floor, NC25 or lower, I feel that a lower RT60 like the .2s mentioned can feel very comfortable providing you have "preserved" upper mid/hi energy (through strategic use of reflections and diffusion). If the room has a more typical background noise level, I agree with Nyal that .4s is right on target.
- LF resonances above 30Hz should not exceed 400ms (300ms preferred)
- Early reflections should be down 15dB from direct arrival for as long as possible (10ms absolutely minimum) to allow the source content to reach the listener without coloration.

Room shape/dimensions, construction systems, HVAC, speaker type/location, listener location, room finishes (which include absorption, diffusion and reflection) are ALL part of the acoustical factors that should evaluated to reach a desired response.

Jeff have you done any work for clients in Canada, specifically near Toronto?

 

[audioguy]

But if I took off your wart and didn't give you what you paid for then I would've redone it for free - I've taken off "extra" skin tags at no charge and the pleased patient usually tells friends which leads to more business yada yada...

I always insure my client is happy (even if the issue is not mine, I will still work to solve it) and as a result, 90%+ of my new business is referrals. Rives apparently doesn't understand that concept or just doesn't give a crap. It may ultimately catch up with him. Or may not

 

[The Bogg]

Open invitation: if any of the acoustics guys (Keith, Jeff, Ethan etc...) are up here for whatever reason (near Toronto) please let me know. I'll gladly pay for a "consultation" just to see if there is any reasonable option for improving the "feel" of my dedicated room.

 

[Jeff Hedback]

Hello The Bogg,

As an acoustician/designer I have not worked in Toronto. But I had the true pleasure, as a session bass playe,r of working in some of Toronto's finest studios in the late 80's. I was playing with an artist on Arista Records and famed Rush producer Terry Brown was our producer. He brought us up to track. Fantastic city.

I should clarify, it was the correlation between NC and decay times (rather than just ETC) that should be looked at when determining acoustical response...along with other factors mentioned such as speaker type, construction systems, distances between spkr/list & boundaries...etc.

I read recently in the speaker design subforum here at WBF a quote by one the JBL/Revel/Harmon engineers who summarized (paraphrasing here...) that listeners preferred low resonance/wide dispersion speakers. My acoustical response model preference is the same...low resonance/wide dispersion rooms. That said, each room requires it's own solution.

 

[The Bogg]

Hello The Bogg,

As an acoustician/designer I have not worked in Toronto. But I had the true pleasure, as a session bass playe,r of working in some of Toronto's finest studios in the late 80's. I was playing with an artist on Arista Records and famed Rush producer Terry Brown was our producer. He brought us up to track. Fantastic city.

I should clarify, it was the correlation between NC and decay times (rather than just ETC) that should be looked at when determining acoustical response...along with other factors mentioned such as speaker type, construction systems, distances between spkr/list & boundaries...etc.

I read recently in the speaker design subforum here at WBF a quote by one the JBL/Revel/Harmon engineers who summarized (paraphrasing here...) that listeners preferred low resonance/wide dispersion speakers. My acoustical response model preference is the same...low resonance/wide dispersion rooms. That said, each room requires it's own solution.

Can you clarify about decay times rather than just ETC, like what decay times you are interested in. What frequencies does the ETC usually refer to? I recall the process sounded like a bunch of "clicks".

 

[Jeff Hedback]

Hello The Bogg,

The "non-intuitive" yet wonderful part of an ETC study is that you're not looking at frequency on either axis. The "Y" axis is dB and the "X" axis is time in milliseconds. You're focusing on the arrival of energy relative to the original (direct) sound arriving at the test mic from the speaker/source. ETC is simply energy over time curve.

In small rooms (less than ~10,000 cu ft), the ETC is used to study how the reflective energy could cause skewing, coloration, shifting...etc.

Decay times (not reverb times in small rooms) are a way of looking at how the direct sound from the speaker decays in the room. This is studied typically in third octave bands and curves or charts are often generated: T60, T30 and other studies are ways of looking at the decay of energy over time at various frequencies.

My very general point (as each room is worthy of unique study) is that the greater the NC of a listening room the greater the decay time could and maybe should be. It's all about balance.

I'll post some graphs to clarify ETC and decay time studies in the next day or two. That is likely a better way to answer your question.

 

[The Bogg]

Hello The Bogg,

The "non-intuitive" yet wonderful part of an ETC study is that you're not looking at frequency on either axis. The "Y" axis is dB and the "X" axis is time in milliseconds. You're focusing on the arrival of energy relative to the original (direct) sound arriving at the test mic from the speaker/source. ETC is simply energy over time curve.

In small rooms (less than ~10,000 cu ft), the ETC is used to study how the reflective energy could cause skewing, coloration, shifting...etc.

Decay times (not reverb times in small rooms) are a way of looking at how the direct sound from the speaker decays in the room. This is studied typically in third octave bands and curves or charts are often generated: T60, T30 and other studies are ways of looking at the decay of energy over time at various frequencies.

My very general point (as each room is worthy of unique study) is that the greater the NC of a listening room the greater the decay time could and maybe should be. It's all about balance.

I'll post some graphs to clarify ETC and decay time studies in the next day or two. That is likely a better way to answer your question.

Ah that make sense. I guess I should've asked Adam for the decay times of my room as well, maybe he still has them.

 

[Norman Varney]

Something like this should be produced. This is a measurement I took of a client's room before we did any acoustic treatment. For a gold star: who can tell me what would be a good thickness of fiberglass absorber to use for this room?

I would propose that any acoustician worth his or her salt produced a report at the end of their work containing measured evidence of the suitability of their room for the task at hand. I think we should (the acoustician community) be able to put in place a set of targets for each measurement from IEC work and from AES and other published work.[/QUOTE]

The answer is likely more than just one type of panel. When we do modeling of say the reverberation times of the room, we plug in all we know about the noise reduction coefficients of the room's construction materials and methods, furnishings, etc. We then add the appropriate acoustical treatments to the room that will get us as close to the desired delay characteristics as possible. Just as one single driver in a speaker box cannot cover all the frequencies well, neither can a single type of panel. Based on the many constraints of the job (physical, decor, budget, etc.) we calculate how much, of what type, goes where. For playback systems, we are usually striving RT times between about 0.25-0.35 from about 100 Hz. and up, with slightly longer decay times below, depending.

Norman Varney
A/V RoomService, Ltd.

 

[Norman Varney]

Open invitation: if any of the acoustics guys (Keith, Jeff, Ethan etc...) are up here for whatever reason (near Toronto) please let me know. I'll gladly pay for a "consultation" just to see if there is any reasonable option for improving the "feel" of my dedicated room.

We'd be happy to help and are headquartered near Columbus, OH.

At your service,
Norman Varney
A/V RoomService, Ltd.

 

[Nyal Mellor]

The answer is likely more than just one type of panel. When we do modeling of say the reverberation times of the room, we plug in all we know about the noise reduction coefficients of the room's construction materials and methods, furnishings, etc. We then add the appropriate acoustical treatments to the room that will get us as close to the desired delay characteristics as possible. Just as one single driver in a speaker box cannot cover all the frequencies well, neither can a single type of panel. Based on the many constraints of the job (physical, decor, budget, etc.) we calculate how much, of what type, goes where. For playback systems, we are usually striving RT times between about 0.25-0.35 from about 100 Hz. and up, with slightly longer decay times below, depending.

Norman Varney
A/V RoomService, Ltd.

Hey Norm,

Great to have you here. This forum is turning into a meeting point for a wide collection of acoustical dudes! You, me, Jeff, Ethan and Keith all here!

I should have been much more specific when I posted this. For one I was only referring to the RT60 above around 200Hz since it ain't much use below that (not high enough resolution). For two I was referring to the upward slope in the RT60 above 1000Hz. Of course 1 type of panel isn't going to be the answer to everything!

Nyal

 

[audioguy]

I would propose that any acoustician worth his or her salt produced a report at the end of their work containing measured evidence of the suitability of their room for the task at hand. I think we should (the acoustician community) be able to put in place a set of targets for each measurement from IEC work and from AES and other published work.

That would be very great idea!

 

[Nyal Mellor]

Hey Audioguy, I actually wrote that originally. Norm forgot to include the

tag at some point so it got muddled up with the rest of his great points!

 

[Norman Varney]

Hey Norm,

Great to have you here. This forum is turning into a meeting point for a wide collection of acoustical dudes! You, me, Jeff, Ethan and Keith all here!

I should have been much more specific when I posted this. For one I was only referring to the RT60 above around 200Hz since it ain't much use below that (not high enough resolution). For two I was referring to the upward slope in the RT60 above 1000Hz. Of course 1 type of panel isn't going to be the answer to everything!

Nyal

Right! Small rooms are hard to measure low frequencies with much confidence. 1" fiberglass board will absorb frequencies 1kHz. and above. Just as important is to know how much is too much, or not enough and where to put it by computer model, subjective and/or objective evaluation.

 

[The Bogg]

We'd be happy to help and are headquartered near Columbus, OH.

At your service,
Norman Varney
A/V RoomService, Ltd.

Hi Norm,

I enjoyed reading your articles in Widescreen Review. Iirc, you were with Owens-Corning in the past? I have lots of OC703 and other products in my room!

Wow this thread has some real "heavy hitters" visiting! I'm definitely considering hiring someone to help with my room, I'll start my own thread so that I don't hijack this one.

 

[Andrew Steele]

Hi audioguy,

Can you post your room layout/dimensions? Treatments, sections, reflected ceiling plan etc would also be helpful if you have them.

 

[audioguy]

Hi audioguy,

Can you post your room layout/dimensions? Treatments, sections, reflected ceiling plan etc would also be helpful if you have them.

Room dimensions are 17.5 feet wide x 22.5 feet long and ceiling about 9 feet sitting on concrete in my basement. Front wall around screen is either diffusive (both sides)or absorptive (top and bottom). First reflection points on side walls are RPG BAD ARC Panels, ceiling in front is mostly absorptive (GIK 242 suspended about 3 inches) and on the rear ceiling is diffusive. Rear wall is covered in RPG Skylines and rear side walls are absorptive with 2 inch thick panels.

Front 8 feet of floor is hardwood and the rest is carpet. All four corners are bass traps and the soffits around the ceiling are traps.
If you look on this first page of this thread, you can see the room prior to changing the ceiling and the front wall (and the speakers !!)

I would also like to add that in an earlier post, I commented on the proposal that I received from Dennis Erskine and Adam Pelz. That was not meant to be a criticism, but rather to point out that neither they (nor, as it turns out, others I have contacted) are willing to guarantee that what they do will solve my specific glare issue. I sure don't mind spending the money but will not do so without assurances that what I pay for will solve the problem. And as we have noticed on other posts, room acoustic companies may be (apparently) willing to guarantee specific measurements (e.g decay, etc) but NOT specific sonic issues. Hence my attempts to keep trying things on my own (with somewhat limited success so far).