Acoustic Treatments for an all concrete room. - AVS Forum
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post #1 of 27 Old 03-06-2012, 09:33 PM - Thread Starter
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I am doing a home theater in my basement. It is an unfinished basement. I was planning on doing drywall this summer, but I'm trying to see if I can just skip the drywall to save some money.

All the walls are concrete block, the floor is concrete, and the ceiling are these weird tile things with wood joists above them.

Even with all the concrete I really don't mind how it sounds as is. I'm not too picky with my audio. I'm just wondering if it'd be worth it to do a few things just to improve the sound a bit.

What would you guys do in this room if you weren't going to do drywall?

Here is the room right now. The measurements are 35' x 13' and 7'2" high.



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post #2 of 27 Old 03-07-2012, 05:44 AM
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Make some acoustical absorber panels and position around the room, get carpeting and pad. If you don't mind the way it sounds now you probably haven't experienced a well treated room and have an appreciation of what you are missing. You know the rooms audio sucks there is no doubt you need to do something.
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post #3 of 27 Old 03-07-2012, 07:13 AM
 
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Contrary to the assumption, there is nothing bad about the concrete walls. And they do not have 'sound' -- unless you are associating their lack of modification of the reflected energy as a problem, compared to other materials that can detrimentally modify the reflected sound.

They, unlike drywall and other commonly used materials, feature an acoustical impedance that is almost totally resistive, meaning the reflected energy will be nearly identical to the incident energy, thus avoiding the all too common effect that many wall covering have of partially EQing the incident energy causing the reflected energy to differ, and as a result when it recombines with the direct signal, the result is coloration.

But that said, to the degree that they are highly reflective, you will need to address the modal behavior and to similarly address the early and late arriving high gain indirect specular energy.


So what you need to do is to develop a concept for the response you desire, and then using measurements (e.g. REW) treat the modes and ascertain the ACTUAL paths of early arriving high gain reflections , for which broadband absorption can be used and then employ diffusion to the degree that you desire a later arriving semi-difuse sound field.
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post #4 of 27 Old 03-07-2012, 09:23 AM - Thread Starter
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So how do I find out where the reflection points are for sound?

I'm literally clueless when it comes to this. I've never done anything like treat a room acousticly before.
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post #5 of 27 Old 03-07-2012, 09:28 AM
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Wood panels, wood panels of different species, lathe and plaster walls, Type X drywall. Such totally detrimental materials in Meyerson Hall, Mechanics Hall, Kennedy Center, Mormon Tabernacle, Cobb Energy Center ... lions, tigers, and bears, oh me, oh my. The whole world destroys wonderful sound. Thank goodness for Red Rocks and Wolf Trap.

Jeremy...
You have a space with walls which are highly reflective, and non-diffusive, of sound energy. I'd suggest dialog intelligibility is way short of where it ought to be. Because of the resistive nature, particularily at the low frequencies of the concrete, you'll need to install or build bass traps and tame higher frequency reflections. So, to your question, given a limited budget, I'd suggest you forego drywall and contact a company like GIK Acoustics or Quest Acoustical Interiors to provide a plan you can execute as time and budget allow.

On the other hand, if "So what you need to do is to develop a concept for the response you desire, and then using measurements (e.g. REW) treat the modes and ascertain the ACTUAL paths of early arriving high gain reflections , for which broadband absorption can be used and then employ diffusion to the degree that you desire a later arriving semi-difuse sound field." makes any sense at all to you, you can come up with your own plan. I would, however, suggest contacting GIK and getting some direction.

Big's suggestion is also not far off the mark as a starting point!
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post #6 of 27 Old 03-07-2012, 10:05 AM
 
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Jeremy, despite the local politics and marketing that goes on here, the larger point was that many assume cinder block walls to be bad simply by virtue that they are cinder block. And thus assume that they must cover them with another wall surface material, that is not the case.

Now that is NOT to say that as they are maximally resistive and thus maximally reflective that you do not have a beau coup issues ranging from bass modes to specular reflections that absolutely need to be addressed. You absolutely do! Which speaks to Big's comment about your having become used to the resulting chaos.

So while others may want to belittle the "and a miracle happens" remainder of what I said - which was completely beyond the scope and purpose of the post regarding the issue of concrete block, and simply meant that a comprehensive strategy needs to be developed and a comprehensive plan then developed that accurately implements that plan - something that historically has not been done to any great degree where only bass traps and first order reflections (maybe - as determined sometimes with a mirror or simply estimating the 'half way point') were hopefully addressed based upon assumption.

If you are going to do this, I suggest taking your time, and whatever path you decide to take; employ measurements (by yourself or whomever you employ) to both objectively verify what is actually happening, as well as to objectively verify the effectiveness of the specific treatments in obtaining the actual response you desire. As there is more to effective treatment than simply hanging 'a bunch' of absorbers and installing a few bass traps in the 'usual places' and calling it a day. You owe yourself more for the expenditure in time and money.

And no, I am not marketing any product nor selling any services.
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post #7 of 27 Old 03-07-2012, 12:19 PM
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Quote:
Originally Posted by dragonfyr View Post

your having become used to the resulting chaos.

A much more politically correct and descriptive way of saying it sucks. I will use that next time.
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post #8 of 27 Old 03-07-2012, 03:37 PM
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A much more politically correct and descriptive way of saying it sucks. I will use that next time.

If someone could come out with a dummy's guide to acoustical design, they would be rich.

I think of myself as a fairly smart dude, and every time I read acoustical related posts I am lost
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post #9 of 27 Old 03-07-2012, 07:44 PM - Thread Starter
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Well bottom line and simply put... would it be worth it to dry wall as far as acoustics go?
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post #10 of 27 Old 03-08-2012, 04:04 AM
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No.

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post #11 of 27 Old 03-08-2012, 06:14 AM
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I agree that doing just the drywall in hope of improved acoustics is a waste of effort. You would need to treat the drywalled room much the same as has been discussed.

Having said that, converting an unfinished basement to finished space, if done in a quality manner and in accordance with your local codes, will add to the resale value of the home. If you DIY the potential increased value will pay for the materials.

So If I were in your shoes I would finish the space and then implement a room treatment strategy.
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post #12 of 27 Old 03-08-2012, 06:59 AM
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...despite the local politics and marketing that goes on here...


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post #13 of 27 Old 03-08-2012, 07:14 AM
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...despite the local politics and marketing that goes on here...


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post #14 of 27 Old 03-08-2012, 07:50 AM
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If there weren't people with significant hands on experience hanging around here it would be the blind leading the blind.
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post #15 of 27 Old 03-08-2012, 08:11 AM
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Drywall -- You do not need it. Applied directly to the concrete little if any acoustics value. It will improve room asthetics.

Acoustic Treatments -- you do require them. They do require various amounts of financial resources (GIK Acoustics is a good place to start). Spend your first dollars on those things that will make the biggest difference and, in this case, acoustic treatments.

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post #16 of 27 Old 03-08-2012, 08:25 AM
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Just a FYI, GIK is one of many sites that also sells DIY materials, Fabric and insulation, for the budget conscious.
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post #17 of 27 Old 03-08-2012, 04:24 PM - Thread Starter
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Ok well I think I am going to wait for drywall then. I can always do that in a year or two. It'll give me some time to use the theater for a good while and just think what I want to end up doing.

Now is there a good website for a noobie to start learning about some basic acoustic treatments I can do to a room?
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post #18 of 27 Old 03-11-2012, 07:47 AM
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Quote:
Originally Posted by jeremytodd1 View Post

What would you guys do in this room if you weren't going to do drywall?

Quote:
Originally Posted by Dennis Erskine View Post

You have a space with walls which are highly reflective, and non-diffusive, of sound energy.

Interesting that no one specifically mentioned sound blankets.
jeremytodd1, If you do not want to invest in a finished basement and want to stay within your budget, without getting sofisticated bass traps, diffusers and absorbers, sound blankets will do the job. ( Producers Choice sound blankets have a good feedback. ) They will take away the reflection, and reduce the chaos.
Installation is simple: just hang them on hooks.
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post #19 of 27 Old 03-11-2012, 10:08 AM
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Quote:
Originally Posted by VB2Go View Post

Interesting that no one specifically mentioned sound blankets.
jeremytodd1, If you do not want to invest in a finished basement and want to stay within your budget, without getting sofisticated bass traps, diffusers and absorbers, sound blankets will do the job. ( Producers Choice sound blankets have a good feedback. ) They will take away the reflection, and reduce the chaos.
Installation is simple: just hang them on hooks.

Welcome to AVS

What occurs with such an approach is that you're merely EQ'ing the reflected energy. The result would be a more dull (HF attenuated), poorly sounding room.

Typically, if one needs to attenuate any reflected energy, it's best to approach it in an all or nothing manner. The physics involved dictate that at least a 4" thick 703 fiberglass panel (or equivalent), mated to a 4" air gap behind the panel to maximize the effectiveness of the panel.

So merely placing a sound absorbing blanket up only absorbs a bit of the higher frequency sound. so the effect ends up with the problematic reflections only they now sound dull.


Good luck

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post #20 of 27 Old 03-27-2012, 08:38 AM
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merely placing a sound absorbing blanket up only absorbs a bit of the higher frequency sound.

Well i did not mean that as a universal solution, but that would be a good start. Better than bare walls i suppose....
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post #21 of 27 Old 03-27-2012, 09:49 AM
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Quote:
Originally Posted by VB2Go View Post

Well i did not mean that as a universal solution, but that would be a good start. Better than bare walls i suppose....

Toole: the AES paper: Loudspeakers and rooms for sound reproduction" section 7.1.2 Attenuating, Reflecting, and Scattering Indirect Sounds
JAES vol.54No6 June 2006


Quote:
Originally Posted by Toole View Post

Although reflections appear not to be great problems, it
is reasonable to think that there must be a level above
which the good attributes are diminished and negative attributes
grow. Obviously an empty room is not a comfortable
listening environment, even for conversation. The
furnishings and paraphernalia of life tend to bring normal
living spaces into familiar acoustical territory. Custom listening
spaces need to be treated. In all rooms absorption,
scattering or diffusion, and reflection occur, and devices to
encourage each are commonly used by acousticians.

It appears that much of what we perceive in terms of
sound quality can be predicted by the anechoic characterization
of loudspeakers. Because most of these data pertain
to sounds that reach listeners by indirect paths, it is proper
to suggest that nothing in those indirect sound paths
should alter the spectral balance.
For example, a 1-inch
(25.4-mm) layer of fiberglass board at the point of a strong
first reflection is effective at removing sound energy
above about 1 kHz. From the perspective of the loudspeaker,
the off-axis response of the tweeter has just been
greatly attenuatedit will sound duller and less good.
Obviously if the purpose of the absorbing material is to
attenuate the reflection, the material should be equally effective at all frequencies.


Given the duplex nature of
sound fields in small rooms, it seems reasonable to expect
similar performance at all frequencies above the transition
region.
In their examination of the audibility of reflections, Olive
and Toole looked at detection thresholds as high frequencies
were progressively eliminated from the reflected
sounds, as they might be by frequency-selective absorbers.
They found that only small to moderate threshold elevations
occurred for low-pass filter cutoff frequencies down
to about 500 Hz, where the investigation ended. Removing
the high frequencies alone is not sufficient to prevent audible
effects [32].

Finally there are the indications that the precedence effect
is maximally effective when the spectra of the direct
and reflected sounds are similar [4], [18], [20]. If the spectrum
of a reflection is different from that of the direct
sound, the probability that it will be heard as a separate
spatial event is increasednot a good thing.

Quote:
Originally Posted by Toole View Post

Thus from the perspectives of maintaining the excellence
in sound quality of good loudspeakers, rendering an
unwanted reflection inaudible, and preserving the effectiveness
of the precedence effect, there are reasons not to
alter the spectrum of reflected sounds. One is free to redirect
them with reflectors or diffusers, or to absorb them
with lossy acoustical devices, but in each case, the process
should not alter the spectrum of the sound above some
frequency toward the lower side of the transition region in
a small room.
It seems reasonable to propose, therefore,
that all acoustical devices used in listening rooms
reflectors, diffusers, and absorbersshould be uniformly
effective above about 200 Hz. For resistive absorbers this
means thicknesses of 3 inches (76 mm) or more.



but if you are not concerned with preserving the accuracy of the direct signal at the listening position, and the blanket is subjectively pleasing to you (or subjectively acceptable), then by all means do what is acceptable to your ears.
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post #22 of 27 Old 04-18-2014, 04:05 AM
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This is the RT60 of my all concrete 15x25x9 room. The lows are crazy. How much bass traps do I need? I doubt the typical 6" thick bass trap will do in this case.
Please help me
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post #23 of 27 Old 04-18-2014, 04:43 AM
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This is the RT60 of my all concrete 15x25x9 room. The lows are crazy. How much bass traps do I need? I doubt the typical 6" thick bass trap will do in this case.
Please help me

You want to focus on the waterfall/decay time chart. RT60 is used for LARGE rooms for the most part.
http://www.gikacoustics.com/understanding-decay-times/

Needless to say you are getting great advice above. Here are a bunch of articles and videos to help you get started on how you should treat the room and why.
http://www.gikacoustics.com/educational-videos/
http://www.gikacoustics.com/articles/
Quote:
Wood panels, wood panels of different species, lathe and plaster walls, Type X drywall. Such totally detrimental materials in Meyerson Hall, Mechanics Hall, Kennedy Center, Mormon Tabernacle, Cobb Energy Center ... lions, tigers, and bears, oh me, oh my. The whole world destroys wonderful sound. Thank goodness for Red Rocks and Wolf Trap.

LMAF!! biggrin.gif
biggrin.gif:D:D:D

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http://www.gikacoustics.com

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post #24 of 27 Old 04-18-2014, 05:40 PM
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Quote:
Originally Posted by myfipie View Post

You want to focus on the waterfall/decay time chart. RT60 is used for LARGE rooms for the most part.
http://www.gikacoustics.com/understanding-decay-times/

Needless to say you are getting great advice above. Here are a bunch of articles and videos to help you get started on how you should treat the room and why.
http://www.gikacoustics.com/educational-videos/
http://www.gikacoustics.com/articles/
LMAF!! biggrin.gif
biggrin.gif:D:D:D
Here's a waterfall chart for your preusal.
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post #25 of 27 Old 04-21-2014, 10:13 AM
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Quote:
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Here's a waterfall chart for your preusal.

Can you post the REW file so i can open it in my program?

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post #26 of 27 Old 04-23-2014, 06:17 AM
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Can you post the REW file so i can open it in my program?
Here it is:
http://ul.to/ljaq23ib
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post #27 of 27 Old 04-23-2014, 07:27 AM
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So would it be best to treat the first reflection points on the side walls and ceiling, then treat the front wall behind the speakers, and then the rear wall, all with absorption panels? I prefer to DIY all of my acoustical needs, and can highly recommend using two layers of 2" OC703 for a total thickness of 4" and then having a 4" air gap behind each panel.

For bass trapping, although it may take some effort to make it look pretty, you can use any type of the pink fluffy insulation cut into triangles and stacked on top of each other in every corner.

Would this not clean up the majority of the room issues , or, at least be the first step in treating a room such as this?, (ie: a room with all concrete walls).
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