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Acoustical Treatments Master Thread - Page 194

post #5791 of 9548
2/6/10 at 5:10pm
Quote:
Originally Posted by Hughman View Post

Quote:


A few years ago I attempted to tame the 31hz peak by purchasing a few bundles of the OFI-48. After weeks of experimentation the only remedy of any significance was to create a wall of absortion floor to ceiling about 8 feet out from the back wall (approx 1/4 wavelength) of the offending frequencies. This was prior to the two rows of seating I presently have which now makes implementation of the same solution a rather unpleasant movie-going experience for those in the back row.

so - - -is the point that we go to the pros for a mega-buck solution?
ASC makes what seems to be an industry recognized product (tube trap) that professes to control the lowest freq.'s. perhaps gik and ethan winers companies have products as well. there is a link earlier in this thread that connects to a diy ASC imitation - no idea if it is as effective as the real thing.
perhaps when kevinzoe logs back on he will have some insights.
walt
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post #5792 of 9548
2/6/10 at 5:16pm
Quote:


Quote:
Originally Posted by pepar View Post

That would certainly pass bass frequencies.

yes, but, would it be more reflective than gom? my guess is that it would, but, how to test?
as stated in my earlier post, i would hope that someone in this ether world would have the answer.
however, my thanks to pepar!
and now to my man cave for some viewing.
walt
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post #5793 of 9548
2/6/10 at 5:32pm
Quote:
Originally Posted by yacht422 View Post

yes, but, would it be more reflective than gom? my guess is that it would, but, how to test?
as stated in my earlier post, i would hope that someone in this ether world would have the answer.
however, my thanks to pepar!
and now to my man cave for some viewing.
walt

One of the acousticians on the thread might have an answer. Otherwise I only know that while there are websites that give test results for commonly used materials, I don't think that door screen is one of them. Is there a reason why you can't/don't want to use what many others have used - GOM?
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post #5794 of 9548
2/6/10 at 5:32pm
I am always at a loss as to why everyone always assumes that "pros" cost mega-bucks? Some pros can be had for $500 for giving advice to do exactly what you you are looking for, and considering how much went into a room cost and time wise...will that honestly break the bank to bring your room alive! The best answer I can give in that arena is ask a pro how much they cost, get references (do they know what they are doing), and then decide if your time and unanswered questions are worth the cost of the technician.

There are often easier solutions than slapping up tons of fiberglass to tame bass modes. A good place to start is to determine if a peak or null is actually due to a bass mode. Then proceed from there.

I am not familiar with OFI-48, but...if it is not unlike other fiberglass insulation, it works best as a frictional absorber. Understanding how the stuff we breathe is behaving in a theater room is of great benefit to determine how to treat your room.

To answer your question regarding screen or plastic...best answer I can give is give it a try! Not much spent if it turns out to be a failed experiment...and you're right....just about everything you can almost think of has been tried at one time or another. It's not often the materials alone...it's the combination of such materials that may or may not make the difference. Best wishes!
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post #5795 of 9548
2/6/10 at 5:37pm
Quote:
Originally Posted by SierraMikeBravo View Post


There are often easier solutions than slapping up tons of fiberglass to tame bass modes. A good place to start is to determine if a peak or null is actually due to a bass mode. Then proceed from there.

What else would cause a null?

Jeff
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post #5796 of 9548
2/6/10 at 5:50pm
Quote:
Originally Posted by SierraMikeBravo View Post

I am not familiar with OFI-48, but...if it is not unlike other fiberglass insulation, it works best as a frictional absorber. Understanding how the stuff we breathe is behaving in a theater room is of great benefit to determine how to treat your room.

The OFI-40/48 material is made by Ottawa Fiber and specs as the equivalent of OC 700 series. The product sheet for the 48 FSK board is below.

http://rds.yahoo.com/_ylt=A0geu.03Gm...-factsheet.pdf
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post #5797 of 9548
2/6/10 at 5:58pm
Quote:
Originally Posted by pepar View Post

What else would cause a null?

Jeff


Technically you are correct. A null is the result of a mode. I should revise that and say if not a null, what else is causing a loss of SPL at a certain frequency...or a dip. Could be several things. First thing to do though is to see if it is a null at that listening position which can be verified just by calculating the modes for the room.

Hughman...thanks for the info.
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post #5798 of 9548
2/7/10 at 5:00am
Quote:
Originally Posted by yacht422 View Post

so - - -is the point that we go to the pros for a mega-buck solution?
ASC makes what seems to be an industry recognized product (tube trap) that professes to control the lowest freq.'s. perhaps gik and ethan winers companies have products as well. there is a link earlier in this thread that connects to a diy ASC imitation - no idea if it is as effective as the real thing.
perhaps when kevinzoe logs back on he will have some insights.
walt

**************
With such a low freq peak, the resistive-type bass traps aren't likely to be the best solution. I think a better alternative would be to use a combination of multiple subwoofers and parametric eq. Then if you still need trapping a membrane/diaphragmatic or helmholtz type would be better suited.
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post #5799 of 9548
2/7/10 at 6:52am
Quote:
Originally Posted by kevinzoe View Post

**************
With such a low freq peak, the resistive-type bass traps aren't likely to be the best solution. I think a better alternative would be to use a combination of multiple subwoofers and parametric eq. Then if you still need trapping a membrane/diaphragmatic or helmholtz type would be better suited.

1. Speaker position.
2. Listener position.
3. Acoustical treatments.
4. Electronic correction.

Many/Most of us do not have the option of #2 as they are usually dictated by room size and layout, seats present, display size and location, etc. In other words ... other factors.

For #1, many times subs can be moved around, but the factors restricting #2 also many times limit #1.

More should be done with #3 but it sometimes runs afoul of aesthetics ... and even room space limitations. Nonetheless, acoustical treatments of room modes can make a HUGE improvement. Certainly moving a sub so as to not excite a particular room mode makes sense - and is free - but the mode is not eliminated .. and other modes are not addressed. Bass traps reduce the reflections that are the cause of room modes ... all of them. Install enough of the right traps and the room's LF response smooths out and sounds amazing. Unfortunately, most people are so unfamiliar with smooth, flat bass that they feel something is missing when they hear it. (But that's another subject entirely.)

Number four is the icing on the cake, but I would strongly recommend that something like the SVS AS-EQ1 (and multiple subs) be used to correct LF response. Simple equalizers don't come close to the improvements from this piece of gear. And it improves over all of the listening positions, not just one. And it works partly in the time domain so it can help with ringing. Electronic correction is not a substitute for acoustical treatments, but it will improve just about any room/system.

Just my $.02.

Jeff
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post #5800 of 9548
2/7/10 at 8:42am
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Hughman - As RT60 is typically associated with concert halls and generally large volume buildings, have you tried measuring a RT20 or RT30 should be a more realistic measurement for the home-based room size? It might be interesting to compare a RT20/30 measurement with your previous RT60 . . .

Just a thought . . .

Quote:
Originally Posted by Hughman View Post

I stupidly started a new thread regarding improving RT60 times in my room but will continue on here in this thread. In summary my room is about 2500sqft which I covered with fabric panels a couple years ago. During that time period I experimented with a few acoustic treatments but felt the overall presentation coupled with the fabric was a too dead sounding room. Returning to the issue I measured the RT60 times and posted the graphs in the initial thread here http://www.avsforum.com/avs-vb/showt...093&highlight=

The past couple days I removed the panels and purchased a case of 2" OFI-48 FSK insulation (Ottawa Fiber) which best approximated the frequency specific absorption values I felt I required. After a day of experimenting with placement of the acoustic insulation I settled on just two 2'x4' pieces placed horizontally touching the ceiling on the left and right front side walls adjacent to the screen. After initially loading up the room with the acoustic panels and measuring about between 2 and 2.5ms across the board and listening to the result it was clear, in an underwater way, the room and music were way too dead for my liking so I decided to try to target RT60 in the mid 3ms range which the results are below, along with an impulse response graph.

Just a note that with a room of this relatively small size the effective RT60 is far from a constant value and easily influenced by typical usage, reclining my 6 theater chairs has a fairly dramatic effect on the overall RT60 as does adding a few people to the arena. As such the multiple conditions the theater will be used should be accounted for and factored into the target RT60.

Though I loved the look of the theater with the fabric on the walls I'll now be leaving the walls bare except for the black velvet on the ceiling and front wall area.
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post #5801 of 9548
2/7/10 at 10:47am
I would also consider the Audyssey SubEQ. The designers of the SVS EQ were of course Audyssey. Trust me when I tell you that Audyssey saved the best elements for their product. The prices between the two are very comparable.
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post #5802 of 9548
2/7/10 at 10:51am
Quote:
Originally Posted by kevinzoe View Post

***********
Hughman - As RT60 is typically associated with concert halls and generally large volume buildings, have you tried measuring a RT20 or RT30 should be a more realistic measurement for the home-based room size? It might be interesting to compare a RT20/30 measurement with your previous RT60 . . .

Just a thought . . .

No I haven't plotted RT20 or RT30 I just used the RT60 tab in REW, is this a new development on the leading edge of typical HT sized room acoustics? A quick search for RT20 on this entire site shows your post is the very first mention of it.
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post #5803 of 9548
2/7/10 at 10:54am
Quote:
Originally Posted by SierraMikeBravo View Post

I would also consider the Audyssey SubEQ. The designers of the SVS EQ were of course Audyssey. Trust me when I tell you that Audyssey saved the best elements for their product. The prices between the two are very comparable.

I do trust you, but think you might be exaggerating a bit.

Using the Audyssey Pro balanced mic would be nice - as I have one - but it's not a deal breaker. Ditto MultEQ Pro. The Pro kits themselves are expensive and that needs to be factored in to the "total cost of ownership" for those who don't already own one. At least there are no license costs to use Pro on the Audyssey Subwoofer Equalizer.

Most people do not need to setup two subs in two independent systems.

Beyond those differences, they are identical.

Jeff
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post #5804 of 9548
2/7/10 at 1:16pm
I finally finished reading this thread from the very beginning. I must say, I was changing my mind (planned approach) several times, as there is lots of contradictions and different opinions

At this point, I decided to start with treating first reflection points (side walls first) and the back of the room (second row is near the back wall). I am still not sure if I want to put any panels behind my speakers (front wall), but most likely yes. I am still shopping around, but definitely I will use 4" for the back wall and probably 2" for the side walls. At this point my room is not treated at all, just the carpet on the floor.
Here is the output from REW, the blue line shows measurements without subwoofer turned on and the brown one shows mains with a sub. Should I be drawing any conclusion from these measurements? I see several peaks and nulls ....

Thanks,
Wojtek
LL
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post #5805 of 9548
2/7/10 at 1:57pm
Hi Jeff,

Mic sensitivity is quite a bit different between the two as well, and after talking with Audyssey repeatedly over this issue, there are significant differences worthy of the minute cost difference...and, IMHO, SubEQ just looks nicer...but I digress . In addition, the setup for the SubEQ is so easy, I generally don't ask much at all to install it. Takes me roughly an hour just for the SubEQ if I don't do secondary verification or any other work. There are distinct similarities, but for an extra few bucks, I would lean toward the SubEQ myself for the additional features.. Just personal preference. Nothing more.
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post #5806 of 9548
2/7/10 at 2:19pm
Quote:
Originally Posted by SierraMikeBravo View Post

Hi Jeff,

Mic sensitivity is quite a bit different between the two as well, and after talking with Audyssey repeatedly over this issue, there are significant differences worthy of the minute cost difference...and, IMHO, SubEQ just looks nicer...but I digress . In addition, the setup for the SubEQ is so easy, I generally don't ask much at all to install it. Takes me roughly an hour just for the SubEQ if I don't do secondary verification or any other work. There are distinct similarities, but for an extra few bucks, I would lean toward the SubEQ myself for the additional features.. Just personal preference. Nothing more.

You're probably right about the calibrated Pro mic being better to use for the subwoofer setup. When I overlayed a Pro calibration on my system, I thought I heard an improvement in the LF and Mains/SW integration. Some of that is undoubtedly due to the better (and individually calibrated) mic.

Jeff
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post #5807 of 9548
2/7/10 at 2:57pm
Quote:
Originally Posted by pepar View Post

One of the acousticians on the thread might have an answer. Otherwise I only know that while there are websites that give test results for commonly used materials, I don't think that door screen is one of them.
Quote:


Is there a reason why you can't/don't want to use what many others have used - GOM?

no, not really. it is a question of the intellectual type - i covered my treatments with gom, but, the superchunks covered in screen might have added to room reflections, (screen vs:gom) . i was hoping for additional insights, but, this is somewhat arcane, i suppose.
this is all new to me, and at some point, a trained pro will need to make a visit.
walt
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post #5808 of 9548
2/7/10 at 3:00pm
Quote:
Originally Posted by SierraMikeBravo View Post

I would also consider the Audyssey SubEQ. The designers of the SVS EQ were of course Audyssey. Trust me when I tell you that Audyssey saved the best elements for their product. The prices between the two are very comparable.

HI,

Is your recommendation of the SubEQ a general one or is there something in my graphs which, in your experience, highlights a specific area I would benefit (apart from the sub 30hz decay times)? The graphs depict the output from my front left speaker which has it's low fequency augmented by the Submerive for which I'm utilizing an outboard Mirage LFX-1 for low pass duties but, presently, I do not use any eq on the sub. Ideally I require a unit which will accept and apply a low pass slope from full range left and right input signals. I'd also prefer to send LFE to the same sub therefore at the end of the day three inputs would be required one with an indepedant crossover frequency and all three inputs preferably balanced.
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post #5809 of 9548
2/7/10 at 5:06pm
Quote:
Originally Posted by yacht422 View Post

no, not really. it is a question of the intellectual type - i covered my treatments with gom, but, the superchunks covered in screen might have added to room reflections, (screen vs:gom) . i was hoping for additional insights, but, this is somewhat arcane, i suppose.
this is all new to me, and at some point, a trained pro will need to make a visit.
walt

If you already feel that maybe a "pro" will in your future, why not just do it now and get it over with? Kind of like ripping the band-aid off quick. It won't hurt as much if you do it now and quickly rather than wait and do it slowly. Heck, you may even decide it was well worth it. If the person you decide to choose is worth their salt, you'll learn more about acoustics in a day than a year sifting through this forum. The problem with this or any other forum is that you have to know the exact question you're seeking to ask, which often leads to another question, etc. Then, you have to sift through a somewhat disorganized jungle in order to perhaps put together an answer for your question. Provided of course that the conclusion or snipets of information are correct to begin with.
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post #5810 of 9548
2/7/10 at 5:13pm
Hughman,

Audyssey won't really allow you to customize LPF. It's entire purpose is to adjust everything automatically...relatively speaking. There is a rudimentary customizable filter interface in the software, but I never use it. Not high enough resolution nor enough range for me. In addition, if you want balanced inputs, you'll want to go with the balanced SoundEQ rather than the SubEQ. If you want a parametric EQ that can be customized to your heart's content, I would suggest looking into the QSC DSP's.

Regarding your RT60, I would focus on trying to get an actual time decay overall and not frequency based. I only use frequency based decays for large venues where certain frequencies are more important than others such as the speech range...it just depends on the application. For small rooms, it can be argued that RT60 really has no bearing. I do believe you had a waterfall plot, too. I don't remember what was there, but equalization will assist in ringing as will seating and sub placement. They are all factors. Best wishes!
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post #5811 of 9548
2/8/10 at 5:04am
Technically speaking, there is no RT in a small room.
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post #5812 of 9548
2/8/10 at 5:15am
Quote:
Originally Posted by Dennis Erskine View Post

Technically speaking, there is no RT in a small room.

Practically speaking, there is.

And even technically, RT exists in small rooms just as for large -- it just starts at a high frequency. Where a large concert hall may have a smooth, reverberant sound field starting at maybe 20-30 Hz, a small room's may start at 200-300 Hz. Everything scales linearly. And modern multiplex cinema theaters are small enough not to fit neatly into the large or small room category.

- Terry
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post #5813 of 9548
2/8/10 at 7:39am
Dueling Acousticians?
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post #5814 of 9548
2/8/10 at 7:43am
Quote:
Originally Posted by pepar View Post

Dueling Acousticians?

Happens all the time in the real world.
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post #5815 of 9548
2/8/10 at 8:23am
Den frequency response plot curve utilizing radio shack SPL meter & tripod center listening area after sound treatment panels & corner superchunk.

Attachment 166325

Sorry for the attachment, as not sure how to make the image show up in post.

Anyways, a look at the results & any comments are most welcome.

Room Set-up-

17' w x 11' d x 8' h
Front main towers full range
Sub xover @ 80 Hz
Early reflection panels: l/ r sides, back, l/ r front & 24" x 64" superchunk left rear corner
Floors wood w/ large rugs (basement underneath)
Walls wood paneling
Ceiling sheet rock w/ R30 insulated attic

vvvvv Thanks pepar, much appreciated ! vvvvv
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post #5816 of 9548
2/8/10 at 8:40am
Copy this image to your desktop and use the "attachments" button (looks like a paper clip).

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post #5817 of 9548
2/8/10 at 9:49am
As much as 20dB between peaks and dips....hmmmm. I don't think the super chunks are a workin'. Have you calculated the modes for your room and is your sub in the corner? You may want to experiment with placement a little. Best wishes!
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post #5818 of 9548
2/8/10 at 9:53am
Quote:
Originally Posted by SierraMikeBravo View Post

As much as 20dB between peaks and dips....hmmmm. I don't think the super chunks are a workin'. Have you calculated the modes for your room and is your sub in the corner? You may want to experiment with placement a little. Best wishes!

Haven't seen the "before" ....
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post #5819 of 9548
2/8/10 at 1:53pm
Quote:
Originally Posted by pepar View Post

Dueling Acousticians?

Not at all - they're both right.

If the second and subsequent reflections are 60+ dB down, then it's a reflection rather than reverb because it dissipated too quickly to register as reverb which is RT60 by definition. But an empty bedroom size space can have real reverb.

What did I win?

--Ethan
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post #5820 of 9548
2/8/10 at 2:53pm
Quote:
Originally Posted by Ethan Winer View Post

Not at all - they're both right.

If the second and subsequent reflections are 60+ dB down, then it's a reflection rather than reverb because it dissipated too quickly to register as reverb which is RT60 by definition. But an empty bedroom size space can have real reverb.

What did I win?

--Ethan


Apparently everyone wins, my room acoustics have improved measureably just by knowing this.
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