or Connect
AVS › AVS Forum › Home Entertainment & Theater Builder › Dedicated Theater Design & Construction › Acoustical Treatments Master Thread
New Posts  All Forums:Forum Nav:

Acoustical Treatments Master Thread - Page 327

post #9781 of 10218
Quote:
Originally Posted by lbrown105 View Post

I have a 67hz ringing issue at most of my listening positions. My room is 33ft long and 14.5 ft wide except in front 8 ft of the room is about 17ft wide
The speed of sound divided by your room width should give you the frequency of your 2nd width mode.

1130 ÷ 17 = 66.5 (close enough to 67Hz)

Can you move your subwoofer to one of the quarter points of the 17ft room width (i.e., 4¼ feet from the side wall) and re-measure? Placing the sub in a null might help reduce the ringing.
post #9782 of 10218
Quote:
Originally Posted by sdurani View Post

Can you move your subwoofer to one of the quarter points of the 17ft room width (i.e., 4¼ feet from the side wall) and re-measure? Placing the sub in a null might help reduce the ringing.

Addendum: that's 4¼ feet from wall to center of the woofer cone, not 4¼ feet between wall and subwoofer cabinet - just to avoid any confusion.
post #9783 of 10218
Thanks I will give it a try this weekend
post #9784 of 10218
Couple questions for you guys. I heard that sandwiching 3-5mil plastic between OC703 will lower the absorption frequency, how dramatic would you say? I ask because I have 3 inches to work with for first reflection treatment so I could either use straight 3" or sandwich plastic between 2" and 1" pieces or even 3 pieces of 1". It will be a bit more expensive for all 1" but if it's a dramatic help, that's the way I will go. Thoughts?

Also, with no reflection panels in the room at all, the rear row of seating sounds much more open, less cluttered and just overall better than the front row, almost like I don't need first reflection panels for the 2nd row, how come the front row suffers more than the back row?

Room dimensions are 18' long by 10.5' wide and 7.5' tall. First row at about 10' and second around 14' from the screen.
post #9785 of 10218

I know the issue of risers as bass traps/broadband absorbers has been brought up a couple of times.  And the end of the discussion usually is that it is complicated and can have negative as well as positive influences on the acoustics of a room.

 

The conversation usually starts with whether cutting holes into a riser to allow the sound waves to interact with the fiberglass or other absorber that lies within the riser is beneficial.  And then it evolves into how many holes.  How big should the holes be.  Where should the holes be.  Etc.

 

I would like to phrase a related question from a slightly different perspective.  I can understand how cutting holes in the riser may help higher frequencies gain access to the absorbent material.  But for some reason, I have this impression in the back of my mind that says that lower frequencies (either because of their wavelength or amplitude?) are not easily "stopped" by ordinary construction materials like drywall, plywood, OSB, etc.  This explains in part why it is so hard to "soundproof" a home theater from the rest of the house and the supports the whole soundproofing industry of clips, channel, drywall, green glue, etc.

 

So my question is whether a riser, constructed of ordinary construction materials like 2x4's to 2x12's, 1/2-3/4" plywood or OSB, nails or screws, and maybe drywall or carpet or 3/8-5/8" wood flooring for example, would really pose an impediment to said low frequencies interacting with any absorbent materials within.

 

At the end of the day, is my 4'x18'x1.5' riser filled with fiberglass already acting as a bass trap of sorts even though there are no deliberate holes cut into it for acoustic considerations?  I have thought about cutting holes into it and seeing what would happen (and I may still do so anyways knowing that I can always just plug them up again before putting carpet down on the riser) but when I think more about it and the reports of the unpredictability of the net results, I've held off to date.  But when I actually measure my room, I have a prolonged decay time at 18-20 Hz. and also between 70-150 Hz.

 

post #9786 of 10218
Quote:
Originally Posted by RossoDiamante View Post

I know the issue of risers as bass traps/broadband absorbers has been brought up a couple of times.  And the end of the discussion usually is that it is complicated and can have negative as well as positive influences on the acoustics of a room.

The conversation usually starts with whether cutting holes into a riser to allow the sound waves to interact with the fiberglass or other absorber that lies within the riser is beneficial.  And then it evolves into how many holes.  How big should the holes be.  Where should the holes be.  Etc.

I would like to phrase a related question from a slightly different perspective.  I can understand how cutting holes in the riser may help higher frequencies gain access to the absorbent material.  But for some reason, I have this impression in the back of my mind that says that lower frequencies (either because of their wavelength or amplitude?) are not easily "stopped" by ordinary construction materials like drywall, plywood, OSB, etc.  This explains in part why it is so hard to "soundproof" a home theater from the rest of the house and the supports the whole soundproofing industry of clips, channel, drywall, green glue, etc.

So my question is whether a riser, constructed of ordinary construction materials like 2x4's to 2x12's, 1/2-3/4" plywood or OSB, nails or screws, and maybe drywall or carpet or 3/8-5/8" wood flooring for example, would really pose an impediment to said low frequencies interacting with any absorbent materials within.

At the end of the day, is my 4'x18'x1.5' riser filled with fiberglass already acting as a bass trap of sorts even though there are no deliberate holes cut into it for acoustic considerations?  I have thought about cutting holes into it and seeing what would happen (and I may still do so anyways knowing that I can always just plug them up again before putting carpet down on the riser) but when I think more about it and the reports of the unpredictability of the net results, I've held off to date.  But when I actually measure my room, I have a prolonged decay time at 18-20 Hz. and also between 70-150 Hz.



Your riser could be operating as a panel resonator currently. It would depend on the resonant frequency of each cavity between the joists. The resonant freq was governed by the mass/density of the membrane(plywood) and the volume of the cavity.

You can google some BBC documents for info on panel resonators.

If you cut holes you then have a helmholtz resonator. I've played with calculators for Helmholtz and you have to take great care to tune the resonator to the center frequency of issue and even more difficult is getting an acceptably low Q which targets a wide enough band to be useful. Helmholtz typically have a very narrow frequency focus so hitting your target is very critical.

There are online calculators to play with which will give you an idea of what to expect. Basically your port will be the diameter of the hole and port length will be thickness of material you drill through.
post #9787 of 10218
Quote:
Originally Posted by Digital_Chris View Post

Couple questions for you guys. I heard that sandwiching 3-5mil plastic between OC703 will lower the absorption frequency, how dramatic would you say? I ask because I have 3 inches to work with for first reflection treatment so I could either use straight 3" or sandwich plastic between 2" and 1" pieces or even 3 pieces of 1". It will be a bit more expensive for all 1" but if it's a dramatic help, that's the way I will go. Thoughts?

Also, with no reflection panels in the room at all, the rear row of seating sounds much more open, less cluttered and just overall better than the front row, almost like I don't need first reflection panels for the 2nd row, how come the front row suffers more than the back row?

Room dimensions are 18' long by 10.5' wide and 7.5' tall. First row at about 10' and second around 14' from the screen.
Hey Chris - glad to see you back.

When I think about using plastic in absorbers I think of it sort like a ported subwoofer. The plastic should bump the performance up a little near the low end. The details are related to size and weight and being sealed, but I don't have an equation or anything. Given that the performance increase is based on resonant behavior, I would not think multiple layers would improve anything - but what do I know?

I have more speculation for you: the difference in sound between the two rows probably has to do with the time delay for the lateral reflections. The rear row will have a longer delay. That's one of the reasons that Toole does not prescribe absorption for those early lateral reflections: they often improve the overall sound quality.
post #9788 of 10218
As far as I have understood it, it doesn't actually increase bass dampening, it just shift the dampening towards more bass dampening by making the higher less dampened.

Please correct me if I'm wrong if anyone has real data on the contrary.

Doesn't mean it's a bad idea, it's much easier to overdampen the top.
post #9789 of 10218
Hey Fred! I finally got HVAC plumbed into the theater so I'm ready to finish it off with treatment.

Now, if the rear row sounds good as is, I'm worried that I'll ruin that openness by treating the front row. I'd like to improve the front row without affecting the rear, therefor, I will have to be very specific when placing reflection treatment for the front row, correct?

As far as sandwiching plastic, it might just end up being a huge hassle as to how it should be applied correctly but I might place strips/full sheets of plastic on top of the 703 to keep a little crispness in the room.

I also wonder how I should treat the front/rear wall. I feel that the rear wall will need absorption to kill rear wall reflections, correct?
post #9790 of 10218
Nightlord, I'm not finding "real data" per se, but I think you will find this link useful, though the designs discussed there do work best with heavier membranes.


Chris, I think you should start with some ETC measurements for each row so we can see what you are preferring and what you're not liking, then we can figure out what needs to be done to make the front row as good as the rear - hopefully. Carefully placed absorption may be the best we can do, but some diffusion may be the right choice. I'm not sure I (personally) can tell based on ETC, but at least that will give you a starting point - and hopefully someone with some studio-design experience can help out.

The need for absorption on the rear wall will at least in part depend on the distance from the rear wall to the listeners. If it's close, the 1/4 wave cancellation might be strong enough to be a problem. Your second row is very close to the rear wall isn't it? Also, the timing of the reflection may be too close. If you find that you want a well-defined ITD, you will probably benefit from a kicker off the rear wall - I'm not sure what the process for that determination will look like, but ETC is the tool again. So we'll need some measurements (distances) and ETC for all the seating positions (or at least a representative sample). Also, you might just go ahead with absorption on the rear wall, because I know you still have bass issues (right?) - so some thick absorption may be the best choice for that reason, and then we can see about "livening" it back up with some plastic or diffusion on top.
post #9791 of 10218
Rear seats to back wall is about 4'. Not sure if you would call that "real close" but..

Yes, I do still have bass issues but not at the moment, subs are disabled. Basically, I was so sick of not having the real estate to apply proper low frequency treatments that I'd almost rather have no subs at all than a wacky sounding room :-/

Also, what is ITD and what is a "kicker"?
post #9792 of 10218
Quote:
Originally Posted by Digital_Chris View Post

Rear seats to back wall is about 4'. Not sure if you would call that "real close" but..

Yes, I do still have bass issues but not at the moment, subs are disabled. Basically, I was so sick of not having the real estate to apply proper low frequency treatments that I'd almost rather have no subs at all than a wacky sounding room :-/

Also, what is ITD and what is a "kicker"?

I am going to have the exact same 'bass' issues with my relatively smallish basement (about 12 feet wide x 18 feet length from screen)... my back row would be about 2-3 feet from the wall boundary...

One solution i am thinking is to limit the low bass to 20hz... and not go below.. or something like that...
post #9793 of 10218
ITD and kicker are terms usually applied to mixing and critical two-channel listening spaces, but they refer to psychoacoustic phenomena that relate to clarity and spaciousness in stereo imaging. When a reflection-free zone is established, such that no high-gain reflections are heard within the first 20 ms or so after the initial sound, you have an ITD - initial time delay or Haas interval. The ITD functions psychoacoustically to keep the perception of the direct sound undistorted. A kicker is a high-gain reflection that signals to the brain that the ITD has ended.
post #9794 of 10218
Quote:
Originally Posted by HopefulFred View Post

ITD and kicker are terms usually applied to mixing and critical two-channel listening spaces, but they refer to psychoacoustic phenomena that relate to clarity and spaciousness in stereo imaging. When a reflection-free zone is established, such that no high-gain reflections are heard within the first 20 ms or so after the initial sound, you have an ITD - initial time delay or Haas interval. The ITD functions psychoacoustically to keep the perception of the direct sound undistorted. A kicker is a high-gain reflection that signals to the brain that the ITD has ended.

Interesting, wiki says this about "kickers":
http://en.wikipedia.org/wiki/Precedence_effect
Quote:
Haas kicker

Many older LEDE ("live end, dead end") control room designs featured so-called "Haas kickers" - reflective panels placed at the rear to create specular reflections which were thought to provide a wider stereo listening area or raise intelligibility.[12] However, what is beneficial for one type of sound is detrimental to others, so Haas kickers just like compression ceilings are no longer commonly found in control rooms.[13]
post #9795 of 10218
Interesting. Thanks for the link.
post #9796 of 10218
I have a question. I was thinking of building frames around my screen and using 4-8 inch thick Roxul safe and sound in them and wrapping them with black felt.

Do you think this could help at all?

post #9797 of 10218
Question: I have a 16 X 22 X 10 purpose built H/T, with an entry opening in the center of one side wall. I have mounted two hollow construction cafe doors to serve as sound blockers, so to speak. My question is, would I experience better pressure from the subs(2)if I replaced the twin 18" wide hollow doors with one 36" solid wood door?
post #9798 of 10218
General statement when going to sound quality, solid door > hollow door. I am not even talking about any level of "soundproofing" here, but a hollow door would tend to flex more, and act like a drum (in a bad way). Plus two doors in a side-by-side setup would tend to rattle more than a single door.


Now, will you notice a difference in your particular room? Not sure. If there are other acoustical issues in the room, maybe not. If this is your weakest link and you are working on other acoustical properties, then maybe so. I just don't want you to think that just because it is "better" that you will actually notice a difference if, say, you have other rattles, or lots of peaks/nulls in the room, etc.
post #9799 of 10218
Quote:
Originally Posted by yacht422 View Post

Question: I have a 16 X 22 X 10 purpose built H/T, with an entry opening in the center of one side wall. I have mounted two hollow construction cafe doors to serve as sound blockers, so to speak. My question is, would I experience better pressure from the subs(2)if I replaced the twin 18" wide hollow doors with one 36" solid wood door?

With 2 doors you introduce more seal potential issues, any reason why you do not want to use just the 1 3ft wide door?


Sent from my iPad2 64GB using Tapatalk
post #9800 of 10218
i felt it easier for our guests to enter through two swing doors rather than one big heavy wooden one.
but, i am considering moving to move bass capable subs( SVS, et al) and the idea of pressurization came to mind. ergo: the question i posed.
I really do not fully understand the room pressurization thing - - - not clear how much better the bass response will be with solid vs: swinging. (if at all - - - do not know how to measure(can one measure pressure??)
post #9801 of 10218
Room pressurization has been talked here in depth, more so the audio forum or the DIY forum, search there for threads.
Acoustics thread is wrong for that, same sound isolation is not acoustics.

Actually I am in same boat as you, adding a double French door to my HT this winter, mine will be outside door, locking pins, extra sealed.

My concern for you is rattles if yours is not really solid.


Via my 64GB iPhone 5s using Tapatalk
post #9802 of 10218
Agreed, this acoustical treatments thread really only touches on how the door would effect the room itself, and thus the reason I only mentioned the hollow door maybe interacting with some frequencies in a more audible way, and put the disclaimer in my statement that everything else depends on room construction, sound isolation, etc.

While there is some overlap, yacht422 might get better responses elsewhere to sound pressurization questions.
post #9803 of 10218
post #9804 of 10218
Quote:
Originally Posted by wse View Post

I need bass traps that look good are these any good?

http://www.vicoustic.com/hifi-home-cinema/products/acoustic-treatment/absorption/panel/473

respectively, this is your HT, right?
5473bd65_ScreenShot2013-03-21at4.59.45PM.png

I have to ask, do you exactly know what "issues" you have?

Rather than asking are these "good looking" panels any good? (I assume you mean "do they work")


I suggest:
You go back to your HT designer, show them where you feel ("hear") there are bass issues in your beautiful HT.
Then, have them show you fact based data on where your sound is acoustic measurement wise, and then they advise you their countermeasure to fix.
(I assume you had in the agreement certain specifications to meet, and if you HT is not meeting those they should "fix" that as part of contractual obligation)


Those wood panels, from their website:
Quote:
Optimized for corner mounting, Super Bass Extreme's elegant wooden front is based on Vicoustic's flagship Wave Wood panel. This is combined with a membrane, two high-density foam layers and a micro-perforated rear panel, with 1mm holes, that acts as a Helmholtz resonator. Designed to provide effective low frequency absorption between 60-125 Hz, it delivers maximum effectiveness between 75 -100Hz.
and graph;


Possibly they could help as part of a broader strategy "solve" you issues, depends......once your issues are clearly defined and understood
post #9805 of 10218
Quote:
Originally Posted by mtbdudex View Post

respectively, this is your HT, right?
5473bd65_ScreenShot2013-03-21at4.59.45PM.png

I have to ask, do you exactly know what "issues" you have?

Rather than asking are these "good looking" panels any good? (I assume you mean "do they work")


I suggest:
You go back to your HT designer, show them where you feel ("hear") there are bass issues in your beautiful HT.
Then, have them show you fact based data on where your sound is acoustic measurement wise, and then they advise you their countermeasure to fix.
(I assume you had in the agreement certain specifications to meet, and if you HT is not meeting those they should "fix" that as part of contractual obligation)


Those wood panels, from their website:
and graph;


Possibly they could help as part of a broader strategy "solve" you issues, depends......once your issues are clearly defined and understood

I wish that was mine. I did my HT myself smile.gif
post #9806 of 10218
Quote:
Originally Posted by wse View Post


I wish that was mine. I did my HT myself smile.gif

ok - I got that from your sig link, that picture was there rolleyes.gif

Have you gone the measurement route to objectively confirm what you subjective are hearing?

Post a pict of your HT, I'm curious what it does look like.
post #9807 of 10218
There are images in you link in your signature that show that room. I was confused too.

To me, the product is made of foam (generally not the best material) and stuffed inside a MDF box with a few slots "routed" out of the front.

Not sure of the price, but since you did your HT yourself, I wouldn't pay for that. With a little bit of time, some tools, and effort, you can make something that looks nice, but is cheaper and probably performs better.

I am generally skeptical of products that seem to focus on the looks of the product first, and then the performance is secondary.
post #9808 of 10218
Quote:
Originally Posted by nickbuol View PostThere are images in you link in your signature that show that room. I was confused too.

To me, the product is made of foam (generally not the best material) and stuffed inside a MDF box with a few slots "routed" out of the front.

Not sure of the price, but since you did your HT yourself, I wouldn't pay for that. With a little bit of time, some tools, and effort, you can make something that looks nice, but is cheaper and probably performs better.

I am generally skeptical of products that seem to focus on the looks of the product first, and then the performance is secondary.

Yes, that was my worries as well!

post #9809 of 10218
post #9810 of 10218
Would placing cork material around the entire walls be a good idea?
New Posts  All Forums:Forum Nav:
  Return Home
AVS › AVS Forum › Home Entertainment & Theater Builder › Dedicated Theater Design & Construction › Acoustical Treatments Master Thread