fiberglass thickness questions

[mike c]

ok, how important are the rear panels?
what do the rear panels do?
are they as effective/useful as the corner and first reflection points?

i know priority goes to the corners and first reflection points.

more room specific questions:
i have 3 small windows at the rear of my room, though im sitting about 13' away.

1) do i board up the rear windows?
2) is it necessary to put rear panels?

 

[bpape]

Priorities do not necessarily go to corners over the rear wall. Though corners are a very efficient placement and will certainly help with decay time in multiple dimensions, if bad frequency aberrations are being caused by cancellations off the rear wall - that MAY be a priority.

Every room is different. I needs to be evaluated and addressed as an entire system. While there are general rules of thumb, one can't say it's always better to do this or that.

As for the windows, that depends on how permanent you want to make it. From a light and sound control perspective - yes, walling them off is the best solution - albeit the most permanent one.

Bryan

 

[mike c]

more background info:

i have 3 244's and 1 242 on each left and right side walls for the first reflection points

i have 3 242's mounted on the ceiling first reflection points


i have a pair of tritraps stacked at the front left corner and a 242 at the front wall (behind the left speaker)


i've already boarded up the two giant windows on the left wall.
before/during/after pics
http://forums.audioholics.com/forums/showpost.php?p=424510&postcount=251

the rear looks like this (old pic)
http://i14.photobucket.com/albums/a330/superribbit/ded HT 1/IMG_5709.jpg

3 windows (one window not seen in the pic)
rear left corner now has rolled up persian carpets hugging the corner where the punching bag is (ultra-low bass trap?)

front right corner and rear right corner has doors so i can't treat the midwall corners, maybe a panel trap above the door is possible.

front left corner you've seen above with the tritrap. so basically, it's not a rectangular room.

i'll try to sketchup it tomorrow

 

[mike c]

sketchup is actually fun.
i dont have the exact measurements, but here is an idea of the room

with this orientation on the sketchup pic:
there are doors on the lower right corner and lower left corner of the room.
the wooden portion on the upper right is a thin drywall connecting to another room.

red panels are 242
black are 244

 

[Alex2507]

Hi Mike,

Having just finished playing around with the Rives Test CD 2 I am starting to have 'Deep Thoughts' regarding room acoustics. I know that you have the more detailed test tones provided by REW and wonder if you have actually been able to hear standing waves coming from specific spots with specific frequencies. Even with the Rives test tones I could definitely hear sound coming from places that I didn't want sound coming from but my seating places my ears about 16" from the back wall.

My primary objective was to see and adjust with a 12 band EQ what was happening front and center of the TV so I didn't want to be moving the SPL meter all over. Fortunately I got that done with some degree of success before being called back to work. If I had more time off, I would have played the problem tones on a loop and walked around with the SPL meter to quantify what my ears found to be odd. I am wondering if you are inclined to do something similar or maybe have already done so.

There is the school of thought that says that primary reflection points shouldn't be treated if the relationship between the speaker, reflection point and seating position meet a certain criteria. I would think that you are aware of that and applied the treatments as your room/speaker geometry didn't meet that criteria. I just thought I would ask about your choice for treatment placement and impressions of the results.

 

[mike c]

ut oh. i never measured anything. if Glenn K told me to jump off a bridge for better acoustic treatment, i might have

see this GiK illustration which i pretty much followed to the letter:

honestly, i never even ran REW in this room, and even if i did, i was only prepared to measure bass frequencies. (FR response)

also, since i've specifically placed my seating position 38% the length of the room from the back, i wouldn't have the rear wall problem you would (but i did start this thread to ask if do need rear wall treatment)

i also did not hear a difference before i put up the panels and after. but that's just me, i can't hear stuff like this

though i'm pretty sure the panels absorb sound and are effective when you are nearfield like you are from your rear wall.

i've also never heard of the train of thought NOT to treat the first reflection points if certain criteria were met.

 

[Alex2507]

i've also never heard of the train of thought NOT to treat the first reflection points if certain criteria were met.

Finding this taught me how to use the search function a little more effectively.

http://forums.audioholics.com/forums/showpost.php?p=411238&postcount=8

 

[mike c]

Finding this taught me how to use the search function a little more effectively.

http://forums.audioholics.com/forums/showpost.php?p=411238&postcount=8

i see, i read that back then and had thought it was more "speaker" specific than room specific

granted also that i havent watched a single movie in this HT since february and i think the panels arrived after that point in my movie watching life

 

[Alex2507]

i see, i read that back then and had thought it was more "speaker" specific than room specific

It is speaker specific in regards to off axis response characteristics. I couldn't remember the details in my first post but I just knew that you must have read that. I'm not suggesting that you do 'anything' with your treatments. Just want to be real clear about that. This is a discussion.

To continue the discussion I'll say that I believe the off axis response of the CMMD drivers in your Beta 50's would be similar to the MMD drivers which has been measured to be good so the post would refer to the Beta's as well. Speaker placement is one of the criteria as well.

Anyway, back to the back and side wall thing. My suggestion of taking measurements isn't going to work for a guy who doesn't have a lot of time. It took me a couple of days to do my thing. I can't wait to do more but that will have to wait.

 

[bpape]

It appears that you've addressed the major issues. However, you're a little shy on bass control in the overall scheme. The rear wall may be a good place depending on if it's causing you specific FR related issues.

As for hitting reflections based on distance, that's one theory. Overall, however, a certain amount of decay control is required in pretty much any room for proper multi-channel reproduction. Where you put it is another matter.

Bryan

 

[mike c]

It appears that you've addressed the major issues. However, you're a little shy on bass control in the overall scheme. The rear wall may be a good place depending on if it's causing you specific FR related issues.
Bryan

what would you suggest?

i was thinking it would be more efficient to replace the 3 244's on my left with 242's (im going to order) and use those 244's as "bass traps" in corners or the back. i will leave the 244's on my right untouched. opinions?

aside from that, i could also build "soffits" on the horizontal corners (ceiling - wall intersections)

 

[avaserfi]

It is speaker specific in regards to off axis response characteristics. I couldn't remember the details in my first post but I just knew that you must have read that. I'm not suggesting that you do 'anything' with your treatments. Just want to be real clear about that. This is a discussion.

Treatment of first reflections is not only related to off axis characteristics of a loudspeaker, but also cabinet resonance. Credible perceptual research has shown that these first reflections will increase resonance audibility within the source material (good) and within the speaker (bad) [1]. So with many typically designed loudspeakers (highly resonant), even those with a quality off axis response, treatment of the first reflections can yield superior results due to the lowered audibility of resonance in such a situation.

[1] Toole, E. Floyd. The Modification of Timbre by Resonances: Perception and Measurement. J. Audio Engineering Soc., Vol. 36, No. 3. 122 - 142 March 1988.

 

[mike c]

so i plan to use 80kg density rockwool for the rear wall to floor corners like pictured below

1) how thick do i have to make it to be effective?

2) in theory, which is more effective?
6" thick 80kg density
or
12" thick 50kg density (but lets assume this is 40kg for the sake of theory)

3) and is it ok to use full wood frames on the sides of these panels? or do i have to put holes on the sides?

 

[bpape]

Hi Mike - sorry, been buried.

I'd say that moving the 244's to the rear corners and/or rear wall is a good idea and use 242's on the side wall.

As for the other...

1. I'd want them at least 4" thick - more is better or 4" with an air gap behind
2. 12" of the lighter material will absolutely be more effective down lower in the bass.
3. A wood frame is fine around the perimeter in this application.

Bryan

 

[mike c]

thanks Bryan, will i get even more of a benefit if i go thicker than 12"

how thick til i reach the point of diminishing returns?