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post #181 of 195 Old 02-02-2011, 09:09 PM - Thread Starter
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Been thinking about the false rear wall...... If I did say 2' filled with standard spary insulation, how much of an affect do you all think it would have?
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post #182 of 195 Old 02-03-2011, 12:08 AM
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Just from looking at some specs on-line, probably next to nothing down low where it takes a lot of mass and/or cubic air to dissipate long WLs. For example, if I did the math right, a 13 x 8 ft x 2 ft thick absorber requires around a 300 lb/ft^3 density (high grade steel territory) material to damp VLF with an air cavity behind it thin enough to be moot (~0.001"/20 Hz) and why multi-plex cinemas don't go low.

IF OTOH this 'false wall' absorber example was flexible, then making it with 'suspended' double panels of 3/4" MDF sheets should work well with just a narrow depth cavity.

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post #183 of 195 Old 02-03-2011, 06:01 AM
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GPM,

The analysis is good, but he doesn't necessarily want to damp 20Hz, that would require extensive amounts, and is difficult to contain with ordinary household construction, so it will be somewhat damped or will radiate away anyway. He wants to damp the higher length modes primarily, above 20Hz, specifically the ~41Hz, ~62Hz and above modes.

He does have a large room working in his favor, and seating placement may be able to avoid problems at the 1,0,0 20.5Hz mode. But this is all theoretical. Very difficult to tell how much of the rest of the house the subs will "see". Only way to tell is to place the subs and then experiment with absorption on the rear wall, or smaller subs in the back of the room.

JSS
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post #184 of 195 Old 02-03-2011, 06:16 AM
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This sounds great lilmike; I will certainly be watching this develop.

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Originally Posted by lilmike View Post

Simulation looks pretty familiar....

I've been messing with the Shivas for over a year now....

This model simulates at ~88 dB with 2 volts, and is -3 dB at 16 Hz. According to conversations with Kevin and direct experience, 500 watts is no problem for this driver, excursion models within xmax at that point (in band - a 15 Hz highpass is not optional), so that's +27 dB of headroom. In theory, they'll make ~115 dB 2pi at 500 watts. Corner loaded and room gain? That's up to your corner and your room.

In my room, a pair of these should get me to 115 dB at the couch well within xmax and the limits of my amp.

Cool part? Each cabinet will be smaller than 2' by 2' by 5'.

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post #185 of 195 Old 02-03-2011, 07:49 AM
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Quote:
Originally Posted by maxmercy View Post

GPM,

The analysis is good, but he doesn't necessarily want to damp 20Hz........

Greets!

Thanks for the confirmation, my math is dodgy enough to sometimes make me wonder if I did it right when I get seemingly ridiculous answers.

Yeah, I'm a victim of typical Southern house construction acting as one huge diaphramatic absorber.

Anyway, it's my understanding that turning the wall opposite the sound wall into a VLF absorber is like attaching a highly damped (massive) passive radiator to the end of a TL, damping all modes along its axial length including its fundamental (Fp) if tuned low enough, hence the example's brute force solutions.

Still, this does nothing for the other axial modes, so am a firm believer in multiple subs properly arranged around the room (or not, if enough of them are used) in 3D these days.

When it comes to dedicated HIFI/HT rooms though, my one serious attempt to deal with these issues was via room design rather than chasing down all the variables and what I use to recommend for such apps until I was ~drummed off another HT forum some years ago for it: http://www.avsforum.com/avs-vb/showt...1#post19930531

GM

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post #186 of 195 Old 02-03-2011, 11:24 AM
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Take a look at the RPG Modex absorbers

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post #187 of 195 Old 02-03-2011, 12:05 PM - Thread Starter
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Originally Posted by noah katz View Post
Take a look at the RPG Modex absorbers
Interesting but there isnt a price on them. I bet they are rather expensive compared to everything else on the site. Tensioned fabric covering 2' thick material mayend up being the way to go.

I'm going to frame panels to cover the entire room so it would match the look going this way. I'm not really familiar with all the stuff out there, just too many different companies to be familiar with everything. I wanted to use one of the companies that sell the sets of hidden tracks to fabric wrap the room but it seems like way to much work unless hired proffesional to do the install.
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post #188 of 195 Old 02-03-2011, 01:00 PM
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They sure are; a quick google search turned up ~$1300 at B&H Photo IIRC

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post #189 of 195 Old 02-07-2011, 12:32 AM
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I haven't forgotten about you here. Just cleaning out a back log of other stuff. This is back on deck now.


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post #190 of 195 Old 02-07-2011, 12:14 PM - Thread Starter
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Quote:
Originally Posted by soho54 View Post
I haven't forgotten about you here. Just cleaning out a back log of other stuff. This is back on deck now.

Kool! Think I'm ordering a pair of JTR8HTs today or tomorrow. Talked to Jeff and he thinks I'll be just fine with the 8's ensteadof the 12's since I'll be crossing them over anyway. Maybe a waste to go with the 12s. Hes getting shipping info now. I wanted to hear these before buying the entire set and not being happy with them. I can demo them in the living room which is kinda close to the size the theater will be but has open ceiling.
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post #191 of 195 Old 02-10-2011, 03:17 PM - Thread Starter
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What do you all think about having this room framed in by 8inch block ensteadof doing two layers of walls (tongue and groove plus drywall)? The ceiling would still need to be beefed up really well.

I ask this because I'm literally covering the room with different materials so whats under them wont be nearly as harmful to the sound as a regular concrete room would be. One of my friends will be using his crew for masonary work so I'll get a pretty good price on the job plus the price of two layers of walls will be expensive too.

One thing I was planning on doing with the wood wall was to predill and glue fill before screwing them up. Then green glue the drywall. Just a side note.
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post #192 of 195 Old 02-18-2011, 08:48 AM
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How does this work?

As you can see, I decided to go with more traditional bracing. I had mentioned doing something different, but in this case I believe this will work out better for space savings reasons.
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post #193 of 195 Old 02-18-2011, 12:06 PM
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Quote:
Originally Posted by audiovideoholic View Post

What do you all think about having this room framed in by 8inch block ensteadof doing two layers of walls (tongue and groove plus drywall)? The ceiling would still need to be beefed up really well.
---
One thing I was planning on doing with the wood wall was to predill and glue fill before screwing them up. Then green glue the drywall. Just a side note.

What is the main objective of your walls?

Are you trying for sound isolation from the rest of the house, or the best SQ in the room?


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post #194 of 195 Old 02-18-2011, 12:42 PM - Thread Starter
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Quote:
Originally Posted by soho54 View Post

How does this work?

As you can see, I decided to go with more traditional bracing. I had mentioned doing something different, but in this case I believe this will work out better for space savings reasons.

Yeah that looks awesome! Doesnt look too awefully hard to build either. The bracing seems pretty straight foward cutting. How big is the actual mouth? Thank you so much man!
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post #195 of 195 Old 02-18-2011, 12:46 PM - Thread Starter
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Quote:
Originally Posted by soho54 View Post

What is the main objective of your walls?

Are you trying for sound isolation from the rest of the house, or the best SQ in the room?

Just thinking about the stucture of the room itself mainly. I dont wont it to sound bad from all the preasure causing problems but at the same time want it to sound the best as well. I think double walls glued and screwed should be fine as long as I take my time with the glue and screw. But at the same time it wouldnt really cost much more at all to have it blocked either. The wiring would be the only issue.
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