Room gain, again - AVS Forum
Forum Jump: 
 
Thread Tools
post #1 of 3 Old 03-06-2012, 09:22 AM - Thread Starter
AVS Special Member
 
kgveteran's Avatar
 
Join Date: Apr 2004
Location: Rochester NY
Posts: 5,738
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 36 Post(s)
Liked: 39
Here is a close mic, no LT EQ is added, but there is a 80hz lopass XO from my receiver.



Here is another graph from head level at the LP, is it normal to gain so much lowend reinforcement of the lowend. BTW i think that would be all four subs measured at the LP.... also, that is an average of three head level positions, very little change from spot to spot, unlike the huge null around 60hz

kgveteran is offline  
Sponsored Links
Advertisement
 
post #2 of 3 Old 03-06-2012, 09:49 AM
FOH
AVS Special Member
 
FOH's Avatar
 
Join Date: Apr 2010
Location: Midwest
Posts: 4,749
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 18 Post(s)
Liked: 213
Quote:
Originally Posted by kgveteran View Post

.......

........is it normal to gain so much lowend reinforcement of the lowend

Absolutely, it's all about your HT space, and it's longest dimension.

If you could measure outdoor first, you could determine a great deal more. But typically you can see tendencies via measurments, even indoors.

Brief re-cap;
Oftentimes room gain encompasses both Boundary Gain, and Pressure Vessel Gain (PVG). Pressure Vessel Gain (PVG) is whereby the longest dimension of the room can no longer support full propagation of the waveform. At this point, the acoustic propagation transitions to acoustic pressurization. The manner in which the sound is reproduced into the space changes from a normal cyclic propagation, to pressurization because the wavelengths are too big for the space.

The frequency at which this occurs is approximately the point whereby half the wavelength of a given frequency is equal to the rooms longest dimension. So, a 20 hz frequency has a wavelength 56.5 feet. So half of that, 28.25 feet, is the point of transition. Any frequency below that point pressurizes the room, and any frequency above that point propagates freely. So in this room that's approximately 28 feet in the longest dimension, from 20 hz downward, the room gives back acoustically.

At this frequency, the results are a gain in acoustic pressures in the room that grows as the frequency decreases. This acoustic support reciprocity, is theoretically 12db per octave. The percentage of the 12 db/octave gain one achieves, entirely depends on the integrity of the boundary walls and surfaces. If it was the theoretical concrete bunker, a full 12db/octave boost would occur. Typically, somewhere between 6-10 db octave could result. Also, in addition to the walls and surfaces flexing, other aspects may affect the point at which room gain begins. Furniture, cabinets etc, anything that consumes a certain measure of cubic feet, may slightly alter the transition frequency merely because the items take up space.

What's your longest dimension in room?

Have you examined the time domain of the LF in your room?

Thanks

------------------------------------
Flat, Deep, Clean, Linear, and Loud
------------------------------------
Active 16.8kw, 7.3 system
(3)Seaton Cat12C up front, (4)QSC K8 sides/rears
(2)Seaton SubM-HP, (4)18" IB
FOH is offline  
post #3 of 3 Old 03-06-2012, 12:07 PM - Thread Starter
AVS Special Member
 
kgveteran's Avatar
 
Join Date: Apr 2004
Location: Rochester NY
Posts: 5,738
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 36 Post(s)
Liked: 39
First off, what an explaination ! My rooms longest lenth is about 15' Seems i have a natural LT working.
kgveteran is offline  
Reply Audio Theory, Setup, and Chat

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off