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Multiple subs vs. bass traps
Multiple subs vs. bass traps
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Old 23rd January 2016, 02:16 PM   #171
Joel Wesseling is offline Joel Wesseling  Canada
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Ten Million dollar anechoic chamber


https://uwaterloo.ca/news/news/next-...facility-opens

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Old 23rd January 2016, 02:38 PM   #172
bentoronto is offline bentoronto  Canada
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Multiple subs vs. bass traps
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Originally Posted by Joel Wesseling View Post
Ten Million dollar anechoic chamber


https://uwaterloo.ca/news/news/next-...facility-opens
No radio-wave echoes! Instructive to consider that those radio wavelengths can be just fractions of an inch as compared to 50+ feet for sub-sonics. Not sure why you'd need any chamber, except to keep out of the Canadian winter weather. Maybe real function is as an isolation chamber, a very different issue.

Even mighty Harman Corp's anechoic chamber didn't/doesn't go very low and needed math tricks to estimate low frequency performance, if I read Toole correctly.

Few truly big-scale anechoic chambers like the biggie at Bell Labs in Murray Hill, NJ, where I fiddled with motional feedback 45 yrs ago. I'm not sure how low that went. Anybody? Or the EMI building??

Do you need to vacuum-clean an anechoic chamber every decade?

Ben
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Old 25th January 2016, 05:31 PM   #173
youknowyou is offline youknowyou  Canada
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Depends on a lot of factors. If you are doing serious construction, it costs only a bit more than the drywall it is substituting for and might need no finishing, unlike drywall. And that's it.

Ben
if you were to build the walls, why not use a couple of feet of fluffy rockwool which will work 10 times better.
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Old 2nd January 2018, 12:53 PM   #174
jpak is offline jpak  United States
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One of the more interesting approaches I have read about is Welti's method of just using two subwoofers (pretty sure this AES paper is freely available), one placed mid front wall and the other mid rear wall to "destruct" room modes. Any thoughts on this vs everything else discussed here?
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Old 14th January 2018, 02:42 PM   #175
JonFo is offline JonFo  United States
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Originally Posted by jpak View Post
One of the more interesting approaches I have read about is Welti's method of just using two subwoofers (pretty sure this AES paper is freely available), one placed mid front wall and the other mid rear wall to "destruct" room modes. Any thoughts on this vs everything else discussed here?
I use that method in my theater. The front Sub is 4x15 IB with the manifold in-room. The rear sub is a 16 cuft sealed sub with a 18" Dayton Ultimax powered by a Crown XLS2500 (bridged).

There was significant improvement in the smoothness throughout the space, and FR at the MLP improved. With just the IB, there was a big null at 20 and 76Hz, now smooth at 20 and much improved at both points now.

Here is the waterfall plot, measured at the MLP, it reflects my house curve EQ, which is why the <80Hz rises.

Room was ideally sized, and then extensively treated. Subjective bass is very smooth and clear. And that IB goes deep, shakes the whole structure, the door will occasionally pop open due to pressure and vibration releasing the latch!
But more importantly, music is crystal clear even at high SPL.

I do plan to add another 16cuFt sealed (identical to the rear unit) at roughly the mid-point sidewall location, almost parallel to the MLP. as a way of further smoothing some of the resonances at 27 and 41Hz.
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Old 14th January 2018, 07:22 PM   #176
scottjoplin is offline scottjoplin  Wales
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Quote:
Originally Posted by jpak View Post
One of the more interesting approaches I have read about is Welti's method of just using two subwoofers (pretty sure this AES paper is freely available), one placed mid front wall and the other mid rear wall to "destruct" room modes. Any thoughts on this vs everything else discussed here?
I've just read the whole thread, if you don't want to do that, start at post #104
This is very interesting stuff. I want to ask whether this method also means the room is not pressurised? It seems to
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Old 20th January 2018, 09:31 PM   #177
jpak is offline jpak  United States
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Originally Posted by JonFo View Post
I use that method in my theater. The front Sub is 4x15 IB with the manifold in-room. The rear sub is a 16 cuft sealed sub with a 18" Dayton Ultimax powered by a Crown XLS2500 (bridged).

There was significant improvement in the smoothness throughout the space, and FR at the MLP improved. With just the IB, there was a big null at 20 and 76Hz, now smooth at 20 and much improved at both points now.

Here is the waterfall plot, measured at the MLP, it reflects my house curve EQ, which is why the <80Hz rises.

Room was ideally sized, and then extensively treated. Subjective bass is very smooth and clear. And that IB goes deep, shakes the whole structure, the door will occasionally pop open due to pressure and vibration releasing the latch!
But more importantly, music is crystal clear even at high SPL.

I do plan to add another 16cuFt sealed (identical to the rear unit) at roughly the mid-point sidewall location, almost parallel to the MLP. as a way of further smoothing some of the resonances at 27 and 41Hz.
Do you think there are any downsides to doing this with a stereo system opposed to home theater?
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Old 20th January 2018, 10:32 PM   #178
bentoronto is offline bentoronto  Canada
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Multiple subs vs. bass traps
Alone among "suspensions", sealed boxes provide negative feedback, assuming the air is more linear than the starched fabric or bubbly foam rubber holding the cone in place.

B.
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Old 21st January 2018, 12:40 AM   #179
jpak is offline jpak  United States
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Quote:
Originally Posted by scottjoplin View Post
I've just read the whole thread, if you don't want to do that, start at post #104
This is very interesting stuff. I want to ask whether this method also means the room is not pressurised? It seems to
Can expand on what you mean by "room is not pressurized"?

Welti's method basically uses the second sub on the back wall to "destruct" the room modes since it is playing out of phase. I have seen measurements from one other system that does this (along with many RPG Modex plates) and the response is incredibly flat and the user says bass response is very even throughout the room.

Full paper is here: https://audioroundtable.com/misc/Welti_Multisub.pdf
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Old 21st January 2018, 08:27 AM   #180
scottjoplin is offline scottjoplin  Wales
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Two sealed subs, one phase reversed is a dipole and so theoretically won't pressurise the room. This link explains it DP_woofer_room
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