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Old 24th January 2011, 10:29 AM   #1
Bkaasen is offline Bkaasen  Denmark
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Default Chambersize in a BLH

What is crucial to pressure chamber size in a quaterwave BLH?
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Old 24th January 2011, 10:50 AM   #2
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The compression chamber acts as its name says . Since air is a 'squeezable' fluid ,the mass of air in the chamber acts like a spring . Its function is to decouple the cone at high frequencies . The membrane is not fully mass loaded as it would be without the chamber , in any kind of labirinth , and under a certain frequency it couples again with the mass of air , making its resonance lower.
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Old 24th January 2011, 12:31 PM   #3
Bkaasen is offline Bkaasen  Denmark
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I have probably expressed myself badly, because I am interested in knowing something about the optimal size of the chamber in relation to a given unit eg. this one https://www.madisound.com/store/prod...roducts_id=846 or Fostex FE108EZ
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Old 24th January 2011, 04:00 PM   #4
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It's a function of the horn's gain band-width (BW), flare factor (M or T) and flare frequency (Fc), or viewed another way, the driver's electrical-mechanical- acoustical properties, so no simple answer.

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Old 25th January 2011, 08:34 AM   #5
Bkaasen is offline Bkaasen  Denmark
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Yes you have right GM - its not simple.

I was so naive and believe that it had something to do with the unit specifications to make.
It surprised me that Fostex own recommendation in relation to FE108EZ is a pressure chamber of 1.53 liters, while I've seen on 6moons that Gemme Audio's Concerti 108 were build with a pressure chamber of less than 0.5 liters
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Old 25th January 2011, 10:15 AM   #6
hm is offline hm  Europe
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Hello,
try a simulation to see where the difference is,
but i miss one point the 108 has a Xmax of 0,26 mm,
thats nothing, also in a large horn you will get dynamic compression
below ~200 Hz and that below 0,5 Watt.
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Old 25th January 2011, 02:20 PM   #7
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GM is correct.

There is a lot off disagreement about an exact formula.
For the FE108Ez , search for : ibR108 horn , on this forum.
In the same part there also is an example of my concerti clone ( 15 sets build at this moment and growing)
Mostly I take the experimental approach ; take the CC larger and adjust by ear.
In the ibR108 ~~ 1.8 L.
In my experience room size is also an indicator!!

To Horst : My ibR108 design sounds like heaven!! but at limited output.
Very good for easy listening in (smaller) rooms of about 25m2.
The younger people are also putting Muse, Linkin Park etc. on.
No complaints about compression.
I do believe that Fostex was a bit conservative with the X-max.
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Old 25th January 2011, 03:34 PM   #8
GM is offline GM  United States
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Quote:
Originally Posted by Leonidas View Post
Mostly I take the experimental approach ; take the CC larger and adjust by ear.
Yes, this is always my recommendation for BLHs since no design routine I've been exposed to or many months of experimentation yielded a 'bulletproof' formula since a theoretical tuning often didn't work as predicted when the horn's out-of-phase output was added to the 'mix', i.e. one's ear 'hears' subtleties from the combining of discrete sources we apparently still don't know how to accurately measure.

GM
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Old 25th January 2011, 03:36 PM   #9
hm is offline hm  Europe
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Hello,
"To Horst : My ibR108 design sounds like heaven!! but at limited output.
Very good for easy listening in (smaller) rooms of about 25m2.
The younger people are also putting Muse, Linkin Park etc. on.
No complaints about compression.
I do believe that Fostex was a bit conservative with the X-max. "

do you made measurements and show us a simulation of membran movement,
the Data are a normed, in german DIN, there is no optimistic or conservativ measurements.
For householt SPL it is enough.
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Old 25th January 2011, 03:48 PM   #10
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To GM : we are on the same line; the practical way!!

To HM : no cone movement measurements, only by eye and finger : very little cone movement for the amount of lows (~70Hz)
Compared it with the Fe126e in a Frugal2 with DAAS32 and ATB for the freq. curves.
I also think we ( you and me) agree : low level ; for "household".
btw I do like your double mouth horns , very clever solution if you are willing to use more then one cone.
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