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Old 8th August 2005, 12:26 PM   #1
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Default Compression Chamber Size

I don't have Mathcad or BLH worksheet and frankly don't understand how to use it. Well anyway!

I was messing around this weeked thinking of using a HiVi A2S as a back loaded folded horn. I'd like a small BLH similar to FE84E enclosure. Loaded the 2" driver into WinISD as a 1 liter vented enclosure, tuned 60 hz and .5"x4.5"x53" tappered vent.

The tappered vent (horn) is 1/16" per 1" for about 45" and (horn mouth) 3/8" per 1" for last 8".

Do I use the drivers 1 liter volume for the compression chamber size?

If not 1 liter volume what would you suggest would work best?


Noob, could use your assistance and suggustions.
Phil
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Old 9th August 2005, 06:53 PM   #2
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When I don't have an existing design already worked out,
I make the chamber larger than I will probably need and
then fill it, either with rocks or packing foam / peanuts.
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Old 10th August 2005, 12:05 AM   #3
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Quote:
Originally posted by Nelson Pass
When I don't have an existing design already worked out,
I make the chamber larger than I will probably need and
then fill it, either with rocks or packing foam / peanuts.
Hi Nelson
Love your horns. Good idea above.

How do I know when the compression chamber is near correct volume? Normally I use WinISD and deside on the best compromises.

How do I know what size the horn mouth should be? I made this horn mouth outlet nearly same as the FE84E drawing but I tappered the horn mouth.

My thoughts are to build the horn length based on port vent needs of the enclosure.

Please look at my horn drawing.
Thanks for your assistance
Phil
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Old 10th August 2005, 08:43 PM   #4
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Of course you know it's the right size when you get the
best sound. I use measurements to help out, but they
don't quite cover the territory, so I let my ears have the
final say.

From my experience in this regard, the performance is just
as sensitive to the stuffing in the chamber as the volume
itself, so you have two degrees of adjustment freedom. This
will tend to keep you busy for a while.

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Old 11th August 2005, 12:52 AM   #5
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Sounds like a plan.... lol, not much different than my other projects.

Thanks, Phil
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Old 11th August 2005, 10:17 AM   #6
Cortez is offline Cortez  Hungary
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By backloaded horns, is there any reason to use a compression chamber at all ?
How does it work ? It just decrease the efficiency cause the air compressed here
wont go to the horn. Or not ?
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Old 11th August 2005, 11:40 AM   #7
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Quote:
Originally posted by Cortez
By backloaded horns, is there any reason to use a compression chamber at all ?
How does it work ? It just decrease the efficiency cause the air compressed here
wont go to the horn. Or not ?
I can't answer these questions, I'm a noob to BLHs.

My believe is to reduce the drivers vented enclosure volume some (don't ask me by how much). This should increase flow thru vent port (the horn). The expansion of air within the horn due to taper restricts air flow back to vented enclosure chamber.

Please, can anyone explain any of this?
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Old 11th August 2005, 12:30 PM   #8
Mark Kravchenko --- www.kravchenko-audio.com
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Default REad this it gives a good explanation:

Download the article on the J-Low and you will have a clear explanation of what a rear chamber does on a back loaded horn. It attenuates the high frequencies at a rate of about 6db/octave. The volume can be calculated but as Nelson pointed out it is better to err on the larger side and pad pr fill it in the get the responce that you want.

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Old 12th August 2005, 05:57 AM   #9
Cortez is offline Cortez  Hungary
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I know that it acts like a low-pass filter, like a reflex enclosure, but what is does with the efficiency ?
The compression of the air particulars doesnt decrease the main sound energy ?
And what about using more then one compression chamber in series ?
The first chamber would be right behind the speaker with a small size, and then a reflex-tube-like
narrow section and then an other chamber with bigger volume, and at the end of this chamber
would start our horn with a small cross section.
This arrengement should have more "low-passing" character, and
due to air-compression the phase shifting wolud be also better.
And the efficiency would be the same cause of the horn ending.
A meditate often about hybrid type enclosures to combine the benefits of these types.
What do you think, is there a chance to achieve this ?
My basic principles: there are 3 ways to improve the bass response:
- BR: both the rear and the front radiation is working is phase
- TL: an open air column resonator helps us to enhence bass
- Horn: we improve the acoustic joint between the low freqs and the radiating area
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Old 12th August 2005, 11:55 AM   #10
Colin is offline Colin  United Kingdom
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If it helps, I came across this in an article by John Crabbe in HiFi News a few years ago:

horn decoupling equation, cavity volume for capacitive shunt reactance to equal horn throat resistance at frequency f, where At = throat area

V(cu in) = (2150 At)/f [where At is in sq ins]

V(cu cm) = (5550 At)/f [where At is in sq cm]

(JC developed a number of horn designs for the magazine in the 50s and 60s.)


Colin
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