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Old 20th October 2010, 11:55 PM   #1
djn is online now djn  United States
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Default How do I design a back chamber for a horn speakers.

I can't seem to find any data on how to design a back chamber for a midbass horn. Is it driver dependent? Thanks in advance.
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Old 21st October 2010, 01:09 AM   #2
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Originally Posted by djn View Post
I can't seem to find any data on how to design a back chamber for a midbass horn. Is it driver dependent? Thanks in advance.
I assume you are talking about honest -to-goodness front loaded horns. You are correct, the size or volume is driver dependent. The concept is called "reactance annulling". Unfortunately, my memory for the equation fails me at the moment.

You should be able to get the equation with a google search. If not, then have a look at the JAES article by Delgado & Klipsch (2000). It has been posted over at the Klipsch site
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Old 21st October 2010, 01:24 AM   #3
bjorno is offline bjorno  Sweden
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Originally Posted by djn View Post
.. Is it driver dependent?..
Hi djn,

Yes, but there is more...

Try interpret the picture information in post # 7:
*
Low frequency horns
*
Use HR to visualize what you learn from the given numbered equations (#10) to (#14) and by that study all the calculated graphs.
*
b
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Old 21st October 2010, 05:09 AM   #4
djn is online now djn  United States
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Well, I have a BIG problem with all this. I can create anything and make it look beautiful in any medium....but I am NO math whiz. I read all the data and links you guys posted but it is all greek to me. I was hoping for something like 2+2=4
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Old 21st October 2010, 01:06 PM   #5
Helmuth is offline Helmuth  Netherlands
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Originally Posted by djn View Post
I can't seem to find any data on how to design a back chamber for a midbass horn. Is it driver dependent? Thanks in advance.
I played around with horn response and build some back-loaded horns.

My conclusion is that the closed volume depends on what resonant frequency you want of the driver. And see it as a closed box.

The resonance frequency is precise in the area where the back-loaded horn has its loading before cut-off. Then the driver is the most efficient in the horn.

Also when looking for a driver you only have to look for a driver witch will resonate around 70-80 Hz and so will work down to 50-60Hz. That are often bas-midrange drivers.

When you use horn response you can change the high cut off with the closed volume but it also effects the low end cut off characteristic.


So calculate it as closed box and try to get the resonance a bit above the cut off of the horn.

And when the horn has good loading the resonance will be suppressed and only where the loading is less a impedance peak appears.

This isn't a formula bit a simple explanation what happens in a back-loaded horn.
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Old 21st October 2010, 01:12 PM   #6
Helmuth is offline Helmuth  Netherlands
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I can't seem to find any data on how to design a back chamber for a midbass horn. Is it driver dependent? Thanks in advance.
Midbas horn you mean a front-loaded horn I guess.

Then agian it is like a closed box and the resonance is near the cut off frequency of the mid horn. So you can change the way the horn falls off at the low end, the point the horn looses loading.

Above that point the only the horn loading will effect the response of your driver.

The force of the voice coil is F= B*l (B force magnet, l length winding voicecoil in the magneticfield). This force driver the cone with area Sd. The resistance of the hornloading and force of the driver will effect the extrusion and Spl produced.

Horn response calculates al this so one doesn't have to be a math expert to design a good horn only fill in the TS-parameters in horn response.
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Last edited by Helmuth; 21st October 2010 at 01:25 PM.
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Old 21st October 2010, 02:12 PM   #7
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Well, I have a BIG problem with all this. I can create anything and make it look beautiful in any medium....but I am NO math whiz. I read all the data and links you guys posted but it is all greek to me. I was hoping for something like 2+2=4
Actually, it really is not complicated at all.

Have you done the google search on "reactance annulling". This, incidentally, is what was presented in the chart that was linked. Although, that introduced background that was perhaps confusing (it was also not needed for what you are trying to accomplish).
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Old 21st October 2010, 03:44 PM   #8
soho54 is offline soho54  United States
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You can use this Excel worksheet I am working on to do it. It is more geared towards THs, but it has an Nd/OD section.

It is designed to be used in tandem with Hornresp. The math is from Leach & Long. http://www2.link.langhofer.at/inspiron/HornPaper.pdf
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File Type: zip Easy Horn.zip (33.0 KB, 47 views)

Last edited by soho54; 21st October 2010 at 03:48 PM.
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Old 21st October 2010, 03:58 PM   #9
Helmuth is offline Helmuth  Netherlands
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Originally Posted by WithTarragon View Post
Actually, it really is not complicated at all.

Have you done the google search on "reactance annulling". This, incidentally, is what was presented in the chart that was linked. Although, that introduced background that was perhaps confusing (it was also not needed for what you are trying to accomplish).
They knew it already a long time ago article from 1955.
http://forums.klipsch.com/forums/sto...d_Williams.pdf

you wil play with this.

Click the image to open in full size.

speaker building is constant trying to stretch the low end with the enclosure. doesn't matter if it is a horn closed box or basreflex. The driver will somewhere resonate and create the cut-off frequency.

And a QTC of 0,7 is seen as most flat but it can go > 1 to have a more flat response with your horn or OB so we can play a bit with that.
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Last edited by Helmuth; 21st October 2010 at 04:09 PM.
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Old 21st October 2010, 11:10 PM   #10
jamikl is offline jamikl  Australia
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djn, I think MJK has a paper about it on his quarter wave site. At least he did have it. There is also a small program called ML which uses the Keele equations
and some driver specs to output the information. If you Google ML you might find it.

The main idea seems to to have the Fs when mounted in the chamber equal to the horn cut-off frequency but as it usual to cutoff the horn above that frequency I am not sure whether it is the frequency that you use the horn at or the cutoff frequency that you size the chamber to. The usual is to build a
bit larger than calculated then to add solid packing in small blocks to reduce the size until the impedance is right or it sounds right. Don't stretch the low end unless you want it to sound like a horn, ie megaphone.
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