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Old 21st August 2005, 09:33 AM   #31
e-side is offline e-side  Netherlands
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Hello,

just another horn question again

I'm still busy designing a back-loaded bas horn for use in my living room. It's getting a bit confusing, because there are several ways to calculate the throat area.
I tried Leach's and Edgar's models and the equations from the BIG FUN article, but the results are different.

For example, with Edgar's method, i get a throat area of 36,78 sq. cm.
According to the BIG FUN article, i should use throat to driver ratios of 0,3 to 0,7 * sd, resulting in St=64,92 to 151,48 sq cm. Leach gives a throat area of 26,57 sq cm for a 50 Hz horn.

I already tried different values with hornresp, but i can't get a very smooth response for a BLH.

Could anyone tell me which method i should use for my BLH??

best regards
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Old 21st August 2005, 09:48 AM   #32
rcw is offline rcw  Australia
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Default back loaded horns

The truth about back loaded horns is that it is not possible to find an optimum since one does not exist.
The optimum back loaded horn is a bass reflex box, and no amount of hand waving will change it.
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Old 21st August 2005, 05:03 PM   #33
Mark Kravchenko --- www.kravchenko-audio.com
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Default Theories and reality

Your up against the great problem we all face when we can't check out the background behind the articles. If they have a bibliography you can generally check the sources for the theories.

The best first question is what are you doing with this woofer? Are you using the horn on a full range driver and augmenting the low end? Or are you making a horn sub?

Mr. Edgar is pretty conscientious in his research. But I think that his equations refer to a front loaded horn with a reactance canceling volume on the rear of the woofer. That statement also depends on the article that you are reading.

Another person who is careful with his sources is the Hornresponse program creator Mr. Mcbean. I have used it for a couple of years and the results are generally in agreement with what comes out. The question is always the same. Are we applying the programs and the theories properly? We tend to always want the smallest package and the lowest extension. Biggest bang for the buck. Sometimes a little less extension can be traded for a better horn and less ripple. Case in point is that length can give you low end potential. But it is a smooth flare rate and the proper mouth size termination that is the most important. Meaning that there will be less to no ripple if the two are in proper balance. The two work in concert. Can't cheat physics!

RCW's statement about a back loaded horn has some merit. There are always the cancellation effects that occur when the horn and the direct driver are covering the same range. The woofer tends to have more intermodulation distortion when it is not controlled by a rear volume of air. That little trick when properly applied makes a horn sing. Mr. Edgar has written quite a bit on that point to.

One other method to check up your results is to use the ML util found on the fullrange driver website. It applies Leach's theories to horn design and it to is quite accurate when you work within its design limits.


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Old 21st August 2005, 07:27 PM   #34
e-side is offline e-side  Netherlands
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Thanks for the replies!

Edgar's math comes from the Show Horn article. All the articles i read have a bibliography, but i think i'm going to use Leach's equations. Using hornresp, they seem to be accurate for a FLH design. For a BLH, the freq response has little dips and peaks, just like Edgar's math and the eq from the BIG FUN article.

best regards
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Old 21st August 2005, 07:59 PM   #35
AndrewT is online now AndrewT  Scotland
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Hi,
why should a back loaded horn be any different from a front loaded horn? Except the high frequency range.
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Old 21st August 2005, 08:34 PM   #36
Mark Kravchenko --- www.kravchenko-audio.com
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Default Front to Back

A front loaded horn has no compression chamber to control the cone. A rear loaded horn does. Ideally the chamber should be sized so as to null the impedance peak that the driver develops as the coupling between the horn and the driver unloads. Obviously a front loaded horn does not have this feature. The bumps and peaks are better understood when you run the impedance response graphs under Hornresponse. They usually coincide with the frequency response peaks. THat is usually a sign that the horn is being compromised somewhere.

This is not always bad. A real in room response of any driver box combination will have similar peaks and valleys. So the real question is if you can live with them.

Check this out:

http://melhuish.org/audio/horninfo.html

Look for : ML Util.zip

THis is an easy way to apply the Leach math.

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Old 21st August 2005, 11:40 PM   #37
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Default Re: Front to Back

Quote:
Originally posted by mwmkravchenko
A front loaded horn has no compression chamber to control the cone. A rear loaded horn does. Ideally the chamber should be sized so as to null the impedance peak that the driver develops as the coupling between the horn and the driver unloads. Obviously a front loaded horn does not have this feature.
Mark
For clarification, the term 'front' and 'rear' are swapped in this description. Ie, a front loaded horn does have a front and rear chamber where the rear chamber is a sealed box, while a rear loaded horn only has what would typically be considered a front chamber. The front chamber is visually between the driver and the horn (although acoustically it is in parallel with the horn - the air the driver moves can either compress the air in the front chamber or drive the horn).
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Old 22nd August 2005, 12:21 AM   #38
Mark Kravchenko --- www.kravchenko-audio.com
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Smile When you stand corrected you stand by yourself

Yep

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Old 22nd August 2005, 07:22 AM   #39
AndrewT is online now AndrewT  Scotland
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Hi,
I'll ask the same Q again.
Assuming that you can reverse the speaker with the magnet pointing into the compression chamber or the magnet pointing down the horn.
Q1. Why should a back loaded horn be any different from a front loaded horn?
Q2. with no compression chamber on either type (FLH & BLH) is the only problem unloading when driven below the horn flare rate lower cut off frequency?
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Old 22nd August 2005, 08:39 PM   #40
Coolin is offline Coolin  Netherlands
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Q1; without the sealed chamber there is no difference.
However the back loaded horn is normally used with a wide range driver to get some low end (out of phase) from a direct radiator and the front loaded horn is not normaly used with sealed back chamber.

Q2; Yes unloading will be more extreme. Then its just an issue of . You can call it whatever you like depending on if its pointing to you or away from you
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