Why, horn, compression chamber?

[tade]

I would like to know the purpose of the compression chamber in a bass horn. i was thinking just make a horn and bolt the driver onto it.
Also, i want to build a horn using two drivers. how do i modify the parameters when aplying them to the horn equations?
I suppose if the drivers are the same, the Fs will be the same. what about the rest?

Thank you so much.

[simon5]

Sd will double, Vas will double, Qts will stay the same.

[AndrewT]

Hi,
I can't get my head around your problem either.
front loaded horn - most folk say needs a rear chamber to sort things out.
rear loaded horn - almost no one boxes in the front of the cone, instead we listen to it.
Why should front or rear loading be so different?

[tade]

Andrew, i see where i was unclear.
i took a sec to clarify.
The A design is one with no compression chamber, i think. B has chambers on the outsides. And C is one i do see on most horns. C seems to me like a box ported with a horn. do you loose that horn goodness with that design?

Thanks for the help with the T/S parameters. Ill play with those during physics! Ironically, where they will most apply...

[mwmkravchenko]

THe rear chamber does two things. It providesa a cushion of air to help control the cone excursion. Acts like a spring. The second reason is that you don't want to get the higher frequency sound through the horn. It really muddies up the sound. THe rear chamber acts like a filter to keep out the highs. Mind you it doesn't filter out all the highs abruptly. If I remember correctly it acts like a first order crossover. or 6 db per octave. THe rear chamber can be sized to work as a crossover. The general idea is the larger the chamber the lower the crossover frequency.

MArk

[Rademakers]

I suppose if the drivers are the same, the Fs will be the same. what about the rest?

You can model it up in Hornresp. Wiring serial will give different results as in parrallel mode.

Mvg Johan

[zobsky]

Originally posted by mwmkravchenko
THe rear chamber does two things. It providesa a cushion of air to help control the cone excursion. Acts like a spring. The second reason is that you don't want to get the higher frequency sound through the horn. It really muddies up the sound. THe rear chamber acts like a filter to keep out the highs. Mind you it doesn't filter out all the highs abruptly. If I remember correctly it acts like a first order crossover. or 6 db per octave. THe rear chamber can be sized to work as a crossover. The general idea is the larger the chamber the lower the crossover frequency.

MArk

point valid and noted.
however, consider the situation of a horn subwoofer which has a lowpass x-overed electronically at line level, ... then the rear chamber doesn't need to act as an acoustic filter (though its "spring effect" may still be desirable.


that said, it is possible to have bass horns without rear chambers, . see thread http://www.audioasylum.com/forums/HU...ges/63017.html

[bear]

The idea of the horn tells you why a front "compression" chamber - actually a thoat - is used: the horn is an acoustic transformer or lever; it takes a small strong motion and changes it into a large weak motion.

By creating compression you have produced a short strong motion.

Intuitively, if you have no throat/compression area, *and* you expand the horn sufficiently, you arrive at an infinite baffle. Similarly, a long "bad" horn looks an awful lot like a TL.

The other purpose of a real "front" chamber with volume on a LF horn is to limit the HF response of the horn.

The *rear* chamber's purpose in the case of a *hyperbolic* expansion is to provide a reactance that permits the horn to operate down closer to the mouth freq/flare rate freq. A typical exponential horn will not make it all the way to that point, it tends to lose effectiveness before the calculated low frequency limit.

Since there are many horns that are "rear" loaded bass horns, it can be seen by inspection that it is possible to have a horn with no *rear* chamber whatsoever. How effective that approach is depends on the rest of the design's considerations.


_-_-bear

PS. the chamber between the diaphragm and the horn is the *front chamber*.

PPS. despite the graphic shown in the earlier post, the volume in the front chamber is usually smallish, not like the cuft used with a ported enclosure.

[mike.e]

Reason for sealed rear chamber - prevent 2HD !

Now,how bad the 2HD is from a driver loaded only on one side,I dont know,I havent seen measurements.

http://www.volvotreter.de/ ->downloads

Horn Loudspeaker Design Part 1, PDF, 881KB
"Horn Loudspeaker Design", by J. Dinsdale
Reprinted from Wireless World, Mar 1974, pp. 19-24.
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