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In the Forum: Horn-Loaded Speakers
In the Thread: Midbass Horns and Real Estate.
Post Subject: I might not be the best person to ask...Posted by anthony on: 10/19/2015
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...because I have never built a big horn such as this.  My knowledge is theoretical only.  But the way that I understand it is as follows...

 xandcg wrote:


1 - in a room around 15m x 9m x 5m (675m³) with the horn placed on the back wall or in the corner, a half-mouth would be more appropriated than full-mouth or would be the minimum requirement?


People build them all kinds of fractions of full mouth and get decent or perhaps even good results.  The basic rule is that the smaller the mouth the more SPL ripple you can expect on the output.  If you are careful, you can probably build a quarter-mouth horn in that situation and get a good result.  A well built smaller horn will probably give better results than a poorer construction on a larger horn.  Note that it is the location of the mouth of the horn that determines if it is free-radiating/1pi/2pi et cetera...the throat or back or any other part of the horn has no bearing on its radiation pattern...just how the mouth is aligned to large things that effectively become extensions of the horn such as walls/floor/ceilings/cupboards and so on.

 xandcg wrote:


2 - how the decision about mouth size (half or quarter) affect the length? A half-mouth horn was a half length requirement?


The length of the horn is primarily determined by three things:  the size of the throat; the size of the mouth; the expansion profile in between the throat and mouth.  Tractrix is one of the shorter profiles, but perhaps is less useful in lower frequency horns because of it length.  The longer exponential profiles and derivatives may be more useful if you really want to get a decent sound at the lower knee of the horn.
 xandcg wrote:

3 - What would be the difference between using 2 identical half-mouth horns and a full-mouth?


Assuming construction is equal, the full-mouth would give higher gain and a more linear (less ripple) SPL.  It is also likely to scare small children if you paint it black.

 xandcg wrote:


4 - How do the use of two or more drivers directly affect the length of a horn?


Well, I don't really see the point of two drivers in a horn.  But setting that aside two drivers will not affect the length of the horn unless the driver causes the horn to use a larger throat.

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