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e-side 17th July 2005 07:30 PM

horn questions

i'm looking around on the web for info about horns. I visited and some other sites, but there are still a couple of things which i don't understand (maybe because my english is not so very well).

- compression chambers.. what's the function of them. Is it possible that rear loaded horns have rear compression chambers, or front loaded horns have front compression chambers ?

- I saw that there a small room between the driver and the throat of an RL horn. How do you calculate the volume this room?

- do rectangular horns need a minimal width?

GM 18th July 2005 04:19 PM


Compression chambers are used only on front loaded horns (FLH) to reactance annull the horn's throat reactance, IOW equalize the pressure on both sides of the driver to 'force' the driver to be linear and maximize its gain near/at the horn's cut-off (fl).

The front chamber is a low pass filter chamber, so in a back loaded horn (BLH), this chamber is behind the driver, with the 'compression chamber' being the room, ergo no reactance annulling capability due to its acoustically large volume (Vb) unless some form of mass loading is used, with a small front horn usually the preferred option. Read Dinsdale's article for more info on this approach.

WRT calculating either and/or both chamber's Vb, Marshal Leach's formulas are accurate, though there are various ways to arrive at it, but DIY folks today usually just find it by trial and error using Hornresp.

WRT minimum aspect ratios, it is not a good idea to exceed a 9:1 ratio (width:height) or it becomes aperiodic (acoustically resistive) in nature.


e-side 18th July 2005 06:44 PM

thanks! it's clear to me now!

e-side 19th July 2005 07:59 AM

At the moment i'm reading the Leach paper on horn modelling, and again i couldn't give myself answers at the following things:

1. I read somewhere that a front-loaded horn should have the smallest possible volume between the driver and horn, while there's a room between the driver and horn in leach's paper (Vf, front cavity). Which one is correct?

2. Are throat and mouth calculations for a front-horn the same as for the rear horn?

3. In Leach's modell you'll have determine Wl and Wh at eq. (14). Are these the same as the low and high cutoff frequency of the system? if so, what frequency for Wh is suited when the low cutoff frequency is 35 Hz?

best regards

GM 19th July 2005 01:58 PM


1) The beauty of horns is their design/performance flexibility so there are few 'absolutes' in horn design. ML's default design is for an optimum compression horn for a given F3 (Fl, Fh), but is hardly the optimum for many apps. For instance you wouldn't normally design a 'fullrange' BLH with 10-12 dB of gain since baffle step requirement is only 3-6 dB.

2) ?? Yes, and no. I mean the math's the same, but what Fl, Fh you choose will be different and so may be the boundary.

3) Yes, though I work from Fl, Fh, which is Wl/(2pi), Wh/(2pi). It depends on the BW you want, so if you chose 3 octaves and the driver can handle it, then Wh = (35*2^3) = 280*(2pi) = ~1760 Hz.


e-side 19th July 2005 05:58 PM

thank u very much GM, but i already have a new question :happy2:

I searched for other material and so I downloaded Michael Zhang's software for calculating a horn based on ML's theory.
When the program designs the horn, it takes f0 ('Horn Cutoff Frequency') as the cutoff frequency (in my case 80,2 Hz), but i thought 35 Hz was the cutoff freq :confused:

Probably it's me who makes the mistake, but i just want to be sure before i design 'n build my new horn.

GM 19th July 2005 07:29 PM


You're welcome! I'm aware of the program (he lives fairly close to me and I helped him some with learning horn design also), but I've never installed the program since it requires also installing Microsoft .NET.

Anyway, I don't understand your Q. What is 80.2 Hz, the driver's Fs? Or is it just a sample design? Or.....?


e-side 20th July 2005 08:55 AM

2 Attachment(s)
Hello GM

I'll try to explain.

I would like to design a horn which has a Fl of 35 Hz and a Fh of 280 Hz (3 octaves). After I filled in the properties of my driver, ML's program calculates several values (as you can see in the first attachment).

As you can see, the Horn Cutoff Frequency (Fo) is 80,215 Hz. Leach says this is the frequency where 'reactance annulling' (?? I don't really understand what it is) can be achieved.

When I use the Horn Design function of the program, the Cutoff Frequency is set to Fo: 80,2 Hz . This results in a 'small' horn (see attachment 2).

I thought that this Cutoff Frequency had to be 35 Hz, beacuse Fo is to achieve reactance annuling.

Does the program use the right cutoff frequency (80,2 or 35 Hz) ??

BTW, if a horn can only cover 2 or 3 octaves, what about the frequencies above these octaves?
For example, my horn covers up to 280 Hz. Are the frequencies above 280 Hz, like 400 Hz, produced well by the system ?

I hope you understand my question now, since it's pretty difficult for me to explain in english :)

e-side 20th July 2005 08:58 AM

2 Attachment(s)
And here's the second attachment.

best regards.

paulspencer 20th July 2005 01:44 PM

I can't find that program ... has anyone got a link?

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