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Old 10th November 2006, 01:58 AM   #1
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Default FLH - question on front chamber

I've just been reading MJK's horn design documents and I have a question regarding the front chamber (coupling volume) to roll-off higher frequencies.

From running a few calculations, it looks as though the coupling volume has limitations regarding how high you can really us this. For example, when you intend to have a roll-off of 4kHz, and you have a 6 1/2" driver and S0/Sd=.5, then the coupling volume is about 9ci. This is less than the included volume (enclosed by the cone and the plane of the rim of the cone). Even at S0=Sd, the included volume is approximately the same as the coupling volume for a 4kHz cut-off, so there wouldn't actually be a way to contruct a chamber as the coupling volume finishes where the horn starts.

So to me it looks like there is an upper limitation on the coupling chamber - probably around the 2-2.5kHz area.

Does this sound about right, or are my figures incorrect?
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Old 12th November 2006, 12:34 AM   #2
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Martin?
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Old 14th November 2006, 07:27 PM   #3
e-side is offline e-side  Netherlands
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There's a practical limitation on front cavity volume. It's almost impossible to create a very small front chamber required for those high frequencies you mention, because you're restricted to driver dimensions, throat surface etc.

You might avoid the front chamber by coupling the driver directly to the horn. I don't know if it will affect sound quality at those high frequencies, but I think this is the only solution to obtain a higher cutoff.

However, I wonder if cone drivers are able to reach such a high cutoff in a horn, because of their mass- and inductance corner frequencies.

You could read Bruce Edgar's article about his midrange horn.
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Old 14th November 2006, 10:05 PM   #4
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Thanks e-side,

I just finished an offline chat with MJK who agreed that there would be an upper limit. I was just looking at it from the point of view of whether to design the cross-over around an low-passed mid or an un-attenuated one.

Can you point to Bruce Edgars' article, please?
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Old 16th November 2006, 01:26 PM   #5
e-side is offline e-side  Netherlands
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http://www.volvotreter.de/dl-section.htm > Articles > The Edgar Midrange Horn.
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Old 16th November 2006, 10:01 PM   #6
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Thank you. I'd found the site but hadn't found the document.
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Old 17th November 2006, 07:45 PM   #7
AndrewT is offline AndrewT  Scotland
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Hi,
extrapolating your question reminds me of the pepper pot tweeter (2inch) in a Tannoy Dual Concentric, which sort of reaches 20kHz and I'm sure other pressure transducers do similar.

It appears that the back of the throat follows the surface of the inverted dome.

I have seen a large horn loaded driver (about 8 to 10inch) that had the rear face of the chamber machined to closely match the most forward position of the cone/surround.

It seems that with careful measuring and manufacture some are able to minimise the volume between cone and throat.

Does this give you any ideas?
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Old 17th November 2006, 11:34 PM   #8
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Thanks, Andrew. But in this case it might be difficult.

I'll keep working on it...
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