Throat 101 advice please

**atilsley** · February 25th, 2011, 01:05 AM

OK, I'm building a new horn....300Hz conical, 8-sided...and will pair with one of the GPA 2-inch drivers.

Should the throat start expanding exactly from 2-inch diameter....or should I build any length of 2-inch 'tubing/tunnel' before the driver?

**Old Guy** · February 25th, 2011, 03:11 AM

Is GPA building 2 inch drivers?

**atilsley** · February 25th, 2011, 07:48 AM

I'm looking at this -

http://www.greatplainsaudio.com/downloads/390series.pdf

If I meant 'large format' instead of 2-inch, apologies.....

**whitebroncoii** · February 25th, 2011, 10:46 AM

Although I am not a driver engineer, I can tell you that HF compression drivers' throat sizes are around 1/2 the diameter of the voice-coil. The Altec large format drivers have a 2.8" voice-coil and a 1.4" throat. The Altec small format driver has a 1.75" voice-coil and a 1" throat. Others;

JBL
2" throat from 4" voice-coil
1.5" throat from 3" voice-coil

Electro-Voice
1" throat from 2" voice-coil (DH2)
1.5" throat from 3" voice-coil (DH1A*, ND6, DH7)
* The DH1A and older drivers had a 1.5" - 2" adapter built-in. The newer drivers require the adapter to be added.

**Old Guy** · February 25th, 2011, 11:07 AM

Originally Posted by whitebroncoii

Although I am not a driver engineer, I can tell you that HF compression drivers' throat sizes are around 1/2 the diameter of the voice-coil. The Altec large format drivers have a 2.8" voice-coil and a 1.4" throat. The Altec small format driver has a 1.75" voice-coil and a 1" throat. Others;

Agreed. There ARE a lot of 3 inch diaphragm 2 inchers out there (BMS, RCF,Beyma,Paudio). I consider them a 1.4 with adapter regardless.

Horn Design 101...download the Horncalc demo and read everything on the site..

HornCalc Tractrix Horn Calculation Software

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GM · February 25th, 2011, 12:27 PM

FWIW, since his horn is conic, Dr. Geddes's website in general and waveguide math in particular is a much better 'fit'. He's apparently removed the info from his website, but it should all be here (and more) in these threads:

Oblate Spheroid Waveguide - Consolidated Construction Thread - diyAudio

Geddes on Waveguides - diyAudio

A couple of others for budding horn designers that's worth reading:

Horn Honk $$ WANTED $$ - diyAudio

Jean Michel on LeCleac'h horns - diyAudio

GM

**Cal Weldon** · February 25th, 2011, 12:44 PM

Here is another link.

http://www.acoustichorn.com/tech/conical-horn-geometry/

**atilsley** · February 25th, 2011, 07:31 PM

Thanks a lot guys, sorry to confuse with the references to 2-inch etc.

I'll check the articles/links, but just wanted to confirm that the horn expansion starts exactly from, say 1.4" where the driver mounts the horn...or is there any tunnel/tube between where horn starts to expand and between the driver?