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Ratings of horns? [message #35780]

Wed, 03 April 2002 14:58

Garland
Messages: 269
Registered: May 2009

Grand Master

I saw the post below on Bmars wooden horn rated as a 800hz horn. This brings up my question: how exactly is a horn rated;ie, is, in this case, the 800hz the 3dB cut-off or what? have been wondering this for a while and was always too lazy to dig into the subject and find out.

Thanks!

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Re: Ratings of horns? [message #35781 is a reply to message #35780]

Wed, 03 April 2002 15:28

Wayne Parham
Messages: 18789
Registered: January 2001

Illuminati (33rd Degree)

Horns are often described by their flare rate. Assuming the horn is a standard Salmon shape or Tractrix, not a hybrid, if you know the type of horn (exponential, tractrix, conical), then the flare rate describes the horn profile. The mouth must have sufficient area to support the flare rate or response will be peaky. But if these conditions are met, then the flare rate essentially sets the lower cutoff. For a tractrix horn, the lower -3dB point is about a half octave above its flare rate. Exponential horns generally work down to their flare frequency. Horns have bandwidth of about three octaves. So its upper cutoff is about three octave above its lower cutoff.

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huh? [message #35785 is a reply to message #35781]

Wed, 03 April 2002 17:00

replay
Messages: 284
Registered: May 2009

Grand Master

for an 800hz flare, 3 octaves brings it to 6400hz. what happened to the top octave? is this where your compensation comes into place?

cheers,
george

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Top octave compensation [message #35786 is a reply to message #35785]

Wed, 03 April 2002 17:11

Wayne Parham
Messages: 18789
Registered: January 2001

Illuminati (33rd Degree)

The mass of the diaphragm and the inductance of the voice coil tend to make the driver start rolling off early. So the horn has to be matched to the driver. It wouldn't make much sense to use a super-tweeter horn on a large driver, because it couldn't reach that high. But most 1" exit drivers are made to work well with radial horns like this. The overall system starts rolling off well before the top octave, but collapsing directivity in the vertical plane tends to provide some acoustic EQ, and then the electrical EQ from top-octave compensation does the rest. The net result is flat response on-axis and along the horizontal plane within the flare angle.

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Re: huh? [message #35788 is a reply to message #35785]

Wed, 03 April 2002 17:21

freddyi
Messages: 48
Registered: May 2009

Baron

Hi George

if your horn has a fairly constant horizontal power distribution (CD type with little or no "neck") then rolloff will start above ~3.5Khz - most of the old-school horns had HF beaming from their natural expansion's long neck geometry which provides on-axis HF acoustic EQ - DB Keele Jr and others worked to develop the new breed of horns - old horns can sound pretty neat in mono

Freddy

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