Horn cut-off distortions and phase

[Pano]

Looking for measurements that any of you may have of horns and waveguides near their low cut-off frequency.
Standard practice is to high pass the horn at least an octave above its cut-off frequency. Is this really needed at home hi-fi levels? Some say no.

So if you have phase, distortion and impulse measurements that you would like to share, please do. Let us know what the horn and driver are, if you can. Also point out what you think are the important parts of your measurements. Actual measurements are vastly preferred over simulations here. Simulations are OK if you can also show us the real measurements.

It will be interesting to see what horns are really doing down there. Thanks!

[Robh3606]

Here's a 1 inch JBL 2425H on a JBL 2307 Exponential horn. It's a 1.2K horn so the sweep starting at 200Hz is well below cutoff. The red is the THD reading for the measurement.

Rob

[CLS]

Wow! As I can see the FR extends well down to 500Hz! And they call that a 1.2kHz horn? Also, the distortion below cutoff isn't any worse. Am I missing something?

[mwmkravchenko]

I'll see what I come up with. I'm doing some work with a different type of tapped horn. I've listened to the baby one for over a month and it does distort below cut off. But I'll do some actual carefull measurements on the bigger brothers. It'll be interesting.

Mark

[gedlee]

Originally Posted by CLS

Wow! As I can see the FR extends well down to 500Hz! And they call that a 1.2kHz horn? Also, the distortion below cutoff isn't any worse. Am I missing something?

Agreed, looks odd to me as well.

[Pano]

Thanks guys. The JBL measurement looks great. Interesting to see that distortion does not rise under the cut off. We don't know what phase is doing, tho..

[Robh3606]

Here's a JBL 2370 Flat Front Biradial with a 2426 1 inch driver. Lowest loading to 630Hz

Rob

[Robh3606]

Wow! As I can see the FR extends well down to 500Hz! And they call that a 1.2kHz horn?

Yes and there is some confusion in thier own literature as well early on it was 800Hz short throw and 1200Hz long throw. It changes part numbers in the Pro catalog and is the H91 in the Consumer catalogs. In the Consumer sheets it's 500Hz until about the late 70's where it becomes and stays a 1200Hz horn both there and in the Pro literature until the 80's when it was retired. Clear as mud.

Rob

[Jmmlc]

Hello,

We have to take care to how such mesurements are presented.

What we see is that the "absolute" THD curve comes nearer to the response curve (passing from 40dB = 1% at 1kHz to #-20dB = #0.1% at 200Hz) when the frequency decreases below the cut-off.
This indicates a 10 times rise in the distortion relatively to the "fundamental". (For further decreasing frequency there will be a frequency for which the THD curve will cross the response curve, at that pont THD will be 50%...).

Another important curve to consider is IMHO the group delay curve of the horn.

Best regards from Paris, France

Jean-Michel Le Cléac'h

Originally Posted by panomaniac

Interesting to see that distortion does not rise under the cut off.

[doug20]

Augerpro has done testing on many horns/waveguides this last summer.

http://www.htguide.com/forum/showthread.php4?t=33682

QSC Waveguides are cheap and impressive.