Conical Horn Dip - diyAudio
Go Back   Home > Forums > Loudspeakers > Multi-Way

Multi-Way Conventional loudspeakers with crossovers

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 16th March 2010, 07:41 PM   #1
MaVo is offline MaVo  Germany
diyAudio Member
 
Join Date: Jan 2006
Question Conical Horn Dip

Hello,

i have a question about conical horns. As seen in the picture, they often have a big dip in their frequency response at the lower end of their bandwidth - or maybe one should speak of two peaks. I would like to know if there are solutions to flatten the response, filling in the dip. Playing around in hornresp i have not found an obvious solution, except making the horn way to big to be usefull.

Kind regards,

Mathias
Attached Images
File Type: jpg horn.JPG (43.3 KB, 450 views)
  Reply With Quote
Old 16th March 2010, 08:44 PM   #2
diyAudio Member
 
Join Date: Nov 2009
Location: Birmingham, UK
Sorry I can't help you directly but the tweeter in classic Tannoy DCs ('pepperpots') is a conical horn which behaves very much like a CD horn (dispersion is a fairly constant 90deg from xover to 10kHz and it also requires 6dB/oct boost from around 5kHz up to make it usable in a 2way).
Exactly in the region you marked however it has a peak rather than a dip which Tannoy fixed with a notch filter. Removing that notch results in that horrible 'horn honk' so typical of nearly all '80s horn-loaded p.a. systems.
I always assumed that it caused by non-linear loading efficiency.

Either way since the problem was very common I'm thinking if you put a nice vintage AlNico driver on an actual horn the FR might even out a bit in real life.
If you're lucky…
  Reply With Quote
Old 16th March 2010, 09:51 PM   #3
MaVo is offline MaVo  Germany
diyAudio Member
 
Join Date: Jan 2006
Thats an interesting anecdote, Charles. I would take a peak allways over a dip, since filtering something away is better than having to amplify. The dip isnt present in a exponential horn and steadily grows when its morphed into a conical one by rising the flare rate T. So i guess its inherent in the conical horn shape.

If someone else has a clue or even a wild guess, please chime in and let me know.
  Reply With Quote
Old 16th March 2010, 11:50 PM   #4
diyAudio Member
 
Join Date: Dec 2002
Location: Planet Earth
The Hornresp model of a conical doesn't include a round-over at the mouth which helps reduce reflections back toward the throat, aka horn honk. The reflections cause peaks and dips at certain frequencies. I'm not too experienced with Hornresp but I think you can add a rounded or exponential section after the conical section. Give it a try.
__________________
Dennis H
  Reply With Quote
Old 17th March 2010, 12:03 AM   #5
MaVo is offline MaVo  Germany
diyAudio Member
 
Join Date: Jan 2006
Great idea catapult

I tried it and it could reduce the dip to about 2db. Although hornresp now tells me that a value called CIR is in a no good range for one horn segment, which means the results of the sim could be less accurate - i just hope that the loss in accuracy isnt the only thing that made the dip smaller.

So, if the dip is a result of mouth reflections, wouldnt adding foam for damping add even more to a balanced sound?
  Reply With Quote
Old 17th March 2010, 01:47 AM   #6
godfrey is online now godfrey  South Africa
diyAudio Member
 
Join Date: Nov 2009
Location: Cape Town

Lumpy response is a symptom of horn resonances, caused by the wave bouncing up and down the length of the horn, kind of like a fast echo.

To smooth it, you need a good acoustic impedance match either at the mouth and/or at the throat to avoid reflection. (It doesn't have to be matched at both ends)

At the mouth, the match will be good above a frequency determined by it's size. A larger diameter will be good down to a lower frequency.

With an exponential horn you can get a good match between driver and throat at lower frequencies - above the horn's cut-off, but below the driver's mass roll-off.

Conical horns are a bitch to match properly at the throat because they don't present a constant acoustic load to the driver - it drops fast with reducing frequency.

So...
With exponential (or similar) horns, you can get a nice smooth response when there's a good match between driver and throat at lower frequencies and a good match at the mouth at higher frequencies, with a bit of overlap.

But...
A conical horn with a small mouth is almost sure to give grief at low frequencies as the horn's badly matched at both ends.

Anyway, there's a couple of other things to play with aside from horn shape:

With cone drivers, the back chamber volume has a major effect on low frequency response. (With compression drivers, you're stuck with what you're given)

Any kind of crossover network (e.g. a series capacitor) will also have an effect on resonances - usually for the worse, but maybe worth experimenting with anyway. That's because it changes the driver's mechanical impedance, and therefore affects matching to the throat.

Hope some of that makes sense.
Cheers - Godfrey
  Reply With Quote
Old 17th March 2010, 01:53 AM   #7
godfrey is online now godfrey  South Africa
diyAudio Member
 
Join Date: Nov 2009
Location: Cape Town
Quote:
Originally Posted by catapult View Post
... I think you can add a rounded or exponential section after the conical section. Give it a try.
and/or an exponential section before the conical section.
Quote:
Originally Posted by MaVo View Post
... wouldnt adding foam for damping add even more to a balanced sound?
That's what Earl Geddes ("gedlee" on this forum) does with his horns. The whole horn's filled with foam. Apparently they're very good.
  Reply With Quote
Old 17th March 2010, 03:29 PM   #8
badman is offline badman  United States
diyAudio Member
 
badman's Avatar
 
Join Date: Sep 2003
Location: Sunny Tustin, SoCal
Quote:
Originally Posted by MaVo View Post
Great idea catapult

I tried it and it could reduce the dip to about 2db. Although hornresp now tells me that a value called CIR is in a no good range for one horn segment, which means the results of the sim could be less accurate - i just hope that the loss in accuracy isnt the only thing that made the dip smaller.

So, if the dip is a result of mouth reflections, wouldnt adding foam for damping add even more to a balanced sound?
Click the image to open in full size.

I added a foam collar, following a beveled profile around the mouth termination of the horn. Open cell foam being what it is is a combination of absorbtion and reflection, so in some respects this acts as an extension, and some as just a diffraction control device. In any case, I got about 1.5dB average ripple smoothing at the bottom end of the response by incorporating the collar you see below. Nothing to sneeze at!

There's a definite improvement in smoothness and clarity with the foam in place. Honk? Haven't heard any yet, though I'm well-loaded with reticulated foam in the throat and the foam termination of the horn.
__________________
I write for www.enjoythemusic.com in the DIY section. You may find yourself getting a preview of a project in-progress. Be warned!
  Reply With Quote
Old 17th March 2010, 04:39 PM   #9
MaVo is offline MaVo  Germany
diyAudio Member
 
Join Date: Jan 2006
Quote:
Originally Posted by godfrey View Post
... Hope some of that makes sense.
Cheers - Godfrey
Thanks, i think it does. So, the roundover seems to work as an impedance match at the mouth. And at the throat nothing can be done without loosing the constant directivity of the horn.
  Reply With Quote
Old 17th March 2010, 04:42 PM   #10
MaVo is offline MaVo  Germany
diyAudio Member
 
Join Date: Jan 2006
Quote:
Originally Posted by badman View Post
Click the image to open in full size.
Thats pretty much what i was thinking about. Until now, i only thought of foam as a HOM reducing device, while this use is more like room treatment for mode smoothing. Probably it works allways in both ways.

Have you tried using a roundover at the mouth instead of foam? Or maybe a combination of both?
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Conical Horn with Markaudio Alpair10 FR Henkjan Full Range 34 4th April 2011 03:26 AM
conical horn damping material... pauldune Full Range 14 14th March 2010 01:07 PM
Midbass Conical Horn - Keele vs Hornsresp which is the better FR? steve71 Multi-Way 28 27th October 2008 07:35 PM
Compensation for Conical Horn Sheldon Multi-Way 1 11th November 2006 10:01 PM


New To Site? Need Help?

All times are GMT. The time now is 05:03 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2