Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Multi-Way Conventional loudspeakers with crossovers

Combating Pattern Flip
Combating Pattern Flip
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 21st July 2018, 10:21 AM   #1
Patrick Bateman is offline Patrick Bateman  United States
diyAudio Member
 
Patrick Bateman's Avatar
 
Join Date: Oct 2006
Location: San Diego
Default Combating Pattern Flip

Horns and waveguides increase their output by directing it into a narrow beam. For instance, a compression driver on a horn may produce as much as 110dB with a single watt, by focusing all it's energy in a narrow beam.

Click the image to open in full size.

One of the downfalls with this is 'pattern flip.' Pattern flip is when the waveguide or horn loses 'pattern control' on one axis but not the other

For instance, the waveguide on this JBL PRX 425 will control horizontal directivity down to about 1350Hz, but it's vertical directivity will collapse at about 3300Hz.

This is caused by the dimensions of the waveguide. It's waveguide is approximately 25cm wide, which means it will control the pattern down to 1350hz. (34,000cm per second / 25 cm = 1360Hz.)

'Pattern flip' can really make a speaker sound weird. You basically have an octave or two where the directivity of the speaker is completely asymmetrical. IMHO, this asymmetry makes it VERY difficult to come up with a crossover that sounds natural. When there are a couple of octaves where the directivity is all over the map, it's not possible to 'voice' the speaker properly.

In my personal experience, 'pattern flip' is one of those 'unsolvable' problems of loudsepeaker design. If you try and fix it with EQ, the speaker just winds up sounding weird. The only appropriate solution is to avoid pattern flip entirely.
  Reply With Quote
Old 21st July 2018, 10:26 AM   #2
Patrick Bateman is offline Patrick Bateman  United States
diyAudio Member
 
Patrick Bateman's Avatar
 
Join Date: Oct 2006
Location: San Diego
Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

The obvious solution: use a bigger waveguide. The JBL DD55000, M2, and 530 all go that route. The larger waveguide prevents pattern flip. For instance, the M2 waveguide controls directivity down to about 900Hz, in both the vertical and horizontal axis. The woofer begins to beam at about the same frequency, so you have a seamless directivity match at the crossover point.
  Reply With Quote
Old 21st July 2018, 10:33 AM   #3
Patrick Bateman is offline Patrick Bateman  United States
diyAudio Member
 
Patrick Bateman's Avatar
 
Join Date: Oct 2006
Location: San Diego
There's a couple of challenges with the approach that's laid out in post #2:

1) sometimes you want an asymmetric pattern. For instance, my new listening room has walls that are 9' tall. But it's very deep and wide. This means that if I use a waveguide with a pattern of 90x90, I'm going to get a lot of reflections off the ceiling and the floor. For instance, if the waveguide is one meter off the floor, and the vertical pattern is 90 degrees, you're going to get a 'floor bounce' just one meter away from the loudspeaker. If you narrow the vertical beam to 30 degrees, the 'floor bounce' occurs at 3.73 meters in front of the speaker. Narrowing the beam from 90 to 30 degrees 'pushes' the floor bounce to nearly 4X further back, which is likely less audible.

2) Waveguides and horns with wide patterns can be difficult to cross over. For instance, if you have a compression driver on a 60x40 waveguide, it's only "working" about 25% as hard as a compression driver on a 100x100 waveguide. (Because it's radiating into 1/4 the space.)
  Reply With Quote
Old 21st July 2018, 10:51 AM   #4
Patrick Bateman is offline Patrick Bateman  United States
diyAudio Member
 
Patrick Bateman's Avatar
 
Join Date: Oct 2006
Location: San Diego
Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

It occurred to me that you can combat pattern flip by using a cylindrical enclosure.

For instance, this waveguide has a pattern of 120x80 and it's 30cm wide. That means that the horizontal pattern is controlled down to 1133Hz. In a rectangular enclosure, the same waveguide would 'flip' at a very high frequency - above 2khz - and the pattern flip would make the octave between 1-2khz sound "weird."

But by putting the waveguide in a cylindrical enclosure, you push pattern flip all the way down to 850Hz, where it's inoffensive.

Obviously, all of this is geometric. If you used an enclosure that's 15cm wide instead of 30cm wide, the horizontal pattern would be controlled down to 2266Hz and the vertical pattern down to 1700Hz.

The only real limitation that I can see, is that the horizontal pattern must be greater than about 100 degrees. This is due to the depth of the cylinder; if the horizontal pattern was 90 degrees, the throat of the waveguide would extend beyond the cylinder. So this design is particularly appropriate for waveguides with a wide horizontal coverage angle.
  Reply With Quote
Old 21st July 2018, 10:59 AM   #5
TBTL is offline TBTL  Germany
diyAudio Member
 
Join Date: Oct 2013
So basically you build a huge horn and 'saw off' the sides which you do not need? I like it Would the polars measured along the diagonals still be OK?

Another solution would be to put woofers both above and below the waveguide and use Horbach-Keele filters. Vertical center-center spacing is a problem, so use a waveguide without a proper mouth roundover on it's top and bottom lip (like the Econowave waveguide) and use small woofers. In order for the woofers to remain beaming horizontally, multiple woofers might need to be arrayed horizontally.

Like this, but with an asymmetrical waveguide:
Image taken from Pseudo-coaxial with narrow directivity (and Horbach-Keele filters)
Attached Images
File Type: jpg _MG_2018_klein.jpg (145.6 KB, 122 views)

Last edited by TBTL; 21st July 2018 at 11:04 AM.
  Reply With Quote
Old 21st July 2018, 05:44 PM   #6
Patrick Bateman is offline Patrick Bateman  United States
diyAudio Member
 
Patrick Bateman's Avatar
 
Join Date: Oct 2006
Location: San Diego
Quote:
Originally Posted by TBTL View Post
So basically you build a huge horn and 'saw off' the sides which you do not need? I like it Would the polars measured along the diagonals still be OK?

Another solution would be to put woofers both above and below the waveguide and use Horbach-Keele filters. Vertical center-center spacing is a problem, so use a waveguide without a proper mouth roundover on it's top and bottom lip (like the Econowave waveguide) and use small woofers. In order for the woofers to remain beaming horizontally, multiple woofers might need to be arrayed horizontally.

Like this, but with an asymmetrical waveguide:
Image taken from Pseudo-coaxial with narrow directivity (and Horbach-Keele filters)
Click the image to open in full size.
Actually, the other project I have on my plate is almost exactly like that.

The reason that I went with a cylinder is because I have a really difficult time making decent looking speaker boxes.

I tried a dozen different ideas to make the box look good, but none of them were palatable:

1) I tried making a good looking box, by taking the time and effort to cut everything properly. But it still looked ugly.

2) I looked on Craigslist for speakers that I could use just for the box. Basically buy an old JBL, remove the drivers, and put my own in there. The problem with that is that a lot of the old speakers have ratty enclosures. And the ones that are in good shape, people want $500-$1000 for them.

Click the image to open in full size.
3) My current speakers are Vandersteens, and I came close to doing what they do: basically wrap the entire thing in grill cloth, so that there's no need for expensive / time consuming finishes.

4) Another idea I had was to buy a NEW set of speakers, and remove all the drivers and put my own in there. The problem with going that route is that most new speakers have a very narrow baffle. No good for a waveguide speaker.

After a lot of pondering, I'm leaning towards a cylinder. Because the shape is made in a factory, it's just about perfect. Ideally I'd finish it like my old Summas:

Click the image to open in full size.

Basically wrap the cylinder in a layer of fiberglass, then a layer of bondo. Sand the whole thing and then paint it.

If I'm not able to make the finish look good, at that point I could wrap the entire speaker in grill cloth a la Vandersteen.

That would make it look a lot like this:

Combating Pattern Flip
  Reply With Quote
Old 21st July 2018, 06:58 PM   #7
marco_gea is offline marco_gea  Italy
diyAudio Member
 
Join Date: Apr 2005
Location: London, UK
Quote:
Originally Posted by TBTL View Post

Another solution would be to put woofers both above and below the waveguide and use Horbach-Keele filters. Vertical center-center spacing is a problem, so use a waveguide without a proper mouth roundover on it's top and bottom lip (like the Econowave waveguide) and use small woofers. In order for the woofers to remain beaming horizontally, multiple woofers might need to be arrayed horizontally.
To me, that sounds a lot like the Rey Audio Warp monitors :
WARP
  Reply With Quote
Old 21st July 2018, 09:57 PM   #8
bwaslo is offline bwaslo  United States
Old guy with soldering iron
diyAudio Member
 
bwaslo's Avatar
 
Join Date: May 2006
Location: Portland, Oregon!
Combating Pattern Flip
Quote:
if I use a waveguide with a pattern of 90x90, I'm going to get a lot of reflections off the ceiling and the floor. For instance, if the waveguide is one meter off the floor, and the vertical pattern is 90 degrees, you're going to get a 'floor bounce' just one meter away from the loudspeaker. If you narrow the vertical beam to 30 degrees, the 'floor bounce' occurs at 3.73 meters in front of the speaker. Narrowing the beam from 90 to 30 degrees 'pushes' the floor bounce to nearly 4X further back, which is likely less audible.
Of course with most living room acceptable speaker sizes, changing the vertical pattern to something narrow only keeps treble frequencies from bouncing off the ceiling and floor, since the directivity goes away below there -- a narrower pattern needs to have a larger dimension to keep the same control frequency, and the asymmetric waveguide instead makes the dimension smaller, pushing that frequency upwards with two effects. Keeping treble reflections off the ceiling is probably easier with an absorber up there.

About 5 years ago I almost got around to making a waveguide similar to your cylindrical cut idea -- Click the image to open in full size.

...but only 'almost'. Seemed like a lot of work and really big.
__________________
[W9MJE] Horn spreadsheet SynergyCalc/; SmallSyns SmallSyns;
Crossover design Xsim; Depot diffusor super-easy diffusors
  Reply With Quote
Old 21st July 2018, 10:53 PM   #9
AllenB is offline AllenB  Australia
diyAudio Member
 
Join Date: Oct 2008
Quote:
Originally Posted by bwaslo View Post
Keeping treble reflections off the ceiling is probably easier with an absorber up there.
Yes it is. I went that way and reduced the reflections by about 3dB. The waveguide was much harder to build, and to get right, and it didn't help with the amount of space it occupied. I could make a better sounding round waveguide and the absorption was much more effective.
  Reply With Quote
Old 22nd July 2018, 12:45 AM   #10
phivates is offline phivates  United States
diyAudio Member
 
Join Date: Jan 2011
Location: Willamette Valley
Is this not a radial horn with its mouth wide open?
  Reply With Quote

Reply


Combating Pattern FlipHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Flip-flop info ejthedj Parts 6 18th April 2012 11:02 PM
Need help combating power amp hum clm811 Solid State 13 21st April 2007 08:14 AM


New To Site? Need Help?

All times are GMT. The time now is 05:05 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki