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Juggling Midrange Location in a Unity Horn
Juggling Midrange Location in a Unity Horn
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Old 20th January 2018, 06:35 PM   #1
Patrick Bateman is offline Patrick Bateman  United States
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Default Juggling Midrange Location in a Unity Horn

Last week I tried an experiment with one of my Unity horns that worked out alright. I thought I'd document the results:

In the commercial Synergy horns, the midrange taps are located approximately 3.5" from the throat. This location is based on a series of criteria:

3) the area of the horn at the location of the taps
2) the desired crossover between midrange and tweeter
1) the geometry of the compression driver

It's really hard to go wrong if you put the midrange taps 3.5" away from the throat, and if you don't want to crunch the numbers that's a perfectly good place to put them.

Arguably, the most important variable here is the area of the horn at the location of the taps. The reason that this variable is so important is because you don't want to have a compression ratio that's too high. For instance, you might think to yourself, "Why don't I just put the midrange taps as close as I possibly can? What could go wrong?

The problem with putting the midrange taps too close to the throat is that the compression ratio will be sky-high, and that will lead to huge distortion figures. I found this out the hard way once, I built a couple of front-loaded-horns using the B&C 8NDL51 and I had a compression ratio that was over ten-to-one. Everything sounded fine at low levels, but once you gave them even ten watts of power, the horn made a cracking noise that sounded like the 8NDL51s were trying to split the walls of the horn.
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Old 20th January 2018, 06:41 PM   #2
Patrick Bateman is offline Patrick Bateman  United States
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Click the image to open in full size.

While my projects had generally leaned towards the use of 2-4 very small midranges for my Unity horns, Bill Waslo opted to use a *single* midrange on a Unity horn. Here's a picture of sphykik's build, based on Bill's "Smally Syns" design.

Small Syns
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Old 20th January 2018, 06:52 PM   #3
Patrick Bateman is offline Patrick Bateman  United States
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Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

So here's the point of the thread:

Last week it occurred to me that we can do a few things if we use a single midrange on a Unity horn:

1) We can move the midrange very very close to the tweeter, potentially even overlapping the tweeter
2) We can narrow the angle of the horn
3) Both of the above

Hope that makes sense. I believe the primary limiting factor of where the midrange drivers are located is the compression ratio. The commercial SH-50 Synergy horn uses four midranges with 4" cones. The taps are 3.5" away from the throat. Here's the math:

SD of a 4" driver =
= pi * radius ^2
= 3.14159 * 5.08cm^2
= 81cm

SD of a four driver array = 324cm

SD of Danley SH-50 at the location of the midrange taps =
3.5 " x 3.5 "
= 8.89cm x 8.89cm
= 79cm

compression ratio of Danley SH-50 at the location of the midrange taps =
SD of midrange array / area of horn at location of the midrange taps
= 324cm / 79cm
= 4.1

In summary, the Danley SH-50 has a compression ratio of about four to one for the midrange array. My front loaded horn with an 8NDL51 was 'pushing it' with a compression ratio of over ten to one. If you used one midrange in a Unity horn, instead of four midranges, you could move the midranges significantly closer to the compression driver, extending the high frequency response. Conversely, if you used one midrange instead of four midranges you could use a coverage angle that significantly narrower.

It's a juggling act. In a home stereo type of situation, it might be beneficial to use fewer midranges and move them closer to the tweeter. This assumes that we don't need to generate 130-140dB of output in the home
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Old 20th January 2018, 07:12 PM   #4
Patrick Bateman is offline Patrick Bateman  United States
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One of the 'fun' parts of this design, and why it's such an interesting puzzle, is because you can vary all three parameters.

For instance, do you want a wider coverage angle? If so, you'll probably want to use more midranges:
Juggling Midrange Location in a Unity Horn


Do you want to use one or two midranges instead of four midranges? If so, you have the luxury of moving the midranges closer to the compression driver. Keep in mid this will impact the phase, so don't go overboard. The slope of the high and low pass will impact both.

Back in the day, Lambda Acoustics offered the TAD 2001 as an upgrade on their Unity horn kits. One of the interesting aspects of the TAD is that it has an exceptionally deep depth. This isn't a huge issue for a conventional horn, but in a Unity horn it creates problems. The depth of the compression driver itself can make it difficult to cross over to the midranges.

Click the image to open in full size.

EAW understood this when they did their "Anya" speaker, which is very Unity-horn-ish IMHO. EAW used the same compression driver that I am using, but they had Celestion modify the geometry so that they could be packed even closer together:
YouTube

(This is a great video BTW, a lot of great info for loudspeaker designers.)
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Old 20th January 2018, 07:31 PM   #5
charlie2 is offline charlie2  England
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The only reason why there are four mid ranges in danley is to compensate physical acoustic drop off as the horn expands and not boosted in eq, these are for big spl
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Old 20th January 2018, 07:41 PM   #6
charlie2 is offline charlie2  England
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Inverse square law applys
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Old 23rd January 2018, 12:02 AM   #7
fuji6 is offline fuji6
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Sorry for the dumb question but, what is meant by distance from the throat? Eg what exact points and path is being measured?
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Old 23rd January 2018, 12:23 AM   #8
bwaslo is offline bwaslo  United States
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Juggling Midrange Location in a Unity Horn
Quote:
Originally Posted by Patrick Bateman View Post
One of the 'fun' parts of this design, and why it's such an interesting puzzle, is because you can vary all three parameters.

For instance, do you want a wider coverage angle? If so, you'll probably want to use more midranges:
Juggling Midrange Location in a Unity Horn
Patrick, what is that picture from? Gotta admire that carpentry work (not to mention the trig calculation required)
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Old 23rd January 2018, 03:13 AM   #9
nc535 is offline nc535
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you don't need any trig - just draw it i(all of it, even the drivers) in Sketchup e.g. and let the CAD tall tell you the angles. When things are tight, a good way to be sure things fit.

BTW: that is the SH-96
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Old 23rd January 2018, 04:54 AM   #10
Patrick Bateman is offline Patrick Bateman  United States
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Quote:
Originally Posted by fuji6 View Post
Sorry for the dumb question but, what is meant by distance from the throat? Eg what exact points and path is being measured?
I took a tape measure and measured from the throat of the SH-50 to the center of the midrange taps. Measured along the walls of the horn itself, so not super-accurate.

I try not to obsess over the geometry thing too much, because it get particularly confusing when you consider that the distance from the throat of the compression driver to the diaphragm of the compression driver should be included also. And that length varies quite a bit from compression driver to compression driver.
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