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Old 19th May 2017, 05:33 PM   #1
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Default Line Sources on Synergy Horns

I've been thinking about replacing my Vandersteens with a set of Synergy Horns. If I was smart I'd just build a pair of Bill's speakers, but I like to tinker!

While crunching the numbers, it occurred to me that there's a real case for using line sources on Synergy horns. Here's why.

Click the image to open in full size.
Here's the front view of three horns. As you can see, they're identical in height and width, with a cutoff of 450Hz.

Click the image to open in full size.
Click the image to open in full size.
Things look a lot different from overhead.
The Synergy horn with 50x50 coverage is 2.5 feet deep.
The Synergy horn with 80x20 coverage is 1.42 feet deep.
And the Synergy using a diffraction slot is a whopping 6.25' deep! Yowza.

And note that's it's mathematically impossible to make a 80x20 horn without a diffraction slot, unless there's a line source at the throat. (That's why there's 10,000 different patents on turning a point source into a line source.)

Click the image to open in full size.
This isn't my living room, but I have the same floor plan. With those big ol' ceilings, vertical directivity control isn't incredibly important.

So there seems to be a much simpler solution, just use a wider angle. Unfortunately, that won't work on a Synergy horn. As you widen the angle of the walls, you get a 'trough' in the output between 1000 and 2000hz. The reason that this happens is that the walls are too wide to provide any horn loading. For instance, 1500Hz is nine inches long. If you keep the coverage angle of the horn narrow, then you'll have a lot of output at 1500hz. As you slooowly widen the horn, you slooowly lose output in the midrange. This is probably less of an issue with two-way horns that cross over from a compression driver to a direct radiator. For instance, Zilch's econowave uses a waveguide with a fairly wide coverage angle, so does JBL's M2 monitor. But they can get away with that because their midrange drivers have no problem playing up to 1500Hz, even 2000Hz. The same is not true with a Synergy horn. As one of the threads on here have demonstrated, there are very very few midranges that can play beyond 1200Hz on a Synergy horn.


In summary: I believe you have three options for a Synergy horn:

1) Fairly large size and narrow coverage, like the SH50
2) Deep and narrow like the SH40
3) If you want shallow depth, virtually your only option is to put a line source at the throat.
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Old 19th May 2017, 05:46 PM   #2
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Right on and IIRC TD had one of the earliest patents or maybe just a patent application? Hmm, think I'm confusing it with his rotary horn that mimic'd a line source.

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Last edited by GM; 19th May 2017 at 05:51 PM.
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Old 19th May 2017, 08:15 PM   #3
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I'm not saying putting a line source at the throat is a bad idea - look at what T.D. has done with the paraline - but there have been a fair number of 90H horns done. 90H qualifies as wide and not very deep. True, most of them cross to the CD below 1500 Hz but to me that is a solution, not a problem.

Another way of describing the difficulty in making a wide Synergy horn is that the wider horn expands faster than the narrower horn, meaning that for mid taps at the same distance from the throat, the circumference of the horn walls at the mid taps is larger. According to one of the Synergy patent rules, this forces a lower crossover. The circumference of the horn at the mid taps should be <= one wavelength at the XO frequency.

Note that if you take this rule literally for your line source at the throat of a Synergy, it will dictate an even lower XO frequency than for the conventional 90H Synergy.
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Old 19th May 2017, 09:13 PM   #4
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Originally Posted by nc535 View Post
I'm not saying putting a line source at the throat is a bad idea - look at what T.D. has done with the paraline - but there have been a fair number of 90H horns done. 90H qualifies as wide and not very deep. True, most of them cross to the CD below 1500 Hz but to me that is a solution, not a problem.

Another way of describing the difficulty in making a wide Synergy horn is that the wider horn expands faster than the narrower horn, meaning that for mid taps at the same distance from the throat, the circumference of the horn walls at the mid taps is larger. According to one of the Synergy patent rules, this forces a lower crossover. The circumference of the horn at the mid taps should be <= one wavelength at the XO frequency.

Note that if you take this rule literally for your line source at the throat of a Synergy, it will dictate an even lower XO frequency than for the conventional 90H Synergy.
Click the image to open in full size.

One idea I had, for a home Synergy horn, is to vary the vertical beamwidth while keeping the horizontal beamwidth constant.

IE, the speaker on the far left will have constant beamwidth in the horizontal axis, but it's vertical beamwidth will get narrower and narrower as you go higher in frequency. An 80x80 waveguide would have the exact same footprint. The advantage of narrowing the beamwidth on one axis is that it will increase output in the midrange, same way that an exponential horn works. But we're sacrificing polar response on the vertical axis, where narrow beamwidth at high frequency is arguably A Good Thing. Particularly for a home speaker. We want wide directivity to cover the audience, narrow vertical directivity to reduce reflections off the floor and the ceiling. The obvious solution is an asymmetrical horn. But an asymmetrical horn suffers from massive pattern flip, and I've personally found that pattern flip sounds really obnoxious.
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Old 19th May 2017, 11:18 PM   #5
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Originally Posted by nc535 View Post
Note that if you take this rule literally for your line source at the throat of a Synergy, it will dictate an even lower XO frequency than for the conventional 90H Synergy.
True, but then a line source can be made to allow a lower XO point, which for me is the goal of any multiple driver HIFI/HT speaker system where stupid high SPL isn't a performance goal.

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Old 20th May 2017, 01:53 AM   #6
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True, but then a line source can be made to allow a lower XO point, which for me is the goal of any multiple driver HIFI/HT speaker system where stupid high SPL isn't a performance goal.

GM
I'm with you there; I've seen line arrays made of 3" full range drivers that actually become full range when you use enough of them.

I've also heard and heard of a few 1" CDs that sound good crossed below 1500 Hz and larger ones down to 500 Hz.

Just enjoyed the irony of going to a line source to avoid a low XO and ending up with a low XO anyway. IIRC, the J3 uses a 1.4" exit CD.
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Old 20th May 2017, 03:25 AM   #7
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Could it be 4-6 4"CDs loaded to some kind of acoustic leans to get the lower XO?
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Old 20th May 2017, 03:35 AM   #8
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Could it be 4-6 4"CDs loaded to some kind of acoustic leans to get the lower XO?
I'm betting there's a pile o' compression drivers in there.

No other way to get the maximum output up to 150dB, unless you shipped a box with a 'house curve' that rolled off the highs.

Almost all of the existing Jericho horns have a wider pattern than the average Synergy Horn. For instance the Jericho J-3 94 has a pattern of 90x40, an average of 65. The SH-50 is much narrower, 50.

So what if you took a Jericho horn and designed it for higher output on axis? And what if you designed some type of lens to keep the depth to a minimum?
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Old 20th May 2017, 04:24 AM   #9
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I'm sure it's based on Paraline principle. But how to get everything below 300hz (?) to 130db???
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