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Multi-Way Conventional loudspeakers with crossovers

Synergy Horn with AMT
Synergy Horn with AMT
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Old 9th July 2019, 04:35 AM   #31
bwaslo is offline bwaslo  United States
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Synergy Horn with AMT
Originally Posted by xrk971 View Post
Thanks, Bwaslo...
xrk, if you have any entrepreneurial inclinations, you should consider putting a kit of that horn together. I wonder if there's a fast/inexpensive/CNC way to cut out foam core pieces? (probably not laser I suppose).

[edit: I just noticed that you also used just one LF driver on the horn. Works really well, doesn't it? I think people get too hung up on high-efficiency, high SPL on Synergy/Unity horns for home use, that's not really the point. At all. Single driver works better for the tweeter's benefit and the asymmetry tends to help smooth the response, at least by eye. Though for PA use, of course SPL becomes pretty much everything]
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Last edited by bwaslo; 9th July 2019 at 04:43 AM.
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Old 9th July 2019, 04:48 AM   #32
Patrick Bateman is offline Patrick Bateman  United States
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Originally Posted by xrk971 View Post
Synergy with an AMT is perhaps one of the best sounding speakers I have ever made or heard. It has the ability to “stun” a listener - that is someone coming by to casually listen will be stopped dead in their tracks and have no choice but to stay and listen and be blown away and speechless. Stunned in other words.

Here is mine with a 30in wide mouth and made all in foam core. Heil AMT and B&C 6.5in Nd driver for mids. Coupled with a FLH for bass, the combo is staggeringly good.

One thing about an AMT is that it lacks the piston power to develop horn loaded gain typically seen with conventional moving voice coil and diaphragm drivers. If you are used to getting circa 10dB gain with conventional drivers, I have found that there is about zero gain with an AMT in a horn.

Important point with construction is that the transition from the AMT to horn walls needs to be smooth as possible and devoid of sharp edges or sudden transitions.
Click the image to open in full size.

For the most part, horns and waveguides don't increase the efficiency of a loudspeaker, they just focus the energy into a narrower beam. For instance, a compression driver on a 1" horn will focus it's energy into a narrow beam below 13,500hz.

Above 13,500Hz, there's very little gain, because there's nothing constraining the wavelengths into a smaller angle. (Because 13500Hz is an inch long, and the throat is an inch long.)

When you replace that compression driver with a ribbon, that frequency where there's no "horn gain" drops significantly, because the throat is so large. For instance, with a ribbon that measures 4" x 1.5" you're not going to have any horn gain at all above 10khz, and little above 3khz.
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Old 9th July 2019, 09:25 AM   #33
grec13 is offline grec13  United States
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Originally Posted by xrk971 View Post
Synergy with an AMT is perhaps one of the best sounding speakers I have ever made or heard.
XRK, what is your xover points?
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Old 12th July 2019, 04:37 PM   #34
tonyman108 is offline tonyman108  United States
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Re: the (lack of) horn gain on a ribbon/planar/AMT.

Patrick, your math is good; it definitely works about exactly as you stated in practice. I use Stage Accompany 8535 "RCD" planar HF drivers a lot. Their exposed diaphragm area is approx. 1.125"x6.5".

I have many measurements of the driver in their factory horn, but not bare. However, SA's published "with-horn" measurements agree with mine quite closely, so I'm attaching their bare-vs-horn measurements here.

One can see that the with-horn sensitivity droops down to meet the 103db/W bare-driver sensitivity right about at 3KHz.

The SA "H8535/70" horns are nominally 50x70 degrees with a 9.5" square mouth.

I have one extra bare pair of these drivers on hand, and would really like to build a 3-way Synergy-ish PA design around them if possible. I'm pretty sure I can cross these over at 1.5K or even a bit lower with a big horn.

I too have always wondered about the 'push back' from the bass / midrange that a planar HF driver like this would experience in a co-entrant horn. I strongly suspect it doesn't matter, but it would sort of stink to spend a lot of effort and $$$$ and find out otherwise.

Anyone have an idea what would be a good methodology to measure the magnitude of the effect... my thoughts were:

A) Disconnect the tweeter, shunt it with 0.1 ohm or so, and measure the voltage across it with the other drivers playing.

B) Make an in-situ IMD measurement. No crossover; play very loud 3KHz bursts into the HF driver, play various other bursts though the other drivers, look for sidebands appearing around +-3KHz.

I'm thinking that B (done with the ribbon driven to a level near its excursion limits) is the meaningful test, but I dread trying it.
Attached Images
File Type: jpg SA8535Bare.jpg (70.2 KB, 64 views)
File Type: jpg SA8535_wHorn.jpg (72.9 KB, 64 views)
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