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Old 25th March 2012, 12:02 PM   #1
nl is offline nl  United States
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Default DIY Unity/Synergy for home use

Hello,

I'm designing a Danley-style Unity or Synergy horn for home use. Here's what I have so far:

Horn: 40x30 rectangular, 40 inches deep. This is much larger than most Danley horns, but that's OK because it's not a touring situation. The effective angle is about the same as a round 40 degree horn. I chose the 40x30 shape because, at 40" deep, the dimensions of the exit are 31"x23". Add 3" for wall width and you get 34"x26". Thus, it should fit through a doorway. Construction is 1.5" MDF.

Drivers: B&C DCX50 and B&C 12PE32. The tweeter on the coaxial DCX50 is apparently not all that great, but I decided to go this way to maintain full coherence.

Crossover: 6khz and 400hz. Instead of having a crossover at 1200hz with a 1" exit driver and some 5" midranges, I'm aiming for a much lower crossover at 400hz and a 2" exit compression driver. Since my power handling needs are much lower, 100W max and more likely no more than 10W for the compression driver, I can use it to the full extension. Digital crossover (for example Apogee Ensemble) and biamping used. So, we can adjust phase, timing, equalization etc. to taste. 24db/octave or steeper slopes to be used.

Placement: the horn mouth size is equivalent to a 1/2-size mouth at 100hz for an exponential horn. Placement is on the floor, with the long side along the floor, so effective half space. The horn will be near the rear wall, so at 50hz, where the mouth size is 1/4 size for 50hz exponential, we will be approaching 1/4 space, since the WL of a 50hz wave is 20 feet long, and 1/4 WL is 5 feet long. The rear wall would be within 1/4 WL at 50hz. I calculate a lower cutoff of 74hz without EQ on this horn, could be better in half/quarter space. With a little EQ, we should be able to go down to 50hz perhaps.

The touchiest part is the crossover from the 2" compression driver to the 12" mid-lows. Since we're crossing at 400hz instead of 1200hz, in effect the wavelength is 3x longer. The 1/4 WL at 400hz is 7.5". So, we are a little close to the 1/4 WL cutoff, since we're positioning the driver at 8". It could be closer, I suppose. Danley talks a lot about putting the drivers close enough together to create a "single driver" type waveform melding. Although I can adjust timing with the crossover, is this close enough to get this "melding" effect? I am also a little concerned about using the 12" driver at a 400hz crossover. Danley uses it at 300hz in the SH50, and the mass-rolloff is calculated at 567hz.

Last edited by nl; 25th March 2012 at 12:05 PM.
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Old 26th March 2012, 04:43 AM   #2
AllenB is offline AllenB  Australia
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Join Date: Oct 2008
A synergy horn has some unique compromises and issues which are not likely to be obvious using standard design techniques. Using a combination of Hornresp and Akabak seems far more revealing.

I became concerned when you said you'd settled on a given dispersion angle. I find that for a given woofer/mid bandwidth, the delicate tradeoffs between bass performance and crossover region performance tend to dictate the angle that supports it. Changing one or the other allows you to change the angle whilst remaining optimum elsewhere, which seems worthwhile as this is going to be a large enough horn anyway.

Using these tools may take time but they will answer your other questions in the process. So may this thread.
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Old 26th March 2012, 07:56 AM   #3
nl is offline nl  United States
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Join Date: Mar 2004
Location: New York
The 40x30 rectangular angle is equivalent in expansion rate to a 40 degree round horn. This has a cutoff of about 300hz with a 2" throat, and a cutoff of about 74hz with a throat equivalent to the cross-section of the horn where the entrance to the 12" drivers is at around 7"-8". The goal of having a proper expansion rate for both the 2" driver and 12" drivers, with extension to 80hz without EQ, was the reason for the choice of the angle, length and mouth size. The 40x30 combination was chosen to make one side shorter than the other, to allow it to fit through a standard doorway easily.
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