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Multi-Way Conventional loudspeakers with crossovers

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Old 6th March 2009, 07:08 AM   #101
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Another way to look at the graph is to consider the equivalent cutoffs of each - although both are nominally 425 Hz horns, the T = 1.34 version needs to be scaled-up by about 60% to have equivalent usable cutoff frequencies. In that event, it might be even better than the AH425 - but it won't fit into an AusPost box any more.

Based on the profound differences between conicals, conicals with smoothed-radius transitions between the driver and horn (Peavey's Quadratic Throat), Dr. Geddes' Oblate Spheroid waveguide, the Tractrix, the family of LeCleac'h horns with T ratios between 0.707 and 1.34, and traditional exponential horns, it's not surprising they sound different. All of the parameters are different - acoustic impedance, the shape of directivity pattern vs frequency, internal reflections, potential mismatch between the internal flare of the compression driver and the entrance to the horn, etc. etc.
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Old 6th March 2009, 08:07 AM   #102
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You were asking about polars. Here's the 288+AH425 at 1 kHz, with the black lines representing 3 dB contours.
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Old 6th March 2009, 08:10 AM   #103
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Same as before but at 6 kHz. No way is it constant-directivity; supertweeter is definitely a good idea.
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Old 6th March 2009, 08:18 AM   #104
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And now for something completely different - an OS waveguide with DE250 compression driver (throat simulation) at 1 kHz.
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Old 6th March 2009, 08:26 AM   #105
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Same thing, again at 1k Hz, this time on a flat baffle. The previous AH425 and OS waveguide BEM simulations were done with free edges on the horn or waveguide.
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Old 6th March 2009, 08:31 AM   #106
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No baffle, edges of the OS waveguide in free air, at 5.662 kHz.
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Old 6th March 2009, 08:35 AM   #107
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This time with a flat baffle terminating the edges, at 5.04 kHz. Most definitely recommended - clear improvement.

All BEM simulations by Bjorn Kolbrek, many thanks for the programming work and extended computer time he put into these.
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Old 6th March 2009, 08:59 AM   #108
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Here's a power factor comparison between the 288+AH425 (thin lines) and an OS waveguide with the simulated DE250 driver (thick lines). All drivers are idealized "perfect" drivers, with the internal throat flare of the driver as part of the horn or waveguide BEM simulation. The phase plugs are NOT part of the simulation, and the drivers are assumed to be free of resonances.

The black line in the power factor is a "bulk" figure; it tells us nothing about where the power is actually going, just that it's leaving the horn and entering the room. It could leave the horn at any angle; this graph doesn't tell us where. The red lines represent the percentage of the energy reflected back into the diaphragm.

The complexity of the preceding figures - all idealized simulations with "perfect" drivers - should give an idea of the complexity of what's going on in the horn, and how FR graphs measured at one location don't tell the whole story. We haven't even looked at the time domain, CSD waterfall plots, headroom, or distortion.

Throw in diaphragm resonances and the complex behavior of phase plugs, and now you get to have real fun. Imagine a different set of CSD waterfall plots for every 7.5 to 10 degrees of emission angle and you start to get an idea of what's really happening in a physical system.
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Old 6th March 2009, 09:39 AM   #109
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Not done yet; here's the 288+AH425 frequency response at different distances. Again, an idealized "perfect" driver with no resonances, flat power response and no phase plug aberrations. Real drivers aren't this good, thanks to the phase plug and the limitations of physical driver materials.

Based on the data, measuring or equalizing the speaker at 1 meter or less would be a bad idea, but 2 meters or further away starts to appear more uniform and stable. You can also see why I'm contemplating a crossover topology with a series-cap highpass filter followed by a parallel notch filter to get the desired curve on the highpass function, with additional shelf-EQ to taste (this depends on listening angle, etc).
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Old 6th March 2009, 04:48 PM   #110
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And just to add fuel to the horn fire, there is also the Iwata camp and the multi-cell camp! (I like both).

Certainly agree with you Lynn about the super tweeter on most horns, as they do beam. I didn't find the multi-cell to beam too much, tho maybe soemone else has found differently. Cal? GM?

The edge termination of the horn can make a big difference, for sure. Beach towels work for me.
The soft or progessive edge was one of Mr. Iwata's big points. You can see it as progressive slots in the photo of his bass horns below. Oddly enough, he did not seem to use it at higher frequencies.
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