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Re: PPSL

Posted by djk on May 18, 2003 at 04:20:25:
"Can you show some more detail and maybe link some references?"
At the time I was looking at both the EV MTL4 and the KEF 104, both had their strengths and their weaknesses. I tried to get the best of both worlds.
EV no longer has the datsheets for the MTL4 on line, and the KEF 104 has been discontinued for awhile too.
"But the thing I'm wondering about is how do you get the anomalous harmonics to be 180o out of phase while having the fundamental in phase."
The wavelength of 200hz is ~68", my first model had the magnet structure of the inverted driver only 1" away from the front of the other cone. The cones are so close together and the wavelengths so long that it still subtracts.
"Distortion caused by the magnetic structure isn't something I would expect to be improved on by this configuration because it seems to include odd-orders harmonics as well as even-orders"
The 3rd harmonic reduction is a function of the low-pass behavior of the plenum. IE: if the plenum acts like a 12dB low pass at 200hz it will roll off the 3rd harmonic of 100hz by roughly 6dB. Obviously no useable reduction can occur much below 80hz or so.
Two interesting stories:
On a box that had the woofers hooked up wrong, ie: in phase electrically, the woofers would just flap and absolutely NO sound could be heard.
Car stereo installer just finishes carpeting a 4 X 12 box, wants to check it out before the customer shows up. He's running a 30W Pyramid car stereo amp full range, no 6th order EQ, no HF, no crossover. It sounds real wimpy in his 30 X 24 garage, he's worried. I hooked up the electronic crossover I brought over that I added 6th order EQ to, along with his 100W Fisher/Sanyo garage system, and the same 30W Pyramid amp. He's stunned, it really thumps now, and can play loud enough to rot your face off. Goes into a Ford Escort with 1.2KW on it, played so loud standing in the garage that I refused to get in the car.