A guy over here is asking me to make some x-os for some boxes he got from a garage sale and which came with drivers but no x-os. The fronts are apparently a Vifa 2 x P17WJ + D25 MTM combo, but to quote him,
"I have a Pioneer D- 608 Receiver which struggles with any speakers under 8 ohm. Reviews in USA and English magazines both said it was "Treble happy" so would not want speakers to be as well."
Does anyone know anything about this receiver? is he correct about about its problem with sub 8ohm loads?? If so what does one do with the vifa MTM combo? I really don't want to wire in series if I can avoid it! What other options are there to keep the impedance up near 8ohms?
(the rears are P17+D25, no real problem there)
"I have a Pioneer D- 608 Receiver which struggles with any speakers under 8 ohm. Reviews in USA and English magazines both said it was "Treble happy" so would not want speakers to be as well."
Does anyone know anything about this receiver? is he correct about about its problem with sub 8ohm loads?? If so what does one do with the vifa MTM combo? I really don't want to wire in series if I can avoid it! What other options are there to keep the impedance up near 8ohms?
(the rears are P17+D25, no real problem there)
Using 2 woofers in parallel will probably lower impedance closer to 4 ohms, wiring them in series would give higher impedance but with a number of drawbacks, such as:
- Lower efficiency of the woofers
-Needed attenuation fo the tweeters
-More critical crossover design
And probably something else...
I'd suggest a better amplifier that would allow driving low impedance loads or... just keep the volume knob not too high.
Cheers
Andypairo
- Lower efficiency of the woofers
-Needed attenuation fo the tweeters
-More critical crossover design
And probably something else...
I'd suggest a better amplifier that would allow driving low impedance loads or... just keep the volume knob not too high.
Cheers
Andypairo
Andy:
I don't think you have much hope with parallelling the Vifa P17WJ's.
I was thinking that perhaps you could get away with presenting a 6 ohm load to the receiver. Sometimes receivers that balk at 4 ohms do fine with 6 ohms.
I ran Subwoofer Simulator on 1 P17WJ to see what happens to one Vifa. Remember, a parallel pair will have half the impedance. Shown is frequency response, impedance and cone excursion. This is for a 56 liter box tuned to 39 Hz. Incidentally, the calculated frequency response shows the VC indictance with a perfect cone-real response will be higher above 1K Hz.
The impedance dip at 39 can be helped by stuffing the ports a little. That will raise the impedance to perhaps 12 ohms.
But the big problem seems to be from 150 HZ to 1500 Hz. In that band, you seem to vary between 8 ohms and 6 ohms. In a prallel pair, that means 4 ohms and 3 ohms. No hope of bringing the parallel pair up to 6 ohm load here.
I wish I could be more helpful as to a solution. It looks like hook them up in series, or hook them up to an audio transformer-the second being a cumbersome, little-used solution.
BTW, Subwoofer Simulator is a freeware program written by a member here. It models your choice of any of 18 different curves on any of 7 different box configurations.
http://www.geocities.com/f4ier/speaker.htm
I don't think you have much hope with parallelling the Vifa P17WJ's.
I was thinking that perhaps you could get away with presenting a 6 ohm load to the receiver. Sometimes receivers that balk at 4 ohms do fine with 6 ohms.
I ran Subwoofer Simulator on 1 P17WJ to see what happens to one Vifa. Remember, a parallel pair will have half the impedance. Shown is frequency response, impedance and cone excursion. This is for a 56 liter box tuned to 39 Hz. Incidentally, the calculated frequency response shows the VC indictance with a perfect cone-real response will be higher above 1K Hz.
The impedance dip at 39 can be helped by stuffing the ports a little. That will raise the impedance to perhaps 12 ohms.
But the big problem seems to be from 150 HZ to 1500 Hz. In that band, you seem to vary between 8 ohms and 6 ohms. In a prallel pair, that means 4 ohms and 3 ohms. No hope of bringing the parallel pair up to 6 ohm load here.
I wish I could be more helpful as to a solution. It looks like hook them up in series, or hook them up to an audio transformer-the second being a cumbersome, little-used solution.
BTW, Subwoofer Simulator is a freeware program written by a member here. It models your choice of any of 18 different curves on any of 7 different box configurations.
http://www.geocities.com/f4ier/speaker.htm
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Andy,
If you friend is stuck with using the Pioneer, it appears that you’re stuck with series drivers. You make a zobel circuit to tame the impedance above 1kHz so it doesn’t get too ridiculous at the xover point to the tweeter. If the amp has trouble with <8ohms, it should be able to handle 12 to 16ohms.
Rodd Yamashita
If you friend is stuck with using the Pioneer, it appears that you’re stuck with series drivers. You make a zobel circuit to tame the impedance above 1kHz so it doesn’t get too ridiculous at the xover point to the tweeter. If the amp has trouble with <8ohms, it should be able to handle 12 to 16ohms.
Rodd Yamashita
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