Parallel cap to create 1.5 way?

[sreten]

Originally posted by boone

sreten
I think I have enough volume to accommodate a moderate increase in Qt
boone

Be my guest, blow your amplifier up.
Don't bother simply stating what you want to achieve.

/sreten.

[Paul W]

boone,
A larger perspective would help us...what are you trying to accomplish? A schematic of the proposed xo would be a great help.
Paul

[v-bro]

4 ohms is not the absolute minimum indeed, sorry..
The capacitance would still be very high...

With a coil it would indeed add up to a 12 db/oct parallel filter (coil series, cap parallel).

That would have to be a coil with value of about 4.7 to 5.6 mH...

Zobels are to correct impedance...

[boone]

Well, certainly don't want to blow my amp. The speakers are:
Top section ------ HiVi B3S in an open baffle, uses Zaphs notch filter and is high passed using the receiver ( JVC RX-F10 ) by hooking them up to the rear speaker terminals set to small and setting the crossover to 200 hz.
Bottom section ----- Rear firing Dayton DA175 ( 1 per side ) in aperiodic boxes, hooked up to the front speaker terminals on the receiver and rolled off using the low pass section of a crossover that was posted on the P.E. site. It starts rolling off at around 1000 hz.
My plan (hope?) when I started these was that the overlap between the rear wave of the B3S and the front wave of the DA175 (which was firing to the rear) would attenuate each other and I would be able to position the speakers closer to the front walls than the 3'-4' normally required for OB's.
So anyway while I have them torn apart to put the final finish on them I wanted to see if I could come up with an inexpensive way to eliminate the overlap and see what that sounded like and so this thread was born.

Thank you
boone

[Paul W]

Cardioid...got it. Are you trying this without measurements? If so, consider an inexpensive microphone like the Behringer ECM8000 and download Speakerworkshop...much better than doing it blindfolded

One way to reduce the rear radiation for use closer to walls is to use an acoustic resistor on the back of the dipole...something like this: rear radiation

Wool filter felt (F7?) seemed to work the best. Real wool is much better than synthetic. McMaster has many grades and thicknesses...or try the local carpet shop, military surplus blankets, etc.
Paul

[boone]

Paul,

My measurement set-up is very crude. Stereophile test disc/Rat shack analogue meter. Look forward to better in the future. I'll try your idea of a felt "grill" on the rear of the speakers to attenuate the back wave.

Thanks to all who helped.
boone

[sreten]

Hi,

The rear wave cancellation idea is certainly new to me.
How well it would work I'm not sure.

Where this capacative low pass filter fits in is still not clear, though
a 2nd order overdamped LC filter would make a lot more sense, the
series L being a far better idea than any resistor value.

Down to 200Hz in an open baffle ? Sure your not losing somethng
from baffle roll-off ? Could add another 0.5 way B3S to extend the
response by one octave.

/sreten.

[boone]

sreten,

Not sure how well the rear wave cancellation idea works myself. When I started these speakers about a year ago I believed that the output of the two drivers (out of phase) would mix and cancel (cease to exist) behind the speakers. Now I believe the sound waves just pass through each other without cancelling behind the speakers and any reduction in spl I measure at my listening position is due to how they combine at that point.

Where this capacitive low pass filter fits in is .... I have a low pass section that rolls off the woofer at about 1K, giving pretty big overlap between the drivers. Kind of a 1.5/dipole/bipole set up? Also found a big iron core inductor in my pile of junk that I think will give -3db at about 350 hz, giving a smaller overlap. Having seen a couple of posts mentioning this series cap low pass ( one by Thorsten Loesch and one by Danny Richie), and never having heard of it before, I was curious to give it a try and see how it sounded compared to the other two.

thank you
boone