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Old 24th May 2013, 03:48 AM   #1
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Default Wiring up which way to go?

I need some advice on the best way to wire up my speakers after adding an extra 8inch bass driver.
This was done to get some better bass depth and attack.

I now have two tweeters and two bass speakers in each box.
Should I add a midrange driver? Or crossovers and L-pads?

Or can I wire up directly without crossovers, wiring up plus to plus and minus to minus on each bass speaker? Or should I wire them up plus to minus to keep them at 8ohms?
The speaker box measures 4900 cubic inches (80 liters)
The speakers are out of the 1960's and 1970's both vibrant and in good order.In appreciation, thank you kindly for any assistance.
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Old 24th May 2013, 06:22 AM   #2
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Oh boy...(deep breath)... John, the easiest way to do this is to add the extra woofers in separate boxes with their own crossover coil (known as a '.5 woofer' here)..... if you add them to the existing box you'll get extra volume but not better bass depth.
First - can your amp handle 4 ohm loads, what is it?
2nd - what are the speakers, (brand & model) - the parameters for the specific drivers are needed to get the crossover & box size & tuning right
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 24th May 2013, 08:18 AM   #3
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Thanks Peter I am way out. "Oh boy...(deep breath)... John, the easiest way to do this is to add the extra woofers in separate boxes with their own crossover coil (known as a '.5 woofer' here)..... if you add them to the existing box you'll get extra volume but not better bass depth."
Because I have existing, reasonably large speaker boxes, would I be better off putting a board, a partition into the speaker box that isolates the two bass speakers? Can I do it that way?

"First - can your amp handle 4 ohm loads, what is it?"
A Rotel RC1070 preamp and Rotel RB1050 poweramp. I do not know whether they can handle 4ohms.

"2nd - what are the speakers, (brand & model) - the parameters for the specific drivers are needed to get the crossover & box size & tuning right "
Magnavox speakers which were Australian made and long gone out of business, as far as I know. For the additional cubic box size I doubled the old size which were a Thiele measure.
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Old 24th May 2013, 10:29 AM   #4
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re:'I doubled the old size" - good, you're on the right path
re:"Rotel RB1050" - good, no problem there
re:'Magnavox speakers which were Australian made and long gone out of business" - damn, I can remember those...
I'd wire up the 2nd woofer in parallel with the first, but with an inductor in series with it, we just have to work out how big the inductor needs to be.. how wide are your speakers..?? - may seem like a silly question, but at the wavelength determined by the baffle width, low frequencies drop off because they're radiating into a sphere, above that freq. they're radiating into a hemisphere. So we size the inductor so it drops off the frequencies above the baffle step frequency to get the fullest bass response
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Old 24th May 2013, 09:44 PM   #5
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The width of the speakers are 10 1/2 inches.
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Old 25th May 2013, 10:36 PM   #6
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Ok, so the baffle step freq is 115/width in metres, which = 426Hz. If we assume the impedance of the driver is approx 6 ohms at this frequency (if you have a multimeter you could measure the DC resistance of the coil) and use an on-line calculator for a first order xover, that gives a inductance value of 2.24mH. This is not critical, just buy the nearest available value, but make sure it's a low DC resistance inductor (= heavier wire = more$$$), otherwise power is eaten up by the resistance.
Another question for you - is the box ported or sealed? If ported you may have to re-tune it for the best low bass oomph.
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Old 26th May 2013, 10:39 PM   #7
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Ported box, when I doubled the cubic capacity of the box, I added an additional 2inch x4inch port.
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Old 26th May 2013, 11:29 PM   #8
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OK, that's good, your box is tuned to ~32Hz. Perhaps if you need more oomph in the bass you could tune it a bit higher, there isn't much down that low... (depends on the kind of music you listen to I suppose)
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 26th May 2013, 11:50 PM   #9
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Default next step

The next step is to cut and fit in a dividing panel, so as to enclose and seperate the two woofers - is that the case?
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Old 27th May 2013, 02:38 AM   #10
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no, no need to divide the space
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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