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I bought four of these 8" woofers last week from Parts Express to use in a pair of low-budget bass reflex tower-style enclosures I am planning on building. At 5 bucks a piece I figured it wouldn't be much of a loss if the end result sounds like shit, but I'd like to try and avoid that.
I'll be using two woofers per enclosure, with the internal volume of the enclosure calculated at 2.514 cubic feet.
The trouble is I can't find an on line enclosure tuning program that will factor in the tuning for dual woofers.
The specs off the PX web site are:
Peerless India W8-12T 12P 8" Paper Cone Woofer 12 Ohm
Well-made, attractive, and efficient 8" woofer that will work well in vented or closed box systems. Buyout, limited quantities. Specifications: *Power handling: 40 watts RMS/80 watts max *VCdia: 1" *Le: 1.93 mH *Impedance: 12 ohms *Re: 10.9 ohms *Frequency response: 40-3,500 Hz *Fs: 43 Hz *SPL: 91.5 dB 1W/1m *Vas: 2.7 cu. ft. *Qms: 2.57 *Qes: 0.72 *Qts: 0.56 *Xmax: 2 mm *Dimensions: Overall diameter 8", Cutout diameter 7-1/2", Depth 3-1/2".
I know from reading this forum for years that there are plenty of people here who can probably calculate this stuff in their sleep, but like Sgt. Shultz, "I know nothing" about this sort of thing. So can one of you please tell me how to tune these things?
I would actually prefer to use a pair of ducted ports like my Focal 826's have. In the Focal brochure it mentions that as the excursion on the drivers increases as the volume is turned up, a point is reached (if the port is too small) where the port sort of ceases to function, and the system starts behaving as if it were sealed.
I'd like to avoid this by also using 2 ports of sufficient size to allow them to function as designed.
Thanks for the help
Follow Ups:
Have you tried downloading WinISD? A very helpful tool.
Hey thanks for the tip. I used the on-line version to calculate that I'd need two 13.86 inch ports made out of 3" diameter tubing.
As an alternative I used a 2.5 inch tube and calculated that they should be 9.32 inches each.
I hope I did it right as a couple of people have suggested that I go with a sealed box.
Opinions are still very welcome.
Go with a sealed box, a vented box with that high of a Qts sounds quite poor.
I'll just have to pad down the 6.5 inch midrange a bit, which is the easy part.
Thanks to everyone for all their help!
You can use a reflex, but watch the power handling
If you can find the Audio article
bill
It's simple, the Qts is too high for bass reflex.
So does that mean I should just build sealed enclosures?
The PE specs say it will work well in a vented system?
I'd hate to lose the efficiency by sealing the enclosures.
In a proted box, good old boxplot says 7.7 cubic feet, per speaker - i.e. 15.4 cubic feet for two. Extension to 28Hz but so what? The 2mm xmax would make that pretty useless.
In your box, sealed, I get about -3dB at 60Hz, with a mild 1dB hump around 110Hz. Not bad.
The port has no effect on midband sensitivity, it only changes the deep bass extension.
Thanks Paul.
Should I stuff the enclosure completely full of insulation, or just attached it to the top, bottom, sides, and back?
Depends on the stuffing. Unless you have access to detailed knowledge of the acoustical properties of the stuffing, experimentation and listening are the order of the day.
I was going to point out exactly the same stuff as Paul, but probably less well.
A couple of things I can add:
1) Most speakers - or, at least every speaker I have owned or modelled - are excursion limited (you can't turn it up beyond X loudness because the cone will move too far) rather than power limited (where the limit is the coil overheating).
2) These speakers require a huge box to work well vented. In a small box (and for these speakers, 100 litres each is small), sealed may be less efficient, in that it will have less output for its lowest half octave, but it may be able to play louder overall than a 100 litre vented box, and have flatter response (less of a resonant peak).
E.g. you feed a hypothetical 2mm excursion woofer a mix of tones at 20, 40, 80, 160, 320, 640Hz
100litre sealed box - at 1.5 watts, it reaches its excursion limit.
100litre vented box, tuned to 40Hz - it can take only 0.5 watts before reaching excursion limit.
...the vented box is more efficient, but at max excursion, the sealed box will be getting triple the power, or about +4dB, for most of its range.
Tried modelling a transmission line?
I think modeling just about anything is beyond my capabilities.
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