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Old 1st May 2006, 10:48 PM   #1
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Default Box design and Active filter

I am looking at building my computer stereo. For the satellites the low end is a 5.25" driver.
If I am going to use active filters and a linkwitz-riley 24dB/oct is 2 cascaded butterworths then I should build a sealed box with a Qtc of .707?

Then I would need a 24dB/oct active LP for the Subwoofer and an active 12dB/oct HP. Would I also expect to have to run the sub 180deg out of phase?

Do my statements make sense? .158cuft seems very small for a 5.25". The satellites willl be a 3 way design.

speaker parameters
fs 46Hz
Qts .478
VAS .278 cuft


.158 cuft is Qtc .707
.41 cuft is Qtc 0.565 (About max volume I am willing to live with)
1.207 cuft is Qtc .49 78.3Hz F3
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Old 2nd May 2006, 12:23 AM   #2
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Yes, a Qtc of .707 is your target for the satellites. The box HP and the electrical HP combine to form a 4th order HP filter. The sub and main should be in phase.

A three way starting with a 5.25" driver seems like a lot of work. What are your plans?

If you need boards for your active crossover or a power supply PM me. I still have a few unsold from the group buy. (due to arrive on May 15th) See the group buy forum for details.
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Old 2nd May 2006, 01:23 AM   #3
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Dayton Tweeter $4.60

The midranges are bose 2 5/8" drivers that I have been unhappy with my measurements. Fs is ~165Hz

My intention is to mount the mid and tweet quite close together and use a 4" PVC pipe to enclose them with dynamat on the walls and using fill.

And the 5.25" woofers are surplus that are pretty large. The dustcap is inverted and they don't play really high so I don't think it would be possible to do a 2 way. The Re value is ~9ohms.


3 ways are supposed to be better and I do like the sound so far. They would be more challenging too. (: I am currently using .37cuft and tuned to 38Hz ported boxes for the 5.25".

And no I don't have any pcbs yet. I was looking at buying the ones from Rod at esp(australia) ESP It looks like your Pcbs are 2 ways. I guess I could use 4 of them. Looks interesting but I don't think its quite what I need.

since a qtc of .707 gives about 60% reduction in my box volume would there be any advantage of building 24dB/oct crossovers this way:
12db/oct with qtc of .707 and additional 12db/oct lp that matches the Qtc of my boxes on the 5.25". The lower Q showing more low end
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Old 2nd May 2006, 02:00 AM   #4
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That would match acoustic slopes, a good thing. You wouldn't quite end up with a L-R crossover but the slight dip in response in the crossover region would probably not be noticeable.

Yes, the group buy boards are single channel two way 2nd or 4th order. If the only active crossover you want is stereo satellite to sub, you would need two. Four boards would make a stereo three way system or four satellites to subs. They offer the capability to do a lot more than you are currently looking to do.
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Old 2nd May 2006, 02:20 AM   #5
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well that changes things alot if Im going to a smaller box... I knew linkwitz-riley 24db/oct were supposed to be .49 Qtc so I was looking for large boxes. I will look into your group buy pcb's a bit more. Apparently ordering from Rod in austraila to canada I can't get insurance for shipping

Currently everything except the sub is passively filtered. The sonys and the mid-tweet are Bi-amped. I find it easier to experiment with passives.
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