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Old 21st September 2006, 10:41 PM   #1
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Default Building Subwoofer Cross Overs?

I am looking for good educational links to self teach how to construct crossovers. I still dont understand what the inductors do with certain ratings or what the caps do depenindg on the rating?

Some help please.

I am looking to build a 70hz-80hz drop off with an 8db-12db decreasing slope towards 100hz.

If anyone has a design in mind...I'd love to see the schematic for it!

Dominick
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Old 21st September 2006, 10:48 PM   #2
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Dominick,

That makes for some big time chokes and caps. Your choices are 6 db/octave, 12, 18, 24 etc. If you choose 12 dB then you will have a choke (inductor) in series with the woofer and a capacitor in parallel. You have to know what the impedance of the driver is at the frequency you wish to XO at. Here is a calculator. Go to 2 way networks. Click and go to second order -12dB.

http://www.mhsoft.nl/spk_calc.asp
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Old 21st September 2006, 10:52 PM   #3
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You sound like you are trying to implement a passive sub crossover. Bad idea. By shopping around, you can buy a complete plate amp for what it will cost you to buy the large inductors and caps for a sub crossover.
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Old 21st September 2006, 11:03 PM   #4
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Ah yes, I did seem to leave that part out didn't I? Thanks LB.
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Old 21st September 2006, 11:03 PM   #5
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hmmm,

A plate amp?

That sounds much easier, but will my output performance suffer?

I am trying to build a sub similar the the Martin Logan Descent. I actually already have the 3 exact subs that they use in the descent!

Now I just need to build an enclosure and supply an amp!

Suggestions?

Dominick
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Old 21st September 2006, 11:07 PM   #6
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Quote:
Originally posted by Dominick22
That sounds much easier, but will my output performance suffer?
Well, going active is generally considered to outperform passive solutions (assuming you don't change other factors), so I would say no, a plate amp will be higher performance.
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Old 21st September 2006, 11:42 PM   #7
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OK,

I looked into the plate amps offered on parts express and the best one they had was 1000 watts at 4 ohms.

If I run all 3 subs in one enclosure, I will need an amp with similar wattage or better capable of a 2 ohm continuous load.

Any ideas?

Dominick
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Old 22nd September 2006, 04:01 AM   #8
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Quote:
Originally posted by Dominick22
I looked into the plate amps offered on parts express and the best one they had was 1000 watts at 4 ohms.

If I run all 3 subs in one enclosure, I will need an amp with similar wattage or better capable of a 2 ohm continuous load.
How are you coming up with those numbers? Are you picking them out of the air or did you use a simulator? How did you arrive at 3 drivers? My sealed 15" sub sits 99% of the time at 1/2 vol on a 250W amp.
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Old 22nd September 2006, 02:21 PM   #9
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well, they are sort of arbitrary numbers.

I am looking to create a balanced for design like the Martin Logan Descent. I want to pretty much do a DIY project of this commercial sub.

It uses 3 10" divers in one cabinet and is pushed by 400 watts rms and up to 800 at peaks. I would like to have about 1000 watts so that I am not pushing the amp to its absolute limits.

And if I wired an amp to all 3 8Ohm subs, the load would effectively be 2Ohms on the amp!

Unless you know of a way to negate this.

Otherwise, I may have to drop the project and build a single sub design.

So, I pretty much need either a way to wire 3 8Ohm subs into a 4Ohm stable amp or find a 2Ohm stable amp.

Thanks,
Dominick
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Old 22nd September 2006, 03:43 PM   #10
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But have you selected the drivers? They are 8 ohm single voice coil?
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