active xover and sub problem! doesn't work!! - diyAudio
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Old 28th April 2003, 11:08 PM   #1
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Unhappy active xover and sub problem! doesn't work!!

I have a 15" pro woofer that has some definite bass capabilities, and will be used as a sub with my soon to be built speakers. I have a 125WRMS amp for it, which is quite nice as well. They match well together as long as you have a preamp before input. I have this preamp, and an active xover before that. But, it doesn't cut out the high frequencies! It was a 12dB low pass @120Hz, but I moved it to a 6dB at 50Hz as well... still got high frequencies. Do I need to figure out how to do steeper? (18-24dB?) If so, what are the formulae for 18 and 24dB filters?

If I had the spare parts, and knew of a filter greater thab 12dB... I'd test before I ordered parts. Thanks for any help you can provide.
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Old 29th April 2003, 12:02 AM   #2
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Default subs

It's not uncommon to need fourth order.
You'll likely have the problem that the pro driver has a lot more sensitivity @ 300 Hz than at 50.
it's just a fact of life with these things.
I'd go all the way with a fifith order-a 16 mH inductor AND a fourth order electronic. It would be quite something to know what would be happening with the phase, tho (A microphone would help)
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Old 29th April 2003, 12:31 AM   #3
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Why not try some of these Line Level Crossovers from Planet 10's site?

http://www.t-linespeakers.org/tech/f...ssiveHLxo.html

I haven't tried them in a project yet, but they seem to be a sensible approach to the problem. Try them in addition to your active crossover to make a high slope crossover.

Hope this helps.
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Old 29th April 2003, 12:46 AM   #4
OMNIFEX is offline OMNIFEX  Jamaica
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Quote:

I have a 15" pro woofer that has some definite bass capabilities, and will be used as a sub with my soon to be built speakers. I have a 125WRMS amp for it, which is quite nice as well. They match well together as long as you have a preamp before input. I have this preamp, and an active xover before that.

Am I reading this correctly? You have the Crossover first,
then the Preamp??

I hope, I've mistaken your termology.

Quote:

But, it doesn't cut out the high frequencies! It was a 12dB low pass @120Hz, but I moved it to a 6dB at 50Hz as well... still got high frequencies. Do I need to figure out how to do steeper? (18-24dB?) If so, what are the formulae for 18 and 24dB filters?

Umm...... How exactly do you have the outputs of the
crossover sent to the amp? You should be using the
Low Out I have numerous crossovers, and never
encountered the problem your having.
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Old 29th April 2003, 08:50 PM   #5
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Thanks all.

colwaiting- that would be an interesting idea... but I am on an extreme budget (as always) which is why I decided to go with active xovers instead or passives. I have the opamps to use, and could not afford the expensive high value inductors.

kelticwizard- when I get a chance to do some more breadboarding, I will try some of those xovers out. Am I thinking correctly when I assume I can link two 12dB xovers in series with one another and get a 24dB? Or is this not how it works? Can I just change values to get it this way?

OMNIFEX- the xover/preamp was on a breadboard... not final... but yes, you read correctly. I did have the preamp last. (have fixed this...) This is just a low pass (no HP). I do get higher (not really high) frequencies when using a 12dB at 104-ish Hz. (I used spare parts) I would say probably up to the 600Hz regions. I can even hear some cymbol crashes... not good. This speaker is amazingly sensitive around 500Hz up. Bass is present, but not overly done (unless EQ'ed and preamped) and the higher areas REALLY sing. It will run a person out of the room with loudness. Thus, I need an xover. Mains will be using 8" Eminence and Selenium horn tweeter, and those woofers SHOULD handle the lower frequencies well enough... should I put a HP xover on them? What frequency?

Thanks
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Old 1st May 2003, 05:05 PM   #6
Wizard of Kelts
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Quote:
Originally posted by trespasser_guy
kelticwizard- when I get a chance to do some more breadboarding, I will try some of those xovers out. Am I thinking correctly when I assume I can link two 12dB xovers in series with one another and get a 24dB? Or is this not how it works? Can I just change values to get it this way?
Tresspasser Guy:

I do not know if you can add two 12 dB Passive Line Level Crossovers together to obtain a 24 dB Passive Line Level Crossover. The T-Line website link I gave in a previous post seems to say that you can cascade first order Passive Line Level Crossovers-more than that, I do not know.

However, I am reasonably certain that you can use a 12 dB Passive Line Level Crossover before the input of an active crossover, a preamp, or a power amp to add 12 dB to whatever slope, (if any) existed before. I would think the same would appy to any slope of Passive Line Level Crossover.

Like I said, I have not used these in any project yet, so this is just conjecture on my part.

You might try opening up a thread to ask about the layout of Passive Line Level Crossovers with a slope higher than third order. I am sure all the electronics mavens on this site will be able to help you out with the circuit.
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