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Old 17th April 2006, 05:11 AM   #1
Sheldon is offline Sheldon  United States
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Default sub/main crossover question

I'm running this speaker system Unity Horn Project Progress with a DEQX for the top three drivers. I'm planning on an active line level crossover between the 15" OB driver and the 12" PR sub driver.

Now, normally one would take into account the roll off of the woofer when designing a crossover to the sub. However in this case, equalization will be done by the DEQX on the combined pair. All I need is for a smooth transition between the drivers. Also, the OB driver and PR sub driver have a range of several octaves where they are both dropping about first order in parallel and the same output (they have the same motor). If I put my crossover in this range, I'm thinking I can just do a symetrical crossover and not worry about the roll off, or in other words, treat them as if they had a flat overlapping range. I'm thinking 4th order LR. Comments?

Sheldon
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Old 17th April 2006, 11:25 AM   #2
lndm is offline lndm  Australia
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I confess that I do not know this system, but this sounds like an opportunity to try one of the transient perfect second order crossovers. These require equalising, and seeing as you are anyway, why not get the rolloff of the second order with the transient response of a first order.
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Old 17th April 2006, 02:28 PM   #3
Sheldon is offline Sheldon  United States
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Thanks,

I'll check it out. I had thought about the transient response a little, which is one reason I went with the DEQX. It seems evident that transient response would be audible at higher frequencies where the transients are key to realistic sound. Is transient response also readily audible at the low frequencies?

Sheldon
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Old 17th April 2006, 02:36 PM   #4
lndm is offline lndm  Australia
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Have you ever listened to a poorly tuned vented enclosure? if so, then you've answered your own question
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Old 17th April 2006, 02:48 PM   #5
Sheldon is offline Sheldon  United States
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Ah, ok let me rephrase the question. If I've badly screwed up the sub design I'll hear it, that makes sense. So I should ask if the difference between a "standard" crossover, ala LR, and a transient perfect crossover be easily audible at frequencies below about 80-100 Hz? It seems no harder to implement the transient perfect crossover, but I'm limited to 2nd order for the common published ones. So would it's advantages likely outweigh the advantages of steeper slopes? Of course, I could try both, but at some point I want to put down the soldering iron and listen.

Sheldon
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Old 17th April 2006, 03:42 PM   #6
lndm is offline lndm  Australia
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I use the example of the badly tuned vented box as the result does resemble the result of poor crossover types. In reality, there are more often problems in even getting the crossovers there. Dealing with low crossovers is one reason why I now go two way (thought that I never would once). Some people say the ear is less sensitive to problems in the lower frequencies. Not mine. I really dislike a lack of continuity in the bass/mid region.
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Old 25th April 2006, 05:29 AM   #7
Sheldon is offline Sheldon  United States
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Ok Ind,m,

I took your advice, thanks. I went to the FRD and played with an 80 Hz crossover until I got reasonable parts values. Here's what I came up with. The first two op-amps are the 80Hz boost and the other two are labled for high pass and low pass. I built it using some TL082, as I had some, and with that frequency, I figured they would be ok. I used 15 volt regs (47uF on the input, 0.1 on the output), powered off the amp rails. It seems to work just fine and sounds good with the limited testing I've done. I do get some noise on power down after about 5 seconds, when the main amp caps run out of juice. It's not a dealbreaker, but I would like to eliminate it. Different op amps? I'm using dual 8 pin versions with sockets, so I can easily change.
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File Type: gif transient perfect second order 80hz.gif (9.4 KB, 122 views)
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Old 25th April 2006, 05:43 AM   #8
lndm is offline lndm  Australia
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It's been a long time since I played with op amps, but I would either get in the habit of turning off my gear in the right order, or build in a mute circuit.

I know there are other members who would answer this Q much better than this.
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Old 25th April 2006, 05:50 AM   #9
Sheldon is offline Sheldon  United States
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Quote:
Originally posted by lndm
It's been a long time since I played with op amps, but I would either get in the habit of turning off my gear in the right order, or build in a mute circuit.

I know there are other members who would answer this Q much better than this.
The crossover is powered from the main amp supply - no separate switch( it's actually mounted inside the stereo amp), so turn off order won't help. I was trying to avoid a mute circuit - lazy, running out of room, but will if I must.

Thanks,
Sheldon
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Old 25th April 2006, 06:48 AM   #10
AndrewT is offline AndrewT  Scotland
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Hi Sheldon,
what are the f-3db (or f-6db) frequencies of the HP and LP out filters?

They appear to be different.

The caps on the HP out seem quite small and result in high value resistors on the HP filter. Does this give rise to noise?
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