| subwoofer use for old cabinets [message #69560] |
Wed, 21 September 2011 12:57  |
 GarlandB
Messages: 25
Registered: July 2009
Location: Natick, Massachusetts |
Chancellor |
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A question for you guys: Would it be worthwhile to hook up my old Theater 4s without the horn and low passed to augment the bass from my JBL 4 pis? I'm mostly interested in managing room anomalies much in the way Wayne suggests using multiple subs. Any suggestions would be appreciated. I have the original Eminence Deltas and also Omega Pros for the large cabinets. The room is 16ft x 20ft x 8.5ft. Wood framed.
Thanks!
Garland
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| Re: subwoofer use for old cabinets [message #69563 is a reply to message #69562 ] |
Wed, 21 September 2011 15:49  |
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Wayne Parham
Messages: 15810
Registered: May 2009 |
Illuminati (33rd Degree) |
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Don't high-pass the mains, let them run wide open. Low-pass the subs depending on their distance from the mains. If you only have a couple subs, make them flanking subs and low-pass them around 90Hz. Put the mains on stands, and put the subs on the floor just beside and behind the mains. One sub beside each main, run in stereo as left main/flank and right main/flank. Each sub should be a couple feet away from the main it is flanking in each dimension, e.g. behind, below and to the side. Make them symmetrical with the mains, mirror images of each other, with the subs just inside or outside. I generally like them to the outside, but I've measured a few rooms that were better with them inside. Either way is better than none, waaaay better.
If you have another sub or two, put them further away, on the other side of the room, and low-pass them around 50Hz. These more distant subs can be put just about anywhere you have room and they'll help. If you have your druthers, put them at side wall midpoints. Another good configuration is four corners, so if your flanking subs are near the front two corners, put a pair of distant subs in the back corners. But like I said, pretty much any location will work. Once you get this many subwoofers in the room, it almost doesn't matter where you put them as long as they're not all grouped together. Spread them around.
You can't re-purpose components from the Theater four π crossovers for subs, although they are still pretty much the same crossover we use today in the mains. The tweeter circuit capacitor that used to be 8.2uF is now 6.8uF, but that's the only difference. Woofer circuits were always unique to the woofer you had, Zobel values changed and sometimes the core splitter components did too. I think the woofer values in your crossover are pretty much the same as what is used in the current model three π model with the Delta 12LFA woofer. So but the point is, your old Theater four π crossover is pretty much the same as the current crossover, but that's no help to you for a sub.
What I would suggest for a sub crossover is an active crossover and separate amp. This can also be implemented as a plate amp. I've used the Rekkhorn F1 sub crossover, and it worked pretty well. It allows variable adjustment of the (24dB/octave) low-pass frequency and amplitude. But honestly, I kind of like this modded Pyle crossover better. It has a gentle 12dB/octave slope, which works very nicely for multisubs which are supposed to be blended with the mains. It's definitely not as cool looking though.
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| Re: subwoofer use for old cabinets [message #69566 is a reply to message #69565 ] |
Wed, 21 September 2011 23:01 |
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gofar99
Messages: 633
Registered: May 2010
Location: Southern Arizona |
Illuminati (1st Degree) |
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Hi Good points. There is a low noise, fast replacement for the NJM4558. Mouser part number 513-NJM2043L it is a direct replacement and a lot better it is $.74 each. I attached the data sheet. I may mod mine with some and see what happens. The caps though probably did the deal for improving the sound.
Attachment: NJM2043_E.pdf
(Size: 160.42KB, Downloaded 53 time(s))
Good Listening
Bruce
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| Re: subwoofer use for old cabinets [message #69569 is a reply to message #69560 ] |
Thu, 22 September 2011 10:47 |
Shane
Messages: 1088
Registered: May 2009 |
Illuminati (2nd Degree) |
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Thanks for the heads up on that opamp. I've got one of the pyle xovers and a pair of subs I've never messed with yet. Course I have a set of Two Towers that I've never gone farther than unfinished boxes so it's not surprising. I need more motivation 
Rolling Hills Imagery - Photography by Shane
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