| Pi 4.5 possible? [message #63416] |
Fri, 16 July 2010 22:54  |
Infrasonic
Messages: 17
Registered: March 2010
Location: Clovis, CA
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Chancellor |
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Hi Wayne!
I was lucky enough to acquire three JBL 4648a's from someone in Kentucky.
http://www.jblpro.com/catalog/general/Product.aspx?PId=74&MId=1
I will have them shipped to me in a week or two. I got them cause it was a sick deal on six 8ohm 2226H's. The Pi4 project has been on my to-do list all year so that's why I got them.
I was wondering if there was a way to make a Pi4.5 with a 2nd 2226H in the mix. Basically the bottom woofer would get a 150hz 1st order lowpass while the upper 2226H get fullrange up to the crossover of yours. Now I know this would be a 4ohm load now and that your crossover is made for a single 2226H at 8ohms.
Is there a way I could make this work for me? I want to have dual woofers used cause I love bass and want all the sensitivity and impact I can get. Btw, this is for my HT so I definitely want that cinema sound. I really want this: http://www.jblpro.com/catalog/general/Product.aspx?PId=84&MId=1 but with your crossover and CD/lens combo. I'd love to have all the bass capability I can get for my mains.
What are your thoughts on this, Wayne?
EDIT: After further pondering I wonder... maybe it would still work with your xover the way I imagine it. It's really late at night and I've had a long week so I am probably wrong but would the xover itself see the full 4ohm load or would just the amp? I figure I make a slightly extended version of your cab (the Pi4) to allow room for the 2nd 2226H. Above that the speaker is a normal Pi4. Now it will have a 2nd underneath this time with just a 1st or xover @ 150hz-ish. Same baffle shared, same amp. Two woofers, two xovers. I sounds like it could work but I am pretty sleepy too. Heh. Just brainstorming.
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| Re: Pi 4.5 possible? [message #63429 is a reply to message #63427] |
Sun, 18 July 2010 03:19  |
Infrasonic
Messages: 17
Registered: March 2010
Location: Clovis, CA
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Chancellor |
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| Wayne Parham wrote on Sat, 17 July 2010 08:24 |
We've discussed this approach several times, and I think it's a good idea but I think the multisub approach is even better. Of course, you can employ both approaches but if you have to chose one, I'd go multisubs. Take those "helper" woofers out of the main loudspeaker cabinets and place them somewhere else in the room.
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Hi, Wayne.
I was originally going to build the Pi4 as is as my next DIY project. These would replace my current left, center and right speakers. I also run a twin vented 18" subwoofer system with two more 18" drivers in storage. I plan to make them into a qual sealed subwoofer system. I will have the multisub configuration in addition to having a trio of Pi4's.
I was hoping I could have a working 2.5way version of your Pi4 with dual 2226H's. The link about the 2.5way is a good resource, thank you. I may have questions about your crossover and the 2.5 approach from that thread though. That guy had 16ohm versions of the JBL 2226.
EDIT: Actually, I do have a question about your response to his thread. In there you mentioned, "Run the bottom woofer off the midwoofer crossover output, but add a large coil in series to limit its output to the bass range.". Just to be clear on this, he can get away with having both woofers hooked to the lowend output of your Pi4 crossover (with an extra filter for the bottom woofer in series for that output) and not have to modify your crossover? It looks like I couldn't do this simply like he did as the final load would be 4ohm. Everything else I can make work. I know the cabinet stuff and all that but the way I handle the crossover always goes over my head. What am I to do? I want to use your crossover network and have two 2226H's. 
Would I be able to have the the top woofer run off the crossover and the bottom just with a 1st order filter around 150hz or would that not work?
| Bill Epstein wrote on Sat, 17 July 2010 19:30 | The 4648s a lot of us got during the tent Sale had 2226Js, 16 ohm drivers, and I suspect that's what you'll find. If so, it's a good thing; the combined 8 ohm load is more benign to an amp, especially a tube amp.
I played around a bit with the old 4Pi crossover and 2 -2226Js back then. The resulting bass seemed way more solid than the 3dB arithmetic boost would indicate.
You say you got 3- 4648As. Well then, use 2 as is for subwoofer duty and take the woofers from the third to build conventional 4Pis. Then play the opening of Lord Of The Rings, the battle at the Black gate. better yet, cut 22 and on of the Boston Concert side of the Police Live SACD. Turn it ALL the way up.
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The guy who sold them to me had two versions for sale and I requested the 4648A and not the 4648A-8. This one came with two 2226H's. I wanted this because I knew I was going to build a Pi4. I haven't received them yet so I cannot confirm but I should have them soon.
Also, I don't use tube amps at all. I have a regular home theater receiver but may upgrade to external pro amps later. I like your advice though. Talk about rock the house audio! That's what I am trying to do but with even more speakers. 
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| Re: Pi 4.5 possible? [message #63433 is a reply to message #63429] |
Sun, 18 July 2010 09:20 |
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Wayne Parham
Messages: 18784
Registered: January 2001
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Illuminati (33rd Degree) |
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Infrasonic wrote on Sun, 18 July 2010 03:19I do have a question about your response to his thread. In there you mentioned, "Run the bottom woofer off the midwoofer crossover output, but add a large coil in series to limit its output to the bass range.". Just to be clear on this, he can get away with having both woofers hooked to the lowend output of your Pi4 crossover (with an extra filter for the bottom woofer in series for that output) and not have to modify your crossover? It looks like I couldn't do this simply like he did as the final load would be 4ohm. Everything else I can make work. I know the cabinet stuff and all that but the way I handle the crossover always goes over my head. What am I to do? I want to use your crossover network and have two 2226H's.
With 2226H (8Ω) woofers, you can connect the midwoofer directly to the output of the crossover PCB, and tie another using a large value coil in series. The first woofer is the midwoofer, outputs connetced directly. It is the only load "seen" by the crossover, because the "helper" woofer is isolated by the coil, and the impedance of that branch becomes very high in the crossover region, sort of taking it out of circuit. At low frequencies, the coil impedance becomes low enough that both woofers are in parallel with each other, so the total system impedance drops slowly to 4Ω at the deepest bass range. But that's OK, most amps can handle that load. All speakers have some impedance fluctuation.
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