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Home » Sponsored » Pi Speakers » Finished Pi 4 with photos
| Re: (Now they're REALLY) Finished Pi 4 with photos [message #60378 is a reply to message #59587] |
Fri, 10 July 2009 12:20   |
Russellc
Messages: 397
Registered: May 2009
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Illuminati (1st Degree) |
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I know this message is getting a little old, but I remember you I believe from the Econowave thread. I have a very similar project,
the same JBL 4507 cabs, I did have JBL 2225H in there which is very similar to the 2226H, but have changed to the 2235H driver, and thats why you see one port plugged. I'm not sure I understood one of your posts, Ihope you didnt alter the length of the tubes inside the 4507 cab. I would restore that if so. The cab can be easily tuned differently by plugging various ports with plumber's test plugs ( 3 inch). All 4 open is 40 hz, one closed is 34 hz or so. This is the same tuning, box volume as the JBL 4430 monitor, one of the reasons I installed the JBL 2235H as it is the same driver thats in the 4430 as well. with 2 ports closed you are right on about 30 hz, and the response is fairly flat. I sometimes use this tuning with thw 2235H driver as well, just a little tighter. With 3 closed, you're at the same tuning, box volume, ( and same driver if using the 2235H ) as the JBL B 380 subwoofer, I think that was 22-25 hz, cant remember now.
Likely your largest difference from the 4PI is something you mentioned in one of your last posts, The difference in length between the H290 and driver ( JBL in the pic) compared to the JBL wave guide and pictured, the Selenium driver. The compression driver shown on the 4507 boxes is the B&C DE 250.
JBL tackled a similar problem with the 4430 monitor by putting a one inch spacer on the faceplate behind the 2433 horn, which moved it forward one inch in relation to the front of the woofer.
Others, like Altec with the A7, made up for the problem by reversing the phase of the HF horn, bringing it closer in phase.
The other difference, is the crossover. They are similar, especially the compensation, but the rest is different, and the 4PI was worked to work on those parts, the JBL wave guide has the E'wave crossover worked out for it. Both would be close for the other, but they arent tweaked as well as their intended application. I also ran into questions, as I also have the H290 and various compression driver, and I tried them in various combinations with the E'wave crossover. Remeber, the E'wave project is just a high freqency unit, waveguide+ compression driver and crossover with compensation. The Low frequency is just a standard 2nd order crossover at 1600 hz or so. It is to be adjusted to your particular choice of woofer. I found with both the 2225H and the 2235H that this standard circuit sounded "OK" but wasnt quite right by a long way. Since I was using the same box size, box tuning and woofer as the JBL 4430 it was suggested to me to use the bass portion of this crossover. I built it as well as the same zobel circuit, combining that with the standard E'wave filter and compensation. Looking at the several projects some members did who have advanced measuring facility produced nice LF circuit foor their particular woofers. Many used the JBL LE 14 A 14 inch woofer, and I noticed the crossover point was pulled down to 900 hz from the standard 1600. The JBL 4430 is said to cross around 1,000, so I figured this would work, and work it has. Doesnt sound bad with the H290 either, oddly and despite the length differences, they seem to both sound fine. One combination I tried on a lark was putting an Altec 802 8G on the H290. A very enjoyable combination! Vintage Altec sound and rock solid imaging from the semi constant directivity supplied by a modern horn/waveguide! Glad to see you got it to sound the way you wanted, lots of lessons along the way.
A question concerning your mounting the horn/waveguide in the face plate of the 4507, you have it very close to the woofer which can be a good thing, but it seems like I remember a brace about there going from front to back? Its been a while since I looked inside my boxes, my HF in still perched on top.
Russellc
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