PDA

View Full Version : Lousy Bass From 4647 Cabinet



Scotty
11-13-2012, 08:34 PM
I recently purchased an older 4647 cabinet that is cut for a single 15-inch woofer, typically a 2225, but in my case, it has a 2226J. I turned the cabinet upside down and cut a hole for a 2370 horn and a 2426J. I am satisfied with most of the sound, with the exception of the bass. It is lacking and muddy. My woofer tester says the 2226J has an Fs of 50 Hz and a Qts of .4. Cabinet volume is now about 4.75 cubic feet. My pencil and paper calculations suggest a port length of 1.5 inches for each of the four three-inch ports. I tried this, and it did not help. I have pushed the cabinet tight against the wall, which helped a little. I have tried different chokes--from a cored 14 gauge with a dcr of .16, up to an air-core 18 gauge, the latter sounding about the best overall. I have tried varying the amounts of cabinet (fiberglass) stuffing. More sounds better, but not good. I have tried different port lengths and numbers, resulting in minimal differences. I have a hefty amplifier, and I am using 10 gauge wire. I have an LR2 to the woofer at 1200Hz and 18 dB/octave up top (for what it's worth, I have found the Mundorf Supreme caps to be the best yet with the 2426J after many long nights of listening comparisons). The cabinet sounds misaligned, and right now, I am out of ideas and a little frustrated. The cabinet measures 30.5 X 20.5 X 17.5 externally. If someone has a comment or a suggestion, I'd love to hear it!

grumpy
11-14-2012, 07:00 AM
LR24 (I'm assuming) on the bottom and 18dB/oct on top...
Seems both unnecessarily complicated... and then not complicated enough :)
You would have to adjust component values for the bottom end and relative
attenuation for the top, but it seems like there are plenty of examples of JBL
networks that would suit this driver set as well as compensating for the horn
(passive EQ)... which it's not clear to me that you are doing from your description.

Welcome aboard!

4313B
11-14-2012, 07:47 AM
The enclosure is probably sitting directly on the floor.

grumpy
11-14-2012, 08:47 AM
good point. Getting the box off of the ground with the horn ~ ear level while listening
helps quite a bit (think pa box on a tripod/pole if you were standing... a good foot or two
if sitting).

Ruediger
11-14-2012, 11:40 AM
You should measure a Qt of 0.31, and an fs of 40 Hz. Without cabinet, without network. The 2226 can replace a 2225, the TS params are very similar. The cabinet You have should be a good match.

Do You have a proper 2226J ?

Try to operate the components without the bass part of the network, just with the highpass for the midrange and a pot for midrange level.

The 2226J is a 16 Ohm driver, take that into account when later You design the lowpass for the woofer. Also take into account that the dc resistance of serial coil will make the driver's Qt worse.

More about this on the same channel next week. So stay tuned and tell us about Your driver :)

Ruediger

Scotty
11-14-2012, 07:25 PM
The cabinet is off the floor, up about a foot high, tilted 10 degrees. It weighs about 100 pounds, and at 55 years old, I don't want to try more than a few feet. Good suggestion.

I had expected the woofer to measure closer to published parameters, and that it would be a good match with the box. My network for the low pass is LR2 using a 4.2 mH 18g coil with a shunted 4.3 mH cap. The high pass is 18dB/octave using a 5.6 Mundorf Supreme, Dayton 1% caps at 17mF, a shunted 18g 1.6 mH coil, a zobel with a 20 mF cap and an 8 ohm resistor, also a pair of resistors for attenuation to match the woofer. I am not new to speaker building, but I feel like I am missing something obvious that is causing rounded sounding bass with poor transient response. I bought the woofer from SalesBaron in Los Angeles off of ebay. I noticed some adhesive residue that never would have made it past the JBL inspections. Could be a poor re-cone job. I have an Ashly EQ in the signal path, so I can compensate some, but it's still a puzzler.

Would anyone care to speculate on how a 2235H would sound in the same box? I have a 2225J, and I am considering a re-cone to a 2235H. The genuine part is $190.00, not including labor. I'd do it myself if someone would sell it to me.

Thank you for the responses.

Ruediger
11-15-2012, 09:23 AM
... I have a 2225J ...

Put that into the box w/o any filter and tell us how it sounds.

Ruediger