Cabinet Resonace

[Wonderboy]

Hi,

I put together a centre channel cabinet for my home theatre system using two 2118 drivers. I did some testing using a new SPL meter I picked up and found that it has a huge box resonance (about 20dB) between about 200Hz to 320Hz. I figured it is most likely caused by the cabinet design, possibley using an incorrect ratio of dimensions. The internal dimensions of the cabinet are 8"H X 29"W X 10.5"D with a slot port in the front of 1"X6", also there is quite a bit of internal bracing etc inside the box to make it even smaller. I was thinking maybe I need another well tuned port maybe in the rear of the cabinet or put a gasket between the driver and the box? I was just wondering if maybe someone else out there might have a suggestion.

Thanks,

Kevin

[jcrobso]

It is a little bit too long for the other dimensions.
Maybe 10" X 20" X 15" would have worked better.
But you have this box, what frequency did you tune it to?
How much stuffing did you use?

[Ruediger]

If 29 inch is the width, and if the drivers are mounted in the middle, then You can subdivide the box into two halfs by inserting a board in the middle. Each half will need it's own bass reflect duct.

By this You can convert the offending 29 inch into non-offending 14 inch.

Ruediger

[Loren42]

If 29 inch is the width, and if the drivers are mounted in the middle, then You can subdivide the box into two halfs by inserting a board in the middle. Each half will need it's own bass reflect duct.

By this You can convert the offending 29 inch into non-offending 14 inch.

Ruediger

Good idea.

Also, what did you design the box too? You should have a target internal volume and a tuned frequency. Where is it tuned to if you measure the frequency?

Are you sure it is the box and not the room that causes the 20 dB rise in output? How do you know?

Also, the JBL spec sheet calls for a tuning of 70 Hz with a 5 square inch port, 3" long in a vented cabinet. I don't know the suggested volume, but you could model it with a computer program. Your single 1" by 6" port is too small area wise for two drivers. I would recommend two 3" ports and I would recommend an internal wall to prevent one driver from exciting the other. Drivers do vary in specification.

[Wonderboy]

I agree, I believe the box is a bit too long. Actually I got the plans for this box years ago from a speaker repair shop here in town where I live. I had woofers in the box before (no problems) and recently replaced them with the JBL's. I would say the box is 75% filled with stuffing, it's not blocking the port. That's a heck of a good idea to devide the box into two separate boxs, why didn't I think of that! Then again it could be the room, good point Loren. I think before I do any more work on this box I will test it in another room and see how that pans out. It might be a while though before I do, I'm now into another project.

Thanks guys for the input and help, it's very much appreciated, sorry I took so long to reply.

Kevin