What do you put in a sealed midrange enclosure?

dogwan

Member
2008-07-05 7:30 pm
Re-building some unique 4-way's with sealed midrange enclosure. Pulled drivers and there is just a piece of dense upholstery foam formed into a circle behind the driver.

Can this be done better?

All my searches lead to stuffing entire cabinet. I just want to know what a good strategy is for a mid specific cubby. In this case it is made up of a round cardboard tube with a MDF cap on the back. It is pretty stout.

My goal would be to smooth the midrange a little to reduce some slight honky-ness.
 

eriksquires

Member
2013-05-10 4:11 pm
Sonic Barrier. I'd actually suggest some thin (1/2") inside, and thick on the outside approach. This will reduce the opportunity for the bass to radiate through the midrange.

Also experiment with Accousta-Stuff. I don't think this would take out the honky-ness though, that's probably left up to the crossover or baffle treatment. Need to measure to understand.

Try some pressure sensitive felt around the midrange. Doubtful it will help but it's worth trying. You can just tape it up and see if it helps before trying to adhere it on.

Best,


Erik
 
Make a Dagger midrange rear chamber. Basically a tall 3 sided pyramid with the driver mounted on the base of the pyramid. Stuff with progressively dense fiberglass. Line walls near driver with foam or felt. There are no parallel walls and the taper acts as a sonic black hole. This design has very little or no coloration and is simple to make out of 3 pieces of triangular shaped wood glued onto baffle with hole cutout. Make it as long as the cabinet will allow (circa 8in to 12in) and adjust size to get close to the ideal volume for whatever Q alignment you want. A factor of 2x within Vas is good. I stuff it with either polyfill (pillows) or fiberglass. Fiberglass works better.

More info here:

http://www.diyaudio.com/forums/full-range/273524-10f-8424-rs225-8-fast-ref-monitor.html

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Here is response with woofer and mid/tweet with XO at circa 600Hz:

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TMM

Member
2007-09-01 8:37 am
Australia
For a 3" cone midrange in 1-2Litres I just stuff the entire chamber with 650gsm polyester. Haven't noticed any difference in expected performance compared to measured on a large open baffle. Optimising the location on the baffle to reduce edge diffraction is much more important than worrying about the rear chamber.
 
If you want to isolate the mids from the woofers, buy some Gorilla Tape at Lowe's. It looks like a black colored duct tape, but it's actually thicker and much stronger and not flimsy, and it's adhesive is better as well.

Rip strips of it, and systematically seal the basket openings on the back of the mids. Might get tricky around the speaker lugs if they are over an actual opening, but smaller strips overlapping can do a good job there.

The benefit will be your mids won't be affected by woofers moving air on their back side and the tape is dense enough to block direct sound on them.

Also, unlike sealed metal-back midrange speakers, it won't echo or have that metal-y sound.
 
Making your own sealed back mid raises the fs a lot and the driver may not have a powerful enough motor to handle such a small volume which is like a very stiff spring. It will have a congested sound. Do you have any measurments of a mid before and after taping he backs up? Is there coloration or is it transparent like a Dagger?


He's talking about a mid and not a mid-bass right? True mids are pretty stiff to begin with. They make sealed-back mids and I've seen companies offer same speaker with and w/o a back with same driver. It's a simple fix and that tape is almost like a neoprene rubber.
 

dogwan

Member
2008-07-05 7:30 pm
I think there is a little confusion here.

The mid-driver is 6" paper cone with pleated fabric surround. The basket is a typical open frame design. I realize now that my original post could be interpreted as meaning the driver has a sealed back.

Also, these are vintage speakers and I am not asking about re-creating the enclosure for the mid-driver. The "sub-enclosure" for the mid driver is sealed already against bass driver interactions. Maybe could be better.

But, what I'm really asking about is what do y'all typically stuff a similar small enclosure for a mid-driver with? Would densely stuffed fiberglass be better sonically than upholstery foam? Is Cotton better for mids than fiberglass?

I'm thinking of lining the walls of the cardboard tube (think Sonotube stout tube) with wool felt and trying fiberglass stuffed into a tube of nylon hosiery (to make a ring behind driver).

The problem is I have to re-glue the mid driver in when I re-assemble the speaker and it's going to be problematic to try several different options.
 
Hi, the stuffing inside serves to convert air pressure into heat
and the best material is wool felt; best if you don't leave it as in sheet form
but modeled to catch the incident wave in order to progressively break it, so
a triangle is the form that follows function.
The effect of stuffing inside a cabinet is to virtually raise its volume, and probably this is caused by measuring some speaker's parameters such as Cms and others that eventually bring to a change in Q; so the speaker sees more volume...

Also, in this case the cilynder probably has the same H x B ratio and the vicinity of the back panel causes the air to bounce back directly to the cone.
The wavelenghts involved might be from 1m to 30 cm, even if we talk about chaotic movement in the box. I'd avoid the "box in the box" style and leave the enclosure for the woofers only :eek: