Adding Polyfill to a speaker cabinet. What to expect?

[thedudeabides]

Don't know if it's going to work but I'm going to try to fill the cabinet housing my 2 mid bass drivers on my MBL 116's to attenuate what to me is a bit of "bloat / ringing" and also tighten up the mid-bass response. The separate cabinet currently has no filling.

The 2 drivers fire sideways. I'd guess the drivers produce from 200hz to 3Khz.

Likely will not measure and will tune by ear.

What should I expect to hear?

Amount of fill required and impact?

Thanks in advance for your comments.

 

[TBone]

Don't know if it's going to work but I'm going to try to fill the cabinet housing my 2 mid bass drivers on my MBL 116's to attenuate what to me is a bit of "bloat / ringing" and also tighten up the mid-bass response. The separate cabinet currently has no filling.

The 2 drivers fire sideways. I'd guess the drivers produce from 200hz to 3Khz.

Likely will not measure and will tune by ear.

What should I expect to hear?

Amount of fill required and impact?

Thanks in advance for your comments.

Sorry can't really suggest here ... although I've added various forms of damping to cabs before, but none similar to your particular speaker.

Can an application of Pollyfill (not familiar with this product) be removed easily?

 

[treitz3]

Yes sir, Mr. TBone. It sure can. Here's a link to an example of what polyfill is...

http://www.parts-express.com/acoust...inet-sound-damping-material-1-lb-bag--260-317

To thedudeabides, IME, it is completely speaker dependent. It also *may* not tighten up the mid-bass response, in fact, it *could* have an opposite effect. I would suggest playing with different amounts and placement within to see what sounds the best to your ears.

Tom

 

[TBone]

and thank you for the clarification, Mr.Tom.

 

[DonH50]

+1 to Tom. You could try one of the speaker design programs, but a simple way is to add an inch, see what happens, add another, and so forth. You'll hear when you go too far.

 

[JackD201]

Have a kitchen scale handy. You'll want to be able to put the same amounts in each. Also be careful not to squish it so density remains consistent. Have fun!

 

[Audio_Karma]

You might want to try some oil based modeling clay, this might help the problems your having here. This the kind of clay that never hardens...

You can start by putting the clay around the speaker opening holes and try putting some around the speaker driver's metal frame of the speaker drivers too...

 

[DonH50]

There was a fad in the 70's and early 80's of putting clay around various things to improve the sound. I personally am glad it died out to be replaced by things like better cabinet bracing, damping, and more secure driver mounting strategies. The clay was a mess and getting it to stay in place inside a vibrating box was a challenge. I used to place the clay then duct tape over it to make sure it didn't end up in the wrong place. People were doing it to everything, from speakers to electronic components (inside and out) to phono cartridges. It might help but would not be my first choice.

 

[thedudeabides]

+1 to Tom. You could try one of the speaker design programs, but a simple way is to add an inch, see what happens, add another, and so forth. You'll hear when you go too far.

Don,

What will I "hear" when I go too far?

This is exactly the anecdotal info I need.

GG

 

[DonH50]

I am not a speaker designer. IME reducing the volume by over-stuffing causes the LF corner to move up so you lose the deepest bass. It may also reduce the output. It is the same as putting it into too small a box. Since I have Magnepans I have not piddled with adding stuffing for some time...

 

[microstrip]

The mid drivers of the MBL are mounted back to back and radiate sideways to complement the omni tweeter. In principle the sound waves from both speakers inside the box are in opposition of phase - like the mids of the Audio Physics Kronos. Most possibly the manufacturer decided to omit the usual box stuffing intentionaly. This is an unusual configuration and I think that it is almost impossible to guess the effect of modifying your speaker with Polyfill -IMHO you will have to try to know! And after doing it, please report on your findings.

I would suggest starting by addind the filling just one speaker, keeping the other unmodified for comparison.

 

[BobM]

Is there a port in the bass cabinet? If so, you might find that plugging that port with something (like a tiny pillow or a sock filled with Polyfill) might just do the trick for you.

 

[Audio_Karma]

Try stuffing the bass ports full of straws...if they have ports on the bottom of the cabinets.

 

[treitz3]

Are these your model of speakers?

Tom

 

[thedudeabides]

That's the one.

Initial listening with various amounts of filling was not positive.

And plugging the port has a similar, negative effect.

Oh well, only out $20 if this is a failure.

Thank you all very much for your input.

 

[treitz3]

That's too bad. One always hopes for positive results. Have you considered upgrading the inductors or capacitors within that particular circuit or is this something you will not even entertain? I have heard those speakers before and I know what you are trying to improve upon.

Tom

 

[Orb]

The joy of audio hobby.
I honestly never knew you could do this, or that it was even popular to do several decades ago
Interested how it goes from a hobby perspective and fingers crossed it helps.
Cheers
Orb

 

[thedudeabides]

Pretty easy. You try different combinations and see what sounds best.

Tried a new setup tonight with high density foam (1-1/2" thick) placed at the bottom of the cabinet.

Initial impression is quite positive.

The challenge is mating / blending the tweeter / midrange carbon petal "pods" to a conventional driver.

 

[DonH50]

Interesting. If it is hard foam I would expect it to decrease cabinet volume, something usually handled by design. Perhaps it moved the response up a bit....

 

[Audio_Karma]

Pretty easy. You try different combinations and see what sounds best.

Tried a new setup tonight with high density foam (1-1/2" thick) placed at the bottom of the cabinet.

Initial impression is quite positive.

The challenge is mating / blending the tweeter / midrange carbon petal "pods" to a conventional driver.

If your liking that you might want to try some memory foam from a mattress topper to put in the bottom of the cabinet. Maybe your like this even better...