Boston Acoustic A150 dust cap question

[Semi_Social]

I recently purchased a set of series II A150's with replacement woofers. Both woofers are poly coned and have the Boston logo on the back and are dated 1988. The only difference in the two is the dust caps. One is a coated woven fabric and the other is a porous transparent screen material. The speaker with the coated cap is sealed very well while the screened cap is not (judged by the "push test"). The air leak is definitely through the dust cap. I can tell a difference in the bass response.. the sealed speaker being tighter base/better sounding. So far I can't find a 2.75" coated fabric dust cap that matches so I am considering changing both dust caps. Would a felt cap seal well and work? Anyone know what the correct cap is for these speakers?

 

[Doug G.]

Usually, you don't want a perfect seal in a "sealed" speaker enclosure. There is supposed to be a controlled leak, usually through the voice coil/spider/dust cap. If the dust cap is solid, air can't flow through there and it will also affect the response.

That being said, I don't know why Boston would have used different caps on the same model speaker. Variations are common, however, as the manufacturing period progresses. Is the plastic/porous cap similar to cloth or gauze caps? Is the coated fabric cap actually air tight?

In any event, if you are more satisfied with the coated fabric driver, I would try to match the other one to it with whatever cap will be the same as the one on that driver. Gauze caps are very common and it would be possible for you to partially or fully restrict airflow through one.

Doug

 

[Doug G.]

I forgot to ask, do you think the plastic, porous cap is original to the driver or not?

Doug

 

[grillebilly]

The original is a finely woven fabric screen. Using a magnifying glass it has a pattern like a window screen.
It's OK for it to "breath" as the cone and surround is separated by the voice coil. At least that's my take.

 

[Semi_Social]

Thanks for your reply Doug.

From looking at refoam kits online the mesh dust cap looks very similar to kits offered by midwest speaker. It's possible one speaker has been refoamed and the other still be factory. The guy I bought the speakers from said he bought original BA woofers off ebay rather than refoaming the ones he had. They both are definately BA woofers and have the same dates stamped on them. Since the one with the better seal (not a complete seal) sounds noticably better than the one with very little seal.. I'm thinking that it's the screen caps fault. I have checked the box and other speakers for leaks with a 15hz test tone and can find no other leaks. I've read that getting a tight seal and the right foam kits are very important with these speakers..

I have just ordered new felt dust caps and I'll give them a try. Hopefully the felt works.

Greg