What happens to a speaker when you remove the dustcap?

[davidallancole]

planet10 (Dave) said in a thread I was reading about removing dustcaps that this happens:

"Keep in mind that as soon as you remove the dustcap, the radiating area will decrease & the Fs will go up (as will nominal efficiency)"

Has anybody measured how much these parameters change?

The speakers I am looking at removing the dustcap on are these:

http://www.thesourcecc.com/estore/pr...roduct=4001024

The Fs is 35 and the SPL is rated at 87 +- 2dB, 89dB from a formula I got from GM. The dustcaps look like they are barely even glued on.

[ashok]

All dust caps are not equal. Some are porus and some are not.
Some have a large volume of air behind them and some do not.
So how much it affects the performance is not uniform.

I would expect the resonant frequency to fall as an additional 'resistance' has decreased . I don't see how there will be any "significant" change in efficiency.

It will change the response of the speaker in the higher frequencies. Mostly for the better . Some shoutiness will decrease but this depends on the cone and other factors. If the dust cap muffled some spurious response emminating from the coil junction, then that will now be higher in level. The location of the dust cap might also be significant in some cases.
So without complete information about all the factors that went into the design of the dust cap , it's hard to say how it will sound without it. For me ..........I think it will mostly sound better..........but I could be wrong with some drivers !

However my experience is that it almost always sounded better. But then your coil gap is now exposed to the elements. So there is no real direct answer . You decide which is better for you. I pick sound over the elements ! As a DIY operation this doesn't matter .
Cheers.

The following picture was posted on one of the the OB threads
here: Fast, fun, Inexpensive OB project

[davidallancole]

Thanks for the response. The speaker I am looking at has a polypropylene cone and dust cap, so the cap shouldn't be porus. The magnet has a hole in the back center of it, so I don't think there would be any compression from the dust cap, but I think I will try and take it off to see if a small tweeter could be shoved into the hole.

Has anybody else ever done this and measured T/S specs before and after? Does the Qt increase from a lose in weight (I am assuming the mechanical Q will go up, but I don't know that for sure)?

[ashok]

I don't think you will find too much change in the parameters.In any case I'll do this for the next driver in the next few days and post the results if I find this thread again !
Cheers.

[davidallancole]

Thanks.

[sdclc126]

OK real bonehead question here - since it's called a "dust" cap, does removing it expose the motor to contamination?

[tinitus]

I have replaced the dustcap with a light foam plug placed at the edge of the voicecoil, and it works wonders ... its on an 8" woofer

[Cal Weldon]

Originally posted by sdclc126
OK real bonehead question here - since it's called a "dust" cap, does removing it expose the motor to contamination?

Yes.

[Saturnus]

Removing the dust cap will technically have several results some of which work against eachother so if it's a good idea will have to depend your application:

1) Higher FS because of lower cone weight
2) Lower FS because of less acoustic resistance
3) Higher sensitivity because of lower cone weight and acoustic resistance
4) Lower sensitivity because of smaller active cone area
5) Higher force factor because of lower cone weight, acoustic resistance and active cone area
6) Changed phase response

Especially the phase response is important if the application is a midrange driver. IIRC, Planet10 on this board makes and sells custom made phase plugs for that purpose. It's really an art form to match the right phase plug with the right driver.

You should also note that overall power handling drops significantly as driver use the trapped air and ventilation of that to cool the VC.

[AKN]

Hi,

Just in case, watch out for vent holes in the cone below dustcap.
Peerless dust cap removal