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/product.aspx?language=en-CA&ref=2006&product=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.
"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/product.aspx?language=en-CA&ref=2006&product=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.
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: http://www.diyaudio.com/forums/showthread.php?threadid=110583&perpage=25&pagenumber=3
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: http://www.diyaudio.com/forums/showthread.php?threadid=110583&perpage=25&pagenumber=3
Attachments
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)?
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)?
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.
Cheers.
OK real bonehead question here - since it's called a "dust" cap, does removing it expose the motor to contamination?
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
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.
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.
Hi,
Just in case, watch out for vent holes in the cone below dustcap.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=103517&highlight=
Just in case, watch out for vent holes in the cone below dustcap.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=103517&highlight=
"OK real bonehead question here - since it's called a "dust" cap, does removing it expose the motor to contamination?"
So davidallancole are you talking about permanent removal or replacement with something else?
Cal Weldon said:
So davidallancole are you talking about permanent removal or replacement with something else?
Most drivers with phase plugs seem to have their air gap exposed . However I think the design usually has a larger than normal air gap to ensure that small particles do not get stuck (?).
Very high effeciency drivers might be a problem with smaller clearances.
With usual woofers and subwoofer the spacing is fairly large to take in rocking of the coil etc. and so should be OK to have the air gap exposed unless you live in very dusty surroundings.
I have also used a foam plug ( made out of a 5mm sheet of open pore foam) . Might be necessary if your driver has ventilation holes around the junction near the voice coil. But if you use a phase plug , that becomes harder to do. I'd just leave it open.
My (old) Mission 780's have a 5 inch bass driver with a phase plug and the air gap is exposed ( by design). I have never had any problems with it even though we live in a very dusty area.
Very high effeciency drivers might be a problem with smaller clearances.
With usual woofers and subwoofer the spacing is fairly large to take in rocking of the coil etc. and so should be OK to have the air gap exposed unless you live in very dusty surroundings.
I have also used a foam plug ( made out of a 5mm sheet of open pore foam) . Might be necessary if your driver has ventilation holes around the junction near the voice coil. But if you use a phase plug , that becomes harder to do. I'd just leave it open.
My (old) Mission 780's have a 5 inch bass driver with a phase plug and the air gap is exposed ( by design). I have never had any problems with it even though we live in a very dusty area.
I took the cap off permanently. These are strong, durable drivers. I was ripping and flexing it everywhere and it seems to have not done anything to it. I will have to hook it up and listen to make sure though. The voice coil gap is quite big (relatively I guess) and it looks like a coax could be made out of it very easily like has been suggested for the Pioneer B20. I don't like the fact that it says it can run up to 3 kHz, meaning the crossover between the woofer and tweeter would be in that no-no area. Here is some pictures.
This is the vent through the pole piece. One could easily shove a small tweeter down there and route the wires through the vent.
This is the vent through the pole piece. One could easily shove a small tweeter down there and route the wires through the vent.
Attachments
There is a bit of material on the former that something like a whizzer could be attached to as well. Has anybody tried attaching a whizzer to a woofer? The coax idea sounds really good with this driver too. The voice coil looks to be 1 1/4 inches. I am thinking something like this might work:
http://www.partsexpress.com/pe/pshowdetl.cfm?&Partnumber=275-025
but I don't entirely know, would it be to hard to cross over to the woofer.
http://support.radioshack.com/produ...ku_id=40-1024&Name=speaker components&Reuse=N
Would there be a problem with a tweeter sitting in the voice coil? How would the magnetic field from the woofer interact with the tweeter?
Or a tweeter like this:
http://www.partsexpress.com/pe/show...409&vReviewShow=1&vReviewRand=2754606#reviews
http://www.partsexpress.com/pe/pshowdetl.cfm?&Partnumber=275-025
but I don't entirely know, would it be to hard to cross over to the woofer.
http://support.radioshack.com/produ...ku_id=40-1024&Name=speaker components&Reuse=N
Would there be a problem with a tweeter sitting in the voice coil? How would the magnetic field from the woofer interact with the tweeter?
Or a tweeter like this:
http://www.partsexpress.com/pe/show...409&vReviewShow=1&vReviewRand=2754606#reviews
Gluing a small wizzer cone will bring up the HF quite a lot . However the actual response depends on the coil and how it's glued to the cone. If the glue is rock solid you will get less treble and if it's flexible like a rubber based glue it will have more treble.
The transition frequency is also important.
I think the response will be uneven but might sound better at first listen to the driver without a whizzer.
How about a piezo tweeter ? I think you will have to make sure the air volume 'inside' the voice coil is fairly filled up to prevent it from becoming a resonating cavity.
The transition frequency is also important.
I think the response will be uneven but might sound better at first listen to the driver without a whizzer.
How about a piezo tweeter ? I think you will have to make sure the air volume 'inside' the voice coil is fairly filled up to prevent it from becoming a resonating cavity.
Most of the drivers i have measured before and after were small. In each case Fs goes up, and efficiency went up. In some drivers as much as 5 Hz (ie 100 to 105 Hz). The ratio of the mass of the dust cap to the cone will largely be the determining factor.
Saturnus covered things off pretty well in terms of what changes & why.
Dust cap removal was just a step in a number of mods. The addition of cone coating material (usually puzzlecoat) brought Fs back down to very close to where it was before dustcapectomy,
High density felt can make a very good phase plug for woofers, and i have used foam earplugs for cone tweeter plugs.
I would block off the pole piece vent if it exists. It would be handy for routing co-axial tweeter wires, but as in this case a woofer that has a pole piece vent does not go high enuff to cross to a tweetr that will fit in the available space -- ignoring efficiency concerns one might try one of the small "full-ranges" from HiVi or JBL/HK (as found in the older iMacs (hmm, maybe i'll try that)
dave
Saturnus covered things off pretty well in terms of what changes & why.
Dust cap removal was just a step in a number of mods. The addition of cone coating material (usually puzzlecoat) brought Fs back down to very close to where it was before dustcapectomy,
High density felt can make a very good phase plug for woofers, and i have used foam earplugs for cone tweeter plugs.
I would block off the pole piece vent if it exists. It would be handy for routing co-axial tweeter wires, but as in this case a woofer that has a pole piece vent does not go high enuff to cross to a tweetr that will fit in the available space -- ignoring efficiency concerns one might try one of the small "full-ranges" from HiVi or JBL/HK (as found in the older iMacs (hmm, maybe i'll try that)
dave
Thanks for the comments guys. As I don't have any other speakers to play around with, I am going to see what can be done with these. I will have to pick up a measurement mic, but I am going to play around with attaching a whizzer and than check into a coax unit. This is going to be a fun exploration.
Depending on the design, you may now get air leakage between the front and back of the cone. If you do, it affects any bass alignment you care to try. I would not do this on any speaker you were going to use for bass unless it is for OB
I plan to put this on OB. I have some baffles all ready made, so I can easily swap them in and out.
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