If I remove the dustcap from a speaker, is the speaker ruined?
The reason that I ask is that I am thinking about trying to DIY some coincident coaxial speakers.
I recently listened to a set of the KEF coincident speakers at Speakerlab in Seattle, and the KEFs do a *lot* of the things that I like so much about the Unity horns which I adore. The KEFs have that incredible ability to articulate sounds in the midrange. I've also noticed with Unity horns that there's an ability to hear details in recordings which are 'smeared' by everything else. It's not an abundance of detail, but a *coherence* which stems from the very very very tight alignment of midrange and tweeter. Basically, once you get the midrange and the tweeter in sync in the time domain, it fixes a whole ton of problems.
I nearly bought them, but the KEF wasn't perfect; it doesn't 'disappear' the way that my Summas do, but the midrange was world-class. (I think the KEF could use a better cabinet.) There's a place in Florida that sells the woofers but they don't have them in stock and I'm impatient. I looked at the Seas coincident coaxial, but at $300 a pair, it's a bit pricey and the efficiency is poor. I'd buy a set of the Insignia coaxials if there were still for sale. (Just discovered them on Zaph's site.)
Anyways, back to the question - if I cut the dustcap off a woofer, is it curtains? I concede that this will change the Thiele Small parameters, and it will alter the frequency response. Both of those things can be dealt with. But will cutting a hole in the cone allow air from the FRONT of the cone to enter the box via the throat of the woofer? I'm thinking the answer is "no" if the voice coil is not vented.
But I've never done this, so I am only guessing.
Picture this, but with me adding a tweeter to the voice coil. (not my pic)
The reason that I ask is that I am thinking about trying to DIY some coincident coaxial speakers.
I recently listened to a set of the KEF coincident speakers at Speakerlab in Seattle, and the KEFs do a *lot* of the things that I like so much about the Unity horns which I adore. The KEFs have that incredible ability to articulate sounds in the midrange. I've also noticed with Unity horns that there's an ability to hear details in recordings which are 'smeared' by everything else. It's not an abundance of detail, but a *coherence* which stems from the very very very tight alignment of midrange and tweeter. Basically, once you get the midrange and the tweeter in sync in the time domain, it fixes a whole ton of problems.
I nearly bought them, but the KEF wasn't perfect; it doesn't 'disappear' the way that my Summas do, but the midrange was world-class. (I think the KEF could use a better cabinet.) There's a place in Florida that sells the woofers but they don't have them in stock and I'm impatient. I looked at the Seas coincident coaxial, but at $300 a pair, it's a bit pricey and the efficiency is poor. I'd buy a set of the Insignia coaxials if there were still for sale. (Just discovered them on Zaph's site.)
Anyways, back to the question - if I cut the dustcap off a woofer, is it curtains? I concede that this will change the Thiele Small parameters, and it will alter the frequency response. Both of those things can be dealt with. But will cutting a hole in the cone allow air from the FRONT of the cone to enter the box via the throat of the woofer? I'm thinking the answer is "no" if the voice coil is not vented.
But I've never done this, so I am only guessing.
Picture this, but with me adding a tweeter to the voice coil. (not my pic)
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I have no experience with this, but here's a DIY coax made from a 5" Monacor woofer with nice pics: click (Dutch, by the way). As you can see this guy's made a cap to mount the tweeter.
Maybe you could close it off if the pole piece is vented, like with the plastic cap on the pictures? On the other hand a vented pole piece might be suitable for pulling through some wires for the tweeter.
Maybe you could close it off if the pole piece is vented, like with the plastic cap on the pictures? On the other hand a vented pole piece might be suitable for pulling through some wires for the tweeter.
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In the bad old days I saw and heard many JBL D-120, D-130, D140 that had the aluminum dustcaps "blown off", they sounded OK without that pinging bit.
Never listened close enough to hear if they were chuffing though.
I did cut the dustcap off a damaged EVX-150 X, which has a hole clear through to the back plate, could not hear chuffing over the sound of the Kapton blisters dragging...
A_tewinkel suggestion is good, if chuffing was a problem the vent hole could be closed.
Art
Never listened close enough to hear if they were chuffing though.
I did cut the dustcap off a damaged EVX-150 X, which has a hole clear through to the back plate, could not hear chuffing over the sound of the Kapton blisters dragging...
A_tewinkel suggestion is good, if chuffing was a problem the vent hole could be closed.
Art
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If you close off the vent you can overheat the voice coils. Not a good idea IMHO.Woofers need to be vented either front or back.
Air can potentially enter the box by going past the coil ID and back up past the coil OD and through the spider (or exit in reverse). However that's probably not that big a deal - the clearances are small, so it would probably just change the Q of the box a bit by creating more leakage. As mentioned, you will be changing the thermal design of the motor. The dust cap won't pump air past the coil anymore. If you keep power dissipation low enough, that should not be an issue. If the motor was not well designed to begin with, you could potentially improve things...
I did this surgery on many occasions, the results are variable.
On big mid bass, you can eventually see the disappearance of a nasty peak in the end of the range, obviously a cavity resonance. This improvement can be heard when running a sweep, and only becomes interesting if the driver is used close to its upper limits. No other consequences. It's sometimes a positive trick.
On small FR, you can have a more annoying disappearance : the Hf are gone. Negative.
With vented poles pieces, I have never seen an influence on the low range, but this on OB where there is already no bass and no pressure for generating aerodynamic noises. I guess it would be very problematic with sealed or ported baffles.
What kind of tweeter are you planning to use ? In front, like the dutch link, or behind the magnet with a kind of horn ? If running passive, this last can help to compensate a phase shift. Last word, if you use the proper solvents for getting rid of the glue (normally cyano acrylate are not used here), it's possible to make something clean and put back the dustcap later, even with paper cones.
On big mid bass, you can eventually see the disappearance of a nasty peak in the end of the range, obviously a cavity resonance. This improvement can be heard when running a sweep, and only becomes interesting if the driver is used close to its upper limits. No other consequences. It's sometimes a positive trick.
On small FR, you can have a more annoying disappearance : the Hf are gone. Negative.
With vented poles pieces, I have never seen an influence on the low range, but this on OB where there is already no bass and no pressure for generating aerodynamic noises. I guess it would be very problematic with sealed or ported baffles.
What kind of tweeter are you planning to use ? In front, like the dutch link, or behind the magnet with a kind of horn ? If running passive, this last can help to compensate a phase shift. Last word, if you use the proper solvents for getting rid of the glue (normally cyano acrylate are not used here), it's possible to make something clean and put back the dustcap later, even with paper cones.
You will need to add a skirt from the tweeter edge to the woofer cone to keep out dust. There is a very big magnet back there and any magnetic dust will find it a nice place to jam up your voice coil.
Yes you will change parameters a bit, but you can always replace the dust cap if you don't like the results. They are a fairly standard part as is the speaker glue.
Yes you will change parameters a bit, but you can always replace the dust cap if you don't like the results. They are a fairly standard part as is the speaker glue.
I ran some plots of this process but I can't seem to find them right now. My experiences were similar to Radugazon. I replaced the dustcap with some phase plugs and I have no complaints.
Basically something like the Seas H1260 which costs $280 a pair:
Using something like the SB Acoustics SB15NRXC30-4 which costs $112 a pair:
An externally hosted image should be here but it was not working when we last tested it.
And something like Seas 27TAFNC/G which costs $66 a pair:
An externally hosted image should be here but it was not working when we last tested it.
The more I look at the tolerances, the more I wonder if I should just find a used set of Kef's with the UNI-Q driver on Ebay though. Getting that tweeter into the voice coil will be tight, and saving $160 might not be worth the risk of trashing the woofers to do the surgery. Hmmm.
I've done quite a few dustcapectomies...
Mostly on full ranges with whizzer cones. On the (unfortunately discontinued) Pioneer B20, a small tweeter mountsd on a cylondrical (1 3/8" dowel) was a successful experiemnt.
As per Radugazon's comment on small FRs i agree, but can be a fix for a pushed in dustcap.
Pwesonally i have moved to what i call co-incedent drivers -- moving the XO low enuff that all the driver are within a 1/4 wl at the XO,
dave
dave
Mostly on full ranges with whizzer cones. On the (unfortunately discontinued) Pioneer B20, a small tweeter mountsd on a cylondrical (1 3/8" dowel) was a successful experiemnt.
As per Radugazon's comment on small FRs i agree, but can be a fix for a pushed in dustcap.
Pwesonally i have moved to what i call co-incedent drivers -- moving the XO low enuff that all the driver are within a 1/4 wl at the XO,
dave
dave
Great driver clinic Dave !
As you seem experimented, two questions :
1. What happens to a full ranger with whizzer cone when the tiny dustcap is removed, and no phase plug yet ?
2. In case that this driver had a vented pole piece, it's always possible to put a tweeter behind the magnet. With some hollow and profiled ring in the coil (instead of a bullet phase plug), can we expect that the whizzer will become a kind of horn for the tweeter ??? A moving horn, wow.
I don't say it's a good solution considering beaming and diffraction issues, just by curiosity.
Sure, but the pleasure of creating is priceless !
As you seem experimented, two questions :
1. What happens to a full ranger with whizzer cone when the tiny dustcap is removed, and no phase plug yet ?
2. In case that this driver had a vented pole piece, it's always possible to put a tweeter behind the magnet. With some hollow and profiled ring in the coil (instead of a bullet phase plug), can we expect that the whizzer will become a kind of horn for the tweeter ??? A moving horn, wow.
I don't say it's a good solution considering beaming and diffraction issues, just by curiosity.
Sure, but the pleasure of creating is priceless !
Ok, thanks, this is a good info. I have a kind of idea, one of these days I will try if I found convenient tweeters. But if a stupid dustcap makes the job of a tweeter....you see what i mean.
I've wondered if my Stephens 8 inchers might play into a coax mode with their vented pole pieces. That would mean trashing the aluminum dust cap though. My 65 year old tradesman ears like the boost at the top from the Fostex coaxes I scored recently although right now I'm enjoying my Philco 6 1/2 FR's, augmented with a pair of Packard Bell 10 inch 2 ways in boxes identical to some HK's I've had for centuries. Rebadging goes back a long way. I do worry about crap getting into the gap.
Hi, I know someone that's done this with a (nice) pair of 12" McKenzie PA speakers. Finding a dome tweeter to match the 98dB efficiency wasn't easy, but having a vented pole piece certainly helped: it gives you somewhere to put the wires for the tweeter.
The dustcap removal may well kill off any high response the driver may have previously, so make sure the tweeter can handle a low XO point.
Chris
The dustcap removal may well kill off any high response the driver may have previously, so make sure the tweeter can handle a low XO point.
Chris
One thing to consider is that the latest KEF Uni-Q is a lot more sophisticated than other coincident drivers. The latest ones have two traits that I think make them much better-sounding than previous iterations, or than the Seas units (Seas licenses some IP from KEF, but don't seem to use their latest technology; the Seas drivers look a lot like the Uni-Q ca. 1995).
The two things they do now that they didn't previously are:
(1) they recess the tweeter quite a bit, and have more waveguide ahead of it. The newer ones almost look like a hybrid between the old ones and the Tannoy Dual Concentric.
(2) they fire the tweeter through a phase plug (which they call a "waveguide" for marketing reasons) designed for their concentric tweeter.
See here:
Having heard a number of KEF Uni-Q based speakers over the last two decades (my KEF Uni-Q experience goes way back to their KAR 160Q car-fi Uni-Q from the early 1990s and the Q15 from ca. 1997, and currently I'm using a set of their KHT-3005SE eggs in a temporary system) the new ones are vastly smoother on- and off- axis, and also need much higher volume levels to sound nasal. (As an aside, in a blind test I found I preferred the KEF eggs to the comparably-sized Tannoy Arena egg, which uses a 5" variant of their Dual Concentric design. The KEFs got louder and imaged better. The KEFs also don't have a front-firing port to diffract off of, and have some interesting baffle sculpting both horizontally and vertically, whereas the Arena's baffle is a flat plane.)
That said, and knowing how creative you are, remember those JBL component speakers you pointed out on DIYMA, the 508GTi and 608GTi? They may offer you a great platform for experimentation. (Here's the 6.5" variant..)
For one thing, they have a phase plug/heat-sink thing in the middle that can simply be unscrewed and removed, so you don't have to worry about diffraction off of glue-edges from an old dustcap.
Second, they have a pretty big vc, so you'd have some space to develop your own waveguide snout and phase plug, to more closely approximate a modern UniQ.
I suspect the cone and motor are at least as good as the SB Acoustics. And they seem to be available right now for <250/pair. With tweeters.
While my only experience is with the C608GTi, given that they have the same vc size I'd be surprised if the 508GTi you mentioned on DIYMA doesn't work the same way.
I assume you listened to the new Q-series, which looks pretty fantastic except for the beancounter's special cabinets, which are not only designed seemingly without concern for diffraction but also lack solidity. After hearing the Q900's, I've thought a few times about buying the 8" Uni-Q's from that Florida shop.
And FWIW, I agree with you about the articulation of the modern Uni-Q in the midrange. Also, the little 3005SE eggs image even better than my reference mains, Tannoy System 12 DMT II guts in closed boxes designed to minimize diffraction.
Though I don't know if that's because the Uni-Q's throw a wider pattern than the Duals.
I'm seriously thinking about selling the Tannoys and using the 3005SE eggs as a "head" atop a bass bin, like the old Waveform Mach 17, with XLS12's in the bass bin because I have enough of 'em on hand to not have to buy new drivers.
They're that good.
PS: I've been meaning to ask you, what program did you use to get the graphs here: Audio Psychosis • View topic - How Much Bass is Enough?
I'd like to look at a few tracks.
The two things they do now that they didn't previously are:
(1) they recess the tweeter quite a bit, and have more waveguide ahead of it. The newer ones almost look like a hybrid between the old ones and the Tannoy Dual Concentric.
(2) they fire the tweeter through a phase plug (which they call a "waveguide" for marketing reasons) designed for their concentric tweeter.
See here:
An externally hosted image should be here but it was not working when we last tested it.
Having heard a number of KEF Uni-Q based speakers over the last two decades (my KEF Uni-Q experience goes way back to their KAR 160Q car-fi Uni-Q from the early 1990s and the Q15 from ca. 1997, and currently I'm using a set of their KHT-3005SE eggs in a temporary system) the new ones are vastly smoother on- and off- axis, and also need much higher volume levels to sound nasal. (As an aside, in a blind test I found I preferred the KEF eggs to the comparably-sized Tannoy Arena egg, which uses a 5" variant of their Dual Concentric design. The KEFs got louder and imaged better. The KEFs also don't have a front-firing port to diffract off of, and have some interesting baffle sculpting both horizontally and vertically, whereas the Arena's baffle is a flat plane.)
That said, and knowing how creative you are, remember those JBL component speakers you pointed out on DIYMA, the 508GTi and 608GTi? They may offer you a great platform for experimentation. (Here's the 6.5" variant..)
For one thing, they have a phase plug/heat-sink thing in the middle that can simply be unscrewed and removed, so you don't have to worry about diffraction off of glue-edges from an old dustcap.
An externally hosted image should be here but it was not working when we last tested it.
Second, they have a pretty big vc, so you'd have some space to develop your own waveguide snout and phase plug, to more closely approximate a modern UniQ.
I suspect the cone and motor are at least as good as the SB Acoustics. And they seem to be available right now for <250/pair. With tweeters.
While my only experience is with the C608GTi, given that they have the same vc size I'd be surprised if the 508GTi you mentioned on DIYMA doesn't work the same way.
I assume you listened to the new Q-series, which looks pretty fantastic except for the beancounter's special cabinets, which are not only designed seemingly without concern for diffraction but also lack solidity. After hearing the Q900's, I've thought a few times about buying the 8" Uni-Q's from that Florida shop.
And FWIW, I agree with you about the articulation of the modern Uni-Q in the midrange. Also, the little 3005SE eggs image even better than my reference mains, Tannoy System 12 DMT II guts in closed boxes designed to minimize diffraction.
An externally hosted image should be here but it was not working when we last tested it.
Though I don't know if that's because the Uni-Q's throw a wider pattern than the Duals.
I'm seriously thinking about selling the Tannoys and using the 3005SE eggs as a "head" atop a bass bin, like the old Waveform Mach 17, with XLS12's in the bass bin because I have enough of 'em on hand to not have to buy new drivers.
They're that good.
PS: I've been meaning to ask you, what program did you use to get the graphs here: Audio Psychosis • View topic - How Much Bass is Enough?
I'd like to look at a few tracks.
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