paper vs coated cloth dust cap
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Hilltroll67
Marginally Competent
In a woofer, a flat or maoderately convex dustcap is just that - a dustcap. If the beastie is shaped like a 'curved cone', it has a secondary purpose.
Bob
Bob
mhardy6647
Lunatic Member
as long as it's airtight, I don't think it matters. It is true that dome-shaped dustcaps are sometimes used as secondary, HF radiators (the Advent/KLH tweeters are good examples), but I don't think that's the case for the Allisons.
FWIW, I have left the dustcaps on when refoaming Allison 10" woofers -- in general, I've had an easier go when I left dustcaps on than when I shimmed. I use a moderately LF sine wave playing at low level whilst I locate the surround to the basket to help keep the VC centered.
FWIW, I have left the dustcaps on when refoaming Allison 10" woofers -- in general, I've had an easier go when I left dustcaps on than when I shimmed. I use a moderately LF sine wave playing at low level whilst I locate the surround to the basket to help keep the VC centered.
OH YES, it DEFINITELY MATTERS.
In a speaker as carefully-calibrated as an Allison, replacing the dustcap will do the following:
1) upset the cabinet tuning- the air leakage through the fabric dustcap, and the flex of the cap itself is ACCOUNTED FOR in the woofer alignment.
2) Upset the midrange frequency balance, at the woofer-midrange crossover. Putting a paper dustcap will cause a PEAK in the midrange response of the woofer.
Definitely not a good idea!!
To be safe: ALWAYS replace the dustcap, with the SAME TYPE cap...
In this case, as was just mentioned, it's relatively easy to re-foam an Allison woofer without removing the cap. That is the procedure I would use (professionally), and is what I recommend others to do as well...
BTW: If anyone needs fabric dustcaps (or felt dustcaps), I have them available. Usually run between $2 and $4 each, depending on size...
Regards,
Gordon.
In a speaker as carefully-calibrated as an Allison, replacing the dustcap will do the following:
1) upset the cabinet tuning- the air leakage through the fabric dustcap, and the flex of the cap itself is ACCOUNTED FOR in the woofer alignment.
2) Upset the midrange frequency balance, at the woofer-midrange crossover. Putting a paper dustcap will cause a PEAK in the midrange response of the woofer.
Definitely not a good idea!!
To be safe: ALWAYS replace the dustcap, with the SAME TYPE cap...
In this case, as was just mentioned, it's relatively easy to re-foam an Allison woofer without removing the cap. That is the procedure I would use (professionally), and is what I recommend others to do as well...
BTW: If anyone needs fabric dustcaps (or felt dustcaps), I have them available. Usually run between $2 and $4 each, depending on size...
Regards,
Gordon.
zintkala
Active Member
www.webervst.com
He builds custom Guitar speakers but has the dust caps you are looking for ask for the "H" harp dustcap.
He builds custom Guitar speakers but has the dust caps you are looking for ask for the "H" harp dustcap.
Kencat
Super Member
I'm glad you replied here Gordon. After reading about the importance of the double dustcap on the Series I HPM-60 for extended upper response of the woofer, I realized that the dustcap was an integral part of a woofer. I don't know that I would have had the confidence to respond so to this post, but I wanted to.
With my suspicions reinforced by someone with much more experience than I have, I'll be ready to offer a word of caution to other posters. At least suggest to do a bit of research on the topic first.
:thmbsp:
With my suspicions reinforced by someone with much more experience than I have, I'll be ready to offer a word of caution to other posters. At least suggest to do a bit of research on the topic first.
:thmbsp:
Hilltroll67
Marginally Competent
Kencat said:
Ah shucks, where's the fun in that?
Bob
lab
Well-Known Member
While I don't deny that the type of dust cap can have an effect on a woofer crossed over at a relatively high frequency, I doubt that choosing paper, poly or felt can make a huge difference on a woofer crossed over below 500 Hz. The inductor in the crossover would filter out any signifigant mid frequency emphasis or reduction.
Mass plays an important part in woofer resonance, Q and efficiency; so maintaining the weight of the replacement dust cap compared to the original would probably be as important- again more so on a small woofer.
If dustcaps could influence high frequencies a bit better you'd see whizzer cones on high end woofers making an effective full range. I'm not saying you shouldn't strive to replace as close to the original as possible, but if someone has refoamed and used a paper instead of a felt dust cap I wouldn't fret especially if the woofer is larger than 8" diameter.
Mass plays an important part in woofer resonance, Q and efficiency; so maintaining the weight of the replacement dust cap compared to the original would probably be as important- again more so on a small woofer.
If dustcaps could influence high frequencies a bit better you'd see whizzer cones on high end woofers making an effective full range. I'm not saying you shouldn't strive to replace as close to the original as possible, but if someone has refoamed and used a paper instead of a felt dust cap I wouldn't fret especially if the woofer is larger than 8" diameter.
Hilltroll67
Marginally Competent
Kencat said:Are we here to have fun? Damn, I quess I got it all wrong.
Ken, note post #11. Advice, speculation, fun, sharing the joy, I'm here for all of that. If the seriousness gets too weighty I'll just pass by the AK bookmark every day.
Bob
soundmotor
super modified
lab said:
Although I'd agree with most of that, in many of the older speaker designs, you had no crossover at all on the woofer, it ran full-range and definitely contributed in the voicing of the speaker overall. Replacing a hard paper cover with felt or cloth would have an acoustic effect in that instance.
Kencat
Super Member
Hilltroll67 said:Ken, note post #11. Advice, speculation, fun, sharing the joy, I'm here for all of that. If the seriousness gets too weighty I'll just pass by the AK bookmark every day.
Bob
Bob, I hope the big grinning smilie in my post showed where my mood was....that was what my face looked like when I wrote.
I agree, it can sometimes get a bit too serious, and I was probably sounding so in my 1st post. Need a smartass every once in a while to chime in with some humour to break up the flow eh?
back atcha.MarkAnderson
Addicted Member
Kencat said:
:yes: ...not that I would do anything like that...
