I've recently refoamed a Hertz ML3800 because the surround was cracking (https://www.diyaudio.com/community/threads/rubber-coated-cloth-surround-cracking.395384/).
Before the operation I measured the TSPs and they were a bit off - but not by too much. I didn't save those but I remember the Fs being around 42Hz and the Qts being around 0.6. I thought that replacing the surround that looked in a very rough shape would help.
It didn't.
In fact I made it way worse. The parameters are unusable. The Vas is basically halved and the Cms too. Qts skyrocketed to 0.8. The SPL dropped too. I remember I measured 93dB.
The TSPs were measured after about 10 hours of break-in at Xmax with a 10Hz tone.
I think that the surround I installed is way too stiff, however it was the only one I could find which looked similar enough and was of the right size and the same material.
I was thinking that if I swapped it for a foam surround (or rubber, if I could find one of the right size) it would be much softer and it might help.
My guess is, however, based on absolutely nothing, and a Google search wasn't successful either. I fear that this operation might be of more trouble than it's worth.
I wanted to ask if anyone did a similar operation and therefore could share how it turned out.
The driver in question has a "double" center spider, even without the surround it is very stiff and doesn't "sag" at all.
I'm attaching the TSPs of the disaster
Before the operation I measured the TSPs and they were a bit off - but not by too much. I didn't save those but I remember the Fs being around 42Hz and the Qts being around 0.6. I thought that replacing the surround that looked in a very rough shape would help.
It didn't.
In fact I made it way worse. The parameters are unusable. The Vas is basically halved and the Cms too. Qts skyrocketed to 0.8. The SPL dropped too. I remember I measured 93dB.
The TSPs were measured after about 10 hours of break-in at Xmax with a 10Hz tone.
I think that the surround I installed is way too stiff, however it was the only one I could find which looked similar enough and was of the right size and the same material.
I was thinking that if I swapped it for a foam surround (or rubber, if I could find one of the right size) it would be much softer and it might help.
My guess is, however, based on absolutely nothing, and a Google search wasn't successful either. I fear that this operation might be of more trouble than it's worth.
I wanted to ask if anyone did a similar operation and therefore could share how it turned out.
The driver in question has a "double" center spider, even without the surround it is very stiff and doesn't "sag" at all.
I'm attaching the TSPs of the disaster
FWIW, in another lifetime we used wintergreen to soften pro slot racing foam tires and mixed in some alcohol to 'taste' for rubber.
Thanks GM.
The driver's surround is a cloth surround, not rubber... but it sounds like your advice would be very helpful otherwise.
The driver's surround is a cloth surround, not rubber... but it sounds like your advice would be very helpful otherwise.
You can but you need a good solvent to unglue current edge, which fully depends on adhesive used.
I would not touch the driver again. Now it works
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Textile surround lasts long. Foam not.
Maybe the surround will still lose up over time and fs, vas, cms, qts will change for better.
A bit more damping in the box can help for higher qts to come a bit down
.
Textile surround lasts long. Foam not.
Maybe the surround will still lose up over time and fs, vas, cms, qts will change for better.
A bit more damping in the box can help for higher qts to come a bit down
Oops! meant to post it on the previous thread. Regardless, if not really rubber, but the pioneer's goop gone hard, then toluene to soften/clean.
I used PVA glue for the attaching the surround to the cone, doubt there's a solvant that works. I'd have to remove the surround while being very careful with a sharp knife.
Regards keeping the surround as-is, it is not an option, unless I sell the driver as is (which I don't feel it's the right thing to do). I want to fix it and not just live with the problem, as it's a pretty good driver.
The TSP are completely off and it's not just a little bit that I can I just deal with it. The parameters were measured after about 10 hours of break-in at Xmax, I can try more time and then measure again but I doubt it will make a difference.
Doesn't model well at all in a box either, this is the FR response as plotted by WinISD (green is using the official parameters, red is after i replaced the surround). It is a 195L reflex tuned to 25hz
I am willing to accept the compromise that in the next 25 years I will have to replace the surround if I go for the foam one, but could it really help with the problem or will it make it worse?
Regards keeping the surround as-is, it is not an option, unless I sell the driver as is (which I don't feel it's the right thing to do). I want to fix it and not just live with the problem, as it's a pretty good driver.
The TSP are completely off and it's not just a little bit that I can I just deal with it. The parameters were measured after about 10 hours of break-in at Xmax, I can try more time and then measure again but I doubt it will make a difference.
Doesn't model well at all in a box either, this is the FR response as plotted by WinISD (green is using the official parameters, red is after i replaced the surround). It is a 195L reflex tuned to 25hz
I am willing to accept the compromise that in the next 25 years I will have to replace the surround if I go for the foam one, but could it really help with the problem or will it make it worse?
T/S Explained
T/S Equations and how each one affects the others
Hmm, specs says a ~28 Hz Fs, so at ~ 42 Hz = stiffer suspension and/or lower mass = lower Vas, higher Qms, Qes
If the spider is stiff, then the surround must be quite flexible
T/S Equations and how each one affects the others
Hmm, specs says a ~28 Hz Fs, so at ~ 42 Hz = stiffer suspension and/or lower mass = lower Vas, higher Qms, Qes
If the spider is stiff, then the surround must be quite flexible
Many thanks for the links, this articles are well written and made it way clearer.
In theory by replacing the surround with a foam (or rubber) one I will be increasing Cms, and since the Mms will stay mostly untouched I should get a
lower Fs (good thing)
higher Vas (a good thing if aiming for efficency, and I want to gain back the SPL I lost replacing the surround)
lower Qes (good thing)
hopefully higher Qms (?) - do not know the Z0
higher efficency as the Vas will be higher and the Qes lower
Is this right? May it cause any adverse effects on the speaker long term?
Thank you again!
In theory by replacing the surround with a foam (or rubber) one I will be increasing Cms, and since the Mms will stay mostly untouched I should get a
lower Fs (good thing)
higher Vas (a good thing if aiming for efficency, and I want to gain back the SPL I lost replacing the surround)
lower Qes (good thing)
hopefully higher Qms (?) - do not know the Z0
higher efficency as the Vas will be higher and the Qes lower
Is this right? May it cause any adverse effects on the speaker long term?
Thank you again!
Cloth surrounds are usually very light it's possible the foam one added both weight and stiffness. The extra weight would explain the sensitivity loss as well as contributing to the worsening T/S parameters.
I already replaced the original cloth surround with a new cloth surround. The surround that is responsibile for this mess is a double wave cloth surround that looks, and is the same size as the original.
I want to replace it again with a softer surround. The foam/rubber surround I'm talking about isn't on the speaker yet
I want to replace it again with a softer surround. The foam/rubber surround I'm talking about isn't on the speaker yet
The manufacturer used a very special type of surround, that allows high excursion with little resistance. This is not typical for cloth surrounds, which are usually for low excursion chassis. So the one you installed is much harder to bend, made for low cone excursion, even as it may look quite similar. This is the cause for the new TSP.
You should have used a high excursion rubber or foam example, allowing the cone more movement. As you measure TSP with quite low voltage, the actual, real performance with high power input will be even worse. It is not the look that has to match the chassis, but the function!
You should have used a high excursion rubber or foam example, allowing the cone more movement. As you measure TSP with quite low voltage, the actual, real performance with high power input will be even worse. It is not the look that has to match the chassis, but the function!
Oh I see I thought you'd already attached the foam surround.
From the other thread it looks like the original surround had already stiffened quite a lot. Nevertheless the T/S parameters hadn't shifted that far from factory.
Did the old surround still feel softer than this new one?
Usually most of a speakers mechanical compliance is governed by the spider, as far as I am aware, unless the surround is ridiculously stiff. I wonder if most of the trouble you're facing is additional weight of the new surround?
It's hard to say really without having the two surrounds to directly compare. Some cloth surrounds are very soft.
Yeah, I figured it out this was the case the hard way. When I contacted the manufacturer about this they couldn't help me as it was a very old component and they didn't have any parts available. So I tried my luck and put a similar-looking part and hoped for the best. Well that wasn't enough🙁
This is the surround that is now on the driver, there are measures on the second picture.
Regarding the "high excursion" part, do you think I should put one of these (h=20mm) instead of the "regular" (h=10mm) type of foam surround? I also found a rubber one, according to the seller, is 18mm tall. How do I calculate the optimal height with respect to the excursion?
Sorry I didn't see your message.
Yes, the original surround needed to be replaced. But when I moved the cone by hand it was somewhat softer compared to how it's now.
It's hard to tell whether or not the surround felt softer or harder than this one as it was very "irregular", there were some spots which were softer than others.
The "new" cloth surround is very light - maybe even more than the original one. The Mms barely changed so I doubt weight is a factor.
First: If I got you right, you measured the TSP before removing the old surround and after replacing it? Or did you trust the factory TSP? These are, maybe, not reliable.
Second: The driver is quoted for an Xmax of 8.5mm, which is not very much (today!). Any reasonable sized rubber or foam surround should do, no need for the extreme excursion type. I would go for the h=20mm version. It should have very little resistance up to 10mm excursion to one side. 10mm may be stretched quite far, if you go for high power at low frequency. Depends on your cabinet and tune, maybe simulate it in winISD and see what excursion you can expect.
IMO you can not have a surround that is too soft, just too hard. The double spider of this chassis should be tough enough.
Second: The driver is quoted for an Xmax of 8.5mm, which is not very much (today!). Any reasonable sized rubber or foam surround should do, no need for the extreme excursion type. I would go for the h=20mm version. It should have very little resistance up to 10mm excursion to one side. 10mm may be stretched quite far, if you go for high power at low frequency. Depends on your cabinet and tune, maybe simulate it in winISD and see what excursion you can expect.
IMO you can not have a surround that is too soft, just too hard. The double spider of this chassis should be tough enough.
Yes, exactly, I measured the TSP before and after replacing the surround. I lost the "old" parameters, but going from memory I remember there was an abnormally high Fs (around 40Hz) and an abnormally high Qts as well, around 0.5-0.6. They were way closer to the provided TSP than the ones after the refoam. Also, I trust Hertz to provide good data as this has usually been the case.
I'll try to get the 20mm foam surround, and then I'll update you with the results, or should I try getting the rubber one (h=18mm)? Is foam really softer than rubber and is it worth to compromise on durability?
I'll try to get the 20mm foam surround, and then I'll update you with the results, or should I try getting the rubber one (h=18mm)? Is foam really softer than rubber and is it worth to compromise on durability?
The proper solvent for PVA (Poly Vinyl Alcohol) is plain Ethyl Alcohol.
Not methyl-wood-rubbing-burning type which are impure (often on purpose)/dyed/contain water but Pharmacy grade 94% type.
What Nurses use after an injection.
I can buy it freely here in Argentina, I know in some Countries it's harder to get over the counter.
You soak joint from both sides, repeat every half hour or so, until glue redissolves into a jelly.
You can now easily separate edge from cone and after wiping mucky adhesive with clean alcohol and a cotton ball you can later reuse both if you wish.
Meaning you destroy nothing.
Well then you've definitely answered the question. If the measured moving mass hardly changed with the surround replacement then the only thing left is the compliance.