Are duct seal, felt wrapping and earthed chassis measurable

[LostForWords]

For that last few weeks I have been reading what I can on the virtues of duct seal for damping and profiling the shape of drive units; felt-wrapped magnets for suppressing the reflection of high frequency waves back through the lightweight cone of the drive unit and the slightly more esoteric idea of earthing the chassis of a drive unit to the negative terminal of the drive unit.

So far I have not seen any actual data that supports their use, but there is lots of anecdotal evidence. Has anybody out there proved that these techniques make a measurable difference?

I am happy to believe that felt might have a marginal effect, but suspect that Fostex, for example, might have access to coating materials that could easily be used commercially to suppress chassis-ringing. I am a little cautious about earthing the chassis when output transformers rely on varnish for insulation!

What do you guys (or girls for that matter) think? Can anybody direct me to some serious study that might confirm the effectiveness of these DIY tweaks or does it have to be try it and see (as I suspect that we are all willing victims of our own enthusiastic tinkering)?

[jrn77478]

Originally Posted by LostForWords

So far I have not seen any actual data that supports their use...

Turn in your S.N.O.B. Audiophile Assoc. membership card, pal. We don't need your kind around here.
Empirical data? Burn this heretic!
Next thing you know, he'll be questioning the efficacy of oxygen-free speaker wires with pure unobtanium connectors.


Seriously, I don't know about the felt backing, but it makes sense. I can vouch for the efficacy of damping speaker baskets. Virtually all of them will ring if excited at the right frequency. For some, that resonance is definitely not subtle. As such, it is easily measured and while I can't lay my hands on a link at the moment, I have seen traces that clearly show it.

[Scottmoose]

In terms of measurements, it is certainly possible to show differences with fairly standard gear (microphones, accelerometers etc). The major stumbling block here though is that what applies to one driver does not automatically apply to another. There are an almost infinite number of possible units & combinations thereof, so it's very much a case of doing it yourself, & applying common sense in terms of broad trends.

[Pit Hinder]

Scott, two ways, two reasons, two results. You can improve a cheap and lousy driver and get measurable results. Or you can get the last hairwidth out of a good driver and you and I are back to sharing the secret that doorbell wire can leave monstermoney cables dead in water.

[planet10]

Ductseal on the basket certainly reduces ringing. Tap the bezel with a screwdriver before and after. How much it affects what comes out the front, once the basket is clamped to the bezel is harder to measure. Its affect will be way down below the main signal and may be hard to extract from the stimulus. May show up in a waterfall, but most of those are really limited in how far they go down -- measuremenst may have to be done in an "anechoic" condition.

Shaping the back of the driver for minimum turbulence -- you can probably pull some data out of some of the longer B&W white paper/brochures.

Felt on the basket/magnet needs to be fairly thick, but anything that reduces internal reflections back thru the cone will reduce time smear. Not as important as a piece of damping on any cabinet walls in proximity to the driver.

Grounding the basket. Tannoy might have some data. Alot of vintage drivers have an explicit basket earth tag. Related to Groundside Electrons. There is a whole thread on that.

dave

[Pit Hinder]

Hmmm - Dave, I think the results will be high enough in the frequency range for not needing an anechoic chamber, digital will do. The problem is - the differences may be TINY, so which affordable soundcard/program/microphone combo has the jeweller´s loupe precision needed?

[SY]

Actually, to see the effects of the mods that actually work, you can do a complex impedance measurement. When you plot it on the complex plane, resonances will appear as little loops. Effective mods remove those loops- VERY easy to measure.

[Pit Hinder]

Hah - one of the few who know that impedance plots can tell secrets? Hail thee fellow!

[InclinedPlane]

Lost, I don't disagree with the claimed benefit of these driver treatments, but I don't see it as something that matters enough, or has enough audible improvement, to justify any effort on these mods. I tried wrapping the stamped steel frames of my drivers with those thick square rubber sticky patches that satellite installers put under their dish mounts before screwing them through a roof and I could hear no differences even though the rubber is a seriously lossy material. I've never heard any differences in the sound with any basket or magnet mods, period. That the mods help I think is concrete. Just not enough to matter in the real world.