What's the dope on tweeter dope?

[DaveThreshold]

I was wondering what kind of goo they use to dope soft dome tweeters. I have Scan speak 9300's and they are so sticky that I don't want to get near them. LOL Seriously though, does anyone know the chemical that they use? After all these years, the speaks are still extremely sticky. The stuff never hardens.

Dave

[dlr]

[i] The stuff never hardens.

Dave [/B]

You REALLY wouldn't like them if it did!

Seriously, it's not supposed to harden. It's a damping compound (I've no idea what any of them use) that has specific application requirements to work optimally. It seems to be one of the critical issues in tweeter unit-to-unit consistency.

[OlogyAudio]

I really wish I knew...
I guess me not knowing exactly might just mean I will find a better goo to use in the future it will just be a giant pain in the butt in the mean time. Sampling about 30 different domes just to find one that’s respectable for a tweeter doesn't sound like a good time to me.

In the mean time... Rigid domes!

[dlr]

Originally posted by OlogyAudio
I really wish I knew...
I guess me not knowing exactly might just mean I will find a better goo to use in the future it will just be a giant pain in the butt in the mean time. Sampling about 30 different domes just to find one that’s respectable for a tweeter doesn't sound like a good time to me.

In the mean time... Rigid domes!

Three questions:

1. What do you mean "find a better goo to use"? This implies that you're applying something yourself. You don't want to do that to an existing dome. The tackiness is a side effect, but necessary for the dome in question. Some are tacky, some not so much so.

2. Sampling to find one "respectable" in what way? The frequency response is the indicator. Tackiness doesn't have anything to do with effectiveness.

3. Are you actually referring to the D2905/9000? the 9300 is not very tacky. I've had those and the 9500, both use the same dome. The 9000 is, however, a lot more tacky I believe. It's also a much older driver and is obsolete whereas the 9300 and 9500 are both current models.

Dave

[OlogyAudio]

I think this might be heading off topic... Since I would still rather like to know what is traditionally used to coat domes.
I guess I was a bit vague with the term goo. I should have said damping solution. There are some 3m materials that look interesting. Viscoelastic Damping Polymer possibly, possibly a thin film thermoplastic elastomer would be interesting... Not just on tweeters but loads of things but I don't want to get too off topic.

As for a respectable raw dome... you have to weed through the masses of domes that are available off the shelf in order to find that one soft dome profile/textile mix/doping that really makes you excited. I doubt that me ordering a bunch of seas raw domes is a feasible solution?

I imagine that its much easier to find a metal dome that performs as expected and has better QC off the shelf?

[DaveThreshold]

Thanks for answering everybody. Edited to add: Maybe a tar based material. I made some layered damping blocks, with tar in the middle years ago, and the stuff is STILL gooey.

Originally posted by dlr


You REALLY wouldn't like them if it did! Seriously, it's not supposed to harden.

Oh yes I know that. I always thought some of the reason is so they would "grab the air" better than with no dope. This is starting to sound like an anti-drug commercial. LOL You should have just said, "Why do you think they call it dope!" Another reason I asked was in terms of speaker building, I've always looked for goo that would never harden. ANOTHER thought is, I wonder if any companies use something like polyurethane to make the soft dome harder. That may defeat the whole purpose though. I have some cheap tweets, and cheap paper mids, that I am going to spray with poly, or lacquer, and see what it does to the response.

Originally posted by dlr

3. Are you actually referring to the D2905/9000? the 9300 is not very tacky. I've had those and the 9500, both use the same dome. The 9000 is, however, a lot more tacky I believe. It's also a much older driver and is obsolete whereas the 9300 and 9500 are both current models. Dave

You really know your Scan Speaks. I just checked, and they are the D2905/9000. For some reason, I can never remember the number. I just made up a list of all the drivers that I have, so I can remember them. I noticed that my Dynaudio D-28-2's seem to be dope free. Dave, and others who want to chime in, since we're going off topic anyway, what sonic differences have you noticed between different tweets that you've tried? So far, and these are older versions, the Focal TC120TDX's that I have are just KILLER! They really sound like a cut above the rest. The thing is, I haven't bought any brand new drivers in a long time anyway, so that's why I'm asking. The Vifa ring radiators seem like they might be real good.

[dlr]

Originally posted by OlogyAudio
IAs for a respectable raw dome... you have to weed through the masses of domes that are available off the shelf in order to find that one soft dome profile/textile mix/doping that really makes you excited. I doubt that me ordering a bunch of seas raw domes is a feasible solution?

I imagine that its much easier to find a metal dome that performs as expected and has better QC off the shelf?

Most of the better soft domes have proprietary doping compounds AFAIK. The best usually still apply the doping manually as well. It's a bit of an art from what I've read, at least for the top-line units.

The doping compound is most likely proprietary as well. Since soft domes have significantly self-damping, the doping is critical. Hard domes seem to be far more uniform probably due to the ease of manufacture and the lack of any manual steps. Hard domes likely make QC much easier and better for this reason. You just have to accept the good with the bad, bad being the phase issues that are inherent to any hard dome.

Another issue is the soft dome geometry and material, of course. The nearly semi-spherical shaped domes (Morel and many mass-market varieties) just don't seem to be capable of reasonable linearity, mostly above 10K anyway. If the damping could be optimized so that the higher frequencies can't propogate to the tip area, then they'd work, but that's where the damping usually falls down. Hiquphon is an example of the best in this area. The larger (meaning deeper) domes have phase issues just as a hard domes do. They also seem to suffer more from any internal reflections for some reason. Internal damping and interior volume shape/dimensions are also critical aspects of tweeters.

It's getting hard to beat some of the better manufacturers for price/performance when units such as the Seas 27TBFC/G are available. Then you have the Dayton RS28A, though it's gremlin seems to be on the QC side if a low crossover Fc is desired.

dlr

[dlr]

Originally posted by DaveThreshold
ANOTHER thought is, I wonder if any companies use something like polyurethane to make the soft dome harder. That may defeat the whole purpose though. I have some cheap tweets, and cheap paper mids, that I am going to spray with poly, or lacquer, and see what it does to the response.

Making the dome harder does defeat the purpose. The damping due to being soft is desired. The intention is to damp higher frequencies to prevent radiation from the tip area at higher frequencies and act more like a ring radiator. Since speed of sound in a harder material, even a soft dome, is much higher than in air, any radiation from the tip area at higher frequencies introduces phase issues that cause non-linearities due to interference.

Originally posted by DaveThreshold
Dave, and others who want to chime in, since we're going off topic anyway, what sonic differences have you noticed between different tweets that you've tried? So far, and these are older versions, the Focal TC120TDX's that I have are just KILLER! They really sound like a cut above the rest. The thing is, I haven't bought any brand new drivers in a long time anyway, so that's why I'm asking. The Vifa ring radiators seem like they might be real good.

I've heard good things of the Focals, but I have no experience with them. I've auditioned one set of Focals in a shop, but they were way to hot for me ears. That probably has more to do with the goals of the designer, though.

I like the Vifa XT19, but no the XT25 as much. The latter is lacking a bit in detail and "air" as I'd call it. I think that this is due to its poorer polar response.

Dave

[OlogyAudio]

Originally posted by dlr

It's getting hard to beat some of the better manufacturers for price/performance when units such as the Seas 27TBFC/G are available. Then you have the Dayton RS28A, though it's gremlin seems to be on the QC side if a low crossover Fc is desired.

dlr

I love that 27TBFC/G I guess I'll leave it at that for now.