metal cone resonances, what direction, how to suppress?

[capslock]

Most aluminum and mag cones exhibit severe resonances, the first of which typically occurs at 4 - 7 kHz. Below, waterfalls usually look way better than any paper, polyprop, hard paper, kevlar, hexacone whatever material.

Aluminum will have strong secondary resonances, whereas magnesium only has one dominant one, and higher orders are pretty benign. Why?

Does anybody know whether the dominant resonance is tangential or radial, i.e. whether the standing wave pattern is made up of concentric rings or rays originating from the center?

This would help to decide what the optimum shape and orientation bits of material (paper, fibreglass) should be that one could glue to the back side of the cone to suppres the dominant resonance. Anybody know why this is not being done by the manufacturers?

Regards,

Eric

[gary f]

Hi

see this tread, someone talk about damping rubber band.

Dampen metal cone resonance: How much is enough?

F

[gary f]

Aluminum will have strong secondary resonances, whereas magnesium only has one dominant one, and higher orders are pretty benign. Why?

I think it is because:
1- Magnesium has better internal damping (if i remember well my engineering courses)
2- Since mag is lighter than alu, Seas made the cone thicker and it is less resonant (from the Thor article by Joe D'appolito)

F

[Pan]

The first series of Excel magnesium drivers had a break up pattern similar to the alu cones with multiple peaks.

/Peter

[Bas Horneman]

Doc B. from bottlehead fame ofcourse coated his drivers with shellac.

That is what I shall be doing.

These days he coats with a butyl coating.

Cheers,
Bas

Someone on this forum also suggested "puzzlecoat" not a familiar term over here in europe..

[SY]

Anybody know why this is not being done by the manufacturers?

Yes, because the cure is usually worse than the disease. If it were just a matter of putting some goop on the cone, smart manufacturers like Seas would do that.

The best way to use these drivers is to have a steep rolloff well below the first big breakup, and use trap filters if necessary.

[SimontY]

Does it lower efficiency or something? I'm guessing it would.

What about coating the rear of an already coated paper midbass driver, would that make it sound softer and warmer, even if there are no large resonance peaks? (Seas H571/W17PPI)

I think I may be punished for saying that...


-Simon

[SY]

With metal cones, it probably won't have much effect until it's really glopped on. With enough glopping, the Q will be higher, fs will be lower, efficiency will be lower, and a whole new set of resonances will "replace" the old one.

Goop is more effective, in general, for cones that are made of pourous materials like paper or cloth.

[5th element]

Right this may get flamed but its what it sounds like aint it.

Anyway if you have read any of my previous posts here you know I use the KX drivers on the SB cards ie DSP xovers.

Now right at this moment (im listening to it ) I have a three way going using the KX.

Tweet SSd2905/95
Mid Excel w15cy001
Bass Peerless 850146

Right Xovers centred at 3500hz and 150 hz

Now. I have the EQ peaking filter set to remove the res peak of the SEAS, I am also using 24db electrical on it, cant do 18 as I wanted anyway. So technically at about 8000hz the peak is already down by about 30 dB anyway due to the xover. BUT if I remove the peaking, by clicking bypass (this is all in real time so I can switch it in and out at will as im listening) I cant hear a difference at all, just on a quick AB.

I played some Mozart and Anastacia's freak of nature to see if differnt music would highlight the peak. None did.

If you deactivate the tweeter and then swtich in and out the peak you can hear the difference, buts its only quiet small.

This is with the W15 tho, small driver 24db xover and peak high.
If this were the W18 however with its peak at 5000hz the story mite be different.

If you have a soundblaster with the EMU10k chip on it I would strongly suggest using the KX with a coupla power amps and trying it for yourself to see what you can and cannot hear.

At the end of the day if you cant hear it why suppress it. Now Ok I just said I couldnt hear it and I am building an acitve xover to replace the KX as its not the best in hifidelity but its not half as bad as ppl would make it out to be. And I am including a res trap.
Buts its very easy to sort out with an active so I added it.

Its just trial and error, which unfortunatly us DIYers cant do easily.
Making ten different passive xovers for one speaker to see what sounds the best isnt practical, but it sure would help.

I think trial and error would help alot of ppl if it could be done. I see loads of posts that say, what xover freq should I choose, is the res peak audible, is baffle step nescessary. Now we want to get it right 1st time so we only have to purchase a minimum of parts, but experimentation is the key. For no logical reason one frquency mite sound better then others even tho two drivers would work well at five others. The KX helps a lot of this, as do some loudspeaker design packages that include real time simulation of what the xover will sound like, but the software costs, but the KX is free!

Anyway hope that helps

Matt

I ranted again oh well.

[SY]

Matt, excellent rant.