Dampen metal cone resonance: How much is enough?

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If one has a closer look at the Fletcher-Munson curves then he can clearly recognise that for the same INCREASE of perceived loudness less increase of power is needed at the upper and lower end.
While you need a tenfold increase at mid-frequencies you need tripling or quadrupling of power for the same perceived increase at the upper and lower end.

Regards

Charles
 
http://www.linkwitzlab.com/mid_dist.htm
"Note 1: Since these tests were done Seas introduced the W22EX001. Like the W18EX001 it has very low distortion, but with 1.75 times the cone area it can move more air. This driver is my first choice for any new open baffle speaker design. The large resonance peak at 5 kHz requires a notch circuit. The PHOENIX pcb provides three optional room equalization notch filters. One of them could be allocated to this task and be patched into the midrange channel. The harmonic distortion of the W22EX001 has a broad peak between 1.3 kHz and 3.5 kHz. The reason for this is that distortion products generated at these frequencies are amplified by the raised frequency response around 5 kHz. The notch filter will not help this situation and the driver should ideally only be used below 1 kHz. The distortion peak at 4.8 kHz in the Seas data sheet is a measurement artifact. There is no increase in distortion."

Obviously mechanical dampening will also damp this resonance.
 
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phase_accurate said:
If one has a closer look at the Fletcher-Munson curves then he can clearly recognise that for the same INCREASE of perceived loudness less increase of power is needed at the upper and lower end.
While you need a tenfold increase at mid-frequencies you need tripling or quadrupling of power for the same perceived increase at the upper and lower end.

Regards

Charles


Hi Charles,

I hadn't looked at this before but it certainly explains some things, especially the fact that speakers sound better when cranked. Effectively at low SPL your ears are less sensitive to low and high freq, and as the spl rises they become more linear??? I imagine that If you measured with an spl meter at low volume everything would show as being flat, but what you actually peceive is somewhat different.

So in effect the problem isn't so much that it requires heaps more power to get the midrange to sound louder, it is more that it requires heaps more power to make the bass and treble sound as loud as the mid. I guess one thing that can be done is pad down the mid, but then you would get a dip in the mid, when the volume is turned up.

Opens up a whole new can of worms for me (ie now I'm thinking how do you optimise speakers so they sound flat at a particular volume level as opposed to measure flat). It would be nice to have my speakers sound good at the volume level I prefer to listen at, rather than the level that annoys the neighbours.

Regards,

Tony.
 
If my math is correct, (I wouldn't mind confirmation on that, because I am not certain), then that peak, at it's height, will cause less than 1 dB rise in the midpoint SPL level.

Depends on the point in space; the resonance will certainly have an effect on the dispersion at that frequency. And the height of the peak will be different at different angles. You also have to take into acount the phase rotation near the resonance. This might be fun to model.

I'm still looking for that 10dB article. I'm fairly sure it was by one of the Old Lions of the British hifi establishment, Crabbe perhaps.
 
Ive been looking for seas mid woof alu cone too but I cant figure out what is so different with alu cone drivers. Im not talking of the breakup but it seems that many other paper cone woofer of the same size have better responces curves... Is there something special that makes alu a better choise for mid, bass or sub application? or I should go for a lower priced viva paper cone mid/woof ?

Vifa
Seas
 
Hi Guss

Please don't be mistaken. Alu cones are not necessarily powerful and stable like what is mentioned in the Seas literature.

I had some 8" alu cone woofers made some years ago for testing. Nominal power was 80 watts using stamped metal frame. Similar kind of peak - about 15dB, real nasty.

My purpose then was to evaluate whether the rigidity was worth that peak. I concluded that unless in a bandpass, where I have a free 12dB roll off, I cannot justify the cost in taming it. Neither can I justify the additional cost in alu cone development as the speaker I was developing was meant for the consumer market.

In the end, I settled for a Kevlar cone. Cheers.
 
For Guss:

I recently did a crossover for a Seas L15RLYP (H1141) that you linked to at Seas. This driver probably has the most wicked breakup node I've seen. Here it is measured on my infinite baffle:

An externally hosted image should be here but it was not working when we last tested it.


Here it is after the filter:

An externally hosted image should be here but it was not working when we last tested it.


All that remains is the miniature peak that showed up right before the main peak. It's 30db down at that point and is inaudible.

Other than the breakup node, this driver is very flat. Harsh breakup nodes often scare people away, but they are reasonably simple to tame with a notch filter. The cost in taming this peak is about $2.50 worth of components, definitely worth it for the gain in cone stiffness and the resulting detail. ;)
 
Guss said:

Zaph, I'd like to know which order you used with your notch. I already have a nice LCR.

Acoustically it's pretty close to 2nd order. Electrically, it's just a single coil. The notch is so deep that I didn't even use an R. The woofer crossover only has 3 components.

An externally hosted image should be here but it was not working when we last tested it.


I've got all the details on my web site: http://home.new.rr.com/zaph/audio/audio-speaker12.html

I brought these down to a DIY meeting in Milwaukee for the guys to hear. The host reviewed the projects here: http://www.audiodiycentral.com/milwaukee090403.shtml I think the Seas L series are some of the better cheap metal cone drivers out there. Scary breakup nodes, but great sound once they are tamed. :up:
 
Thread revival! Sorry, was searching round and came accross this!

I have the M8a which I intend to use in a 3 way (with RS52 and RT2-EA) and after reading this thread, I have done some tests with regard to notch filters. I had certainly intended to use one, it'll be an active crossover anyhow so not difficult to implement, and the peak looks quite drastic at about 2khz (a further one at about 6.5khz but this is far beyond the crossover). Crossover is planned at 820Hz, 24db.

I have been using computer music software to simulate this crossover, with a 24db highpass on the B3N (being used in this test for mid/high, it's own breakup is controlled with an analogue filter) and 24db lowpass on the M8a. A parametric EQ is being used to implement the notch.

I've found that firstly, full range the M8a breakup is very evident, the 6.5khz one more offensive imo. With both main breakups notched it is evident this is a very smooth driver, obviously significantly attenuated high end but smooth otherwise. With the 24db lowpass applied I haven't bothered with the 6.5khz notch, it is too far out of band to be concerned with. The 2khz breakup has a filter though.

I've found that solo'ing the woofer (with no contribution from the B3N) the breakup is indeed audible, found by taking the EQ in and out. This is despite the breakup region being well over 24db down (820hz crossover point, 2khz breakup, don't know exact figures). It is by no means a large difference but it is one that all of you would hear I'm sure :)

Playing with the B3N on as well and adjusting the notch on the M8a it is clear that any change is significantly masked by the B3N's output. Now the difference between notch and no notch is very hard to distinguish I found. Without the notch a tiny amount of forwardness can be percieved on some types of music. Applying more extreme cut or boost gives clues as to what to listen for but even with this the difference is at best miniscule.

So, that's my results! I will give consideration as to whether I'll use an analogue notch in the actual design. The breakup may be more audible with the proper top end and a better integrated crossover, but the the notch may intruduce more complication than it's worth with regard to phase shifts!
 
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