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Old 24th September 2005, 02:22 PM   #1
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Default Seas W18EX-001 and notch filter

I'm planning on partnering a Seas W18EX-001 with a set of 45" Newform ribbons using an active crossover over at 1250 khz (48 db/oct on the Newform side, 24 db/oct on the Seas)

I've seen recommendations that a notch filter be added at 4.8 kHz to address some reasonance modes on the Seas. With a 24db crossover I'm trying to determin if the notch filter is still needed (I should be 48db down at 5 kHz)

Thoughts? Opinions?

Thanks

Kelly McDonald
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Old 24th September 2005, 03:56 PM   #2
paulhfx is offline paulhfx  Canada
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Kelly,

I think the w18 is an excellent driver - I'm using it in an active dipole design I'm completing now.

However, that resonance is very obvious and difficult to get rid of with a simple nth order crossover alone. My crossover is at at 1600Hz 4th order and definitely needs the notch filter. I would suggest that your setup will too, even with the lower crossover point.

Incidentally, why the W18 rather than W22 when you're using a 1200 Hz crossover?

Paul
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Old 24th September 2005, 05:11 PM   #3
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Thanks, I'll give that a try.

I did look at the W22, but my rule of thumb for selecting the cross-over point is to give myself a full octave of wiggle room. . That way I can always play around with different slopes and even move up the cross-over point if needed.

With the W22 that would have put the crossover point at 1 kHz which is the at the low end of the Newforms response

There is also the additional volume, the W22's needed just a little too much space for my design. (Vas of the W22 is amost twice the W18
s)
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Old 24th September 2005, 08:27 PM   #4
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A notch filter will tame response discrepancies, but you run into a problem where any distortion products which excite the resonance will get amplified considerably. Seas no longer prints the distortion curves, but the ones I have here show that harmonic distortion in the W18 rises to about 3% around 1.6 kHz. Notch filters won't help; those products are caused by the motor itself after the signal hits the voice coil. That higher distortion might show up as a bit of extra brightness in the upper mids, with perhaps a loss of transparency, but only excited by certain program material. I would advise crossing W18s no higher than 1200 Hz with a steep crossover like a LR4 to make sure 1600 Hz is minimally excited. The W22 is a bigger driver, so all other things being equal the peak will occur at a lower frequency, and so the distortion peak will also happen lower.

Metal cones are not inherently bad, but they have limitations to be worked around just like anything else.


Cheers,
Francois.
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Old 24th September 2005, 08:53 PM   #5
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Quote:
Originally posted by Kelly McDonald
Thanks, I'll give that a try.

I did look at the W22, but my rule of thumb for selecting the cross-over point is to give myself a full octave of wiggle room. . That way I can always play around with different slopes and even move up the cross-over point if needed.

With the W22 that would have put the crossover point at 1 kHz which is the at the low end of the Newforms response

There is also the additional volume, the W22's needed just a little too much space for my design. (Vas of the W22 is amost twice the W18
s)
oops me = stupid I thought you were using a dome sry
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Old 24th September 2005, 08:55 PM   #6
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Quote:
Originally posted by DSP_Geek
A notch filter will tame response discrepancies, but you run into a problem where any distortion products which excite the resonance will get amplified considerably. Seas no longer prints the distortion curves, but the ones I have here show that harmonic distortion in the W18 rises to about 3% around 1.6 kHz. Notch filters won't help; those products are caused by the motor itself after the signal hits the voice coil. That higher distortion might show up as a bit of extra brightness in the upper mids, with perhaps a loss of transparency, but only excited by certain program material. I would advise crossing W18s no higher than 1200 Hz with a steep crossover like a LR4 to make sure 1600 Hz is minimally excited. The W22 is a bigger driver, so all other things being equal the peak will occur at a lower frequency, and so the distortion peak will also happen lower.

Metal cones are not inherently bad, but they have limitations to be worked around just like anything else.

paper generally gives you a little more to work with as far as keeping resonances low

from what I understand that the seas after around 1.5khz isn't gonna be low distortion like it is from 300-1khz... it's just not a midrange for a 3-way system

luckily this is a 2-way
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Old 24th September 2005, 10:23 PM   #7
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Quote:
Originally posted by Audiophilenoob


paper generally gives you a little more to work with as far as keeping resonances low

from what I understand that the seas after around 1.5khz isn't gonna be low distortion like it is from 300-1khz... it's just not a midrange for a 3-way system

luckily this is a 2-way
Softer materials _generally_ (not always) tend to have higher distortion than metal, merely by virtue of more flexing, but their resonances are muted precisely because the flexing tends to damp out modes, so paper can be considered more forgiving than metal.


Francois.
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Old 24th September 2005, 11:59 PM   #8
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Quote:
Originally posted by DSP_Geek


Softer materials _generally_ (not always) tend to have higher distortion than metal, merely by virtue of more flexing, but their resonances are muted precisely because the flexing tends to damp out modes, so paper can be considered more forgiving than metal.


Francois.

ringing is far higher and dampening far lower in a metal cone/polycone/magnesium cone

yes alum/magnesium won't flex quite as much in general ... but resonances are incredibly small in comparison to metal with a treated paper cone.... you rarely see good paper speakers with large notchs like nearly all polycones/seas/SS/alum coned speakers.... and usually due to weight the paper cone can play higher in frequency better, if the speaker is well designed of course... unless other things are influenced

there are several speakers I can name with low MMs and a soft dome/paper cone that in fact have lower non-linear and linear distortion than PLENTY of the BEST metal/polycones... the particular one I'm thinking of in fact has lower midrange distortion than the Seas M15 and SS 8545, and I believe the W15... it just fails in the distortion below 300hz area to best them

paper = generally best for midranges... at least from my listening experiences
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Old 5th March 2012, 11:04 PM   #9
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I have a pair of Seas W18EX001 and would like to try as stated above...that is I plan on bi-amping actively at about 1800 hz. Does anyone have a workable notch filter for the 4.8khz peak....thanks
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Old 6th March 2012, 07:51 AM   #10
Lojzek is offline Lojzek  Croatia
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Quote:
Originally Posted by DSP_Geek View Post
I have here show that harmonic distortion in the W18 rises to about
3% around 1.6 kHz. Notch filters won't help; those products are caused
by the motor itself after the signal hits the voice coil.
Hi,

I dissagree. The distortion at 1,6 kHz is nothing but a manifestation of
4,8 kHz peak caused by the membrane and should be appropriately
attenuated with some sort of filter. It is very common to have these
distortions with metal cones and they are "always" 3x smaller in frequency
then the actual peak frequency. If peak frequency would be removed,
so would the distortion be too.
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