soft vs hard mid-woofers cones: audible directivity characteristics?

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crazyhub

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Joined 2005
Hi all,

During the design of my last two-way using a soft material mid-woofer (SEAS U18), Alex, one friend of mine, simply replaced the U18 with a L18 (alu hard cone); filter was modified as to obtain the same (on axis) fr response, same acoustic LR4 Fx_2kHz; comparison was instant by using the crossover emulator of LSPcad. An obvious high-mid clarity using the L18 was the result of this quick test.

Alex thinks that one of the advantages of hard vs soft is the higher membrane break-up which allows better directivity pattern thus better in-room power response and for him this was the main reason of what we heard.
Comparing these 2 drivers on SEAS graphs, the measured difference is not obvious to me:
THE ART OF SOUND PERFECTION BY SEAS - H1571-08 U18RNX/P
THE ART OF SOUND PERFECTION BY SEAS - H1224-08 L18RNX/P
At the moment I don't find out the reason of this strange difference (harmonic distorsion is low enough on both drivers so I thought it should not be audible at average listening level)...
Any ideas guys?
 
jerome69

jerome69

Member
Joined 2008
Hi Hubert,

Directivity is not the explanation of this difference of sound. A directive driver doesn't mean less clarity. Directivity is essentially a function of size : the diameter, geometry of the driver and the size of the baffle. Imagine the sound of a 5" and a 8" with the same cone, the 5" will sound more clear because it's less directive ?

This is the difference between high end drivers and normal drivers. Better "clarity" in the operating area. It 's rather a function of the motor and the cone.
In your case it simply means than the aluminium cone has a better non linear distortion than than the woven polypropylene cone. To test this you use Linkwitz distortion test with burst wave. A complex test very close the way we listen music. With normal test like Zaph's tests you don't see anything.
See:
Midrange distortion test
http://www.diyaudio.com/forums/multi-way/162364-sls-test-neo3.html

Cheers.
 
6

6.283

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Joined 2008
2pi-online.de
L

LineArray

Member
Joined 2008
dipol-audio.de
crazyhub said:
Hi all,

During the design of my last two-way using a soft material mid-woofer (SEAS U18), Alex, one friend of mine, simply replaced the U18 with a L18 (alu hard cone); filter was modified as to obtain the same (on axis) fr response
Click to expand...


Hello crazyhub,

the question is how similar is "same" in this example.

In the manufacturers sheets the ALU version seems somewhat pronounced
around 850 Hz which occurs even under angles and might also show up
in the power response.

A slightly more "present" quality of the sound could be the result and
especially voices sounding different.

A waterfall spectrum of both speakers would be interesting too.

If you take the "soft cone" version and use a parametric EQ, you might
try, whether you can imitate the sound of the AL Version to some
degree by making it slightly hot around 1Khz.

If differences in decay are the main reason, you will not succeed in
making both speakers similar by EQing.

I know of some AL cones which have very short decay throughout the
midrange and up to the lower treble.
 
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C

crazyhub

Member
Joined 2005
to 6.283:
thanks for the link to Klippels file. I tend to agree with you that in the presented case the audible differencies aren't due to directivity behaviour.

to alspe:
Klippels link demonstrates that stiffer cones allow to minimise directivity because it act purely pistonic higher in fr.

to David:
In Zaphs charts the CSD plots are rather in favour of the U18...

to Jerome:
Except a H2 problem close to 700Hz, also seen on the Zaphs fr and impedance plots (but less in my own U18), the distorsion is of same amplitude for both drivers; moreover the U18 doesn't suffer from odd orders distorsions in the upper-mid du to the huge break-up of the alu version. My 2-way distorsion 90dbs/1meter:
An externally hosted image should be here but it was not working when we last tested it.



to LineArray:
I agree: similar fr response isn't identical...
<<< A slightly more "present" quality of the sound could be the result (...of the pronunced 850Hz area) and especially voices sounding different.
*** I said improved "clarity" but enhanced "warmth" is a better world. "Warmth" doesn't come from upper-mid, right? rather from mid/low-mid. Unfortunately I'm not able to continue comparisons or measurements or EQuing this speaker...
If my memory is good, we tried to EQ the U18 but didn't succeed in giving it a similar sound, so I'm pretty sure the difference was intrinsically due to the L18 properties.

Thanks guys for your replies!
 
A

alspe

Member
Joined 2007
Seems that stiffer cones are good if they are in multi way (more than 2) speaker and crossed higher than 2nd order slope. For example L22 for bass, L15 for mids + tweeter, 4th order slopes. And where cones are driven harder.

But how much worse distortion behaviour of softer cones matters in real world IF we can make speaker bigger, more sensitive? For example WTW with U/CA18 soft cone versus WT with L18. Former is 4-6 dB more sensitive.
 
4

4lexander

Member
Joined 2005
Hi all,
An externally hosted image should be here but it was not working when we last tested it.

Here is a comparison of the directivity of loudspeaker U18RNX and L18RNX

first graph : 30° off axis
second graph : 60° off axis


The two graphs represent the loss of SPL from the level in the axis (so the relative losses)

I think indeed that the defining difference in low treeble is caused by this gap.
On a free field space, or in an anechoic chamber; i think the difference in directivity is not audible, but in a room normally reverberant the indirect field is affected.

Alex.
 
dantheman

dantheman

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Joined 2008
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LineArray

Member
Joined 2008
dipol-audio.de
dantheman said:
Here's some speculation about cone materials:
mckenzie acoustical design: madspeaker

...
Dan
Click to expand...

Cone dimpling ... i like it. I think it is locally and directionally altering
stiffness. I guess you have to analyse the major disturbing modes for
each type of driver carefully to apply that kind of "useful destruction"
in a less is more manner. Very interesting.
 
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dantheman

dantheman

Member
Joined 2008
Sorry, not sure what happened there. I just copied and pasted from my blog and it didn't work... Appears not all are working on the blog either. :/

http://voicecoilmagazine.com/media/klasco409.pdf

The Art of Speaker Design, Part II

http://www.loudsoft.com/default.asp?site=products
http://www.loudsoft.com/default.asp?site=FINECone.asp
http://www.loudsoft.com/loudsoft/my files/FINECone Tutorial 2.0.pdf
etc...

Sound Radiation and Propagation
There is so much on the Klippel site!

Benefits of Acoustic FE/BE Analysis
Benefits of Acoustic FE/BE Analysis

I did some stuff on it as well:
audio blog: Cone Stiffening
audio blog: Cone Damping
audio blog: Surround Damping

I actually did a whole lot more, but that's just a brief run down of what I found FWIW.

Dan
 
DBMandrake

DBMandrake

Member
Joined 2010
crazyhub said:
Alex thinks that one of the advantages of hard vs soft is the higher membrane break-up which allows better directivity pattern thus better in-room power response and for him this was the main reason of what we heard.
Click to expand...
This supposition is back to front.

A hard cone driver being used below its initial cone breakup frequency is the same or more directional than a "soft" cone driver of the same diameter at the same frequency, because the entire cone is moving as a piston, thus the radiating area is the full size of the cone, and directivity is dictated only by the diameter and geometry (depth) of the cone.

A "soft" cone of the same diameter such as paper, depending on the design and damping of the cone is potentially less directional because at higher frequencies above the onset of initial cone breakup there is greater movement near the centre of the cone than the outside, (at least if the cone damping design is right, it's not always the case) thus the effective radiating area is reduced and dispersion improved compared to a rigid piston.

Most full range drivers rely on this to some extent, and an extreme example of this principle is the B&W 6.5" Kevlar FST midrange driver which makes use of controlled cone breakup to greatly extend both it's on axis frequency response as well as its off axis response compared to similar sized drivers.
 
4

4lexander

Member
Joined 2005
DBMandrake said:
This supposition is back to front.

A hard cone driver being used below its initial cone breakup frequency is the same or more directional than a "soft" cone driver of the same diameter at the same frequency, because the entire cone is moving as a piston, thus the radiating area is the full size of the cone, and directivity is dictated only by the diameter and geometry (depth) of the cone.

A "soft" cone of the same diameter such as paper, depending on the design and damping of the cone is potentially less directional because at higher frequencies above the onset of initial cone breakup there is greater movement near the centre of the cone than the outside, (at least if the cone damping design is right, it's not always the case) thus the effective radiating area is reduced and dispersion improved compared to a rigid piston.

Most full range drivers rely on this to some extent, and an extreme example of this principle is the B&W 6.5" Kevlar FST midrange driver which makes use of controlled cone breakup to greatly extend both it's on axis frequency response as well as its off axis response compared to similar sized drivers.
Click to expand...
Hello,

How do you explain the graph above ?
 
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