Why is this woofer so difficult to drive properly. - diyAudio
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Old 7th April 2006, 09:41 AM   #1
beppe61 is offline beppe61  Italy
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Default Why is this woofer so difficult to drive properly.

Dear Sirs,

please excuse my maybe silly question.
I have a pair of Dynaudio speakers, 3 ways with these woofers (one per speaker):
http://www.gattiweb.com/images/dynaudio/24w75.pdf
I have great difficulties to find an amp that can drive properly these speakers in the bass region.
The bass response is always weak and out of control.
I am asking to any expert if from the specifications (Qts?) one can understand why and on the other hand which would be a very easy to drive woofer for example.
I mean, is it possible to understand from specs if the driver is easy to drive foe an amp or not ?
I am very interested to hear advice.

Thank you so much.
Kind regards,

beppe
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Old 7th April 2006, 09:49 AM   #2
Did it Himself
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The 'control' will be dependent on a whole load of interacting factors such as the box, tuning, crossover and driver itself. Inherent damping, group delay and inductance will play a big part in the sound in the bass region.
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Old 7th April 2006, 09:50 AM   #3
Geenius is offline Geenius  Netherlands
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Default Re: Why is this woofer so difficult to drive properly.

Quote:
Originally posted by beppe61
Dear Sirs,

please excuse my maybe silly question.
I have a pair of Dynaudio speakers, 3 ways with these woofers (one per speaker):
http://www.gattiweb.com/images/dynaudio/24w75.pdf
I have great difficulties to find an amp that can drive properly these speakers in the bass region.
The bass response is always weak and out of control.
I am asking to any expert if from the specifications (Qts?) one can understand why and on the other hand which would be a very easy to drive woofer for example.
I mean, is it possible to understand from specs if the driver is easy to drive foe an amp or not ?
I am very interested to hear advice.

Thank you so much.
Kind regards,

beppe
It has a very weak magnet (very high Qes) in combination with a soft cone. Not the ideal parametres for good bass definition.
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Old 7th April 2006, 10:41 AM   #4
beppe61 is offline beppe61  Italy
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Location: torino
Default Re: Re: Why is this woofer so difficult to drive properly.

Quote:
Originally posted by Geenius
1) It has a very weak magnet (very high Qes)
2) in combination with a soft cone.
3) Not the ideal parametres for good bass definition.
Dear Sir,

thank you so much for your extremely kind and very valuable reply.
Let me please ask you something more (I am very ignorant but eager to learn).
1) So low Qes means a powerful magnet, right?
Very interesting.
2) which data shows the softness of the cone?
The Qts maybe? and if so high Qts means soft cone?
3) Could you give me some example of very good drivers for the bass frequency range?

As I said I heard my speakers sounding good only when driven by very high-current power amps, able to give high peak current.
And this is unfortunate beacuse this kind of amps usually do not come cheap.

Thank you greatly again for your very valuable advice.

Kind regards,

beppe

P.S. I looked at your site. Truly impressive indeed.
My sincere congratulations !

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Old 7th April 2006, 03:50 PM   #5
sreten is offline sreten  United Kingdom
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Hi,

are you considering fitting alternative bass drivers ?

In that case we would need the specs of the boxes.

The Scanspeak driver is more suited to a 2-way than a 3-way.

Qts is formed from Qes and Qms.

Qms is usually high, so Qts is near but lower than Qes.

Low Qts (therefore low Qes) does indicate a powerful magnet system.

The "softness" of the cone is related to its material, metal cones are hard.

However the idea you must have hard cones for good bass definition
is simplifying matters too far, there are a myriad of infuences.

The Scanpspeak driver would be good on an open baffle with
something like the FR125S, possibly with a supertweeter.
You'd need a sub for the bass end.

/sreten.
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Old 7th April 2006, 05:27 PM   #6
beppe61 is offline beppe61  Italy
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Quote:
Originally posted by sreten

1) Hi, are you considering fitting alternative bass drivers ?
In that case we would need the specs of the boxes.
The Scanspeak driver is more suited to a 2-way than a 3-way.
2) Qts is formed from Qes and Qms.
Qms is usually high, so Qts is near but lower than Qes.
Low Qts (therefore low Qes) does indicate a powerful magnet system.
3) The "softness" of the cone is related to its material, metal cones are hard.
However the idea you must have hard cones for good bass definition is simplifying matters too far, there are a myriad of infuences.
4) The Scanpspeak driver would be good on an open baffle with
something like the FR125S, possibly with a supertweeter.
You'd need a sub for the bass end.
/sreten.
Dear Mr. Sreten,

thank you sincerely for your kind and valuable reply.
1) Actually l was looking for a confirmation, from the reading of the specifications, that this woofer is not the easiest load for an amp, having tried more than one without satisfaction.
Now I understand that the magnet is too small for such a driver.
To answer to your question, I have not decided.
I am trying to evaluate if it would be better to look for a more powerful amp that could drive adequately the driver or change completely the loudspeker for something easier to drive.
What do you suggest?
2) Thank you very much for your extremely valuable explanation.
So the Qts is a very fundamental parameter.
3) Perfectly clear. No question.
4) Are you talking of the 24W75 ? it is a Dynaudio driver actually.
Could you elaborate your suggestion?
What would be your choice? rebuilding the speaker, maybe with different driver, or choosing another power amp ? and if so which kind of power amp?

Thank you so much again.
Kind regards,

beppe
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Old 7th April 2006, 09:46 PM   #7
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I would certainly agree with the above comments. Another indication of a weak magnet is the Bl for 4.3. For a woofer I'd expect roughly twice that. I didn't see enclosure size and tuning (if ported) figures, they will have an effect on your problem.

Woofers I have had very good luck with are the Scanspeak 25W/8565-01. (But watch out for that 2.5kHz peak, it needs a trap to suppress it adequately.) The specs are representative of a woofer that is easy to design with, and easily driven. The lower the Qt the more "damped" the speaker is, to simplify a bit. 0.30 to 0.34 works out well for me, and is usable in both sealed and ported enclosures. (I prefer ported, with the box tuned to a bit less than 20 Hz for full range bass. )

I plugged the Dynaudio numbers into the LEAP quick design utility, and the best sealed design was 110 liters; the vented box was 257 liters, tuned to 20 Hz. All designs showed peaks; in these two cases the peaks were 2-3 dB in the 40-50 Hz region. Other versions had higher peaks, and I would guess that that is your real problem.

So my 2 cent suggestions: try a trial box or two, sealed and ported, to see if the drivers can be rescued. Just a quick, but non-leaky, box to try out the sizes. If that is unsatisfactory, then I would suggest new drivers as less expensive than a new amplifier, and you'd be correcting the problem at the source.
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Old 8th April 2006, 10:46 AM   #8
sreten is offline sreten  United Kingdom
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Hi,

I'd consider changing the bass unit in the speakers,unless as a
whole they can be sold for a good price and fitting a new driver
would ruin their value.

/sreten.
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Old 8th April 2006, 05:29 PM   #9
beppe61 is offline beppe61  Italy
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Quote:
Originally posted by Curmudgeon

I would certainly agree with the above comments.
Another indication of a weak magnet is the Bl for 4.3.
For a woofer I'd expect roughly twice that.
....
Dear Mr. Curmudgeon,

thank you so much again for your kind and valuable reply.
I wonder from where all the Dynaudio fame comes if their drivers are so poorly performing.
On the basis of your words I understand that Scanspeak drivers are so much better.
When you say " The lower the Qt the more "damped" the speaker is, to simplify a bit. 0.30 to 0.34 works out well for me " are you referring to Qts ?

I think that I will go on replacing these speakers.
Are so unfriendly to use that make me nervous.

Thank you very much indeed.
Kind regards,

beppe
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Old 8th April 2006, 05:35 PM   #10
beppe61 is offline beppe61  Italy
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Quote:
Originally posted by sreten
Hi,
I'd consider changing the bass unit in the speakers,unless as a
whole they can be sold for a good price and fitting a new driver
would ruin their value.
/sreten.
Dear Mr. Sreten,

on the basis of all the valuable advices I am getting here, I think that the value of this kind of speaker is not so high.
Actually I have two pair of Dynaudio with these drivers:

one 3 ways pair
24W75 + D52 + D21

one 2 ways pair
23W75 + D28

After all I could try to sell the domes and burn the remains.
Thank you very much indeed.

Kind regards,

beppe
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