Why is this woofer so difficult to drive properly.

[beppe61]

dear Beppe,
cause my bad english I have believed understand that Aloia or Alabarry was "solved" the problem of bass in your room and without any other variable. I have understood bad.
I am skeptical about ADCOM because I have tested last year 5400 model, and bass was not good, to my ears.
Maybe old 545 was better. I don't know.
Just my personal point of view, of course.
Cheers,
Inertial

No problem Inertial.

The moral of the story is: no amp can fix a "wrong" driver.
And, consequently, no speaker can be better than its components.

Regards,
beppe

 

[sreten]

Now I am open to suggestion for a nice (and not too expensive)
2 way bookshelf good with all kind of music (let's say "universal").

If you mean a design take a look at this :

http://www.zaphaudio.com/audio-speaker17.html

/sreten.

 

[beppe61]

If you mean a design take a look at this :

http://www.zaphaudio.com/audio-speaker17.html
/sreten.

Dear Mr. Sreten,

It's just wonderful !
Actually I think that a speaker like this could be the ideal solution.
How is the woofer speaking of Qts, Qes, Fs, SPL, Vas and Xmax ?
As you see I did my homework (eh, eh).
No more high Qts !
Do you have a direct experience of this speaker?

I will study the link deeply.
Thank you very much for your always kind suggestion.
Kind regards,

beppe

 

[sreten]

Dear Mr. Sreten,

It's just wonderful !
Actually I think that a speaker like this could be the ideal solution.
How is the woofer speaking of Qts, Qes, Fs, SPL, Vas and Xmax ?
As you see I did my homework (eh, eh).
No more high Qts !
Do you have a direct experience of this speaker?

I will study the link deeply.
Thank you very much for your always kind suggestion.
Kind regards,

beppe

Hi,

I don't have any direct experience of this speaker.

I do admire Zaph's no nonsense approach to speaker design.

There is a wealth of information available on his site, including :

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

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

The parameters for the L18 are fine and Xmax is good.

I'll just quote Zaph :

Overall, I don't think you can get better drivers for anywhere near these prices.

/sreten.

 

[Bose(o)]

That was my first solution! It's good that you're learning, and quickly might I add. I remember seeing the light and returning after about a year of study.

BTW, I love zaph's projects, they stem from a requirement to get a lot of bang from a little buck (relative for hi-fi).

Dear Inertial,

now the problem is clear: it is intrinsic with the drivers (woofers).
The use of a more powerful amp only mitigates the problem without solving it.
So a change of drivers (difficult) or of the speakers completely (easier and maybe more logical) is the way to go.
It took me quite a long time but in the end, and above all with the extremely kind and precious help of the Friends here, I can say I have understood the reason of my unsatisfaction.
Now I am open to suggestion for a nice (and not too expensive) 2 way bookshelf good with all kind of music (let's say "universal").

I sincerely thank you all.
My best wishes,

beppe

 

[beppe61]

Hi,
I don't have any direct experience of this speaker.
I do admire Zaph's no nonsense approach to speaker design.
There is a wealth of information available on his site, ...
/sreten.

Dear Mr. Sreten,

I hope I will understand a bit of those valuable advice on speakers building.
I will report my final "achievements".
Thank you so much again.

Kind regards,

beppe

 

[beppe61]

That was my first solution!
It's good that you're learning, and quickly might I add.
I remember seeing the light and returning after about a year of study.
BTW, I love zaph's projects, they stem from a requirement to get a lot of bang from a little buck (relative for hi-fi).

Dear Sir,

I have read so many replies that I have been overwhelmed by the huge amount of information and I am a little confused.
So thank you very much as well.
Nevertheless it is very hard for me to understand why such a poorly performing driver (i.e. 24W75) has been built.
And if I remember well it was not cheap at all.
I mean, if the magnet is not big enough well ... make it bigger.
Maybe I am missing something. I do not know.
What I know is that I bought two pairs of speakers on the basis of the brand reputation and I made a mistake, actually two mistakes.

Thank you very much again.
Kind regards,

beppe

 

[redunzelizer]

Nevertheless it is very hard for me to understand why such a poorly performing driver (i.e. 24W75) has been built.
And if I remember well it was not cheap at all.
I mean, if the magnet is not big enough well ... make it bigger.
Maybe I am missing something. I do not know.

Looking at some of these electrically underdamped Dynaudio drivers (24W75, 17W75, and similar "big coil" units from that period of time) one should take note that these were never intended to have any "large magnets" or "suitable" Thiele/Small params! Dynaudio obviously instead put a lot of effort in achieving very low compression (both mechanical & thermal), improved airflow within the motor and such. Therefor the badly "missing damping" at resonance was to be managed by a specific cabinet design, namely the Variovent, giving huge "controlled leakage".

From my own experience I would say that you will not be able to achieve any satisfying results with neither closed nor vented boxes. The obnoxious high Qts will simply forbid that. But there still is an excellent chance to get deep and quite clean bass from these, either by mimickring one of the older Variovent designs (but then with applying a tad more enclosure volume!) or by creating a highly reactive Transmisson Line which effectively counteracts upon the driver's nasty resonance.

A TL design in this case could be very preferred, for letting the(se) driver(s) do what they actually can do quite well: reliably working at higher excursions and extreme power levels. It must also be taken into considerations that these cones are somewhat flabby (very "weak" in common terms) which will hit back on you when using smaller enclosures producing too much pressure acting back on the cone(s).

IMHO: This driver needs "air" to behave. And really lots of it...


regards

 

[fiak]

Yes, 'redunzelizer' got into the point.
Variovent or aperiodic design is an extension to the closed box system.
The sound produced is flat, which is a must for classical or jazz music. They are also used as monitors in studios.
On the other hand, if you play pop or rock music they sound poor at the lows, brilliant at the mids and relatively ok at the highs.
Dynaudio is one of the best loudspeaker unit companies, in our days and if the speaker is of their design and properly constructed, should be no problem.

 

[Bose(o)]

IMHO: This driver needs "air" to behave. And really lots of it...


regards

By air, you mean Open Baffle?

 

[redunzelizer]

By air, you mean Open Baffle?

No. Definitely not. Otherwise I would have mentioned.

Open Baffle can be great for drivers behaving well on their own, the said villain of above definitely needs some wicked control. The requirement of "air" should point toward quite large enclosures with lowest possible (back-)pressure acting on that cone type.

Some other things (regarding this particular driver) I had to reckognize during rereading this thread:

Changing inductors within the x-over to types with lower DC resistance will not do anything about the initial "problem", instead indroduce a new one. Your budget will explode. Feel free to use real good air cores with higher DC resistance. In case the Qts is that bad already, an additional half or one ohm will not change the *type* of problem at all, which has to be taken care of by enclösure design *anyway*. Your ears will thank you.

BTW: Low-ohmic Inductors can be very bad and deteriorating, when used out of dogmatic reasons only. Get the *right one* instead.

And here is an example of what I'd recommend to never do in this case:

8.0 Keep exisiting setup and add a bi-amp subwoofer as funds permit.

8.1) Add subwoofer or two with active xover. Look at plate amps to allow built in crossovers if limited technical assistance is available.

8.2) Set crossover with -12 db/oct after the 3 dB peak of the 24w-75 this will fix a number of problems with this driver in the smallish box. This will fix the bass peaking that will always exist given Qts > 0.8. Thusly Xmax will then be lower allowing better distortion performance.

Again there is cost, but IMHO it's far worse than that:

Any such setup completely ignores the fact that the unwanted bad transient response of any such "filtered" box will just not go away. It will only be "moved" into the stopband of the filter, thus attenuated a bit, but in worst case now even the filters own resonances add up to these bad transients.

This would not fix "a number of problems" with *this* driver in the smallish box.

regards

 

[beppe61]

Yes, 'redunzelizer' got into the point.
Variovent or aperiodic design is an extension to the closed box system.
The sound produced is flat, which is a must for classical or jazz music. They are also used as monitors in studios.
On the other hand, if you play pop or rock music they sound poor at the lows, brilliant at the mids and relatively ok at the highs.
Dynaudio is one of the best loudspeaker unit companies, in our days and if the speaker is of their design and properly constructed, should be no problem.

Thank you Sir for your kind explanation.
If I understand well I could keep my Dyn speakers for classical and jazz and maybe add a nice JBL pair for rock and pop.
This is just "puzzling".
I have always believed that a really "good" (i.e. properly designed) speaker should be "good" with EVERY kind of music.
If the Dyn are not right with rock and pop in my vocabulary they are just do not right in general.
I remember the old days when the seller in the audio shop asked: excuse Sir, do you listen to classical, then AR.
Do you listen to rock, then JBL.
It seems to me that years pass but nothing changes.
To end this my ramblings I have realized that these Dynaudio woofers are a strange kind of beasts and of the worst type.

Kind regards,

beppe

 

[beppe61]

Just out of curiosity I found these parameters for Dynaudio woofers:

model Qts Qes
15W-75 0,4 0,6
17W-75 0,8 1,1
Esotec 17WLQ 0,4 0,5
Esotec 20W-75 0,5 0,7

Is it reasonable to say that the Esotec 17WLQ is the best and the 17W-75 (smaller brother of mines) is the worst?

Please consider that I am try to understand and learn.

Thank you very much indeed.
Kind regards,

beppe

 

[phase_accurate]

Any such setup completely ignores the fact that the unwanted bad transient response of any such "filtered" box will just not go away. It will only be "moved" into the stopband of the filter, thus attenuated a bit, but in worst case now even the filters own resonances add up to these bad transients.

I agree with you partially. Adding just some arbitrary highpass wouldn't help the transient performance indeed. And the higher filter order doesn't make it better of course.
But a well designed EQ network could improve transient- and frequency- response.
And it wouldn't cost an arm and a leg either.

Regards

Charles

 

[sreten]

Hi,

I'll just point out again replacing the bass drivers in the 3-way is perfectly feasible.

The 24W-75 is a 8" driver in a 9" frame.

The box volume of 37L is appropriate for 8" to 10" reflexed or sealed.

My understanding of the variovent is that it reduces a sealed box
Q, effectively making the the box volume larger by up to ~ 30%.
However it does nothing for power handling.

The kevlar cone Monacor SPH-250KE models well as a straight
drop in replacement, though you'll have to expand the hole.
Keep the stuffing and vary the variovent.

/sreten.

 

[forr]

Hi SRETEN

---Whilst what you say is technically feasible it has one fundamental flaw.
That is :
the necessary negative impedance of the amplifier will interact
with the complex impedance of the complete speaker and
drastically alter levels in the midrange and treble regions.
The technique is ideal for active speakers and active subwoofers.---

I agree, negative resistance is for an active solution. Even in this case, the non-constant inductance of the voice-coil has to be taken in consideration.

If time permits, I will draw how to make a negative resistance with only three resistors around a power amp.

It has been suggested to use a Linkwitz transform. There is an other technique, an equalizer for little boomy "enclosures", which seems to be more flexible, due to Sokol.
References :
B.J. SOKOL "Practical subwoofer design", Wireless World december 1983, pp41-43.
Ian HEGGLUN "Speaker feedback" Electronics World, may 1996, pp 378-382 (covering many aspects of subs design)
Has any one tried the Sokol's solution ?

 

[beppe61]

Hi,
I'll just point out again replacing the bass drivers in the 3-way is perfectly feasible.
The 24W-75 is a 8" driver in a 9" frame.
The box volume of 37L is appropriate for 8" to 10" reflexed or sealed.
My understanding of the variovent is that it reduces a sealed box
Q, effectively making the the box volume larger by up to ~ 30%.
However it does nothing for power handling.
The kevlar cone Monacor SPH-250KE models well as a straight
drop in replacement, though you'll have to expand the hole.
Keep the stuffing and vary the variovent.
/sreten.

Dear Mr. Sreten,

this option really intrigues me exceedingly.
Thank you so much for your extremely interesting advice.
On this topic of " STRAIGHT DROP IN REPLACEMENT " I have a further question.
In order to establish if a driver can be usable for this operation it must have the same following electrical parameters:
1) impedance
2) sensitivity (I mean same dB/1W)
a part of course of physical dimensions constraints ?

This technique is extremely interesting to me really.
This opens a new scene for my situation.

Thank you very much indeed.
Kind regards,

beppe

 

[Tomac]

The kevlar cone Monacor SPH-250KE models well as a straight
drop in replacement, though you'll have to expand the hole.
Keep the stuffing and vary the variovent.

I tried that driver in a 50L sealed box. Came up pretty well. Isn't hard to drive at all. Should work with variovent too.

 

[sreten]

Hi,

The Morel MW 265 could also work as drop in replacements.
Need to check the cutout diameters.

Available in matched pairs.

Near identical parameters - except for Qes and thus Qts.

MW 265, a pair order no. I-753018 EUR 228,00
21 cm bass driver with high quality cone

* power handling (continuous/programme) = 150 W
* resonance frequency fs = 30 Hz
* impedance R = 8 Ohm
* sound pressure level SPL = 90 dB (2,83V; 1m)
* DC resistance Re = 5,2 Ohm
* voice coil inductance L = 0,58 mH
* effective piston radiating area Sd = 219 cm2
* effective mechanical mass incl. air load 23 g
* equivalent volume of compliance Vas = 88,6 l
* total Q factor Qts = 0,44 (Qms=2,16, Qes=0,55)
* maximum peak linear excursion vibration xlin = +/- 3,5 mm
* mounting diameter d = 194 mm
* overall diameter d = 222 mm
* mounting depth (not countersunk) t = 65 mm

/sreten.

 

[beppe61]

Hi,

1) The Morel MW 265 could also work as drop in replacements.
Need to check the cutout diameters.
MW 265, a pair order no. I-753018 EUR 228,00
21 cm bass driver with high quality cone
...
2) Near identical parameters - except for Qes and thus Qts.
...
/sreten.

Thank you Mr. Sreten,
1) I know the brand. Quite famous.
Maybe Monacor option is cheaper.
2) If I understand well Qts and Qes are correlated in some way ?Is there a formula ?

Thank you very much.
Kind regards,

beppe