Diaphragm diameter and high frequency response.

Printable View

09-15-2007, 09:25 AM
beppe61

Diaphragm diameter and high frequency response.

Dear Sirs,

I have a technical curiosity.
From this forum I understand that JBL's new 476Be has extension up to 40kHz :blink:
An exceptional achievement for a driver with a 4" diaphragm.
For instance the also wonderful old jbl 375 should have a much more limited high frequency response.
My question is: what could be the main reasons of such an exceptional high frequency performance for the 476Be ?
A lighter diaphragm? a much more powerful magnet ?

Thank you very much indeed.
Kind regards,

beppe:D
09-16-2007, 07:34 AM
Maron Horonzakz

Several things come to mind 375 v 476... diamond pattern surround and Be phrams,, Phase plug redesigned (coherent phase plug) some EQ in xover....The 476 doesnt do much above 20K the super tweeter carries on from there.
09-16-2007, 08:07 AM
Hoerninger

In addition to the previous answer, the high frequency limit depends on
- driver moving mass
- driver voice coil inductance and
- front cavity compliance.

In a real world horn design, the composite high frequency rolloff is a complex combination of all three corner frequencies taken together.
More details can be found here:
http://www.xlrtechs.com/dbkeele.com/...TS%20Paras.pdf
_________
Peter
09-17-2007, 11:57 PM
Zilch

Quote:

Originally Posted by beppe61

Dear Sirs,

I have a technical curiosity.
From this forum I understand that JBL's new 476Be has extension up to 40kHz :blink:

Citation please; I'm not seeing that in the specs anywhere....
09-18-2007, 03:52 AM
4313B

Quote:

Originally Posted by beppe61

My question is: what could be the main reasons of such an exceptional high frequency performance for the 476Be ?

From various conversations I gathered that the extended response to 40 kHz was kind of a surprise to everyone. Evidently the dip around 20 kHz is temporary. You might want to send Steve Schell a PM.

Quote:

Originally Posted by Maron Horonzakz

The 476 doesnt do much above 20K the super tweeter carries on from there.

We were informed that the 476Be was allowed to run full out despite what the published voltage drive curve might indicate. I think if one runs the network through spice that will be revealed but I could be wrong. It's been a few years since I examined the whole thing. The super tweeter is a technical requirement for the originally intended marketplace.
09-18-2007, 07:25 AM
grumpy

1 Attachment(s)

this is what I got when I ran it some time ago... -grumpy
(10Hz - 100KHz)
09-18-2007, 07:28 AM
4313B

That looks familiar, thanks grumpy.
09-18-2007, 08:40 AM
Titanium Dome

1 Attachment(s)

Quote:

Originally Posted by grumpy

this is what I got when I ran it some time ago... -grumpy
(10Hz - 100KHz)

Man, once that thing gets going, it's pedal to the metal. :drive: (That's too weak, see below.)

Grumpy, have you done the 045Be?

(Thanks to Ed "Bid Daddy" Roth.)
09-18-2007, 09:02 AM
Earl K

476Be to 40Khz

Quote:

Originally Posted by beppe61

My question is: what could be the main reasons of such an exceptional high frequency performance for the 476Be ?
A lighter diaphragm? a much more powerful magnet ?

- Everything mentioned so far contributes , as well as ;

- I believe that some of the credit ( for the response extension ) needs to be given to JBLs' newer gap topologies ( of course, I'll readily admit that I don't actually know if JBL implemented the design principles of this patent into the 476Be or 2452 drivers - merely a guess ) .

- A close read of JBLs' 1991PATENT # 5117462 will show what I'm geting at .
- Venting the voice-coil & the domes' surround into the phase plug, has very tangeable benefits ( so says the pdf ) .

<> :)
09-18-2007, 09:43 AM
grumpy

1 Attachment(s)

Quote:

have you done the 045Be?

Guido did:
http://audioheritage.csdco.com/vbull...&postcount=107

here's to 100KHz w/045 network... (8 ohm "virtual test fixture" for all network loads)
09-21-2007, 11:36 AM
beppe61

Dear Sirs,

I apologize for my belated reply
Unfortunately (or luckily for someone) from Monday to Friday I have no access to Internet.
Thank you very much indeed to all of you for the very kind and valuable replies, as always by the way.

I have another question on the 4" diaphragm drivers subject.
I found this extremely interesting JBL tech paper I am attaching:
http://www.jblpro.com/pub/technote/tn_v1n08.pdf
I am referring to figure 4.
I cannot understand if the on-axis freq response is relevant to the mentioned drivers after that equalization is applied or not.
As I say I found this article extremely valuable.
After all it seems that big diaphragm drivers should be the driver of choice when an accurate reproduction of high frequencies is the goal differently from what I believed.
When well executed, these drivers have a very wide bandwidth and extremely low distortion.

Thank you very much again and kindest regards,

beppe
09-21-2007, 12:05 PM
grumpy

only "equalized" by 2350 horn.

compare 2440 curve with this plot:
http://www.lansingheritage.org/image...2440/page2.jpg

later in the article, when comparing driver distortions, it is mentioned that driver
level and response matching(EQ) are required.
09-21-2007, 12:34 PM
beppe61

[quote=grumpy;186215]
compare 2440 curve with this plot:
http://www.lansingheritage.org/image...2440/page2.jpg
later in the article, when comparing driver distortions, it is mentioned that driver level and response matching(EQ) are required.

Thank you very much indeed for your very helpful reply.
So EQ is required to get this response.
I understand that it should be not detrimental to the sound anyway.
But now I wonder if also the 476Be needs EQ.

Thanks again and regards,

beppe
09-21-2007, 01:01 PM
grumpy

To be clear, I tried to say for Figure 4 in the article (and for the 2440 spec sheet), that
the characteristics of the 2350 horn are required (not -electronic- EQ).

Then later in the article, it is described to use EQ to compare driver distortions,
ensuring you are measuring them the same levels, verses frequency.

The 476 is indeed "EQ'd" as used in the Everest II as the passband characteristic
of the crossover network is not flat. This does not mean that an external equalizer
is required (It also does not mean that it is impossible to change the sound more to one's
liking by using one).

I'm sorry if this is redundant. Sometimes I tend to condense what I attempt to say
too much :)
09-21-2007, 01:27 PM
beppe61

[quote=grumpy;186227]
To be clear, I tried to say for Figure 4 in the article (and for the 2440 spec sheet), that the characteristics of the 2350 horn are required (not -electronic- EQ).
Then later in the article, it is described to use EQ to compare driver distortions, ensuring you are measuring them the same levels, verses frequency.
The 476 is indeed "EQ'd" as used in the Everest II as the passband characteristic of the crossover network is not flat.
This does not mean that an external equalizer is required (It also does not mean that it is impossible change the sound more to one's liking by using one). I'm sorry if this is redundant.
Sometimes I tend to condense what I attempt to say too much :)

It is not redundant at all, at least for me. Thanks for the explanation.
Now I have understood much better the all issue.
Kind regards,

beppe