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Guido
12-16-2003, 03:27 AM
Last night I compared the 3134 and 3135 (4430,4435) networks in detail.
Why there is a difference in the section for the HF driver? Seems that this one comes in earlier (means at deeper frequency). For what reason?
The other thing is that JBL reduced the HF output for 2 dB. See spec sheet or compare the 2 vs 2,5 uF Cap in the HF line.

Please enlighten me:)

Robh3606
12-16-2003, 04:49 AM
I always thought they were adjustments to match the different low frequency driver levels between the 2 systems.

Rob :)

Guido
12-16-2003, 01:35 PM
Hi Rob!

Why should they reduce the high frequencies then?
Confusing:confused:

Robh3606
12-16-2003, 02:26 PM
I have to look at the schematics but I think they set the overall level with both the resistors and the series caps. I think what they are doing is reshaping the curve to adjust the compensation to work at the higher level. Giskard has posted voltage drive curves for both crossover and they are different however they maintain the same performance and compensation in both speakers.

Rob:)

Ian Mackenzie
12-17-2003, 02:53 AM
I will need a great German Beer to quench my thirst when I finsh the explanation okay!

I recall explaining this on the earlier forums and Rob in certainly on the money.

Starting with the 4430/4435 sensitivity, the latter is 96 db and the former is 93 db.

Thus the horn on axis response must match these levels and within the design of the overall network offer a degree of mid band level shift boost (in the case of the 4430) and cut.

Looking at the schematics, R5 effectively sets the overall sensitivity of the horn driver.

As you can see R5 is shunted across the driver and forms a voltage divider with the series resister R4 and the bandpass Eq contour network defined by R201, C9/10 and L1.

The bandpass filter provides an inverse of the mass rolloff response of the 2425/6 driver and associated 2344 bi radial horn.

The effect of the variation in values for the C9/10 in either network reflects the low pass time constant of the filter and the resulting response shape. The larger value of c9/10 in the 3135 provides more voltage peaking of the filter and resulting output in the 1-5 kertz range.

The effect of R201 is to raise lower the Hf extension by varying the Q of the filter.

The effect of R 202 is to provide boost/cut in th 2 khertz area which is attenuated to a preset level by R4.

The crossover values are different in either network to allow for summation of the drivers with the all pass 2 nd order filter, the crossover points are identical.

Because the drivers are in phase, the networks function is to cancel the resulting peak/null at the crossover point. The effect of horizontal displacement is critical for a smooth response.
The 2234/2235 may have different acoustic centres at this frequency hence the chosen values.

I hope this explanation helps.....time for a beer.

Ian

Guido
12-17-2003, 03:27 AM
:spchless:
Thanks Ian!


The Beer "thing" could be a problem. Australia is still on my "To Do" list.
Christmas will be in Argentina.
New Years Eve who knows where? But not Australia.
2004 maybe South Africa

So we have to wait until 2005 or you pass by here in Bavaria
:cheers:

Ian Mackenzie
12-17-2003, 03:36 AM
No problemo.

Ian:cheers:

Tom Loizeaux
12-17-2003, 05:21 AM
What a great post! It's people like you, and that kind of response, that make this Forum so valuable.
It also shows how careful the JBL engineers were when they designed these pro studio monitors. There are reasons why we should stick with the original model drivers in these vintage monitors. To me, the message is to upgrade componants, or add bypass caps in these crossovers, but be careful to maintain the values set by JBL. I, for one, don't know enough about crossover design to knowingly improve on the factory designs.
Thanks again for an informed post.

Tom

4313B
12-17-2003, 07:40 AM
Originally posted by Tom Loizeaux
What a great post! It's people like you, and that kind of response, that make this Forum so valuable.
It also shows how careful the JBL engineers were when they designed these pro studio monitors. There are reasons why we should stick with the original model drivers in these vintage monitors. To me, the message is to upgrade componants, or add bypass caps in these crossovers, but be careful to maintain the values set by JBL. I, for one, don't know enough about crossover design to knowingly improve on the factory designs.
Thanks again for an informed post.

Tom Finally! Someone is getting what I've been trying to convey for several years now! :) I guess it took Ian to re-articulate it ;)

Ian Mackenzie
12-17-2003, 07:58 AM
Tom,

To the extent of replicating the response plot in this instance it would be advisable to use identical JBL components and crossover values.

In the case of using a different JBL woofer or a JBL midrange driver this is not beyond the realms of possibility provided the user has the means to participate in *experimentation with access to a measurement set.

However one cannot necessarily have the same expectations about the intended performance as specificed by JBL in the original design.

*This should only be attempted by an experienced user to avoid disappointment.

That said, the 2344/2425/6 driver set has been successfuly used by myself and others on the forum ( incl Rob 3606) with the 2122H midrange driver. Some adjustment of the low pass crossover element values is required to obtain an idealised response.

Where the user has access to an adjustable or variable active crossover network this is a convenient means of making adjustments to arrive at an idealised response where using other JBL drivers but is no guarantee of a successful implementation.

In this respect the original slopes and transfer function of the JBL passive 3134/35 networks may no longer prevail. This in turn will effect the resulting subjective outcome in reference to expectations of the original design.

The use of hi quality parts, particularly in the high pass capacitor elements is recommended.

Ian;)

Robh3606
12-17-2003, 04:38 PM
Nice post Ian!

Rob:)

boputnam
12-17-2003, 06:17 PM
Originally posted by Giskard
Finally! Someone is getting what I've been trying to convey for several years now! :) I guess it took Ian to re-articulate it ;) Now maybe he can apply some JBL Blue to them baffles! Whoa... :slink:

Ian Mackenzie
12-17-2003, 09:35 PM
Oh Shucks,

Maybe some blue splashes this weekend.

Ian:D