2420 and 2405 sensitivity

[reVintage]

Hi,
I have just bought a pair of 2420 to try(instead of my old Altec 808-8A) with my small 1kHz LeCleach-horns to be used from ca 4Hz and up. Below that I have a pair of 200Hz LeCleach together with 2440. No problems with these as they are biamped.

I was thinking of using 2405 with a passive simple filter from where the 2420 rolls off. But before I buy a pair of the premier I have to know the real life sensitivity of both. Will not dampen the 2420. Have anyone measured the two separately or together?

[Robh3606]

Why not use JBL's numbers from the spec sheets? The sensitivity of the 2420 on a horn is about 110db so there is a 5db gap between the two. You would have to measure the 2420 on your horn to get a hard number for the actual 1 meter sensitivity. That said you could find it easy enough just doing relative measurements.

Rob:)

http://www.jblpro.com/pub/obsolete/2405.pdf

http://www.jblpro.com/pub/obsolete/2420.pdf

[reVintage]

Hey,

So you didn´t expect me to be smart enough to read the specs;)?

I asked for IRL measurements! No reason to trust the spec. sheets even if it is JBL.

[Robh3606]

I asked for IRL measurements! No reason to trust the spec. sheets even if it is JBL.

You would trust someones measurments you don't know over the manufacturers data sheet??;) Just do your own they are the only ones that will matter especially with an uncommon horn.

Rob:)

[reVintage]

So you don´t trust the other guys here?

Still, is there anyone else who has measurements of the two, separate or together?

[Robh3606]

So you don´t trust the other guys here?



LOL There have been several times that we have done independent measurements and compared them and in some cases they were spot on. Not so in others.

In your case you want to know if you can run 2405's with a passive network and not attenuate the 2420. The problem you have is you need a measurement using your horn because the horn used affects the actual measurement. Using the numbers in the JBL spec sheets the answer is no.

Get a 2405 as a loner and do a set of relative measurements to see what the actual differences are.

Rob:)

[Mr. Widget]

In your case you want to know if you can run 2405's with a passive network and not attenuate the 2420. Is that what he was asking? I thought that might be what he was getting at but assumed I must have misinterpreted him... there is no way this will work, whether you trust JBL or John Smith, the 2405 is several dB less sensitive period.

Widget

[Robh3606]

Hello Widget

That's what I got out of it. I agree there is a significant difference, about the only tweeter I know of that hits the 110db mark are the Fostex's which are quite a bit more expensive.

Rob:)

[toddalin]

Don't worry about it.

Use a 3106 or equivelent circuit. There is no attenuation of the mid driver relative to the tweeter, other than in the tweeter's range. JBL didn't seem to care about the difference in dB.

If you just want some sizzle, just use the tweeter portion of the circuit and let the mid run wide open. Even if the tweeter is not as loud, you will hear it in its range because the mid is not cutting it up there.

It only takes one piccalo to be heard above an orchestra.

[Mr. Widget]

Use a 3106 or equivelent circuit. There is no attenuation of the mid driver relative to the tweeter, other than in the tweeter's range. JBL didn't seem to care about the difference in dB.When JBL recommended the 3106 network it was in conjunction with a separate high pass network for the mid compression driver which not only blocked the low frequencies below it's intended range but also padded the mid compression driver down to match a given woofer... every JBL woofer was lower in sensitivity than the 2405.


Widget

[toddalin]

When JBL recommended the 3106 network it was in conjunction with a separate high pass network for the mid compression driver which not only blocked the low frequencies below it's intended range but also padded the mid compression driver down to match a given woofer... every JBL woofer was lower in sensitivity than the 2405.


Widget


It was not the 3106 that reduced the mid relative to the woofer, it was the 500/800 Hz crossover that was already in the cabinet. The attenuation associated with the mid out of the 500/800Hz crossover was passed on to the tweeter, so relative to the mid, there was no additional attenuation other than that in the tweeter's range.

[Mr. Widget]

It was not the 3106 that reduced the mid relative to the woofer, it was the 500/800 Hz crossover that was already in the cabinet. The attenuation associated with the mid out of the 500/800Hz crossover was passed on to the tweeter, so relative to the mid, there was no additional attenuation other than that in the tweeter's range.Exactly my point... and that is why the 3106 wouldn't work for him.


Wdget

[toddalin]

Exactly my point... and that is why the 3106 wouldn't work for him.


Wdget

Then I think you missed the point.

He is bi-amping the mid and using an electronic attenuator to reduce its level, and the 3106 would just ride on top of that, just as it would if the mid were reduced though a passive 500/800 Hz crossover network.

But either way, the signal that is going to the mid, and any attenuation to that point relative to the woofer, is passed on to the tweeter and the mid is not reduced (as you are suggesting that it needs to be) relative to the tweeter to bring these two into harmony.

Besides, contrary to your posts, JBL agrees with me and it is specified in Pro-Notes 1-8 to use an electronic crossover for the mid and to let the 3106 ride on top of that. Do you disagree with the Pro-notes too?

[Mr. Widget]

Then I think you missed the point.
I must be getting old... I had to take a fresh look at those networks. You are right... if used as intended, I would disagree with JBL.

The lower output of the 2405 would not blend well using the 3106... the measured output would be shelved and the resulting sound would be quite dull... if we take JBL's recommendation from a historical perspective, one where a 375 driver was considered acceptable without a tweeter, I suppose we can understand how they might consider having the response above 10Khz being down by several dB as acceptable.


Widget