JBL L150 Bypass LPAD resistor values

[jfine]

I'm wanting to bypass the LPADS on a set of L150's.

They have parts express LPADS installed.

When I measure the LPAD of either the mid or high, straight up 12 o'clock, I get ~19ohms parallel circuit, and ~4.5ohms series circuit.

This thread here
http://www.audioheritage.org/vbulletin/showthread.php?4306-values-on-resistors-in-Lpad-circuit-L96

has a chart for example needing a -3db attenuation, I would need 19.4 & 2.3. I saw another chart online that was about the same thing.

I have an original LPAD that measure 18.5 / 3.5 @ 12 o'clock.

Is it OK to be off +/- a few ohms in an attenuation circuit like this, or is it critical in order for the driver to see 8 ohms?

Also that link explains to remove the hard wired mid band attenuation resistors as well. The L150 has the same mid band attenuation, but I don't see a need to remove them unless the measurement somehow involves that circuit as well?

[Wagner]

I'm wanting to bypass the LPADS on a set of L150's.

They have parts express LPADS installed.

When I measure the LPAD of either the mid or high, straight up 12 o'clock, I get ~19ohms parallel circuit, and ~4.5ohms series circuit.

This thread here
http://www.audioheritage.org/vbulletin/showthread.php?4306-values-on-resistors-in-Lpad-circuit-L96

has a chart for example needing a -3db attenuation, I would need 19.4 & 2.3. I saw another chart online that was about the same thing.

I have an original LPAD that measure 18.5 / 3.5 @ 12 o'clock.

Is it OK to be off +/- a few ohms in an attenuation circuit like this, or is it critical in order for the driver to see 8 ohms?

Also that link explains to remove the hard wired mid band attenuation resistors as well. The L150 has the same mid band attenuation, but I don't see a need to remove them unless the measurement somehow involves that circuit as well?
Your question is convoluted

What is it you are trying to accomplish? Elimination of the L-pad, period? OR, removal of the L-pad and substituting fixed stepped attenuation level choice(s) using resisters, like networks with a switch (0 -3 -6dB etc)?

OR eliminating the L-pad but substituting a resistance value that gives you the output level you like now as adjusted with the L-pads?

[jfine]

Your question is convoluted

What is it you are trying to accomplish? Elimination of the L-pad, period? OR, removal of the L-pad and substituting fixed stepped attenuation level choice(s) using resisters, like networks with a switch (0 -3 -6dB etc)?

OR eliminating the L-pad but substituting a resistance value that gives you the output level you like now as adjusted with the L-pads?

I'm trying to use resistors in place of the LPADS. So #3.

What I really need to know is, I'm coming up with 19ohms on the parallel circuit, and 4.5ohms on the series circuit.

I'm wondering how close this balance need to be.

For example, let's say I end up using 19 and 2.5 (instead of 4.5). Will the 2 ohm difference affect what the driver needs to see? I'm not talking about sonically, I'm more concerned with the driver itself. I ask because I'm seeing on the web different results in the series number based on the parallel number I have now. Hope that made sense.

[Wagner]

Will the 2 ohm difference affect what the driver needs to see? I'm not talking about sonically, I'm more concerned with the driver itself. I ask because I'm seeing on the web different results in the series number based on the parallel number I have now. Hope that made sense.
No, I do not understand what this means either, especially the part "what the driver needs to see?"
When that first appeared I thought it was a typo and you meant amp

I can't help you, your question is beyond my ability to comprehend. Don't know why we keep referring back to the L-pad when I now understand your goal to be to get rid of them?

There are plenty of threads here detailing that process (it ain't that hard, UNLESS you want tailored, customized values/responses derived from pot settings and your room etc)

Maybe someone else can help you
Sorry, but good luck with your project
Thomas Wagner

[jfine]

Hmm. I dont know how to make more clear. new scenario.

I have an attenuation circuit, and the parallel resistor is 19.4, and the series resistor is 2.3.

It is apparent that in order to achieve a different db attenuation, you would change the above values according to some formula.

Now, according to this chart, post #4,

http://www.audioheritage.org/vbulletin/showthread.php?4306-values-on-resistors-in-Lpad-circuit-L96

the above resistors should give -3.00 db.


Now let's go back to my LPAD. When I measure it, when I hit the parallel value of ~19, the series value is ~4.5. I would like to use this setting when I replace the LPAD (soundwise).

However, you can see how the 4.5 value seems to be very high compared to the chart. (maybe the lpad is faulty from partsexpress, although all 4 of them measure this way)

So you can see why I am confused. If I replace the LPAD, should I use the above chart and use 2.3 for the series resistor, or should I go by what the LPAD tells me and use 4.5 for the series resistor?

That's why I'm asking if +/- 2 ohms on the series side is going to be an issue somewhere.

[Wagner]

Hmm. I dont know how to make more clear. new scenario.

I have an attenuation circuit, and the parallel resistor is 19.4, and the series resistor is 2.3.

It is apparent that in order to achieve a different db attenuation, you would change the above values according to some formula.

Now, according to this chart, post #4,

http://www.audioheritage.org/vbulletin/showthread.php?4306-values-on-resistors-in-Lpad-circuit-L96

the above resistors should give -3.00 db.


Now let's go back to my LPAD. When I measure it, when I hit the parallel value of ~19, the series value is ~4.5. I would like to use this setting when I replace the LPAD (soundwise).

However, you can see how the 4.5 value seems to be very high compared to the chart. (maybe the lpad is faulty from partsexpress, although all 4 of them measure this way)

So you can see why I am confused. If I replace the LPAD, should I use the above chart and use 2.3 for the series resistor, or should I go by what the LPAD tells me and use 4.5 for the series resistor?

That's why I'm asking if +/- 2 ohms on the series side is going to be an issue somewhere.
Are you taking your measurements with the L-pads in or out of circuit?

The charts are an ideal, I doubt the tolerance on the L-pads is any better than 10% at best. Two drivers from the same batch can differ an ohm or two as for VC DCR

I wouldn't shoot for (or count on) a specific response from any of the theoretical (mathematical combinations) any more than I would believe the dot marked "FLAT" on a foilcal was indeed indicative of so

It's a starting point, only by testing will you know if the results translate as indicated or desired

Can you hear the insertion of a 2 ohm resister? like a padding resister, yeah, will you hear it? I can't answer that

All I can tell you is this (now) if you have some values that you KNOW you LIKE and WANT then quit worrying over what the chart "says"

You (if I am understanding you) already KNOW the values to use to get the results you want, so what's to question?

You have your answer right in front of you with actual measurements; if your measurements are consistent across all 4 of them as you report (and that is the sound you want), then again, where's the question?

[jfine]

Are you taking your measurements with the L-pads in or out of circuit?

Out of circuit.



The charts are an ideal I doubt the tolerance on the L-pads is any better than 10% at best Two drivers from the same batch can differ an ohm or two as for VC DCR

Can you hear the insertion of a 2 ohm resister, like a padding resister, yeah, will you hear it, I can't answer that

All I can tell you is this (now) if you have some values that you KNOW you LIKE and WANT then quit worrying over what the chart "says"

You have your answer right in front of you with actual measurements; if your measurements are consistent across all 4 of them as you report (and that is the sound you want), then again, where's the question?

I just did know the consequences of not using what appears to be a formula from the chart.

Those ratios just did not match my lpad, just want to do it correctly. Thanks for the help. :)

[Wagner]

Out of circuit.



I just did know the consequences of not using what appears to be a formula from the chart.

Those ratios just did not match my lpad, just want to do it correctly. Thanks for the help. :)
I am not trying to break your balls

What is "correct" here, now that it's been established, is the SOUND you now enjoy with your L-pads set at a specific spot, correct?

So, THOSE VALUES ARE THE (CORRECT) ONES TO USE and forget about "just want to do it correctly" as defined by some chart!

All of this assuming you are going by your ears and not actually measuring for/shooting for an objectively specific response or output

That's all I was and have been trying to say (and determine with my questions)

[jfine]

I am not trying to break your balls

What is "correct" here, now that it's been established, is the SOUND you now enjoy with your L-pads set at a specific spot, correct?

So, THOSE VALUES ARE THE (CORRECT) ONES TO USE and forget about "just want to do it correctly" as defined by some chart!

All of this assuming you are going by your ears and not actually measuring for/shooting for an objectively specific response or output

That's all I was and have been trying to say (and determine with my questions)

Cool appreciate it. I use that method when adjusting VTA on a tonearm, ears only.

Here is an lpad calculator:

http://www.sengpielaudio.com/calculator-Lpad.htm

it would seem that you want a final Z value of 8 ohms, given an initial speaker impedance of 8 ohms.

I do not believe that the measurement of my lpad 19/4.5, would equal a Z total value of 8 ohms.

Is this not a problem? (ears aside)

[Wagner]

Cool appreciate it. I use that method when adjusting VTA on a tonearm, ears only.
:nutz:

[Wagner]

Cool appreciate it. I use that method when adjusting VTA on a tonearm, ears only.

Here is an lpad calculator:

http://www.sengpielaudio.com/calculator-Lpad.htm

it would seem that you want a final Z value of 8 ohms, given an initial speaker impedance of 8 ohms.

I do not believe that the measurement of my lpad 19/4.5, would equal a Z total value of 8 ohms.

Is this not a problem? (ears aside)
I give up
Now we're back at post #2
I have NO idea what in the $%#@ it is you want, or are trying, to accomplish

Good luck to you with whatever it is
Thomas

[jfine]

I give up
Now we're back at post #2
I have NO idea what in the $%#@ it is you want to accomplish

Good luck to you
Thomas

Actually you're back at whatever post you think you're at, not me. I asked a question is all I did. If you do not know the answer, then by all means don't let it get to you.

[grumpy]

Just duplicate what you measure at the lpad setting of your choice.

If you change the values to match a table it won't necessarily sound the same
(yes, the crossover passive parts are expecting to see a nominal load,
but in this case, the operating design includes this, so don't fret over it).

[Malefoda]

(...) If you do not know the answer, then by all means don't let it get to you.

Just duplicate what you measure at the lpad setting of your choice.
If you change the values to match a table it won't necessarily sound the same(...)

Strange I caught the meaning right from the first question, as Grumpy did ;) Anyway, old thread exhumated, my very question indeed.
I say it again so people can find their way and maybe some help chime in.

The lPad attenuation technology is so bad that it does not match values that are requested by maths and laws of eletrconics to maintain the wanted impedance, that is a fact. jfine mesured it.
To change Lpad for fixed reisitors you have two choices:

1- use the lpad values mesured (impedance off but sound level will be the same as lpad setting)
or
2 - use re-calculated resistor values for a precise point (got that -xxdB you wanted and impedance kept fine, but may sound different from what you had at lpad and foilcal settings).

jfine, have you done it? What route one should take? Right now I'm leaning toward what Grumpy said...


In my case, HF pad real-life measures 5.8Ω and 7.2Ω for -5dB on foilcal, math calls for 3.5Ω and 10.3Ω in order to maintain 8Ω impedance.
I am not used to simulation tools, but on an online simulator I got a -5.13dBV for my 5.8/7.2Ω, does that mean it does attenuates as advised but the impedance?
In fact I have no idea what the impedance changes on the sound at all... volume, frequency response...

Thanks
Matthieu

[jfine]

jfine, have you done it? What route one should take? Right now I'm leaning toward what Grumpy said...

In my case, HF pad real-life measures 5.8Ω and 7.2Ω for -5dB on foilcal, math calls for 3.5Ω and 10.3Ω in order to maintain 8Ω impedance.
I am not used to simulation tools, but on an online simulator I got a -5.13dBV for my 5.8/7.2Ω, does that mean it does attenuates as advised but the impedance?
In fact I have no idea what the impedance changes on the sound at all... volume, frequency response...

Thanks
Matthieu

Just saw your post, what I ended up using was what the LPAD calculators show, as you say, what math calls for.

The LPADS I had did not change much from the middle position, (let's call it 5), to position 4 or 6. When I say change I mean the measurements did not change much, as I mentioned the LPAD had a parallel value of ~19ohms, series value ~4.5ohms. Which did not compute using the online formulas.

I tried many different resistor combinations, since I had the xovers out on a breadboard anyway, and made a smaller board for sand resistors.

I ended up using a 3.1db cut on the mid, 2.4 & 18.65 (2.4, 18.5 were the actual values used), and 4.44db cut on the highs, 3.2 & 11.99 (3.3, 12 were the values used).

Really sounds much better, to me, this way. Maybe because I'm using sand resistors vs LPADS, or maybe because the proper resistance was used instead of an LPAD that was obviously not calibrated correctly. BTW, I have stock LPADS too and they also did not follow any logical formula. Lately been eyeballing my L300 LPADS....

[Malefoda]

Thanks for the feedback, I may try fixed resistors with computed values for my next move.