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Old 30th October 2005, 11:20 PM   #1
Frankx is offline Frankx  Italy
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Unhappy L pad and series resistor effect on sound

I need to use in a passive c\o an hi efficency woofer with a low efficency tweeter and midrange. To match those different efficency the woofer emission have to be lowered with an l pad.
My ask is:
- how the l-pad will influence the sound of the woofer?
- If the control of the amp on the driver (overall damping factor) is lowered (is true?), can I decrease the R2 value of the l-pad lowering the impedence seen by the crossover but also increasing the damping factor?
This woofer exibit a very nice control on the bass waves, i need to keep this nice feature but also to decrease his output.javascript:smilie('')
confused
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Old 31st October 2005, 01:10 AM   #2
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Default Re: L pad and series resistor effect on sound

Quote:
Originally posted by Frankx
I need to use in a passive c\o an hi efficency woofer with a low efficency tweeter and midrange. To match those different efficency the woofer emission have to be lowered with an l pad.
My ask is:
- how the l-pad will influence the sound of the woofer?
- If the control of the amp on the driver (overall damping factor) is lowered (is true?), can I decrease the R2 value of the l-pad lowering the impedence seen by the crossover but also increasing the damping factor?
This woofer exibit a very nice control on the bass waves, i need to keep this nice feature but also to decrease his output.javascript:smilie('')
confused

besides effecting the obvious dynamics it should effect nothing

preferably a resistor woudl be best if you can calculate the exact value but a L-Pad induced no audible problems for me in the past
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Old 31st October 2005, 01:44 PM   #3
sreten is online now sreten  United Kingdom
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Location: Brighton UK
Hi,

Hmmm, I'm guessing somewhat here that you haven't included
Baffle Step correction.

With full BSC a bass unit needs to have a nominal sensitivity 6dB
higher than the midrange unit - consequently usually its the
midrange that is padded down to the bass unit.

L-pads on bass units are usually a disaster as the series
resistance no only wastes lots of power it will significantly
increase the Qts of the bass unit alignment in the box giving
less damping.

Hard to say more without harder information.

/sreten.
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Old 31st October 2005, 03:21 PM   #4
Frankx is offline Frankx  Italy
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Hi Sreten

Yes you are true: at this time I haven't included Baffle Step correction but I guess it needs however some kind of attenuation: the tweeter is an accuton c12, the mid accuton c79. The woofer is a beyma 8lw30 rated 95 db. both in closed box. To extend the low freq. I use two sub with 15" eminence in a aperiodic box actively equalized. The bass section (beyma & eminence was used in the past with an audax pr170z0 and a vifa ht26 tweeter.
This one is an experiment, althoug seems a bit crazy to use pro gears with the accutons it works pretty well driven with active amplification (partially active: c12&c79 passive lr 12db plus behringer ultradrive & 3 power amps).

You say <<L-pads on bass units are usually a disaster as the series
resistance no only wastes lots of power it will significantly
increase the Qts of the bass unit alignment in the box giving
less damping.>>

Can you explain why??

If the lpad is a voltage divider, I am not shure to understand but why I can't gain some "damping" reducing the value of r2 in the l pad , obtaining to decrease the impedence (just a couple of db not more: my amp can tolerate it) seen by the c\o but also gaining some impedance compensation and damping capacity? Exactly like when you use a resistance in parallel to a woofer to partially compensate the impedance peak you obtain a better damped sound because ofthe increased overall capacity of absorbing the back current produced by the driver.
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Old 31st October 2005, 04:10 PM   #5
sreten is online now sreten  United Kingdom
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Hmmm,

a bass driver theoretically sees a virtual short (the output
impedance of the amplifier) which is usually academic due
to the series resistance of the series crossover inductor.

see : http://www.mhsoft.nl/spk_calc.asp

New Qts with series inductor.

Any significant increase in this series resistance can be offset
by reducing the parallel resistance but the parallel resistance
values required are hopelessly impractical.

/sreten.
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