Using Fostex R82B 200W L-pad to control bass level, insane idea or could it work?

Fostex R82B 200 Watt L-Pad

  • 8 ohm Attenuator
  • Attenuation 0 to 40 db or more
  • Input 200 watts

So im making an 3 way speaker with AT 18h52 as bass driver, it will be crossed about 850hz.

I have been thinking about using passive radiator instead of reflex port, (8" SB20PFCR-00) and i would like to be able to control bass level after doing the crossover without changing components.

Troels uses these attenuators with horns and thinks of them highly, so i was thinking could it be used as well for bass?

1: Power: My amplifier checks out i think, i has: 100w at 8ohm and 200w at 4ohm so attenuator should be able to take this power
2: Heat: Since it will be produsing heat, i was thinking making closed box size of the attenuator with opening to outside. So it will be basically a small refrigerator in its hole.

Insane? Probably yes but could it work?

I am open to better ideas as well..


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Typically, using passive component style xovers makes the woofer the least efficient. Then you bring down the other drivers to meet it, as well as comp for baffle step. That coupled with the typically power hungry woofer leg of the circuit, the heat involved in the Lpad resistor or trace power dissipation, as well as the changing woofer rolloff alignment due to the added resistance; usually are why they are not used on woofers.

If you are choosing this as a way to Boost the bass when you want to, this is not the best method. Usually this is done by; biamping the woofers, using EQ or Loudness circuits, or a parametric/graphic EQ or DSP.
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Thanks for the answers!

Actually my problem with controlling bass level is quite opposite, damping down the bass level not adding it up.
What im worried is not having too little bass, but too much.

I have one of these scandinavian small living rooms in major city/apartment building that has concrete walls and floors and will reinforce low frequencies.. We often have problems with too much bass on reflex speaker, and many dampen or close reflex ports completely to fix this.

I thought about it, and i don't think my idea will work on this case because of "high" crossover point for bass 850hz, instead of 100hz.
As i understand it, attenuator can only dampen whole signal (bass woofer) and cannot be made to only cut part of it off (in speaker).
So i would be cutting out low midrange as well which is not what i want to do..

-But lets say i would have 4way with low crossover point 100hz, and attenuator would control the level under that frequency.

If i only want to lower the level, then the normal position would be 100% full volume.
I would measure the woofer when making crossover with attenuator 100% level in place, so it would not force extra damping on tweeter&midrange.

-Now the question is, would attenuator at 100% volume be basically same compared to straight wire, no losing sensitivity?
-If yes, this could work as dampener (not adding up), right?
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You can put a capacitor across the series section to lift the midrange. This probably should be combined with a capacitor in series with the shunt leg to increase the overall impedance in cases of high attenuation.

Herein lies your limitation. If you didn't need the L-pad to remain variable then you could continue to simply create EQ curves.
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