L-pad without impedance correction?

Bedimbe · 19th June 2008, 06:46 PM

I got into speaker building a bunch of years ago, but that faded once I began studying sound engineering and got really into the whole thing. But now a few years later, I find myself in need of a pair of speakers, so I start thinking about building them myself, because simply put, it will be a fun project. So I started designing a pair of 2-way passive speakers, and at this point I'm in the middle of planning, and hit a problem while designing the crossover prototype (I will (most probably) make changes to it after listening and measuring the speaker).

The problem I face now is this: I will obviously need to attenuate the tweeter, and a stationary (non-adjustable) L-pad seems like the way to go. The problem is that I haven't planned on using any impedance correction networks, and now I'm wondering how the L-pad will behave as the impedance varies according to the frequency? Is impedance correction a must for using L-pads, or can I get around that, and if so is there anything I should take into consideration?

tINY · 19th June 2008, 11:54 PM

The easy way to do this is to use a series resistor, not only will it attenuate the speaker, it will isolate the resonant peak from the cross-over network.

Then, you just need to scale the LPF to the new "tweeter impedance".

-tINY

Bedimbe · 25th June 2008, 01:29 AM

Quote:

Originally Posted by tINY

The easy way to do this is to use a series resistor, not only will it attenuate the speaker, it will isolate the resonant peak from the cross-over network.

Then, you just need to scale the LPF to the new "tweeter impedance".

-tINY

I was just thinking that tweaking the cross-over afterwards would be easier afterwards if I was using an L-pad, since then I could just make changes to the attenuation later on, and tweak the high-pass according to the same impedance as before. I am now mainly thinking about what the varying impedance will do to an L-pad, and to what impedance I am supposed to design it?

tINY · 25th June 2008, 08:15 AM

If the load impedance isn't relatively flat across the frequency spectrum, then the attenuation from the L-Pad won't be either...

You can close your eyes, pretend that the impedance of the tweeter is mostly flat and use the impedance value about an octave above resonance - and hope for the best.

-tINY

Bedimbe · 25th June 2008, 11:59 AM

Thanks, that was what I thought. I guess I will have to do some impedance correction after all.

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19th June 2008, 06:46 PM	#1
Bedimbe Gear interested Join Date: Jun 2008 Location: Tesjoki, Finland Posts: 3	L-pad without impedance correction? I got into speaker building a bunch of years ago, but that faded once I began studying sound engineering and got really into the whole thing. But now a few years later, I find myself in need of a pair of speakers, so I start thinking about building them myself, because simply put, it will be a fun project. So I started designing a pair of 2-way passive speakers, and at this point I'm in the middle of planning, and hit a problem while designing the crossover prototype (I will (most probably) make changes to it after listening and measuring the speaker). The problem I face now is this: I will obviously need to attenuate the tweeter, and a stationary (non-adjustable) L-pad seems like the way to go. The problem is that I haven't planned on using any impedance correction networks, and now I'm wondering how the L-pad will behave as the impedance varies according to the frequency? Is impedance correction a must for using L-pads, or can I get around that, and if so is there anything I should take into consideration?

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19th June 2008, 11:54 PM	#2
tINY Lives for gear Join Date: Jul 2004 Location: Orygun Posts: 5,716	The easy way to do this is to use a series resistor, not only will it attenuate the speaker, it will isolate the resonant peak from the cross-over network. Then, you just need to scale the LPF to the new "tweeter impedance". -tINY

25th June 2008, 08:15 AM	#4
tINY Lives for gear Join Date: Jul 2004 Location: Orygun Posts: 5,716	If the load impedance isn't relatively flat across the frequency spectrum, then the attenuation from the L-Pad won't be either... You can close your eyes, pretend that the impedance of the tweeter is mostly flat and use the impedance value about an octave above resonance - and hope for the best. -tINY

25th June 2008, 11:59 AM	#5
Bedimbe Gear interested Join Date: Jun 2008 Location: Tesjoki, Finland Posts: 3	Thanks, that was what I thought. I guess I will have to do some impedance correction after all.