First-Order Lowpass Filter with a Cap

Taterworks · 13th October 2007, 04:17 PM

Hi, everyone.

I've seen a couple of examples where in a parallel crossover, a capacitor in parallel with the midbass was used as a lowpass filter. Can this be done without the load ever appearing to the amplifier as a dead short?

Svante · 13th October 2007, 07:59 PM

No, a first order lowpass typically has a coil in series with the driver. Just a capacitor in parallel with the driver will not be healthy for the amplifier.

It is possible, but hardly clever, to use a parallel capacitor combined with a series resistor. This will attenuate the signal in the passband by 6 dB.

Taterworks · 14th October 2007, 02:49 AM

What about the DiAural crossovers? They use a cap in parallel with the woofer, and an air-core inductor in parallel with the tweeter.

owdi · 14th October 2007, 04:12 AM

Quote:

Originally posted by Taterworks
What about the DiAural crossovers? They use a cap in parallel with the woofer, and an air-core inductor in parallel with the tweeter.

Links? That sounds like a basic series crossover.

Dan

planet10 · 14th October 2007, 08:30 AM

Quote:

Originally posted by Taterworks
What about the DiAural crossovers? They use a cap in parallel with the woofer, and an air-core inductor in parallel with the tweeter.

http://www.t-linespeakers.org/tech/filters/diaural.html

The diaural XO differs from a basic series XO in that it adds a power wasting resistor in parallel with the woofer. (it did get them a patent & lots of hype)

To use a cap as a low pass filter you need to have it and the woofer in series with something else that ensures that the amp has something to drive above the XO frequency. (ie a coil & a tweetre in a basic series 2-way)

dave

Svante · 14th October 2007, 01:43 PM

Ah, yes, that's a series crossover. It does not work without the inductor.

...or...

Without the inductor, it can be seen as the RC filter I wrote about. The tweeter will blow pretty soon, though, without the inductor.

audiobomber · 14th October 2007, 01:55 PM

Quote:

Originally posted by planet10

http://www.t-linespeakers.org/tech/filters/diaural.html

The diaural XO differs from a basic series XO in that it adds a power wasting resistor in parallel with the woofer. (it did get them a patent & lots of hype)

LOL! Is that what all the hype was about? I remember reading about the amazing circuit that was going to revolutionize the speaker industry, and countless raves over some little demo speaker that outperformed the big boys. Then suddenly..... dead silence, no more talk about DiAural crossovers.

Your post brought up a few questions, so I did a search and found this. http://www.diaural.com/, which pretty much answers all of them.

13th October 2007, 04:17 PM	#1
Taterworks diyAudio Member Join Date: May 2007	First-Order Lowpass Filter with a Cap Hi, everyone. I've seen a couple of examples where in a parallel crossover, a capacitor in parallel with the midbass was used as a lowpass filter. Can this be done without the load ever appearing to the amplifier as a dead short? __________________ If it works, but you don't know why it works, then you haven't done any engineering. Taterworks Audio (nothing for sale)

13th October 2007, 07:59 PM	#2
Svante diyAudio Member Join Date: Feb 2004 Location: Stockholm	No, a first order lowpass typically has a coil in series with the driver. Just a capacitor in parallel with the driver will not be healthy for the amplifier. It is possible, but hardly clever, to use a parallel capacitor combined with a series resistor. This will attenuate the signal in the passband by 6 dB. __________________ Simulate loudspeakers: Basta! Simulate the baffle step: The Edge

14th October 2007, 02:49 AM	#3
Taterworks diyAudio Member Join Date: May 2007	What about the DiAural crossovers? They use a cap in parallel with the woofer, and an air-core inductor in parallel with the tweeter. __________________ If it works, but you don't know why it works, then you haven't done any engineering. Taterworks Audio (nothing for sale)

14th October 2007, 01:43 PM	#6
Svante diyAudio Member Join Date: Feb 2004 Location: Stockholm	Ah, yes, that's a series crossover. It does not work without the inductor. ...or... Without the inductor, it can be seen as the RC filter I wrote about. The tweeter will blow pretty soon, though, without the inductor. __________________ Simulate loudspeakers: Basta! Simulate the baffle step: The Edge

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