Extending small drivers low frequency range with opamps?

jsd · 9th March 2004, 05:57 AM

I have some 4" speakers that definitely start getting louder at around 1500Hz and finally levelling off around 2000Hz.. I want to cure this by maybe adding 6dB/octave from 2000Hz down. Any way I could use a Linkwitz Transform to do this? How would I calculate the values for the resistors and caps?

Another (possibly very stupid) thought I had was that I could just use an active low pass filter @ 450Hz from the buffer output. Then I could parallel the output of the LPF with another buffer connected to the first buffer. I'd have to have some way of adjusting the balance, or the lower frequencies would be flooding out everything else. Maybe a pot on the output of the LPF?

Any other suggestions/ideas? I have some TL082s laying around, and DIP sockets so atleast if it turns out bad I can slavage the op amps (yeah I'm cheap.. I'd try and save a $1.50 opamp.. but cost was one of the reasons I decided to build a chipamp!).

Thanks for any help or insight anyone might provide.

sobazz · 9th March 2004, 06:25 PM

Are the speakers baffled? Sounds a lot like baffle step diffraction to me, and BSD can be compensated passively at line level using three components... all you need may very well be two resistor and a cap...

sreten · 9th March 2004, 06:41 PM

http://sound.westhost.com/bafflestep.htm

is a good place to start, though we are talking
morelike 150Hz to 2KHz than 1.5KHz to 2KHz.

As its only 6dB active correction is not necessary.

sreten.

9th March 2004, 05:57 AM	#1
jsd diyAudio Member Join Date: Mar 2004 Location: New York	Extending small drivers low frequency range with opamps? I have some 4" speakers that definitely start getting louder at around 1500Hz and finally levelling off around 2000Hz.. I want to cure this by maybe adding 6dB/octave from 2000Hz down. Any way I could use a Linkwitz Transform to do this? How would I calculate the values for the resistors and caps? Another (possibly very stupid) thought I had was that I could just use an active low pass filter @ 450Hz from the buffer output. Then I could parallel the output of the LPF with another buffer connected to the first buffer. I'd have to have some way of adjusting the balance, or the lower frequencies would be flooding out everything else. Maybe a pot on the output of the LPF? Any other suggestions/ideas? I have some TL082s laying around, and DIP sockets so atleast if it turns out bad I can slavage the op amps (yeah I'm cheap.. I'd try and save a $1.50 opamp.. but cost was one of the reasons I decided to build a chipamp!). Thanks for any help or insight anyone might provide.

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9th March 2004, 06:25 PM	#2
sobazz diyAudio Member Join Date: Apr 2003 Location: Jutland	Are the speakers baffled? Sounds a lot like baffle step diffraction to me, and BSD can be compensated passively at line level using three components... all you need may very well be two resistor and a cap...

9th March 2004, 06:41 PM	#3
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	http://sound.westhost.com/bafflestep.htm is a good place to start, though we are talking morelike 150Hz to 2KHz than 1.5KHz to 2KHz. As its only 6dB active correction is not necessary. sreten.

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