Help with Linkwitz Transform and Leach Amp

[wigginjs]

I just assembled and implemented Project 71 at ESP using the following component values.

R1 = 29.4Kohm
R2 = 422Ohm
R3 = 110Kohm
C1 = 0.197uF
C2 = 0.1uF
C3 = .051uF

All resistors metal film 1/4w 1%. All capacitors metal polyester 250V.

These are calculated per the linkwitz spreadsheet mentioned in the article to give a f3= 20Hz and a Q of 0.8. It is connected to my stereo leach amp (both channels are driven with the same input) and each channel of the leach amp is connected to one of the voice coils of my Dayton 15" DVC in a ~3ft^3 sealed enclosure.

I wired the linkwitz transform up on a switch so I could A/B test. Using a test CD and playing tones of around 20Hz I hear NO DIFFERENCE between the input alone and the output of the linkwitz transform. I don't mean a little difference, nothing, they sound exactly the same. Any ideas?

[acenovelty]

This from Rob,

"A quick word is warranted here, to allow you to determine if the speaker you have will actually work in a small sealed enclosure. The Linkwitz transform circuit (or EAS principle) will allow any driver to extend to 20 Hz or even lower. A good quick test is to stick the speaker in a box, and drive it to 50 or 100W or so at 20 Hz - you should see a lot of cone movement, a few things will rattle, but you shouldn't actually hear a tone. A "bad" speaker will generate 60 Hz (third harmonic) - if you don't hear anything, the speaker will work in an equalised sub.

If a tone is audible, or the speaker shows any signs of distress (such as the cone breaking up with appropriate awful noises), then the driver cannot be used in this manner. Either find a different driver, or use a vented enclosure. ",
also,
"A simple test for drivers is to apply a signal at 20Hz from a clean audio oscillator. Using an amp of about 100W or so, and with the driver mounted in an enclosure of no less than about 28 litres (1 cubic foot), increase the level until the amp starts to clip - this will be immediately audible! Just below the clipping level, listen carefully for any audible frequency that is not 20Hz (which itself is virtually inaudible). In particular, if you hear 40Hz or (more likely) 60Hz, the speaker is distorting, and generating harmonics. With a good driver, you should be able to see the cone rushing back and forth, but should only feel the air movement - no audible harmonics should be heard."

My leach amps play the subs down to 20 Hz without the circuit, so it has never been necessary to futz around with anything. Sorry I can't give you better info. The Leach amps have always been so good that I never messed around with trying to improve on it much.
Bass improvement can be achieved by changing the bias current higher than 100 on a regular LOW-TIM or the Superamp. All my Leach amps have at least 50000uF on each rail though.
Speaker?

Rob's always good about answering questions.

Prosit

[Maxhawk]

I punched your values into PSPICE and looks like you should be getting about 3dB of gain at 20 Hz. I don't think your values are right because the 15" Dayton DVC is 13 dB down at 20 Hz.

[Maxhawk]

Here are the values I get with the spreadsheet:

Choose C2=0.1uF as you did.

R1=7.4K
R2=33.1K
R3=33.2K
C2=2.6uF
C3=0.57uF

And attached is the new bode plot for the circuit, which matches the one in the spreadsheet.

[Maxhawk]

And here's the spreadsheet. Did you forget to punch the 15" DVC parameters into the 'BOX' tab?

[wigginjs]

Heh, no, thats isn't what I did. I'm pretty embarressed actually. I had changed the value for "k" in the spreadsheet (the notes said k > 0) to 0.1 to get lower component values. I was under the impression k only affected the component values, but looking back at the graph it really changes things with the frequency response too. Thanks for all the leg work you did, it only confirms what I already know to be true.

As a note to anyone else using a linkwitz transform, do not make k < 1 and play around with some values higher than 1.

[pro]

You must change only the values in bold.
The value of K is not bold, so the sistem calculates it for you.
You must only ensure that it is not negative.
Ciao.