605 time delay crossover

[donaldpatten]

This is for you lucky 605 Duplex owners
It describes a crossover that is time delay corrected for the offset caused by the woofer / HF horn VC magnet placements.
It turns out that fixing the delay also takes care of the phasing problems too,

Also included is a test signal you can play to verify the time delay on any two way system.
This would help you set the delay for any active XO.

This information was lost in a move by Apple/MAC to close the URLs.
The new URL is:

www.donpatten.com

Click on X-Over or DIY

Sorry for any inconvenience this caused.

Don

[Alien_Shore]

Don,
This is an impressive body of work you've done! Much of it is still over my head a bit, but I'm studying up...
I'd like to try and use this for my 604E, so I may hit you up for some tutoring if you're open to that.

[donaldpatten]

Mike
I would love to.
Frist: Tell me about your self, your 604E and what test equipment, cpu software you have ( or can beg bos ) . Can you do freq response, impedance curves, look at scope traces of pulses, etc.

Don

[Alien_Shore]

hah! Can I call ya? My fingers would hurt typing all that!

[donaldpatten]

Mike
We need the woofer to be a flat impedance from 400 Hz to 4000 Hz. Do have Fluke 87 DMM?
Add a Zobel to your woofer . This is a series R & C across the woofer . Pick the values that give a flat Z curve. Use an L Pad to find the proper R (10 ?).The C ( 30 uF ? ) can be several caps in parallel

Make a CD of the test signal on my web site. and have it repeat 10x or more

To get the delay time we need to play the test CD , with the woofer on, and look at the acoustic signal 12 inches on axis with a scope and almost any omni microphone. Connect the HF horn in series with a 4uFd cap.
This gives you a bare foot woofer and a single pole HF high pass crossover.

Sync the scope with the amplifier output and turn the HF on and off.
Note the LF peak and the HF peak. Estimate the time between the peaks (300 to 500 micro seconds )

Don

[Altec Best]

Mike
We need the woofer to be a flat impedance from 400 Hz to 4000 Hz. Do have Fluke 87 DMM?
Add a Zobel to your woofer . This is a series R & C across the woofer . Pick the values that give a flat Z curve. Use an L Pad to find the proper R (10 ?).The C ( 30 uF ? ) can be several caps in parallel

Make a CD of the test signal on my web site. and have it repeat 10x or more

To get the delay time we need to play the test CD , with the woofer on, and look at the acoustic signal 12 inches on axis with a scope and almost any omni microphone. Connect the HF horn in series with a 4uFd cap.
This gives you a bare foot woofer and a single pole HF high pass crossover.

Sync the scope with the amplifier output and turn the HF on and off.
Note the LF peak and the HF peak. Estimate the time between the peaks (300 to 500 micro seconds )

Don

Very nice explanation Don ! Thanks for helping out Mike....

[Alien_Shore]

Do have Fluke 87 DMM?

Not the fluke, but I do have a good DMM - Extech 22

We need the woofer to be a flat impedance from 400 Hz to 4000 Hz.
Add a Zobel to your woofer . This is a series R & C across the woofer . Pick the values that give a flat Z curve. Use an L Pad to find the proper R (10 ?).The C ( 30 uF ? ) can be several caps in parallel

I have not yet built a test enclosure for this speaker, so I assume that you are speaking about all free-air values.
I installed DATS on my desktop PC; it is much more modern than my laptop, so I was thinking I might get more accurate results. Here is the free air test result on the woofer:

Make a CD of the test signal on my web site. and have it repeat 10x or more
To get the delay time we need to play the test CD , with the woofer on, and look at the acoustic signal 12 inches on axis with a scope and almost any omni microphone. Connect the HF horn in series with a 4uFd cap.
This gives you a bare foot woofer and a single pole HF high pass crossover.
Sync the scope with the amplifier output and turn the HF on and off.
Note the LF peak and the HF peak. Estimate the time between the peaks (300 to 500 micro seconds )

OK, I can use DATS for my 'scope. I have a calibrated condenser mic that I've been using to make FR measurements. I'll start now on the zobel and take a few measurements and report back.

Thanks for the help, Don.

[Alien_Shore]

Some quick bread-boarding and I managed to derive a Zobel that looks pretty good against your design parameters:



The textbook calculator suggested C1=6 uF and R1=9.2 ohms.
With experimentation I finally arrived at real-world values of C1=18.33 uF and R1=10.14 ohms.

[donaldpatten]

Mike
The curve shows 7.5 ohms 500 Hz to 5k Hz. This is a critical number, and is the design load impedance for the low pass filter.
C1 to C5 also L1 to L5 are calculated from this value along with the delay time. The next step is to build a lows pass filter and check the delay.
I have enough spares to bread board so you can test it with your 604.
PM me your shippiing address full name and phone number.
Please verify your test set up with an 8 or 10 ohm resistor.

Don

[Alien_Shore]

Don,
Here's my first attempt at measuring the woofer using the new zobel and your test chirp:



I'm a bit lost on how to compare the HF...when I isolated just the HF, the pulse intervals seem to line up to the LF pulses (when each is measured independently). I don't know how to discern the difference in the delay between the two...

Oh, and as far as testing the DATS rig, yes, I did that thoroughly using precision resistors and caps I have on hand. All those calibration tests were looking good.