Active filter board GB

[AndrewT]

Butterworth characteristic requires Q to be 1/SqRt(2)=0.707
A three pole Butterworth uses a cascaded pair of passive single pole and active two pole.
The passive has a Q=0.707, this requires the active two pole to have Q=1.0

[BobEllis]

Phillipe -

Q refers to the shape of the filter - lower Q filters have a shallow initial rolloff before reaching their final rolloff. Higher Q filters have sharper corners and may even have a peak before rolling off.

I've forgotten the Q of a butterworth filter, but there is more to it than the electrical filter slope. You need to combine the response of the driver with with the filter to get the net acoustic response you desire.

You may find that you can use a 2nd order electrical filter to achieve a 3rd or even fourth order target depending on the drivers.

Before inexpensive simulators, we used the named filter shapes because there were tables to help us calculate component values. Now just plug your measured data into a sim program and adjust the filter to reach your target response.

It's a little more work with free programs, but you can use an electrical simulator like LTSpice to generate a filter with the transfer function created in something like speaker workshop. Simulate, build, measure, adjust the sim to match measured data, repeat.

[AlanElsdon]

Hi Bob,
I was just wondering (since there seems to be little activity on the Forum) whether there was any (good) news for those of us on the waiting list?
Thanks
Alan

[BobEllis]

Yes, Alan, I'm just about ready to release the leftovers. You should be hearing from me shortly.

[F1 FAN]

There is Leftovers? Whats the possibility of snagging 2 boards?


Thanks Fred

[dick van nierop]

I might have 6 unused boards and a whole lot of opamps, R's and Cs. Hang on and I'll let you know soon.

I might also have a hard wired 2way bread board with
- input amp with possibility of baffle step (as this approached the desired transfer function better than a 1st order baffle step)
- possibility of 2nd order baffle step
- 2 2nd order LP filters (order 1-4 to be selected with hard wire and jumpers)
- 2 2nd order HP filters (as LP)
- 2 delay functions (1-2 to be selected with hard wire)
- a peak/notch filter (can be inserted in LP or in HP filter)
Everything with multiple R's (easily changable and selectionable with jumpers).
See attachment of block schematic of the board.

Anyone interested? (I can send photos and a more detailed description).

[fredlock]

Can you post the pictures anyways? I want to see it. Thanks.

[dick van nierop]

I have to withdraw part of my offer. I can spare
- 2 unused boards
- 12 opamps OPA 2134
What's the price of boards and Opa's these days?

The offer of the bread bord will have to be postponed for (probably) months. Nonetheless I include a picture of it (sorry for the small size but the forum doesn't allow a better picture. Mail me and I'll send a better one).

Dick.

[dick van nierop]

Hi all

Subwoofers often have the option of changing phase.
Does anyone know how this is done? Is it in fact a timeshift function?

Thanks
Dick.

[AndrewT]

probably done with an opamp and switch to convert between inverting and non-inverting mode.
Some have an adjustable phase control. How?