Linkwitz ASP Custom Build

[DQ828]

I have purchased the latest Linkwitz ASP PCB's with the hope of using them to run my 3 way active speakers that are at the moment supplied by a MiniDSP setup.

Hmm, well maybe I have bitten off more than I can chew, I am hoping you might be able to help me with a few questions.

I have downloaded Linkwitz Filter Circuits Tool V4.1 (LFCT) spreadsheet & studied the schematics, spread sheet, Function Block Diagram etc, & read through the active filter section of the Linkwitz & Elliot Sound Products site. I should mention I know very little about electronics & couldn't cut the mustard when it came to advanced maths at school, just so you know where I'm at.

I figured as a starter I would use the setting I have come up with for the MiniDSP to build the ASP's & then do some experimenting, as necessary. I did the whole speaker measurement thing with the DSP so I have a base to work with & the bits to do the testing when the time comes.

I have been able to work out how to adjust the crossover sections to suit my purposes, but when it comes to the filters I am a little lost. I have listed some starter questions below & hopefully the answers to them will answer other questions I have.

1. My existing DSP has the ability to dial in a Negative Gain Shelving High Pass Filter, which the MiniDSP calls a "High Shelf", but the LFCT spreadsheet, doesn't seem to be able to do "Negative Gain". CAN IT BE DONE? IF SO HOW?, an I missing something? I want to use it to slowly drop the level of the HF, which I do with the MiniDSP
2. The LFCT spreadsheet show Inverting & Non Inverting filters, DOES THE INVERTING FILTER CHANGE THE PHASE BY 180 DEGREES? IF NOT, WHAT DOES IT DO?
3. WHAT TIME DELAY WOULD A 180 DEGREE PHASE SHIFT CAUSE?
4. The MiniDSP allows me to apply a Negative or Positive Notch Filter, which they call a "Peak Filter" CAN A POSITIVE NOTCH FILTER BE DONE WITH THE LFCT spreadsheet? IF SO HOW?
5. In the Linkwitz Function Block Diagram and the schematics they have several Shelving filters where the nominated frequency points are outside the drivers frequency range, like a SLP Dipole EQ 30-400 (frequency I assume) that is directly before the Midrange output? when the Mid takes over at 92Hz not 30 Hz, and I assume the 30Hz signal is long gone by the time it gets to that point. I DON'T UNDERSTAND.

Can you help me please

[Drew Eckhardt]

Originally Posted by DQ828

$

• In the Linkwitz Function Block Diagram and the schematics they have several Shelving filters where the nominated frequency points are outside the drivers frequency range, like a SLP Dipole EQ 30-400 (frequency I assume) that is directly before the Midrange output? when the Mid takes over at 92Hz not 30 Hz, and I assume the 30Hz signal is long gone by the time it gets to that point. I DON'T UNDERSTAND.

Can you help me please

The shelving low pass filter extends below the driver's pass-band so that its amplitude and phase response has a minimum impact on the cross-over function.

If it ended at the bottom of the mid-range pass-band instead the mid-range would have a fifth order cross-over slope (due to the 6dB/octave dipole roll-off) that wouldn't sum correctly with the woofers.

[DQ828]

Originally Posted by Drew Eckhardt

The shelving low pass filter extends below the driver's pass-band so that its amplitude and phase response has a minimum impact on the cross-over function.

If it ended at the bottom of the mid-range pass-band instead the mid-range would have a fifth order cross-over slope (due to the 6dB/octave dipole roll-off) that wouldn't sum correctly with the woofers.

Thank you

[Davey]

Some of the capabilities a DSP gadget like the miniDSP has can't be created with the architecture of the Linkwitz ASP boards.....or must created with an alternative method.

You might take a look on this page for some basic analog building blocks which can be the basis of an ASP for a specific project.

Active Filters

I dare say analog design/implementation of this sort is considered pass'e by many in the DIY audio community nowadays.

Cheers,

Dave.

[preiter]

I'm unclear on why you would want to do this.

The Linkwitz ASP is a very specific solution, not a general purpose crossover.

There was a group buy a couple years ago for some highly configurable general purpose filter boards. If you can find a few of those lying around, it would be a much better solution.

The MiniDSP would be my first recommendation though, why are you dissatisfied with it?

[DQ828]

"GETTING CLOSER ALL THE TIME"

I'm getting there slowly, I'm seriously over measuring & have made the last changes for the time being. The plan now is to finish the second board & spend some time listening.

I have ditched the suggested tabletop PSU & purchased a very nice little XP Power PSU from E14, not cheap, but it is surprisingly small & looks very well made, should fit in the case nicely.

I won't be making the case until I build the Twisted Pear Dac/Preamp, then I will build both cases together.