DSP active crossover

[Edward]

Thanks Geoff.

I'll pop over to Cricklewood to get some.

I need to open up the Magnum K2s by breaking the rear seals. I think somewhere you mentioned you did similar. Any hints?



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[Jazid]

Capacitive reactance formula is pretty standard.
Xc=1/2(pi)fC.

That is impedance of the capacitor is determined by the reciprocal of approx 6.3 times the capacitance in farads times the frequency. So If you know the impedance of the tweeter and the crossover frequency you can find a capacitance of equal value at that frequency and it will cross over at the - 3dB point there. Assuming 6.3 ohms tweeter impedance and 5 kHz crossover the cap would be around 5uF.

If you are using the cap as a circuit protector then you might want to be prudent and lower the value a little to increase the impedance at low frequencies, after all there is already a crossover in place!

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[walpurgis]

The Magnum K2 used the DT3 tweeter. Goodmans recommended a series 3uF capacitor filter with this if I recall for system builders. I have the relevant literature somewhere. The DT3 was also marketed as the Axent tweeter for home build users and I'm fairly sure had a built in 3uF filter.

[Qwin]

What Walpurgis said.

Just work out the frequency you want to use as your limiting factor (protection), without interfering with driver output/crossover. Remember the crossover point is not a cliff so you need to take roll off into account. So a value at least an octave, maybe more, below the crossover frequency.

[Edward]

Thanks guys (James, Geoff and Ken)

I had a quick looksee at the tweeter and mine does not seem to have the inbuilt filter. See pic later here.

So I will just split the difference and put a 4uF cap in and keep 3 and 5 caps spare. And also use that other well know hifi tweak of crossing my fingers.

Pics of the tweeter, mid and bass

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[Jazid]

Well if the driver is 8 ohms as it claims the 4uF is perfect fit. I believe impedance usually rises near crossover point as its a resonant frequency and if so this should deliver minimal interference with the x-over and maximum protection against whoopsies from the amp/DSP end. If you wanted to go an octave lower (I wouldn't unless it sounded wrong) then use the 5 and 3 in series and you've got the 8uF required. Less protection though. Don't worry, its neither exact nor critical

[Halfway Tree]

You may already know this, so apologies in advance if you do, but when you build your x-over/eq in JRiver DSP Studio add a Mute checkbox at the beginning of each channel configuration. Then when you fire up for the first time you can mute all channels except the woofers and that enables you to be sure you have the channel routing correct and you are not sending the woofer signal to the tweeter. It's also useful just to be able to mute any channel during listening tests etc. That mute checkbox has saved my tweeters a few times! Together with the suggested cap you'll have double protection. About the only weakness of JRiver's DSP Studio IMO is that it doesn't graph the x-over/eq - that visualisation would help to eliminate mistakes. MiniDSP is very good in that regard.

[Edward]

Thanks Gordon. I use the checkboxes for other features in JRiver and good idea to use them at the individual filter level to check routing etc as you mention.

Yes it would be great if JRiver had similar graphs that MiniDSP has. And it would be good if JRiver's 'analyzer' in their DSP studio also had a toggle to show the effects of how the channels are being processed by the various settings. The only toggle is with/without JRiver's internal attenuation.

Currently I'm being distracted on this most important audio project by tennis, footie and work.

[Edward]

Hi Gordon

Appreciate if you could have a look at the following screenshots and let me know if I have got it right.

My plan is to have the normal L/R channels mapped to the bass drivers, the surround L/R channels mapped to the midrangers and the Rear L/R mapped to the tweeters. I have used the passive crossover points of 800hz and 5,000hz. Will start with a 4th order (24db) slope. Once I plug things in I can adjust from this baseline.

What I'm not clear about at this stage is what negative or positive gain I need to apply to each channel to start with? Or will I just derive this by trial and error later on? What did you do?

Cheers


Output Format



Copy Channels



High Pass Filter




Low Pass Filter

[Magna Audio]

Won't comment on the Jriver side of things not used it as X/O, do try lower than 4 order though.
I've found 4th order okay on sub horns and mid bass but further up the frequencies it kills feeling / mood - very driver dependant I guess. If they are good quality you want to let the loveliness play on a bit.