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Old 12th December 2006, 11:02 AM   #1
mikee55 is offline mikee55  United Kingdom
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Default Linkwitz Transform-help spreadsheet

Hi all,

I need to go shopping now. I cant figure out what values I enter on Calculator page of the Linkwitz Transform spreadsheet?

What is f(p) and Q(p) ?

Please can someone reply, richie00boy if poss

Thanks mikee55
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Old 12th December 2006, 11:36 AM   #2
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Default A pic to jog your memorey

Heres a snapshot.
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Old 12th December 2006, 11:39 AM   #3
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Fp is the new resonance frequency you want to extend down to. Qp is the new 'Qtc' you want to end up with.

If Qp is less than 0.7071 then -3dB point is lower than Fp
If Qp is 0.7071 then -3dB point = Fp
If Qp is more than 0.7071 then -3dB point is higher than Fp
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Old 12th December 2006, 11:50 AM   #4
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Default Hello, sir

Glad your on line, hope you're well. I still don't have a clue.By the way, I've built three seperate boards. Do I just choose any values or is it not that straight forward?

Cheers Mike
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Old 12th December 2006, 11:59 AM   #5
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Put 0.7071 in Qp
Put 30 in Fp

That will make your sub go down to 30Hz.

See how that comes out.
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Old 12th December 2006, 12:05 PM   #6
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Default Done

Okay done that.Heres a snap. Can I choose any frequency?

Cheers Mike
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Old 12th December 2006, 12:34 PM   #7
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I don't know what you mean by choose any frequency. Now you have told it what response you want you need to pick values of C2 to get practical resistor values. Try 100nF.

Also note that the DC gain is 11.51dB, which is ok. To go lower needs more gain, so 30Hz seems a good target.
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Old 12th December 2006, 12:50 PM   #8
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Default Hi Rich

With 20 hz the gain is 18.56dB. I was thinking this is within the limit of the Transform circuit. I figure this would extend the system well for the odd movie. When I said choose any frequency I meant any that would be within the gain limit, which I think was 20 dB, that would extent the low frequency limit as low as possible. I've never had a speaker system go that low, so my curiosity says tune it as low as poss.

Cheers mike
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Old 12th December 2006, 01:10 PM   #9
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OK I see now. Yes 20Hz is within 20dB gain, but check excursion - I think you will find the sub hitting it's limits on films with that much extension and wanting a decent level of sound.

You will get some reinforcement from the room anyway, it might be too much trying to hit 20Hz flat. If it were strictly for music you could try for 20Hz, but films hammer subs.
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Old 12th December 2006, 01:16 PM   #10
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Default Cheers Rich

Considering, it'll be more for music, I'll try lower, can allways turn it down for movies. If the driver complains I'll change the Transform.

I'll be off to Maplin then. Will email or come here if I have any grief.

Many thanks again, sir.

Mike
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