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Old 27th November 2001, 05:49 AM   #1
Ignite is offline Ignite  Canada
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I realize this is probably possible, but I lack the electrical know-how to implement it. What I'd like to do is have the "new" Fc controllable by a pot or something, so that one could adjust the equalization to match room gain. Is this possible?
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Old 27th November 2001, 06:18 AM   #2
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Please tell us more about your idea.
Where do you want to use this filter ? Loudspeaker ? between amps ?
What do you want to do with it ?

Janne
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Old 27th November 2001, 06:59 AM   #3
Ignite is offline Ignite  Canada
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Before my subwoofer amp, line level.
Essentially a standard Linkwitz Transform circuit for an Adire Tempest (Fs = 18.8Hz, Qts = 0.38, Vas = 317L) in a 4.5 cu ft enclosure for a Qtc of 0.71, except with a variable "new" Fc, so that I could adjust the amount of gain of the circuit. Then I could equalize for any room's gain for maximally flat response.
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Old 27th November 2001, 07:38 AM   #4
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Do you have any adjustable low pass filter in your subwoofer amplifier ?

Janne
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Old 27th November 2001, 07:49 AM   #5
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With that driver in a closed box room gain might be desireable. It will start it's roll off around the point where you room will start to gain (< 35 Hz).
Placed in a corner you will be very close to what would be the flattest bass reponse possible with that driver.
Qts is a little low for a closed box which will give a small peak in the bass around 30-40 Hz which can be adjusted with a band rejection filter, but that is hard to do over internet.
In theory it's easy, but needs trial and error development in reality.

Janne
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Old 27th November 2001, 09:37 AM   #6
djk is offline djk
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The Marchand Bassis can duplicate the Linkwitz Transform and is variable. http://www.marchandelec.com/wm8.htm Note that curve B is a Linkwiz Transform function.
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Old 27th November 2001, 10:33 AM   #7
argo is offline argo  Estonia
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It would be interesting to see the variable Linkwitz transform circuit. So far I havenít figured out how to implement this.
I also searched for variable frequency and variable Q (Bass boost) circuit with constant gain but with no great luck. So I decided to gather together the little info I had about active filters and draw such a circuit for simulation. Simulation has run good so far. There is nothing new - just standard variable hi pass filters and variable gain circuits linked together. I believe I have seen something similar in the web somewhere also. Again itís not Linkwitz transform but lets you raise or lower the Q and/or frequencies you want to boost if this is what you are after.

Argo
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Old 28th November 2001, 04:40 AM   #8
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djk: I don't want to buy something really expensive when the circuitry is probably not hard.

Hedlund: I thought this too. I however am not placing the subwoofer in a small room and certainly not in a corner. So the ability to flatten out the response more is desireable.
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Old 28th November 2001, 05:17 AM   #9
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Ignite,

what is the input resistance of your subwoofer amplifier ?
Can you regulate the volume ?
If so, are you close to full trottle, or can you accept a 6dB drop on the signal ?

Janne
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