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Old 2nd April 2007, 07:51 PM   #1
Wizard of Kelts
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Default Network Suggestions Needed: +6 dB @ 84 Hz

I'm working with transformers and speakers. What I have been trying to come up with is a network, preferably simple, with the following characteristics.

0 dB 20,000 Hz down to 120 Hz
+6 dB @84 Hz
0 dB from 60 Hz on down

I have set up a simple spice schematic. I tried a capacitor in parallel with the transformer secondary but the response dropped off over 120 Hz or so.

Here is one schematic:
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Old 2nd April 2007, 07:53 PM   #2
Wizard of Kelts
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Here is another.
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Old 4th April 2007, 04:34 AM   #3
Wizard of Kelts
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Well, just to make things clearer, I would like to know a simple circuit to transform the voltage across the load, (R2), in either of the two circuits so it resembles the BOTTOM curve, not the top.

Is that possible? Does anyone have any ideas?
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Old 5th April 2007, 05:48 AM   #4
Wizard of Kelts
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I really do need some help here, or at least some advice.

After messing around for several weeks on this, this is the schematic I came up with. I am self-taught, and have some idea about LC circuits but I am really hoping for some help from somebody familiar with them.

Below is the schematic. It seems to work fine for a trafo with a 2mH inductance, but I don't know if that inductance gets it done as far as coupling factor goes. Most audio Xformers are of greater inductance I am told.

I was hoping to scale the values for an audio transformer of greater inductance if such an audio transformer is necessary. However, my scaling efforts seem to change the shape of the output curve radically.

A) Can anyone tell me how to scale the values of this circuit so that the curve is preserved with a transformer of much greater inductance?

B) What would be a good inductance to make the transformer?

C) If this circuit is not good, does anyone have any suggestions for a better one?
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Old 5th April 2007, 06:02 AM   #5
Wizard of Kelts
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And here is the waveform it gives. The shape of the waveform is what I want, but I am not sure this circuit is the right one to deliver it. The 8 ohm load at R2 is a substitute for a loudspeaker, although the ohmage does not seem to vary the circuit much.

The proposed use is a PA cab, so high frequency response is not really of the essence.

If this circuit is not good, any idea on how to achieve this shape peaking at 84 Hz?

Any help on this is greatly appreciated. I have been trying this for months.

The graph is below. Click on the thumbnail and a waveform will become evident.
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Old 5th April 2007, 06:23 AM   #6
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Peter,

Are you trying to suck out a room resonance?

dave
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Old 5th April 2007, 03:37 PM   #7
anatech is offline anatech  Canada
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Hi Dave,
He is peaking the response.

Hi Kelticwizard,
This looks like an odd loser network. You would have to either resonate the woofer in that region and may possibly have to pad down the other drivers as well as use a bandpass on the woofer.

Do you have a response "suck out" there, or you trying to add some impact to bass hits?

-Chris
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Old 5th April 2007, 05:23 PM   #8
sreten is offline sreten  United Kingdom
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Hi,

One things for certain, you cannot treat the loudspeaker as a resistive
load at these frequencies, it is anything but that, and will interact
severely with any input network.

Now a sealed PA speaker with Qts = 2 and Finbox = 85Hz, easyish.

/sreten.
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