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Old 31st December 2007, 07:20 PM   #1
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Default Bi amping component set with (2X) 2 channel amps

I have a Dynaudio 240 set and are very power demanding drivers.

I acquired an A/D/S/ PQ20 to run the set with (not sure of the impedance of the set but would think it was somewhere between 2.9-4). The amp should make a clean 125-150 rms per side.

I have a chance to get another PQ20 and was wondering about bi-amping the set by using the supplied passive XO for the woofer and then use a like value cap to filter the tweeters.
I would loose the XOs 3 tweeter attenuation points and have do some wiring but think its very doable.

This way I could use one PQ for the woofers and one for the tweeters.

I have never done much with passives but if I remember correctly I think if impedance load as seen by the OX changes, the points of filtration change also, meaning that if I dont use the tweeter on the Dyna XO it will change the XO point.this would be bad if true.



So am I crazy for considering such a project?????

I still think that (2X) PQs to the Dyans would be killer!

I only wish the PQ was a 2 channel amp.would make life soooo much easier!!!


Thanks for any advice
-JH
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Old 31st December 2007, 07:49 PM   #2
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Quote:
I have never done much with passives but if I remember correctly I think if impedance load as seen by the OX changes, the points of filtration change also
That is true of 1st order filters, but only per XO section. Since the inputs to the HP and LP sections are paralleled, if you leave off one set of drivers the other section's -3dB point and slope should be unaffected.

I don't know how complicated those filters are, but Dynaudio has been known to be a proponent of 1st order crossovers with proper impedance compensation and phase correction. At least when they sold raw drivers.

I wouldn't be surprised to see a very complete filter inside your boxes, certainly more than a cap in the tweeter circuit.

If you want to continue to use the passives, it would be worthwhile to try to isolate the HP and LP sections and either use them in their entirety or make a duplicate of one section for the other amp.

Does Dynaudio disclose any specific information about their crossovers?

A PQ20 bridged on a pair of tweeters... Is this a great place or what?

Tim
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Old 3rd January 2008, 11:46 PM   #3
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I have found another set of "X-250" passive XOs on fleabay (same that comes with the 240 Dynas).

You are correct that they come with more than one cap for the tweeter....

Would I be OK using one set of the XOs for the Mid and the other set of OX's for the tweeter????

Seems like this would be toooo easy!
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Old 4th January 2008, 02:15 AM   #4
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I would let the tweeters use the crossovers as is, and replicate the lowpass sections for the woofers. You could also do like I am and run one amp for the right and the other for the left channels to help seperation. You'll still be able to independently control level with the deck either way.


(oops, didn't read your last post entirely.. that seems like a winner, you were lucky to just pick up the crossovers, good deal )
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Old 4th January 2008, 04:08 AM   #5
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You could passively bi-amp them. Assuming the crossovers are parallel type there should not be an issue.

Buying a second set of the same crossover would be a waste. Without a driver pair connected on to each crossover both amps would see a essentially a short at some frequencies with most crossover setups.

Passive Bi-amping may not be worth the expense.


Rod Elliot information on Bi-amping
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Old 4th January 2008, 01:07 PM   #6
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Quote:
Without a driver pair connected on to each crossover both amps would see a essentially a short at some frequencies with most crossover setups.
Looking at the network from the speakers' perspective, yes. But, looking from the amp's perspective:

Any component that would be a short or low impedance at some frequency will have another component in series that is open or high impedance at those same frequencies. An exception could be a zobel on a 1st order tweeter network, but that would still have a resistor in series.

The end result is there will be a set of reactive components still in circuit demanding some amount of power and consideration from the amp in the frequency band of the set of speakers still being used on that crossover.

The easiest way to remove this concern is to disconnect the first series component (cap) from the unused tweeter network, and the first series component (inductor) from the unused woofer network. At that point, everything following will be out of circuit.


Tim
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Old 4th January 2008, 11:08 PM   #7
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Click the image to open in full size.

(pic of XO)



Quote:
The easiest way to remove this concern is to disconnect the first series component (cap) from the unused tweeter network, and the first series component (inductor) from the unused woofer network. At that point, everything following will be out of circuit.
I measured the impedance for both drivers (3 ohms each).
Any idea if removing the unneeded components from the respective XOs will change the load as seen by the amp?

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Old 4th January 2008, 11:19 PM   #8
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Quote:
Originally posted by tsmith1315


Looking at the network from the speakers' perspective, yes. But, looking from the amp's perspective:

Any component that would be a short or low impedance at some frequency will have another component in series that is open or high impedance at those same frequencies. An exception could be a zobel on a 1st order tweeter network, but that would still have a resistor in series.

The end result is there will be a set of reactive components still in circuit demanding some amount of power and consideration from the amp in the frequency band of the set of speakers still being used on that crossover.

The easiest way to remove this concern is to disconnect the first series component (cap) from the unused tweeter network, and the first series component (inductor) from the unused woofer network. At that point, everything following will be out of circuit.


Tim
I am talking from that amp side.
As an example what is a 12dB /octave filter with no driver connected? At a certain frequency the reactance will be equal between the C and L. It would not be a complete short primarily due to the DCR of the inductor but I would not do that to my equipment. I said most crossover setups as some will not have this risk like a 6dB oct filter.
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Old 4th January 2008, 11:53 PM   #9
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Quote:
Originally posted by Jonny Hotnuts
Click the image to open in full size.

(pic of XO)





I measured the impedance for both drivers (3 ohms each).
Any idea if removing the unneeded components from the respective XOs will change the load as seen by the amp?

Assuming you want to keep the same sound you would not remove any inductor or capactior from there. If you are going to passively bi-amp you could likely remove some resistors if they are in a L-pad configuration and use the amplifiers gain to adjust.

You should show the bottom of the crossover pcb and probably draw it out similar to the link below if you want a better understanding of what parts of the crossover are doing what.

Parts express layout
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Old 5th January 2008, 06:05 AM   #10
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Quote:
As an example what is a 12dB /octave filter with no driver connected?
Ocool, you are quite correct. There would be resonance with a diving impedance around the particular frequency where reactances are equal.

Quote:
Assuming you want to keep the same sound you would not remove any inductor or capactior from there.
Removing or disconnecting unused components would open the unwanted tweeter or woofer circuit. That would leave only the filter for the speaker being used in effect.
In *absolutely* no way would that have a negative effect on the remaining speaker's sound. The only effect it will have is to remove the load of the unneeded components from the amp.

For some reason, I can't get the crossover picture link to work. I can't even get Fiat Forum to load...

Tim
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