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In Reply to: RE: high pass for maggies posted by m0reilly on April 22, 2014 at 12:38:18
Your pro audio amp probably has a volume control, so i should be quite easy to put in a simple line level crossover between the sub(s) and SMGa. It can be firs or second order. The only requirement is that the preamp can output enough voltage to compensate for the insertion loss.
If you use a commercial XO, the slightly more expensive Behringer (3400?) is reputed to sound significantly better.
Follow Ups:
i do have line level filters just for the subs, but again the LOS and feeding the maggies with another set is less than marginally ideal. heck... so the $99 special behinger 2310 Super-X Pro is not capable...darn. may be cheaper just to get two inexpensive plate amps and call it somewhat good...
If you have line level filters for the sub using a Y spliter and inserting a 68 nf cap between the pre amp and your MF amp (input impedance = 31k) will give you a first order HP filter to your SMGa's at 76 Hz with no appreciable insertion loss. This might not be ideal but for about $5.00 at least you can see if you are in the ballpark. As Satie says if your pro amp has gain controls then you should be able to match the gain of the MF amp.
Edits: 04/22/14
cool, though i had recently tried my pre's (t-61) second tap w/the filters to the sub amp (crown x2000), and the output to the mains dropped quite a bit, along with having to turn the power amp all the way up just to get any bass to come through the subs. because of this, i'm thinking an active solution would be my only option atm. i'll see if i can find more info re those behringer units...
Your preamp has a rather high output impedance so driving anything in parallel to the active XO will eat its gain and roll off its bass and treble. It should have sufficient voltage to do the job once the impedance of the load is sufficiently high. The Behringer and A3cr pose a 7.6 kohm combined load - which is way too low. So you would need to add a resistor in series to the lower load - something around 20k so that the combined load is 15k. still low but not terrible. Ideally you would want the combined load to be above 20k and preferably close to 50k.
Have you tried the high pass section of the crossover for your SMG? You can do the XO right out of the preamp and use the dedicated subwoofer out and high out (for SMG) or for dual subs use the Low outputs and high outs for the SMGs, if you aren't doing that now. If you are doing that, are you looking for an alternative because the sound of the Behringer is cruddy on top?
It's good to see I was on the right track. With an output impedance of 1.5K for the pre, and a net load impedance of 7.5K for the two amps, the ratio is only 1:5, well below the recommended 1:10.
This is an excellent example of several good components not matching up and producing a rather disappointing result.
I am not sure, but I suspect the problem you had with low output with the two amps in parallel may be due to the low input impedance of your Crown amp (10 Kohm unbalanced). In parallel with the MF A3, the resultant impedance is only 7500 ohms and this may be a difficult task for your preamp. The lower the load impedance the more current is required to achieve the same voltage level.
With a series cap to the main and your 2nd order passive LP filter to the Crown, you are biamping (passively rather than actively, but still biamping). Using an active xo would be achieve the same thing.
Perhaps Davey could comment as he knows a helluva a lot more than I do about these things.
the crown has an input sensitivity switch for 'hifi' line level input, unless this too is not enough.
The input sensitivity switch changes the gain (gain = 20*log(sqrt(P*8)/sensitivity) where P= power of the amp at 8 ohms. It has nothing to do with the input impedance.
Edits: 04/22/14
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