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-   -   dB loss by using passive crossovers? Active vs Passive and 1st vs 4th order (http://www.diyaudio.com/forums/multi-way/37601-db-loss-using-passive-crossovers-active-vs-passive-1st-vs-4th-order.html)

Hybrid fourdoor 10th July 2004 11:18 PM

dB loss by using passive crossovers? Active vs Passive and 1st vs 4th order
 
This week on Red Vs Blue


I tried the Passive Line Level Crossover (PLLXO), and I was amazed at how much the volume was reduced (using 12dB XO), so then I got to thinking about how when I did a past project and one speaker was full range and the bass driver had a 12dB Low pass and it was tremedously lower in volume.

Yet now almost the same drivers are being filterd by active crossovers (directly coupled to amps) and they are about the same volume. And many poeple say that when you go active you can use lower powered amps (including Vance Dickason).

So is this because passive crossovers (high level) attentuate the volume by some degree (3dB, 6dB....)?

Would a 1st order speaker be louder than the same speaker with a 4th order (with in the majority of the frequencies, obviously on the roll off freq, the 1st order will be louder)? And active speakers will have "inferred" higher sensitivity?


Also just real quick, when using active crossover on a tweeter, its a good idea to still put a capacitor in line right? To block any possibilty of DC. Do you just use a cap, that puts the XO point lower than you expect you'll use the active XO on (say 1Khz or something low like that if you plan on a 2-2.5Khz active XO point)?


Thanks!

Hybrid fourdoor 11th July 2004 08:45 PM

So nobody knows if passive crossovers lower the output of a speaker system?

BillFitzmaurice 11th July 2004 08:50 PM

The problem with inline crossovers is that they use high value resistors and that causes a lot of insertion loss. You don't have the same problem with passive crossovers at the speaker level because they use inductors, not resistors, and insertion loss is far less.

An active crossover is more or less silimar to an inline but it is amplified to eliminate insertion loss. As compared to a passive crossover at the speaker where insertion losses are of perhaps 2dB worst case you could go with less amp power if you want to be quite technical about it, but the main reason why you'd use smaller amps is because with an active crossover you have at least two of them, compared to one with passives in the speaker.

You use a DC blocking cap on HF elements with an active crossover to protect the driver primarily from turn-on transients, with the cap the size of a 6dB filter at 1/2 the corner frequency.

A passive 1st order will sound louder than a higher order only because unwanted frequencies continue to be reproduced, but you'll only notice it with one driver operating. As soon as you hook up the other driver the power above/below Fc goes to the other driver. 1st order is frowned upon for lack of HF protection and for allowing too much overlap of frequency ranges that leads to IM distortion and comb-filtering in the crossover region.

moamps 11th July 2004 09:16 PM

Re: dB loss by using passive crossovers? Active vs Passive and 1st vs 4th order
 
Quote:

Originally posted by Hybrid fourdoor
I tried the Passive Line Level Crossover (PLLXO), and I was amazed at how much the volume was reduced (using 12dB XO), so then I got to thinking about how when I did a past project and one speaker was full range and the bass driver had a 12dB Low pass and it was tremedously lower in volume.
Hi,
Attenuation in PLLXO's passband usually isn't so high (smaller than 1dB). This crossovers type is very sensitive to loading impedance, and yours may be too small. Any schematics?

Quote:

And many poeple say that when you go active you can use lower powered amps (including Vance Dickason).
This is a fact from physics.

Quote:

So is this because passive crossovers (high level) attentuate the volume by some degree (3dB, 6dB....)?
Usually no. Only some subs with a huge inductor in series may suffer from evident power loss on the inductor's resistive component.

Power loss in passive crossovers isn't problematic in small power systems (ca 100-200W). In PA systems (power to ca 100kW), the active approach has several advantages.

Quote:

Also just real quick, when using active crossover on a tweeter, its a good idea to still put a capacitor in line right?
Yes, if you don't have DC protection circiut built in.

Regards
Milan


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