Question about an active front stage

[msrpIZtooMUCH 10+ year member]

If you have a 2 way front stage that is equiped with pasive crossovers and the manufacturer suggests (for example) 125 watts per side then you decide that you want to dump the passive crossovers and instead use an active crossover, how much power do you give the tweeters? And the low frequency driver? Does the 125 watts X 2 remain.....125 watts X 2 for the tweeters and 125 X 2 for the LF drivers? I don't have any particular sets of speakers picked out and this is just an example, but I do have a few options and I was hoping that there were some guidelines that would hold true regardless of which set of speakers are used.

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[req 5,000+ posts]

no real guidelines. they mainly look at dynamic power (ie: varying power because music has varying frequencies). the way passives work is they switch the frequencies to each driver on an passive basis. meaning they dont require power to run (other than what is being supplied by the amplifier), but as the music plays, the crossover will send the midrange\bass frequencies through the low pass filter and the midbass will see that power from the amplifier, and so on with the tweeter though the highpass.

the thing about music is that it should never make the amplifier produce 100% power due to the resistance of the voice coils rising with said frequency being played, due to music having a myriad of frequencies playing, and due to you having a volume knob and a brain.

the 125w suggestion is a THERMAL dissapation limit. meaning if you pump 125w into those components, chances are something is going to burn if you drive it a little too hard one day.

so in reality, if you pick components and switch to acive - its a guessing game what frequencies the speakers work best at, and what power ratings they should be given. your best bet is to start active and skip the wasting money part.

 

[msrpIZtooMUCH 10+ year member]

Update:

There is a set of new-old-stock MB Quart components (the old school German made ones) that I have my eyes on (they are practically free, so no cash wasting here). I found out that the HF drivers and the LF drivers used to make up this component set were also sold individually. I then looked up the individual drivers and this is what I found:

HF driver: 110 watts max (6 ohm voice coil)

LF driver: 40-100 watts (4 ohm voice coil)

Thats all the info MBQ gives. I happen to have TWO of the PG Tantrum 500.2 at my disposal. Those amps will do 125 watts in 4 ohm stereo. I am tempted to use those two amps to run the front stage in conjunction with an Audio Control 2 way active xover I have. Keep in mind that this set up will only play from 200hz and up....I have midbass drivers in to doors to cover 60hz-200hz....I don't know if that makes a difference but I thought I would trow that out there.

Questions:

If I were to use the PG Tantrums to run the MBQ drivers and I were to keep the gains on the amps down at a appropriate level do I still run the risk of overheating the voice coils? Wouldnt the gains being down in and of itself limit the heat applied to the voice coils?

 

[mlstrass 5,000+ posts]

You should be fine with the gains set correctly. My 4 channel is around 90wpc, so the channels pushing the tweeters are set at like 1/8 on the gain and channels for the mids are about 1/2 way. I prefer to have an amp with more then required power, so I don't have to push it very hard...