Help with understanding power distribution in actively crossed over systems ?

gabripeic

Member
2020-02-07 4:57 pm
Hi. I need help with understanding actively crossed over systems. The thing that confuses me is if i for example use 40w woofer and 20w tweeter and have active crossover how do i match the levels? Correct me if I'm wrong but if i use lower power amplifier for tweeter than woofer than tweeter will have lower gain. So am I supposed to use same amplifier for woofer and tweeter and let the crossover handle power distribution or am i missing something?
 

Sangram

Moderator
Paid Member
2002-09-25 11:01 am
India
So am I supposed to use same amplifier for woofer and tweeter and let the crossover handle power distribution or am i missing something?

Ideally yes.

You do need to match levels like Bill says, the power distribution is handled by the input signal.

For baffle step a simple R-C-R circuit is usually sufficient and can be driven directly from the woofer crossover output. Look at Rod Eliot's pages on BSC.

Wattage rating on speakers is a complicated concept, one does need to respect the limits mentioned in that rating, but each manufacturer has a different method of determining the rating.

What is absolutely important is sensitivity, the tweeter will be a lot louder than the woofer for a given power input (mostly true unless we're talking a large pro woofer and 1" domestic dome) and this level needs to be adjusted for accurate reproduction.

Once this is done, the music itself handles power distribution because the quantum of energy per octave varies across the audible range. Hence power ratings are not critically important in crossover design. It is rare for a domestic setup to exceed 10W of average power input under even the most extreme listening conditions.
 

jamesblonde

Member
2015-01-04 2:28 am
Hi. I need help with understanding actively crossed over systems. The thing that confuses me is if i for example use 40w woofer and 20w tweeter and have active crossover how do i match the levels? Correct me if I'm wrong but if i use lower power amplifier for tweeter than woofer than tweeter will have lower gain. So am I supposed to use same amplifier for woofer and tweeter and let the crossover handle power distribution or am i missing something?


Gain and maximum power are independent things, as others have mentioned. The amplifier gain required to match drivers will depend on the efficiency of the respective drivers. The power requirements per driver will also be different and will depend on the frequency range allocated to each driver. Try to match the overall gain and power requirements per driver and then fine tune any excessive gain with digital attenuation.
 
@gab - "Correct me if I'm wrong but if i use lower power amplifier for tweeter than woofer than tweeter will have lower gain."

I think that for the same line level audio at the input, a 100W amp will be playing louder than a 20W one...generally speaking.

When you say active crossover, I'm thinking a miniDSP or a filter circuit implemented with R's, C's and OpAmps. Usually those have a "level" control on each of the woof / tweet outputs. That's how you adjust and compensate for differences between
the woofer sensitivity and its amplifier's gain - and - the tweeter sensitivity and its amplifier's gain. Each being different.

I've seen designs going back 40 years now, where the woofer amplifier is much more powerful than that intended for the tweeter. So I'd say in general, you dont have to use the same amplifier for your woofer and tweeter. Using the level controls on the active crossover, you should still be able to easily match the sound level output between the two drivers, in all except the most bizarre woofer - tweeter - amplifier combinations.

I'm sure a popular choice is a tube amp "on top" (powering the tweeter or Full-Ranger) and a solid state amp "on the bottom" powering with woofer. That's what I have; a <20W tube amp driving a Full Range, a >50W amp driving a Woofer. I match the levels by acoustic measurement; using a microphone, REW and a broadband noise source called "pink noise". Basically just turn the knob until the woofer loudness matches the tweeter, as picked up by the microphone and displayed in one of REW's real time frequency analysis plots.

Since I'm a bass hungry kinda guy, if I do it by ear I usually end up bass heavy in measurement.
 
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gabripeic

Member
2020-02-07 4:57 pm
Thank you all for the help i was not expecting that much help that quickly.
I am in a process of building a sound system and I am considering different options and this just confused me a bit. I will see if i will go active between woofer and tweeter. From subwoofer to woofer definitely active crossover at around 80hz.