Active or passiv

[kro5998]

I have almost finished building my enclosures and was planning to do the filtering entirely passive.However after the speakers i am planning to build some amps and am now considering to go the"active" way.
The enclosures are a 100 Ltr TL for the low end.These are fitted with 2 helmholzresonators for dampening the 2 typical impedance peaks.
For mids i am using 2.5 Ltr sealed enclosures. I was thinking of filtering at 300 and 3000 Hz.

I have the following to considder.
1. what about baffle step compensation?
2.What about impedance correction,is it needed?
3.What about frequency responce correction(rise in high's etc)?
4.What filter slopes and what type of filter to use.

In theory all this is possible active or passive.Which should i use?

Any comments/discussion is welcome.

Regards.
Kro5998

[klitgt]

You should definitely use active filtering between the low and mid/high at 300 Hz. This will eliminate the coil that filters the frequencies above 300 Hz with the woofer and the capacitor that filters the frequencies below 300 Hz with the mids.

With active filtering the low end drivers will be coupled directly to the power amp and this gives much more control and better defined bass.

Of course the active filter has to be made with top quality parts.

[sangram]

Depends on which side your skills lie, and which you would like to do....

Doing too much correction with a passive crossover may kill the sound. If your speakers need a lot of correction, then you're probably better off going the active route.
If however you've carefully selected drivers, thoughtfully designed good boxes, and only need minimal correction, a passive will put less components in the signal path (again, theoretically).

As you said, both are possible. And obvously, you will have to correct for all problems (baffle step, Impedance correction) whether you're doing active or passive. The mechanical restrictions will remain and will require correction, and it's best to minimise those first.

Normally 24 db/octave Linkwitz is what mass market products use, but there are some new ellipsoid filters I was reading about on Rod's site (NTM?MTM?), and different people prefer different topologies.

Again the selection of filter type and slope will depend on your drivers and how well they integrate with each other in the real world and in their enclosure, playing real music.


Edit: According to Rod Elliot impedance correction is not required in active crossovers. My bad. Good site to visit if you're looking at some more info to help making up your mind.

[Nemophyle]

you dont need impedance compensation with an active filter, if this is what you are talking about

[keyser]

I had the same dilemma. Ultimately I chose to use an active filter between bass and mid, and a passive one between mid and high.
Correction should be easier with an active system; a passive correctionnetwork is constantly modulated by reactive components, the loudspeaker.
Crossing in the active domain means lower losses, and thus is the preferred option. As you already have the amps, i think i'd go active if I were you.

[kneadle]

Just a question, if not an observation:

Doesn't actively crossing over, especially mid-to-low, also relieve the amplifiers of unwanted frequencies so that they can drive more efficiently?

Dave

[Hornlover]

Active crossovers eliminate more problems than they create. Bi-amping is really necessary if you want a SOTA system. Not only is the filtering part of the problem simplified, you have better damping on the woofer (because of the direct connection), more dynamic range, lower IM distortion, etc. I have bi-amped literally hundreds of systems, and not one system sounded better with a passive crossover. The improvement with an active crossover varied from subtle to very dramatic.
The only real downside, is the need for another amplifier. The amps do not need to be identical. The one powering the mids and tweeter can usually be lower power. I actually prefer to mix my amps. I prefer solid state for the bass, with its higher damping factor, and I prefer tubes or low power class A (like the JLH variations) for the mids and highs. Some people swear by having identical amps, and if that is your preference, thats fine. It still sounds good.

[kro5998]

Thanks for the replys.
I will probably go for active for the low end and passive for the mid/high's.

As for the Amps, i am going to use class D (ucd) for the woofer and class A for the mid/high's (not planning to use tubes though)

I looked up Rod Elliots site before and found it very usefull.Has anybody build the active crossovers he suggests?
I am a little concerned about extra noise/hum generated by the extra components in the signal path.
Anybody know of a well proven design for an active linkwitz/riley crossover?
For the mid/high crossover i was thinking about 6 dB/oct for best phase response.

Kro5998

[kro5998]

Forgot to mention, i am using a Peerless CSC217 for the low end and a Vifa 10BGS 119/8 for the mid's.Not sure about the tweeter yet but has to be about 87 dB.

kro5998

[paulspencer]

I wrote a wiki on crossovers which covers active vs passive, which you might find helpful