How is it decided whether a system with three drivers is a 3-way, a 2.5-way or a 2-way plus subwoofer? Is it just the degree of separation of the crossover points, or is there more to it? I read that a 3-way crossover cannot simply be designed by combining two independent 2-way crossovers, but this seems to be exactly what is done when the lower crossover frequency falls below a certain point. Are there any rules?
Just guessing ; but if using a separate amplifier with high pass/low pass for the bass and the cut-off frequency is around 80/120 Hertz, then it is a sub-woofer.
Active system
2.5-Way uses a woofer with a first order low-pass as low as affordable to boost the LF and relieve the midrange of some Doppler distortion and lower the impedance peak at resonance
3-way uses a passive XO with at least 3 separate drivers.
Bass (Woofer) Midrange ( Squawker/Talker ? ) High frequency (Tweeter )
Active system
2.5-Way uses a woofer with a first order low-pass as low as affordable to boost the LF and relieve the midrange of some Doppler distortion and lower the impedance peak at resonance
3-way uses a passive XO with at least 3 separate drivers.
Bass (Woofer) Midrange ( Squawker/Talker ? ) High frequency (Tweeter )
A subwoofer is generally defined as a speaker, usually seperate from the stereo cabinets, designed to reproduce from ~100Hz down to as low as possible.
In a 4-way, the bass driver might be asked to go from Fo (lower cutoff) to 300 or 400Hz. A mid/bass would cover there to, say 2kHz, then the upper-mid would do from there to 8kHz, then a super-tweeter (usually ribbon) is used to get somewhere up to 30kHz.
You are correct in thinking that a pair of 3-ways with a pair of subs would be a four-way system. You would be wrong in thinking that is was a 4-way speaker. These are a single cabinet, with four different drivers covering different parts of the frequency range.
The ~.5 way speakers usually have the following (we'll take 2-way for example)
A tweeter, crossed at 3kHz (this is usual, but not necessarily optimal), then one of the mid/basses is brought in at 3kHz. It's electrical input is then left alone. Further down the requency range (ie, where bass rolloff has started) you'll get a second mid/bass, playing the same stuff as the first, but without midrange duties. The idea is extra bass efficiency at rolloff, so you can put off rolloff for another few Hz. The ~.5 is defined where there's a mid/bass driver that has the bass frequencies in common with a driver specified for LF. These drivers are usually the same for aethetic purposes, and it makes it easier to predict what will happen (different LF drivers have different LF signatures, ie, deep, fast, smudgy). If you combine two drivers playing LF, the bass you'll get will be a mixture of characters, which isn't always a good thing - one driver will show up the other's shortcommings.
HTH
Chris
In a 4-way, the bass driver might be asked to go from Fo (lower cutoff) to 300 or 400Hz. A mid/bass would cover there to, say 2kHz, then the upper-mid would do from there to 8kHz, then a super-tweeter (usually ribbon) is used to get somewhere up to 30kHz.
You are correct in thinking that a pair of 3-ways with a pair of subs would be a four-way system. You would be wrong in thinking that is was a 4-way speaker. These are a single cabinet, with four different drivers covering different parts of the frequency range.
The ~.5 way speakers usually have the following (we'll take 2-way for example)
A tweeter, crossed at 3kHz (this is usual, but not necessarily optimal), then one of the mid/basses is brought in at 3kHz. It's electrical input is then left alone. Further down the requency range (ie, where bass rolloff has started) you'll get a second mid/bass, playing the same stuff as the first, but without midrange duties. The idea is extra bass efficiency at rolloff, so you can put off rolloff for another few Hz. The ~.5 is defined where there's a mid/bass driver that has the bass frequencies in common with a driver specified for LF. These drivers are usually the same for aethetic purposes, and it makes it easier to predict what will happen (different LF drivers have different LF signatures, ie, deep, fast, smudgy). If you combine two drivers playing LF, the bass you'll get will be a mixture of characters, which isn't always a good thing - one driver will show up the other's shortcommings.
HTH
Chris
That is correct, if there is more than two octaves between the crossover points then you don't need to worry about the interaction so you can combine independent filters.
RichieBoy are you sure that's correct? I always thought when using passive XO that it had to be much wider than that;
3 -> 3.5 octaves or more to avoid interaction, one of the reasons for the ROT 300-3000 band-pass for the midrange.
OK, perhaps my cynicism got the better of me...
As far as the original Q goes. 'a 3-way crossover cannot simply be designed by combining two independent 2-way crossovers' - several things need to be taken into account - out of band response of the drivers, sensitivity matching, BSC, and where the woofer will be tuned. Ideally, this should be below most musical info to avoid group delay problems etc. The low 30s is good, there being nothing useful below there. A well designed woofer will take all this into account and integrate well with the upper drivers, most subs are an afterthought and won't...
As far as the original Q goes. 'a 3-way crossover cannot simply be designed by combining two independent 2-way crossovers' - several things need to be taken into account - out of band response of the drivers, sensitivity matching, BSC, and where the woofer will be tuned. Ideally, this should be below most musical info to avoid group delay problems etc. The low 30s is good, there being nothing useful below there. A well designed woofer will take all this into account and integrate well with the upper drivers, most subs are an afterthought and won't...
Simple, at LF optimum placement in the room will likely not be the same as the mains. So build a few subs and place them for best response. Sub drivers also tend to work best as dedicated LF only units.
Then build a great 3 way with an honest 1/2 space 60Hz response.
Cost, size, sensitivity, SPL, desired directivity etc all need to be considered before deciding what drivers xover freqs etc to be used. Lots of measuring too.
I don't know, but the further apart the frequencies ( the wider the pass-band ) the less interaction there is.
Warning WAG follows, if 3.5 octaves is reasonable; then add an octave at each end.
This would mean ~ 150 ---> 6000 should give little interaction, would take a really wide band driver to go from 150 to 6k but I'm sure they do exist, Foster/Fostex/Coral spring to mind. I think the problem is beaming tho
Warning WAG follows, if 3.5 octaves is reasonable; then add an octave at each end.
This would mean ~ 150 ---> 6000 should give little interaction, would take a really wide band driver to go from 150 to 6k but I'm sure they do exist, Foster/Fostex/Coral spring to mind. I think the problem is beaming tho
Nothing usefull below 30 hz for you but SOME music has content below 30Hz.
You should really be less concerned about your needs (or opinion on subs being useless, which is scientifically wrong) and maybe as the OP what his needs are
It's a fairly meaningless question. The system will still need to be designed taking into account the reactances of the drivers involved in system if doing it passively and the design goals of the system in total.
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