What is a 3 driver 2 1/2 way speaker? (1 Viewer)

[Ed C]

I have seen a number of speakers with 3 drivers described as 2 1/2 way. I know what a 2 way speaker is and what a 3 way speaker is however I am puzzled by what 2 1/2 way means. Any thoughts?
Thanks

 

[Bryan Acevedo]

It means that it uses 3 drivers, and the crossover is tapered.
Basically, the tweeter will be crossed over at some frequency. And one of the woofers will get all frequencies below the tweeter crossover point. Then the last woofer will get only lower bass frequencies, like say lower than 800 Hz. So for part of the frequencies only the tweeter or one of the woofers is playing. But for all the lower bass frequencies both woofers are playing. I hope this makes sense.
My Klipsch RC3 center channel speaker is supposed to used this type of design. I like the sound of it, but I don't know how the 2 1/2 way is affecting it. I think Polk also uses this technology, but I don't know of any others.
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Thanks,
Bryan
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[Jack Lee]

When I've seen "2 1/2", the 2 mid-range drivers are the same, e.g., a 1" tweeter and two 6.5" cones. You're not really getting more bass extention, per se, in this set up. It's more like doubling the mid-range power, kind of like a 3dB bass boost. Also this arrangement is used for bi-polar set-ups.
A three way should have three progressively increasing drivers where each driver covers a different frequency range: (1", 4.5", 6.5") or (1", 6.5", 8") are pretty common. The former driver arrangement gives the clean midrange typical of a 4.5" and a little extra bass from the 6.5". The latter configuration is more typical of the bare bones tower w/ bass extension to 30Hz or less.
[Edited last by Jack Lee on September 23, 2001 at 01:00 AM]

 

[Patrick Sun]

Jack, that's not really true, what you've describe is more of a MTM setup where you indeed increase the midrange due to both drivers having the same filter in their crossover network.
I built and designed my own 2.5-way speakers that I use for my main speakers.
The reason for rolling off that bottom 0.5 woofer/driver is to provide baffle step compensation without lowering the overall efficiency of the speaker itself.
The baffle step is what happens to the bass under, say, 500Hz because from the low end bass to around 500hz, the bass is radiated all around the speaker (called 4 pi space) and thus roughly 1/2 of the bass is lost towards the backside of the speaker (anywhere from 3dB to 6dB). Above 500Hz, the drivers will radiate those frequencies forward into the room (2 pi space).
So, by using an 0.5 woofer which is rolled off anywhere from 200Hz to 700Hz (each design is different, and entails plenty of experimentation), you recover that loss due to the baffle step and it fills in the bass without the need for additional padding down the tweeter in order to obtain and relatively flat overall frequency response, and this props up the overall speaker efficiency. Otherwise, you'd be left with a speaker that was probably 3dB less efficient/sensitive to the input power.
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[Edited last by Patrick Sun on September 23, 2001 at 01:06 AM]

 

[Ed C]

Great responses.
Thanks!