2 vs 2.5 vs 3 vs 3.5 vs 4 ways

[Sony]

Please correct if I am wrong:

- 2 ways is adequate for a simple project without much crossover design trouble. Easy to get good results. Adequate for monitors and compact speakers.

- 3 ways may achieve much better results if crossover designed correctly or an active crossover is used. More adequate when a deeper bass is intended, not affecting the purity of the midrange.

- 2.5 and 3.5 ways allow the two previous designs to have a more solid bass. There are many options at crossover design, being possible to obtain good results even by mixing different orders filters. Also adequate for array design, with woofers in series or in paralel.

- 4 ways is preferable over 3.5 ways when a large sub-bass woofer with high sensivity is used (15" 97dB for instance), usually crossed somewhere between 100 and 200 Hz.

Regards to all members!

[joe carrow]

I could be mistaken, but I do not believe there is a solid convention for calling these different arrangements by a number. I guess you could say that the "0.5" is just a subwoofer in a different box- is that right?

Also, you forgot about 1 and 1.5! Can't forget about full range drivers

Overall, I am a believer that the sound is a sum of its parts, and can be described fairly well by frequency response, phase, dispersion, distortion, stored energy, cabinet resonance, diffraction, etc- and any of the strengths or weaknesses you have attributed to one type- well, you could find another type to show a counter-example.

I'd say that your descriptions are about right, but the biggest factor in deciding how many drivers to use is how much money you've got!

Oh, and one other thing- the 0.5, to me, refers to a subwoofer crossed over actively below the threshold of directionality (below 80 hz or so- so) and it "doesn't matter" where you put the sub- it plays mostly in mono.

[Sony]

Joe,

Just to clarify the "2.5" and "3.5" formats, the 0.5 means the second woofer rolls out at a different frequency than the crossing-point beteewn the first woofer and the tweeter, but both go to 0Hz.
Two examples:

2.5 Ways:

First woofer and tweeter corssed at 2.5KHz; Second woofer crossed at 500Hz. First woofer goes from 0-2.5KHz and second from 0 to 500Hz.

3.5 Ways:

Tweeter: 5KHz - up
Mid: 800Hz - 5KHz
Woofer 1: 0 - 800Hz
Woofer 2: 0 - 200Hz

[joe carrow]

Sony,

do you know of any examples of projects that have woofers with overlapping frequencies for the woofers? I know that the commercial JBL TR-225 does something like this and would be described as a 2.5 system... so you say that the difference between a 3 way and a 2.5 is that in the 2.5 the midrange does not have an electrical highpass?

In my opinion, for home hifi stuff, the only suitable system to use frequencies that overlap so much would be something to counter baffle-step. For example, a bi-pole, or a second woofer on the front crossed over so it comes in as baffle step decreases the level of the other...

interesting stuff!

[Zaph]

When ".5" is included in the designation of a multi-way system, it usually implies that the ".5" woofer is where the baffle step compensation takes place. That woofer is rolled off at a frequency equal to the baffle width wavelength.

2.5's are common but somewhat harder to design, but 3.5's are almost never used because in a 3-way, the frequency where baffle step comp is needed takes place in the midrange driver, not the woofer.

Somwhat more common is a 2.5+sub, which can't really be called a 3.5.