Please explain the "two and 1/2 way" crossover to me.

[Racket Scientist]

I understand that if you have a speaker with a tweeter driver on top and two same sized woofers below it that many crossover designers will roll off the mids from the bottom woofer. Apparently there are some lobing issues or some sort of destructive interaction from leaving both woofers with significant program material in the mids. I currently have some speakers I'm trying to decide whether to modify (Klipsch KG 5.5) that have this configuration but the woofers are both fed the same signal with a crossover to them below 1.5 KHz. Is this issue something that some designs don't have much problem with for some reason? I've been considering upgrading to one of the Crites crossovers, but it seems silly to invest more in a possibly flawed design. I don't have the resources to design a better crossover - is there anyone out there who designs new crossovers for vintage speakers at reasonable prices?

[chlorofille]

With 2 woofers playing the same freq range, you will get a blurred image. I tried that with one of my TMM (2.5 way) Scanspeak builds and decided to scrap that design. Instead, roll off the lower woofer according to the freq transition of the baffle step. If for example your baffle width is 8'', I would crossover the lower woofer at around 570Hz by preferably a 2nd order filter. The great thing about 2.5 ways is the lower midrange has some serious authority and can sound very full and rich.

[Cal Weldon]

A 2.5 way can be as simple as hanging a large coil on the lower woofer, assuming the woofers are wired in parallel.

[Racket Scientist]

Originally Posted by Cal Weldon

A 2.5 way can be as simple as hanging a large coil on the lower woofer, assuming the woofers are wired in parallel.

I had proposed doing just that, but had been told that the rolloff would be too gradual to have much effect and that the rest of the crossover would have to be redesigned to compensate for the addition for some reason. I also have a pair of Pioneer HPM-900s where the woofer is allowed to run "wide open" and had considered a crossover upgrade for them as well - my discussion of adding an inductor prompted that response.

[Racket Scientist]

Originally Posted by chlorofille

With 2 woofers playing the same freq range, you will get a blurred image. I tried that with one of my TMM (2.5 way) Scanspeak builds and decided to scrap that design. Instead, roll off the lower woofer according to the freq transition of the baffle step. If for example your baffle width is 8'', I would crossover the lower woofer at around 570Hz by preferably a 2nd order filter. The great thing about 2.5 ways is the lower midrange has some serious authority and can sound very full and rich.

The things that bug me about the speakers currently are some "horn coloration" and stridency to the treble and a lack of integration with the bass - almost the feeling that the mids have been EQ'd out. I'm hoping that with a Ti diaphragm upgrade, some treatment of the edges of the horn, and a crossover upgrade I can end up with a much nicer speaker. Do you think the above mods plus adding an inductor to roll off the lower woofer would address the issues I have?
Also, the speaker is 12.25" across on the baffle (with 2 X 10" woofers). What frequency should I shoot for to roll off at?

[chlorofille]

With a wide baffle like that, the BSC calculator results in a freq transition of 372Hz.
However you mention that there is some stridency in the mids and that could be due to some break up issues in the 10'' cone. No doubt with crossover mods and proper BSC implementation the speaker can sound great. Huge dynamic capabilities.

[tinitus]

Originally Posted by Racket Scientist

..... but had been told that the rolloff would be too gradual to have much effect.......

........and that the rest of the crossover would have to be redesigned .......

you will mostly use bigger inductor than a calculator tells you

yes, probably needs further modifications

[sreten]

Hi,

The fundamental aspect of a 2.5 way, or any 0.5 way is the arrangement
of the two drivers, one being gradually rolled off early. This automatically
on a large flat baffle would cause the response (compared to one driver)
to rise by 6dB towards the bass. However in a cabinet the box exhibits
6dB of baffle loss, and requires BSC, "baffle step compensation", one
way of do it is via two bass/mid drivers in 0.5 way configuration.

Converting your Kipsch to 2.5 way will leave the bass level untouched
but reduce mid and treble levels by 6dB. Many high efficiency designs
simply ignore BSC and try and use near wall / corner placement.
(With the stated senstivity, BSC is certainly being ignored.)

BSC's speakers need to be away from walls and corners, and
consequently give good imaging, they also interact well the
room nodes very low down with a correct bass alignment.

Its get complicated with larger speakers with drivers near the floor,
and would very much depend on the drivers themselves having a
rising response to work well for this case IM0, as this would allow
some BSC adjustment, or make BSC less than 6dB effectively.

Some details here :

http://www.audiokarma.org/forums/sho....php?p=4218745

The c/o is relatively simple, but not easy to change without measurements.
Bass : 1mH, 24uF+2R : to twin bass/mid units
Treble : variable resistor/Lpad, 2.5uF, 0.6mH, 8uF : to tweeter

rgds, sreten.

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[speaker dave]

A 2.5 way crossover means a system with 2 woofers but different crossovers for each. One (the one nearer the tweeter) runs up to the tweeter crossover while the second one has a rolloff some octaves away. What you get is better vertical dispersion because you don't have two woofers running in parallel at mid frequencies. At the same time you get the full bass power handling of having two woofers for low frequencies.

Rolloff rate is key because if you rollof the lower woofer too slow, then it won't be at a level enough below the uppper woofer to improve the vertical directivity. If you roll it off too fast then the extra phase shift will mess up the on axis response. It only works well with a steady first order rolloff (for 45 degrees phase shift).

A first order rolloff is just an inductor, right? The problem here is that you woofer itself looks pretty much like an inductor, so adding an inductor in series will shelve down the midrange but not roll off at the right rate. This is what the Pioneer guys were telling you.

Doing a proper first order rolloff either requires a conjugate on the woofer to make it look like a resistor, or a heavily damped 2nd order network, essentially the same thing.

David S.

[jrenkin]

Originally Posted by speaker dave

A 2.5 way crossover means a system with 2 woofers but different crossovers for each. One (the one nearer the tweeter) runs up to the tweeter crossover while the second one has a rolloff some octaves away. What you get is better vertical dispersion because you don't have two woofers running in parallel at mid frequencies. At the same time you get the full bass power handling of having two woofers for low frequencies.

Rolloff rate is key because if you rollof the lower woofer too slow, then it won't be at a level enough below the uppper woofer to improve the vertical directivity. If you roll it off too fast then the extra phase shift will mess up the on axis response. It only works well with a steady first order rolloff (for 45 degrees phase shift).

A first order rolloff is just an inductor, right? The problem here is that you woofer itself looks pretty much like an inductor, so adding an inductor in series will shelve down the midrange but not roll off at the right rate. This is what the Pioneer guys were telling you.

Doing a proper first order rolloff either requires a conjugate on the woofer to make it look like a resistor, or a heavily damped 2nd order network, essentially the same thing.

David S.

Dave, sorry to ask, but what is a "conjugate" on the woofer? Thanks.