2nd order x-over, but which one?

[oquela]

Which 2nd order slope is preferred (or most common) in a PA enclosure (8 ohm 15 inch woofer + 8 ohm compression horn) linkwitz-riley, butterworth, or bessel? and Why?

I've done a search, but can't get a def. answer

PS: obviously not meant for Audiophile listening, but for covering medium sized crowds, probably outdoors.

[ttruman]

Hi oquela,

In my understanding of crossovers alignments, the Butterworth has its peaking lobe in a downward direction of 15 deg. This alignment would probably be best if the units were placed on stands that put them above the crowd. The Linkwitz alignment (0 deg peaking lobe) would produce better dispersion if the speakers are to be used level with the crowd or placed on the ground. This is assuming time aligned drivers however. Check out the link below.

http://www.rane.com/note160.html

[Inductor]

Originally posted by oquela
Which 2nd order slope is preferred...

Interview With Dr. Rod Crawford - StereoNET Australia

"At one time I used to worry about the type (Butterworth, Linkwitz-Riley) of Xover, knowing their different theoretical characteristics in terms of phase etc (a Canadian called Bullock wrote a great summary paper that I read while at Linn) but now feel that you cannot get to even approximate them with real drivers. I know that 1st order Xovers have some theoretical advantages in terms of phase etc but in practice they can lead to much more distortion as drivers start to break-up, poorer dispersion patterns caused by drivers interacting over a wider range of frequencies etc."...

[dlr]

Originally posted by oquela
Which 2nd order slope is preferred (or most common) in a PA enclosure (8 ohm 15 inch woofer + 8 ohm compression horn) linkwitz-riley, butterworth, or bessel? and Why?

I've done a search, but can't get a def. answer

PS: obviously not meant for Audiophile listening, but for covering medium sized crowds, probably outdoors.

I've certainly never built a PA speaker, but the principle concerning the crossovers will be the same. The difference would be in the listening environment, outdoors vs. indoors and in your case a horn vs. the more common dome tweeter for non-PA setups. The area of coverage is greater since PA systems aren't set up for a "sweet spot" as in home hi-fi and I suspect that the power response is more important than on-axis response or some limited off-axis position response.

The Butterworth 2nd (BW2) order does not have an off-axis lobe, only the off-order BW has that. It does, however, have a 3db peak on-axis. The odd-order BW has the off-axis lobe, but it flat on-axis. Listening on the lobe axis would actually not be recommended due to the lobe (a peaking on that axis).

The Linkwitz-Riley 2nd order (LR2) would more likely provide a more even response due no on- nor off-axis lobing. There will be a small difference in the overall power response vs. the BW2, but I'm not sure that the difference will be very large.

The Bessel, IIRC, will have less total group delay, but I'm not convinced that it's audible. It also does not have a flat summed response, but the difference there, again, may not be very audible if done well.

In the end, I would suggest an LR2. Considering as well the large woofer (15") with only one other driver, the horn, you'll likely have a lot more trouble with the integration simply due to the widely disparate dispersion characteristics. The crossover type will probably be the least important issue, but I'd still not recommend the BW2 due to it's on-axis peaking.

Dave

[dlr]

Originally posted by dlr

The Butterworth 2nd (BW2) order does not have an off-axis lobe, only the off-order BW has that. It does, however, have a 3db peak on-axis. The odd-order BW has the off-axis lobe, but it flat on-axis. Listening on the lobe axis would actually not be recommended due to the lobe (a peaking on that axis).

I should say that listening on the main axis for the BW2, having the peak, may not be the best location. I've never made one, so I can't actually comment on its sound. However, listening on the lobe axis for the odd-order BW that peaks on the lobe axis would definitely not be recommended. The odd-order BW is flat on the design axis and that would be the recommended position.

I can't actually recall ever having seen a loudspeaker design by anyone using the BW2. Back before the Linkwitz-Riley, there may have been some examples. I think that the odd-order BW was most common and in some cases the even-order Bessel were used. There were also, I believe, some BW4s around, but the legs of the crossover were adjusted to get an approximate on-axis flat response, a compromise. The power response in the crossover region would be altered n that case.

It's all about tradeoffs.

Dave

[oquela]

Thank you for the responses! very helpful. I'm leaning toward the LR x-over....will post back w/results.

[ttruman]

Originally posted by dlr

The Butterworth 2nd (BW2) order does not have an off-axis lobe, only the off-order BW has that.

dlr is right. Thanks for correcting me and not letting inaccurate information be presented. I misread the article. Sorry if it caused any confusion.