active x-over configurations

Soundhound and everyone else who is actively multiamping speakers,

I am having a lot of fun using Marchand XM-44 3-way. I like the changes from passive x-over. Having said that, it also introduces a host of possibilities and questions about driver interactions that you previously only left to the speaker designers. What frequencies and slopes (with related phase changes) are you all using out there and what configurations are your drivers in?

threers:

I assume you’ve read page 2 of this thread.
http://ubb.outlawaudio.com/ubb/Forum14/HTML/000110.html

Unfortunately I don’t have active bi-amp system but there’s a remote possibility I may in the future. So far, I gather that active crossover is better than passive one when calibrated properly. That can also mean no crossover is better than any crossover especially when there’s no need for calibration. I’ve heard about such speakers. Lowther and Fostex (plus a few others) both make full range drivers. I don’t think they are truly full range since they start to roll off quickly below 40 Hz but going up to 20 KHz at relatively flat response is pretty amazing. Except for a few types of music, this kind of driver may be a possible alternative to active bi-amp configuration.

I use Linkwitz/Riley 24db/octave slopes at 60Hz between woofer and subwoofer and 500Hz between woofer and high frequency horn. The exact crossover frequency and slope is totally dependent on the speaker drivers involved. Linkwitz/Riley crossovers have the advantage of the drivers being in phase through the crossover point, but they must still have their voice coils physically aligned in the vertical plane for there to be the flattest response. This is why some manufacturers use stepped baffles with the tweeter recessed farther from the listener than the woofer.

soundhound:

High frequency horn meaning tweeter?

Tweeter and woofer crossover at 500 Hz is unusually low. Which model is it?

No, he means a horn. They reach much lower than a tweeter does. 500 hz sounds in line.

Ok, then how high does it go before rolling off?
It it’s 20k Hz, that’s quite a range. In fact, I’d like to look it up.

I forget exactly (and it depends on the horn), but they can reach that high.

Soundhound,

Your configuration is very interesting. I have ribbon panel mids good from 10KHz to 166 Hz. (Super) tweeter goes to 25K. I have left the passive x-over for this alone. I cross my woofers at 200 Hz and sub at 50Hz -- all 4th order as well.

What size are your midwoofers. Mine are 10" that are good to 600Hz. The tricky stituation is that my two woofers (originally designed to do midbass as well as bass) have different range even through they receive the same signal. The bass woofer rolls off at 150Hz.

I want to raise the crossover frequency for the woofers from 200 to ~450Hz to get a little more punch in the upper bass region, but I may have to change the lower driver that rolls off at 150 Hz.

I really like my midrange ribbons -- they are really good with vocal reproduction. I am just greedy at this point and get that right "coloration" of deep baritone and bass sound as well. I want that note ...CIL... as intoned by Sparafucile in introducing himself to Rigoletto to be as deep and forboding as the bass can render it.

Thanks for all the advise so far.

Yes, my "tweeters" are horns, and yes, they have a range of 500Hz to 20kHz. Good compression driver horns can easily pull off this feat. My woofers are 15" and are short-horn and reflex loaded.

This is a link to pictures of my system:

http://community.webshots.com/user/soundhound

Holy smokes SH! You could give THX a whole new meaning!

soundhound:

Your main’s short horn woofer versus center’s JBL woofer, won’t that cause any mismatch? I guess not, otherwise you wouldn’t have set it up that way. Just wondering how it works.

For front L/R I'm running an old pair of homemade (about 1970) bass reflex speakers (originally Altec 416As but went to JBL2226Hs) with Altec 511 horns and 808-8A drivers. I'm using a dbx Driverack PA electronic crossover (originally homemade, then Marchand, then dbx.) I'm using 4 channels of an Outlaw 7100 for amplifiers. Surround L/R speakers are Altec Model 19 driven by 2 more channels of the 7100. Front center is phantom. Subwoofer is an 18 inch Velodyne. The whole thing is driven by a 950.

For Soundhound: Do you need 2 15 inch woofers for the center channel or is it for balance/symmetry? Did you build your center channel?

regards, Jim Roy

>>>For Soundhound: Do you need 2 15 inch woofers for the center channel or is it for balance/symmetry? Did you build your center channel?<<<

It is for symmetry and the two 12" woofers can keep up better with the main's 15" ones. The horn is the same 511/802G combination as on the mains but the crossover has been raised to 800Hz to better integrate with the tonality of the mains. The matching is actually extremely good between the mains and the center. The 511 horns all have about 20 pounds of Aquaplas applied to the exterior of the horn to make them completely inert - the metal horns have a tendency to "ring" when rapped with your knuckles otherwise. The center 12" woofers are modified JBL 4412 cabinets.

[This message has been edited by soundhound (edited July 23, 2004).]

>>>Holy smokes SH! You could give THX a whole new meaning!<<<

The four JBL 2245H/4645 18" subwoofers are THX certified, as are my surrounds, but nothing else in my room is (the tube amps would undoubtedly flunk THX tests - I feel so bad....). I did not buy them becasue they are THX certified, but they just happened to be the ones I wanted (and I worked at JBL at the time). The subs are THX certified for commercial cinemas and there is also a version for home use as part of the K-2 system. I modified the tuning of the cabinets so that I get flat response down to 10Hz, while in stock form they go down to 20Hz.

[This message has been edited by soundhound (edited July 24, 2004).]

Soundhound,

When you say your x-over frequencies are 50Hz and 500Hz, what are your actual highpass and lowpass frequencies?

They are at 60Hz and 500Hz. A high pass and a low pass at each.

Soundhound,

I have been advised by some that the highpass and lowpass poles be staggered a half octave to ameliorate an "in phase notch". I am thinking that there are "real world" inefficiencies given the different drivers and electronics that results in less than a unity in the crossover octave. But I am also thinking that if the frequencies are staggered, there should be an additive amplitudinal change (a spike rather than a notch) in the doubled over region. What is your opinion on this?

I am just bouncing ideas at you before I order more frequency modules. I have not had a chance to measure the speaker output as a whole yet. I've only worked on individual drivers so far with truRTA.

With a 24 db/octave Linkwitz/Riley crossover network, the point between the low pass and the high pass sections is 6db down if both filter sections are at the same frequency. A 6db voltage dropoff, when summed, equals flat response through the crossover point. Assuming that the speaker drivers themselves physically have their voice coils on the same vertical plane, the frequency response in-room should be flat through the crossover region if the filter sections are at the same frequency.

With a Butterworth filter, the point between the crossover sections is only 3db down. When summed, this will yield an excess of energy through the crossover point. This might be what you are hearing about, but it is not an issue with the Linkwitz/Riley crossover network.

[This message has been edited by soundhound (edited July 28, 2004).]