Which x-overs for Alt-Scalas

[Blvdre]

I've been pondering an upgrade path for my LaScalas for some time now. I thought I was going to go the K510/K69A route until I realized the Klipsch saleman had quoted me wholesale prices, thinking I was a dealer I suppose. If it seems too good to be true, it probably is. So I made up my mind to go with the Altecs, grabbed a set of 511B's on the cheap, and have a pair of Bill's brand new 902-8's on the way. I'd like to add a tweeter to the mix as well, maybe the APT-200.

I currently am running Wright's WPA3.5 monos with a WLA12 pre. I really like the sound of this combo, very natural. My listening levels are reasonable, and given the positive reviews about the SET/ 1st-order x-over combo, I'd like to give this set-up a try. I did a search and found that people seem to favor either the standard A, Al's A, or the DHA x-overs. I'm trying to figure out what would best suit my needs. I like the idea of the DHA providing a constant load to the amp. Don't know about Al's A's, only his Universals which I am currently running with my stock LaScala set-up. Any opinions, comments, guidance are welcome.

[Daddy Dee]

The Eminence tweeters are very good. If you should want to use that tweeter as a drop in replacement for the K77, of course, no crossover mods are required. You can get the same tweeter with a K77 type horn as a CT125 from Bob Crites. If you should want to use the top end of the LaScala cabs, that little guy will drop in the same cut out as the K77.

[Deang]

Don't know about Al's A's, only his Universals...

Same network -- they're called Universal Type A's. Probably not the best network when you only have 3.5 wpc and you're trying to get into the zone with a watt or so.

With that driver/horn, you might be better off raising the crossover just a little -- up to 500Hz. The 908 has more extension than the K55, so you're going to have to start rolling it off at some point. People have different ideas about this. If you really dig the crisp "tweeter sound", cross to the APT200 sooner -- say 4500 or 5000. Personally, I think it's better to take advantage of the 908's extension -- I would cross at 7500Hz. You can do that with a simple Type A, just change the 13uF to a 20uF, the 2uF to 2.5uF, and add a .17mH coil between tap 4 and squawker positive.

[Blvdre]

OK, so I am familiar with the Universals - that's what I'm currently running w/my K55's and 77's. Dean, I was thinking of crossing the 902's even a bit higher to give them some breathing room, say 600Hz - what would the appropriate coil value be? I'm right with you on the tweeter crossover, seems a shame not to let the 902 do it's thing - 7500Hz sounds good to me. One more thing; what model autoformer is used in the A?

[JohnA]

902's and 511Bs don't need a tweeter. They peak at 106 dB/w/m, and if you bought the -8Bs, you'll need a substantially redesigned crossover. I did this for a 511B/902-8B on a Peavey FH-1. The crossover point is 1k and it takes out the 106 dB hump from about 600 to 2k.

[Blvdre]

My understanding is that the driver impedance wouldn't be an issue with the A, I'd just need to change the tap settings on the squawker autoformer to match the driver levels. It wouldn't be the first time "my understanding" was wrong I've never heard of a LaScala bass horn being crossed over that high. Anyone ever try this, and if so, how did it perform up there? I do like the idea of smoothing out the horn response. Yeah, I originally thought about running the system as a two-way, but it seems most end up adding a tweeter later on.

[Deang]

"I was thinking of crossing the 902's even a bit higher to give them some breathing room, say 600Hz - what would the appropriate coil value be?"

Your power levels to the 902 are going to be so low it's not worth worrying about. Just use the stock coil and bring the squawker in where you want it.

"...what model autoformer is used in the A?"

T2A -- BEC had that one put into production, just order directly from him.

"My understanding is that the driver impedance wouldn't be an issue with the A, I'd just need to change the tap settings on the squawker autoformer to match the driver levels."

Just the opposite; the Type A is not like the ALK -- you need to change the primary cap value with every tap to keep the crossover point the same.

"I've never heard of a LaScala bass horn being crossed over that high..."

Not quite sure what you mean here.

Just try what I suggested -- no sense in reinventing the wheel.

[Blvdre]

Thanks for the clarification, Dean. So if I want to change the squawker level, I would change the tap (from 4 to say 3 to reduce the output...) but would have to change the auto-former primary cap (20uF) to a appropriate value in order to preserve the x-over point, or am I not getting it?

"I've never heard of a LaScala bass horn being crossed over that high..."....this was in response to John's design, which crosses at 1k to the squawker.

[JohnA]

I meant my crossover to be an example. For a few reasons, the La Scala shouldn't ge crossed at 1k. 600 to 700 Hz would be very good, though. I also built a similar pair for Peavy MF-X1 and an FH-1 bass horn that crossed at 650 Hz.

Attached it the model's predicted response for the Peavey-Altec system. Notice the response above 10k. In a live performance, especially with females through Shure 55 mics, these things sound really sweet. There is bass distortion only I hear, typical of the Peavey woofer.

[Blvdre]

Thanks for the clarification, John. Interesteing, a peak at 10K, and then it drops off, albeit very gradually. Did you find the high end adequate? I've ordered parts for the type A, seems like a good place to start - thanks to Dean for the appropriate component values. I'll report back with my impressions.

[JohnA]

Yes, I found the top end to be VERY adequate. I first ran the 902/511B on top of my La Scalas crossed at 600 Hz with just a capacitor. It sounded very much like the La Scala squawker and tweeter. However, the 902-8Bs buzzed on bass notes, even listening to acoustic jazz at same levels.

I used this response curve measured by Shaun in my model as I didn't have a signal generator at the tme. Since, I've been too lazy to test them. Note the hump below 2k. The high peaks are probably a bit above 107 dB with the bulk of the response at 106. Then the response falls from there. If you don't include someEQ you might not be entirely happy with the sound.

[bluesboy]

This crossover was designed for use in a Altec 511/902 LaScala three way set-up. Contact Al at ALK engineering for a price on a parts list and schmatic if you want to build it yourself.

[Blvdre]

Thanks for posting that John. Gives me an idea of what to expect. According to what I've read on the forum, the repsonse can be shaped passively, yes?

Bluesboy, is that an APT-200 you're running for a tweet? Just wondering what your impressions are, as that set-up looks identical to what I'm cobbing together. Yeah, I did consider going with one of Al's crossovers. I currently am running his universals, and was considering building an extreme slope running a two-way. The concensus on the forum seems to be that the type A or similar 1st-order is the way to go, if running low power SET. Dean was nice enough to provide me w/some specific suggestions, so I'll run with that and see how it sounds. BTW, your crossover looks like a variant of the Universal.

[bluesboy]

The tweeters are Beyma CP-25s. Al designed this network specifically for the 511/902 , LaScala bass bin set up. It's an easy build and sounds awesome.

[Deang]

Al designed this network specifically for the 511/902

Looks like an ALK. I can't possibly imagine what he would change on that network to make it work "better" for the 511/902.

[bluesboy]

It's too bad we can't get Al himself to chime in on this.

[cjgeraci]

I have lived with a pair of new 902s from Great Plains since last year and absolutely love them. I have also had a variety of different networks in my system from Al's Universals to his extreme slopes (and now gone to active) as well as tweeters such as the APT 200, Beyma CP25 and JBL 2404. The tweeters went on the shelf after the switch over to 902s (except for 2404s, which are now in the rear because of K77s). More than enough on top.

As far as crossover points, as long as you never lean into it, you could conceivably get away with leaving the lower squawker at 400 hz, the Universal's point. Terry has crossed over his 902s over at 400 hz. Maybe you start with the stock Universal As and try it for a while. Terry had said that he has slammed his pretty good and they survived that low. I still felt a little bit uncomfortable given that these are aluminum any time that I was running them at 400 or 500.

There is also no doubt to my ears that the 902s sound better the higher that you can move that bottom crossover point. I now cross mine over at 1000 hz because of some different drivers I have added to my Khorns to cover the midbass area, and I've tried various points from 500 hz on up. So, if there if there is somehow to move the crossover point to 600 at some point, I would do it.

Carl.

[bluesboy]

My results are pretty the same as Terry's. I've been running the 902s with 511s and ALK universals crossed at 400hz in my corner horns for over a year now without any problems. And I play them pretty loud at times. Just ask my wife!