Question about X1-SLAMM "klones"

[Markw]

Hi Jon / Thomas

(This is my first post)

I have been following your X1-SLAMM "klone" project with interest, and have a couple of questions. At what angle are the top and bottom 7" drivers relative to the tweeter? What distance is the array focused at?

I'm contemplating doing something similar on my current project, an active MTM using Focal drivers. I calculated an approximate 3 degree angle on the baffle for a "focus" distance of 3 to 3.5 metres (it depends on driver spacing). Is this similar to yours?

Cheers

Mark

[JonMarsh]

The angle is greater than that in the "Klones". I'm travelling on businesss and don't remember the exact angle right now.

Considerations include the effective dispersion of the 7" drivers up through 2.5 kHz, in the region of the tweeter crossover. The intent is to produce a smoother vertical polar response through the crosover region, (considering that midwoofer performance up to 4 kHz affects this), and to allow a more uniform room power response.

This is similar to what we did with ThomasW's Acoustats, with an inverted V focused a relatively short distance in front; in this case, it is the horizontal dispersion which is of concern.

Depending on the listening distance you want, if you build somehing like this, you may want to build a test enclosure with independent mid and tweeter modules which can be aimed and adjusted; the actual SLAMM is like this, with variable front to back offset for the tweeter, and front over hang for the upper 7" driver; this is more for aiming the height of the lobe in the crossover region; the angle isn't adjustable on the modules.

The "Klones" use a different crossover than the actual X1s; the latter use a 2nd order all pass, while the "Klones" use a 3rd order network, with the drivers in phase, and damping coefficients adjusted somewhat in the crossover region. The 3rd order crossover has a wider vertical dispersion, and flatter power response. Designer's don't necessarily agree regarding that benefit; if you have low ceilings, then the 2nd order or a fourther order may be desirable, in principle, but since above the crossover point, tweeter polar radiation extends vertically, reducing dispersion in the crossover region seems only to compromise the overall room farfield power response, so I elected not to go that way.

YMMV.

I was planning on wrapping up a lot of documentation for the X1 tomorrow during a vacation day, but at the moment I'm stuck in Chicago, and don't know when I'll be back in the Bay area with any certainty.

Best regards,

Jon




Earth First!
_______________________________
We'll screw up the other planets later....

[Markw]

Thank's Jon

I have designed a prototype enclosure today, with the ability to change the angle of the midbasses between 0 and 18 degrees. Also the tweeter baffle can move from in line with the midbass to 100mm behind. I'll build it tomorrow (well, I'll start anyway).

I'm going to start by to using it with an active 4th order L-R crossover at 2400Hz.

I'm am eagerly awaiting the write up on your X1 klones.

Hope you get home ok, I have a friend who is stuck in Detroit, it has affected us all, even on the other side of the world.

Regards
Mark

[JonMarsh]

Hello Mark,

With the setup you describe, you should be able to experiment well. Something to watch out for with a 4th order L-R, besides a narrow vertical window in the crossover region, is the relatively week power response in the crossover region. If you listen primarily near field, you won't find that a problem. If you use the speakers in a larger room, with more farfield listening, or some, you will notice changes in the room power repsonse. That's why Bullock proposed a compromise crossover which has a slight bump on axis, but a smaller dip in the power response. If you have any electronic crossovers with variable slopes or Q, it's a good way to suss out how the drivers will interact.

I've found two ways to "play" with an early prototype that way; I keep a few Marchand boards in different configurations built up, some wired for 3rd order, some for 4th, and I've also found LSPCAD pro very useful because of it's ability to filter a to mimic the crossover reponse with music or test signals real time through a good sound card.

Well, I was luckier than some; I got back on Friday, only a day late, but many in our company travelling this week didn't; the guy who used to be my boss is stuck in Detroit and is just going to stay and work there next week, too.

Friday *was* going to be a vacation day, with a big part spent doing the write up on the Klones; now, I'm going to see if I can get a day off next week, but it may have to wait until after travel the following week, which doesn't exactly float my boat! 'Course, the last thing I'm interested in now is a few thousand more miles of travel....

Have a good weekend.

Regards,

Jon




Earth First!
_______________________________
We'll screw up the other planets later....