60 degree VOTT?

[GM]

Greets!

The 816 is exponential so its dispersion is frequency dependent. To confine 'x' BW to 60 deg will require a much longer/larger CD horn.

GM

[cclark65]

ok, I am going to start a new project...I would like to make midbass and midrange cabinets based on the 816 cabinet type, but I want them to have a 60 degree dispersion. I am assuming that the current ones are 90 degree to match up with the 511 and 811 series horns.

How would I go about adjusting the cabinet to make them a 60 degree. I would like to keep them about the same size, and have a trapezoid shaped. But I really want to keep the horn loading for efficiency.

Current setup is 15" midbass on 816 clones, 12" midrange on the same size of cabinet, just no port and shortened up for the 12" driver. I am running 1.5" horns on top...I just got my 4th MRII564, that's what started the thought process. I am using subs below 100Hz, so the midbass doesn't need to go really low.

Any ideas to get me started would be awesome, and somebody please correct me if I am wrong in my thinking process somewhere!

Thanks!

[cclark65]

So really I don't need to worry about dispersion until I get up into the 2000 Hz range or so using the MRII564 horns.

I guess that comb filtering and other odd nuances don't happen close enough at the lower frequencies to make a difference? It's definitely very noticeable in the HF range, that's for sure, that's why I want to go with 60 degree horns. I even toyed with the idea of mounting them sideways to use the 40 degree side, and using 3 per side to get the 120 degree dispersion with minimal interference between cabinets.

Onto the 2nd part of my project then, I want to make the cabinets trapezoid shaped for nice splaying...I am guessing I can just make them deeper to keep the cabinet volume the same, right?

[GM]

Greets!

Can't say as I agree with that per se, around 1 kHz is the point most often quoted. Really, it depends on the app and why Altec offered such a wide selection of CD lens. What you do want to do is match the polar responses as best you can in the XO BW so that it sounds seamless both on and off axis.

Comb filtering begins in earnest when the distance is >WL/pi and is quite obvious at 1 WL if the sources aren't focussed, which means a short focal length 'sweet spot'. Not a problem in a typical HIFI app, but can cause real intelligibility problems in a prosound app.

To keep the same Fb, yes.

GM

[cclark65]

I guess the reason I figured 2000Hz is because I believe that's about as low as the 564 horns will go and maintain directivity. Lower than that and they can't control it as well.

I am really not very good at the designing process, that's why I am asking for advice, and please excuse me if I don't understand it right away, but I'll get it eventually!

Here are my crossover points that I am currently using:

18" Subs run from 40 to 100
15" Midbass runs from 100 to 500
12" Midrange from 500 to 1200
1.5" HF from 1200 on up.

I'll have MRII564 horns on the HF, so if I am reading this right, I should try to make the midrange cabinets have a 60 degree horizontal dispersion also, but really don't need to worry about the midbass ones, right? or am I barely getting into the frequencies in the midrange that I don't need to worry about it too much yet?

[GM]

Greets!

Understood.

Hmm, the 564s won't be 60 deg@1200 Hz, so you want the midrange to match whatever it is at this point. Again though, it really depends on the app. I assume this is for portable prosound, so if you feel the need for only a 60 deg coverage angle, then it should stay this down to at least below our head transfer function of around 800 Hz, fanning out to 180 deg down around 100 Hz. Normally this is done by stacking relatively small horn cabs and either using 64Bs or stacking 564s to get it.

Unfortunately, this probably requires re-doing your system from the midbass-up ($$$).

GM

[cclark65]

I was aware that the MRII564's wouldn't provide 60 degree coverage at the lower frequencies, I think they are only predictable down to about 2000 since they are so small.

Going a little further into it, I currently have separate cabinets for subs, midbass, midrange, and HF. This way I can still stack them up myself! I have no problems building an entire new set if I can get the performance I am looking for...I figured I would have to anyway. I get a lot of marine grade 7 and 9 ply stuff from shipping containers, so I have a fairly good supply of 3/4 plywood that is pretty much free for me.

So, saying that I stick with the 1200Hz crossover, I have no clue how to predict what the coverage pattern is at that frequency. If I move the crossover frequency up to around 1600 or so, then I get into problems where I need a phase plug in the midrange...which I do have 4 from some EAW cabinets that I am considering using.

My main goal is to improve not only the intelligibility of the system, but I also want to get more volume out of the drivers by narrowing the pattern down a little bit. The use of these speakers is indeed for portable live sound, lots of loud rock stuff usually. I will say that I get a lot of compliments on the clarity and punch that this system has when I have one stack per side, but when I put 2 stacks per side, I start running into problems that I am hoping to alleviate with 2 stacks covering 120 degrees with a narrower seam instead of so much overlap with the 90 degree horns. If the cabinets need to be a bit larger, then I am not opposed to it as long as I get a better sound out of them!

[GM]

Greets!

I never really delved into the Mantaray design too much for a variety of reasons, not the least of which is it's not easy to DIY in wood, ergo my comments are based on simple, lowest distortion conical WGs similar to Tom Danley's various Unity concepts except with what I consider a smoother driver/WG transition.

If you accept the need for at least a 60 deg h/v pattern to 800 Hz, then the WG ideally needs a throat transition radius = ~16.95" out to 60 deg (or use Geddes theoretically superior math solution), extending until its dims are at least 20.83" across, then flip it out to 90 deg until its dims are at least 27.78" across. I didn't plot it out, but the XO point can be lowered to whichever is higher, 500 Hz or whatever its 1 WL axial length winds up being, and what I recommend since it will help intelligibility, especially in a stacked 120 deg array due to being so much smaller than the midbass/lower mids WG.

Another reason to use a lower XO point is a higher XO = smaller driver/throat = longer/bigger midbass/lower mids WG.

Note that to keep the HF response ~intact out to the MR64B's 16 kHz, the initial expansion out to where it's at least 2.08" across needs to start out round, smoothly transitioning to square.

WRT using wood products in general, and especially used plywood, smoothing/sealing the horn's surfaces is required for best performance. The 'Devil's in the details' when it comes to hi-perf designs.

GM