community RS325i

6 community RS325i came in today with a load of gear. Ive got dim memories of seeing them in an old catalogue, but nothing more and i can't seem to find anything about them on the web. 

im interested in what kinda 15inch driver u would use to get the most out of this kinda design.
the horn, being so short, is going to have very little directional control, and having a very wide cross section on the throat its going to beam just as much as if it was reflex loaded, literaly just as much. this is easy to fix, with a narrower throat, and/or a simple phase plug spltting up the cross section of the source radiating. such an easy thing to do that this (the existing format) must be a deliberate and planned part of the design. i guess that the little bit of dospersion control given by the horn might match the beaming near the top of the range well. clearly they are not designed for stand alone use unless ur in a hall which id 5m wide by 30m long.

anyway, i made a prototype for a ported 12inch mid horn which covered a similar angle, just a bit wider dispersion and filled a similar role to whats going on with that cab there as far as the bandwidth it covered and the different passbands which made it up, only my one was designed to work one a side, and could at most be used 2 per side unless u stacked verticaly as well. i also went for a much longer horn and although in the end i was disapointed, at first i though it would be an excelent modular soloution for what i wanted to do with the parts, money and requirements i had, but it did end up being given away, and actualy dumped i think (the prototype horn itself was made of a scrap pile mix of chip board and mdf), cos the problem was i still ended up with a big difference in gain at the bottom of the range were the horn was having less effect, and relying on the port tuning more and more. it could have been evened out with eq in theory, but thats a bit rubbish, and wth the coupld of dedicated mid drivers i stuck in it, i was a bit worried about the excursion.

it ended up going to replace some jbl ported mid horns above 2 x 15inch jbl scoops and a 2inch beyma comp and horn with beyma slots, all of which designed in the 70s, were it would have been an improvement, being almost identical in design concept, but playing a bit lower and giving better hight for stacking, but it ended up getting left outside round the back of the small town nightclub i donated it to, and after a rainy month, they bothg came toa predictable demise.

anyway, i decided after this that i thought it(and this kinda format for systems) was such a nonsuccesful and outdated compromise that ive ditched this idea totaly and written it off as obsolete and gone for a different format for my own mid sized never ending hobby system.

a more modern distribution of passbands, taking advantage of newer driver tech (but still quite old school in its philosophy, high sensitivity and headroom for example) using a dedicated cone midrange driver on a phase plugged horn (ive got a couple of options now for that one, but both are 10inch drivers, (one being a tms mid horn and the other one being very similar and unless i dont get hold of the second option, then it should come with the original parts and not need phase plug mods), obviously topped of a smaller format (1inch) comp driver and matching small horn, rather than this (before mentioned, and used in the system in the original post which got me thinking/ranting about thos again) old school large comp and tweeter format (with a xover point always and inevitably right smack in the middle of where ur ears are most able to pick holes in things) i seem to see this method a lot in comunity boxes, and although it might be a little too bright for some at times and need a dose of eq, they are cabs which do generaly sound very good.

the low mid horn im working on at the moment is a direct resul of trying to avoid these problems, and of course as many folks here have had a crack at it, it is something which we are all informed is quite hard. magic almost. i bought it up a while ago, and i recently mentioned i was going to have another go. apart from trying to get some measured shareable results when i finaly get round to doing a prototype, ill post some plans with this one, which are something i dont normaly even have when i build, and will also mean that apart from letting others have a play with the idea if anyones interested but dont have the pacience to wait for me to finaly, if ever, stop dithering about and finaly put together another part of my rather expensive baby. not to mention that this time i will have to share my results, even if they are no good (as to the plan s, ill try to do em this weekend, but be warned, i only ever do realy rough plans with general dimentions for the different lengths and volumes and that, the rest i do it as i go. this will probably not be much better). actualy, that could be cool. one of you cad designing wizz kids migh be interested enough to draw it if it proves to be interesting and in that way, calculate every angle and length down the the half mmand degree.

i am going to have to fold it though, cos i dont want to port it, and im going to try to use a mix of smooth folting, narrow horn cross section through the fold, and , all on a more than 80cm front loaded horn with eithera martin audio inspired 2 dimentional phase plug/first section or a small smooth, octagonal and progressive shape changed (like from and octagon to a narrow rectangle, if u get me) front chamber with the reverse mounted driver acting as its own phase plug (and in this case, a slightly shorter horn. i need to make a prototype of each, and see if either of these methors, combined with a very light tight yet powerful midrange driver being used in low mids, i can get away with a 350hz xover point (or higher) and try out the trick that fk1 seem to have mastered(or tony andrews in general, right back to the tms low sections)....

anyway that was a big rant and way off topic. sorry.
back to the thread at hand....

ok getting back to the example for the 3way mid/top cab format in the OP; what i think is interesting about the 15inch driver is that it would have to have (in a sealed box) a strong low frequency responce with highish xmas and a qms which lets it move, but a much weaker midrange, so that with the gain from the short horn loading it all adds up to create a flatish  frequency responce curve.

this seems kinda strange, cos the characteristics which make a driver like this (mid BL, high qms and probably qes, therefore high qts, probably a low fs, created by a not so light mms combined with that high/floppy qms. also, i guess it could or would probably mean the driver would have a high Le, as this would help keep the mid high frequency down a bit relative to the low mid, but not have such an effect on the 'speed' of the driver. this though (high Le or low coil inductance). im not sure about this one, so please correct me if im wrong, as i understand it the coil inductance doesnt so much act as a sort of parametric eq on a low q filter at a particular point in the upper range, but actualy cuts the Mid highs righ out like a low pass filter at some point.

anyway, what im interested in is what are the ts parameters for the kinda driver they use in these cabs? it just sounds like the parameters u would want to get a flatish responce from such a short ported horn on low mid, for me is just the kinda driver which when hornloaded sounds mushy in the mids and high mids, even if u cross over at 1khz. reflex bass driver (beyma 12g40, P-audio C15mb 400)  in a mid horn, clearly not good!!

on the other hand, the tipical 12 or 15inch mid range horn driver (rcf L12P110k, Beyma 15mi100, pd 122) with a strong BL, highish Fs with low Mms and very tight Qts amd good inductance, in spite of holding its own on the low mids/upper kick range, it would have a very uneven sound with very strong clear mids but not much lows, and realy have troubles with its xmas between the horn f3 and the hemlotz tuning frequency. so here we have a tight, delicate midrange horn driver needing all the help it can get in the bottom of its range, but getting none right there were it realy needs it!!

whats the soloution then?


Edited by thepersonunknown - 01 March 2014 at 3:44am

Yea not so much beaming at all then. I didn't think it was like that, I thought it would have its xover points at more standard frequencies. Its a much more interesting cab than it looks. Still, I'm still very curious about the 15nch driver and what's going on with that lttle flare.

The EV-15L were, I believe the most common 15 used in cabinets like these. I had four of the 4896 flares, 2 with 15L's and 2 with 15B's. Ended up swapping the B's with L's to keep everything consistant.

That link is to your desk top.

csg wrote: 6 community RS325i came in today with a load of gear. Ive got dim memories of seeing them in an old catalogue, but nothing more and i can't seem to find anything about them on the web.  does anyone have an old data sheet etc knocking around?  sorry for the really bad pic, the camera on my phone is not feeling well... 15" on a really short horn, reflex load M200 on a good length flare 2 peizos ( yes, loverly!) on a refraction slot flare ( may try stiking a reasonable 1" BMS etc on that instead..) with a lot of the 2K range from the very loud M200 taken out they sound rather ( surprisingly) good, just not sure quite what to do with them.