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-   -   Help with 2x15 bass box please? (http://www.diyaudio.com/forums/pa-systems/224724-help-2x15-bass-box-please.html)

phmosele 1st December 2012 08:56 AM

Help with 2x15 bass box please?
 
Hi

I am looking to build a pair of 2x15 bass speakers (not subs - everything below 50Hz will be cut) for a light PA system for a 3-piece band/karaoke situation in your average dive bar/pub-club situation. No crazy synth basses or techno/dubstep; toughest task will be kick drum, which is why I plan on cutting everything below 50, give or take a Hz or two.

There are a few caveats for you though.

First is that the box needs to be based around four of these, which I picked up at 50 bucks a pop on super-sale: Celestion 15" Professional Woofer 8 Ohm 299-418 I'm afraid options here don't include "sell them and buy four of THESE BABIES" guys. Please try to restrain your natural selves; trust me, I know hard that will be:). Site has all the T-S parameters for you.

Second is the maximum size is 36x24x18 or they won't fit in the truck.

Third is I only have tools and ability to build 90-degree corners, so I'm afraid esoteric horns are out (I wish).

I would expect the best design would be a ported box given the above constraints. I wouldn't have a problem if the best design turns out to be sealed, but the guys who are stumping up the cash appear to have been convinced (ummmm, possibly by me actually:o) that the best design is one where air comes rushing out of a port or two. So it would probably make life easier for me if we could make that happen please; I don't remember the last time I saw a sealed 2x15 anyway. I have 6" and 4" tube.

It also ocurred to me that it it might also be possible to divide the box into two halves if that would be better for our purposes.


Thanks very much for your time.
Regards
Phil

apexaudio 1st December 2012 03:40 PM

I suggest you simple horn-reflex box in post #22 thread:
http://www.diyaudio.com/forums/pa-sy...ne-aray-3.html
Regards

phmosele 1st December 2012 11:55 PM

Hi
I will look into that, thank you
Phil

phmosele 2nd December 2012 01:10 AM

Quote:

Originally Posted by apexaudio (Post 3265662)
I suggest you simple horn-reflex box in post #22 thread:
http://www.diyaudio.com/forums/pa-sy...ne-aray-3.html
Regards

Hi Apex. In that diagram, the 2x15 design is the one at the bottom, correct? (650x900x440)?

I could build a pair of those with the tools I have, but at the moment the extra depth (650mm=25inches) is too big for my truck. But I have two extra questions for you please.

First, how would a box like this outperform a "normal" 2x15 ported "box" please? More efficiency? Longer throw? lower, more solid bass (I only want 50-150Hz; I crossover into top units at about 150Hz). It is too big for me right now, but if these horns are a lot better than a simple bass reflex "box" I might look at them for next time.

Second thing is you mentioned Phase. To me, phase means having a 2x15 box where they have been incorrectly wired so one driver is moving out and the other is moving inwards, and the signal cancels itself out. Otherwise, it could mean having a pair of 2x15 boxes where each pair is correctly wired, but somehow one PAIR is moving out when the other PAIR is moving inwardes, and again, the signals cancel out.

But you seem to be saying that for these horns I need to wire them correctly so that in my world all the 4 bass drivers would be moving forward together and moving backward together - to me that is "in phase" and everything in my world would seem to be good.

But now it seems to be "good" I have to activate the phase switch on my crossover??? Can you please explain a little more about how phase is working here please? Is it putting one of the 15s out of phase with the other one in each box please?

Or is it wiring both speakers in each cabinet correctly so that all four speakers would move in and out together (my understanding of "in phase") but then I hit the switch on my crossover and "something happens" to the overall bass that would seem to make things "wrong" but in reality it makes them "right" when the horn boxes get placed under their top boxes. Perhaps the horns are in phase with each other, but out of phase with the top cabinets. I am a little uneasy here... to my mind, all speakers should be moving in and out together, so it is possible I do not understand "phase."

Is this something that would only occur if I build these horn-reflex designs? As I said, I think I am going to have to go with bass reflex first time because of the horn size (width and height are fine, but 25-inches deep is probably too big for my truck right now).

If I build simple bass reflex boxes, would I have to worry about "phase" then? I could always hook it all up and just flip the phase switch on the crossover to try it out. But that would only work if the 15s are wired up "however they need to be wired up for this to work." I put that in "" because if I do not wire them how they are supposed to be wired before I apply power, then flipping the crossover switch won't do what it is supposed to.

Do you have a link to a wiring diagram for a pair of 15s (either bass reflex or horn reflex) that I could follow before I test these in the presense of critical band members please? It would be hard for me to deliberately wire up speakers "wrong" unless I understand why wiring them "wrong" will eventually make them "Correct."

Thank you very much
Phil

mr. doom 2nd December 2012 03:02 PM

Short horns generally are used for kick bins as they can give a bit of boost in the 75-300hz
region.
As you are going to these for subs and might eventually stick (real sub drivers) in the cabs I would do a simple G-sub as big as will fit in your truck.
Google parallel speaker wiring diagram and it will give a 4ohm load on your amp if you are running it in stereo... just keep positive to positive and negative to negative...What amp are you using btw?

Those are NOT sub drivers with the 3.5mm xmax and want a large box to get bass but will work "ok" as kick bins if you don't push them too hard.

phmosele 3rd December 2012 09:56 PM

Hi
Thanks for the input. I took a look at the drawing and I am not opposed to that design in principle at all, but I have a couple of problems with it. It is deeper, at 26 inches, than I can carry, and it is for two 18s and not two 15s. I'm not entirely sure, but I would think that changing the internal volume and the driver configuration would change the port requirements dramatically wouldn't it?
Thanks
Phil

mr. doom 3rd December 2012 10:50 PM

yep, shrink it to your dimensions.
 
Quote:

Originally Posted by phmosele (Post 3269023)
Hi
Thanks for the input. I took a look at the drawing and I am not opposed to that design in principle at all, but I have a couple of problems with it. It is deeper, at 26 inches, than I can carry, and it is for two 18s and not two 15s. I'm not entirely sure, but I would think that changing the internal volume and the driver configuration would change the port requirements dramatically wouldn't it?
Thanks
Phil

You will be lucky to get 7cft out of a box that size, a 50hz vent for a 200liter box with that design should be around 2.5" tall and only 2" deep if my maths are correct.

phmosele 3rd December 2012 11:09 PM

Hi
I really am hamstrung with size, as well as drivers. It isn't an ideal situation and I understand some compromise is in order. Maximum size I have at the moment is 22x16x34 internal, which is about 9cuft before bracing and drivers. I'm not sure if the drivers actually come out of the overall volume (which I guess pegs me pretty much as a noob).

Parts Express' support guys modeled them as being reasonable performers with a pair of 6"x 3/4" ports per box. My expectations are reasonable (unlike some posts where guys want earth-shaking 30Hz long-term for 200 bucks all in) but if I can get a bit better performance out of the design you suggest, then I would be silly not to take it. But, as I am building em for someone else, and I don't need a lot of help to look silly, I would be really grateful if you could confirm the correct port size for this box before I start sawing away. I don't know how much leeway one has with box volumes before ports become ineffective, and I have trained these guys to expect to feel moving air. Just like in the extremely expensive JBLs they like so much.

I was looking at the 184 sub designs at the same location, and I could add a couple of those with the Eminence and let somebody else hump em if they want to.
Thanks
Phil

phmosele 3rd December 2012 11:16 PM

But one option has just opened up; someone is likely to be getting a bigger truck soon (not sure when soon is and I shouldn't hold my breath on someone else) but it would allow for a slightly bigger box of 36x22x22 internal. I have to go with what I can rely on right now, but would it help to have this slightly bigger size please?


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