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-   -   4 - 2 x 15 reflex bass cabinet help (http://www.diyaudio.com/forums/pa-systems/225781-4-2-x-15-reflex-bass-cabinet-help.html)

Mr dB 15th December 2012 11:18 PM

4 - 2 x 15 reflex bass cabinet help
 
Hi there, i'm new to this place, seems like a helpful one too. So I ask you please help me out if you can?

I currently own 4 - 2 x 15" reflex cabs, the dimensions are 60x60x85cm. I will place a good 5-6cm of insulation inside them, but I am unsure as to which drivers would best suit them? something around just under 100 per woofer would be great, and if I can get near 1000w rms each side from a pair then I will hunt for that.

However, I understand that you can't just stick in any powerful woofers, and so some expertise on what woofers would be good with the size of these cabs, would be great.

Point to note, there are 4 port holes with no piping in them, so depending on what drivers I get, I will make the length of them suit.

I've seen some Eminence delta 500w LF's ... any good?

Any help would be great, sorry if it makes no sense i;m so very tired!

Cheers,

Tom

chris661 27th December 2012 12:46 PM

Still no replies..

Download WinISD Pro, and play around with some different drivers. The Eminence drivers are generally known to be decent: I'd told they're very difficult to kill.

I suspect that a pair of 15"s in a cabinet that small won't produce any real bass, but plenty of "kick" in the 120Hz region.

You might be better off blocking one of the driver holes, and using one driver per cabinet: you'd have a much better chance of getting some <80Hz stuff out of it. Consider blocking some of the ports, too (WinISD will be able to tell you what to do with them).

Chris

Mr dB 28th December 2012 04:40 PM

Thanks for the reply :)

Well I did some playing around, and with some Delta 15 lf 500w drivers (2 in each cab) it reckons I can get a solid 70-80Hz. Which tbh, from 15" in a small cab, isnt bad I don't think. Lets hope the maths doesn't lie.

For me 70-80Hz as my first system, ill be pleased with :)

Oh has anyone got any advice on tweeters or 2" comp drivers? my flare dimensions are 390mm x 240mm, but I can't seem to find a a flare that size. But ill keep looking. Can anyone suggest a good 2" comp driver?

Xoc1 29th December 2012 12:36 AM

1 Attachment(s)
given the size of the cabinet is approx 118 Liters per driver you could probably tune for a lower response than 70hz. Driver recommendations are usually dependent on your location. I suggest you add your location to your profile as this is a global forum!
Practical port size depends on what you can fit in the cabinet. Personally I would probably try for at least 6 X 10cm diameter ports for a double 15" to keep the port velocity down.
A pair of Eminence Kappa Pro15LF2 should be capable of a -3db response at 40Hz in this sized cab.

Mr dB 29th December 2012 05:33 PM

Thanks for your reply, that looks very promising thank you!

I live in shropshire, UK. So ill do that in a mo!

Ok well atm, the port sizes are 4cm (not big enough) So ill have a go at making them 10cm.

wadding? yay or nay?

Xoc1 29th December 2012 09:42 PM

You will need some plastic drain pipe or similar tubing. See what you can source that will fit on the speaker baffle and use that to size the port holes. From that you can then calculate the total cross sectional area of the port. The ports need to be longer as the area increases. The small ports are probably sized to just use the thickness of the speaker baffle, unfortunately this makes them ineffective at higher power levels as the port velocity is too high.
Wadding is not necessary for a sub. What frequency are you planning to use as the upper frequency limit for the 2 X 15" cabs?

chris661 30th December 2012 10:32 PM

These guys sell quite a range of Eminence, Fane and Faital Pro drivers, and their prices are decent.

I hadn't looked so closely at the cabinet volume - looks like there's plenty there (I've seen other 2x15" cabs where the drivers barely fit in the cabinet, and assumed similar).

The driver that Xoc1 has suggested will do about 125dB per cabinet, down to ~40Hz.
You could run a 1kW amp into it fairly safely: excursion goes to ~8mm one-way around 60Hz (that's probably the most I'd ask from them). The progressive suspension used in most PA drivers ought to stop them bottoming out, but listen carefully to check if the drivers are being abused.

For high power use, adding a low-cut filter below port tuning is mandatory. The cabinet provides no resistance to the cone motion below Fb, so the drivers will quickly bottom out.

Chris

Mr dB 2nd January 2013 11:50 AM

Hi guys, sorry for the late reply, been away for new years. Speakers have arrived, got some Eminence Delta 15- LF's (I know not the absolute best, but I have a budget here guys! im only 18! haha)

So I've had a look at making the port holes bigger, but there just inst the room, unless I want to break the front of the cab cause it would be too weak. (the holes would be too close together)

So my only worry is blowing the speakers :( because the port holes are too small, I understand that the air needs to escape quickly at high volume, but truth is I wont be using them at full
tilt much! So how much risk is there of that happening, if I leave the ports how they are?

Oh and my upper freq limit will be about 150-160Hz max! Perhaps lower, not sure yet.

Tom

wintermute 2nd January 2013 11:56 AM

The problem with small ports is that the velocity of the air is too high and makes chuffing noises, I don't think that there is any risk of blowing the speakers unless the box tuning is not right (too high) and the speakers unload at frequencies you expect them to be ok playing.

Tony.

Mr dB 2nd January 2013 11:58 AM

Ok I get it now, so the only real way of checking, is loading them up and listening?

Would flared ports help expel the air better?

Tom


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