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poorbutproud 30th June 2002 04:15 PM

Newbie needs PA subwoofer advice
 
Hi all,

Seems like all the DIY info I find on web is based on "home theatre" or "car audio" design. I am a musician with a need for a subwoofer. I have a pair of Mackie SRM450 active speakers which handle the high and mid ranges but want to build my own subwoofer because, well, I'm poor. I looked at buying the discount bottom-of-the-barrel subwoofer cabinet and amp but am still coming up with price totals of about $1200.

But an 18" speaker and a subwoofer from Parts Express add up to about $350. I have just recently built my own MIDI drum brain and electronic drum kit, so I think building a speaker enclosure and assembling these two parts is not beyond my intellectual capacity. Does anyone have a URL that fits my needs, or have pertinent advice? Am I dumb to think there's a difference between a "home theatre" application and a "live PA" application of my scale? All I need is an XLR input and, I guess, a lowpass filter circuit to filter the signal for the 18".

Thanks for any guidance.

pinkmouse 30th June 2002 05:32 PM

Hi chuck.

It so much depends on what you want; is this a sub for stage use, or for your own use at home...

For stage use, if you have a decent PA, sub is not your problem, as long as you have a line out or D.I. the PA will take care of it, and if you need sub in your stage sound, then you are the first musician that ever does in my experience ( apart from drummers!!! : ) )

The difference between a home theatre/hi-fi system and real life is amazing, any domestic sub will not even slightly have the welly to fill a decent sized venue, and if you did, you would need major amounts of boxes and amps.

Home theatre runs at very low levels, despite what some people think, in comparison to real world PA, and most domestic speakers and amps cannot cope with gigging volumes reliably for any length of time.

We have all been poor, and I know what you mean, but , to be honest, PA subs need power and quantity, or it doesn't work, and if you're just gigging, sub bass is not a factor, it's the tunes that count.

Sorry if I've got it all wrong...

Al

haldor 1st July 2002 11:38 PM

I suggest you try lurking on http://www.live-audio.com/ for a while. These folks really know PA gear plus there is killer sub construction project going on there as well. Warning, most posters make their living from PA work and can be short with newbies (downright savage with posers).

Beside the speakers, unless you are building horns (not an easy project for a newby) then the subs are going to take a lot of power to develop any real kick. Plan on 2400W amp power per pair of 18" drivers. That will set you back about $600 for an amp (I like the RMX2402 for budget, PLX2402 if you can afford it).

Don't consider car or home theater speakers for PA sub use. The requirements are very different, plus real PA speakers are much more efficient (more SPL per watt) than HT subs.

Phil

Brett 2nd July 2002 05:02 AM

<b>Warning, most posters make their living from PA work and can be short with newbies (downright savage with posers).</b>

I've suggested this forum to people before, and given them the same warning, but I was ignored and the posters were disembowelled.

For your own wellbeing, <b>do not mention you are an audiophile</b>. Lurk and learn, then ask sensible and thought out questions and you'll get valuable answers.

haldor 2nd July 2002 04:27 PM

Quote:

Originally posted by Brett
For your own wellbeing, <b>do not mention you are an audiophile</b>. Lurk and learn, then ask sensible and thought out questions and you'll get valuable answers.
Very good advice Brett. These are not the people to ask about directional wires or the audibility of different kinds of solder, but they are the right people to ask about how to do sound in larger venues at high SPL levels (clubs and concerts). They are passionate about what they do and $100K for a rig is not at all unusual.

Phil

poorbutproud 2nd July 2002 06:11 PM

Haldor, Brett, thanks for the site link and caveats.

Pinkmouse, here is a clarification:

I will be playing small venues with little or no PA and want some super low end for dance music oriented genre. It's basically a unit with myself playing drums and keys and sequences, an upright bass player and an electric bass player, and ocasionally a DJ. Suffice to say it's a cross between Drum n Bass and, well, drums and bass. If we play larger venues that have subs, then we of course won't need it. Right now though, living in the middle of nowhere and faced with tiny college eateries as our main venues, we want subs. The SRM 450s by themselves are enough to fill a small (>150 occ.) room, but they don't provide that thumping bass (Frequency Response +/- 3dB = 55Hz - 18kHz; Frequency Range (-10 dB) 45Hz - 20KHz).

Ideally I'm looking to build a single enclosure with single 18" speaker. I have seen designs that incorporate Helmholtz resonators to dampen the enclosure's natural vibration frequency, I don't think I need to get that involved unless so told by the people who know.

So to conclude, yes, I need it. And it's not for home use. It's for live rooms. I have no power amp currently, just a mixer. the SRM450's are Active.

It looks like this may not be the forum for me?

thanks again

pinkmouse 2nd July 2002 10:19 PM

Ok Poorbutproud, this may not be the ideal forum, but I think we can be of some help...

I don't know if it ever was published in the States, but Fane made a book of basic pa boxes to use with their drivers, and in it were several reasonable designs.

The one I know works quite well was what is known as a W bin, I think it had 2 x15 inch drivers firing into a common folded horn. It had a high effeciency and sounded quite good.

If you can track down the plans this may be the way to go, and it might even be posible to split the box in two and make 2 smaller bins, one for each side of the rig.

I belive each box could handle about 800w, which is about right to match the rest of your system

Sorry if I am a bit vague, but it was about 15 years ago that I built these boxes, and my memory is not what it was!

The other possibility is to look and see if the manufacturer of your main speakers makes a matching sub unit, although this could be more expensive, it will be made to match the rest of your system, and should perform better out of the box, so to speak, and will not require you to build an active crossover as well.

Good luck

Brett 3rd July 2002 06:55 AM

Hi Po',

I've got a couple of sub ideas for you. The first would be to visit <a href="http://www.btinternet.com/~speakerplans/sp/">Speakerplans</a> and specifically investigate the <a href="http://www.btinternet.com/~speakerplans/sp/page11.html">186 Horn</a> with an Omega pro 18. The drivers can be obtained at Speaker City or Parts Express for reasonable money. The designer, Rog Mogale, is very experienced at designing and installing rigs (look at the system pix on the site) and the 186 is a peach from what I've heard. Two a side, side-by-side, placed on the floor, especially near a wall will get you 45Hz @-3dB with 108dB efficiency. They are big, but so are many of the direct radiator boxes, and the horns will have a cleanliness (low distortion) and a <i>SNAP</i> to the sound DRs can't compete with. They don't look to hard to make either. Rog has other designs on the site you might like too.

Because of the damping the horn places on the driver cone due to better impedance match with the air, a driver in a horn can actually take a lot more power than it's rating would suggest. Tom Danley discusses this on the Live Audio LAB subwoofer board about 2 weeks ago IIRC. All of Toms and Mark Seaton's posts contain gold to be mined. Spend some time and read this.

http://www.prosoundweb.com/community/forum.php?board=3 (discussion)
http://www.prosoundweb.com/lsp/ (LAB plans and drawings)

A pair of these will eventually be my home subs. Live the Maxell ad!

I'll also second pinkmouses suggestion of the Fane book. Substitute drivers for the Fanes should be easy to find by studying the TS specs.

That should keep you busy for a while. Come back with more questions and we'll help further if possible.

HTH
Cheers

PS: the price Parts Express list for the Omegas isn't what they charge. Last quote I got was $US170 ea for 4. I'd build the 186's myself and add some EQ at the bottom for even more oompf at the bottom in smaller venues.

zoombies 7th July 2002 06:49 PM

Hi, Poorbutproud, I play drums and lately have taken an interest in electronic drum kits. Do you know of any links where I could find info. on making a MIDI drum brain and electronic drums. thanks.
oh, i do have a good bit of knowledge in building my own electronics, so pages with schematics, etc. would be of some use

poorbutproud 8th July 2002 05:31 AM

howdy zoombies, and other would-be-DIY e-drummers,

A couple people have written me about the DIY midi drum brain. There are a couple of places you can find schematics on the web, but I basically modded a kit available from PAiA

http://www.paia.com/midibrn.htm

They release their schematics for most of their basic circuit projects. I built the combination Drum Brain and Sensor Board. The Mods I made are basically:

1. taking the piezo disks off once I made sure all 8 channels worked

2. soldering 1/4" jacks onto leads from the board

3. building trigger drums with 1/4" output (still in process)

4. replacing the Power Supply (necessary)

5. Making my own custom enclosure.

I can take pix of the brain for you if you're interested.

A word of caution. This usage is about $180 USD all told. Plus, you have time invested in building and testing. It comes with no samples or output except MIDI, and that is nearly UNCONTROLLABLE at the board except for velocity/sensitivity adjustment via the peak-detect-and-buffer trimpots. I personally think that if you want to have samples of decent quality and aren't some Assembly programming / RS232 IC burner madman, then you need to just bite the bullet and buy a module. I'm using it in conjunction with a desktop at home to render samples on a 1.5 ms latency soundcard, and same with live shows (laptop). So for me, paying an extra $300 for four or five great sounding kits and a bunch of garbage drum sounds didn't make sense.

And I CERTAINLY didn't need to pay $3000 for the V-Drums and a drum brain that stopped at 50 kits & wouldn't let you even load samples!!!

Hope that helps, feel free to email me with further questions about the brain, custom e-drums, or requests for more detailed instructions / photos,

"poorbutproud" (I think you can see the concept behind this nick now ) :D


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