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

diyAudio Moderator Emeritus
2002-04-03 7:15 pm
Rotherham, England
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
 
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

Member
2002-01-07 6:02 pm
<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.
 
Brett said:
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
 
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

diyAudio Moderator Emeritus
2002-04-03 7:15 pm
Rotherham, England
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

Member
2002-01-07 6:02 pm
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

Member
2002-05-30 9:49 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
 
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
 
Oh BTW thanks pinkmouse, haldor, and Brett for your great starters! I was very very surprised to see the experts at LAB recommending a 12" driver instead of a 15 or even 18 for lowest frequency response with best power. Also, I did a search for "Fane" on the web plus a few other variables, and got a lot more resources for design and building than I was finding previously.
 
Hi poorbutproud,

I know what you mean about the 12" drivers for the LAB sub. That's horn design for you, sort of a "everything you know is wrong" experiance for me. I trust Tom Danly knows what he is talking about (he is the chief designer for ServoDrive and they make the best subs on the planet). If you are talking about a ported box (or direct radiator) then the bigger the better, but a horn is very different. Just like a 2" horn mid/tweater will crank out an amazing amount of inband sound, while a 2" direct speaker would be barely audible.

Working from memory the LAB has usable output down to around 30 Hz, which is plenty low enough for live sound reinforcement. I use the 30 Hz high pass filter in my sub amp to prevent shreading the driver cones when the kick drum mic gets bumped or dropped.

Phil
 
I second that, The bigger the better in your situation. A 12" would be flopping all over the place.

Poor? Go with Eminence. They have a few 18" models worth buying from $75 (yes, I said worth buying) to about 200. I would get the Sigma model. I think partsexpress has it for 160 ish. Put that In a 5 or 6 (maybe smaller) cubic foot box (for god's sake use plywood, not mdf!!!!) and brace the hell out of it. As far as amps go, ask somebody else.

Leave the top or a side removable and you could sleep in it.

If you get the $75 dollar model, do stereo subs!!!!
here is link$75 Eminence CAST FRAME!!
-andy
 
bostarob said:
I second that, The bigger the better in your situation. A 12" would be flopping all over the place. -andy

Hi bostarob,

If you were talking about the typical HT sealed or vented 12" sub I would agree with you but you really should to take a look at what the LABHORN project is about before making statements like that.

http://www.prosoundweb.com/community/forum.php?board=3

The LABHORN is an very serious PRO subwoofer being hosted as a DIY project on the Live Audio Board. The principle designer is Thomas Danley of Servo Drive (this guy is the preeminent sub designer on the planet, if you haven't heard of Danley or Servo Drive then you need to educate yourself on what is happening in subwoofer technology), take a look at http://www.servodrive.com/servo/bt7.shtml if you want to see something else that Danley has designed.

Eminence has developed a custom 12" driver for use in this project called the LAB12, here is a picture of the driver
http://www.prosoundweb.com/lsp/customdriver1.jpeg.

Each sub uses a pair of these drivers. A pair of these 12" drivers will push more air than any 18" and do it with less distortion and cone breakup (much faster bass too).

4 of these subs (they are designed to be used in groups of 4) will deliver 147 dB @ 1 Meter from 28 Hz to 100 Hz and require 1/4 the power that direct radiating subs would require to get the same SPL). Flopping is not a term I would use to descibe this subwoofer. Bass that will pin you to the back wall of the arena is more like it. If you were to buy subs like the Labhorn from a commercial vendor they would probably set you back around $3K to $4K each.

Phil
 

Brett

Member
2002-01-07 6:02 pm
Well said Phil. You saved me typing out basically the same thing.

It seems some people just don't get how superior horns are in this sort of application, and just how different they are from DR's. But once you've experienced it, it's not soon forgotten. The generousity of Tom and Mark in doing this project at all is amazing.

I'm building a pair of LABs for my living room: EQ'd flat to 20Hz and placed as per Mark's suggestions, I don't think I'll need to upgrade again for a while.:D Flat against the rear walls, and painted the same semi-gloss white, they'll hardly take up any room and blend in well.

Cheers
 

Brett

Member
2002-01-07 6:02 pm
bostarob said:
Well, I guess I am a big dummy. With number as impressive as that, I will need to look into those horns.

But, this is a budget project.
The projected sales price of the LAB drivers is between $US150-250. Numbers aren't settled yet as they aren't in-store as I type, but they will be within the next month.

For a pair of LABs (4 drivers), you would only need about 6 sheets of 2400mm x 1200mm (8' x 4') of quality ply per enclosure. If you are able to DIY, then even at max price the project comes in under poorbutproud's budget.

Mark Seaton has also suggested the Adire DPL12 as a substitute for deeper bass, lower peak SPL applications. Read all about it here
http://www.prosoundweb.com/community/read.php?board=3&id=144164

The 186 horns from speakerplans would cost similar money to the LABs, for 4 enclosures. They are smaller, so are easier to move, depending on what size vehicle you have. If you have a truck, the LABs may even be better in some ways as they are designed to fit within standard truck pack dimensions.

Cheers
Brett
 
Where can one learn about horn theory and design?

I apologize for previously being too hasty in my relpies...

Those LAB drivers look very expensive (impressive!)

Why foam surrounds!? http://www.prosoundweb.com/lsp/customdriver2.jpeg]Pic II[/URL] Eminence is priced well, but I couldn't imagine a speaker like that selling for much under $300. Wouldn't it be cheaper to build the 186 with an 18"?

Poor also stated that he wants one enclosure. I don't know if that statement still stands.
-andy
 
Excellent responses, all.

I am definitely willing to build two enclosures, I had just *assumed* (ha, ha) that I didn't need to do so for small venues.

My rationale was that a single sub would be sufficient for driving my volume until I realized a need for additional reinforcement above my SRM450 pair. This is especially true in my opinion, because the lower range is much less directional (depending where you cut it). I guess I could budget up to a $400 setup for two drivers, a crossover and an amp. Forget about the plywood/finishing cost, it's free to me :D

Yes, the specs on the LAB project are awesome.
I see Eminence speakers for it are shipping now at +/- $150 for the initial shipment. If I can find an amp which matches them (totally clueless there at the moment, need to read more) and a crossover system (maybe I build my own bandpass circuit eh?)
then I'll be set!

For others who are curious like me, I found this for different eclosure shapes:

http://www-user.uni-bremen.de/~carnivor/horn/hornfolds.html

BTW I checked the prices on the two ServoDrive lines, being curious about the mechanical nature of their amplification... whoohoo!! that stuff is for "stadium." I'll be back to them *after* I get a recording contract! heh.

Anyone who can tell me just how to match amplifiers to speakers based on specs, I'd appreciate it.

thanks loads, poorbutproud