Let's build some scoops!
Yup, it's amazing what you can knock together with an old washing up liquid bottle and some sticky-backed plastic, so why not take a break from building that Warhammer Blood Marine battle fortress and try some of these bad boys instead!?... Paul C. the US Distributor of Saxrax products takes us on a short guided tour, complete with pictures and plans so you can build some of these scoops too!...
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Jan 2008 - This dancetech site has alot of sections, thousands of pages, but this pa section gets well over a million hits a year - almost all those visits are from new people - If you would like to add any type of article or video on building cabs or anything like that to do with PA or live gigging tech or lighting etc you get links to your company or site or whatever... this whole sections due for a re-write tbh, but on with the show anyway...
(the following text/section was written/started back in '97 or '98 and added to from time to time)
PA SYSTEMS INTROWell here we are.....PA is short for 'Public Address System', and comes originally from army bases, and factories/plants etc, before the advent of amplified gigs & clubs.Incidently, just a bit of historical stuff here: The first amplified rock concert given in the UK was by Tommy Steele believe it or not !!....er....
PA systems can be as simple as a mixer going into a pair of powered speaker cabs, all the way up to sodding great 100.000 watt modular systems. Whatever the system, the end desired result is to get the sound to the listener at an even level wherever they are positioned in the venue.
Speaker cabinets are designed to provide the loudest and most balanced sound for a given amplifier input, and utilise different designs to do this depending on the cabinets intended job. Matching the speakers to the cabinet volume & resonance is one criteria, and cabinet design can cause the outgoing sound to be dispersed widely at a short distance for venues such as a small club, or to project the sound a long distance, such as when one wishes to project a sound to the center and back of a large concert hall or venue. Getting the right cabinet design & positioning makes all the difference.
Ok.... In a big venue, obviously the requirements for a PA sound system are going to be different to that of a system in a small club, even though the volume may actually be higher in the club in proportion to the system used by the large venue.
Above, is a picture of a typical large venue system. The main PA contains the Bass stacks... As you probably know, bass sounds are omni-directional, we dont really percieve them as coming from a directional source as much as higher frequencies... So the bass bins radiate bass out and around the venue....
The lower & upper mid-range stacks, and tweeter/treble units in the main PA are 'LONG-THROW'... designed to penetrate to the back of the hall as well as possible... but this can leave a dead spot around the center, so to re-inforce the signal at the back & center of the hall, overhead 'Flyers' of mid-range & treble/tweeter units are 'Flown' above the main PA angled downward... These units' cabinets and treble units are of a 'SHORT-THROW' design, and fill out the sound nicely, creating a reasonable balance throughout the venue !
For smaller live venues the main PA would be comprised of soley 'Short-Throw' units... Medium venues would be well covered by a mix of Long & Short-throw units.
On this picture, you can see a typical club efficient system....The bass-bins pump out bass to the floor, whilst the top end and mid-range is handled by 'Flown' units suspended around the dance-floor. Treble end frequencies are easily absorbed by soft matter such as humans !!... so by flying the top-end units above the floor angled downward, and then balancing the mix between Bass and Mid/Treble end with an active cross-over or graphic, you can keep the music crisp and pumping. I have to say, that this is an art not too difficult to achieve, yet it seems to elude alot of club owners..... The amount of times my friggin' ears get wrecked by over-the-top treble ended systems really shags me off.....which is why I'm usually dancing somewhere around the back or sides of the main dance-floor, or right up front with my head in the bass-bins....in fact, anywhere to escape the horrible sizzling, ear-frying treble !!
As I said above....Higher frequencies are more directional, and become more so the higher you go... The directional characteristics of a sound is known as the 'BEAM' as for a car head-light... and Tweeters are the most directional of all.
'Bullet' tweeters give great projection over distances, but have a very narrow conical 'Beam'... You can use 'Slot' Tweeters as an alternative, which give much greater width of dispersion, but don't carry the treble sound very far.
Horizontal dispersion with 'Bullet' tweeters (Conical H.F pattern 'Long-Throw')
Horizontal dispersion using 'Slot' tweeters (Broadbeam HF pattern 'Short-Throw')
DIFFERENT CABINETS-TYPES OR 'ENCLOSURES'Ok... outside of the odd mega-complex design theories out there, most cabinets or 'Enclosures' fall into 3 basic types:
- SEALED BOX (infinate Baffle)
- TUNED REFLEX
- HORN LOADED
SEALED BOX / INFINATE BAFFLEThe simplest of all, being a straight.....er....sealed box !!....Just like your average hi-fi speaker. Because there is no way for the air behind the speaker to escape, this design offers the greatest 'damping' effect on the back of the speaker cone. This can be good to get the most out of the speakers power handling, but usually bottom end bass-response is lower than with other designs.... So to build a bassy sealed-unit requires a damned big box !!!
REFLEX ENCLOSUREOk.....these units add an open port or vent to allow air to escape from inside the box....The size of the port is critical to the 'Tuning' of the system. What you get with a reflex design, is greater bass from smaller box sizes, so this technique is often used by small hi-fi manufacturers to get some 'Oooomph' into the bottom end of their speakers.
HORN LOADEDThese units are used for bass and bottom mid only, there are various designs such as the 'W' Bin......and they are all extremely complicated to design.....but basically, the inside of the cabinet contains chambers and tunnels, often combined with reverse mounted or angle-mounted drivers, designed to 'Throw' the bass out over distances. They are used where good high-frequency extended bass response and excellent directivity is required for large venues.
So... That's a few basics... To build up your own system, it's probably best to begin with 'Full-Range' modular cabinets... 'Full-Range' means the cabinets contain Bass, Mid & Treble speaker units, kinda like a massive hi-fi speaker... you can multiply these as you expand by simply lining them up side by side... All you need to go with the Left & Right cabs is a decent stereo power amp, say between 250 & 500 watts per channel, and your decks & mixer !!
If you want to expand further from there, you can add dedicated bass-bins, and switch to a 'Bi-Amped' system.
BI-AMP SYSTEMRight... Bi-amping.... nope, it ain't an amp that likes to shag other amps of both genders!... It simply means you split the signal coming from the mixer into 2 frequency ranges..
Bass / Lower-mid & Upper-mid / - AND - Treble... simple huh?... Most hi-fi type & nearfield type speakers with a bass/mid & treble tweeter split off the treble to the tweeter at around 10K.....but how d'you do that?.... Well, you need to use a cross-over unit.
CROSS-OVERSOk... There are two types of cross-over - Passive & Active - both types split the incoming signal into component parts of different frequencies according to the units design and intended use. The cross-over allows the frequencies in a full-range incoming signal to be distributed to the correct type of speaker that can utilise the signal best by operating within it's intended bandwidth.
The other function of the cross-over, is to protect against speaker damage that can occur when low frequencies are fed to midrange & treble units.
PASSIVEA passive cross-over, is the type as you have inside your hi-fi speakers. It is a bunch of electrical components mounted on a curcuit-board that need NO power supply.
ACTIVEAn active cross-over is an electronic device, (usually rack-mounting), which is connected between the mixer & power amps. The frequency spectrum is split before it is amplified, and each loudspeaker recieves it's own correct bandwidth of sound delivered by it's own dedicated amp.
Ok... Crossover points are to an extent determined by the speaker cabinet design, but are mainly influenced by the type and design of speakers used.... But here are the usual cross-over frequency ranges for the various typical system...
|2 way system||bass to treble||3 kHz - 5 kHz|
|3 way system|| bass to mid
mid to treble
| 500 Hz - 1.5 kHz
3 kHz - 5 kHz
|4 way system|| bass to low-mid
low-mid to mid
mid to treble
| 200 Hz - 400 Hz|
800 Hz - 1.5 kHz
3 kHz - 5 kHz
|super-tweeter||-||5 kHz - 10 kHz|
ROLL YER OWN!Oh yes!... Cos what you really want to know is...."How do I make one?"... correct?... Well, the cabinet plans at the top right of this page is some stuff just for you i scanned from an old Fane book I got at a car-boot sale for 50p... I have added a plan for a basic 'Full-Range' enclosure that can be used to build a cool system. All you have to do is build 2 of these babies to get off the ground... You can then upgrade by building another pair so you have 4 cabinets in total... One pair with a decent stereo power amp should be plenty fine for some serious party sounds, then just add more units... Each cabinet can be made from one sheet of 8' X 4' timber... So before you click for the plans, read this page about construction methods. I've done alot of wood & construction stuff, even a few studio's, the notes & construction tips are taken from my own woodworking experience based on looking at the plans.
Lastly I'd like to add... I'm not an acoustic's 'tech-bot'... These may not be 'State-of-The-Art' etc... 'latest design technology' etc... but that aint the essence of any TRUE 'Dance' music vibe to me... For me it ALL comes from squat-parties & warehouse-parties, house-parties, sounds, community-center jams, street-jams, small clubs etc etc... These boxes follow the fixed laws of acoustics well enuff for that scene... they just aint like for your Tina-Turner concert tho !!...
So I just thought these plans would be useful to bang up some boxes of a weekend for those kinda activities... When we were starting we had like some crappy 200 watt DJ-unit with speakers ting... big but crappy with an amp... we thought it was superb, you could blast anyones cheezy hi-fi away for parties, so you get asked to do parties endlessly!! :-) .. THAT is the whole flippin idea of having a little sound!... serious... some people start off at school or college with a few crappy but LOUD boxes they knocked up, and play parties after parties, and in a few years they are doing a club etc... Thinking back, I can remember the sound of that system we had... it was well off, and boxxy as hell !!, but it had BASS & THUMP!!... & it was loud!
Boxes like the ones in the plans on this page will make are a BIG step up from that sort of cheap 'disco' kit we used to play parties with... and in quantity, adding units together, these designs can fuel a decent sound just fine; well up to playing house-parties, smaller-clubs & warehouse gigs etc... and when you go to those sort of gigs this is the sort of boxes you hear :-)
CLICK HERE FOR IMPORTANT CONSTRUCTION TIPS
We'd like to see more use of the PA/Gigging/Live forum for questions and chatting, so we're adding in a Link here 'cos we just realised there is no link in the PA-Section (*sigh*)
There's so little PA resources on the www, so feel free to join the forum and lets try and build it up - With our forums you can add file-attachments to forum posts if you are registered, so plans or pictures etc can be added with posts!!
Alternatively, leave some user comments on this page via the form below...
'PA page for noobs'
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Each page contains a downloadable plan as a gif image, sized to print-out onto an A4 page.
EASY BASS CAB FOR 15"/18" BASS - (single or double!!)
[Kindly supplied by Celestion uk]
[also can build as 10"/12"/15"/18" + tweeter for full-range]