300 people, 1 square room, 1 confused DJ

[DJ_Ghost]

Hi all, my first post here and I apologise for the ignorant questions I am about to ask. I’ve been looking in the FAQ for the last hour and a half and haven’t quite found the answers I’m looking for, so if they are there and I missed them, I apologise in advance for being dense.

 

 

Okay, I’m a DJ and need to set up a PA for a DJ (not a band or choir or so on) in a room with a standing capacity of 300. I’m awaiting the data for an exact size of eh room, but from memory I estimate it to be about 20m long and 10 or 15 wide. It is mostly square with remarkably good acoustics.

 

 

In the past we have found our current PA has been sufficient for the room when half to ¾ full, however we are looking for an ideal PA set up when full, since we are looking to spend some profit.

 

 

Now we have the basics (mixing desk, twin cd decks etc..) so we are aiming to upgrade our amplification and speakers. I’ve spent 2 days looking up amps and speakers and what we might need and I’m no closer to knowing.

 

 

I’ve had advice to aim for 10 w per person, but that gives us a figure of 3000w or 3kw, which seems excessive, given that up to now we have been using a 600w amp for rooms half that size with no complaints and plenty of headroom.

 

 

I found a page in the FAQ that suggested a useful base for calculations would be;-

 

 

 

Base4d on a speaker sensitivity of 1w 1m 100mb

100dB @ 1m

94dB @ 2m

88dB @ 4m

82dB @ 8m

76dB @ 16m

 

Adding 6 db for every doubling of the wattage (to rms max, obviously) and subtract 4 db for each doubling of metres.

 

 

I must be missing a variable here because that gives me a figure of 8 watts, which can’t be right.

 

 

Please help me out here, my eyes are going square and my head is pounding from staring at the screen.

 

 

I am leaning towards about 1200w amp and appropriate speakers, but can’t actually give any logical reason other than it “feels about right” which is not exactly how I like to work.

 

 

Sorry for the message length.

[Rob_Beech]

3dB is a doubling of volume. To get this we theoretically need to double the power. However in practice we stumble across inefficiencies such as loss down longer cables and more so, power being dissipated as heat in drivers.

 

However, a perceived doubling of volume is between 6dB and 10dB. To increase by 10dB we need to multiply the power by 10. So a system that we perceive as twice as loud could be 10 times the power of another system. By now you should start to see why you may get figures that seem ridiculous.

 

That all said, your figures are incorrect.

 

When we double the power we get a 3dB increase in SPL (before we take loss via heat and other methods into account).

 

When we double the distance we lose 6dB in SPL. so your SPL figures are correct, but you quoted it wrong.

 

giving a number of watts per person is 100% pointless. It gives you NO information whatsoever. Whoever told you that, I would refrain from taking any more advice from them. Seems harsh but it's true.

 

If a box has a sensitivity of 100dB 1w/m if we put 10watts into it we should theoretically get 110dB. at 16 metres (which is near the back of your room) you should with 1 box only and no people in the way get (all in theory) around 86dB. In fairness this is probably loud enough for people at the back as they're the ones likely to not want to dance to that particular song.

 

So yes, 10watts will do it. for all the people. But of course, in practise this doesn't work. If we want to double the volume again we need 100 watts. double again and we need 1000 watts. (perceived volume).

 

And then we need to look at headroom. With program material with no dynamic range we can use a 10watt amplifier. Where we have a dynamic range, the DJ's announcements may require 20dB of headroom above the average level of the music. And instantly we're looking at 1000watts into that speaker. Or 2 Speakers with 500watts each into them.

 

All in all, it's what you do with it that counts. The more efficient a speaker is the louder it will be for a given input power in watts. It will normally dissipate less in heat aswell making it more efficient still when you give it lots to think about. They also tend to be very expensive.

 

If your current system normally does the job and you just have a few gigs per year where you think you need more. Why not hire a larger system from a local hire company.

[DJ_Ghost]

However, a perceived doubling of volume is between 6dB and 10dB. To increase by 10dB we need to multiply the power by 10. So a system that we perceive as twice as loud could be 10 times the power of another system. By now you should start to see why you may get figures that seem ridiculous.

 

Ah yes of course, thank you , now it is all falling into place.

 

giving a number of watts per person is 100% pointless. It gives you NO information whatsoever. Whoever told you that, I would refrain from taking any more advice from them. Seems harsh but it's true. [/qote]

 

Actualy that does not sound harsh to me at all. I had a strong feeling it was useless info when I got it.

 

[qote]

If your current system normally does the job and you just have a few gigs per year where you think you need more. Why not hire a larger system from a local hire company.

 

Ah, this is what we usualy do, but as we get more and more popular we are finding we are doing more and more capacity gigs, we are now at the point where it is no longer cost efficient to hire for the bigger gigs, there being so many of 'em.

 

Thanks for your advice, it is much aprecaited.

 

Ghost

[Killyp]

Rob's word is basically gospel - you almost always need what seems like a huge increase in 'watts' to get any useful increase in volume, hence why watts shouldn't really be used as a way of measuring a system's capable output.

 

As for improving your current system, a budget would be useful. Simply adding in a pair of bass bins can add a huge amount of headroom to a system as the low frequencies gobble up most of the headroom of a system way before mids/top frequencies do.

[smalljoshua]

What equipment (Make/Model) are your current speakers/amps?

 

What is your budget?

 

What is your time frame?

 

Josh

[Sound In Gloucestershire]

also what type of music? big difference between cheese and drum n bass!

[DJ_Ghost]

Cheers for the help lads,

 

 

Okay budget is in the region of £1000 or so. I'd love to get away with spending more like £400 but I'm realistic and don't expect to be able to.

 

Ideal time frame is about 3 months or so.

 

We do have a lot of contacts with places that give us very good discounts and get what we ask for very quickly. No idea how that came about, something to do with one of the lads who edits our magazine.

 

Music type is punk, post punk and Goth.

 

 

Current equipment is;-

 

 

Amps

 

1 Warrior 600, 2 channel amp

 

With a back up amp we usually use as a spare being a skytec 2 channel, sorry I can’t recall its model as it is currently on loan to a friend for practicing. I’m not that impressed with it but it was bought in an emergency when we blew an amp with 30 minutes to go to a gig and it was all the local DJ stores had in stock so it was that or cancel.

 

 

Speakers

 

That’s harder to answer than you might think, as a musician friend of mine built them after we loaned the old ones to a band who promptly blew the cones.

 

All I know is they are rated 400w each (RMS), are 8ohm impedance two way speakers. 1w 1m 100db

 

 

We also have a matched pair of Soundlab 300w RMS, 8 ohm impedance, not sure of the w/m/db on them as I don’t have them handy (They are currently set up in a small venue ready for tomorrow). They have been a lot better than we initially expected and give a surprisingly clear and crisp sound but are not as reliable as we would like (I’ve had to effect repairs on them 4 times so far).

 

They do seem to get a better performance from the Skytec amp than any other speaker we have treid with it.

 

We’ve a set of emergency back ups that are 300w RMS 8ohm 3 way speakers of uncertain make and model supposedly with 1w 1m 100db but seem to out perform all other models of similar spec that I’ve used in volume, clarity and reliability.

 

 

Sorry about the vagaries,

 

 

 

We don’t usually use bass bins, as the type of music we play seems to sound terrible with too much bass and bass bins have always given us a dreadfully bassy sound. I’m uncertain as to whether this is just that all the bass bins we have had demoed are poor or not though.

 

 

Mixer;

Mixer is a KAM GMX 5 Pro, 4 channel plus one master, which I’ve currently got set up in my radio studio.

 

 

Microphones

 

We have dozens but tend to prefer our two Sure PG58s both for DJ announcements and radio presenting. Local bands keep asking to borrow them as well, so I guess they must be half decent.

 

 

Cables et al,

 

You name it and we have about a half dozen or more, most technical failures we have ever had have been cables so now we don’t take any chances.

 

Other,

 

Oddly we have about a half dozen DI boxes. Not something you often see DJs need but we do occasionally need to lend them to bands and we got a good deal on a batch. I have my suspicions that one of the lads was thinking of assembling a band PA, since he picked up a 12 channel FOH mixer at the same time, and has occasionally done some small band set ups in pubs and so on.

[The Boogie Man]

Looking at your gear list a couple of ideas spring to mind before you rush off to buy a whole new rig.

You could set your second set of cabs further down the hall as "delays" (as your a disco, sorry is that what they're still called) your point source isn't as crucial as with a band.

 

 

If you have added subs before, but either with no xover or on the same channel from your dj desk, that may be why they didn't sound good. You have a mixer, try running a set from a different out on that, or use a cheap berry xover to get control of the different freqs.

 

just my 2p

[Rob_Beech]

Of course if you did this you'd require a unit to delay these speakers and separate amplifier channels to do this. It would mean fairly long speaker cable runs too. I try and use powered boxes when I'm doing THIS type of delay.

[stagemanagement]

If you decide to run "delays", as suggested, then a DBX Driverack will act as a crossover for adding bassbins, will give you a bit of EQ for putting across the system AND allow you to delay a couple of the "outs" for the speakers halfway down your rooms.

Brand new, you'll get one for around £300; second hand, you might get one for half that.

 

It'll also allow you to store presets, so if you're using a few local venues regularly you will be able to recall the preset for that venue after the first few gigs - meaning a slightly faster setup time! :D

 

It'll also let you put a bit a bit of limiting on the systems for protecting your speakers from the people who borrow them and bring them back broken! :)

[Rob_Beech]

It'll also rip your HF drivers to bits if you take the power from it unintentionally of power trips and you use amps that don't mute the outputs on power off (RMX series are an example of a none budget amp that do this).

 

If you really must EVER own a piece of equipment from a manufacturer who refuses to add a few pence to production costs to save people hundreds of pounds in blown diaphrams then let it be the 260. Failing that, the Behringer DCX2496 is a cheaper option, its a better unit too and contrary to popular completely blind and misguided and often arrogant belief, it won't break on you within 8 seconds of opening the box.

 

 

Rob

[smalljoshua]

Feel free to recommend a Driverack but don't recommend a Driverack PA. Have a search on here for reasons why. If the OP feels the need to get a cheap LMS (Loudspeaker Management System) then have a good look at the Behringer DCX2496.

 

Josh

 

Edit: Crosspost with Rob

[stagemanagement]

It'll also rip your HF drivers to bits if you take the power from it unintentionally of power trips and you use amps that don't mute the outputs on power off (RMX series are an example of a none budget amp that do this).

 

If you really must EVER own a piece of equipment from a manufacturer who refuses to add a few pence to production costs to save people hundreds of pounds in blown diaphrams then let it be the 260. Failing that, the Behringer DCX2496 is a cheaper option, its a better unit too and contrary to popular completely blind and misguided and often arrogant belief, it won't break on you within 8 seconds of opening the box.

 

 

Rob

 

Fair play Rob, I forgot not everyone uses them with Macro's and the like!

But I've never known them to break - if somone's knicked all the MX5's or XTA's then I use it when our nasty BSS Omni decides to stop working mid-gig.....again!

 

N.B - This is just OUR Omni that does this, not an issue )that I know of) with BSS Omni's

[DJ_Ghost]

You have a mixer, try running a set from a different out on that,

just my 2p

 

This prompts the question - Why did this not occure to me before. :)

 

I did mention I'm an idiot right?

 

One day I may tell you about the whole day I once wasted trying to figure out a solution to getting a decent microphone level for my interent radio show out of a computer Mic before realsiing if I just plugged my proper vocal Mic into my mixer and pluged the mixer into my sound card I could use that instead of a PC Mic, and I could then also use two Pro twin Cd players, giving me the ability to cue 4 CDs at once instead of trying to play MP3s off my hard drive. :D

 

Still, having figured that out my radio shows improved imensly overnight.

 

Edit to add;- Apparently the "in term" now is "party" for some reason. I think I prefer "Disco", "party" makes you think aunty Jane might show up and chat up your best mate after one too many gins.

 

Ghost

[sleah]

2p's worth.

 

Looking at the kit you have, that you are clearly happy with, then £1000 is going to get you a lot.

I'd suggest a system in the region of 2kRMS will do nicely, either instead of the current one, or along side it.

Already mentioned, look at Behringers offerings for amps. For speakers take a look at Class-D, they would fill your needs very well, at a reasonable cost.

In fact, why not talk to Class-D for a complete amp/speaker package?

 

This is they: http://www.classd.ltd.uk

 

You've really gotten yourself bogged down with figures. Someone speccing a west end musical or stadium gig needs to consider numbers to that detail, but you don't - at all!!

There are so many variables - even the height of the speakers just as significant as the number of watts, if a speaker is at an angle to the other it will make a difference, put a bass (or full range) cab in the wrong place and you'll loose a lot of bass.

 

For what you are doing (and indeed myself) the market is saturated with gear that is more than adequate and will give pleasing results for next to no money.

 

You've certainly come to the right place for advice!