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Dj's United

Andy Westcott

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Posts posted by Andy Westcott

  1. I can't believe this thread is still going.

     

    Most (all?) chassis amps arrive with no volume control - no problem, use the one on the mixer, that's what it's for. S/N ratios are of little cosequence these days - mixers no longer use nasty little 741 op amps and carbon resistors in the signal path.

     

    Burning a speaker out by under-powering it?

    So if I severely underpower one of my bass bins by attaching a portable CD player's output to it, the speaker will smoke like heck, yes?

     

    No, obviously.

    The RMS value of the vaveform supplied (The equivalent DC level which would produce the same heating effect) would have to be higher than the rate at which the speaker's voice coil could dissipate that heat produced, and given thermal inertia this could be quite a bit higher than the speaker's continuous rating for short periods.

     

    Flat-topping the waveform increases that heating effect, which is why heavy distortion might cause damage. Not the distortion itself, but the extra 'invisible' power you are pumping to the speakers.

     

    Worst of all, this clipping of the waveform can be cuased by an overdriven amp, an overdriven mixer or even be in the recorded music. Have a look at some waveforms from R&B pop crap - it might surprise you.

     

    Enough to make you afraid to turn on the PA system at all!

  2. My opinion?

    The disco shop owner should perhaps get himself educated in such matters in order that he will stop giving hideously incorrect and ill-founded advice.

     

    You can damage speakers by under-powering them, can you?

    So unless I run my amps at full output all the time I may burn out my speakers...

     

    It is as silly as it sounds, but still these obviously incorrect myths get repeated by those not in the know - I just wish they'd get on with selling stuff/playing music or whatever, rather than pretend to understand something they so obviously do not.

     

    Sorry - rant over! :D

  3. ...but I haven't seen any that are ten times the efficiency - the ones I have seen are, maybe, up to 10db/w/m better than a reflex bin.

     

    I still think I'm right, and you're wrong!! :)

     

    A 10dB power incease is precisely that - multiplying the power output by 10 - the definition of a Bel. 20dB is a hundred-fold increase and 30dB is a thousand-fold increase.

     

    I also think you may be confusing dB with bytes, looking at the strange figures you give, such as 1,024 and 8,192!

     

    Let's look at some figures slightly more representative of the real world than the ones you used:

    2 speaker cabinets, one having an efficiency of 97dB with 1 watt at 1 metre, and a horn outputting 107dB under the same conditions.

     

    It doesn't matter what power you put into the cabinets, the horn will remain 10dB above the reflex. (Power compression ignored here.)

     

    Therefore, reducing the input to the horn to 1/10 of a watt will cause it to output the same SPL as the reflex. It is 10 times more efficient as it requires 1/10 of the power to do the same job. The maths in this simplified example really is that simple. :)

     

    Happy New Year! :)

  4. Holiday?

    Can any of you really afford holidays??

     

    I went away to Cornwall with the brats last year which not only cost a lot, but there was then spending money plus 3 lost bookings I had to turn away as I wasn't going to be here.

     

    'Tiz an expensive thing to indulge in.

  5. Look - just give me the flamin' money.

    What I send it on is my business...

     

    OK - nice new QSC amps so I can run my speakers up to their full potential - when the need arises. And some new Martin lighting effects I could do with, as my current lighting is pretty old, tired and not entirely what I think I should be using.

     

    There - all gone. :(

  6. Good point, and yes, efficiency means a lot.

     

    However, any decent PA driver should be able to provide reasonable efficiency within its design frequency range, so to my mind the greatest contribution to a speaker's efficiency is the design of the cabinet.

     

    There are many different enclosure designs out there, but I group them into three broad groups:

    1. Sealed cabinets.

    2. Ported (tuned/reflex) cabinets, including bandpass.

    3. Horns.

     

    Sealed cabinets are rarely seen in bass enclosures for PA work simply because they are too inefficient, and the bulk of typical DJ-type bass speakers are of the ported design. These give a good compromise between cost, size and bass response.

     

    The most efficient, but also the largest are the horns - these can have efficiencies up to 10 times that of a typical cabinet, meaning that placing a ported cab and a bass horn side by side, the horn would only require one tenth of the power to produce the same volume output - brilliant!

     

    Just to get a taste of the 'big stuff', below is a diagram of a bass horn capable of floor-shaking response to below 30Hz - bear in mind it sits in a corner and is eight feet tall... !

     

    http://myweb.tiscali.co.uk/andyspatch/hosting/sensurround.gif

     

    Incidentally, tweeters and sometimes also midrange units are often horn designs in PA speakers.

  7. Just for the sake of argument, even if such a product did exist, there would be many regularly used tracks which wouldn't appear on there, as they never charted. Buy the tracks you can use is my advice.

     

    And I agree with the rest - this cannot be legal so don't even consider it. The quality would be guaranteed rubbish too, if you needed another reason.

  8. Same as Sandy - if short notice I get the client to sign at the venue. I always use a contract these days, as I feel it's the only way to ensure both the DJ & the client have the same details. That way mistakes shouldn't occur.

     

    As for deposits, I don't normally take one and so far this hasn't cuased any problems. If I started to get a lot of short notice cancellations I would review the situation, but for now everything's fine.

  9. Good advice, especially from Vokf.

    I take my teenage daughter along to parties like this mainly so she can discuss songs with the endless stream of kids. And once they find out what your name is, it gets even better! (Maybe introduce yourself to them!)

     

    As for High School Musical, the music is actually pretty poor and uninspiring, and most tracks sound the same, and I'm very pleased to announce I don't own anything from the films, and yet I do a lot of kids' parties - how do I manage?? I simply don't play it - no-one really seems to mind, and as mentioned, older kids do find it a bit naff anyhow.

     

    So - take along help, female if possible, play mainly modern stuff but be sure to take your oldies along too, and enjoy it! smile icon

  10. Yep - radial polishing only - that's the way I always understood it.

     

    A light scratch at right angles to the track only damages a portion as wide as the scratch itself which the interlaced nature of the CD, and the error correction can compensate for, but a scratch going round with the track may damage too much of the track for the system to cope with.

     

    As this thread is now 2 or 3 years old I'd better list my results:

    I did use T cut in the end, and a moderately damaged CD which played but with occasional glitches now plays OK, although a really badly gouged CD could not be repaired in this manner.

     

    Incidentally, the Skyfish/Rods rubbish is still being preached, although there are now plenty of sites debunking the idiots. Good to read for a laff though. :)

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