Had a bit of a nightmare recently with unexplained feedback/bass rumble.

Rig is 2 x Mackie SRM450’s on tripods, 2 x flightcased Technics decks and 2 x i-pods running through a Vestax PMC170a mixer (leads from which goe through little box thing that I believe provides a balanced XLR cable to the speakers). Also mic plugged in but switched off with level right down.

All this kit was on a table with no padding/cushions or anything under decks and one speaker 6ft? to left in line with table and other in front again 6ft ish away from table.

When I soundchecked with i-pod running through and vinyl everything seemed fine but when I was eventually asked to play (at 10.45! * Student Ball) with need to get volume up this horrendous feedback type noise appeared. Result * had to shut down system for a short while and then finish night off with volume down and bass turned down a bit * embarassing for me and frustrating for champer fuelled up-for-it punters!

Problem I now have is how do I suss out what the cause of the feedback is as I can’t replicate these circumstances at home. My suspicion is that my mixer may be responsible in some way either in terms of a fault or I am not using the various trim, fader, master volume properly OR that the location/set-up of the rig is wrong. I don’t believe the decks or the speakers are the issue. Anyone got any ideas and suggestions about how I can investigate * basically I don’t want to risk turning up to a booking without feeling that I’ve got this sorted or at very least a few solutions I can try on the night whilst dj’ing. Do PA hire companies do ‘system tests’ or do you think I should just get the mixer looked at initially? Any advice welcomed.

You say you cant recreate this problem?

mmmmmm

Was it on every track you tried to play or one in particular?


Sounds to me like a earthing fault, Possible through the ipods at a guess, I had a similar thing many years ago, It turned out that the ipod's volume settings through the mixer/amp went all pete tong............

ill keep this short and sweet, your kit if fine....


the feedback is through your decks or a mic you left on, my money is on your decks because you could not isolate them from the sound system...

why are you playing vinyl anyway......

any club with a beefy sound system will have concrete pillars built for the decks... u can't do this on a mobile...

so think hard about how you setup, 6ft from ur speakers is way too close...

Sounds like acoustic feedback caused by the turntables.

Google "freefloat turntable" - £20 will get you a pair to solve your problem.

BK I think we get the message LOL

nik

Edit note:

BK Sounds' reply appeared four times but I've deleted the duplicates which now makes Niks reply look a little out of context

Thanks for this - would these work underneath a flightcase or would I be better off buying some foam?

Cheers

John

Ive used the floats and didnt find it helped in some locations...

its trail and error im sorry...

The floats have little circles where the decks feet sit in, theres some kind of ball inside the freefloat to isolate the deck, giving a reduction in bass rumble. Don think they would work to their full potential with a deck still inside its flightase........

Floating mats will help with the low conducted frequencies but if you're playing it that loud you may also get direct radiated coupling through the air. (like microphony).

I'd leave the vinyl at home as Marky says for mobile use unless you can plan your setup with feedback in mind each time (rarely possible), it's fine for installation..those DJ boxes aren't just plonked anywhere you know but are usually part of the design of the building if they expect vinyl performances.

Your problem is the flightcases. They stop the rubber mounted feet on the decks from doing their jobs as they put a nice piece of dense foam all the way round the deck, nicely transmitting the vibrations to the platter and needle. Taking your decks out of the cases would probably cure it, you're not packing a huge rig so the bass can't be excessive.

From experience, I'd say that the Freefloats are not an ideal solution, wobbly and prone to damage eventually (due to being inflatable).


Don't know if you've heard of A.S.S. soundsystems, but they used to make some serious speakers (now only doing very expensive hi-fi stuff) and Tony A.S.S. has developed some deck isolators for use in the most demanding nightclub environments. They are made of a composite sandwich and have been used to good effect by a number of the members of pro audio forums.

There's a thread here if you're interested, with pictures, and testimonies, and you can contact him via the forum if you like.

http://www.speakerplans.com/forum/forum_po...=14576&PN=1

P.S. I've got no commercial interest or links with these, but I've listened to and engineered on Tony's systems for a number of years, and have benefitted from his wealth of knowledge on a number of occassions, so thought I'd let you in on what he's offering our forum members.

Nothing wrong with using vinyl AT ALL...a decade or two ago, there was no choice.

It just causes feeback problems, that's all (if the vinyl deck is your problem which is probably is).

Your Technics should be OK....flightcase is the issue I expect as has been stated.

To replicate?

Set up at home, turn everything up as you would and open the turntable fader to 0db or whatever you have. All OK?

Turn down and put the needle on a record (no need to play it). Open the turntable fader slowly until you get feedback (if you do).

Let us know what happens.

Cheers to all for the advice - never used this forum before and it's been a godsend to be honest - probably saved me good money taking my kit to a PA company for testing etc.

Will try out suggestion of the 'home test' as soon as I can but bit confused by when you say 'you don't need to play it' - isn't it the actual music being played at the loud volume that causes the feedback or have I got the wrong end of the stick?

From what various people have said it seems that I need to stick to the following next time I play out:

- It's very unlikely that there is anything wrong with my kit (I did use it successfully a couple of weeks ago in smaller venue with flightcases on pillows - that time to avoid needles bouncing!)

- Take decks out of flightcases and put on isolator mats (have ordered the one's Norty has put me onto - Cheers for that)

- Keep the speakers as far away as possible from the decks and position forward of them (not in line of sight)

- Keep my mic unplugged completely from mixer unless using it

- On my rig don't take bookings where I think more than say 100 people will be dancing or it's in a room any bigger than a small school hall/typical medium size pub function room type

Are there any other basic rules on this I should apply? Also, with my rig is there a maximum distance between speakers I should be aware as far as dancefloor experience goes?

Thanks again for all your help.

John

Connecting everything and turing it up WITHOUT the needle on a record will probably not cause any feeback in normal cases.

As soon as you put the needle on a record (do this as stated in my post above - with everything turned down and slowly open the fader) will 'complete the circuit' as it were, as the needle is 'connected' to your flightcase/table/whatever to the floor to the speaker cabinets to the woofers and that = bass and that = a rumble at xx Hz.

Doesn't matter if you play records or not although you might as well test it with them playing as well (make sure your neighbors do not mind!).



Keeping your speakers as far away as possible is good for vinyl but you can run into other issues...if they are nearer the crowd and more of a distance away from you then you cannot get to them as easily if they were in front of your rig.

People playing around with them could happen...drink spillages etc.

Or in your case on stands...even near walls is not advisable.



That's like unplugging a CD player after it has been used and plugging it in again to cue a track. No need to unplug your microphone when not in use at a gig...simply close the microphone fader channel.



Expect the unexpected...that applies to everything.

Did anyone mention the Freefloat? lol

Sorry about the quad post, dunno what happened, maybe i was drunk, or something.

Oliver

Finally got round to the home test (been away for a while) and did what you suggested. Couldn't play the record at that 'peak' volume due to room size, my eardrums etc but when just the needle was on the record there didn't seem to be any feedback. It did however alert me to the sensitivity of the deck itself as just knocking it made a big noise! Do you think this means that it was maybe the vibrations of the bass when the tune was playing that caused the feedback or are there any other tests I could do?

Thanks again for your help.

John

Could have been vibrations of bass.

And yes...put the needle on a record and tap the deck anywhere..it will make a noise wherever you tap it.

Usually though, putting the needle on a record and turning everything up will help with isolation problems but again all comes down to acoustics and layout of speakers/room.

Use a concrete block!

Been offline for nearly a month due to moving house/isp.

So, have the isolators from Tony arrived, and what do you think of them if they have? I've heard lots of good things about them from other users but as this is a different forum I'm interested to hear your comments

Isolators have arrived and look good but haven't had a chance to use yet - will try and remember to give some feedback on this forum when I have. Cheers