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Feedback issues at loud volume with full bass

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valve head777 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote valve head777 Quote  Post ReplyReply Direct Link To This Post Posted: 30 November 2017 at 12:20am
In my experience, mid feedback is arm based, low frequency feedback moves the whole deck. Quite rare for mid to effect deck tho. Was wondering if a medium delay (1-2ms)/between deck and mixer/preamp would have a positive effect. Obviously this doesn't work with mixing, but in the context of the op's use......?
Another idea would be to use an out of phase signal feeding a small speaker near the deck. Better if the phase angle could be manipulated to adjust for room nodes etc. Just a thought....
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Darkstar Quote  Post ReplyReply Direct Link To This Post Posted: 30 November 2017 at 1:20am
There is a club in my area which has one of the worst "everything" for vinyls:

- Two meter deep walls, they are also made out of fossil stones
- Literally underground, this makes the stone wet as well
- Bass is hard to control for reasons both above and below
- Console deck is right in front of audio stack
- Console is also tilted down on X axis from performer point of view, not really good for vinyls
- Audio stack consists in 2x2.18" BR and 2x2.15"+2" BR cabinets, hall is 14sq.m only
- Roof is a stone arch getting narrower towards the sound system, which is placed is flat to the wall
- There's more, but I'll stop here as it's getting silly.

People tried and failed at playing vinyl there and I almost believed there was no way out, however all it took was for someone to walk in with two specifically designed foam-rubber risers. These were matching the console deck's angle perfectly, isolating the turntables from vibration and were glued to a sturdy wooden plank with huge cloth pads underneath.
These did the job, however I think it worked so well because the problem was mainly caused by vibrations rather than sonic interference. That is either correct or it solved both issues at once.

Speakers were also placed to minimize movement of the tonearms: stack each side of the performer with the furthest bass driver being not more than a meter far from the decks, tops on top of the subs were aimed so that there's no direct sound towards the source. Mono stack would be heaps better, but wouldn't be practical for matters of space. Embarrassed

Edited by Darkstar - 30 November 2017 at 1:24am
Bass =/= Enough
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Post Options Post Options   Thanks (0) Thanks(0)   Quote charlysays Quote  Post ReplyReply Direct Link To This Post Posted: 30 November 2017 at 10:37am
Originally posted by toastyghost toastyghost wrote:

There are experimental tools that try to do this sort of thing but - latency, linear actuation and so on are very large problems in the way.

Dampening and using a surface that doesn’t transfer energy in the first place is a lot easier. Airborne problems occur at really daft levels but then you can design a cardioid array or similar to minimise it. Again this is always location dependent and on temporary setups you’re not likely to have time.
 
I think that was the issue I had in my nightmare venue.
Place was quite small with lots of pointless low partition walls. Upstairs so everything made of wood/ plaster board.
Whichever way we tried setting the subs up the bass would batter the DJ booth- to get good bass pressure on the dancefloor the DJ would always be getting battered.
Even after hanging the decks from the ceiling with slabs of foam underneath them there was airborne low sub feedback. Totally did my nut in!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 30 November 2017 at 5:28pm
Originally posted by valve head777 valve head777 wrote:


Another idea would be to use an out of phase signal feeding a small speaker near the deck. Better if the phase angle could be manipulated to adjust for room nodes etc. Just a thought....

OH. Butt kicker - those things drummers put in their stools - installed under deck table, fed from a DSP, to provide suitably phase shifted signal? Or is that just going to provide another set of problems?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 30 November 2017 at 8:12pm
Originally posted by studio45 studio45 wrote:

Originally posted by valve head777 valve head777 wrote:


Another idea would be to use an out of phase signal feeding a small speaker near the deck. Better if the phase angle could be manipulated to adjust for room nodes etc. Just a thought....


OH. Butt kicker - those things drummers put in their stools - installed under deck table, fed from a DSP, to provide suitably phase shifted signal? Or is that just going to provide another set of problems?


Not a broad enough range and impact isn’t what you want. You need a sub capable of matching the SPL at the deck position. In a club we have done this in, that was a dual 15” reflex box.

It’s not as simply as inverting polarity either. It took many hours of delay, filter and all pass tuning to get a result that works. Even then we still had to rebuild the entire booth out of concrete too.

Note that hope works doesn’t have vinyl issues with Tony’s isolators since we convinced Liam to remount the breezeblock supports and pour a solid concrete top.

Edited by toastyghost - 30 November 2017 at 8:14pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote valve head777 Quote  Post ReplyReply Direct Link To This Post Posted: 30 November 2017 at 9:52pm
AA very simplified idea, I know it's not as simple as reversing the phase of a monitor speaker......
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Xoc1 Quote  Post ReplyReply Direct Link To This Post Posted: 01 December 2017 at 11:27pm
If you have a hifi turntable and you want the best from it you would probably invest in a wall mounted turntable shelf - The wall would be a supporting wall so would be rigid as it would be compressed by weight.
Thats probably impractical for a DJ, as who wants to face a wall! So first thing to do is find the most rigid floor area to mount the turntable. Easy if you are in a basement with a solid floor - On upper floors there will probably be areas with rigid beams underneath - these will vibrate less than the floors spanning the beams. Then you want to interface the turntable to the floor with a column. This could be a brick pier It could be a column made of steel, It could even be a 50 gallon drum full of sand.
You want to isolate the column from any surrounding panels thay could transmit vibration back to the deck.
The whole thing can be capped with stone / concrete slabs. 3 point supports for the slab can help reduce vibration as they give good stability - isolating mounts can be effective up to a point but any direct air vibration to the turntable will have no way to dissapate. Bit like numpty DJs who leave the lids on the decks.
Big blocks of foam usually sound crap - but are usually found in situations where the turntable mounting / booth was terrible anyway.
All sounds like a lot of hassle but back in the pre digital days when turntables were the only thing, this would often be the difference between a dance club that was sucessful, and one that was just just another place that sold beer.
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