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Sweet Spot Expander

Preserving your stereo image.
(+2, -2)
  [vote for,

Sorry for the long-winded post. If you read it all the way through I’ll post a quickie next time, promise!

Stereo is a clever trick, using two speakers to fool your ears into thinking there is a soundstage in front of you with musicians placed at various points between. Problem is, it only really works in the ‘sweet spot’, centered around the apex of an equilateral triangle formed by your head and the two speakers so that the speakers are phase aligned and at the same volume level. Outside of that space the illusion collapses and sound appears to come from two separate speakers. The sweet spot extends back a fair way, but is extremely intolerant of side to side movement, which causes real problems when monitoring music in a studio, especially when mixing.

Nearfield monitors (ie small accurate speakers – IT types: you can stop thinking of screens now) which are used for mixing in 99% of situations, tend to be mounted on top or immediately behind the mixing desk, forming an equilateral triangle with your head. This gives you an accurate stereo image so long as you sit dead centre behind the desk, but as soon as you move to one end or the other (and studio desks tend to be around 2-4m long) you end up in front of one speaker or the other. If you move to the extreme left end (usually where the drums are) you will find yourself in front of the left monitor and everything positioned hard left in the mix will jump in level, anything positioned hard right will virtually disappear. You cannot work on balancing the mix from this position, which leads to sore legs as you scoot the wheely chair up and down the desk, or sore arms and neck as you try to keep your head in the sweet spot and operate the knobs down one end at the same time. Shorter engineers do not have the second option.

It would be a simple matter to build a small signal processing unit that could compensate for the changes in level and phase– just turn down the left channel and delay it slightly as you move left and vice versa, dynamically moving the sweet spot up and down the desk. However, the unit would have to lock on to the position of your ears to know how to react and compensate appropriately. Ultrasound transceivers on top the monitors could triangulate the position of your head, but would most likely confuse the engineer’s head with that of the producer / guitarist / hanger-on, so I would suggest instead a pressure sensitive strip that resides in the foam padding below the faders. The engineer will usually rest his wrists here or at least touch this at the point where he is working and will provide a pretty good fix on where his head is.

Voila, an accurate monitoring position that moves with you while you work.

wagster, Dec 07 2004


       I'm not on a subject I'm good with here, so ignore me if this is stupid, but I take it that using headphones wouldn't work?
david_scothern, Dec 07 2004

       // across a large table littered with knobs?//   

       Anne Summers party?
skinflaps, Dec 07 2004

       or a cabinet meeting.
etherman, Dec 07 2004

       [DS] - Unfortunately headphones sound different to speakers, primarily because when you listen to speakers you are hearing a mixture of the recorded sound and the reflected sound bouncing off the walls of the room (reverb). Headphones give you a much more accurate rendering of what is on tape: pure sound with no reverb, but speakers give you a much more accurate rendering of what the average listener hears when listening to the music from a pair of speakers. Monitoring is a complex and much argued-over subject, but it is generally agreed that when mixing music (contemporary at least) you should usually be listening on an accurate representation of what the average listener hears.   

       [Tabs] - Actually on top of a mixing desk is acoustically one of the worst places to place speakers due to the sound bouncing straight up at you from the metal desk surface. There was a plan once to design a virtual mixing desk using VR gloves and goggles in an acoustically 'perfect' room. I may post this here some time.
wagster, Dec 07 2004

       Why calibrate the triangulation to the wrist rest on the desk when a specially modded collander (or, for the faint at heart, hat) could be used for the same purpose? Would a wireless signal to the triang. system disrupt the sound from the speakers?
calum, Dec 07 2004

       This would work too. As would wireless deely boppers.
wagster, Dec 07 2004

       There's also a low-tech solution to this.   

       Wear a hat with two strings attached (four strings if needing quadrophonic control) - the strings are tethered to pulleys on each speaker box and the rotation of each pulley controls its speaker volume - pull away from a speaker and the volume is boosted, while the volume of the speaker you move towards is softened. The required sensitivity of control is simply a matter of gearing.
ConsulFlaminicus, Dec 07 2004

       [Consul] - This could also solve the final piece of the puzzle that I did not address for fear of 'doing a Vernon', the problem of off-axis response. The frequency response of a speaker changes as you move off axis, so this system would really work best if the monitors swivelled around to follow your head. I was thinking of silent electric motors, but now I think your string technique could be adapted to achieve the same effect. Maybe the speakers could be mounted on their own volume knobs and attached to your head with elastic so that they could swivel to face you and control their own level at the same time. Eyes painted in the middle of the drivers would also give the impression that they were watching you work.
wagster, Dec 08 2004

       Personally I think daves comment is more to the point and I can see your objections to it are valid.   

       It seems to me that if you wore "really big lounge shaped" head phones then your motion would be automatically tracked wherever you go and you get the sort of distortion found by the average listener...
madness, Dec 08 2004

       I used to do some custom installation and maintaining work in film recording studios. Put a infra red LED 360 degree emitter on your head or on each ear. Put a IR detector at each end of the board and let that signal go through 339 comparators to drive different amp/speaker/phase channels. Five average positions for sound mixer/dashing instant date for female client aftermix dinners, on the board = five channels each side.
mensmaximus, Jan 12 2005


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