This i food for thought
Let’s start first with 2 channel speaker listening. Basically what we hear is the sum of the response from each speaker. The sound is distributed in the recording so as to sum in the middle of the two speakers. That’s how recordings are made. When we put two speakers in a room we thus then invisibly divide the room along a line that runs perpendicular between the speakers. This is where the sound from the two speakers sums. If you sit anywhere on that line, you get a fairly balanced left-right image of the sound. You also are dividing the room into two sound pressure zones, left and right, each zone being pressurized by the speaker in that part of the room. Now, sound (air) pressure is what the speaker driver creates. This is what then vibrates the eardrum and what the brain interprets as sound. You won’t find much mention, or at least I haven’t, about sound (air) pressure in audio writings, so hope you understand what I am referring to here, as it’s vital to understanding Master Set.
Thus, we have a situation where the right speaker is filling the right part of the room with sound pressure, and the left speaker is filling the left part of the room with sound pressure. And the sound pressures meet in the middle. If only one speaker is playing, it will fill the whole room with sound, and you instantly recognize that all sound is coming from that one sound source. But with both speakers playing you are recognizing that the sound is coming from the middle of the two sound sources.
Now, the two parts of the room will invariably be different, in size, shape, and reflective and/or absorptive properties. One part of the room will be larger than the other, even if only by a very small amount, though it is theoretically possible for the two parts to be perfectly alike down to a decimal point or two, in practise this is not too likely to occur. Anyway, this larger part of the room will require slightly more sound pressure than the smaller part of the room in order for the sound to sum perfectly in the middle as designed.
Remember, each speaker is playing at exactly the same level from the amplifier, and should be equally balanced in signal level. These equal power levels are then put into the room, and the larger area needs just a little more sound pressure to equally fill the area with the other part of the room.
I hope this is not confusing anybody, but I think that it is a different concept from the common audio thought, or at least it was to me.
Anyway, you then must adjust one of the speakers to be louder in order for the sound pressure in each part of the room to be equal and perfectly sum in the middle. This is what Master Set does, and why each speaker is set individually in the room and in relation to the other speaker. In the end, you have one speaker slightly closer to the rear wall than the other one. Room gain will give the closer speaker slightly more sound pressure to fill the slightly larger area.
When the sound pressure is equal in both parts of the room, then the sound will sum perfectly in the middle creating a single source of sound. And because of the equal sound pressure levels anywhere in the room, the sound will be virtually the same anywhere in the room.
That is what is being done with Master Set.
Some points about Master Set:
The long wall in the room works best. Remember, the room is invisibly divided by the two speakers. Dividing along the long wall gives a more square shape and the sound will more evenly fill the space without reflecting off the walls. Dividing along the short wall gives a long narrow shape that will be very subject to wall reflections. BUT, if the room dimensions are fairly close, you can set up along either wall without too much difficulty.
Listener should sit at least a foot away from a wall. You can get some sound bounce off a wall if you sit too close. But you don’t have to move too far away from a wall.
The equal sound pressure throughout the room usually negates any need for room treatment or correction. Experience will tell you about this, once you listen. I’ve seen little to no correction in the Master Set rooms that were done professionally.
You will be able to sit anywhere in the room with the sound only differing in perspective, like changing seats in symphony hall, or any concert venue.
The steps of Master Set are analogous to those of focusing binoculars:
- Adjust lens to one’s head/set speakers apart in room for good centered sound.
- Focus the fixed lens on the object/set the “anchor” speaker in the spot of smoothest bass
- Focus the adjustable lens to match the fixed lens/set the other speaker to match the bass level of the “anchor” speaker.
The hardest part about doing DIY Master Set is listening to the bass line and hearing the plonky, unevenness, and then finding the spot that mitigates this. This is usually not easy to hear, and will test your patience. However, you can just guess with this. But it makes it a lot harder to find the matching level with the other speaker, as the bass mitigation spot does give you a reference point to match.
Master Set is a close to rear wall set, rather than a set up way out in the room.
In the first step, you move one speaker out until all sound is heard from just that one speaker. There is then a small area of 5 or 6 inches where this occurs. If you move the speaker out farther, it reconnects with the other speaker. This small area is where the moved speaker disconnects from both the rear wall and the other speaker. It’s setting is independent of both. I can only say that this is desireable, and a tenet of Master Set, but I can explain no more.
Obviously, the speakers could be set anywhere in the room and you could somehow match the sound pressure levels as described above. But it would be hard, and a real trial and error process, but you could do it, and have very good sound.
Master Set will allow you to fully hear what your system is capable of doing. It’s a great way to evaluate your system. Music tends to sound better with Master Set so you tend to find that you’ve got a better music system than you thought, and that’s always a plus.
I hope all of this helps, and that I have not confused anyone.
Steve
