Originally Posted by yacht422
How do we handle two subs using this procedure? One on, and one off?
And, if the subs are at very different distances from the listening position, should not the distance for each be handled individually, per test?
i.e. If the left sub is 16' from prime, set this distance in D2, and test per outline. Then, for the sub on the right, which is 20' from prime, set that distance in the D2, and proceed as per outline.(after turning off the left side sub)
1. I assume the subs are in their optimal positions as well. With subs on opposite sides of the room, set the phase knob of one to 0 and the other to 180 or whatever angle gives you the best frequency response using "Quick Measure". Afterwards, then for each individual sub, set level to 72-73dB if you have 2 subs for a combined 75dB or so. The math isn't precise in the real world so 2 subs set at 72dB will not necessarily produce s combined 75dB, but its close enough anyways
2. Reverse the polarity of the LF speaker. All other speakers MUST be disconnected. You need to listen only to the 2-subs and LF speaker only.
3. Have a variable (external) frequency source that you'll use to vary the frequency over several values around the xover ferquency. If its 80Hz, then i'd take measurements every 5 Hz starting from 60Hz and up to 100Hz.
4. For each test frequency and (with RS meter in hand), vary the sub distance setting until you read a minimum SPL value on the RS meter. Make sure its the minimum by varying the distance around it in 0.5ft increments. You should be able to notice a rise in SPL reading as you go beyond or before the minimal point.
If, for example, the distance to get a maximum null is 8 feet, you'll also get another null at 16 ft, 24ft etc. Thus value is a function of your room dimensions. Please note these values down as you go!
5. Repeat steps 3 & 4 for the next frequency.
You can tabulate the data as i have in my simple attachment. Note that the term "1st NULL" refers to the initial distances i got the null. The term "2nd NULL". To decide which NULL column to use, I choose the one where the dataset had the least variance for all frequencies used in this test. Once i decided on the colum of data to use (2nd NULL in my case), i then computed the average distance from that column and then used that as the new distance value in the "Subwoofer Distance" setting menu.
In my case, it was 31 ft, yet the actual physical distance from my sub to my listening position is 12 feet. The two do NOT have to match. Th is OK. Folks who use Audessey are familiar with this as well.
6. Reverse the LF speaker polarity to normal (!!!)
and re-connect the rest of your speakers to the amplifier.
7. Enjoy some deep bass LFE music/movies. This procedure is well worth the effort in all cases, imho. The bass sounds amazing and the subs seamlessly integrate well with the mains
Speaker Phase Calculations.zip 8.056640625k . file