Originally Posted by Craig John
Level matching has the inherent problems of room acoustics and distance from the measuring position influencing the settings. In other words, if one sub is further away from the measurement location than the other, it's level will be set higher.
Gain matching two subwoofers at different location points will yield dissimilar output levels so you'll still
have to set the one higher than the other.....robbing dynamics and headroom.
The other option, is, of course, using the acoustics to benefit the situation, because after all, it's free output. Using identical levels means that
A) You'll achieve better coupling
B) Less distortion.....even though two subwoofers may be spaced at weird distances in relation to each other, the coupling achieved when properly level matched will bring about lower levels of harmonic distortion.
So even though you might think that whatever free output you're gaining is void due to the gain level differential, you're actual gaining more than you realize. More so then just putting both gain knobs to the same level.
B) Not everyone has their subwoofers positioned in awkward dissimilar locations, so in the event that two subwoofers are spaced a few meters apart, coupling will be easy to achieve and the benefits are threesome (hmm...)
1) Woofer modulation effects will be reduced
2) Once matched in phase and in level will result in a 5-6 dB output improvement across the frequency band that falls to within 1/4 wavelength
3) Those that don't understand 1/4 wavelength sound wave summation, please read my explanation on that......it's somewhere in the archives...look for it....
4)It's just cool.
So basically, you have two subs, and you want to gain match them. Set both in the center of the room.....set both 6" away from the cone......then turn the gain knob to the same level........
But comb-filtering can effect the levels...even to within 1 inch ! Nevermind that one, I misspoke.
Then, it won't have as much headroom as the other sub.
Setting identical gain levels will yield different output levels if both subwoofers are located in different locations so if you want to compensate then you'll adjust the gain...O
...and ONCE AGAIN you'll end up with more distortion, reduced dynamics...
When combined, the higher-set sub will peak before the lower-set sub. You'll either be overloading the higher-set sub or under-utilizing the lower-set sub.
Or......Or...you'll end up with dissimilar output levels if both subs are evenly gain matched and both subs are in different locations...which means :A)
Each sub will have different proportionate SPL levels per location even though both subs are achieving the same amount of work required, their net SPL will be dissimilar....B)
A disproportionate amount of SPL per sub is not always a good thing. Oh no. Because if you measure your frequency response with two subwoofers, one achieving 80 dB's and the other measuring 75 dB's due to dissimilar locations but equal workload (because that's the great thing about gain matching, you've got equal workload power between both subs right ?) but...well, the levels will be offfffff.
So let me poke and prode...and change the gain just a tad, to equalize the levels.. Ooops...now I've just added 35.3% harmonic distortion products to the table because I've compensated for the distance irregularities.