Subwoofer phase is a pretty simple concept in speaker/sub integration, but it is often overlooked by people starting out. Typically a subwoofer has either a phase switch (often labeled with either 0/180 or normal/reverse settings) or a phase knob (which allows more granular control of the phase).
This is sometimes misunderstood because the idea of a crossover point is viewed as a ‘brickwall’ or an immediate hand-off from the speakers to the subwoofer at that frequency. In reality, there is a fairly wide range where the speakers and sub overlap.
The basic concept is for the speakers and subwoofer(s) to be working together in this overlap area instead of fighting each other (constructive versus destructive interference to use physics terms). This is accomplished by adjusting the phase (and possibly position) of the subwoofer to get it in sync with the main speakers (in a purely home theater setup, an argument can be made that coordination with the center speaker is more important).
Below are two graphs showing the frequency response in my home theater with my Hsu VTF-2 sub and Ascend Acoustics CBM-170 mains using the 0 degree and 180 degree phase settings. In this example, the 180 degree setting results in a pretty flat response (close to +/-2db from 20Hz to 130Hz), but the 0 degree setting has a very large drop (greater than 15db) in the crossover range.
180 degree phase setting (click to enlarge):
0 degree phase setting (click to enlarge):
Measurements using standard setup at position 3 in room diagram.
I’m finally getting around to putting down some more notes on the AV123 get together earlier this month. Here is a summary of the equipment present and some comments:
Theater room:
Mains: Rocket RS1000
Center: Rocket RSC200
Surrounds: Rocket RS850
Rears: Rocket RS550
Subs: 2x Rocket UFW-12
Pre/pro: Emotiva LMC-1
Amp: Emotiva LPA-1
Sources: Denon 2910 and Onix CD-2 w and w/o Perpetual Technologies P-1A
Etc: R-DES parametric EQ on subs, plasma display, Panamax power
I assisted Dave Tremblay, the inventor of R-DES, with measurement during the sub EQ process using the setup listed earlier here.
Multichannel audio room:
Mains: Onix Reference 3
Center: Onix Reference 100
Surrounds: Onix Reference 1.5
Sub: Rocket UFW-12
Pre/pro: Emotiva DCM-1
Amp: Emotiva MPS-1
Source: Denon 2910
Etc: R-DES parametric EQ, Panamax power
Smaller theater room:
Mains: ELT LRS with PBS powered woofer stands
Center: ELT center SE
Rears: ELT DPA dipoles
Sub: ELT SW-10SE
Receiver/source: Pioneer combo
Etc: 30″ LCD TV
Two channel room:
Mains: Rocket RS760 and XLS (Onix Reference 1.5 for a period of time)
Integrated amp: Onix/Melody SP3 and Onix X-empower beta unit
Source: Onix XCD-88 and Onix XCD-99
This room got a LOT of attention because both speakers are new, the SP3 is a popular item at the moment, the X-empower is new, the XCD-99 is new, and the designer of both the RS760 and XLS (Danny Ritchie from GR Research) was in the room discussing the speakers.
Static display:
Rocket RS850 in piano gloss rosewood finish
Strata Mini speakers
Onix Reference 1 and Onix/Melody SP3
Rocket UFW-10
Onix CD-2
Emotiva DMC-1 based receiver (using D2Audio amp module)
Emotiva BPA-1 two-channel, bridgable amp
Audio Protien rack
One of the focuses of the GTG, SOCS and MMK for the Perpetual Technologies P1-A, was not really on display, but there were multiple sessions to demonstrate the measurement technique, discuss the SOCS corrections, and demonstrate the difference SOCS makes in playback.
