phase shift control on amp

[huggybear77]

I have a 2 channel 2 ohm stable amp rated @ 200w driving 2 SVC 4 ohm 10" each rated @ 180w (all peak ratings). The amp has all the standard controls, x-overs, low/high pass, bass boost, etc. and one that I have a basic understading of, phase shift w/ a range of 0 to 180 degrees. I currently have it set @ 180 based only on what I think sounds cleanest. I am looking for an in depth definition of the concept of phase shift. I know that it has to do w/ sub positioning, and space in the vehicle. Due to the relatively low power of both the amp and subs (wired in parallel w/ the gain set @ about 3/4 , bass boost minimal, set on low pass dialed in @ 35 hz running off sub preouts. the box is 2'6"x1'3"x1'6" and is ported. The subs are facing the rear in a mid sized S10 Chevy Blazer. Based on the info I've given I would really appreciate any input I could get on this.

[spitvalveV2.0]

phase is basically the position of the wave. Concerning a sine wave, we have amplitude and frequency, which we all understand very well. We also have phase, which affects performance when combining waves. If we had two identical sine waves, with one 180 degrees out of phase, we flatline the response. We call that "destructive interferrence." You can experiment with this yourself, actually. try flipping the polarity of just one subwoofer in your car. leave the other normal. See how the bass response drops like a rock? phase!

now, the 0/180 degree switch is basically your polarity switch. Say your bass wave starts by pushing the cone out, then in, and repeat. flipping the switch will effectively make the cones pulls the cone in as its first motion, rather than push out.

Why does this matter? The bonehead explanation is that phase can induce a mild time delay. We use phase in the car to compensate for unequal speaker pathlengths, such as the difference in distance between the drivers side midrange and the psasenger side midrange. But the subwoofer can also play a factor as well! your subwoofer has to mesh with your soundstage every bit as much as your tweeters must mesh with your midranges! disjointed phase (at the driver's ear, and this distinction is important!) can lead to disjointed sound. in the case of your car, putting the amp at 180 rather than zero resulted in a flatter phase response at the drivers seat in that region.

you would find that if you had a knob rather than a switch, you could improve the sound even more :)

[huggybear77]

I mustve misled you, all the controls are knobs. I have the phase turned to 180, because the lows seem to hit harder from where I sit in the rig. Other than the gain, I have all the knobs either @ all the way down, or all the way up based on sound, alone. My question now is, am I damaging the subs by having the phase dialed into 180? I'll take your advice and try different degrees of the phase, thnx

[Greg200SE-R]

Is that a DLS amp?

If you're gonna play around with the phase control, do it from the driver's seat - either position the amp so you can reach it, or have someone else adjust it slowly. each turn of the phase knob will change the sound for a given location, so sit in your usual place and find the best setting. If your deck has a 0/180 phase switch, then trying both will give you more range to play with... Within reason, correct phase will ideally make your sub-bass mesh with your midbass speakers better, and all bass notes will carry a more crisp impact. Great for SQ.

For SPL people, adjustable phase will make little difference outside the car.