Phase/crossover in subs (1 Viewer)

[carl_b_byrne]

I hope someone can clear this up for me. I do not understand the use of a phase control on a subwoofer. I did do a search in the sub/speaker forum but could not find a satisfactory answer. Is it essential? My little sub doesn't have one, but i the future I will upgrade. Also, can somebody give me a 2 dollar version of crossover. DOes it basically mean the point where the sub takes all bass (ie if set at 70 hz, the sub will play only sounds 70 hz and below?)

Thanks muchly

 

[Wayne A. Pflughaupt]

Carl,

First, welcome to the Forum!

I’ll answer your second question first. Yes, simply put the crossover is what determines what frequency the sub will start to play. A 70Hz point means it handles everything from 70Hz and below. Sub crossovers are also known as “low pass filters.” In other words, they only let the lows through to the sub.

At the same time, the rest of the speakers need a “high pass filter” to allow everything but the lows to go to them. Typically the receiver can do this with its speakers set to “small” in the menu.

Regarding phase, it’s basically a time-delay adjustment. The situation is that the sub is typically in a different place than the mains – like in a corner – so its signal reaches your ears at a different time than the mains do. This results in irregular bass response. Many subs have only two phase settings – 0 and 180 degrees. But as you can see, the best phase adjustment will be one that’s continuously variable.

Regards,
Wayne A. Pflughaupt

 

[Cees Alons]

Carl,

Yes, that's basically what the crossover frequency is. Of course it's not a "switch", i.e. at that frequency about equal amounts of sound go to the sub and to the original channel. But above it, the sub quickly gets less and below it (as quickly) more.

The phase switch lets you change the phase . See it like this: a speaker driver's cone has to move in and out periodically to make a sound wave. When two different speakers - let's assume they get exactly the same signal - are "in phase", they move out and in together. When they are "not in phase", one moves in exactly while the other moves out (and vice-versa). That's not economic, because when one driver tries to higher the pressure in your room, the other tries to lower it! The'd better be "in phase"!

You can change that by changing the two wires on one of the drivers, but that's a bit difficult on a sub, because you generally use the line-in level and not speaker-level connections. You would have to change all the other speakers (assuming they are mutually in phase).

That's why they have a phase switch on more expensive subs: so you can switch it until you feel your bass is loudest.

The problem isn't as dramatic as I painted above, because in practice the other speakers DON'T get the same bass-signal as the sub!


Cees