Nissan Guy emailed me with how to tune polarity with an RTA so I thought others might be wondering what I was talking about. This is what I told him.

Well, you can't tell absolute polarity with an RTA. Let's make up a sample system to make it easier to explain.
1. CD H/U (doesn't matter which)
2. Active crossover with sub, midbass, mid and tweet output.
3. 3 amps, monoblock to the subs, 2 channel stereo to the midbass and 4 channel stereo to the mids and tweets so everything is crossed over actively.

To keep things simple there will be no overlap or underlap in this system. Crossover points of 80 hz from sub to midbass, 200 hz from midbass to mids and 3000 hz from mids to tweets.

Hook everything up and get the gains all set, ready to go?

Play pink noise over the system and look at the RTA. Is there a drop out at 80 hz only? Subs could be out of phase with midbass. Dropout at 80 hz and 200 hz, midbass is probably out of phase. Dropouts at 200 hz and 3000 hz could mean the mids need to have polarity reversed. And finally if the is just a dropout at 3000 hz your tweets could be out of phase with the mids.

Of course you could also have dropouts at 80 hz and 3000 hz, this could mean that yours subs and tweets are out of phase or it could mean that your midbass and mids are reversed at the measuring position. It can take some trial and error and just because there is a dropout at a crossover frequency doesn't always mean you can flip the positive and negative wires and see the desired results. But tuning like this with an RTA can't hurt.
Of course if any change makes it sound worse to you even though it looks good on an RTA put it to how it sounds best as an RTA can "lie".

First off, that's a great write up Dereck. I think it helps people conceptualize the effects of phase even without an RTA.

Second, I have been lied to by many RTAs. My current one is the best that I've ever used, and I'm still finding better ways of tuning by ear.

As for tuning absolute phase: I've got a graph that I should post showing 15 degree adjustments in delay between my midbass and subwoofer. For this I find an RTA does not lie.

Adam

absolute phase would require the use of no xover at all, otherwise it wouldnt be absolute phase, anything else would add phase anomalies of various degrees, unless the the xover is done is true digital

I have been told that absolute phase is basically just making sure all positives are hooked up to positive, and all negatives are hooked up to negative, which of course will usually lead to some speakers being out of phase at the listening position. Is that not correct? Anyways it really has no bearing on what I posted other than semantics.

Then would RTA not show this and then all you do is reverse the wiring on the terminals from where your Phase is out?

Just so people don't get confused:

Polarity is an electical term.

Phase is an acoustical term.

^^Old school Stereophile analogy.

Another way to break down phase and polarity is, Polarity is 0 or 180 degrees, phase can be 0 to 360. Polarity is generally affected by hooking the wires up right. Phase is determined by every piece of hardware that can shift it (passive crossovers for example) as well as the interior of the vehicle (due to speaker placement etc).

^^^Very good description Dereck!

I don't think that one can be improved any more, I'll call up Vance and have him put that in his next edition for ya!

(you'll get royalties, don't worry)

Adam

They are both electrical terms............

^ Phase angle is an electrical term and it is 0 to 360 degrees as stated
Polarity is electrical and it is 0 or 180 as stated
Phase is also an acoustical term and in conversations on the topic where you bounce between electrical and acoustical terms it is a decent way to bridge between acoustical and electrical topics.