Subwoofer Phase

hku

What is the easy way to adjust the phase and polarity of a sub?

kuntasensei

Phase and polarity are related. Polarity is basically the positive/negative connections to the amplifier. For most subs with built-in amps, you don't have to worry about polarity at all. In my case, I run a passive SVS with an external rackmount amp. Also in my case, I get better integration with my other speakers by reversing the polarity at the amp (i.e. hooking the red wire to the black terminal and black to red). Even with passive subs, 90% of systems will still work best with polarity properly connected (i.e. red to red, black to black).

Now here's how the two relate: Phase is basically the same as controlling the polarity of the speaker, at least on a basic level. So on subwoofers that have a 0/180 phase switch, 0 = red to red and black to black and 180 = red to black and black to red. You're essentially reversing the polarity of the speaker. Where things get complicated is with variable phase controls, which can finely tune the phase of the subwoofer compared to that of your other speakers. Still, for the vast majority of setups, 0 degrees will be the best setting. Otherwise, you would basically need a RTA to determine if there's a better phase setting to mesh with your other speakers.

Now here's where things get complicated: The speaker distance/delay settings in your receiver also affect the phase correlation between your subwoofer and other speakers. To understand what I'm talking about, play a test tone near your left main's crossover point, then change the subwoofer distance in your AVR. As you bump it up and down, you may notice an increase or decrease in level as the subwoofer moves closer or further away from being in-phase with that speaker.

So the easy answer to your question is this: For the majority of setups, you should set phase to 0 degrees and ensure that the polarity of the subwoofer is correct (i.e. red to red, etc.). If you then set your speaker distances properly, odds are good that you'll end up with good settings for your system. If you then feel like tweaking, the ideal way to double-check that your subwoofer is in phase with the other speakers is to run frequency sweeps with a SPL meter and graph the results or use a RTA to check response near the crossover setting for each speaker.

If you have a receiver that uses Audyssey MultEQ XT and do the mic placement properly, you shouldn't have to worry too much. Audyssey not only ensures proper speaker distance settings, it also checks polarity of each speaker and adjusts its equalization in the time domain to help prevent phase cancellation/reversal on each channel.

Now... if you're talking checking phase with multiple subwoofers in the same room, that's a WAY longer story.

ls7z06

Good info. I have found Audessy does a good job but I always have to go back and correct for speaker size to small, cross over to 80Hz, and for some reason.... it always thinks my old DSW Pro 500 sub is much further away than it is, so I correct that too. Other than that, it seems to nail other speaker distances and level matching when checked with a SPL meter. And the equalizer settings seem fine as well. But the sub distance puzzles me. Sorry about jacking the thread.

kuntasensei

The speaker size issue is an Onkyo issue, not Audyssey. Audyssey asked Onkyo to make the threshold for "full range" 40Hz. Onkyo decided to use 80Hz. So if your speaker can go down to 80Hz (and most bookshelf speakers can), it calls them full range. Audyssey recommends setting them back to 80Hz after equalization, so you're good. If they detected as full range, Audyssey EQ'd them across the whole range, so when you change the crossover to 80Hz, your equalization will still be consistent.

As for the subwoofer distance: Audyssey detects acoustic distance, taking into account the entire signal chain. For instance, if you don't bypass the crossover or low pass filter on the subwoofer itself (or turn the crossover dial to its maximum), that can induce delay that will throw off the subwoofer distance reading. Also, if you have a subwoofer too close to a wall and are getting some resonance, the wall can mimic a passive radiator and throw off subwoofer distance (and frequency response, for that matter). If you read my above post, phase is very much related to the proper distance settings and the subwoofer's physical distance is often not quite the best distance to use for a good transition from speaker to sub across the crossover range. If your subwoofer is out of phase with your mains or has reversed polarity, Audyssey often adjusts subwoofer distance to compensate. That said, if it's several feet off, you might need to reevaluate your subwoofer placement and settings before trying another run-through, making sure that your sub is at least 3-6" from nearby walls and that you have the sub's crossover bypassed or turned to its maximum.

An additional issue is placing the mic too close to a room boundary during Audyssey's equalization, especially during the first position when it's doing all its distance/delay readings. The reflection off of the back wall can alter the reading such that it gives you a massively incorrect distance. Audyssey's a great tool, but it definitely involves some critical setup to get the most out of it.

w_coyote

I agree-good info, but what if you have dual subs and they are not the same distance from the lp. Does phase come into play here or does audyssey adjust for the difference

kawizx9r

w_coyote wrote: »

I agree-good info, but what if you have dual subs and they are not the same distance from the lp. Does phase come into play here or does audyssey adjust for the difference

If you have 2 different subs, thats something youd have to set up manually unless a receiver actually allows for the direct connection of 2 subs. You would manually have to adjust the phase switch so the subs and main speakers do not "compete and cancel" out each others bass frequencies. You'll hear a difference if you play with it, one setup will give you much stronger bass while if set in the other direction, will give you weaker bass because frequencies are being cancelled out.

kuntasensei

Audyssey will EQ around any cancellation/phase issues caused by dual subs and give you a good general equalization for the room (since it's using data from multiple points in the room). That said, it'd be more ideal to use a system that can handle each subwoofer independently, such as Audyssey and SVS' AS-EQ1. Still, as the previous poster said, it's best to get them lined up as much as possible using test tones on your own. That's why most dual sub users will either locate them next to each other or run them as stereo subs off of the main pre-outs.

Lancito

I have my Epik Sentinel working best with the phase switch at 180. It reduced my modal ringing significantly. However, I will be transferring my system to a different room. My question is, will the phase 180 still be the best setting for me? Or will the phase change because of the different room?

Any thoughts?

Thanks thanks!

danz1906

hku wrote: »

What is the easy way to adjust the phase and polarity of a sub?

Welcome to the Club!

kuntasensei

Lancito wrote: »

I have my Epik Sentinel working best with the phase switch at 180. It reduced my modal ringing significantly. However, I will be transferring my system to a different room. My question is, will the phase 180 still be the best setting for me? Or will the phase change because of the different room?

Any thoughts?

Thanks thanks!

The room has an effect, so you'll just have to find out. My SVS gets better response with phase reversed too.

TNRabbit

The phase can change if you even move the sub 1 foot.