R/E/P => R/E/P Archives => Acoustics in Motion => Topic started by: jimmyjazz on April 25, 2010, 12:38:54 PM
Title: Subwoofer phase
Post by: jimmyjazz on April 25, 2010, 12:38:54 PM
I'm not really sure what forum to post this in, but I suppose this is as good as any. Can I get a little advice about integrating a subwoofer into my room, and specifically some advice about phase?
I am not high-passing my mains, and my sub has a 0/180 phase switch, along with the usual level and crossover pots. I did some crude amplitude measurements using a warble tone CD and (don't laugh) a sound level meter on my iphone (I said don't laugh), and to my ears, the "lumpier" response where the sub seems to be in phase with the mains sounds better than the "smoother" response where they appear to be out of phase. Of course, I have no access to phase plots, so I can't be sure what's going on, and I am fighting room modes, but regardless, I have slammed into my own glass ceiling when it comes to this topic. (I do have access to a very nice Level 1 Norsonic sound level meter, and I'll probably repeat my measurements with it, but I don't think it will change the question.)
So, is relative phase between a sub and mains often audible for reasons other than pure amplitude response? Am I missing something here?
Title: Re: Subwoofer phase
Post by: franman on April 25, 2010, 08:17:45 PM
"Generally" (and I use that term generally, as sub applications vary widely) you want to integrate the sub into the mains so there is the best add at the crossover point.. the best sum. Then you can adjust the level and eq on the sub to make for the proper extension if this is what you're looking for. Out of phase response (at the crossover point) will result in a deep notch which is typically not what the object is...
Of course this gets more complex when you have overlapping response between the mains and sub (such as your situation) and when you are making a true 4-way (or 3-way) system by adding the sub then the response of each component loudspeaker needs to be considered separately then the sum is examined to adjust the phase (or time) between the system elements. This is how we set up our larger systems, starting with the woofers typically and adding in the other bands while testing at the mix position.
Hope this helps in some way.
FM
Title: Re: Subwoofer phase
Post by: jimmyjazz on April 25, 2010, 08:55:58 PM
It does make sense, Francis. Of course, I have a million questions. Let's start here:
With the sub off, I see some excessive peaks and valleys in the mains response, and the frequencies (above their rolloff) all line up very well with axial modes. Would you suggest I start there when trying to find the "right" crossover point?
It seems silly to just randomly pick the crossover point without accounting for real-room response issues, but maybe I'm over-thinking it.
Title: Re: Subwoofer phase
Post by: martindale on April 25, 2010, 09:34:15 PM
JimmyJazz, I'd agree with Fran that "generally" you'd want the best add at the xover point---however, occasionally what looks best on an analyzer might not "sound" best to your ears---you say your room has some modal activity and you might "prefer" some bands slightly elevated, which could be the case with the sub "out of phase." I'm guessing your sub is not physically married to the mains, and you might try moving it even a few inches and you may have different activity. If you have access to a processor which allows for delays and/ or very sensitive eq adjustment, you can also adjust very small increments and see very profound results. Your mains may not need to be rolled off electronically but rather let them naturally roll off; then bring the sub in to "fill" where the mains roll off. However, I do suggest using a standard 80 HZ or 120 HZ point, as this jives with the way most professional systems are set up. If you would like to "look" at your response using some better equipment, PM me, I'm in Austin and we have some high end analysis equipment---and we keep a few film and video post houses tuned, so we're deep into the subwoofer thing. Getting subs to sit right with mains is tweaky and especially in some of our film rooms where we have several subs! .....we work hard getting the time alignment between all speakers correct.
Title: Re: Subwoofer phase
Post by: jimmyjazz on April 26, 2010, 11:23:35 AM
Thanks, martindale. Small world! A couple of comments:
-- you are correct, my sub is completely moveable relative to my mains
-- I am bringing in a new set of small "main" satellites in a couple of weeks, and this will all get repeated, so I'll wait until then to give you a shout and see if we need to get together. Can you PM your contact info?
Title: Re: Subwoofer phase
Post by: franman on April 28, 2010, 01:48:47 PM
Take it away Mark... (glad there's a convenient hookup there)...
FM
Title: Re: Subwoofer phase
Post by: Bill_Urick on April 28, 2010, 09:08:55 PM
jimmyjazz wrote on Sun, 25 April 2010 12:38
Subwoofer phase
I've been going through one of these for a couple of years now.
Title: Re: Subwoofer phase
Post by: jimmyjazz on April 30, 2010, 01:01:32 AM
Turns out Mark and I have several friends in common. I look forward to finally meeting him and having a local acoustics pro clear out some of my mental cobwebs! I'll report back once we get this room shot in (hopefully) a few weeks. Thanks, everyone.
Title: Re: Subwoofer phase
Post by: compasspnt on June 06, 2010, 08:42:31 PM
How has it turned out?
Any joy yet?
Title: Re: Subwoofer phase
Post by: jimmyjazz on June 06, 2010, 10:11:28 PM
Funny you should ask . . . I screwed around with that sub quite a bit, but really never got it to "play nice" with the mains. In the meantime, you might recall from another thread, I bought a Quad 909 amp. I liked it so much I bought a set of Quad 22L2 floor-standing loudspeakers, and while they're not ready for quite pipe organ material, they're absolutely fantastic on everything else -- and I don't need the sub.