Subwoofer Phasing: A noob question...

hondahirny

Okay folks, my first post on here. First of all, I must comment on the hilarity of all the posts i've perused by TUnit. I know a guy that sells Amsoil, so he loved the Amsoil cardboard sub....

I'm looking for an education on the phasing of audio signals in a car setup. I've been running my HU and 4 speakers for some time in my Civic. Recently, i've finally had the funds to drop in a sub. What did i get, Polk, of course. I've been loving my MMC690 6x9's. They're the speakers that made me a Polk customer. So, getting on to the sub...

I purchased a c300.2 and two db804 8" subs. They're designed for 0.35 cu ft each in a sealed box. I made mine a dual 0.4 cu ft, trying to account for the displacement of the woofer. I hooked up my amp and speaker wiring, following all the polarities. I mounted the box with the speakers facing and only inches from the fold-down back seat. I did this so i can haul heavy objects in the trunk without worrying about hurting the subs. With the seats down, the woofers sounded decent. By "decent" i mean that i heard clean bass, but rather little punch. I tweaked my gains and it still seemed like i really had to beat on them to feel and hear any bass. With the back seat up, which is what i really want, they could hardly be heard or felt. I would tweak the sub level on my HU and i could barely tell the difference in the sound between the subs up and down. This was even when i knew i was approaching the Xmax rating on the woofers. I was starting to think Honda put Dynamat in the back seat!

Anywho, i got the idea (from reading posts on here about component speakers) to try and reverse the polarity. I reversed only one woofer and heard a huge improvement. I then reversed the 2nd woofer and the wonder of my "new" sound was incredible. I can now listen to all kinds of music and can really tell the difference with the subs on/off. When i play some hip hop, those little guys produce excellent "feel" as well as audible sound. Even with relatively little woofer movement (far below rated Xmax), i can really hear the bass, even with my back seats in their fully upright and locked position. So whether it's a little Ice Cube or Charlie Daniels Band, these babies are rockin! Not bad for 300W.

As an additional "experiment" i hooked up only one of the db804's bridged on the amp. In that single speaker config, the polarity seemed to make no difference in the sound. Both polarities sounded good.

So, with the subs facing the back seat in a sealed box, was I getting some odd phase cancellation? Sorry for writing such a long post, but i wanted to be detailed in what i did and i'm hoping the replies I get are educational to everyone. I'd like to know about what considerations are needer in regards to phase/polarity in a multi-speaker setup. My experience in acoustics is with acoustic microscopy, so my work is in the MHz range, not Hz/kHz. I also only work only with one transducer at a time. I now have six and i'm confused

Thanks in advance,

Martin

MacLeod

Welcome to the Club, Martin.

Phase is a funky thing and can cause all sorts of issues with your sound. However it is weird that your subs sound better out of phase. Its been my experience that subs seem to work better in phase.

Still, it is possible that you were getting cancellation by the way the trunk was made or angles of the seats or whatever. Its probably a case of the trunk causing the subs to cancel each other since running a single sub made no difference.

It all depends on the interior of the car and where your speakers are mounted and its not always easy to fix as you could have one speaker out of phase by only 90 degrees which cant be fixed by swapping polarity. Doing that only yields you 0 degrees or 180 degrees. Its also possible to have certain frequencies out of phase! Now thats a real pain to fix!! There is talk that Zapco is coming out with a processor that will allow you adjust phase by the frequency which will be an instant best seller for the tweakaholics.

hondahirny

Thanks very much for your input. I've seen a lot of your posts and i was hoping that you'd be one of the folks that would reply. You really know this stuff!

I talked to a car audio buddy who's been in this for some years and he was quite surprised himself that the phasing made that much difference. At first, i thought i screwed up making my first box, but my experiment with the single speaker ruled that out.

While I was disappointed with the bass in the default setup, this swapped polarity really got the bass going. With only 300W RMS and two little 8's, i'm getting so much bass that i can't believe anyone would even want more. I now can't picture going much higher than what i can deliver already. Although, those Polk SR-series 12's look sweet

I'm thinking of putting some type of sound deadening in the car, as at lower volumes, the road noise in my car kills the listening experience. Any thoughts on Dynamat vs. Second Skin Audio vs. (insert sound deadening company here) ? Don't need some gold-plated, $400sq/ft product, just something quality/reasonable price that will work and stay where i put it...

MacLeod

Are ya 100% sure you got the wires right. Im just really suprised in phase subs sound bad.

Dynamat is the stuff I like best and use. Start out with the door kits for like $80 and go from there. You can never have enough damping for not only sound proofing but for damping resonance which can also kill sound quality!

And just as an aside, the MMC650's are 6.5" speakers and the MMC690's are the 6x9's.

hondahirny

Yeah, i checked the polarities throughout several times and they do sound better when reverse polarity.

From my previous statement, a single sub sounds fine either polarity with the seats up or down. Having the seats down gives just a bit more bottom end (i'm assuming less attenuation from the back seats). When two subs are hooked up, the difference in running them correct/reverse polarity is huge. Both subs normal hookup - low bass, one sub reversed and other normal - good bass, both subs reversed - still good bass. I must have the flux capacitor hooked up backwards or something... Or could it be the cross-drilled cones on my db804's causing phase cancellation with my 3/4" medium densisty carboard enclosure?

In all seriousness, a car audio buddy of mine said that if i faced the woofers towards the rear of the car, the trunk cavity would give the bass more room to build up (and make the trunk rattle). Now, i haven't tried that, as i like the fact the very durable and woofer-free backside of my box faces the trunk. I haul tools sometimes and don't want my tool boxes having their way with my gear. I'm just glad i was able to achieve decent bass with my subs set up the way i have them. Just confuses the shiznit out of me why it works this way.

Thanks for the recommendation on the Dynamat. Gotta start checking Ebay for a good deal on that stuff. Paying full price on that stuff just seems... well... like paying full price.

exalted512

Bass sounds best when it reflects off something, thats why in trunk cars, most of the time the subs face toward the back. In all actuality, its best to keep the subs about 3" away from the very back of the trunk, but for most people, its just not feasible.

As far as second skin vs. other, check out www.sounddeadenershowdown.com
Ive used several different types of deadeners and if you want the best, use second skin. If youre on a budget, use Raammat. I would not even consider anything else.
-Cody

MacLeod

Ah! That explains it!

I missed the part where you said you had the subs facing toward the front (no suprise as my ADD kicks in with any post longer than a paragraph). This way can easily create cancellation.

The wave fires into the car but there is also a wave that bounces off the trunk and then into the car (usually thru the rear deck) and this cancels out the first wave. An easy way to prove this is to open the trunk. If your bass increases, thats your problem. Opening up the trunk allows the second wave to escape out instead of back into the front of the car and colliding with the first wave.

hondahirny

Thanks to Mac and exalted for your additional info. I appreciate the thumbs up on the second skin, as it's specs seem to outdo the dynamat for about the same price/maybe less. My car is older, so i'm not going to dynamat the whole car, but the doors, while the toughest to insulate, will probably be first on my hitlist for sound deadening. As funds allow, i'll do the floor and trunk as well.

Seems like phase cancellation is the agreed-upon cause, just not fully understood where and how exactly. Having one sub be "indifferent" to polarity while two being picky, it's a bit odd. I'll play around when i feel like wire swapping the subs some more and i'll see how it works out on the sound. Maybe i'll be able to track it down and give you an update. I just made a cd with a bunch of test freqencies in the sub range, so i should be able to take into account audio wavelengths in any kind of phase cancellation. Most of that stuff is pretty basic math, so i should be able to figure it out. Thanks againg for all the expert feedback!

MacLeod

I dont know if its possible with your box, but try flipping them around so that theyre pointing toward the back of the car and see if that makes a difference. Im willing to bet it will.

hondahirny

I really like the fact that when i put heavier items in the trunk, the more fragile speakers and amp are protected, by being sandwiched between the back seat. The back and sides of the box are more durable, so they face the trunk. It also makes my toys less obvious when i pop the trunk.

There's no easy way for me to try it, as i bolted the heck out of the box, for safety during any potential car accident. Otherwise i'd try it, just to hear the difference.

hondahirny

Update... Played around with various speaker polarities again today. Now it seems that the polarity makes no difference with either one or both speakers. The subs now have over 20 hours on them, so maybe when they were new, they somehow behaved differently. I've heard of speaker break-in, but this was a bit odd. After all that **** around, now it doesn't matter. "The Rock says. It doesn't matter what polarity you use!" Thanks for everyone's input anyhow. It was edumacational...