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Thread: Delayed Bass

  1. #1

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    Default Delayed Bass

    Hello guys, I just recently installed an SVC mm2084 8-inch sub in a .35 cu.ft. box in my backseat of my Honda civic where the rear center armrest used to be. The sub fires towards the front passengers and is powered by a hifonix titan txi6406 with ch3 and ch4 bridged feeding 340rms at 4ohms.

    From where the sub is located now, the sound seems to bounce of the dash and windshield to make it appear that the bass is coming from the front which is what I wanted in the first place.

    The problem is, If I set the subsonic filter on the amp lower than 35hz, there seems to be a noticeable delay in the bass coming from the sub and is not in sync with the sound coming from the front speakers (db 651).

    My current settings for the front are hi pass at 40hz. Sub is set to 35hz subsonic and 90hz lowpass.

    Can someone help explain why the bass from the sub is delayed if the subsonic filter is lower than 35hz? Thanks in advance.

  2. #2

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    Its not actually "delaying" the bass.

    Usually, anything over 60-70 Hz and the sub starts to pull to the rear pretty good. The lower frequency stuff (25-40) is such a big wave that its very hard to locate. Since your sub is firing to the front from the trunk, you are possibly getting some cancellation from the back wave bouncing off the rear of the trunk and coming back into the cabin out of phase. This cancellation is usually in the 70-90 Hz range in my experience.

    So this means that the lower frequency stuff is being played at a higher level than the higher frequency stuff and since the lower frequencies are harder to locate, it seems the bass is coming from the front.

    Now when you set your subsonic filter to 35 Hz, its cutting off all those omnidirectional frequencies so all youre left with is the more directional higher bass frequencies and you notice it behind you now more.

    Id wager that when you set your subsonic filter to 35 Hz that you lose some energy in your bass as well.

    Best thing to do is to turn off your subsonic filter, or at least tune it lower. 35 Hz is way too high a cut off point for your bass. I wouldnt go any higher than 15 Hz for a cutoff.
    polkaudio sound quality competitor since 2005
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  3. #3

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    Thanks for the explanation sir. I tried setting the subsonic to the lowest setting at 15 hz, but the "foot drums" still seem to be a fraction of a second out of sync with the music from the front speakers.

    The sub isn't actually located in the trunk but iside the cabin mounted in the center of the rear passenger seat, and also serves as an armrest for the rear passengers.

    From my understanding of your explanation, I tried lowering the low pass to 60hz with subsonic set at 15hz, to eliminate the frequencies which are being cancelled out (so as not to waste amp power producing these frequencies which get cancelled anyway).

    The result was I could barely hear anything from the sub with the bass eq@45hz set to "0". But when I set the bass eq to +12db to +18db, the sub really pounds those foot drums! There is still a very very slight "delay" in the "foot drums" at high volume but is no longer so obvious at low to mid volume. Thanks MacLeod, this works for me though I still wish I could totally eliminate the "delay". :D

    Now I have a new problem... the amp seems to heat up after only 15 minutes of playing at half volume with the bass eq at over +12db (it doesnt shut down but the protect led turns on and its really hot).
    :(
    Last edited by Manilaboy; 09-27-2007 at 02:52 AM.

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    When ever you set your gains for the amp I assume you had the bass eq set to flat. Now when you set your bass eq to +12db you have basically increased your gain to the subwoofer. Even though you may not be able to hear it you are probably sending a clipped signal to your sub causing your amp to overheat. I would expect you are trying to get too much out of a single 8" driver. Iwould lower the level on the bass EQ. Next try turning your front crossover (highpass) to 90hz or so. YOu may have som cancellation do to the overlap of these crossover frequencys. Since your sub is in the passenger compartment you are gitting direct sound. Since it is bouncing off the windshield you might try to reverse the polarity on the sub and see if that helps. Iwould do all the testing with the bass EQ@ set to flat and the Subsonic filter off.

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    Try wiring the sub out of phase with the front speakers.

    A sub is a slower working speaker than a mid or tweeter so it takes longer to fire and the wave also take longer to form. So add that to the fact that its further off and youre going to hear it later.

    The best fix is to add time delay to all front speaker and leave the sub alone. But if you dont have a processor or a head unit with TA then wiring the sub out of phase might fix it.
    polkaudio sound quality competitor since 2005
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    polkaudio SR6500 --- polkaudio MM1040 x2 -- Pioneer P99 -- Rockford Fosgate P1000X5D

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    Installer4life and MacLeod,

    Thanks for your inputs, I played around with the crossovers to avoid overlapping and possible cancelation as you suggested and chose 60hz high pass for the front and 60hz lowpass for the sub.It worked!!! The sub seems louder now and I can hear it pounding even with bass eq set to "0". At half volume, when I set the bass eq to +6db, its really loud (comparable to the +12db setting before), and the amp no longer overheats at that lower setting. I'll try reversing the phase this weekend, and I hope it works in removing the small delay. You guys have been very helpful, thanks again :)

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    Guys, I just wanna report on what happened when I reversed the phase of the sub, bacause I was amazed at the results!

    In reversed phase, the bass seemed to pull back towards the sub, that is, it no longer seems to be bouncing off the windshield and instead seems to be centered around the sub. In fact, when I put my ear a few inches from the sub's cone just to check how loud it is, it's really deafening! More than that, listening from the driver's position, the bass is perfectly in sync with the front speakers.

    Curious about this phenomenon, I tried experimenting a bit and swapped the positive and negative terminals back to their original position. I put my ear a few inches from the sub and it's no longer that deafening. The bass seems to be coming from the front now, so I tried to locate where the loudest bass was by leaning towards the windhield. It seems the bass was forming in the area in between the dash and the windshield which is where the bass is loudest. Since the sub is facing forward, I figured the sub is "throwing" the bass into the windshield, and the delay I was hearing was the "reflected" bass which takes slightly longer to reach my ear than the sound directly coming from the front speakers.

    I tried experimenting some more by angling the sub so the bass gets reflected off the dashboard instead of the winshield (to still make it appear the bass was coming from the front the way I like it). I finally got the perfect position to get the bass bounce off the dash, and since the dash is closer to my ear than the windshield, I was able to eliminate the delay :)

    I'm just curious though, what mechanics are involved in reversing the phase? Why does the sub seem to "throw" the bass (like a ventriloquist) in normal phase, and "pull back" in reversed phase?

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    The best answer is there is no answer. The problem with a car is there are so many different types of materials that either reflect or absorb sound. Many times you have to play around with the speaker locations and angles of the speakers, such as you did, to find the best location. Also because of these materials and locations whenever you wire up your speakers, even though you may wire the positive and negative terminals to the positive and negative terminals of the amp correctly, it doesn't mean that the speakers are in phase. Whenever there is a crossover brought into the mix, depending on crossover slope(6,12,18,24 etc) this also throws the speakers out of phase. I used to work for CC and every manufacture of subwoofers wanted their boxes in a certain location in our thump room becuse it made them sound better. Same thing for your car. If your sub was in the trunk you probaly would not have had this same problems but since you put it in the cabin these issues arrived. But that is a good thing. Now when one of your buddies can't get his system to sound as good as yours you will be able to help him out. Just a quick point to help you out. a 6 db crossover slope is 90 degrees out of phase, 12 db slope is 180 degrees, 18 db is 270 degrees and 24 makes a complete circle of 360. Also when your sub bounced off the windshield and came back it was 180 degrees out of phase. Remember that a woofers moves in and out and realistically there is no positve and negative of a speaker. Because of your experimenting you now know more than most about tuning a car system. Very few people take into account what you just did to improve your sound. This is whats fun about doing it your self. Good job.

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    Thanks a lot sir, especially for the tip on slope-phase relationship, it will be very helpful for something I wanna try out next... a three way active front setup using a pair of JL 6-inch subs and a pair of mmc650's hehe :)

    Update: I read up on this phase thing on wikipidia, and couldn't understand most of what I read haha, so I guess I'll just trust my ears on this one, and rely on helpful tips from you club polk gurus! :)
    Last edited by Manilaboy; 09-29-2007 at 02:36 PM.

  10. #10

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    Quote Originally Posted by Manilaboy View Post
    Thanks a lot sir, especially for the tip on slope-phase relationship, it will be very helpful for something I wanna try out next... a three way active front setup using a pair of JL 6-inch subs and a pair of mmc650's hehe :)

    Update: I read up on this phase thing on wikipidia, and couldn't understand most of what I read haha, so I guess I'll just trust my ears on this one, and rely on helpful tips from you club polk gurus! :)
    3 way active is nice. The passive crossovers that come with components usually acount for the phasing issues. This also helps to explain why people who buy the same equipment but have different cars end up with one car sounding better. Its hard to explain that to someone. Good Luck.

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