Car subwoofer suddenly "missing" bass - AVS Forum
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post #1 of 9 Old 03-26-2009, 09:54 PM - Thread Starter
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I have a Power Acoustik FUBR-12 connected to a Power Acoustik LT980/2 amp.

Today I was messing with the crossovers and I noticed that "Put On" by Young Jeezy didnt sound like it normally does. If you've heard this song on a powerful setup, you know this song has a crazy bass line. It has three distinct bass levels: super loud upper-low range, loud low range and booming super low range.

I turned this song on and I noticed that I'm missing two of the three different levels of bass now. Like they're just not there. It goes from sounding normal to I can see the sub pounding but no bass coming from it.

Did I blow the sub? There's no distortion at all when bass does play from it so I dont think that's it. I also pulled the sub from the box and there is no visible damage to any part of the sub.

I have been rockin this setup for a few years now and I wouldnt consider any other setup. I listen to a lot of rap with deep bass and this setup is pretty amazing. I'm definitely not an audiophile, but the bass is deep, loud and clear.

I know a lot of people like to crap on Power Acoustik, but every person I've met that has a better system has had to pay at least double, most of the time triple just to get better bass than me.

FUBR-12
1800w Peak
700w RMS
2 ohm dual voice coils

LT980/2
980w peak
220w x 2 @ 4 ohm
280w x 2 @ 2 ohm
560w x 1 @ 4 ohm bridged

I currently have the sub wired to the amp using a series configuration and bridged.
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post #2 of 9 Old 03-27-2009, 05:20 AM
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Since you said you were playing with the crossovers, you didn't accidentally change one, did you? I'm quite familiar with this song, as I demo it in my car all the time. I don't mean to nitpick, but I believe there are 4 distinct bass frequencies that are used almost extensively throughout the song. If you listen from the beginning, they cycle through twice I believe starting with the highest frequency.

If you listen starting at the beginning, are you only hearing the first note and then missing everything from there on out until the cycle repeats? If so (and you used to hear the other notes before), it would seem you flipped on a HPF cutting out the lower frequencies. If you are only hearing the later notes in the sequence, it would seem you dropped you LPF to a lower frequency. Let us know which of the four notes you are hearing.

Though, if your sub doesn't seem to play the fourth note in the sequence, don't be too concerned. Not too many sub/amp combos can handle that note cleanly. Jeezy likes to use some pretty low frequency notes in his songs.

I doubt your sub is blown, since it is playing something. Speakers don't blow for only certain frequencies. It's kind of an all or nothing. It is possible that some of the circuitry in your amp got messed up (which could eliminate certain frequencies), but again is highly unlikely. Also, please explain a bit more about what you mean here: "I can see the sub pounding but no bass coming from it"
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post #3 of 9 Old 03-27-2009, 05:32 AM
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Might check to ensure that your series wiring is still in place.
If you lose the jumper side, you'll be

a) driving only one coil and
b) running bridged to 2 ohms (+rise)

Nothing fundamentally wrong with the power acoustik / kole / spl brand, aside from the gimmicky lightning pad on those 2ch LT-series amps.

I had a MOFO15 that was musical as a trainwreck, but absolutely violent.
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post #4 of 9 Old 03-28-2009, 11:53 PM - Thread Starter
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Thanks for the responses guys.

While I've ha his setup for years I admit I am a noob when it comes to tuning it. My old car had an aftermarket deck which made it a lot easier to tune because the deck had an equalizer. It new car is a 2007 mazda6 and because of the peculiar dash and head unit setup, I was forced to stick with the factory deck using a hi-low converter.

Consequently, tuning this setup has been a nightmare due to the fact that I can't adjust any settings besides base and treble.

Right now I have it running in a series running one channel which puts the sub at 4-ohms 220w RMS. On the amp itself, I have the gain at a quarter turn from the minimum setting, bass eq at a quarter turn (min 0db max 24db), subsonic at the minimum setting of 30hz. My crossover has a selector switch that includes HPF, Full and LPF. It is set to LPF and at the lowest setting of 30hz.

This seems to give me the deepest, richest base, but I know there is a lot more in this setup, but I can't seem to find the combination of settings that will make me happy. Any time I try and mess with these settings the results are as desbribed in my OP, I lose the low deep bass while the higher bass doesn't seem to play at all.

What I meant by I can see the sub pounding but no bass comes out is that when the base drops from that first note on Put On, the sub is moving. I can see the sub's excursion, but no sound is coming from the sub, just movement.

My limited understanding of how the crossover works tells me that the amp should be blocking any input that is above 30hz. Is that correct? I also know that accordin to Power Acoustik the lowest frequency that my sub should respond to is 34hz. this doesn't really seem right to me because the way it's set now, I can hear the low bass, but the amp should be dropping everything that my sub can play. Turning up the LPF to 50hz does nothing except make the bass I can hear louder, but it losses that booming quality.

What exactly is the subsonic filter? I've read that it's pretty much the same thing as the LPF but I don't understnd it's exact purpose.

The missing bass occurs when I raise the gain past it's current setting or turn up the bass equalizer. That's when only the higher bass plays but the 2nd, 3rd and 4th note in Put On just cause the sub to move without sound. If I bridge the amp and pump 560w to the sub, the higher bass plays a lot deeper, but the lower bass doesn't play no matter what I do. The sub just moves a lot more than with one channel.

Does turning up the gain or bass equalizer cause the frequency of the sound to drop out of the sub's response range?

What settings should I start out with and how should I adjust them to find the optimum levels for each setting?

I'm really sorry for the noob questions, but I'm at the point where I can't get it to work and google has ceased to provide any insight.

Thanks.
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post #5 of 9 Old 03-29-2009, 07:18 AM
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No worries, Karma; We'll getcha fixed up.

Your subwoofer connection to the amp. You want to run the voicecoils in series, bridged to the amp. Like this:



Speaker wires from the bridged outputs of the amp to one coil pos/neg, then a jumper wire on the other coil pos/neg.

That should give you the most available power without blowing anything up; Your amp's not stable bridged into 2 ohms.

At the headunit - bass boost off, bass to 'flat' (not plus or minus anything) These settings adjust the shape of the wave (distortion), which can bring you into clipping. However, you can turn them back to your preference after the filter adjustments - unless you're way out of spec, it's fine to turn 'em up a little.

Now the gain. Turn it down. You may have it set too high to compensate for the lack of volume. Also, down may look like up, because gain is typically represented as input sensitivity. 8 volts will be 'down' and 0.2 volts will be 'up'.

If you really want to get into it, you can set your gain using a multimeter;

roughly, voltage=sqrt(ohms*watts). A little too precise for our purposes, really.

Onto the filters. Try this;

On the amp, the switch should be at 'LPF'
set Subsonic filter 30Hz
set LowPass filter 90Hz

Realistically, 90 is a little on the high side, but it's a good place to start.

Subsonic filter is basically a 'highpass' filter. In other words, frequencies above your chosen setting are 'allowed to pass'. Lowpass filter is essentially the same, in reverse.

Together they form a 'bandpass' arrangement - trimming out either end of the spectrum, leaving a 'passband' of unbothered frequencies.

Your passband is simply too narrow. By choosing an SSF and LPF so close to eachother, the response +/- the chosen bandwidth is attenuated heavily, meaning your sub is hardly 'allowed' to play anything at all.

The filters are not a brick wall; The idea is that the frequency you select will be attenuated at a particular rate, and continue in a progressive slope. If you set the filters as I suggested above, you'll still be able to hear a 29Hz or 91Hz tone, but it will be much quieter.

Crummy drawing:
Code:
Suggested settings and 'response graph'
        .-~~`````````~~-.     
       SSF30          LPF90

Current settings and graph
        .-~~-.                       
       SSF30,LPF35
With all that nailed down, play your music at a reasonable level, and turn the gain up to match the bass with the music's level. Hopefully that helps and now you can know what to expect when you make further adjustments.

Happy bumping;
Blake
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post #6 of 9 Old 03-29-2009, 11:24 AM - Thread Starter
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Dude you are the man!

I have my sub bridged, running the gain a little past quarter turn on the knob, subsonic at 30hz, bass boost turned off, bass at -2 on the head unit, LPF at quarter turn (only shows min of 30hz and max of 500hz) and all I can say is wow.

My system is bumping harder and cleaner than ever! Looks like I found that sweet spot I was looking for.

Thanks again dude. The subsonic was what was messing me up. I was turning the subsonic up with the LPF instead of opposite the LPF.

Now, any suggestions on getting rid of the rattle in the trunk?
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post #7 of 9 Old 03-30-2009, 05:26 AM
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* Don't use too much, though - it does expand.
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post #8 of 9 Old 03-30-2009, 09:39 PM
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Using that stuff can be bad especially with no experience with it, Ive seen people mess up trunk lids with it and make it have convex "dents"

A good dampening mat, check out B-quiet.com
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post #9 of 9 Old 03-31-2009, 05:33 AM
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He's right, be careful how you use Stuff - it can do damage if you overdo it. And it's incredibly sticky.

Best way to go for rattles though - mat is to mass load - lowers the resonant frequency of a ringing panel - but for rattles, you want bracing, not massloading.

Google sounddeadenershowdown for a comparison of mat products.
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