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dtbingle 06-05-2013 09:17 PM

Weird audio - standing waves and resonances
 
I have a question for everyone driving a liberty KK with aftermarket audio equipment. I'm running Polk audio db 651s in the doors powered by a Rockford fosgate r300-4 and a mtx tr5512-04 powered by an infinity reference 1600a. My headunit is a pioneer deh3400ub. While listening to music, something doesn't seem right. It's almost as if certain notes from the sub are inaudible and then others are overpowering the mids and highs. I've messed with my gains, crossovers, and head unit settings, but it just never seems right! I was wondering if anyone has experienced a similar thing in their KK and if so, how they made it better. Also, how do you have you sub(s) positioned/direction they are facing? I'm not sure if its just my subwoofer and how it's designed, my head unit, or even if its something about a liberty being boxy and creating a scenario where waves interfere in a unique way where some stack and some cancel. Any suggestions or personal experience is appreciated!

MtBJet 06-05-2013 10:41 PM

Quote:

Originally Posted by dtbingle
I have a question for everyone driving a liberty KK with aftermarket audio equipment. I'm running Polk audio db 651s in the doors powered by a Rockford fosgate r300-4 and a mtx tr5512-04 powered by an infinity reference 1600a. My headunit is a pioneer deh3400ub. While listening to music, something doesn't seem right. It's almost as if certain notes from the sub are inaudible and then others are overpowering the mids and highs. I've messed with my gains, crossovers, and head unit settings, but it just never seems right! I was wondering if anyone has experienced a similar thing in their KK and if so, how they made it better. Also, how do you have you sub(s) positioned/direction they are facing? I'm not sure if its just my subwoofer and how it's designed, my head unit, or even if its something about a liberty being boxy and creating a scenario where waves interfere in a unique way where some stack and some cancel. Any suggestions or personal experience is appreciated!

If you can, try switching the phase on the sub. It won't, or shouldn't have anything to do with positioning... low end frequencies are pretty much non-directional. Do the tuning with something that has a good (20-20k), relatively even range... ie: don't use rap etc (covers the range but is heavy on the highs and lows). Is the sub housing home made? Does it have the required air space? Is it sealed or ported? Make sure your amp is set to 4ohms, not 2, this way it will match your speakers resistance. Tune from zero and make small changes. tune with two people... you in the driver seat and a friend adjusting. This way you don't leave your position as tuning changes. in a sense you become a human pink noise generator. Try tuning without using any of the base boost settings and with the low pass on... work from low (32) to high (320) and stop where you feel frequencies aren't being lost. Broad changes at the amp. small changes at the hu, assuming it has good capability in that area. It'll take time.

dtbingle 06-06-2013 06:04 AM

You make a ton of good points and have excellent instructions in there. I definitely left out a lot of info about my setup, so time to fill in the gaps haha.

Quote:

Originally Posted by MtBJet (Post 15525612)
If you can, try switching the phase on the sub. It won't, or shouldn't have anything to do with positioning... low end frequencies are pretty much non-directional.

I HAVE tried switching the phase of the sub via head unit (between normal and reverse phase). You can hear a very subtle difference with reverse phase, but I wouldn't necessarily say it's any better. For positioning, I have tried facing towards the back hatch placed in the left, middle, and right side of the trunk. Also tried same thing with sub facing upwards. Sub facing back is much louder and sounds better. Sub facing up is very quiet except on harder bass hits.

Quote:

Originally Posted by MtBJet (Post 15525612)
Do the tuning with something that has a good (20-20k), relatively even range... ie: don't use rap etc (covers the range but is heavy on the highs and lows).

I tuned both amps with an oscope and head unit on flat. From there when gains were tuned to their max without distortion, then I adjusted the eq levels down to a good balance (minus the standing waves issue). The sub actually sounds/hits perfect for kick drums and the maybe dozen rap songs I have, but then for extended bass notes and notes that I wouldn't consider to be a kick drum in other music genres, it's many times either barely audible or overpowering.

Quote:

Originally Posted by MtBJet (Post 15525612)
Is the sub housing home made? Does it have the required air space? Is it sealed or ported? Make sure your amp is set to 4ohms, not 2, this way it will match your speakers resistance.

Sub housing is homemade. Standard rectangular box with the sub and aeroport on the same side. Built to 2 cubic feet, which is the ported volume recommended by MTX. Initially had it in MTX's preloaded enclosure with same problem, which is why I built the new box. I don't think there is anyway to switch between 4 and 2 ohms on either amp, but the speakers/sub are all 4 ohms running on their own channel.

Quote:

Originally Posted by MtBJet (Post 15525612)
Tune from zero and make small changes. tune with two people... you in the driver seat and a friend adjusting. This way you don't leave your position as tuning changes. in a sense you become a human pink noise generator. Try tuning without using any of the base boost settings and with the low pass on... work from low (32) to high (320) and stop where you feel frequencies aren't being lost. Broad changes at the amp. small changes at the hu, assuming it has good capability in that area. It'll take time.

My head unit only has a LP 12db/octave filter that I can't turn off and my sub amp also has a 12db/octave filter that I can't turn off either. Head unit is set to crossover at 100hz while sub is ~120hz. For high pass, there is no high pass filter on my head unit, and I believe a 12db/octave filter on my door speaker amp. The high pass filter on the amp is set to 80hz (preset by factory and only crossover setting available). All loud and bass boost settings are completely off.

I will try your suggestion of tuning the crossover with two people so I don't have to run back and forth. I think I will start off with the amp crossover set at ~150hz (MTX operating frequency 29-150hz) and then adjust low to high on the head unit to the appropriate place and then if a steeper crossover is needed, have another person lower the amp crossover until it's good. Could it just be the sub and how it's designed? It's perfect for kick drum/rap but problematic for other genres of music.

huntb 06-06-2013 08:29 AM

Sounds like the issue is with your low pass filter. If you have a filter set on your HU and also on your amp you are creating second order filters that are going to have a much higher Q factor. This will create an underdamped situation. This means that at your center frequency, it is going to sound much louder than it will at other frequencies outside of your filter. You need to be able to set either the HU filters or the amp filters to pass through.

Try setting either the LPF on your head unit or amp to the highest frequency available and leaving the other as is.

dtbingle 06-06-2013 09:13 AM

That makes perfect sense and I will try that for my ride home from work. Set my amp to its highest (320hz I believe) and then mess around with the head unit LP.

EDIT: I was also thinking about picking up a decibel meter to see how the frequency response curve looks like to try and spot the problem frequencies to level it out. Has anyone done this/how well does it work?

dtbingle 08-28-2013 09:06 PM

Figured I would post back here for an update. This problem is still there. My ported box has just given me a fun time (....not). I've tried the MTX TR55-12 in MTX's preloaded box and a custom built box with an aeroport incrementally tuned from 27hz up to 40hz. No go. I recently got a new sub, an alpine type r, 12 in 4 ohm DVC. Also tried incrementally tuning the ported box from 27hz to 40hz, same issue. However, I tried stuffing the port with a blanket to simulate a sealed box (a very oversized sealed box), and it seems to lessen the problem quite a bit while the other frequencies still are just as loud. Going to build a sealed box to Alpine's recommend spec and see if this helps. Ordered the pioneer 80prs and if the sealed box doesn't help too much, then hopefully it can be EQ'd out.

huntb 08-29-2013 07:22 AM

Quote:

Originally Posted by dtbingle (Post 15848192)
Figured I would post back here for an update. This problem is still there. My ported box has just given me a fun time (....not). I've tried the MTX TR55-12 in MTX's preloaded box and a custom built box with an aeroport incrementally tuned from 27hz up to 40hz. No go. I recently got a new sub, an alpine type r, 12 in 4 ohm DVC. Also tried incrementally tuning the ported box from 27hz to 40hz, same issue. However, I tried stuffing the port with a blanket to simulate a sealed box (a very oversized sealed box), and it seems to lessen the problem quite a bit while the other frequencies still are just as loud. Going to build a sealed box to Alpine's recommend spec and see if this helps. Ordered the pioneer 80prs and if the sealed box doesn't help too much, then hopefully it can be EQ'd out.

I have NEVER been a fan of ported boxes. When I was younger I wanted them but only slotted ports. Those cheapo plastic round ports will vibrate at their natural resonance which could be influencing your issue. Get a sealed box. Tighter, more accurate bass is always better than louder, sloppy bass.

dtbingle 08-29-2013 12:00 PM

Quote:

Originally Posted by huntb (Post 15849154)
I have NEVER been a fan of ported boxes. When I was younger I wanted them but only slotted ports. Those cheapo plastic round ports will vibrate at their natural resonance which could be influencing your issue. Get a sealed box. Tighter, more accurate bass is always better than louder, sloppy bass.

Im finding this out quickly! My original box had slotted and my new one has a 4 in aeroport. Both sound sloppy to me. Sealed it is!

Also, just listening I can't really tell its not as loud as a ported. Modeling it out in winISD only shows the sealed is 2db less at the ported's peak, so they're basically the same volume until you're critically comparing them.


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