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Discussion Starter · #1 ·
Hey everyone, need some help with my system. I seem to have no bass from around 58 to 80hz. I went through the frequency steps and when I got into that area it sounds out of phase. I checked all connections and everything is fine. the subs and mids are cross over around 80 Hz. I’ll have to check to be sure but its somewhere around there. they play wonderful up to the 50 Hz area then they slowly taper off to sounding out of phase. any idea what could be causing this? the link to my build is here
http://www.diymobileaudio.com/forum/diyma-member-build-logs/108941-2010-jeep-cherokee-build.html
 

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what kinda box?
size of box?
if it is ported what is the port tuning?
what kinda subs?


need more info
 

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put your subs in a sealed box to give them a more flat roll off and they will start to play up in that range better. unless however, you care about imaging, and doing that would make your sound stage go behind you, which is bad. but if you chose to use coaxials for your door speakers, i would assume sound stage isnt your concern. have you boosted your lowest eq setting?
 

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Also check to make sure your amp doesn't have a High Pass Filter (HPF) enabled. This would override any settings on your HU.
 

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Discussion Starter · #5 ·
sorry i guess i should have put more info rather than linking my build.
i have infinity kappa 6x8's in the front doors, 1" soft domes in the dash, 6.5" infinity kappas in the rear doors. 1 WMD shallow mount 12" in a seald box in the rear. the highs are powered by a planet audio HVT754 4ch and a mmats 1400.5 on the sub.
i have been into car audio since the early 80's so i know how to settup a system, its just i have never had a problem like this. could the mids be canceling out the subs in the upper bass area?




 

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Is that plexiglass covering the sub? That would harm the less omnidirectional bass in that region. If it sat much higher than the cone, maybe it wouldn't. And, as cool as it looks, I would think the sub is seeing some cancellation being located near the middle of the vehicle too. Maybe if the sub was closer to the very back you wouldn't have that particular cancellation. Just speculating.
 

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Discussion Starter · #9 ·
Well I have used a very similar setup in my jeep liberty and had no problems. I have also used the plexi as a speaker grill in many other applications also with no problems. moving the sub to the back would be impossible since the sub enclosure runs across the rear seat area, and the amps are under the floor in the front. Have other people had phase problems due to the sub being towards the front of the cargo area?


 

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I'd remove the plexi and try again...

You are seriously boundary loading the sub like that... different vehicle, could be causing a cancellation not found in the smaller interior of the Liberty?

It also looks like a pretty long throw sub, with little space for excursion...

Slot/boundary loading can be awesome when done right, but I donno about that one... even if it's "working", it doesn't look "right"...
There is a science to it, that I don't know enough about to explain why I feel this way... I just know I've tried different things myself over the years to varying degrees of success..
 

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What are your xover set at? If you use 12dB/12dB on high and low you have to run them out of phase to be in phase. Before you do anything just (like Andy says) mess with the phase and try it. Is easy to set overlap in xover at 80hz or so and play a 80 tone or music with good bass there. Fade sub in/out (at a low sub gain) and compare bass to test phase. Can also test the rest of speakers. Then your ears will tell you the real story.
 

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Man, that's a sweet looking false floor! Is it possible to rebuild it with the amps in the front and the sub in the back? That would at least shorten the power wire run (not that it would make any difference)
 

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Discussion Starter · #14 ·
Thanks for all the ideas to try. right now I am working 12 hr night shifts so i will have to get to it when i can. I will try switching the phase of the sub, removing the plexi and maybe even pointing it a different direction, and completely disconnecting the high amp to isolate just the subs to see if there is any cancelation from the mids. I hope it’s something as easy as reversing the polarity of the sub. I really like my plexi cover and would hate to lose it. also if all else fails I might just have to make a new box with the sub to the rear of the jeep.

another think i forgot to mention is that the sub bass is extreamly loud. and im talking very low like in the 30 hz range ive tried to tame it with the eq but the lowest setting is only 60hz
 

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Thanks for all the ideas to try. right now I am working 12 hr night shifts so i will have to get to it when i can. I will try switching the phase of the sub, removing the plexi and maybe even pointing it a different direction, and completely disconnecting the high amp to isolate just the subs to see if there is any cancelation from the mids. I hope it’s something as easy as reversing the polarity of the sub. I really like my plexi cover and would hate to lose it. also if all else fails I might just have to make a new box with the sub to the rear of the jeep.

another think i forgot to mention is that the sub bass is extreamly loud. and im talking very low like in the 30 hz range ive tried to tame it with the eq but the lowest setting is only 60hz
In my experience, subs facing up in my car cause the 40-80 hz bass to suffer. For example, I had this box:



...And just low bass. So, I built the following box, with similar specs, but different shape/woofer orientation:



And, now it slams from 20 - 100 hz. Same sub. Same amp. Same settings (I actually cut 100 hz on the PEQ from +1 down to 0)
 

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Could be making it act like an out of tune bandpass too.
This^^

I just dealt with the same issue, mine sounded/measured like 80Hz was out of phase, had me pulling out my hair and tuning was impossible.

In my setup, my sub was flush with a false floor. I had put a cargo mat over the whole thing for a factory look, it turned out to be restrictive enough that the sound would be redirected under the false floor to escape elsewhere, causing the issue.
Your problem appears to be the same, I would start by removing the cool looking plex cover and see if that does the trick.
 

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Discussion Starter · #17 ·
I sure hope you are wrong. LOL i have today off so im going to try some of the simple tricks suggested already and hope they work. if not the plexi will come off. then if that doesnt work the box will get rebuilt. :(
 

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Move to the back seat and listen to those tones. If they are much louder you have a local null at the drivers seat (cancellation- I would be willing to bet this is the issue). I don't think removng the cover is going to do you much good (it should be acoustically small at those freqs).The bad news is if it is cancellation then you will likely need to move the woofer to fix the issue. This could cause issues at other freqs. Car audio is full of compromises.
 

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Discussion Starter · #19 ·
well your right. i switched the polarity of the subs and same problem. then i isolated the subs by removing the high amp. same problem. i moved my seat up as close to the dash as i could. there it was back in full force. sat in the back it was a little better but seems like the only place it sounds completely dead is the driver seat. i cant remove the plexi till i go home in a few weeks but like snake said i'm starting to think it wont make a difference. if removing the plexi doesn't work and i have to rebuild the box, where should i place the sub? as close to the rear hatch as i can? or somewhere else?
 
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