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altoncustomtech

Distortion or not?

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Alright, I've been trying to figure this out since I finished the new install. The Q's and Sundown amps sound amazing, they really do. I've never had anything that sounds like they do, so deep, so accurate and SO forceful, they're really quite amazing. However, I noticed a strange phenomenon right after installation that I kind of chocked up to the fact they were still very tight. After several months of playing it got worse instead of better, and at the car show last November I discovered something interesting about the phenomenon and have been studying and working on the how and why of it since. Problem is, I can't find any good information on it. So at this point, you're probably wondering what the hell I'm talking about.

This phenomenon I'm referring to is as best I can describe it, some sort of acoustical distortion. When I first installed the Q's and Sundowns I noticed that on certain songs it would sound like there was distortion when the bass would "hit". I'm not talking songs like "a milli" or "top back" or some other bass heavy song either, I'm talkin' songs like the Eagles "Hotel California" and "Take It Easy". In particular it was the hard, snappy drums that I noticed first. I IMMEDIATELY got my o'scope back out and double checked everything and verified the gains were set correctly. No distortion at all according to the o'scope and it's wonderful software :D. Confident everything was alright and assuming it was just my ears needing to adjust to the sheer force and output of the new setup I continued to monitor the situation especially since it seemed I was the only one who could hear it. I noticed as time went on that I would hear the distortion anytime the music was turned up loud until the car show in November. At that car show I was playing the system wide open, for all it had pretty much the whole time I was there and it sounded absolutely beautiful. No distortion, no nothing which REALLY caught my attention!

After the show I went home and played around with it and discovered that the ONLY time I hear it is when the van is closed up. I can still hear it if something like just the front windows are down, or one door is open, but if I open the van completely up its gone. So I've been trying to figure out exactly what the distortion is called and most importantly WHY I'm hearing it AND HOW can I remediate it if that's even possible. Which brings me to posting this topic. I know someone will know what's going on and I'm sure it's WAY simpler than I've made it as I explained it here. Most of the research I've done into distortion has been 97% electrical distortion with very little good information on anything having to do with distortion related to acoustics which is where I am sure my problems lies. That or I'm not looking for the right terms.

Thank you for the help guys, I'm looking forward to the lesson on this one.

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Where do you mid drivers start to roll off and where do you have your sub drivers crossed ???

My mids start to roll off at 32 htz for critial listening (I normally bring that up to almost 100 when jamming very loud). And my subs are crossed at 54 for SQ and I will change that to 70 when jamming ...

Reason for asking is that my 6.5s usually handle that "snappy drum" sound ...

just throwing questions around ... thanks, Randal ... :drink40:

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So you think the distortion is a product of the accoustic's and not mechanical noise from the driver? Maybe you are getting cancellation/destructive distortion in the frequency range that the sub and mids share. Have you reversed phasing to see if it helped?

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Sure its your driver and not your vehicle? Localizable?

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Thanks for the replies guys.

Where do you mid drivers start to roll off and where do you have your sub drivers crossed ???

My mids start to roll off at 32 htz for critial listening (I normally bring that up to almost 100 when jamming very loud). And my subs are crossed at 54 for SQ and I will change that to 70 when jamming ...

Reason for asking is that my 6.5s usually handle that "snappy drum" sound ...

just throwing questions around ... thanks, Randal ... :drink40:

The subs are crossed at 70hz, the components at 100hz. Snappy drum sound was probably not the best way to leave the description. It's the fundamental that goes with the drum that the subs play when I first heard it. Now, at any point in time if it's turned up loud enough I can hear it whether it's a drum beat or a deep bass line.

So you think the distortion is a product of the accoustic's and not mechanical noise from the driver? Maybe you are getting cancellation/destructive distortion in the frequency range that the sub and mids share. Have you reversed phasing to see if it helped?

Yeah it's definitely not a noise from the driver. As mentioned when the van is completely open there's no noise to be heard but sweet music. I have nearly as much phasing testing as a person would ever want to in attempts to find a solution to another problem. The phenomenon was evident no matter the phasing of the subs or speakers.

Sure its your driver and not your vehicle? Localizable?

Alright, gotta admit this I cannot absolutely rule out. While I've not been able to localize it to any particular panel, trim, etc. in the structure of the van that doesn't mean it's not the problem. Reason being that by the time it's loud enough to hear the distortion type sound everything is already so energized it's hard to localize much of anything, lol.

I wish there was some way to get a recording of it. It straight up sounds like distortion, but goes completely away as soon as the van is opened up. There's no distortion on the scope, and as best I can tell it's not any of the body/trim panels. The entire rear of the van has one layer of deadener on it, with two in trouble spots and CCF as well. There's a very good possibility it could be a panel or structural support somewhere but I've not been able to locate any problems anywhere yet. I've definitely gotten more rattles and things loose with them but when I hear and find them I take care of 'em so I dunno for sure.

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The sound you describe sounds like either a mid out of phase or a panel that is shifted/relieved when you open up the van. let us know what you figure out.

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The sound you describe sounds like either a mid out of phase or a panel that is shifted/relieved when you open up the van. let us know what you figure out.

Wonder if he applied pressure to different panels through out the vehicle / held a piece of plywood in the cabin at different positions / angles, if the noise would lessen. Kinda shooting in the dark at this point, at least with my experience.

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Listen to the sub only, mids only etc and see if the phenomena follows one or the other or only together.

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The sound you describe sounds like either a mid out of phase or a panel that is shifted/relieved when you open up the van. let us know what you figure out.

The sound you describe sounds like either a mid out of phase or a panel that is shifted/relieved when you open up the van. let us know what you figure out.

Wonder if he applied pressure to different panels through out the vehicle / held a piece of plywood in the cabin at different positions / angles, if the noise would lessen. Kinda shooting in the dark at this point, at least with my experience.

We did a crap load of testing Saturday since the weather was actually decent for once. I had my little brother and a buddy of his lean, press and lie on all the different panels and surfaces of the van. The only thing I was able to discover doing this is that it looks like there's a possibility that the roof braces have come loose from the roof panel. I haven't had a chance to pull the ceiling cover all the way off yet, but what I saw when I pulled it down enough to look up there wasn't very reassuring, at all. I did my best to shove some CCF in between for now and see what I can do about it in the long run later. Unfortunately the CCF didn't change the weird sound much at all at very high volumes though helped a bunch at mid-high levels, so it is definitely part of the problem as I'll describe below.

Listen to the sub only, mids only etc and see if the phenomena follows one or the other or only together.

I have actually done this many times before, and of course only heard the phenomena when the subs played AND the van was closed up. However, that changed a little this time around. After finding the roof braces ripped loose from the roof panel I went about doing this test once again and found a VERY interesting difference. It only really made the sound badly when the mids and the subs played together. Upon further testing I found it would only do it when the rears were playing with the subs, no weird sounds when just the fronts played at mid-high levels though it would return at very high levels but was localizable to the roof. So now at this point I'm looking very hard at what's wrong with the rears and was finally able to find an answer. It seems the rear HPF filter on the HU doesn't work at all. I played some bass heavy music with the rear door open and the 100.4 is kicking the living crap out of them. Turned on the HPF on the amp and viola, the sound is gone.

It seems that with the HPF on the rear channels in the HU not working and the door being closed (which puts the 6.5's right there by the subs) caused an interaction with the pressure from the 12's that made the sound, the best I can figure. Either way, the problem is pretty much solved.

Thanks you guys for all the help and suggestions!!

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