Where does the flapping noise come from?

[Ray De Man]

Ok guys I have this very annoying sound coming from the rear-end, somewhere near the petrol tank and bumper bar. It only makes this flapping noise when the subs hit very low notes. Yes everything else vibrates but this is the most annoying.

Car has been sound deadened on the rear shelf and boot lid. Where is the place should I S/D now and any ideas where the flapping noise is or what's flapping?

Oh instead of making another thread, is there a solution to stop my windscreen from popping out from the top? I guess this is due to the roof vibrating the windscreen out of place. This has happened approx 3 times already and is getting to be a pain as have to call someone to refit it.

Cheers in advance

[StoneX]

Parcel shelf against the rear window?

[Ray De Man]

No I don't think its that, it's much lower. From outside the car standing at the back, it looks like it's coming behind the bumper but it could be the boot floor. Any ideas???

[camstatic]

Those pesky air filters that are in the boot behind the bumper! My system has torn those to pieces and they flap around like crazy and make one hell of a noise. Cut out paper element and replace with air filter foam.

[Ray De Man]

How do I get to them? I guess there is one on either side?

[camstatic]

Not sure on the VX, just pull out the spare tyre and they're right behind it on the VP. A quick lift of the boot carpet should reveal 'em.

[Ray De Man]

Cheers Camstatic, i'll have a look later.

Any ideas on my windscreen problem?

[camstatic]

Too much flex! There isn't really much you can do, you could try sound deadening the hell out of the roof inside the hood-lining, but it'd be expensive and time consuming... If you could deaden the roof enough to get its resonant frequency below say... 20Hz, you might have a better chance of keeping the glass where it is.

Explanations of resonant frequency can be found all over the web, but the general gist of it is: The more something weighs, the lower resonant frequency it has. Sound deadener works by making panels in your car heavier, in turn lowering their resonant frequencies to (hopefully) lower than the car stereo emits, stopping vibrations and rattles. You can even tape up door lock linkages and things, making them heavier to lower their Rf.

[holdenboy]

strengthening the roof (in between the bracing ribs) will minimise the flex in the roof and therefore the top of the windscreen. You can do this by either sound deadening the sheet metal or glueing like 6mm MDF to it.

[StoneX]

What are you running to pop your windscreen out???

[Ray De Man]

Ok thanks guys, I guess i'll need to remove my headlining and dynamat it or like HoldenBoy said 6mm mdf. Is the headlining easy to remove? I guess I have to take all six side panel things off then remove the light, is there anything else?

Im running 6.5" kicker comps up front, clarion 4 way 6x9 rears (to be replaced by kicker coax for rear doors) then have two 12" kicker L7's in custom ported box. One Pioneer 400rms amp to power stereo speakers and a Alpine 1000rms amp to power the subs. Uprated battery to the yellow top opima and runs of 4gwg. Not a very big system i know but it's pooping the windscreen.

Does anyone roughly know what DB i'll be putting out, 120-140DB or much less? Clarity is there and of course the bass, do you think i'll need anymore improvments guys?

Cheers Ray

[StoneX]

That's weird that you're popping the windscreen with that gear...

You can't really estimate the dB level without hearing it.

[Ray De Man]

I know, it may of been when I was running four 12" Kenwood's DVC in a custom enclosure, that was just bass but these Kickers have clarity and SPL. Two Kickers rule over four Kenwoods anyday. There is pressure from my current system and if I open the cup holder rest in the back the pressure is even more.

I also found that these Commodores keep a lot of sound in the cabin, not alot escapes in other words can't hear alot from outside. You just hear the panels vibrating or flapping but that's about it.

[holdenboy]

Yeah i suppose it would depend on what the box is tuned to, if its flexing the roof that much i'd say its tuned really low......but with only 1000wrms its unusual to be causing that much flex.

Anyways SPL wise its hard, even if i had a listen to it i could still be 5-6db off. At a real rough guess i'd say 140-143ish.

As far as improvements go, i think upgrading the 4awg wiring to 0awg would yeild an improvement...maybe minor but minimises the chance of damaging the amp / subs through voltage drop and clipping. Other than that its hard to say what you could do to inprove it without looking over the system and having a listen.

[Ray De Man]

This is the box I'm running http://www.kicker.com/L7_subboxes. It doesn't say what it's tuned too. I did more RMS going into subs such as the 3 I tried, JL Audio, Soundstream, Kicker but they kept going into protection mode then the horrid whining/buzzing sound. Was running the proper cables for them but with no success. So.... I ended up buying the Alpine and 4 months down the line (touch wood) it's still going strong.

I monitor amperage going to the amp with Stringer gauges. Mono amp goes as low as 13.7 normal usage but at really low notes it drops to 12.8 (maybe lower), this is with engine running on idle!

I want to get the DB tested but just don't know where. Any ideas???

If you were close Holdenboy you could of had a listen....

As far as upgrading the 4awg, I want to leave that untill I can figure out if I can run dual alternators or just use a bigger unit and also who installs them? At the moment I don't think there is any point in adding 0awg as it's on stock alt.

Am I right in saying this, bigger alt/0awg = more power to the amps but does this add more DB?

[holdenboy]

In answer to you first question......there should be a specialist car audio retailer near you that either has a Termlab SPL meter or knows where you can have access to one. Theres always the option of going to a SPL competition also, that way you'll get to meet other SPL guys and get some more "hands on" help and tips for your system. Check www.dbdragracing.com.au or mobileelectronics.com.au for any events coming up.

In answer to your second question....basically yes, power in is power out.


I would personally upgrade to 0awg before doing any major (and expensive) mods on your charging system. Yes you will benefit more from a second alternator but for the cost vs outcome factor i'd say 0awg is a better choice firstly.

I run 4000wrms into two 15s in my car, stock alternator (VR). Yes i do have a second battery close to the amp and several 95mm sq. runs of welding flex (its more than double the size of 0awg). The second battery is a D31 YT but the front battery is stock at the moment. I wouldnt bother with upgrading the alternator in my system for two reasons. 1) It would put me into a higher class in sound comps, 2) I honestly cant see the cost vs outcome scenario being worthwhile.....that money could be better spent towards a bigger amplifier, another YT for the front, more power / earth cabling etc etc.

Sorry for the rant but hopefully you get the point there (Upgrade to 0awg before spending serious $$$ on a dual alternator setup).

[Ray De Man]

No worries about the "ranting" it's all about learning and i'm still learning. So no offence taken.

You have a serious system there Holdenboy, by the sounds of the gear you have i bet it sounds mint and at 150DB!!!

I guess i'll leave the dual alt but I always thought/told that running a second battery will put even more strain on the charging system?

So i'm gonna take your advice get some runs of 0awg and a second D35. Question is does this pass as roadworthly?

What class would I enter as if I was to participate in SPL contest?

Sorry for all the Q's

I appreciate all the help your giving me.

[holdenboy]

1) I personally dont think adding a second battery will place much more of a strain on your charging system, as adding a second battery will basically "halve" the work your front battery has to do, which dosent really change the strain on the charging system......maybe a little more, but nothing major.

2) It would depend on where / how you mount it i suppose.....maybe installing it in its own battery box would be sufficent, dont know...you guys might have different rules down there

3) If you were to compete in a proper db drag racing event then you would be in street b (assuming you only have the one battery when you compete.....two batteries puts you into street c - where i am)
If you do score in the lows 140s, you'll be fairly competitive and i wouldnt be surprised if you walk away with a trophy for first or second

[acarmody]

Have ya solved the flapping noise yet. Cause I have a VX Berlina and there are two one-way flaps in the boot, I was told it was there to let air out of the car when you shut the doors or boot so you don't have to slam them shut. I basically just sound deadened over them, no adverse effects, but solved the really loud flapping noise when the bass hit.

Wow your popping your windscreen with 1000wrms? I have two 12" L7s with 1400wrms in 2 cubic foot each sealed enclosures, roof doesn't even flex, well much, I wouldn't put my mobile on there. I'm hoping to get some ported enclosures soon, when my dad and I get some free time we'll make some.

[Ray De Man]

I will have to see if I can get a battery box, such as a racing one and clamp it to something or weld in a bracket. I will need to check with vicroads before I do anything.

I guess I never thought about the battery in that way, halving the work load but thats a good point.

Street B will be the one I would compete in until I know what DB I'm hitting, once that's done I'll upgrade. I doubt if I'll get a trophy, I'm sure the other competitors will be running better systems, more power or more better branded subs. I'm in it for the fun factor and the sence of acheivement but a thophy would be nice :-))

Cheers for all your advice.

Ps. When i compete i'll let you know the results...

[Ray De Man]

Acarmody, I checked out the source of the rather loud flapping and yes it is the air vent things. I'm thinking of doing the same, just cover it with sound deadener but maybe perce it with some holes so it's not blocked completely.

Yeah i'm running just 1000rms into them @ 2ohms but yes it's strange. I think but I might be wrong is that with a port you get more volume, where as a sealed you get more thump!

What amp are you running mate?

[Ray De Man]

Ok I did the soundproofing on those poxey flaps, sounds better but looks like I need to do the outside as I can still hear them!!! I did SD the whole boot floor aswell and that clearly made a difference. I guess the next project will be the roof, hopefully at the weekend.

[acarmody]

I'm running two Cadence ZRS-6000D amp 700wrms each to bring it to 1400wrms at 4 ohm. I will hopefully get around to building some ported box(s) one day.

Have ya had the same guy look at the windscreen seal? I might think about getting someone like O'brien to look at it or someone. I've only sound-deadened the boot and the door and I've never had a problem with the windscreens or roof. The parcel shelf carpet though what a pain in the rear, kept flapping and hitting the windscreen hard, really loud. So as lazy as I was I jammed some spare link-pin bushes between the rear windscreen and the carpet, much much better.

[Ray De Man]

I have used O'brien's 3 times already. He has checked the condition of the rubber but it is perfect condition. I think ported is the way to go but that's what I recommend with these subs. Are you using the 2008 version of the L7 or earlier model?

I can't at the moment hear the parcel shelf as all I can hear is the bloody front windscreen vibrating. I only usually go upto volume 20 on the stereo, 27 max (I think 62 on the Pioneer) but I can't see anything out of my mirrors just a very blurred image.

How did you get your amps mounted, on firewall or on sub boxes? I got my two on firewall and they overhang over the centre seat rest.

Have you got the carpet piece the covers the boot lid? I bought one for mine from a Calais, Made alot of difference and stopped a few more vibrations from the rear-end.

[StoneX]

...The parcel shelf carpet though what a pain in the rear, kept flapping and hitting the windscreen hard, really loud. So as lazy as I was I jammed some spare link-pin bushes between the rear windscreen and the carpet, much much better.

My anti-parcel shelf vibration monkey... His hands are jammed in the gap and has stopped the rattling. Errr... window isn't that dirty anymore


Ray De Man... Does your vision blur at all with that setup? On certain songs I can't read number plates of cars in front of me due to me vibrating... I haven't had any issues with window seals and my subs are in sealed boxes designed for sound quality