Rear seat baffle dimensions

Topic: Rear seat baffle dimensions (Read 4717 times) previous topic - next topic

Rear seat baffle dimensions

March 28, 2007, 08:07:14 PM

Anyone have any dimensions of behind the rear seat? My subs are getting out of their tiny boxes and going infinite baffle (Eclipse 88100.4/TC Sounds TC-7...they like sealed boxes up to 7 cubic feet or IB with 650w of power handling/tons of excursion) but I need some measurements of how to cut the mdf baffle. In a little more than 2 weeks, I could do the measuring myself, but can cut the board before then.

I'm not sure if I'll remove the flimsy slanted bracing behind the rear seat on either side, but the plan is to use a primary baffle cut to fit up against the rear bracing (and sealed off around the edges or where cutouts are necessary such as at the top middle), then a secondary one that will attach to the back of the baffle that will hold the subs and give some front clearance for the 1.5" of max forward excursion. This second one will be easily replaceable in case I want to go larger than 10", compared to having to pull off the sealed baffle and resealing.

I know at least one person has done this before (12's in back seat, 10's in rear deck) so I'm assuming there's already measurements somewhere around here

Rear seat baffle dimensions

Reply #1 – March 29, 2007, 12:53:35 PM

I'm not shure if it got deleted frim this site or not. But I am running that same setup in my 84. I drilled out the spot welds on those cross braces. I let the center up and down brace. I put 2 12's behind the seat and 2 10" in the rear deck. On mine I used 2 pieces of wood not one solid piece. I used cardboard to get the right shape for the wood piece. I don't have any dimensions as I did this before I had any internet about 6years ago. Also make sure you seal all the holes in the rear deck and also seal the areas between the rear seat and the outer body panels. I will add that I tried several times to use one piece of wood but it was to large to fit in the truck and then into position. Also if you have 10's out might want to put them under the rear deck facing upward. I know my 10's you can't even see them unless you stick your head in the trunk and look up at them. Then when you open the trunk What box?, What Speakers?, Hell my stereo is factory it just thumps like that cause the factory used to make good stuff! LOL As for mounting the woffers under the deck I just cut out some ply wood 2 layer of 3/4" and bolted them to the deck and then the speaker to it. Also to seal the holes in the rear deck I used fiberglass resin with the glass hairs in it. I taped over the holes on the underside then did the fiberglass on top. And to seal up the behind the side panels I used expand foam. I also use tape to keep the foam from expanding any where I didn't want it to. hope this helps

P.s. The better you seal the trunk the louder and better the sound. Also I remeber reading something about boucing sound off the rear window increases the DB level. Ofcoruse that info is from back in the day when I was a punk kid with the boomin system fever.

Rear seat baffle dimensions

Reply #2 – March 29, 2007, 01:42:08 PM

Ah, it was you with that setup. I think the rear window thing has the same effect as aiming your subs backwards when in the trunk. The additional distance, if only a couple feet, before the sound hits your ears helps increase perceived output. I'm going to try through the rear seat first, if I'm not happy, I'll move them to the rear deck. Anything really is better than what they're mounted in now, but even so, these subs extend quite low in their small boxes.

Sealing the back seat off isn't a problem, and I still have a good 60 or so square feet of RAAMmat left. Plan on using a ton of open cell foam under there also to help control rearend/exhaust noise.

As far as using two boards, if thats the way to do it, thats fine. I'll give the cardboard thing a try as soon as I get some large enough. This will be done after I get around to installing my eD 7kv.3 subs in the doors. Their suspension can take ~170w free air before it starts to get sloppy (26v on amp's output playing a 50hz sine wave at 0db). Surprisingly, they can play pretty cleanly up to 3KHz also, but with probably 5db falloff that high. Just waiting for them to send a replacement dual 4ohm as one says 4 ohm on the back, but the multimeter gives me 2.3 on each coil. Other gives me 4.3/coil. :rolleyes:

Rear seat baffle dimensions

Reply #3 – March 29, 2007, 06:18:06 PM

well good luck and hope you like the way it sounds. On a side note the way turning the sub box bacwards in the truck is to get rid of cancelation between the front wave and back wave(reflected wave) of the sound waves moving around in the trunk.

Rear seat baffle dimensions

Reply #4 – March 30, 2007, 02:30:49 AM

Quote from: ipsd;137122

well good luck and hope you like the way it sounds. On a side note the way turning the sub box bacwards in the truck is to get rid of cancelation between the front wave and back wave(reflected wave) of the sound waves moving around in the trunk.

I've heard so many theories on this that I gave up trying to get a definite answer (as to why the rear waves cancel out less).

My only concern with firing through the rear seat is the thickness of it all. Sure its cheap foam, but not sure how much it'll actually absorb. Then again, it may not matter too much. Was playing my 7kv's today and they can "handle" 20hz tones just as well as they can play 50 or 100hz, just have to watch the gain levels when going that low. No bottoming out or anything.

Rear seat baffle dimensions

Reply #5 – March 30, 2007, 09:40:46 AM

As for the seat thickness don't worry about it. I left all the foam in my seat. If you do this right you have sealed up the front of the woffer to the interior of the car and the sound has no choice but to come thru the interior to your ears. Trust me this will make a big difference in the amount of low end sound. Since I have done this to my car I have done this to many other cars for friends and such. Eevery time that ask me what did you do to make it so loud. I say nothing. That is how effective this setup is. This setup is like making the interior part of the box the woofer is in. Not really but it shure sounds that way. As of right now my real amp is in the shop getting fixed. All I have to power my subs is an old Pyramid amp. I bet this thing puts out maybe 25watts a side and I still have good low end not near as loud. But highschoolers ask what do you have in that thing? I want my soundstream back. Then they won't ask me questions they'll be to def from the sounds of my subs. LOL

Now for the theroy on for the speaker canelation thing. When your box is in the trunk the sounds waves bounce around the trunk. These sound waves have a (+) or (-) just like the speaker wires. The + is positive sound wave and the - is negitive sound wave.
So when these + and - sound waves meet the cancel each other out and then you have zip. Just think about this math equation. (1 )+ (-1)=0. That is what is happening inside you trunk. Now when you turn the box around the wave length it changed so the (+) wave and the (-) wave don't meet and cancel each other out. The best way to see hear this is hook one sub up normal pollarity and then hook up the other backwards. Yes they are both playing but they are making almosy no sound. That is the cancelation. Now if you are to unhook just one of those sub you have lots of sound. No the cancelation isn't doing anything anymore.

Rear seat baffle dimensions

Reply #6 – March 30, 2007, 07:35:04 PM

I know perfectly well what cancellation is (an extreme example is simply free air. No sound because nothing stops the front and back waves from colliding). I've just heard too many "theories" on the forward/backwards thing that I gave up bothering to get an explanation.

Technically, it shouldn't matter which way the sub is pointing, as going forward or backward WILL cause the sounds waves to bounce back upon itself when it hits something, to cancel out much of the output. The only way to prevent this is an infinite baffle install to keep the front waves from EVER seeing the rear waves. No normal box will be able to absorb the rear waves (or front waves if firing inward), with much of it escaping to cancel out the wanted sound waves.

Can't remember where I read it, but the most plausible theory has something to do with the total distance of wave travel. If the sub firing back, hitting a reflecting surface, and coming back to itself is the same distance as the woofer is to the seating position, the least amount of cancellation will occur. Say your ears are 6 feet away from the back side of the woofer, and the front of the woofer is 3 feet in from the far side of the trunk. The 3ft + 3ft reflection = your 6 feet of distance from the woofer. For whatever reason, this setup gets MUCH more to your ears than if it were pointing forward, with the woofer itself in the same position of the trunk. as to why this works, I haven't a clue, but its like a 10-12db difference.

...or maybe its 2x ear distance than reflected distance. Don't remember.

Rear seat baffle dimensions

Reply #7 – April 01, 2007, 01:28:59 AM

All I can add at this point is things I may have left out. I also took that insulation stuff that was behind the rear seat back and glued that on the front of the baffle board. Yes I did cut out the holes for the woffers in it. Just added that to help with and vibration noises. Also I took some metal brackets and fastened them to the bottom of the baffle board and then uesed the seat belt bolts to hold the metal braket down to the car. This added alot of strengh to the board. I had to mount the metal in a vise and use a hammer to bend it to the shape of the car. I also drilled and used nuts and bolts with red locktite to hold the Baffle board in there. Also to help with a neat apperance on the I used silcone calking on the metal boady parts where the wood meat up to it. Then when after you bolt it up use a old rag to wipe off the excess silicone. I coverd the black side of the board in black carpet. I wish I would have thought about it at the time but you could use a router to cut a groove in the wood to hide the wires. Another tirck I used in my car with my sound stream amp was to cut a think steal plate the size of the amps on bottom. I then welded some square tube on the backside of the steel plate. I ran the wires through the tubing and out to the amp. Then I welded some steal plate on the bare end of the tubing. I mounted it right at the end of the shelf in the trunk on the vertical part at the front of the big dip in the trunk. When mounted it looks like the amp is floating. People were always amazed when they seen it. "What is holdong that amp up? , " Is that amp floating?" Had many people ask me that. ALso to mount the woffer to the wood I went to the hardware place and bought some of those things that you put behind the panel that are threaded and then used a bolt to mount the woffer. Works great and the bolts are way stonger than those wood screws lots of people use.

Rear seat baffle dimensions

Reply #8 – May 14, 2007, 10:07:56 PM

How many spot welds did you have to drill out on the brace? I've drilled out the ones that I can see, yet the thing's still stuck in place (even with a good kick). It appears the entire thing is welded, along with the top and bottom pieces of the center brace. Don't want to keep drilling until the center one separates, thinking of just dremelling out the brace now. Won't be able to reuse them then, and will have to get some parts to make my own new bracing mounted from the inside of the vehicle.

edit:
and this was with a 1/2" drill bit. Still grabbing for some odd reason.

Rear seat baffle dimensions

Reply #9 – May 14, 2007, 10:35:04 PM

Guys word of advice that cross brace in the rear of the car is to prevent structural stress,i wouldn't remove it.

Rear seat baffle dimensions

Reply #10 – May 15, 2007, 12:25:25 PM

Yeah, I'm not going to keep drilling until the metal no longer exists. Picking up some additional mdf to sandwich the subs and will mount through the holes already drilled (yet still attached? They are NOT spot welds on my car.). 3/4" spacer with routed out recessed area, along with 3/4" back board should be more than enough and keeps the braces intact without worrying about excursion clearances between sub and brace.

Rear seat baffle dimensions

Reply #11 – May 16, 2007, 10:02:55 AM

If you remove the brace and install a brace that is as good or better you shouldn't have a problem. I've had my car this way for 5 years and not a single problem from it.

Rear seat baffle dimensions

Reply #12 – May 17, 2007, 07:07:40 PM

I doubt you'd run into many, if any, problems even without any of that bracing if you don't beat on the car. Either way, factory bracing is pretty much left intact and everything was a success. I haven't even sealed anything up, yet it sounds like I'm getting at least 10-15db more output from my subs (they were in undersized sealed boxes before). It sounds like I get more bass with my volume at 30 than I was getting at 45 so I set amp gains and turned sub preouts down in headunit for now (until I get my 7" midrange speakers). It overwhelms the front stage crossed at 63hz/18db.

Only problem is the first baffle I was doing I did upside down and had to fix, so its slightly shorter than the other one...but its the drivers side so the spare tire will help make up for weight differences :p Additional bracing hasn't been done yet, but those will come later although I don't think they're even needed on my install, with how evenly the baffles pull on the mounting bolts.

The subs weigh 20 lbs each and truly rock for IB with 18mm of xmax and a whole 1.5" of xmech one way.

edit: Pictures! Of course, it isn't complete, but surprisingly I have no rattles except from the one bolt/washer that has no nut attached. Right baffle I used a rotozip and router...left one I switched out for the jigsaw/router. Same results, but much quicker and less sawdust. Turned out good enough without any tools to cut straight lines or circles. There is about 1" of clearance between the subs and cross braces.

Rear seat baffle dimensions

Reply #13 – May 17, 2007, 09:03:34 PM

So how should I do the amps? The small one's easy, but the 17" long full range amp is a it harder. Tempted to keep the trunk well, so maybe floating amps above/behind the subs? Should be pretty easy with the right brackets.

Rear seat baffle dimensions

Reply #14 – May 18, 2007, 04:15:26 PM

Ditched the floating idea due to price and weight of strong braces, so how's this amp shelf look (just thrown together to give myself time to think it out)? I'm thinking I should modify the brackets to give myself a much steeper angle for the amps, but dunno.