narf

hey, i want to mount replace the 10" woofer in my rear deck with a JL Audio 10w7. Now having taken a look around, i think the stock unit is firing down into the trunk (though im not sure), which seems like a dumb idea. I want mine firing into the cabin, and then ill build a cabinet to hang directly below the rear deck (in the trunk).

Looking underneath everything in the trunk, there is a metal brace the runs from one side of the car to the other. There are holes for the sub to breath, but it doesnt seem as though the brace is removable...

Do i have to cut through it to get my sub in here or can the metal brace be removed somehow? Does any know its function?

Do i need to remove the back seats (which arent foldable) to remove the sub?

Thank you


Richard

Diesel Benz

- Remove rear seat cushion,
- remove rear seat backrests,
- remove rear head restraints,
- remove paneling from C-pillars,
- remove rear shelf

and you should have access to the speaker.

narf

what about the metal brace? Should i cut through it and just leave a hole for the new sub?

Or should i remove the whole brace? Whats it for?

edit: im referring to the metal brace in the last two pics...

Diesel Benz

It is your car but I wouldn't touch the metal parts, they are accurately designed to reach the body stiffness. I doubt the car would pass inspection at my place if any of similar parts were cut.

rob13572468

first of all, the whole issue of the sub firing into the trunk or into the vehicle is a misnomer: any sub works equally well either way in that the sound vibrates on *both* sides of the sub the same amount. the reason the sub is mounted with the magnet facing up is purely practical: it keeps the sub basket and magnet from hanging down into the trunk area and taking up space. you can mount your new sub either way and the performance will be the same; just keep in mind that if you reverse the direction of the sub you must also reverse the polarity of the wires to keep overall system phasing the same. (you may still need to mount the new sub the other way since the larger magnet may not fit in the stock position)

secondly, the "metal bracket" is part of the unibody structure: that is to say it is a load bearing brace and doe contribute to the stiffness of the vehicle. that being said you *can* cut a mounting hole as long as you do the following: cut the hole using a jigsaw and metal blade to the size of the mounting diameter of the subwoofer that you want to use. then you need to source some 1/8" plate steel and cut a ring about 5/8" larger with the same diameter hole and weld it to the existing brace. then drill mounting holes and mount the sub. the ring and the sub together will provide more than enough reinforcing to accomodate for the removed section.

finally, you should note that the sub that you want to use (jl w7 series) is not well suited at all for this application... the existing sub is an infinite baffle subwoofer, meaning that it is designed to work with very large enclosures, effectively using the trunk as its enclosure. most JL subs work in small sealed enclosures (10w7 is optimal at 0.75 cu ft) so your ideal solution would be to not only cut the hole but build an enclosure that mounts to the underside of the rear deck and (or on top) and provides that .75 cubic feet. if you simply drop in the 10w7 it will work but not very well and its power handling will be very low.

narf

thanks rob for your very informative post.

i didn't know this...

my goal was to mount the sub in the stock position in the rear shelf, and then build a sealed enclosure to hang below the rear shelf, exactly as you recommended.

I am now, however, having some doubts. The "metal bracket" seems to hang a good 10 or so cm below the rear shelf. The sound would then be "leaking out" between the shelf and the enclosure unless i

a) remove the metal bracket completely and mount the enclosure directly up against the rear shelf

or

b) remove a section in the middle of the rear bracket and mount the enclosure and mount the enclosure as stated in a)

neither of these options seems to be good, even though several people seem to have removed and/or drilled holes in this braket in their w211s to accommodate a larger sub.

Will the "leaking sound" be a problem - and should i just forget this mounting option, and put the sub somewhere else, or can i mount it against the bracket after drilling a larger opening for the magnet of the 10w7 and reinforcing the bracket?


edit:ed because i cant spell...

rob13572468

ok i see what you are trying to accomplish... there are a couple different ways you could do this... the most important aspect is to make sure that the sub enclosure is tightly sealed. one way to set up an enclosure would be to cut a square opening in the shelf and reinforce it the same way as with the round hole. then build a square box that would fit through the opening so that part of the enclosure is above the metal bracket and a smaller part below. the main issue is that the metal braacket that you are referring to is the actual rear shelf and then the trim is mounted several inches above.

the problem is that there is no easy way to do what you want to do without most likely building a complex shaped enclosure. the ideal position for what you want to do is to have the sub facing up with the face of the sub just below the grille this will mean that the enclosure top would be ~5 inches above the metal shelf but just below the trim level. since the w7 mounting depth is something like 9 inches the enclosure will also have to extend another 5 inches below the deck. as i posted this is why cutting a rectangle in the metal shelf and having the box fit through will allow you to build a basic rectangle box for the sub.

narf

alright, i follow what you're saying, and im starting to wonder if it really is worth all the effort.

I suppose there are three factors involved.

1) Effort - Im willing to spend time and energy making things right if it ends up being worth it...

2) Trunk space. 0.75cu ft isn't an awful lot of trunk space to sacrifice
3) Sound quality.

If sound quality isn't compromised by building a 0.75 cu ft enclosure and mounting it in the trunk, i'd be willing to sacrifice the trunk space, especially since the required effort is considerably reduced. If sound quality however will be better mounting the subwoofer according to my original plan, im going to have to break out the power tools.

So, i suppose i now ask you this:

How will it sound if i put the subwoofer in a sealed enclosure in one of the rear corners of the trunk. I assume its still best to remove the stock unit, and leave only leave a hole in its place for the sound to propagate in to the cabin (or could i be wrong again).

ajent420

This is what I ended up doing with my W210....Not exactly what you are/want to do, but I ended up with what your asking about.

And it sounds F-ing sweet!!! Nothing like getting bass back in your ride.

https://mbworld.org/forums/e-class-w210/203690-how-adding-sub-your-stock-bose-system-line-output-convertor.html

rob13572468

yes, you can mount the subwoofer in a box and stick it in the corner of the trunk and believe it or not it will actually play louder at lower frequencies than if you were to mount it in the rear deck. the reason for this is because of something called acoustic loading: every enclosed space has a transfer function which is an equalization effect that causes certain frequencies to be boosted or cut simply by operating a speaker in that space. placing a woofer box in the trunk usually will create a very nice boost at ~45 hz which gives the bass a nice 'thump'. there is one drawback to placing the woofer in the trunk and that is that the some of the acoustic energy will transfer into the vehicle structur causing lots of different rattles, mostly in the trunk lid. the only way to combat this is to pull the trunk apart and coat every surface in a sound dampenign material. additionally, you will still need to at least remove the factory sub to allow a passage for sound to come into the vehicle.

the deck mounted box is really the best way to go as far as overall result. firing the sub upwards into the rear window also results in very nice bass with noticable low frequency boosting but without the annoying rattle problems. the bass will also sound very clean and clear since the acoustic energy is directed using this arrangement.

to answer your question, yes you can simply mount the box to the underside of the metal shelf and fire the sub up from there (as long as you are ok with the box taking up the space). you will still need to cut the 10" hole to allow the sub to sit flush with the metal shelf and fire through unobstructed. you will also want to line the area between the shelf and the top trim with insulation to limit possible rattling of the rear trim itself (e.g stuff fiberglass insulation between the metal shelf and the top trim all around the sub opening so that the energy flows directly up.

ajent420

Kind of off topic Q for Rob...would you point a sub box in the trunk upwards towards the rear deck? I've never seen anyone do that as most people tend to point the sub towards the rear. I point mine towards the side of the car that has the greatest distance to travel (In this cars case, towards the right side...)

narf

Thanks again, Rob, for your insight. Since the enclosure for the 10w7 needs to be 1.34ft3 i need to run out to my car and figure out if i can sacrifice that kind of space hanging directly from the metal shelf. Im afraid (especially with the mounting depth of this woofer) that the enclosure might hang too far down, making access to the rear of the trunk akward.

If the size isn't too bad, i think this is the best solution, as its nowhere near as complicated as monuting a woofer directly to the rear deck and building an enclosure around it as i originally intended.

ajent420 asks an interesting question - does the orientation of the woofer in the trunk play a significant role on the sound experienced in the cabin?

rob13572468

if the sub is ported directly up through the rear deck then you want to point it straight up since the trunk space is effectively seperate from the rest of the vehicle. if you are simply placing the sub in the trunk then you will b e more likely to achieve better performance by facing the sub 90 degrees off axis from the plane of the opening (e.g any direction except up or down). the reason for this is again the transfer function of both the vehicle interior and the trunk. there are actually two ways to calculate optimum placement: one is to place a test enclosure in the trunk and a frequency analyzer in the driver seat. then white noise is played through the speaker and the resulting function is recorded at the microphone in front. the enclosure is then turned through 360 degrees and the test repeated until the best overall response curve is obtained. the second method is to take the finished enclosure and set it in the trunk and simply move it around while playing music until you get the best bass response. method one is the ideal way to do it.. method two is pretty much the way everyone does do it (including alot of supposedly high end manufacturers... reus... cough)

in your case... you are empirically correct... pointing the sub to the side works very well in mercedes vehicles because it has the greatest overall distance perpendicular to the face of the sub. in many other vehicles the front to rear direction works better (though usually resulting in licsense plate rattle. as before a quick test while turning the enclosure will determine the best overall position.

rob13572468

i didnt realize that the 10w7 needs 1.25 cuft... thats going to make a pretty big encosure back there once you figure in the 1" MDF. i was thinking of the 10W6v2 which is 0.75 cuft. you may want to consider going to the w6 instead since it is a far better overall match for your particular situation. the main difference between the two is in how the woofers handle heat dissapation and excursion at very high power levels. that being said the 10w6 plays *very* loud and low even when moderatly powered. either way you will want to look into building this type of enclosure (see attached pic) which is ideally suited for under deck mounting.

narf

Maybe a 10w6 is a better idea in that case...

at the risk of sounding like an idiot - i cant figure out your drawing. It that a picture before "folding" it into a box? Or is in the enclosure viewed from above with "wings" for mounting to the rear deck?

rob13572468

its a side view... the idea is to build a box that is wide but shallow so that the overall top-bottom dimension is very small. the problem is that the magnet will not fit in such a shallow design so in the middle you would fiberglass an area just larger than the magnet assembly that would extend further. the end result would be that as you looked into the trunk you would see a box that was maybe 24" wide but only 5" tall except in the middle where it would drop down 9" to accomodate the sub.

narf

now thats really smart. thanks rob. you tha man!

do you think this is something i could accomplish myself (i'd obviously have to look into working with fiberglass - something i haven't done before), or should i just not bother, and try to find someone to make it for me? You have any clue as to what something like this will cost me?

Thanks again.

//Richard.

rob13572468

if you have basic woodworking skills and access to a table saw then you can build a standard rectangle box without issue. as long as you make sure that you are building the box to the proper dimensions and volume and it will sound great.

working with fiberglass or body filler takes a bit more skill but is not overly difficult... the box that i described basically starts out the same way: you build a wide and shallow rectangle box. then you cut a hole for where the magnet will protrude past the existing surface and proceed to add a dome made out of filler material. this can actually be made much easier with some simple improvisation: set the speaker in the box so that the magnet end is sticking out. now you go buy a plastic salad bowl that is sized so that you can set it on the surface of the box and it covers the magnet. screw the bowl to the box with 6 screws. go get a gallon can of bondo and mix up a batch and start spreading it over the bowl until you have built up a 1/2" layer. sand it smooth and you're done... (see attached pic)

as i said, its certainly something you can DIY if you have some basic skills and the time to do it. you can also get it professionally made for around $200-$400.