Audio/technical question

[68_Mercedes]

As I've mentioned before, we have an audio sponsor for our '67 W108 250S, and plan on using it in audio competitions at some point in the future. We're in the process of working on the audio design, and it has been suggested that the metal divider between the passenger compartment and the trunk is going to cause a problem with sound quality. It has been suggested to me that this divider needs to be cut out. However, I'm uncertain as to what negative effects this might have in the long run. Per my understanding, these vehicles are basically a "unibody" design.. so I'm wondering if that divider might actually serve some purpose beyond just being a simple divider. Does that divider serve in any way as some sort of a structural support, and would it potientially harm the vehicle in any way if we were to cut it out????? I would appreciate some assistance on this, as I am very wary of just going in and hacking out pieces of my car......

[Mark V]

I think its safe to say this panel adds torsional rigidity to the body structure in the critical area of the rear suspension and removing it would be detrimental.

[68_Mercedes]

That's pretty much what I was thinking. I'll have to do some thinking to figure out how to keep this panel intact and still get to the level of sound quality we are hoping to achieve.... Any suggestions would be appreciated...

[psfred]

Buy a Chevy.

That panel (which should in fact be in ALL cars) is what protects you from rear impacts. Whithout it, the passenger compartment will spread out and collapse.

Cutting holes in it will reduce the crash safety much more than you might think.

Peter

[Mark DiSilvestro]

Were you planning some sort of mega-woofer box for the trunk? There are subwoofer units that can fit under the front seats, but those might not provide the level of sound you're looking for.

That rear panel also serves as an additional firewall, in the event of a rear end collision rupturing the fuel tank - one reason I've resisted the urge to cut speaker holes through the rear shelf in my old Benzes.

Happy Motoring, Mark

[68_Mercedes]

Originally Posted by Mark DiSilvestro

Were you planning some sort of mega-woofer box for the trunk? There are subwoofer units that can fit under the front seats, but those might not provide the level of sound you're looking for.

Happy Motoring, Mark

Actually,yes, quite an elaborate woofer system indeed. But I am not willing to compromise the car for it... Hmmmmm will have to do some thinking about this....

And no, I don't think the underseat idea would quite get us to the level we're hoping to achieve....

[Mark DiSilvestro]

After some experimenting, I came up with an acceptable audio system for my '60 Fintail that didn't involve cutting large holes or leaving expensive components in plain sight for thieves. Behind my drivers side dash, I installed a 100 watt amp, with a lighted toggle switch to supply power. The amp drives a pair of 2-way cube speakers, each rated at 50 watts and mounted on the rear floor. Plugged into the amp's RCA input jacks is a stereo adapter cable that connects to the headphone jacks on a Panasonic CD player or Panasonic FM/cassette player that sits in my center tray, between the front seats. When the car is parked, I usually fold the armrest down to hide the players or sometimes I lock them in the trunk.
It sounds decent, with more than enough volume, even with the windows open. And I can connect to any future audio player that has a 1/8" headphone jack - minidisc, MP3, I-Pod. There's now even a small sattelite radio unit availible that plays through a headphone. The old tinny Becker radio remains in the dash to convince nearby hoodlums that there's no expensive audio system in my car.

Back to the subwoofer idea - awhile back someone posted here on the car audio forum about his system using a single compact Blaupunkt subwoofer under his seat. Would a pair of them, one mounted under each seat be a possibility? Or perhaps 4 would fit.

[68_Mercedes]

The bad thing here, is we're not looking for "decent" or even "good" sound quality.... we're looking to put this car in audio competitions, which means we need awesome sound quality...... So somehow I have to manage to use the trunk without tearing the car half to hell.... (scratching head).... how bad would it hurt the car to cut 2 holes in the divider... say big enough to install 2-12" subs or 2-15" subs (preferrable)????? If necessary we could even build some reinforcement braces to help to counteract our cutting the holes in the wall.... Can anyone say how much the car depends upon this divider wall in regards to structural concerns?

[68_Mercedes]

Oh, also, the subs I intend to use require 2.5 cubic feet of box space to accomodate them, which is why they wouldn't work under the seat......

[Mark DiSilvestro]

You could add braces, though the ultimate test would come if you ever got rear-ended. And any large holes in that divider would negate any fire resistance there. Though, with the gas tank mounted under the trumk floor, you would still be somewhat safer than many other old cars, especially '60s Fords, where the gas tank WAS the trunk floor!

Happy Motoring, Mark

[68_Mercedes]

I'm not too worried about the fire resistance. With a little work, I can compensate for that I believe. Part of my work involves fire barriers, and how to design them, so I think I could implement some features to retain fire resistance.... My main concern is damage to the structure should I cut holes in the wall....... I'm thinking that just cutting 2 holes in the wall shouldn't compromise the integrity of the wall too badly, atleast not so much that I can't compensate with some additional bracing. But I need to know how much of a factor this wall is in the structural stability of the vehicle before drawing a definite conclusion........

[cth350]

The side walls where the rear roof pillar meets the rear quarters is no less than 5 layers of steel welded together. It's easy to slice apart using a sawzall.

In your case, I'd do what the racing folks do, start by perforating the wall in a honeycomb fashion. Remove the metal in the flats. Don't damage the ribs. You need to do it with a chassis punch. Presuming of course, that you want the job to look good. There are some engineering guidelines for size and location of the holes. It's a question for a mechanical engineer. Also, you can weld a series of stiffeners to what's left.

You get extra credit for keeping the job as "original" as possible. In this case, that means factory parts. You'll find that correct benz firewall material is about 60$ for a piece large enough for one car. You might want to use it on what's left of that back panel to cut down vibration. Then again, its sound deadening quality may be exactly what you don't want.

-CTH

[WANT '71 280SEL]

Mark, are you saying I shouldn't mount any 6x9's in my future fintail's rear dash? I wouldn't care much for keeping the original look so long as it wasn't TOO much of a change. I understand he's talking about something else, but would it be alright to just cut two holes there for some speakers behind the back seats? Also, where would I be able to mount front speakers (preferably w/o cutting into the door panels?) You can PM me if you wish, sorry for hijcaking 68.
Thanks
David

[M_Anker]

I have a 1970 280SEL, and the rear deck has cut outs for three 8.5 by 3 inch speakers. I used a very unconventional design where I installed a pair of three inch full range drivers made by Tang-Band (www.partsexpress.com) which sell for around $12 each. I vented the back wave into a miniature transmission line box that converges where the cutout for the center speaker is. I used 3/4 inch think cherry boards with the edges all radiused to make the speaker baffles, and another cherry board to make the port plate with two flared ports. It looks really nice, and sounds decent. I didn't want to cut any more metal out than I already had to work with, so I used the small drivers. It is very clean and detailed sounding, but lacks bass. I wonder if a small subwoofer could be built into the back seat rather than cutting any steel.

I'll have to post pictures of my setup. It is very unique, and really keeps the wood trim style rather than black grill plates all over everything.

I also used a pair of 3.5" auto speakers in the front speaker housing. So I basically have a three channel system, a right-rear, center-front (two discrete channels, though), and a left-rear.

I wouldn't hesitate to cut the top deck, as there should be die-cut plates there already. The back plate is a bit questionable unless you plan to span the whole panel with steel bars.

[Mark DiSilvestro]

Early '60s Pontons and Fintails don't have speaker cutouts on the rear shelf. The shelf and divider are solid panels, with only small holes to secure the seats and trim. I believe this was designed to reinforce the rear body and provide a firewall in event of a rear end collision. So I found a way to provide decent sound in my Fintail without cutting holes and tempting thieves. I put a pair of heavy but compact two-way cube speakers on the rear floor, powered off my 100 watt amp. It doesn't make my whole car pulsate, like those thousand watt, rolling boom-boxes that the 'Ricers' drive, but I'm very pleased with the sound.

My '72 W114 250 originally came with a Becker Europa 4-speaker stereo radio so it DOES have two 4" x 6" factory speakers, mounted in cutouts on the rear shelf, but that shelf has another steel panel below the speaker holes that still blocks off the trunk. That extra steel panel does inhibit bass, so when I replaced the radio, I mounted a pair of Sony 6 x 9s in the under-dash cardboard panels to replace the pair of original, tinny 3" Beckers that were mounted on the footwell side-panels. My original 4 x 6 rear shelf speakers now just add a little 'surround' sound for the back seat area.

Happy Motoring, Mark