107 560SL subwoofer idea

[donbryce]

I'm getting very exited about an idea for a sub for my SL, and thought I would share. It seems like the trunk is very well sealed off from the passenger cabin (gas tank and steel bulwark), plus it's very small to begin with and I would like to save some luggage space.
Right now, I have one of those 'kinder seats' (came with the car) that really aren't big enough for an adult, so it's going to go in favour of a custom storage space.
Not having seen, except pictures, how the original storage area is constructed, I'll assume a plywood panel on the bottom and one on the backside, both carpeted. What I'd like to do is set up the sub so that no matter what is in the storage space, the sound from the speaker will never be covered. That eliminates the 'floor' panel and rear panel (if it were built out from the backside).
I want to use one of the newer shallow sub designs that require only 2" - 3" of mounting depth. That should allow for 1 12" sub mounted on one or the other side of the 'floor' panel, with a total enclosure volume of about 1 cu.ft utilizing the entire back 'seat' area/depth.
Then, I'll make a panel to cover the 'seat' area, looking just like the original with carpet, but mounted about 2" over the panel that the speaker is mounted on. I'll make a grille on the front side, across the width of the back, again about 2" high, so the sound will always be exiting forward.
I'll loose only 2" - 3" X the depth X the width of the rear storage space, the speaker will never be covered with luggage, and will be almost completely hidden.
I'm not sure what to expect with the bass firing into a 5 sided box, with one side only 2" from the cone surface, but it might just work. Comments?

[GSMITH]

I went a little overboard but I never used the space behind the seats.
Audio Upgrade to my 86 560SL No Humps.
The above setup left everything original.

The original setup without the seat was a ply cover over the bottom that a lot of people just mounted 6x9 speakers into. This is the way I got my car and I was not happy with the setup when the top was down. The back is covered with carpet between the side panels.

Do not loose your excitement but....
I do not think you will get a good bump with the 12" unless you can seal the back side and 1 cu/ft is not enough for 2 - 12". Sealing the back will be difficult unless you are good with fiberglass. There are a lot of lumps and bumps under the seat and nothing is straight. You will also need to mount an amp in the 2" gap that will cause it to overheat.

I think you will have a hard time getting it to sound good unless you can also get some midrange speakers mounted somewhere. You can mount 4" in the front but they will not give you much mid range.

Your concept is good but if you change your design to a 1 - 10" ported the end result will sound better because of the limited space. Do not worry about the direction of the bass output. Unlike mids to highs bass in not as directional. That is why the trunk mounted subs still sound good.
Not that this is a good option in the SL since it is very well sealed off and would be very difficult to port into the interior.

If all you want to do is add a little bass there are slim bass boxes that could be mounted under the front seats.

[BoomInTheTrunk]

check these out you can have small boxes with them check ebay for the prices they will be was cheaper.
http://www.kenwoodusa.com/Car_Entertainment/eXcelon/Subwoofers/KFC-XW1200F

Best part is that the boxes only have to be 1 cubic foot. so one box that is about 6 inches tall all the way across the back seat area should do it.

[donbryce]

Originally Posted by GSMITH

.....I do not think you will get a good bump with the 12" unless you can seal the back side and 1 cu/ft is not enough for 2 - 12". Sealing the back will be difficult unless you are good with fiberglass. There are a lot of lumps and bumps under the seat and nothing is straight. You will also need to mount an amp in the 2" gap that will cause it to overheat.

Input greatly appreciated GSMITH. You have expended a lot of effort in building your system, well done fabrication, and I'll bet it rocks. However, what I'm after is a 'stealth' set-up that doesn't occupy the rear storage area.

I think you are right on with the back of the enclosure molded to the contours of the floor. I found a great article on building one with this technique, and that was my plan. I lost it, but this one is pretty close to what I'd try: http://www.talkaudio.co.uk/vbb/showthread.php?p=799862

I would mount the amp in the trunk.

For front staging, I'm going to use 4" Eclipse 8243 2-ways in the dash, for now, and will investigate larger door mounted speakers, for mid-bass and fill, later.

I have an Infinity Basslink in my 380SE, which I'm very happy with, and a Kenwood WOOX in my Mazda, which I'm not so happy with. The parcel shelf in the 380SE is acoustically transparent, and the Basslink is just what I'm striving to duplicate, but without the space issue. I'd like to try the Basslink in the SL, and experiment with porting from the trunk to improve sound transfer. I did that in my streetrod with some success. However, I'm straying off-topic a bit...

BoomInTheTrunk, it seems like these shallow subs are something fairly new? I was thinking of these when I dreamed up my concept, as they only need 2 1/2" depth and .625 cuft. Not available yet though.

http://mobile.jlaudio.com/jlaudio_pages.php?page_id=213

[jfilipcic]

I did a 10" sub in my passenger side foot well in my w124 cabrio. All said and done it took approximately 5 1/2" away from the foot area and 3" of it was useless anyways. I have since the picture changed the sub from the Bazooka in the picture to Focal.
Hope this helps.
Joe

[GSMITH]

Interesting new SUB design but 3ohm is strange. You might want to make sure your amp choice will be stable under 4ohms if you get that one. Since you are mounting horizontal you could go with the 13.5" in April.

After rereading your original post your real question is about the box shape. What you will have is a bandpass box. See http://mobile.jlaudio.com/support_pages.php?page_id=151 for some basic information. I like your idea but there is no way of knowing how it will sound until after you make it. There are some sites I have seen that try to calculate different box designs response but your final results may not be what you simulated.

Since I have not heard either of the boxes you have I can only tell you about my experiences. I had a bazooka tube in a 126 mounted in the trunk ported thru the first aid hatch in the rear deck. It was quite boomy but not a lot of punch. It worked ok with the stock 5x7 speakers. Not sure if your 380SE has the first aid kit but it made quite a difference after I removed it and propped the cover open. I thought about putting the same tube in the 107 but after looking into the amount of chamber gain I would lose when the top went down I decided against it. I really wanted to go with 2 12's but they ended up to big for my design. The 2 10's ended up giving me what I wanted which was a good balance between boom and punch and not have everyone know when I drive by. Yes it rocks in the car with the top up or down but if your more than 5' away it is not annoying. At least at my normal listening level that is way too loud for the spouse. I do have to reduce the bass level when the hard top is on to adjust for the chamber gain.

I think if you do not add the second layer so you end up with a bandpass and instead have a sealed box it would sound good. If I wanted to use the space behind the seats I would build a sealed box and just cover the speaker with a flat grill painted to match the interior to protect it. Firing the bass forward is not that important considering (from JL audio) "sub-bass waves vary from 56.4 feet (20 Hz) to 11.28 feet (100 Hz)".

I would be interested how you ported your street rod. Got some pictures?
It would be pretty hard to port from the trunk of the SL and still be able to put the top down.

[donbryce]

Originally Posted by GSMITH

After rereading your original post your real question is about the box shape. What you will have is a bandpass box. See http://mobile.jlaudio.com/support_pages.php?page_id=151 for some basic information. I like your idea but there is no way of knowing how it will sound until after you make it. There are some sites I have seen that try to calculate different box designs response but your final results may not be what you simulated.....I think if you do not add the second layer so you end up with a bandpass and instead have a sealed box it would sound good. If I wanted to use the space behind the seats I would build a sealed box and just cover the speaker with a flat grill painted to match the interior to protect it. .

Interesting read, but I wonder if what I'm contemplating will really be a true 'bandpass' design? If the speaker is sitting in a sealed 'box', facing up, it would then require another enclosed box with a port to be a bandpass, right?

All I was thinking of doing was making a sealed enclosure of the required volume, with all sides except the front baffle for the speaker done in fibreglass, contoured to the floor and sides of the rear compartment. The carpeted panel sitting above the baffle/speaker of this enclosure would only act as solid place to put luggage or whatever, and the opening across the width (facing front) would not be a port, just, well, a 'vent' to allow the sound out. I did up a crude drawing to illustrate. In reality, the enclosure would probably be deeper to achieve a minimum of 1/2 - 3/4 cu. ft.

I was thinking that the set-up would work even better if the majority of the surface of this panel were made of some stiff mesh, or plywood with lots of holes drilled into it, with carpet over it. On my 380SE, I find that the thin masonite hatch-covers over the first-aid kit and storage compartment (thin plastic themselves) as well as the sheet metal package tray are what I'd call 'acoustically transparent' for bass. In other words, unless there is a steel tank full of gasoline and a heavy steel 'wall' between the bass source and the listener (as is the case with the SL), sheetmetal and masonite don't interfere with good bass transfer. I'd think carpet would act very much the same.

Of course, having the trunk space to let the sound waves bounce around in would help too....lots of theory here, I guess, but I'm basing my guesstimate of how this setup will perform more on what I've experienced with the few I've built myself. I'm no expert either, just a DIY'er and I love to try different stuff, and I know you know what I'm talking about!

Originally Posted by GSMITH

I would be interested how you ported your street rod. Got some pictures?

I documented the 2 systems I built and rebuilt in my rod on my website. Grab a coffee while it loads, it will finish, believe me...
http://bryceandbernie.homestead.com/SoundSystem.html
The 'ports' are really just a couple of holes in the steel wall separating the trunk from the cabin, covered on the inside with grilles and carpeting in the trunk. This, plus the 380SE experience, convinced me that it doesn't take much to let the bass 'out' from the trunk to your ears.

Joe (jfilipcic), that's a really inventive design. Very little volume though, what does it sound like, and how do you keep passenger's feet from accidently punching out the speaker???

[GSMITH]

Great Rod!!!! I had to laugh at the MB wiring harness. I hope it was not one of the biodegradable ones.

I am rethinking the sub in the trunk. There is an air passage way from the trunk thru the top cover compartment to the side panels in the rear. That is how the original owner ran the wires for the amp in the trunk and how I ran the power wires from the battery. The biggest problem I can think of is if the side panels end up squeaking and rattleing. Not sure how much a difference there would be top down vs top up. But between the cabin loss and the soft top getiing in the way the only way to know is to try. If it works you would not have to lose the rear seat. Thanks to the PO I do know if the side panels are cut open you will get road noise from the rear wheel wells. Also the plastic in the side panels is pretty brittle after 20 years.

It would be easy to throw the basslink in the trunk with a temporary setup to check it out.

If you go with your original idea I do not think putting holes in the cover panel would make any difference. Since you like to try different things it would be easy to try to make this setup a bandpass and play around with the port before you covered it.

I have not seen any 107's with speakers in the doors. From the pictures I have seen with the door panels off makes me think there is not much room. I have been thinking of creating speaker pods where the map pockets are but it might make it harder to get in and out of the car.

[GSMITH]

Found this today
Special request (PICTURES), repair photos reference section

It does not look like there is any room in the doors for speakers.

[donbryce]

Yeah, that's a pretty full door alright. I'm sure though that about an inch depth inside the inner door skin could be available about where the front of the map pockets are.
I like the idea of building a pod just above the front of the map pocket, kind of extending the pocket upwards to accomodate a 5" - 6" speaker. I'm looking for grey vinyl, and carpet, to match the interior now.
All ideas are on hold as the SL is sharing the garage with the SE, and I can't open the doors enough to remove the panels. When the @#$%^& snow melts in March, maybe, I'll move the SE outside and get at the SL interior again.
I'm definitely going to try the basslink in the SL, as you suggest, as this would still be the easiest solution.

[jfilipcic]

[/QUOTE]
Joe (jfilipcic), that's a really inventive design. Very little volume though, what does it sound like, and how do you keep passenger's feet from accidently punching out the speaker???[/QUOTE]

Believe it or not, there is approx .5 cubic feet there. Sounds good for what I listen to and had lots of punch even with the top down. The Pioneer deck I'm using has quite a bit of EQ capabilities and has 4 volt pre-out, so I can tweak it a bit and the amp doesn't have to work as hard.

The grill is quite rigid. Passengers feet are not really an issue.