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boxed

Mounting Subwoofer Behind Seat onto Engine Wall

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I recently upgraded the entire sound system on my 2000 Boxster. The final addition to the system were pioneer premier 8" shallow subwoofers that I made custom enclosures for to fit nicely behind each seat. The enclosures fit perfectly but at the moment, they are not mounted firmly against the engine firewall. They are just sitting in place. They don't sound bad, but I can tell that I am losing some of the energy due to movement.

I would like to know if there is any risk to drilling into the firewall so that I can add some brackets and then utilize machine screws to mount the brackets and enclosures.

Has anyone done this before or does anyone have any suggestions?

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Not sure if I can add any help, though I've been keen to do a similar install myself.

Are you able to show any pics of the sub and enclosure.

More so, any tips at all on how you made the box? Material, technique etc?

Thanks!

Oh, and for me, in my last car, I mounted the sub only using velcro. It looked to be some industrial strength ones, but that stuck to the carpet like glue and never moved about. Cheers!

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I will take some photos for you as soon as I get a chance.

I actually constructed the boxes with wood and then lined the inside with insulated material making sure that I kept the volume required by the pioneer sub.

Since the back wall shape is not symetrical or straight I actually took 3 coat hangers and cut them so all that remained were 3 long wires....

I then began with the side nearest the center console and I bent the coat hanger in such a way that it followed the contour of the floor and the engine firewall, then I did the same thing with the 2nd coat hanger and did the contour closest to the door. When I was done, I had an exact contour of each side... I laid those on my wood, marked them with pencil and I now had the shape for an exact fit of the vertical pieces of wood that matched the floor and back fire wall...

The 3rd coat hanger gave me my side to side (horizontal) shape at the top...

I used the 8" shallow pioneer premier subwoofer (TS-SW841D) becuase the total depth of the speaker is only 2.5" - Perfect for a behind the seat application... What I like is that I now basically have a seat massager as the bass vibrates the seat perfectly with the music... It is an awesome feeling...

I like your idea of Velcro... I had the same idea before and had bought some, but unfortunately the Velcro I did get didn't lock into the carpet... I will have to keep looking as that would be a great way to do it without bolting to the firewall, and If I want to remove them, I could do it easily...

Thanks for the input..

Edited by boxed

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Ok, I took some photographs... I lined the enclosures with the closest color I could find. I will eventually replace it if I find something better, but for now, they are fine. The outer material I found at a fabric store, it is not carpeting which I thought would be too thick and hard to work with. The material is a plush velvety material (not shag).

Hope these help.. I showed one side, but the other is essentially the same.

post-20606-1186679012_thumb.jpg

post-20606-1186679023_thumb.jpg

post-20606-1186679032_thumb.jpg

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Are the enclosures you made a sealed box? If so, why do you think bolting them to the engine cover would help the sound??

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No, they are not sealed, they are open in the back.. I didn't have additional space (I had to balance the needed volume for the sub and the space between the seat and the firewall). I agree, if I could seal the back, then I wouldn't have to worry about it... Sealing the back is also tricky because it is a very odd shape.

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Ok, I took some photographs... I lined the enclosures with the closest color I could find. I will eventually replace it if I find something better, but for now, they are fine. The outer material I found at a fabric store, it is not carpeting which I thought would be too thick and hard to work with. The material is a plush velvety material (not shag).

Hope these help.. I showed one side, but the other is essentially the same.

How does it sounds? Can you give me an idea how much volume is required for that woofer?

David

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Hey guys, you seem to be asking me more questions than trying to address my initial question of screwing into the firewall... Can anyone help me?

I am happy to answer anyone else's questions also along the way yet I do need some input on my original issue...

Ok, how does it sound? I am driving it with a pioneer premier headunit that has rca outs for front, rear, and subs that go to my amp. The voltage out is very good from this unit compared to others such as alpine, etc. I have an ipod connection with it and the subwoofer, eq, frequency cut off (high and low pass) controls, and gain controls from the head unit are superior to other brands...

The amp is a 4 channel 1500 watt premier amp.... I have the rear speaker mod in it and replaced the 3.5" speakers that came with it (2 on each side), with 3.5" kickers (huge improvement). Since the front speakers already had a lot of gain and sounded good, I decided to drive the front speakers with the head unit (50 watts), then I have the rear speakers on 2 channels of the amp, and the 2 subs on the other 2 channels....

The sound is awesome! With top down and on the highway, I get full spectrum all around me along with great bass vibration on the seats. If I turned things up enough I would not be able to hear the sirens of a police car if I were on the highway, top down, and it drove past me....

The issue with the bass and why I want to lock them down is that I get the low, low response and the vibration to the seat, however, what is missing is the smoother/longer lasting bass sounds that you would get if it were constrained. The kick occurs (probably 60% of what it could be) but then the resonance dies...

This would not occur if the cabinet were locked in and not resonating at the same rate as the speaker... I do have the high and low pass settings set correctly, so I know this is not an issue. I currently compensate for the loss by boosting gain on the amp a bit for the subs and overcompensating the eq a bit...

The sound right now is awesome... I am a big sound person and work a lot in the studio recording, so I just would like it that much better.

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Hey Boxed,

Thanks for the reply and photos. Nice setup. I'll use your idea with coat hangers. Nice one....

As for securing it down. Can I ask on why?? Is the box shifting from side to side? Is it falling forward upon braking, or are you trying to psuedo seal it with the back firewall.

Anyway, for me, in a amp install I did, I had a problem where the amp would topple over. Not good. So I used a metal bracket to kinda hold it up right on the floor.

Please see my dodgy drawing. This way, the floor would brace it and it wouldnt fall forward. Again with velcro, it should hold fairly well, and it won't be permanent.

As for not being sealed in the back, I'm pressuming you must have made the box fit fairly snug. Any tips also on that.... I just know that a sub normally doent work well in free air applications

Thanks

post-19327-1186757517.jpg

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The enclosures are the width of the back (door to center console) so they do not shift side to side. Also, they do fit flat on the floor (thanks to the coat hanger trick). Since the back fire wall is not just an angled flat plane (it is quite an odd shape), it would be difficult to easily seal the back of the cabinet, that is why I left them open in the back. Because of the coat hanger trick also, and the fact that I angled the front of the cabinet a bit, the weight of the sub actually forces the cabinet to the back wall, so I do not have any issue with tipping at all.

I like your idea of the bottom bracket. Is there any issue with bolting to the floor??? Also, if I could get velcro to stick to the carpet, I would prefer that to any other option.... If I sell the car, I would probably take those out and replace the stock radio... Right now the way I set everything up (head unit, amp, subs) I can change everything back to original in less than an hour... That is a huge plus...

What happens with the sub is that as it pushes air inside the cabinet, the cabinet may actually push forward a bit, losing some of the energy... I want to make sure I utilize as much of that energy as I can... That is the only reason I want to lock it down somehow...

One thing I can do also is simply move the seat back far enough so that it touches the cabinet and keep it there (This way, the seat becomes the securing mechanism).. While I could easily do that on the driver side since I am the only one that drives it, however, the passenger side is person dependant as people always move the seat forward and back...

Do you have a brand and number for a velcro that will attach to the carpet???

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By the way, nice job on that pseudo drawing of yours... I forgot about giving you the tip on how to avoid tipping (no pun intended)... Easy, read my note above...

Angle the front face where you mount the sub... The weight will keep the box toward the back firewall... The bigger the angle the more shifting of the center of gravity toward the back... In fact, technically, the more you angle it, the more depth you would have for a thicker sub...

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Good thinking on angling the sub. Let me see how I go.

As for mounting the bracket to the floor. Again, no sure, but with a bracket long enough, or even bent slightly to force it back you may not need to

As for the brand of velcro, I'm actually located in Australia, so probably not going to be of any help. Though it did look like the stuff found here http://www.velcro.com/industrial/index.html

Hope it helps.

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I took your diagram and enhanced it a bit... You can get an idea of the back contour, seat location, and sub with tilted back to keep weight back. You can see if you move seat slightly back it actually presses the enclosure to the back firewall for a temporary fix until it is held down some other way.

post-20606-1186925752_thumb.jpg

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Sorry if this sounds negative but you're never going to be able to get the deeper and tighter bass that you're after with the rear of the enclosure open. Even if you secure it to the firewall with bolts (velcro is good to hold in position but not as a means to seal the mounts), this is only going to marginally improve the situation. My advice would be to try to enclose the mounts that you've already made and that way they really would be very easy to remove when selling your car. You'll hear a huge amount of difference if you do this!

Also, is there any reason why you're driving your front speakers from the HU and not the amp. You would be better off driving the front speakers off your amp and using the HU to drive the rear speakers to provide a small amount of infill. The way you've set it up sounds like there would be a bias towards the rear speakers which is never good from a SQ point of view.

Good luck - looks like you're nearly there with a good set up!

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Thanks for the input. I appreciate it.

As for why driving the front speakers with the head unit... I actually tried both ways, and frankly, the front speakers just didn't need the external amp. The pioneer head unit sounds great to begin with and has plenty of power to drive the front speakers. The front speakers have always sounded great.

This of course wasn't the case for the rears... There are 2 on each side, and getting good sound out of them was next to impossible with the head unit...

Having that extra power from the amp made them totally come alive.

As for biasing the rears, I am not doing that at all, the balance in the car is perfect. You can't tell where the sound is coming from, because it is perfectly all around you...

Doing it the way I did allows me to control the front speaker eq and frequency cut off points separately from the base and the rears... So I am actually able to tune each speaker for the frequency range each speaker type excels in...

As for closing the back of the enclosure. Why is that different than just locking it down and using the back firewall as the rear wall of the enclosure? Doesn't that yield the same effect? I am not sure I understand.

Thanks again for taking the time to read the thread and responding...

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Thanks for the input. I appreciate it.

As for why driving the front speakers with the head unit... I actually tried both ways, and frankly, the front speakers just didn't need the external amp. The pioneer head unit sounds great to begin with and has plenty of power to drive the front speakers. The front speakers have always sounded great.

As for closing the back of the enclosure. Why is that different than just locking it down and using the back firewall as the rear wall of the enclosure? Doesn't that yield the same effect? I am not sure I understand.

Thanks again for taking the time to read the thread and responding...

Are your front speakers only the dash mounted speakers? Have you replaced your front speakers? If not, that's the next thing you have to do - either go for a set of co-axs or a component set is more ideal. This will improve the sound quality immediately. I imagine that your amp will provide more power and a much cleaner signal to your front speakers which is where you should be aiming for the sound stage to be coming from. The rears should ideally be used simply to add in some fill rather than trying to create a "surround sound" which isnt great from a SQ standpoint. But if you like your system that way then enjoy it.

You're never going to create a sealed enclosure (I imagine that's what your subs require although they could be designed for ported or freeair - can you let us know) using the rear firewall as you have the carpet in the way. Any area where the sound waves have the ability to escape or be altered effects not only the sound but also the efficiency of the enclosure and the sub. Looking at your pictures, you've drawn the rears as angular surfaces. This means that it will be very easy to enclose using a couple sheets more of wood, some screws and some silicone sealant on the joins. Make sure to also build in some binding posts so that the boxes can be removed easily. Attach the boxes to the car using some velcro if you want and you may want to add a grill to the woofer area to ensure it doesn't get damaged.

You've done a great job on the enclosures so far but you really do need to seal them to get anywhere near as good as you expect.

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Thanks for your input...

As for the front speakers, I have components in there. It was an easy thing to change over. The original Porsche speakers don't come close to giving the quality of sound.

I will check on the subs per your question. They sound pretty awesome right now and everyone can't believe the sound and power that comes out of the system.

I just personally know it can be better so I am trying to get every last ounce of energy I can out of them.

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I just personally know it can be better so I am trying to get every last ounce of energy I can out of them.

creating a sealed enclosure should do it and will tighten up the bass as well!

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You know, honestly... Today just for grins, I turned the stereo on and put on a song with some good bass in it... I was standing outside the car with the seat forward... I held the cabinet very tightly against the firewall and referenced the sound...

I then took the cabinet and moved it away from the firewall so the back was open.... What was interesting was that there was no audible degradation of the bass at all from one position to the other... Makes me wonder if I need to lock things down at all.....

Hmmmm, wonder how I can simulate a closed enclosure and compare... Might have to make me up a square stand alone box just to test things....

BTW - These pioneer premier subs are really nice....

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I was in my friends brand new Boxster with the top of the line Bose system with a sub in it... I must tell you, I have trying to get a better sound, but my system made the Bose sound in the new Bosxter sound like a tin can, something out of a little hand held radio. After that experience, I have a new found appreciation for what I put in my car. The mids and highs are crisp and clear and the bass is as precise and massive as you wish to stand.

Thanks to everyone that gave me input so that I could make this system sound as good as it does...

Bob

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5'9" and I would agree, any taller and it would be difficult... Being 6' in a Boxster in general is a bit tough... Luckily I don't have that issue.. I am pretty comfortable, as have been my passengers so far... But if I were any taller I probably would not have been able to put the subs back there... I am glad I did though, the experience is unique, Kind of 3D as you get both sound for the ears and vibration for the body...

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I seriously think you should seal the back side. No matter how tight u mount your woofer enclosure to the rear fire wall. Its not gonna sounds right.

If spacing is the problem u r facing, you should consider doing it with fiber glass . All it will take is less than a quarter inch thickness!

5'9" and I would agree, any taller and it would be difficult... Being 6' in a Boxster in general is a bit tough... Luckily I don't have that issue.. I am pretty comfortable, as have been my passengers so far... But if I were any taller I probably would not have been able to put the subs back there... I am glad I did though, the experience is unique, Kind of 3D as you get both sound for the ears and vibration for the body...

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