[greenhorn]

I've seen a lot of holes being made in the car's sheet metal to install speakers, and usually haven't thought much of it. But seeing a sub mounted in a correspondingly big hole in the space behind the rear seats made me suddenly wonder if doing so would impact the structural integrity of the car's body? I mean if it were redundant, the manufacturer would have removed it themselves right ?


Dear Mods: I've Put it here because this is not exactly an ICE specific query, but rather related to the body of the car

[jinu_joseph]

Originally Posted by greenhorn

... But seeing a sub mounted in a correspondingly big hole in the space behind the rear seats ...

Sorry dont follow what you mean here.. are you saying that actual holes were made in the body of the car to fit the Subs.???

Drilling holes in the metal body of the car is a strict No no especially where the holes would be exposed to the elements of nature as it could induce rusting. Remember the body of the car especially the metal parts are treated for anticorrosion.

Also regarding structural integrity it would depend on where the holes are being drilled, if it is into the bars that form the core structure of the vehicle then yes. And its effect would be felt mainly in an accident.

Most cars today provide for the requisite holes and spaces for mouting ICE components and should not require drilling holes or cutting out metal parts of the car.

[greenhorn]

I was talking about a sub in the shelf behind the rear seats in a sedan

[jinu_joseph]

There is nothing wrong in creating holes in the Shelf aka rear Parcel Tray. The shelf has nothing to do with structural integrity of the car.

[kaushikkrishnan]

Making those holes do make a small dent in your pocket

But on structural integrity, as long as it is not too big and done by a professional it would not cause any structural damage

[Sinner666]

Originally Posted by jinu_joseph

There is nothing wrong in creating holes in the Shelf aka rear Parcel Tray. The shelf has nothing to do with structural integrity of the car.

I guess what greenhorn was talking about was not the parcel tray. AFAIK In most sedans, the parcel tray is not supported on hooks and side beams, but there actually is a sheet of metal in which the parcel tray is fixed onto. This is the case at least with the Esteem.

[Sankar]

Making large holes on the monococque is a strict no no for me. The hole greenhorn refers, which is probably atleast 10 inches in diameter, to is in the main structure of the car body, so it might have a negative impact on the strength of the monococque.

Holes on door and boot panels may not pose much of a issue, but still i wouldn't want ot do it on my car for fear of corrosion.

[specialist1968]

Making a hole in a stressed member definitely redistributes the stresses (in a different way than what it has been designed for) and hence should not be encouraged. At times manurafturers give provision for cutting holes in the sheet metal. In cars like the SX4, there is a sheet metal in the place of rear parcel shelf and there is no provision given for cutting AFAIK.

[DerAlte]

As a body member, it is just what it is - a non-structural body member. The members that make the rear of the body rigid for twisting movement is the body itself - pressed edge profiles. Compare the sedan-hatch pairs (like Indigo-Indica, Vento-Polo, Corsa, ...). In hatches the the hatch is the strengthening member.

Most sedans have holes already in that horizontal member for 6x9 (sometimes 6.5") speakers. Cutting out a bigger hole for an 8-12" sub is not going to make a diff, since it is not the horizontal surface that is providing stiffening - here also the pressed edges would do that.

If one still wants to strengthen the hat-rack not to take any chances, 2 lengths of 10mm rods brazed / tag-welded (along the width) on the underside will get that horizontal member going strong once again.

As far as redundancy is concerned, they really wouldn't - one will land up with an unsightly broad (fore-aft) fiber hatrack without support that sags and spoils the interior looks. Better spend the $5 rather than lose $50million business, no?

[Sutripta]

Originally Posted by DerAlte

In hatches the the hatch is the strengthening member.

Hi,
Don't get it.

Also, what is 'pressed edges'?

Regards
Sutripta

[DerAlte]

1. The hatch door, mating with the 'pressed' () opening of the hatch
2. The edges of any panel which have been pressed (as in press-formed) into an L, Z, C or even more complex profile to resist bending. Even the 'hat-rack' member is a press-formed part

Err... why am I showing a light to the sun? *chiding myself*

[ramie2400]

Dosent make any difference to accomodate a 10 or 12ich on the parcel shelf tray,as few cars in today does not come with the sheet metal also these days hardly anybody installs the sub on it.

[Sutripta]

Originally Posted by DerAlte

1. The hatch door, mating with the 'pressed' () opening of the hatch

Hi,
You mean the flap covering the huge hole in he bodywork, attached by two hinges and held down with a latch, adds strength?

Regards
Sutripta

[DerAlte]

LOL Your 'flap covering' reminds me of the anecdote about Einstein's entry/exit facilities for his dog and cat.

Primarily the periphery of the huge hole. In extreme cases it is the hatch door. Disclaimer: I am not a body designer. I have seen only a simulation of body torsion on Catia for Smart in the previous century.

[navin]

Originally Posted by greenhorn

I've seen a lot of holes being made in the car's sheet metal to install speakers, and usually haven't thought much of it. But seeing a sub mounted in a correspondingly big hole in the space behind the rear seats made me suddenly wonder if doing so would impact the structural integrity of the car's body?

Originally Posted by DerAlte

As a body member, it is just what it is - a non-structural body member.

Most sedans have holes already in that horizontal member for 6x9 (sometimes 6.5") speakers. Cutting out a bigger hole for an 8-12" sub is not going to make a diff, since it is not the horizontal surface that is providing stiffening - here also the pressed edges would do that.

Originally Posted by Sutripta

You mean the flap covering the huge hole in he bodywork, attached by two hinges and held down with a latch, adds strength?

Most major car manufacturers resort to complex mechanical solutions using FEA / FEM to ensure the structural safety of their cars. As such cutting into body panles without understand the laws of physics can lead to pre-mature structural failure especially if the car is caught in a side-on or rear-end accident. In fact the repair of monococque chassis in case of an accident is something that should be done with utmost care. I have seen many a case where small garages have welded back the rear of a car with no concern to the integrity of the structure. Modern monocoque/unibody is so sophisticated that the windshield and rear window glass are also considered as to contribute to the structural integrity of the car.

Haivng put that disclaimer behind us, I can say with confidence that it is not diffuclt to understand which body panels can be modified to accomodate larger speakers.

a. Door Panels. If the hole is enlarged from say 5" to 6" there should be no problem provided that the door panel is repainted to ensure that rust does not have access.

b. Rear parcel tray. In Hatchbacks these are not structural and in fact are made of very light fiber-like material. In Sedans they are partially structural. By that I mean that the pressed edges (where the structural members are built by folding the metal several times) are what takes the bulk of the stress. Enlarging a hole made for a 6x9 to that that can accomodate a 8" woofer makes little difference. As a rule I do not recommend 10-12" or alrger woofers in the parcel tray more for acoustic reasons than structural (but that is a topic of another discussion).

c. Rear Seat brace. In many cars there is a metal sheet that streches across the width of the seat and this is definitely structural. Some cars like the ANHC where the seats do not fold may belong to this category. In same of the early Contessas for example there was a metal sheet behind the seat (the rear seat in the Contessa did not fold either). In such a case if this metal the area needs to be strengthened by welding a box channel across the widht of teh car. Another option is to weld to pressed channels diagoanally across the width of the car in the shape of an 'X'. The 'X' is lighter and if the panels an pre-stressed (by pressing) they provide adequate strength. I have done the same to a Contessa when my intent was to build a Transmission line sub in the trunk of the Contessa. The sub occupied greater than 80% of the trunk's volume.

Fortunately bass has long wavelengths. This means that bass waves penetrate right through the car seat and in most cases there is no need to cut the rear car seat panel. If this panel is cut the area around the holes so made MUST be strengthened. The best and easiest method I have seen is by using pre-stressed pressed metal like mentioned above. I wish I had photos to show you but I have seen TV shows that show how to do this and I assume many of you have seen the same. I think these shows come on "Discovery Turbo".

On these shows I have also seen them strengthening monococque cars by bolting (huck bolting is even better) a square tube to the engine bay (which is where most of the twisting stress occurs). Bolting is better than welding in many cases as the bolts can distribute and relieve stress while a welded joint will crack if stressed beyond it's capacity. If those who have Honda Accords and Skoda Octavia (I have only seen these 2 cars at close quaters but assume others too have this) look under your car, they will see about 3 (I think 4 or 5 in the Skoda) layers of sheet metal rolled into a frame rail that runs between the 2 subframes. That IS the basic "frame" of the monococque. Then there is a better made front frame that supports the drive train and another one in the rear that supports the rear axle. The front and rear frames are bolted to the "frame".

Here is a picture of a typical monococque
http://www.caradvice.com.au/wp-conte.../monocoque.jpg