7 replies to this topic

[BMWTurbo]

Hi Guys,

On a whim, I've decided to downsize my system and make it a little less complicated and imposing in the boot. Now trying to make it less imposing might not make all that much sense given the images below, but I should get back a fair chunk of boot space by moving in the direction I'm looking.

I want to run my JBL in IB alignment, but I'm in two mind which way to face it. I can face it towards the front of the car, fitted to a solid baffle that would be attached to the seat back or I can fit it facing rearwards, in a build out/box of sorts to seal it against the baffle and let it vent into the ski port also.

Foward Cons :-

• Cone very close to the smaller cross sectional area ski port\
  
• It will be ticky to deaden the area or steel that extends beyond the skiport size to the cone size
  
• Might create some strange response curves due to the shape decrease in cone area of the ski port
  
• Woofer magnet/basket exposed
  
• Extra stress on the seat back (woofer weighs 17kgs)

Foward Pros :-

• More space available in boot
  
• Potentially simpler install
  
• Cone facing directly into cabin space
  
• Big basket visible from boot

Reaward Cons :-

• Extra work required for smooth transition between the woofer back to the rectangular skiport shape
  
• Extra work for shaping 'enclosure'
  
• Will absorb more room from boot space
  
• Potentially have a strange response curve
  
• Will need grill for cone

Rearward Pros :-

• Big basket visible through ski port (menacing)
  
• Extra volume and length in transition from cone to skiport shape
  
• Basket protected
  
• Boot will look cleaner after install
  
• Woofer not supported by the seat back

Now, I'm happy to go down either route to me there isn't much between it in the asthetics/fabrication side of things. I'mmainly interested in SQ with this arrangement, that is the ultimate goal.

Any thoughts or suggestions on which avenue might be better suited to SQ?

 Sub_Area.JPG   50.55K   16 downloads
The sub area I have to work with...
 Front_Facing_Centre.JPG   51.77K   16 downloads
Forwards Facing Centre shot...
 Front_Facing_RHS.JPG   54.13K   15 downloads
Foward Facing Righthand side Shot
 Rear_Facing_Armrest.JPG   51.05K   15 downloads
Rearward facing through the Armrest
 Rear_Facing_Centre.JPG   54.43K   14 downloads
Rearward Facing Centre Shot...
 Rear_Facing_LHS.JPG   53.73K   14 downloads
Rearward Facing Lefthand side...
 Rear_Facing_Side.JPG   53.36K   14 downloads
Rearward Facing Righthand side...

[Luke352]

I'd be facing it Forward but sit it back from the ski port a couple of inches and make some kind waveguide (don't think thats the right term) that starts off about the same size of the sub's outer diameter and goes down to the size of the ski port to help prevent any issues from rough edges etc...

Luke

p.s. Do you know what part number your Morel's are, I've been looking around and can't seem to find anything the same as them, I've decided after listening to them that since I'm probably going keep this car longer then I thought I would, I may as well stop being soft and start cutting door trims etc..

[BMWTurbo]

Thanks Luke,

I was planning on making the waveguide arrangement with the sub facing rearwards, mainly due to the extra length there so I could get a nice smooth transition. As mentioned my concern is colouration of the bass. The VDO's seemed to work well in the 'V' formation guided to the skiport size, so I guess I sort of have tried this already to reasonable effect, though I was directing the front of the cones, not the rear.

You can see the attached image, (I haven't got the link here showing the sub rear), but this is a rearward facing 18 in IB. Tthe difference is it has a large opening area facing towards the cabin. I assume that this does fire into the seat backrest, so in actual fact what I'm thinking mightent be as bad as I'm envisaging.

My concern with firing it foward is the 'guide' even if I make it 100+mm long will be a fair restriction as opposed to the 200mm+ long guide i can make with it facing rearward. Obviously the magnet will reduce the crossectional area slightly also so this needs to be allowed for. Maybe I should make two boxs and trial both





Side note :- My mids are Morel HCW8's (don't believe you can buy new anymore). There is a pair on the forsale forums atm from up north. I must say though, after removing the subs on sunday, I was suprised how much of the was coming from them, even though they are crossed over at 63Hz 24dB roll-off LP. I think the mids were blending extremely well and bringing it all forward.

I'm still having some issues bringing centre right more the the right, but hopefully can nut it out.

Cheers
Ben

[DG Phil]

You may have vent/mechanical noise issues mounted this way also.

Phil

[jas]

reverse mounting of subs just doesnt sound as clean or effortless. Rear port vent noise plus mechanical noise can sometimes be heard.

for my W12GTI mk2s the box isnt all that big, infact a free air/ infinite baffle setup would take up the same amount of room as my sealed box.....so actually there really is nothing to be gained from IB setup as far as more boot space is concerned. However due to the fact that the 12 and 15s share the same depth (therefore same motor design) your box would be a lot bigger than just the sub itself

Ive just check the jbl site and it recommends a 1.5cubic foot enclosure. Thats not too bad. If you do your calculations that area between the rear shock towers should easily be enough to fit that sized box (if you use a single 15inch). Im loosing 360mm external depth with my sub box which isnt too bad for such a deep sub. You could even just squeeze the sub into a 340mm external depth box if you needed to. Efficiency and power handling are increased using a sealed box above the IB situation (you can have IB sealed boxes too but i feel that it really defeats the purpose of a sub box).

Edited by jas, 19 March 2008 - 10:44 AM.

[BMWTurbo]

Cheers Guys,

I hadn't thought too much about the mechanical/air movement noise. That does concern me.

I think I'll face the sub fowards and create a smooth transition between it and the ski port. I had thought about sealed Jas, but after mucking around with my VDO's, a sub not even designed for IB and hearing the quality over both sealed and vented, the decision to stick with IB is hard to deviate from. I'm wanting this to be extremely tight and have good extension(not asking much). Efficiency isn't too much of a concern I should have 600WRMS + available to power the sub.

If this all fall in a heap and sounds like A$$ I'll have to revert back to the VDO's

For interests sake, here is the front of the other image I posted previously.

[jas]

Ive only heard IB a few times and it has been impressive seemly more linear than a ported or sealed box....but nowhere near as loud or controlled at high volumes.

i assume those vdos were the peerless drivers???

what boxes did you try before trying IB??

from what ive read about the gti subs on other forums is that they are quite good in IB setups....well let us know how it goes....especially since i own a gti too

Edited by jas, 20 March 2008 - 06:24 AM.

[BMWTurbo]

jas, on Mar 20 2008, 05:52 AM, said:

Ive only heard IB a few times and it has been impressive seemly more linear than a ported or sealed box....but nowhere near as loud or controlled at high volumes.

i assume those vdos were the peerless drivers???

what boxes did you try before trying IB??

from what ive read about the gti subs on other forums is that they are quite good in IB setups....well let us know how it goes....especially since i own a gti too

To be honest Jas, I didn't notice too much level drop from running IB when compared to sealed. Now my box was around 85-90L volume, which was where I got the nicest response from memory with winISD. I tried the same box vented and sealed, but did adjust the tuning. Vented was clearly louder, but since running IB I was able to blend the front to the sub much easier. This could be due to having more experience also, but the settings aren't all that different to what I found with the sealed and ported worked 'best'.

The VDO's are supposedly Peerless XLS's. I can't find the VDO PN in the Peerless catalogue though.

I'm hoping the JBL will cope with higher levels due to the nature and design of the sub. It the VDO's can produce almost the same level (to ear) as when sealed with not too much loss in control, then I expect teh JBL will also.

Will hopefully grab a couple of sheets of MDF today in preparation for the weekend I might have some results next week...

In doing some quick sketchs/calcs last night, the ski port measures 230mm wide by 320mm high. However the actual area I want to employ is roughly 230mm square, due to closing the opening up so that it doesn't fire into the armrest support.

The sub is about 360mm diameter to jsut clear of the surround, so I'll be reducing from the 360 to 230, which is only 65mm reduction each side and possibly a bit more on the bottom and less on the top. Oer a 100ish mm height, the transition doesn't work out to be all that bad in reality, so I've convinced myself I'm happy with it

Edited by BMWTurbo, 20 March 2008 - 03:45 PM.