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Discussion Starter #1
Hi all, debating a subwoofer setup for my 1990 LS400. I currently have a cheapo 8" in the stock location (rear deck). I certainly want more output than a single 8" or 10" can provide. This is a problem for multiple reasons

-The trunk is very well sealed from the cabin. Behind the rear seats is solid metal, no ski pass-through.
-Fuel tank is located in the trunk, on the other side of the rear seats. Not only is this a problem as far as blocking bass (especially when full) but it sits directly under the rear deck hole for the sub.
-Rear deck has a hole for an 8" sub, could be enlarged for 10". 10" ultimax will not fit with any amount of cutting, fab or adapters unless the rear window comes out (not in the plans)

I don't want to cut the rear deck metal and attempt an array of IB subs, so what's the best bet here? Box in the trunk and hope for the best? Bandpass through the stock sub location? I want to do things the "optimal" way but I'm coming up short.

My thoughts are to buy another ultimax 10", build a box put 1kw to it and call it a day. But I think this will not be optimal for SQ. Appreciate any thoughts.
 

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This would be a really good application of a bandpass box with the port firing through the factory subwoofer hole. I would probably use an external or semi external port that extends through the hole and seal up around it.
 

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Discussion Starter #3
Not entirely sure I'd be able to vent straight up either, gas tank may interfere with my box placement. FFS. AFAIK its not a great idea to add 45 degree bends to the bandpass port which is what I'd likely need to do.

Another thought I had was an angled mounting adapter to put my Ultimax at the correct angle to mount under the rear deck hole and clear the fuel tank? Is that just a dumb as hell idea? I cant imagine the bracing being ideal in that setup if I just use MDF.
 

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huh, I assumed a port in a bandpass box would work similarly to a typical ported box (mass of air). Maybe the interaction is different. Obviously bends can create turbulence but if its just 45s than that shouldn't matter.

the angled baffle idea could work as well. IB subs can sometimes be run through manifolds with less open area than cone area. I've heard as low as 50% works fine.
 

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The 8" hole would be fine for a 10" or even 12" sub, no need to cut metal.

45 angles on vents is not really a big deal, it is done all the time, including slot ports going around the box making multiple turns. Is it better to make it straight? Sure, but it works well so don't worry about it.

MDF sucks, use Baltic birch instead

It might be easier to make a slot loaded pair of tens than deal with funky angles and braces.
 

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Discussion Starter #6 (Edited)
Yes the angling will be a pain to properly support the size of woofer I want to use. Can you elaborate on how a slot loaded enclosure would work? Would that also fire through the trunk? I did a cursory search but couldnt find much info about them.

The size of the hole in the deck isnt the problem so much as the mounting depth, I believe I have something like 5 inches of depth before I hit the fuel tank.

EDIT: Thanks to Bayboy for linking me to this thread with a nice box design for a dual opposed 8 manifold that'll fit the LS400. Still not sure if I'll be satisfied with that output, I'll also look into a 4th order setup of some kind...
 

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Not entirely sure I'd be able to vent straight up either, gas tank may interfere with my box placement. FFS. AFAIK its not a great idea to add 45 degree bends to the bandpass port which is what I'd likely need to do.

Another thought I had was an angled mounting adapter to put my Ultimax at the correct angle to mount under the rear deck hole and clear the fuel tank? Is that just a dumb as hell idea? I cant imagine the bracing being ideal in that setup if I just use MDF.
I wouldnt worry about a 45 in a port. Look at some T line designs, they literally will have a U bend in the port. i would say look at stepping up to a nicer IB 10 inch sub or think about some form of 4th order ported through the rear deck.
 

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My vote is either 1-2 subs in IB via a manifold, or a 4th order blow through the OEM location

As others have said, the 45 degree may not be a major issue, and perhaps is a better compromise than the alternatives of other potential solutions that don’t quite get enough sound into the cabin.
 

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I have the Bassbox Pro program if you want me to plug some specs in and see what bandpass designs it comes up with. Thanks.

Still not sure if I'll be satisfied with that output, I'll also look into a 4th order setup of some kind...
 

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5" will get you a lot of shallow 12", but shallow subs are usually a trade off on excursion which you really need for IB.

Given all the constraints, I would go 4th order and deal with getting the port to a baffle.
 

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Discussion Starter #11 (Edited)
EDIT: Answered my own questions with research. From the Parts-Express forum, I've found that "It doesn't matter if the port is all the way inside the box, all the way outside the box, or anywhere in between. Just make sure and use the correct end corrections"

So for a 4th order box to work, I'll want to work within the constraint of having the box height and port length match perfectly to the rear deck. Sounds tricky but with a decent program and some trial and error, it shouldn't be impossible.

Any ideas on how to design this box with my massive trunk (I'm thinking 3-3.5 cubes should be easy enough?) would be appreciated but I think I have enough info to go on for now. Thanks everyone.
 

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I like Ali's suggestion. A couple of shallow 12's in an IB manifold firing through the rear deck should provide some pretty good bass.
 

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honestly just having that 8" hole is plenty for bass to travel through if you put a sealed box anywhere in the trunk, as its omni directional. just a thought incase you want to go a simpler and more compact route than a bandpass port firing directly into the car, id bet it would sound better too.
 

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Discussion Starter #14
I like Ali's suggestion. A couple of shallow 12's in an IB manifold firing through the rear deck should provide some pretty good bass.
Depth wouldnt be the issue but mounting circle would. Here's the design I was looking at. So I think 2x 10" would work, 12" might be pushing it?

Sealed might be cool too, but I can't imagine there won't be significant attenuation from the trunk being so sealed from the cabin?

However I was able to mount my Ultimax 10 free air. Excuse the mess.

275837
 

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I would try 12s in the IB manifold, if the opening starts to choke out the bass you can turn the 12s down but you cant turn the 10s up. And price isn't much of a difference.

You could try a triangle shaped manifold similar to this but on your rear deck opening obviously.
 

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Discussion Starter #16
I will have to build up a manifold and see what my fitment options are, if I could do 2x 12's I think that'd be perfect. I just worry the placement of the fuel tank will limit my ability to do that. Mounting depth wise my room would be near infinite but cutout diameter may put me too close to the fuel tank. Weight would be the only other consideration.
 

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I like Ali's suggestion. A couple of shallow 12's in an IB manifold firing through the rear deck should provide some pretty good bass.
Wouldn't that look like a series tuned 4th order bandpass?
Might as well have the manifold designed as a bandpass, and then the some estimate of the trunk volume can be used to select speakers that use the whole trunk like a box?. It would look like an IB from the trunk... and look like a box with the truck lid shut.

One could use a pair of 15" into the "manifold" andit will still be a bandpass.
 

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Wouldn't that look like a series tuned 4th order bandpass?
Might as well have the manifold designed as a bandpass, and then the some estimate of the trunk volume can be used to select speakers that use the whole trunk like a box?. It would look like an IB from the trunk... and look like a box with the truck lid shut.

One could use a pair of 15" into the "manifold" andit will still be a bandpass.
If the rear chamber is huge like an IB, and the front chamber really small, and the front chamber port big area and short it might be a bandpass technically, but it will act like an infinite baffle for all practical purposes.

You can go play around in a box design program to prove it

If it were me I would build a proper 4th order bandpass, because the only hard part will be the port and the manifold will be just as big of a headache to build in that space.

A pair of 4" PVC pipes would be easy to bend with heat (after some practice) and easy to mount to a Baltic birch plate on the factory 8" location. Using two ports will make the ports longer, which probably helps in this case. Sanity check the port velocity and you should be good.

But I really do like IB, so that isn't a bad choice either.
 

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Discussion Starter #19
Thanks Focused I think the bandpass box may be the way to go, it just seems designing it will be the challenge. Not sure how dual ports affect the length/area I should use? But yeah IB is lovely but in this application my driver choices are pretty limited.
 

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If the rear chamber is huge like an IB, and the front chamber really small, and the front chamber port big area and short it might be a bandpass technically, but it will act like an infinite baffle for all practical purposes.

You can go play around in a box design program to prove it

If it were me I would build a proper 4th order bandpass, because the only hard part will be the port and the manifold will be just as big of a headache to build in that space.

A pair of 4" PVC pipes would be easy to bend with heat (after some practice) and easy to mount to a Baltic birch plate on the factory 8" location. Using two ports will make the ports longer, which probably helps in this case. Sanity check the port velocity and you should be good.

But I really do like IB, so that isn't a bad choice either.
I think we are saying the same generally the thing...
  • The smaller chamber manifold part are the same in what we both are taking about... it is either a tuned chamber bandpass, or it is not tuned and more of snorkel.
  • My box is larger as it uses the whole trunk. So maybe 1000 litres? And one could say it looks like an IB when looking into the truck with the trunk lid open. Whether that helps or not depends mostly on what subs are used.
 
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