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Old 10th October 2006, 07:42 PM   #1
aaronp1 is offline aaronp1  United States
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Default interesting sub enclosure question?

I have a small hatchback. I wanted to build as well a stealth or hidden enclosure for my sub. I want also the low end of bass at comparable volume to like 35 hz bass. I could see the problems, but then thought IB in the rear shelf. Isn't this supposed to be good for low bass characteristics but low on volume in general? Acceptable w/ enough power, right? I don't have much power. I then thought, oh my shelf is not fixed so I'd need to fix it and seal it to the sides and put rubber between it and the hatch & seat. I then thought, oh, will the trunk effectively act as a sealed box? I thought about escape routes for the air. I thought, why not build a box the shape of the trunk (in fiberglass to make it countour around the back of the wheel wells and look stock) w/ carpet on the inside, except there would be a rubber-sealed door and opening the size of the opening of the hatch. When you open the hatch, this door would need to be opened to put stuff in the trunk cavity. Then I thought, sealed isn't as good as vented at this size, so why not tune the box to be a EBS (extended bass shelf) for the low low bass. Then, when you put stuff in the trunk (when you have to) you can somehow adjust the port to tune it to the new box volume. As the box starts out huge, a box even half the size would be enough to tune it to like 30hz, no? About tuning the port, use a PR and add weight to the cone or something as you go? I read that PRs have the steepest cutoff rate but this wouldn't matter w/ such a large box able to make the bass go so low. And doesn't the cabin of the car create a 12db/octave increase, suiting PRs to car audio more? Sound good?

Aaron
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Old 10th October 2006, 07:46 PM   #2
Did it Himself
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PR and vent have the same cut-off/slope characteristics.

Basically IB will only give you as deep as the natural resonance of the speaker itself, and the same Q, or roll-off. Same for vented/PR.

The idea about tuning the box when the boot is loaded is one I've thought about but I think is unworkable in practice.
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Old 10th October 2006, 07:57 PM   #3
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Go with a small sealed and an LT circuit. Get a driver that has a large Xmax.
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Old 10th October 2006, 08:27 PM   #4
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As the guy has said he's on a budget I think that route is not viable.
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Old 10th October 2006, 10:35 PM   #5
aaronp1 is offline aaronp1  United States
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Ritchie,

Happen to be writing from Borehamwood, Hertfordshire as we speak as I'm visiting my dad's half sister out here. He's from here. I live in the Pacific Northwest, in Oregon.
So, you are saying that vented/PR have the same characteristic as IB in that can only manage what the speaker is rated for in terms of resonant frequency? I thought most subwoofers are around high 20s and above hz. I may have some fundamentals wrong here.
My idea has been simplified: to use the trunk (or boot) only when totally neccesary, which isn't that often. I'd just keep the box tuned to an empty scenario at all times, and suffer poor sound when I need to use the trunk. So my question is for this, can a box be built w/ a door and multiple latches that would perform acceptably?
So, if I do this, what would be the best plan for the order? I suppose just vented or vented EBS as I don't want multiple compartments in the box if I need the trunk. And I'll have enough space for a port. I want low end but also want a range as I listen to hip/trip-hop, IDM/electronic but also rock. I hear car cabins naturally improve the range.

Aaron
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Old 10th October 2006, 10:52 PM   #6
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Oh you were the one asking about the Beetle, weren't you?

Can you post a picture of what you're talking about? Do you mean you want to mount them on that shelf that flips up when you open the hatch?
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Old 11th October 2006, 09:53 AM   #7
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Hi hope you're enjoying England, but murky at the moment though. Basically what I'm saying is that IB is like using the driver in free air. No box can ever make the resonance frequency of the driver lower than free air, so the Fs and Qts of the driver will determine how low it goes.

A sealed box raises Fs and Qts. A vented box will vary how it's tuned depending on the chosen alignment. I think the easiest thing might be to do like everybody else does and just make a box for your drive unit and mount it in the boot.

If you want to use the boot space as a box you need to make sure your drive unit can work with such a large volume. You will need a large Vas, probably 150 litres at least.
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Old 11th October 2006, 10:09 PM   #8
aaronp1 is offline aaronp1  United States
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Lothar34:

I mean I was thinking about yes, mounting them to the rear parcel shelf that flips up. I was thinking I'd have to make it fixed down. But I'm considering that this won't give me the volume at low or any end of the bass spectrum. I'm considering builiding a box in the shape of the trunk (so like five cu. ft.) that is vented and tuned low. It would have a door that opens so that if I really needed to use the trunk, I could put stuff in the sub enclosure. I'd at that point turn the sub gain down or listen to the music quietly as I believe (tell me if I'm wrong) that a box tuned too low for it's (now) too small of a volume could cause the sub to overexert itself easily and sound poor anyways. The port was tuned for an empty enclosure, but the stuff in it decreases is volume but not it's tuning. I don't need the trunk very often, so that's why I'm considering doing this over: a) the small sealed enclosure that I have which doesn't sound as good and b) a large enclosure that I have to take out of the trunk and come back for when I want to use the trunk. Why not just make the enclosure as large as possible (even fiberglass the trunk making a mold of it and carpet it (on the inside for largest size and stock curves) but w/ an access door that latches down tightly across the front of the cavity of the trunk. On my Beetle the cavity opening is on one (upwar sloping) plane, but on a non-hatchback you'd need to make a door the shape of the trunk but not as far-back reaching so that it could open then lean back against the open trunk 'door'. On a trip when you want to listen to your sub, if you can't use the back seats for stuff get a roof rack and put your stuff up there in a collapsible cargo bag.
My main technical question comes to: can you latch a say MDF door panel down to your MDF say box with enough force to make it an effective enclosure? Many latches and a grooved lip w/ a thin layer of rubber? No rubber?
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Old 11th October 2006, 11:49 PM   #9
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I believe so.

I, a long time ago, made an MDF cabinet that was hinged in the back. I just used some big weatherstripping around the edges and for a latch I used a big thumb screw that screwed into a coupling nut on the other side. I could probably get a good 20 ft*lbs on it by hand and that back panel never moved at all.
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Old 12th October 2006, 09:06 AM   #10
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If you reduce the volume of a box the tuning frequency will rise.

If you make a huge vented (or sealed) box the response will be likely very droopy and power handling poor.
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