[BBB]

Building a custom enclosure for my SI-SQL-12 subwoofer and looking for some feedback on the box design. I have 15" x 25" clear opening to work with along the rear seat opening between the rear strut framing. Shooting for a sealed box volume of 0.90-0.92cft for an end result around 0.75-0.77cft installed. Box will be 13 ply birch plywood. Planning to rear fire at a 45 or 30 degree angle as shown in the profiles attached. Really hard to design an angled enclosure with such a small sealed box requirement for this sub!

So the idea is for the box to be centered against the rear seats firing towards the trunk, with the final height of the surrounding false floor buildup at 4" high to hide all wiring/cables below for amplifiers. Currently building out the false floor, but need to do the sub enclosure first in order to build up the false floor around it. Pic for reference. Don't hate on the temporary rear seat mounting on cutting boards and mess of wires 😣. Just looking for some feedback on the design before I build as it is my first custom box to build on my own. Any help would be greatly appreciated.

 

[lithium]

As long as you did the math for volume correctly and have enough depth to install the sub than it literally doesn't matter what shape the enclosure is. Maybe mock it up with some cheap MDF first?

 

[DaveG]

60 degree box doesn't look like it has 4" to absorb your 4" trunk floor lift. Your trunk floor won't clear the sub, no?

 

[BBB]

60 degree box doesn't look like it has 4" to absorb your 4" trunk floor lift. Your trunk floor won't clear the sub, no?

It’s close, but not overly worried about it with the offset of the baffle from the front face. I just didn’t want the bottom 3-4” of the sub to be firing directly into the face of the false floor.

That’s actually why I wanted to do an angled baffle given I didn’t have enough clearance above to keep it 90 degree above the false floor. Also, after reading all the discussions about standing waves, etc., I am trying to add some angles. Just not sure if I’m going to be losing anything by tilting the firing angle, etc. I have searched around, but there doesn’t seem to be much on the subject that I can find.

 

[lithium]

What standing waves? Think about it this way, what is the wave length of 50hz?

 

[BBB]

What standing waves? Think about it this way, what is the wave length of 50hz?

I understand that standing waves are longer than the length of the car in my case most likely. But from what I have read, bass cancellation can be an issue if you are pointing straight towards the trunk as well. Also seemed the consensus was that for whatever reason, boxes with more curves, angles inside sound better. Be it less flex or whatever people believe the cause is. So why not give some extra angles if I have the tools to do so. Hope that makes sense.

I did read up, but I’m pretty new to all of this. I can go on all day about how the best way to design and construct building, but it will take a lot more experience to talk about car audio on the same level. Though I’m enjoying learning a new hobby so far. It’s the right mix of research, design, and elbow grease for my tastes.

The rewards I’ve reaped so far in my musical listening experience in the car has already been impressive. Looking forward to actually knowing what I’m doing beyond a cursory level. Lol

 

[Noah117117]

I understand that standing waves are longer than the length of the car in my case most likely. But from what I have read, bass cancellation can be an issue if you are pointing straight towards the trunk as well. Also seemed the consensus was that for whatever reason, boxes with more curves, angles inside sound better. Be it less flex or whatever people believe the cause is. So why not give some extra angles if I have the tools to do so. Hope that makes sense.

Bass cancellation coming off the side of the trunk would be an sbir effect that is caused by the back wave negatively summing with the wave going toward the cabin. The closer the driver is to the wall, the high in frequency the cancellation is, the further from the wall, the lower in frequency. Though, at the same time, the higher frequency effect will be high in amplitude (more null) than the low frequency one just based on the intensity of the sound being reflected.

Assuming you cross your sub at 80hz, then it should only be contributing to sound 1 octave higher. If you assume it that then our target frequency is 160. Do some math and a 160hz backwave corresponds to about 20 inches. That means as long as you keep the subwoofer within 20 inches of the back and side walls you should be fine. Placing the sub in the middle of the cabin is actually the worst thing you could do as all the nulls would match and create a single, deep null.

As for pointing a subwoofer, well there's really no such thing. The wavelengths subwoofers play are so much longer than the enclosure that they wrap around it and play omnidirectional front to back. Pointing would refer to placing the sub driver closer to the trunk which would have a higher sound power amplitude compared to if the box was flipped around. The sound would still be radiating in all directions, it would just be further from the wall.

Curves and edges tend to make more rigid enclosures, but they are certainly not going to sound inherently better than a square one. Especially due to standing waves. The only time I've ever seen people need to worry about standing waves is when creating huge cylindrical subwoofers that are 6ft tall+ for home theater. As for rigidity. If the panels don't have resonance withing the passband of the driver, you aren't going to hear anything coming from the box. This is very easy to do with the small enclosures of car audio. For a 1ft3 sealed box, you probably can get away with 3/4mdf or plywood without any bracing at all. I also hear some people claim that cabinet flex will cause a loss of energy being produced by the subwoofer, but I've never seen a measurement that supports that idea. I thought it when I started making enclosures but after I put my home theater subs on spongy isolation platforms that I could rock them back and forth on without any audible loss, I don't see how a tiny bit of wall flex could be any worse.