Enclosure shape on Port box, does it matter?

[Affray]

Hi All,
Hope someone can help

I've been watching a lot of videos, reading up all over and learning how to use winISD. All with the result that the more I learn the more I realise how little I know

Anyway, for my sub, a 13w7 winISD has recommended a ported box at 171.92 litres and thankfully I have the space I'm still fine-tuning the port, but the tuning frequency will be around 20.43 hz and it will be a slot design that is run externally outside of the box to keep things simple (current size is 76mm by 369mm by 1031.8mm).

The question for now is the design of the "sealed" part of the vented box.

I have two very crude drawings above, A & B. From a design point of view having a box that goes all over the place as in B would be better as it would allow me to minimise the workspace lost in the back of my van. I can do a design like A but B would be better. Work-wise there is little in it, yes B is harder to build, but A would require more altering of shelving racking etc.

My concern/question is would the different enclosure shapes of the "sealed" part of the box make any difference to the sound (air being compressed to different pressures within an odd shape box say or harder for some parts to escape/enter via the port) or does it make zero difference?

Huge thanks in advance

Click to read more...

 

[SlugButter]

The shape is probably fine, but getting a 20 HZ port tune is going to be nearly impossible in a vehicle. Your port would probably need to be as long as the car.

 

[SlugButter]

The “B” box could have some issues if it’s a low profile and that sub magnet sits close to the opposite wall. the closed side will pressurize more than the side with the port. if that magnet is 3 or 4 inches from touching the back wall and allows free flow of air behind the magnet, the shape should be fine.

 

[Affray]

Thanks for the reply
Design B would be low profile, thankfully though I have done some measuring and thinking since and the enclosure can be 1.2m high, 0.4m deep (can add a bit more) and 0.5m wide, which would give me roughly 240 litres (excluding driver displacement etc). Sub wood go at the bottom of the box.

Which leads onto another question should the end of vent pipe/port be next to the sub or can it away from it by? Say sub at bottom of enclosure, end of port at top of enclosure?

Thanks for the heads up on the length of the port, thankfully though that isn’t a problem. It’s being fitted in the back of a long wheel base transporter. Running 2.5m of 4” inch plastic pipe one way and then turning it around to come back will be the easiest part (he says naïvely ). A vent of 5 to 6m should be fairly straightforward.

 

[Affray]

This might help to explain things
Current enclosure is in the Center just behind the ladder (blank plywood panel)
The port pipe could just be run down and back, along the roof of the van as luckily it doesn’t need to be pretty

 

[Bobbytwonames 5,000+ posts]

This might help to explain things
Current enclosure is in the Center just behind the ladder (blank plywood panel)View attachment 37619

First question is why do you want a 20 hz. tune when most music has a sweet spot around 33 hz.?

 

[Bobbytwonames 5,000+ posts]

This might help to explain things
Current enclosure is in the Center just behind the ladder (blank plywood panel)View attachment 37619

That's a fukkin construction connex. That is a nice yellow Stabila level in the pic. That is the best part of the pic.

 

[Affray]

That's a fukkin construction connex. That is a nice yellow Stabila level in the pic. That is the best part of the pic.

Na, its the 12 pack of Red Bull Man has to have his priorities in life!

First question is why do you want a 20 hz. tune when most music has a sweet spot around 33 hz.?

It was simply what winISD recommend for the 13w7 was where the 20hz came from. It doesn't need to reach down to 20hz and I would be quite happy with it being around the 33hz mark.

At the moment I'm trying to answer the questions I have and things I need to consider before I sit down to design anything. With luck BassBox Pro will be arriving today, so I was planning to start entering the details into there and then post back with more questions

 

[akheathen Premium Member]

you must have done something wrong in winisd.... the fs is about 24hz or so. tuning down to 20 will likely destroy that sub in no time, as well as leave a whole lot of output and efficiency on the table, especially in a space like that. in the picture, is that up against the cab section, front of the cargo area? would "b" box be down there at the far wall lower right of the picture? port placement and orientation largely depends on enclosure placement. in one area, that setup would compound and give some great output in the passenger compartment. in another place, it will make things muddy with cancellation or unloading. another thing is that its hard to give advice when the picture is nowhere near similar to the dimensions you provided and the 13" driver. "b" would have to be at least a meter wider than the space provided, or it would only fit a 6" driver, at best. as it looks in the picture, theres a possibility of the shapes of the chamber to act as porting, or at least individual chambers, possibly something in_between, with near incalculable response. we need a bit more clarification. biggest thing to take away and concider is the fact that tuning below resonant frequency can cause serious unloading issues and make the driver over-extend on very little power, so keep it at 24hz and up.

 

[Affray]

Thanks for the reply and me make a mistake in winISD? Highly likely Free air resonance is 23.5hz, so I'll take your advance and set 25 hz at the lowest tunning point.

In regards to the rest, well a picture is worth a thousand words so hopefully, this will explain things

A hole has been cut through the bulkhead with the enclosure in the back of the Van, and the sub firing directly behind/underneath the driver's seat. It's a ready-made infinite baffle setup up, but that would mean changing the sub. I'll do that if needed, but I would prefer to try to make a vent box work first as that's just wood and time, new sub is time and money.

Hopefully design A now make more sense, its huge!!, easest box to make, but a lot of shelving etc to alter.

Design B on the other hand is the opposite way around, the height of the extension to the left is probably to low and would need to come up higher, but hopefully it gives the general thought

Thinking on it I could go for something like this, Design C

 

[akheathen Premium Member]

you know, you may want to think about doing a bandpass, then fire the port as close to the passenger door as possible. you will get a ton of db gain at low frequencies, so 34hz might be a better choice. if you stick with ported, still fire the port in the same location, but the sub can fire more to the middle bottom of the cab, if you want. if you opt for lower tuning, it will be very peaky, and less musical. good for a lot of rap songs, or playing tone/bass tracks. another thing to note is play with port size. larger ports will need less length for the same frequency, but also can be more peaky. smaller ports will need to be a lot longer. id suggest an area of 14 square inches per cubic foot, maybe as low as 12 or 13. the bandpass port is kind of inverse of that, to a point. too large shouldnt cause any unloading issues, since, after-all, its still technically in a sealed encolsure on the back side. im a little rusty on bandpass numbers, but i think i recall a 2:1 ratio of front and rear chambers yielding decent results, but dont quote me on that.

 

[Affray]

Thanks for all the feedback, it’s extremely useful

SQ is my priority over SP (would be nice to have both mind ), but SQ out of the two. So I’ll change the tuning frequency to 34hz as recommended and also have a look at a fourth order bandpass which sounds fun to build

Advice on were to best place the port and sub (or just the port) is hugely appreciated as I have always wondered about that. Stuck directly behind the driver seat has never struck me as the best of places, its my only real limitation

 

[Affray]

Quick update
I've been playing around with BassBox 6 Pro (very useful manual) and I have come up with the following design on it

After allowing for displacement, the box volume is 100 litres or 3.531 cubic feet.
Port is a round pipe with an internal diameter of 102mm (4-inch sh*t pipe in short as I have loads of it ) at 1109mm long x 3 (to deal with the vent velocity)

This gives me a tuning frequency of 25hz and an F3 of 23.61hz and this response.

Does it all look right?

 

[Bobbytwonames 5,000+ posts]

Quick update
I've been playing around with BassBox 6 Pro (very useful manual) and I have come up with the following design on it

After allowing for displacement, the box volume is 100 litres or 3.531 cubic feet.
Port is a round pipe with an internal diameter of 102mm (4-inch sh*t pipe in short as I have loads of it ) at 1109mm long x 3 (to deal with the vent velocity)

This gives me a tuning frequency of 25hz and an F3 of 23.61hz and this response.

Does it all look right?View attachment 38059View attachment 38060View attachment 38062View attachment 38063View attachment 38064
View attachment 38059
View attachment 38060
View attachment 38062

View attachment 38063

View attachment 38064

Port is too small. Shoot for 33 hz.

 

[hispls 5,000+ posts]

most music has a sweet spot around 33 hz.?

Even "most" synthesized **** rarely goes that low and that would be rare to find outside of pipe organ concerts or that slowed crap or test tone tracks.

Advice on were to best place the port and sub (or just the port) is hugely appreciated as I have always wondered about that.

In theory it shouldn't matter provided there's a port width of clearance around inlets. In practice there will be some difference unique to your vehicle and the placement of the box but you can't guess until you have tested it installed and differences should be inaudible or nearly so.

This gives me a tuning frequency of 25hz and an F3 of 23.61hz and this response.

Give it a whirl, use some caulking or other non-permanent adhesive to affix the port and you can always test various lengths of port especially if you have 4" pipe left over from jobs or whatever.