Subwoofer Cabinet Design

[Kevin Lee]

I plan on building a subwoofer and making my own cabinet for it.
Here is the driver I am getting for it:

https://www.parts-express.com/dayton-audio-rss315ho-4-12-reference-ho-subwoofer-4-ohm--295-466

What plate amp is recommended?

What program if any is recommended to find the optimal dimensions for a rectangular prism cabinet?

 

[shadyJ]

These questions would be better asked in the DIY Corner.

A popular and easy program to use to gauge good cabinet sizes is WinISD

As for plate amps, I would be looking at 500 watt plate amps among these.

You can also use an outboard amplifier. It would be less expensive and make the subwoofer build a bit easier. Plus, there is a lot more selection of outboard amps to choose from than plate amps.

 

[Kevin Lee]

These questions would be better asked in the DIY Corner.

A popular and easy program to use to gauge good cabinet sizes is WinISD

As for plate amps, I would be looking at 500 watt plate amps among these.

You can also use an outboard amplifier. It would be less expensive and make the subwoofer build a bit easier. Plus, there is a lot more selection of outboard amps to choose from than plate amps.

Thanks!
I did consider those but i could not find an outboard amp.
What would you recommend?

 

[yepimonfire]

Thanks!
I did consider those but i could not find an outboard amp.
What would you recommend?

I'd just use a pro grade amp like a Crown drive core. You'll get more bang for your buck, it will be stable down to 2ohms, and it's likely to supply all the power you'd need.

Sent from my SM-G360T1 using Tapatalk

 

[shadyJ]

Thanks!
I did consider those but i could not find an outboard amp.
What would you recommend?

I think this one would work well for that driver. If you crank it too hard though, it might have enough juice to fry the driver, so it isn't an amp you want to push really hard with just one of those drivers.

 

[OscarJr]

Behringer makes some ok stuff, but those inuke amps are severely over-rated, just FYI. Kept to under 1% THD, it puts out ~640W RMS. Still not too shabby, but I personally prefer to have a few extra watts on tap to not stress the amp, but also to keep the signal clean to minimize potential thermal damage to the speaker.

That sub has a 2.5" voice coil, so I don't know how much power compression is being accepted to attain that 700W RMS rating. It does have a 4-layer coil and somewhat decent venting, so it's not too bad for $150.

If you can still get them, the buyout 3" flared ports that they had for $5 are JBL-twins. They use an elliptical flare throughout the entire port, as opposed to a straight cylinder with a radiused end. The elliptical shape is much much, better. So much that Bose sued JBL over their patent on this, and won!

https://www.parts-express.com/flared-port-tube-3-id-x-11-l-with-5-flared-ends--269-165

 

[annunaki]

Behringer makes some ok stuff, but those inuke amps are severely over-rated, just FYI. Kept to under 1% THD, it puts out ~640W RMS. Still not too shabby, but I personally prefer to have a few extra watts on tap to not stress the amp, but also to keep the signal clean to minimize potential thermal damage to the speaker.

That sub has a 2.5" voice coil, so I don't know how much power compression is being accepted to attain that 700W RMS rating. It does have a 4-layer coil and somewhat decent venting, so it's not too bad for $150.

If you can still get them, the buyout 3" flared ports that they had for $5 are JBL-twins. They use an elliptical flare throughout the entire port, as opposed to a straight cylinder with a radiused end. The elliptical shape is much much, better. So much that Bose sued JBL over their patent on this, and won!

https://www.parts-express.com/flared-port-tube-3-id-x-11-l-with-5-flared-ends--269-165

Thanks for the info. That is a good price.

Design note to consider, if using 3" round vents with that driver, my guess (without modeling), is that you will need 3-4 of them to keep the vent velocity down if planning to an enclosure that is designed for flat response.

For 12" woofers (depending upon the tuning frequency and design goal) dual 4" vents are usually the name of the game (or more) so as to keep the vent velocity to the <=17m/s range (inaudible).

I typically shoot for at or under 12m/s vent velocity with my designs but I am a bit eccentric at times. I personally cannot stand vent noise at any level. All in balance though as I have to be careful that the first vent resonance does not push into the audible range in that case.

 

[OscarJr]

Thanks for the info. That is a good price.

Design note to consider, if using 3" round vents with that driver, my guess (without modeling), is that you will need 3-4 of them to keep the vent velocity down if planning to an enclosure that is designed for flat response.

For 12" woofers (depending upon the tuning frequency and design goal) dual 4" vents are usually the name of the game (or more) so as to keep the vent velocity to the <=17m/s range (inaudible).

I typically shoot for at or under 12m/s vent velocity with my designs but I am a bit eccentric at times. I personally cannot stand vent noise at any level. All in balance though as I have to be careful that the first vent resonance does not push into the audible range in that case.

I agree with you on all points, for traditional cylindrical ports with flared ends. But from everything I've read, JBL's Slipstream port design is among the best of the best, with supposedly a very very low noise floor of it's own. I've read JBL's white-paper describing port non-linearity investigations, and I'd be willing to bet two of these would likely suffice, even when designing on borderline port vent air speed scenarios.

 

[annunaki]

I agree with you on all points, for traditional cylindrical ports with flared ends. But from everything I've read, JBL's Slipstream port design is among the best of the best, with supposedly a very very low noise floor of it's own. I've read JBL's white-paper describing port non-linearity investigations, and I'd be willing to bet two of these would likely suffice, even when designing on borderline port vent air speed scenarios.

Vent velocity cannot be corrected by some "magic port". It is simply a function of the surface area of the port and how much volume needs to move through it (controlled by the driver in question and the size of the enclosure). Yes, you can smooth out the flow and help it reduce the chance for noise, but if you need X amount of vent surface area to keep vent velocity at <17m/s there is no way around that.

Example: Driver A needs 27 in^2 of vent area in a 3.2 ft^2 enclosure tuned to 25hz to keep vent velocity below 17m/s.

3" vent = 7.07 in^2
4" vent = 12.57 in^2

In this example one would need four 3" vents to get the job done and likely could get by with two 4" vents depending upon the actual vent velocity. The flared ends may make up for the 2 in^2 of shortfall with the 4". However one could not "get by" with three 3" vents as the gap to the needed surface area and the vent velocity are going to well exceed even what a high quality flared vent may correct for.

In this example, I would actually recommend a slot vent as it is easier to incorporate though adds to the enclosure complexity a bit.

 

[OscarJr]

Vent velocity cannot be corrected by some "magic port". It is simply a function of the surface area of the port and how much volume needs to move through it (controlled by the driver in question and the size of the enclosure). Yes, you can smooth out the flow and help it reduce the chance for noise, but if you need X amount of vent surface area to keep vent velocity at <17m/s there is no way around that.

Example: Driver A needs 27 in^2 of vent area in a 3.2 ft^2 enclosure tuned to 25hz to keep vent velocity below 17m/s.

3" vent = 7.07 in^2
4" vent = 12.57 in^2

In this example one would need four 3" vents to get the job done and likely could get by with two 4" vents depending upon the actual vent velocity. The flared ends may make up for the 2 in^2 of shortfall with the 4". However one could not "get by" with three 3" vents as the gap to the needed surface area and the vent velocity are going to well exceed even what a high quality flared vent may correct for.

In this example, I would actually recommend a slot vent as it is easier to incorporate though adds to the enclosure complexity a bit.

I am not insinuating the "correction" of mandated vent velocity. What I am referring to is the "rule of thumb" of 10% mach 1 which of course translates into ~ 34m/s. Half of which is 17 m/s for optimum results (5% Mach 1). Why is it "there" in the first place? That is rhetorical question of course. It ultimately arose from the fact that [traditional] vent noise and vent SPL compression was/is due to non-laminar flow at the port ends. Empirical data showed that keeping the vent velocity to a maximum of mach 0.1 greatly subdued this effect by slowing down the whole operation (and not addressing the turbulence at the port ends that robs performance), and hence the "rule of thumb" of ~17m/s was born, and it works great.

But it wasn't the air rushing through the central axis of the port that was causing the problem---the issue was the air pressure expanding at the exits of the ports [under high power operation] due to turbulence and creating vortices that robbed the wavefront of it's pressure, and thus SPL. The elliptical port shape (or rather very nearly elliptical) helps with port linearity exactly where it counts, at the port ends. Hopefully you can see now where I'm coming from. The whole 17m/s rule of thumb was to minimize port noise by slowing down the whole port operation by way of up-sizing the port, where as elliptical-shaped ports help to control port compression at the points of interest without having to up-size the port to slow down the whole operation. Therefore, for a given diameter, in an ellipticalish port, vent velocity can exceed mach 0.1 (somewhat) and be more linear than a typical port of the same internal diameter. How much more can be tolerated could be argued to death of course because there are practical limits as you can't just go infinitely small. None the less, it will exhibit better linearity throughout it's operation so one can get away with a "smaller than traditional" sized port, and still be OK.