214l Adire Alignment actually 203l?

[SammyXP]

Hey guys, I'm in the process of building a subwoofer with a Dayton DVC 15 in a 214l Adire Alignment. Just for kicks, I modeled up the enclosure in Unigraphics to get a visual for how large it will be. When I subtract the air volume from the enclosure, I only get 12361.6 in^3 (202.6l). This is with careful measurements of the driver and a pair of 3" flared ports.

I'm all about forgiving a small discrepancy and just getting on with building it - but 7% seems pretty significant. I did a little bit of searching, and came across this exact figure in reference to '"apparent volume increase" that occurs from the addition of dampening foam on all sides of the enclosure'. (from here).

So if you're adding dampening foam, should the enclosure be constructed 7% smaller than the alignment calls for? When I plug in 203 liters (in lieu of 214l) in WinISD, the port length changes by 1.3". This does seem rather significant.

So what do I go for? 214l-7%? Or bump it up to 214l?

[Scott Simonian]

I think you will be alright following the normal design. I have the same one but with the Adire Tempest. Great sub! Just be sure to line those walls with some dampning foam.

[SammyXP]

I plan on using fiberglass insulation to line the walls. I modified the dimensions to allow for a built-in amplifier enclosure (don't trust the seals on the amp), so my overall dimensions have grown slightly. I'm jus tnot sure whether to grow them to account for 214 liters, or 200.

Also - the Adire Alignment calls for '11" long center tubes'. Does that mean that the center cylindrical section of the flared port kit is 11" long? That would make sense, because most of the enclosure design software packages I've plugged these numbers into are putting these two 3" ports at a good bit longer than 11".

[ThomasW]

Forget about using damping to increase the apparent size of the box. Size the box appropriately for the tuning you want, then use damping to fine tune the performance .

When they're referring to the center section that's just the straight piece between the flares. It's not the total length including the flares

[MDJones]

Size the box appropriately for the tuning you want, then use damping to fine tune the performance .

Hmm...

I believe you are referring to damping material used in sealed enclosures (polyfil etc.), but I think his question was referring to the acoustic damping material that is simply attached to the walls. You can fine tune polyfil, but is there a way to fine tune the acoustic foam (like what I am using for my sonotube)?

I am curious as to how to treat the volume of acoustic damping as well...

[ThomasW]

You can vary the depth of the foam, add poly or fiberglass. I don't think you'll need it though...

[SammyXP]

The Adire Alignment actually calls for 64oz of polyfill. So it does seem like they're compensating for additional volume, no?

I believe I'm going to go ahead and build to the actual volume for this alignment (214l). It seems that the fiberglass insulation on the walls shouldn't impact that calculation by too much.

ThomasW, thanks for confirming the center tube length thing for me. I was starting to get confused when every formula I used gave a port length of around ~18" for a 214l box tuned to 15.4Hz (with two 3" flared ports).

[ThomasW]

So it does seem like they're compensating for additional volume, no?

Since Dan and the boys at Adire do such a good job with their cabinet designs, I haven't bothered to reverse engineer them.

It's certainly not usual to put damping material in a ported box to absorb higher frequency noise that isn't completely filtered out by the crossover

[SammyXP]

Yeah, I wouldn't bother messing with their plans if I weren't putting this amp enclosure in it. Furthermore, to increase the WAF, I also had to drop the height, so it's still the same design, just different proportions (closer to a cube).

It's certainly not usual to put damping material in a ported box to absorb higher frequency noise that isn't completely filtered out by the crossover

Did you mean to say it's certainly not unusual to put damping material?

[ThomasW]

Posting before drinking my mourning coffee is a bad idea.... :B

Yes unusual...so use the damping

[SammyXP]

I figured - but an engineer never builds on assumptions. Thanks for fielding my obsession for details.