why design angle into sub enclosure?

[Infinity_Addict]

my friend said that when you design a (sealed) enclosure, it is better to make a paralellogram type box (where either the back piece of MDF or mounting piece of MDF is at an angle) rather than a square box (all 90 degree angles) because it takes a little bit longer for the sine waves coming off the back of the subs to reflect back at an angle to the back of the subs, thus creating some disonance because the sub will be producing a diff freq by the time it reflects back(considering it changed freqs). why is this good?

what angle is most preferable? rather, which will create optimum performance?

also, if anybody has designed a good box for two 12" Infinity Kappa Perfect DVQs, please let me know.

or if you're super cool and want to design a simple box for me, please do! mounting depth = 7" (178mm). cut-out diameter = 10-7/8" (277mm). compliance volume Vas = 3.31 ft3 (94.28 L). and [i dont know if you need this but just in case] free air resonance Fs = 22.01Hz. space is not an issue.

 

[[email protected]]

Bizzarre one this:

With subs, where soundwaves are so long, then you will not get any standing waves or other nasty interactions on the cone, you simply get a change in air pressure in the car.

With mids, then absolute, minimising standing waves inside the enclosure is important.

 

[Infinity_Addict]

so i've heard

yes. i've read sub wavelenghts are large, something like 54ft(20hz) to 11ft(100hz) and yer box needs to be larger than half of a wavelength in order to get standing waves, thus, it generally isnt a problem with sub enclosures.

but what exactly is a standing wave and why is it bad? anybody know the technical side?

 

[zobsky]

a standing wave is a wave formed within an enclosure (and maybe folded between 2 sides) that can be exxagerated wrt other frequencies.

Regarding the non-parallel walls, the reason is related to standing waves, . but has more to do with ensuring that the waves reflected off the rear baffle doesn't bounce back and possibly interfere with the wave emnating from the driver rear, possibly leading to
1.cancellations / exxagerations
2. depending on the cone material, if the reflected wave is strong, it can pass back through the (relatively thin) cone material further smearing the front wave due to its phase / delay difference

hope that helps

 

[Infinity_Addict]

well then

i should definately angle the rear baffle. is there a specific angle i should use or will any angle do?

 

[Bill Fitzpatrick]

You don't need any angled surfaces on a sub. Period.

That should be the end of it but it probably won't be.

 

[Variac]

All the posts add up to one thing: You don't need the angle for a sub. Speakers handling higher frequencies would probably benefit from it.
I believe that's what Zobsky is referring to.

Am I really agreeeing with Bill?

 

[Bill Fitzpatrick]

Am I really agreeeing with Bill?

Don't feel too bad. You didn't have much choice this time.

 

[Variac]

Actually I don't mind agreeing with you, I just don't like people picking on innocent quivering newbies. Better to attack the tough old guys like me! We say some pretty stupid stuff too

 

[micb]

The main reason for a slanted back is so the enclosure can sit flush against the rear seats which is often slanted itself.

 

[ChevS-10]

You can always put a insulating material in the box to act as sound deadener, most of the time manufacturers recommend this anyway. It may make you feel better.

 

[Infinity_Addict]

ok, thanks all!