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-   -   how does length, height an depth affect sound (http://www.diyaudio.com/forums/subwoofers/216517-how-does-length-height-depth-affect-sound.html)

rockironwebb 20th July 2012 12:20 PM

how does length, height an depth affect sound
 
Hello, I am still fresh to the diy speaker world. I finished build my first project about a month ago and I am hooked. I went with the tri trix components and built my own vented enclosures. I am amazed at what $200 can sound like.
I am also amazed at the low end that these little speakers produce, but I would still like to build a sub. My budget is currently $200-250. But I already have a sheet of 3/4 MDF and basically all I would need for the box. I don't have any corners available to place my sub and I don't think the wife is going to like the look of one just sitting against the 4 foot of wall space that is available. I am considering an under couch design. I have not yet looked into any enclosure design software, but my biggest question is....at what point do length and depth dimensions start to affect sound? I am just assuming that even if the internal volume stays the same, longer, wider, shorter must at some point start to change the sound. How should I go about this?

TheBaronGroog 20th July 2012 02:11 PM

If the internal volume of the enclosure and the port volume remain the same the sound shouldn't really be affected much as the wavelenths the enclosure will be producing will be longer than the enclosure itself-the enclosure's physical location and near by boundaries will make more of a difference.

Einric 20th July 2012 02:36 PM

Look at the PartsExpress project "The Boogieman".
It was designed to go under a couch.

Itsmee 20th July 2012 03:56 PM

In an ideal world, you would want to keep to the golden ratio of 1.61803399, to reduce standing waves and minimise cabinate resonance, the cabinate internal dimentions ratio would be 1.618 (H) x 1 (D) x 0.618 (W).

1audiohack 20th July 2012 04:08 PM

Quote:

Originally Posted by Itsmee (Post 3098787)
In an ideal world, you would want to keep to the golden ratio of 1.61803399, to reduce standing waves and minimise cabinate resonance, the cabinate internal dimentions ratio would be 1.618 (H) x 1 (D) x 0.618 (W).


Nope. That only comes into play when the dimensions of the enclosure become acoustically large. Enjoy a degree of design freedom, a gift from the physics of small room acoustics. :)

TheBaronGroog 21st July 2012 09:40 AM

Quote:

Originally Posted by Itsmee (Post 3098787)
In an ideal world, you would want to keep to the golden ratio of 1.61803399, to reduce standing waves and minimise cabinate resonance, the cabinate internal dimentions ratio would be 1.618 (H) x 1 (D) x 0.618 (W).

60Hz = 5.745m wavelength, so it needs to be a BIG enclosure to get standing waves with a bass driver

TheBaronGroog 21st July 2012 09:51 AM

Quote:

Originally Posted by Itsmee (Post 3098787)
In an ideal world, you would want to keep to the golden ratio of 1.61803399, to reduce standing waves and minimise cabinate resonance, the cabinate internal dimentions ratio would be 1.618 (H) x 1 (D) x 0.618 (W).

60Hz = 5.745m wavelength, so it needs to be a BIG enclosure to get standing waves with a bass driver

kristenruna 21st July 2012 10:13 AM

The height of the enclosure and the driver placement will affect standing waves.
60hz quarterwave tube length= 340mps/60hz/4= 1,41m.
Mass loading it (bass reflex port) will make it even shorter for the desired tuning frequency. I built a 1.05meter MLTL that reaches ~35hz (designed by MJK).

Research Mass loaded transmission lines (MLTL).
A hybrid of bass reflex and a transmission line. This could help you reach down to your drivers resonant frequency. May require some math skills if you cant find any existing designs for your drivers and desired low freq. extesion. (google: MJK quarter wave alignment tables)

A mltl with (tri-trix drivers?) although tuned high due to size constraints:
Speaker Design Works

Itsmee 21st July 2012 10:29 AM

1audiohack and TheBaronGroog.

You are correct, I was thinking multiway not sub woofer.

rockironwebb 21st July 2012 01:03 PM

Thanx for the info, decisions to make
 
I am not sure of what to do. I have read about the importance of sub placement and I am a little frustrated by my options. I think I may drop the under couch idea, I would hate to do all the work and then have it turn out to not work out there. I am going to attach some photos of my space. Please give suggestions. Forgive the messy house, we have had my nephew over. One spot that had slipped my mind would be behind the lazy boy near the window or next to the lazy boy by the couch. Everything is sitting where it normally does, except when we watch movies we slide the lazy boys to be facing the tv and speakers directly.
OK I guess I don't have enough cred to attach, so i'll try drop box links.

https://www.dropbox.com/s/39rwrsqauc...721_063133.jpg

https://www.dropbox.com/s/bvhkhoiakr...721_063145.jpg

https://www.dropbox.com/s/iw2g1u6s94...721_063204.jpg

https://www.dropbox.com/s/7h7h9x7ar1...721_063529.jpg

https://www.dropbox.com/s/k3lgnrwxq5...721_063803.jpg


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