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The effect of the box on tuning mid-bass...

12.11.181.9

Posted on August 9, 2003 at 12:00:17
Audiopolous
Audiophile

Posts: 3046
Location: New England/ Providence
Joined: April 24, 2002
Hey all,
I just finished my first, ground-up, high end set of speakers. Sucuessful meaning cost was less that $600 and sound is more than $5000.

After 2 weeks of hard core messing with different types of filling, I settled on just traditional dacron. 100g's each for a .5ft3 box. The box has a 2" MDF front baffel, a dado brace in the middle and 1" top,bottom,sides,back. VERY SOLID BOX. Howeveer, upon playing a piano the other day I got thinking about the box acting like a sounding board. Mabye using less filling and a wood that is not quite as hard and thick (insert innuendo here) to improve overall "warmpth" in the mid-bass aera. I get the feeling this is asking for muddiness, but is there any...well sheerly artisn views on these effects?
Share the thoughts and happy listening.
~A~

 

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Re: The effect of the box on tuning mid-bass..., posted on August 9, 2003 at 12:26:49
What's the woofer? qts, fs and measured box impedence peak(s)?

How wide is the baffle? Did you compensate your crossover for it?

Magnetar



 

I agree with Magnetar..., posted on August 9, 2003 at 12:46:01
Charles Hansen
Manufacturer

Posts: 6984
Joined: August 1, 2001
the most likely culprit is the change is radiation efficiency when the dimensions of the front baffle approach an appreciable fraction of a wavelength. This results in a change of solid angle that the driver "sees" changing from 2 pi steradians to 4 pi steradians. This effect has popularly been called "baffle step" or "diffraction loss".

(It is normally quoted as creating a 6dB step, although I'm suspicious that the effect is really that great in a normal listening environment, due to the proximity of the floor and other walls in the listening room.)

Nonetheless, it does create an audible effect and needs to be accounted for in the crossover design. It is normally difficult to measure this effect with any accuracy unless you have a lot of specialized tools to do so. It's probably easiest to look in Olson's book and find the graphs for the enclosure shape that best approximates yours. Then scale the frequency appropriately to account for the ratio of dimensions from your cabinet to Olson's. Finally, you can try for the full 6dB compensation, but I think I'd probably start with around 3dB as a starting point, and adjust by ear.

Good luck,
Charles Hansen

 

Re: The effect of the box on tuning mid-bass..., posted on August 9, 2003 at 13:29:18
Howeveer, upon playing a piano the other day I got thinking about the box acting like a sounding board. Mabye using less filling and a wood that is not quite as hard and thick (insert innuendo here) to improve overall "warmpth" in the mid-bass aera. I get the feeling this is asking for muddiness, but is there any...well sheerly artisn views on these effects?

So what you're asking about is having the enclosure play more of a role in the sound by contributing a bit more coloration of its own acting more like the sounding board of a piano or the body of a violin, etc.?

If so, that's certainly a valid approach in my opinion and could indeed warm things up a bit. Though I think you're the only one who'll be able to answer whether such an approach will work for you. With such a relatively small enclosure, it wouldn't be too terribly difficult to try a few things and see if they take you in the direction you want to go.

Good luck!

se




 

More - cabinet materials, posted on August 9, 2003 at 14:34:04
Well, I wonder what the cabinets are made of?

I like baltic birch or maple plywood with concrete backer-board laminated to it. Mostly braced with two by two pine screwed with course thread drywall screws and gorilla glue.

MDF sounds dull and "thuddy."

Probably a teeny little baffle on the speakers he built. It's a shame to pad down the bass driver just to get good bass.

Magnetar



 

Re: The effect of the box on tuning mid-bass..., posted on August 9, 2003 at 15:37:37
Audiopolous
Audiophile

Posts: 3046
Location: New England/ Providence
Joined: April 24, 2002
The woofer is the Vifa p17wj-00-08 and the Fb is 40.38Hz. and the F3 is 50.82. did not account for he size of the front baffel.
~A~

 

Very Good!...but..., posted on August 9, 2003 at 15:40:28
Audiopolous
Audiophile

Posts: 3046
Location: New England/ Providence
Joined: April 24, 2002
WHere can I find reading and learning on this? I am surely ready for advanced design steps as this and would like to indulge!
Thanks!
~A~

 

The baffle is 2" thick. (nt), posted on August 9, 2003 at 15:42:17
Audiopolous
Audiophile

Posts: 3046
Location: New England/ Providence
Joined: April 24, 2002
~A~

 

Re: The effect of the box on tuning mid-bass..., posted on August 9, 2003 at 16:48:57
RBP
Industry Professional

Posts: 3381
Location: FL.
Joined: December 26, 1999
I would line the entire inside surfaces with 1/2" felt as Yamaha does on the better /older speakers. Silicone it in. A brace inside the enclosure is mandantory from front to back and side to side for mid area wall resonance control or simply build a larger box around what you have with layers of felt between them.

The fq's from 130 to 750 must be muted in the material of the enclosure.
Audio Asylum® Signature line: Hearing is believing.

 

Re: Very Good!...but..., posted on August 9, 2003 at 17:01:26
WHere can I find reading and learning on this? I am surely ready for advanced design steps as this and would like to indulge!

Here you go:

Loudspeaker Diffraction Loss and Compensation

se




 

Re: The effect of the box on tuning mid-bass..., posted on August 10, 2003 at 07:56:54
Narrow baffles are anti-matter when it comes to bass response and speaker sensitivity/linearity. If your box is .5 cubic foot then my guess is because of using typical audiophile approved narrow baffles you now have to take away 6 db of sensitivity from your speakers midrange to compensate. For details look at Steve E's link. You could build wings and attach them to the baffle that slant back a bit (or build some bass horns for your midwoofers!) and gain some of the sensitivity back. Or build a 3-way and set the little box on top of proper sized bass enclosure that requires no midrange padding.


Magnetar



 

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