how to build the best bass cab?

[bottleneck]

Hi!

I've had a lot of help from Mr.Widget about some DIY speakers I'm going to build.

I thought I'd widen the net and ask you guys in general (who have built bass cabs) some questions..

Ok, so you're going to get a carpenter to make some bass cabs for you. Each is going to house 1 x Tad1601a. It's a ported box, with 2 x ports per cab.
You're going to rest a smith horn with a tad4002 on top, and just put a slot over that.

The bass cab, you know how many litres you want it to be.

You know you want an MDF construction, with birch over the top, and heavy hardwood bracing.

The carpenter is a good woodworker, but no speaker builder.

What else do you instruct him to do?

e.g.
1) Is there an 'ideal' baffle width?
2) I've read (Olson) that curving baffle edges is a good idea. Is there a width beyond which this becomes irrelevant?.. I could ask him to 'chamfer' the edges if it helped.
3) Avoiding non-parallel sides.
I thought about angling the front panel back, leaving the sides parallel.. - is there an angle which should especially be used? e.g. 10 degrees, 15 etc.
It would be hard to angle the sides - and still keep a domestically acceptable shape/shape that I can rest the horn on top.
4) The bracing - any particular type of bracing better than other?
5) What about the damping material inside. I know there is trial and error here regarding placement and quantity, which I can experiment with myself. What's the best stuff (generally) to use to stuff a cab with?
6) What else would you specify the guy to do?


I have other questions, but if I can give the carpenter a full description of what to do, I'm sure I can end up with some decent cabs!

Interested in what you guys think..

Cheers!

[Gary L]

As far as bracing goes I'm not sold that the material makes much difference except in price.

I am not an expert but I do like to marry the fronts to the backs and the sides together like this.



I also try to avoid the formation of 90 degree pockets by leaving the braces short so they don't meet inside.

Use your waste materials where ever possible.



Glue and screw all joints so there is no chance of rattles/separations later.

The interior stuffing material is an art within itself and getting it right is tricky. Some spend big $$ on special dampening material and others use polyfill from walmart or an upholstery shop with varrying degrees of success & failure.

The final step is in the port tunning and this must be done to suit your ears and room. What is right in one set may not be perfect in all sets or to all listeners and rooms. My ears play tricks on me and I am sure another would re-tune the cabinets to his/her liking. I would suggest you buy a few extra tubes so you can mess around and get this as right as you like.
I will repeat an old saying a carpenter once told me "Dam, I cut this board three times and it's still too short".

I bought a dozen port tubes and cut them 4, 5 & 6" and still can't decide which I like best!

Have fun.

Gary

[Robh3606]

I would go with low noise flared ports. Easy to get at Parts Express and install. Just have him cut the mounting hole you can install and tune later.

Rob

[Mr. Widget]

As far as bracing goes I'm not sold that the material makes much difference except in price.

Use your waste materials where ever possible.

If I have it available, I laminate my 3/4" finnply scraps together to make 1.5" by 3.5" (2 by 4s) that I use for bracing. I think the softwood lumber that you used in the photos above would be fine for cabinet bracing, my recommendation for hardwood bracing is to avoid using MDF or thin strips of noodly wood. You don't want some wiggly bits in there that take up space and offer little or no structure.


Widget

[bottleneck]

great! thanks for the help so far...

basically what I will instruct so far is -

1) glue spare ply cut offs together for bracing, or use cheap hardwood.

2) Use flared ports. These them? http://www.partsexpress.com/pe/showd...number=268-352 I presume I just cut to size.. after he makes the holes and counter-sinks them for me.

3) Brace front/back and side/side with batons. Other than that, use bracing that doesn't reach the ends to prevent 90 degree angles (bad for standing waves?)

4) glue and screw the screws.



That's it so far... keep em coming!

What about the damping material ? loose wool? space age nano-fibres-warp-ten? old socks?

[grumpy]

I would add that if you happen to be able to install bracing that doesn't exactly
split panel resonances in 1/2, that they're less likely to be simultaneously excited
... good for some things, not so much for speaker cabinet panels.

Last time I built a -large- cab for industrial noise simulation, I used construction
adhesive between birch ply (outside) and MDF (inside)... no rattles. Used lots of
drywall screws to "clamp".

I'd be interested in hearing about other 'laminating' methods.

[Gary L]

If I have it available, I laminate my 3/4" finnply scraps together to make 1.5" by 3.5" (2 by 4s) that I use for bracing. I think the softwood lumber that you used in the photos above would be fine for cabinet bracing, my recommendation for hardwood bracing is to avoid using MDF or thin strips of noodly wood. You don't want some wiggly bits in there that take up space and offer little or no structure.


Widget

I could not agree with you more Widget! My comment went more to those who think expensive maple or oak will be a better choice.

BTW, Oak should never be used inside of a cabinet because it gives of tanic acid fumes that could easily destroy foam and/or paper cones.

Double thick ply wood is more stable then almost any solid hardwood!

If you do use regular 2X4s make sure to use ones that have been around a year or two and in a dry environment.

Gary

[Gary L]

I would add that if you happen to be able to install bracing that doesn't exactly
split panel resonances in 1/2, that they're less likely to be simultaneously excited
... good for some things, not so much for speaker cabinet panels.

Last time I built a -large- cab for industrial noise simulation, I used construction
adhesive between birch ply (outside) and MDF (inside)... no rattles. I'd be interested
in hearing about other 'laminating' methods.

Construction adhesive is great for laminating good ply to the MDF!

Never, ever, ever do what I did on my first project!

Had a bunch of left over solid red oak panels all glued up and 5/8th inch thick. Planed them all down to 1/2" and laminated this to all exterior panels.







We love them because they go perfect with the rest of the furniture I made and sound great.

Durring the heating season when the air is very dry, the solid oak splits and in some of these splits I can insert a nickle right down to the MDF!

Gary

[Mr. Widget]

I would add that if you happen to be able to install bracing that doesn't exactly
split panel resonances in 1/2, that they're less likely to be simultaneously excited...

Excellent point.

I'd be interested in hearing about other 'laminating' methods.

When I work with MDF and Finnply, I always veneer the plywood or finish it in some way so I can get away with a good wet out of wood glue with a coarse paint roller or glue spreader and then staple the hell out of the plywood to the previously completed MDF box. I am terrible about documenting my work, but this thread does show the cabs and bracing prior to putting the Finnply on the outer surface.

http://www.audioheritage.org/vbullet...ead.php?t=9812

Widget

[grumpy]

Thanks for the info & link Mr. Widget!

To get back to a few more of Bottleneck's questions:

[Grumpy's current thinking/opinon]

Ideal baffle width? Not exactly. It's more of a design parameter (tradeoff).
Worth googling "baffle step compensation". Narrow baffle designs appear to
correlate with improved imaging, but I'm not convinced this is "required."

Rounding or chamfering (bevelling) cabinet edges?
Can have measurably and demonstrably audible effects
... can be masked by worse effects, or other delayed/diffraction sources.
... possibly less important if the device directivity is such that the cabinet
edges are not "in-view" of the sound propagation.
... rounding has better potential in this area than a sharp bevel.

Width, beyond which this is irrelevant? I don't have a "rule of thumb" for you.
I would think wider than most would consider without just installing in a wall.

Insulation?
Fiberglass works quite well, but can cause some discomfort in handling the material.
Opinions are many and varied regarding other materials.

[cooky1257]

Modeled on Tannoy 215 cab bracing.
Building mastic type adhesives are used for the joints to the main box and the rear of the drivers are joined to the bracing via a blob of white tack type putty.
Cooky

[stephane RAME]

The massive building with its reinforcements between sides.

Stéphane