Statements Modified

[NPF]

After collecting parts for a few years now it is now time to start moving on this project. This will be a modification to the original statements. The major difference being the box design. The main difference will be to add complexity to the design
To be short, this is to build in a double walled box. In between will be filled with very fine white silica sand. Ribs every three inches grooved into the internal and external walls to separate the walls and maintain stiffness. This does three things: 1) it is an excellent damper - dampens out all passive box vibrations. 2) Isolates the external walls from the internal = allows for any kind of hardwood to be used on the external rather than veneer. 3) Adds stiffness to the side walls and back wall.
I have currently already built a pair of speakers in this fashion and a sub and the difference blew me away. The bass is amazingly clean and crisp. Being able to use hardwood for the external gives durability over the long run and also adds to the beauty of the system. The internal structure will be standard MDF.
I will try and attach the drawings and see if they go through....
I may have to mess with the crossover some... we will see. The front baffle width has increased from 11.5 to 12.5. The internal volume has remained roughly the same. Due to the sidewalls being 1.75 thick this reduced the internal width a bit. I made up for it by increasing the depth and height of the cabinet to get back to the right volume. The crossover will go under the bass for easy access. This is also where the sand will be added and flowed in.
Currently this is slightly on hold till I finish up building my cyclone dust collection system. It appears that I am highly allergic to the wood that I am using ~ Bolivian Rosewood. So far this is coming along and shouldn't take too long. Happen to have almost all the parts laying around... and then I will be back on track for this.

So, just thought I would throw this out there...
Nate

[AdelaaR]

Cool project ... make sure to incorporate some hydraulic lift system somewhere because those babies are going to be heavy
That center is the 2RCC, right?

[---k---]

I think this is overkill to the extreme, ... but that is what makes a hobby fun, eh. I look forward to seeing your progress. Good luck.

[impala454]

I imagine you'll definitely have to mess with the XO some by changing the baffle dimensions. I'm sure Curt or Jim could chime in on that. Sounds like a complicated project!

[kmibb]

Sounds like it's going to take a ton of work with negligible payoff. What you should maybe consider is a translame constuction with resin filled sides like DoubleTap uses in his Vapor Sound Cirrus.

Here are some pictures

http://techtalk.parts-express.com/showthread.php?t=219795

[NPF]

To each his own I suppose.
Without numbers on what the damping factor is for his epoxy matrix it is hard to argue. But, I would be surprised if it was half as good as just nice loose sand. Maybe if he used an epoxy with a higher fracture toughness but that is doubtful as those are very expensive. Fine silica sand is an excellent damper due to the fact that the grains of sand rub on each other dissipating energy into heat. The whole idea is to loose energy rather than the transfer of that energy. The rubbing action produces heat and huge losses in the energy due to this = very good damper. Adding an epoxy matrix will limit this effect and now you are counting on the loss of energy coupled between the matrix and the aggregate in this case and then within the molecular structure of the matrix. Over all epoxy matrix isn't too bad as such goes.

In his case, he actually needs some of the strength from the matrix due to no internal ribs.
I would have to say though, if I were doing what he did I would have made a jig and punched holes (larger than the slot) through the bulkheads through the slot as I was cutting out the bulkheads and then added several dowels to form vertical ribs. This would have aliened the whole set up (= far easier to assemble) and given the stiffness needed. Then there would not have been any need for the epoxy matrix.

Sand is also far cheaper than epoxy. Since I'm a cheap sucker I think I will stick with sand. Also, another benefit of the sand is that I can take it back out. If I ever need to move these or transport them across the county it is not to big of a deal to take the sand back out.

Ultimately it all doesn't matter, because I'm going to do what I'm going to do unless some one can give some real numbers on why not to do it. Numbers speak not a wim of someones opinion - same goes for mine . It really isn't that hard to do. Just takes a bit more time that is all. And, yes I do also enjoy wood working so not really a problem there.
As far as the effect of the sand or not >> I can attest that yes it does make a significant difference. Having already built a pair of tower speakers using this method it really does work. If you haven't tried it than you do not know what you are missing. I would never go back and do it the other way after the experience unless it was just a simple bookshelf speaker or something like that... it is worth the extra effort.

By the way, I really do not mind the critical comments - keep them coming! You can always TRY to change my opinion! Good Luck! .... and who knows you just might on some things....

So, onward ho!
Nate

[BeerParty]

The front baffle width has increased from 11.5 to 12.5. The internal volume has remained roughly the same. Due to the sidewalls being 1.75 thick this reduced the internal width a bit. I made up for it by increasing the depth and height of the cabinet to get back to the right volume.

Increasing the width of the front baffle is usually considered a no-no, so if you could figure out a way to get them back to the designed width that would be better. I'm sure if you thought about it enough you could come up with something. This would be a lot easier than trying to redesign the crossover (unless you want to redesign the crossover 8O ).

Also, the Statements use a transmission line so the depth of he cabinet is critical as well. You could probably get away with an extra inch or so, but I wouldn't change it more than that. If you can, try to get the extra volume by adding height. Several curved versions of the Statements have done this with good results.

[cjd]

Increasing the width of the front baffle is usually considered a no-no
<snip>
Also, the Statements use a transmission line so the depth of he cabinet is critical as well..

Yes to the first. Absolutely.

To the second - yes, but only the mid "tunnel" dimensions are critical. Of course, that means you can't really make the cabinet any deeper than designed.

That doesn't leave much wiggle room on dimensions once you nix width and depth.

[NPF]

Quoted from Jim:
"Curt and I talked about a deeper midrange transmission line and the cabinet can be much deeper with out affecting the sound. The proportions of the Statements look very good to my eyes. I don't like the look of real deep cabinets.

Sorry!

Jim"

I think it was also talked about later on in the main thread as well how non critical it was. I didn't make it that far into the thread tonight...

Baffle width... maybe, but not convinced on that either. To a point yes. There were those who kept the edges sharp rather than rounded over which I would link would become pretty similar to the width increase that I'm looking at with rounded corners. I ran some over the thumb numbers a few years back and came to the conclusion that this is not quite as critical as claimed... unfortunately it has been to long and I do not recall how I came to that. I should try and dig that up and see if my logic was wrong.

Thanks for the feed back,
Nate

[Jim Holtz]

Quoted from Jim:
"Curt and I talked about a deeper midrange transmission line and the cabinet can be much deeper with out affecting the sound. The proportions of the Statements look very good to my eyes. I don't like the look of real deep cabinets.

Sorry!

Jim"

I think it was also talked about later on in the main thread as well how non critical it was. I didn't make it that far into the thread tonight...

Baffle width... maybe, but not convinced on that either. To a point yes. There were those who kept the edges sharp rather than rounded over which I would link would become pretty similar to the width increase that I'm looking at with rounded corners. I ran some over the thumb numbers a few years back and came to the conclusion that this is not quite as critical as claimed... unfortunately it has been to long and I do not recall how I came to that. I should try and dig that up and see if my logic was wrong.

Thanks for the feed back,
Nate

Curt would have to weigh in on exactly how much the depth of the mid tunnel can change without impacting sound but the rule of thumb for changing any dimensions is 10%. Driver spacing or driver arrangement must not change. The crossover is tied to their positions on the front baffle. They can slide up or down as a group but not individually.

Baffle width is the most critical of the dimensions on all speakers and must adhere to the no more than 10% deviation from the original design.

Hope that helps!

Jim

[NPF]

Thanks Jim!
Yea I agree with the 10 percent rule. My main point for the criticalness of the front baffle was simply that is is not so critical that it is absolutely a ridged requirement that it must be the exact same. Yes, the more it is changed the more deviation you will have to the original design... the question is when can your ear actually pick up on this change and how settle of a difference is it. 10% seems to jive with what I came up with a while back. Right now I am just under that number on the front baffle and I think I'm willing to live with it as is unless someone can produce good rational not to.

As to the driver spacing, I understand - no change there.

The depth may pose a different problem though... Maybe I read too much into what was said and pushed it some. I am currently at 20% difference there.... Here is the main problem: In order to have the sides filled with sand the walls have to grow in thickness. I reduced the internal width as much as I could. But the upper driver has to breath to the lower chamber and to the port at the bottom. As you reduce the width you then start to reduce the cross sectional area between the side walls and the mid-transmission line and closing off the passage that allows the upper driver to breath properly. If I remember right this was sized so that the upper and lower driver would be balanced. Thus, in order to maintain the breathing cross sectional area through this area I had to increase the depth to compensate. It is not as simple as just increasing the height to obtain the original volume. Plus, I suppose I do like the over all proportions as it sits right now.
The simplest answer is to try and get someone who has a pair of these to add a quick and dirty 3.5" extension to the mid lines and see if they can actually tell any significant difference and what would that difference be. Maybe I should build one speaker the original way and one the way I'm proposing and see if there is any difference... I'm currently set up to build three full sets of these so it may be worth it...

It would be interesting to do an A/B test.... anybody know of anyone with these in the Seattle area?

Nate

[NPF]

O, one more thing... (haven't really given this much thought yet, but just an idea)
On the transmission line, could I just increase the cross sectional area to accommodate the extra length? Haven't really studied transmission lines out but on ports as you increase the cross sectional area the port must likewise grow in length. Would this not work here as well?

[NPF]

Seems that port length is almost directly perportianal to cross sectional area. Thus, if I add 20 percent to the cross sectional area ~ 5 X 6 inches instead of 5 X 5 that this should get me back into the ball park in being in the right spot again since I'm 20% longer.

Any thoughts?

[Jim Holtz]

Sorry, you are in uncharted territory. You'll have to see if you can get in touch with Curt for answers.

Jim