Geddes on Waveguides

And Oh, by the way, I myself came from a poor schooling background, had lots of early disiplinary problems, etc. - I was a true juvenile delinquent. It is possible to excell no matter what your background is. One cannot use the background of ones upbringing as an excuse for failure. But, fortunately I can offer my kids something better. Hopefully they will make the best of it. But, that too is not within my control either.
 
gedlee said:


You have to play the hand that you are dealt.


Very true. ;)

(..though note that I really wasn't suggesting the read with regard to you, but rather any cultural effect it might have on your young son. Also, the author is NOT a youth - I believe his perspective was on 30+ years on-and-off habitation in Thailand.. which started in his mid-to-late teens.)
 
gedlee said:

They just aren't up to the private schools because of things like "no child left behind" etc. that prevent the public schools from being top notch. Public schools target the lowest achiever - there is no accomodation to excell.

I can't say for certain what they are like today.. but I had a BROAD spectrum of US schooling (across the country, public and private). At no time did I feel like private schooling offered any additional incentive to excel over *good* public schooling - at least in general. IMO (and my experience) there were four real advantages to a good private school, a slightly more aggressive curriculum, better teachers on average (they could pay more), moderately smarter students (simply because they had the ability to select smarter students), and perhaps most importantly - a better student to teacher ratio (..and this is in comparison to a *good* public school). With the exception of the student teacher ratio though, there wasn't a great disparity. The kids that weren't really that smart were often just "passed" - it didn't substantially "slow down" or diminish learning because of them. Finally, I only found in some "magnet" schools (and even then only in a few classes), an emphasis on excellence. (..and several teachers in both public and private schools did provide an accommodation to excel - but it was always a teacher specific thing.)
 
ScottG said:


I can't say for certain what they are like today.. but I had a BROAD spectrum of US schooling (across the country, public and private). At no time did I feel like private schooling offered any additional incentive to excel over *good* public schooling - at least in general. IMO (and my experience) there were four real advantages to a good private school, a slightly more aggressive curriculum, better teachers on average (they could pay more), moderately smarter students (simply because they had the ability to select smarter students), and perhaps most importantly - a better student to teacher ratio (..and this is in comparison to a *good* public school). With the exception of the student teacher ratio though, there wasn't a great disparity. The kids that weren't really that smart were often just "passed" - it didn't substantially "slow down" or diminish learning because of them. Finally, I only found in some "magnet" schools (and even then only in a few classes), an emphasis on excellence. (..and several teachers in both public and private schools did provide an accommodation to excel - but it was always a teacher specific thing.)


My son goes to a Montessori School, which I have to say I find impressive. Nathan excells at math, some two to three years ahead of his public school grade and the Montessori system handles this with no problem. When I look back on my own experiences, I too could have excelled, but the motivation wasn't there for me to do so. I was a troublemaker because I was bored. When I got to college (which I barely got into) I found a need to really apply myself for the first time and I did. I went from mudane grades to excellent and finished college with a 4.0 in my last two years and all the way through graduate school. Apparently the capability was there, but the public schools just could not seem to bring this out of me. I had to do it myself.

I hate to generalize on things like this, but I just have not found the public school approach to be motivating to the exceptional student. And perhaps they shouldn't - its a complex problem. For us the answer appears to be private schools and I'm OK with that.

We really need to take this off line.
 
"The foam in layers may work, but I worry about the interface between the layers. I would certainly NOT glue this. The effect of these layers vibrating, etc. concerns me which is why I use a block."

I wouldn't want to risk filling the interstices with glue, either.

I can't imagine vibration being a problem what with the foam being lossy and nearly transparent.

My thought was to literally sew the layers together in a few spots and secure it to the hoen with a few smears of RTV in the moth area.

"So when someone asks how will "such-and-such" act, its only a guess, and likely not a very good one at that. In my experience small deviations from the ideal/optimum cause large deviations in the results. So it doesn't take much of a change for an intuitive guess as to the results to be way off."

Can I interpret this as you have no comment and smoothing that edge in the XT1086 which seems to alreadybe a deviation from the ideal)?

Thanks
 
noah katz said:
"The foam in layers may work, but I worry about the interface between the layers. I would certainly NOT glue this. The effect of these layers vibrating, etc. concerns me which is why I use a block."

I wouldn't want to risk filling the interstices with glue, either.

Spray adhesive like "Super 77" from 3M might work just fine. A thin spray on each side to be bonded and hold them together while the glue is wet. I really doubt that there would be any significant loss due to the glue.

Sheldon
 
noah katz said:
[BI can't imagine vibration being a problem what with the foam being lossy and nearly transparent.

My thought was to literally sew the layers together in a few spots and secure it to the hoen with a few smears of RTV in the moth area.

Can I interpret this as you have no comment and smoothing that edge in the XT1086 which seems to alreadybe a deviation from the ideal)?
[/B]

Vibration of the layers probably isn't a big issue - correct.

I like the sewing idea, but I'll stick with a solid block.

Correct on the comments - changes to changes becomes too far from the "known".
 
Sheldon said:


Spray adhesive like "Super 77" from 3M might work just fine. A thin spray on each side to be bonded and hold them together while the glue is wet. I really doubt that there would be any significant loss due to the glue.

Sheldon


We use 3M spray adhesive - 99 not 77, its more permanent - to hold the plugs in. This glue really does seal off the pores quite readily and have to be carful not to get it on any surfaces that transmit sound. It doesn't really spray "thin".
 
Sheldon said:


Spray adhesive like "Super 77" from 3M might work just fine. A thin spray on each side to be bonded and hold them together while the glue is wet. I really doubt that there would be any significant loss due to the glue.

Sheldon

Remember though that the change in interface will affect the sound. There is a loss as you cross boundaries. even if the boundaries are thin glue-up layers.

I haven't looked but I'd wager there's a two-part foam that can be poured and molded into any three dimensional shape you can build a mold for AND has the appropriate "phase plug" properties. It would yield a relatively homogenious and inexpensive solution.

Like a NERF football...

Matt
 
y8s said:


Remember though that the change in interface will affect the sound. There is a loss as you cross boundaries. even if the boundaries are thin glue-up layers.

I haven't looked but I'd wager there's a two-part foam that can be poured and molded into any three dimensional shape you can build a mold for AND has the appropriate "phase plug" properties. It would yield a relatively homogenious and inexpensive solution.

Like a NERF football...

Matt

You would loose that wager as the technology to make "open cell" foam is considerably more complex than to make "closed cell" foam. All two part foams are closed cell.

How do they get "open cell"? It takes a special formulation that leaves a combustive residue in each cell. Then they set up a combustion chain that bursts each cell igniting it and then on to the next, etc. This is not feasible to do in small blocks.
 
"How do they get "open cell"? It takes a special formulation that leaves a combustive residue in each cell. Then they set up a combustion chain that bursts each cell igniting it and then on to the next, etc. "

How delightfully bizarre.

That might make some interesting furniture for unwanted guests :)
 
gedlee said:


You would loose that wager as the technology to make "open cell" foam is considerably more complex than to make "closed cell" foam. All two part foams are closed cell.

How do they get "open cell"? It takes a special formulation that leaves a combustive residue in each cell. Then they set up a combustion chain that bursts each cell igniting it and then on to the next, etc. This is not feasible to do in small blocks.

Clearly you've spent some time to reduce your costs!

Have you considered sending the design to NERF and telling them it flies when thrown?
 
jzagaja said:
Dear Earl,

Let consider 15 sq. meters room made of glass (windows). If I put ribbons in the corner then side walls can work as conical waveguides. Is it a good idea?

When I put Unity horn clones in my car, I leveraged the idea of using a physical boundary to extend the horn mouth. You missed one thing though;

What about the throat?

What happens near the diaphragm of a loud speaker is critical; this means that if you screw up the throat, you'll cause problems that can't be fixed.

Knowing that, how do you create a proper interface between a riboon and a room?

Once you figure that one out, you'll be on your way.