Triangle-pyramid shaped speakers

[kneadle]

You need not to make a pyramid with only 4 sides.
make them left and right sloop 10-15 degrees angle.
And the same with the backside.
Baffle, bottom and top still is at usual.

I think the idea behind a tetrahedron is to avoid the hassle of baffling and porting. If you match the drivers to the volume, the tetrahedron takes care of the rest.

Dave

 

[kneadle]

The thing with the wavelength and the room size is indeed quite a hot topic in this context:

2.) If there is no "room for a wavelength" it is still possible to generate sound. For our hearing it is not necessary to have a soundWAVE to hear sound. Sound PRESSURE alone is sufficient. So it is still possible to generate low frequency sound in a small room. If the room in question were airtight the SPL could easily be calculated using the ratio of room volume and linear displacement of the woofer.

It is, indeed, a hot topic. Those giant waves are certainly audible, at least as far as we think they are when we are listening. In the first place, our brains might be inventing the frequencies (that's psychoacoustics, so I'll stop there). In the second place, just because a room is too small, or a box is too small, doesn't mean the wave will not "unfold" as it were, at least enough to "be" there. This has something to do with compression, and at this point I become ignorant.

On the other hand, when a car is blasting away, it annoys most people because they're standing some distance away from the source, which means that they can hear the bass frequencies after they've completely unfolded. Hence, I was always pissed at the high school kids for waking me up from 100 yds away with their contemptible devil-rock bass frequenicies. I moved, and now it's not a problem.

Dave

 

[SY]

The safety issue is an easy one- get a nice sponge rubber ball and stick it over the point. Red is the preferable color; yellow will narrow the soundstage, blue tends to grain up the highs. And avoid black, since it will upset the rhythm, timing, and pace.

The nonparallel sides thing that Dave mentioned is nice (what's more important is the nonuniform baffle shape), but it's counterbalanced by the "vee" facing the driver focusing the back wave. I tried a cabinet shape something like this once and had a terrible time with midrange reflections back through the cone. Whatever you do, damp that vee thoroughly! Tetrahedra have plenty of standing waves of their own (it's just not as easy a diff eq to solve as rectangular boxes), so don't let the fancy cabinet shape fool you into underdamping the sides, either.

There's a nice piece of software from FRD Consortium which will allow you to predict the effect of the triangular baffle on frequency response.

Oh, and Skinny's physics teacher made that comment about bass; I'd recommend that the school board fire that teacher for being as incompetent as my physics teachers were. It pains me to see how bad science education is in this country, and the number one reason is that teachers spend too much time learning pedagogy and feel-good subjects and not enough time studying the subject that they'll be teaching.

 

[kneadle]

which piece of software is it? The Asymmetrical Response Pattern Estimator ?

If that's the one, how does it work?

Thanks
Dave

 

[SY]

The one I use is called BDS. It's overlayed on Excel. It takes a little bit of practice, but even a software dummy like me got it to work.

 

[kneadle]

OK. That's a super program. As far as I can tell, this shape of a baffle, a 21" equilateral triangle, produces a fairly flat response with the 6 1/2" driver (or vice versa), depending on where I place it.

The only thing I don't understand about the inputs is the "Edge Size" variable. It's never explained in the companion Word document. I don't know what it means and I don't know what unit the number represents.

At any rate, I'm having too much fun with an Excel spreadsheet.

Or, I could be reading the thing completely wrong.

Oh well.

Dave

 

[kneadle]

I managed to model a design, then graph the response.

purple=6 1/2"
yellow=5"
blue=1" dome

any comments?

Thanks
Dave

 

[planet10]

yellow=5"
any comments?

If you could balance the rise with the roll-off it would be ideal. May i suggest a Vifa P13, which is behaved well enuff that there are at least a few tweeters that match nicely with a single XO cap.

dave

 

[kneadle]

That's what I was thinking. The 6 carries sub 1k, the 5 carries the mid highs, and the tweeter takes over for the highs.

And that's precisely what I don't know how to do. A DIY shop would help me design it, wouldn't they?

Thanks,

Dave

 

[scoolman]

A question and a couple of thoughts:

What type of music do you like, (or how much bass do you desire)?
If you like full bass, you will probably not be satisfied with a 0.3 ft*3 box regardless of its shape and driver chosen.
On the other hand, if you built a 16"(w) by 16" (d) by whatever height you need bass (sub) cabinet to go under this, your bass problems would be solved, and the upper cabinet would be closer to ear level for better imaging. Small children and pets would also be less likely to impale themselves. Beer and candles still could not be placed on top. A bass cabinet is a good first diy project. Perhaps the easiest way to power/integrate this would be to get something like this: http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=300-792.
The project cost would at least double (sorry) from $200.
For the upper cabinet, I would look around the net for free diy kit designs appropriate for your cabinet size, published by the amazing people who know how to design and measure crossovers (this is not at all easy, and requires lots of time and knowledge), and share this knowledge with the masses.
May these people have a very happy holiday!

 

[kneadle]

Thanks for the info.

The cabinets I have are not my own design; I inherited them. My younger brother, in the errors of his youth, mashed in the cones on some of the drivers in it. They were good-sounding up till that point.🙁

Therefore, I thought I'd introduce myself to DIY speaker design since I already had a tested and solidly built HiFi design, modifying what I have. I know these things must have been great-sounding at one time, before someone shoved a pair of cheap 5" midbass drivers to replace a woofer and a tweeter.

I do NOT need deep bass. I want a decent frequency spectrum that's relatively flat from a reasonable high to a reasonable rolloff. If these babies can get below 75Hz before the F3 (look at me! I'm using HiFi lingo!) and can get to 45 before the F12, I'd be thrilled. The key is "reasonably flat." Not super-duper. I'm no fool.

These would then serve well as a B setup in my A/B nearfield monitor configuration.

I looked around, and Madisound seems to be a good place to get crossover advice, affordably.

Oh, and $400 would spell instant death. We have a kid on the way and if I spent that much on more audio equipment--ZAPP! I'm dead.

Thanks,
Dave