Full-Range Speaker for Computer Speakers

[yuri768]

I'm sure this forum gets that question a lot. Well, to begin I should say I'm not a dedicated hobbyist; I'm not really a hobbyist at all. I'm a college art student, and for my final project in a wood design class I'm building some speaker enclosures. The shape is roughly a dodecahedron, with the bottom truncated so that it looks a bit like a drop of liquid sitting on the table. The speaker will go on one of the faces, which point up at about 110 degrees from horizontal. Material will be 1/2" Eastern Birch veneer plywood, and each face will be about 5" in diameter (or less, depending on speaker choice). This design might result in plain audio murder, but my expectations aren't high. I currently listen to .mp3s from my 4 year old Dell plastic speakers, and I'm satisfied with that.

The question: I settled on full-range speakers because my enclosure can't fit two or more drivers on a single face. So, which full-range speakers should I use? Maximum pricing is about $100 for both drivers; I would like to go a lot lower.

The Fostex FE-103 look attractive in terms on pricing and design but I don't know where to buy one. Would I even hear its quality with my design?

[planet10]

Your cabinet shape should be really good ... there was a company called Design Acoustics that did a dodecahedron... and i remember a diy artiticle as well.

You don't see this kind of thing often as they aren't for the faint of heart as far as build goes,

The FE103e would work well, but you may want to port them to get more bass. Have you calculated the internal volume of the "box"?

You buy stock FE103e from Madisound. http://www.madisound.com/catalog/pro...roducts_id=266

dave

[planet10]

Originally posted by planet10
... there was a company called Design Acoustics that did a dodecahedron...

Found a link..
http://www.hifi-museum.com/pa/da/da_index_p.htm



dave

[Henkjan]

nice, I like rgular shapes

this is what I built for my daugther:

so, you have yr second driver proposal... this is a 4 liter periodically damped cabinet, see thread

other candidate driver would be the markaudio CHR70 (or the Alpair6 if you stretch the budget)

[speakrsrfun]

I say go with a pair of CHR-70's from Mark Audio ( www.markaudio.com or www.alpair-usa.com/). Not the most efficent drivers but will outperform the STOCK Fostex drivers in many areas and efficiency will matter less near feild. In a 7-10 Ltr ported box you'd get great near feild responce down to the 40's (you would be lucky to get 100Hz out of a stock fostex) and they image like mad so with them being so close to you it is alot like headphones just not nearly as involved.

One thing I have noticed with the CHR-70 when run next to a Fostex FF85K is that the top end is a tad less refined in the CHR-70, or should I say it's a tad more recessed in the CHR-70. Now for near feild this is almost a Godsend, it seems the very subtle and slightly resessed top end make these little guys perfect for near feild due to the lack of listener fatigue. I'm not saying the CHR-70's lack top end sizzle, far from it, they just have it in a very smooth fatigueless way, kind of like comparing Metal dome tweeters to Silk dome tweeters.

Good luck on the build and take lots of pictures I'd really like to see how you do on this, Peace and happy building.

[planet10]

Originally posted by speakrsrfun
Not the most efficent drivers but will outperform the STOCK Fostex drivers in many areas and efficiency will matter less near feild... CHR-70 when run next to a Fostex FF85K

Note that the FF85 is quite a bit different than the FE103 (and even somewhat unique amongst the Fostex drivers) and that a generalization based on it is going too far. With inexpensive drivers like these, there are always going to be places where one is ahead of the other & visa-versa.

Yuri, what kind of amp do you have? That can help push your driver choice.

dave

[HareBrained]

I don't see a need to "truncate" the structure. I think that would greatly increase the complexity of the build and decrease the volume too much. Guessing at the volume being ~6" sphere, that's ~113ci (1.9L). The CHR-70 in that volume, heavily stuffed with polyfill, ~2 oz wt., would net an F3=92Hz and the Qt would still be less than 1. (IOW, an acceptable enclosure but I wouldn't go smaller.) The CHR-70 can be purchase (as a pair of drivers) from alpair-usa.com. The Alpair6 likes the small box a little better but the F3 is a little higher at 107Hz. Both will sound hugely better than the Dell's. The Fostex 103 is a solid choice as it'll be the best in the very small vented enclosure.

There are a couple of Tang Band drivers that would work well but most would have you researching xovers to control the anomalies in the output, and that's probably beyond your desire and objectives. You'll also see that Mark Audio has a Aplair 5 but that's a slightly different driver and would not be suitable for the application unless you have a subwoofer and some other electronics.

If you could go larger, all 3 of those drivers would benefit. The frame of the CHR-70 is 5" across. The Alpair is 4.5" and the 103 is ~4.25". The CHR-70 is the cheapest at ~$60 for a pair. Then the 103 at $80 for a pair. The 6 will set you back ~$130. These are shipped prices.

[planet10]

Originally posted by HareBrained
Guessing at the volume being ~6" sphere, that's ~113ci (1.9L).

Built from a pentagon capable of supporting a 4" driver it is going to be much larger than that.

Vol of dodecahedron = 5/2 * tan(54°)^2 * tan(arcsin(1/(2*sin(36°)))) * a^3 = ~7.66 * a^3

where a is the length of 1 edge. This needs to be about 7.5 cm minimum (internal) --> 3.2 litre. That is a pretty tight fit, going to 9 cm would give 5.6 litre

dave

[loninappleton]

I can't help but be thinking from the monkeywrench department of art criticism.

If this is an art project, a regular geometric shape (as is shown in the answers) has been done before in audio.

As art, I always thought these were interesting and acoustically designed by a master. Not exactly the same size but still pretty compact:

http://www.lovecraftdesigns.com/



Another arty treatment in PVC:

http://www.t-linespeakers.org/projec...uke/index.html

[yuri768]

Wow, thanks for all the information.

planet10, the build hopefully won't be excessively difficult. The faces will be milled with a CNC Router with flat sides. Next I'll use a table saw to create the correct internal angles. I'll use custom bent metal brackets with screws to assemble it, just bending one bracket at a time, checking to see if it works, etc. I think I need to use wood glue to seal the enclosure but would rather not because of the strange gluing angle, any ideas on how to clamp it well? And, if I intentionally port it, does it need to be sealed at the joints? The speaker hole and screw holes will be milled as well, and the bottom I'll keep removable using thumb screws that double as rubber feet.

Henkjan, thanks for the reference!

HareBrained, my desire to truncate it comes mostly from visual preference; I made a little graphic to show the silhouettes. I'm not sure about your math...I did some research on the volume of a dodecahedron and it is roughly 7.66 * a^3, where a is the side length. If my side length is 5", a full dodecahedron is 15.68 liters and my truncated design, which I'm guessing has about 60% volume, is 9.43 liters. If my side length is 4" (more likely) the full dodecahedron is 8.03 liters, and 60% is 4.82 liters.