Bookshelf Sphere with dual concentric ports ?

[jimbo1968]

I want to make some bookshelf speakers for my office/dining room. So they should be good for all day close range listening at my PC, but also able to take a bit of volume when I'm not at the PC.

This from one of the fonken threads interested me.

Originally Posted by GM

WRT mid-range/upper mid-bass clarity with vented alignments, the pioneers of audio found that placing the driver inside a tube that was in turn the inside of the vent tube or 'ringing' the driver with many small vents as an acceptable variation was the most acoustically efficient which in turn minimized driver/vent crosstalk (comb filtering) due to the vent's high Q decay, so has anyone tried either yet?
GM

I fancy building a sphere, about diameter 10" (roughly 9 litre), with the drivers encircled by a ring of ports (say 12 of them). I got a bit lost in the Fonken thread about whether to model it as BR or something different.

So I welcome your opinions on choice of driver (cheap shipping to UK preffered eg up to about $250 for the pair shipped). And how many and size of port.

I've just been listening to my FR125s in sealed 7l with the subs turned off, and they sound good to me, but I guess the aim should be more bass from a smaller driver.

I like the idea of the front firing ports, because the sphere is great for pointing in whatever direction you like, and I won't have to worry about the port's close relationship with the wall.

[jimbo1968]

Oh yes, the driver MUST have a circular frame for aesthetic reasons.

picture added for effect.

[chrisb]

Originally Posted by jimbo1968

I want to make some bookshelf speakers for my office/dining room. So they should be good for all day close range listening at my PC, but also able to take a bit of volume when I'm not at the PC.

This from one of the fonken threads interested me.



I fancy building a sphere, about diameter 10" (roughly 9 litre), with the drivers encircled by a ring of ports (say 12 of them). I got a bit lost in the Fonken thread about whether to model it as BR or something different.

So I welcome your opinions on choice of driver (cheap shipping to UK preffered eg up to about $250 for the pair shipped). And how many and size of port.

I've just been listening to my FR125s in sealed 7l with the subs turned off, and they sound good to me, but I guess the aim should be more bass from a smaller driver.

I like the idea of the front firing ports, because the sphere is great for pointing in whatever direction you like, and I won't have to worry about the port's close relationship with the wall.

Aside from the sensitivity penalty the FR125 driver pays to achieve its amazing bandwidth (the "Hoffman premium"), it works amazingly well indeed in small sealed or resistively vented enclosures such as the mini-onken or




http://homepage.mac.com/tlinespeaker...odic-plans.pdf


But I'd be careful trying to maximize bass response of the FR125s in a "conventional" vented (BR) enclosure - you'll likely find its characteristics a X-max limit rather disquieting.

[jimbo1968]

Any good threads on 'resistively vented' ? I suppose lots of holes around the back will be fine, and a lot easier to do.

[planet10]

The circle of holes as a port can be seen in the literature going back a looonnnggg ways.

I doubt you'll get lower bass out of a small driver than an FR125. 9-10 litre is larger than i'd be comfortable with... of the many FR125 boxes we built, my favorite were the 4.5 litre boxes Chris posted a picture of.

Aperiodic damping is still as much an art as a science.

dave

[jimbo1968]

Note: I'm not planning to de-commision my FR125s, so driver choice is OPEN.

CHR-70 seems popular and I spotted this thread "Can CHR-70 work in a tall MilliSize (DeciSize?) Onken" which is 9 or 10litre.

Dave, any chance you could estimate me a size for my ports (for a CHR-70)?
edit: By estimate you could just let me know the area and length of the 6 ports in the above design, (or is that the commercially sensitive bit?).

[Alex from Oz]

What about using a passive radiator instead of ports?

Cheers,

Alex

[jimbo1968]

Think I'll try CHR-70 in 12l wooden salad bowls, tuned to 50Hz.
Then maybe experiment with stuffing in the ports.

[planet10]

Originally Posted by jimbo1968

(or is that the commercially sensitive bit?).

Yes. Because of the Danish licence.

dave

[jimbo1968]

Dave, I'm not sure which bits of the Art of Fonken design have been posted (I'm trying to find all the relevant posts). But maybe I could ask a few questions here:

Which of the curves shown would you start with ?

Do you use the modelled area and length and the only difference is that the ports are restrictive? Or do you have tweaking rules such as 20% longer or 15% less area or something like that?