Anyone build a Rondo Inspired Speaker?

[batsong]

Anyone try to build an Auditorium 23 Rondo type enclosure?

 

[xrk971]

This is a perfect fit for Foam Core with its ability to bend and have curved walls. What are the cabinet dimensions and what driver is used? I would probably make a smaller version. Max dimension is 30 in tall limited by foam core max size for $1 sheets. Is it a bass reflex or a MLTL?

 

[batsong]

It is more like a baffle, as it is sans bottom. The discription page in link mentions DIY 'plagiarism', but I remember how cool these seemed when they first came out and have since wondered about the sound.

 

[xrk971]

Batsong,
OK, open bottom - a semi open baffle design almost. Easy to try in FC. Do you know what size driver this is or driver model number so I can get specs?

 

[batsong]

8"

6moons audio reviews: Auditorium 23 SoloVox

 

[norman bates]

FLEAWATT : Fleawatt Betsy Cello Speakers

this guy built them for his betsy drivers.

 

[jimbro]

Betsy looks out of place in that beautiful cabinet. One case where a cover is needed.

 

[Philfr]

Hi all,
6moons audio reviews: Musical Affairs Grand Crescendo
and "process" :
Musical Affairs on Vimeo
Phil.

 

[xrk971]

FLEAWATT : Fleawatt Betsy Cello Speakers

this guy built them for his betsy drivers.

I don't think it looks any more out of place than the green colored driver that is on the Auditorium23 speaker.

Fleawatt and @Cervelorider are one and the same. He builds nice stuff, maybe he can comment on the sound this speaker makes and construction technique? If it truly is an empty open box with the bottom open, the sound coming out might be kind of a mess - some damping would seem to be called for.

I will try to simulate this in AkAbak - maybe I will try it with a budget Visaton BG20? I will have to estimate dims from the photos though - this appears to be quite a voluminous speaker. I am thinking a 5 in driver would be pretty nice to have to get the cabinet a little more compact.

 

[batsong]

The Musical Affairs Grand reviewed in the link posted above holds a 12" driver. The article shows enclosure construction in detail and describes effective damping techniques.

 

[KLBIrd]

Bending the wood would be a real challenge. I'd like to see some actual performance figures before I would ever consider such a radical scheme. What driver did they use?

 

[xrk971]

OK, I looked at the review for the Musical Affairs. This looks like it is intended to be semi-resonant body like a violin with the "vent" a tall slot at the back along the whole height - like a terminus restricted open baffle. Open baffle high Qts high efficiency drivers should be used. Makes perfect sense to use the BetsyK for an economical approach. Those PHY's cost 2000 Euros! The use of triangular wooden blocks for an anechoic wall at top and bottom is interesting - but egg carton acoustic grey foam may be an easy alternative there. There is also a wedge deflector directly behind driver to prevent reflections back into cone. Very interesting design but as the reviewer said, very sensitive to placement - by mere mm's makes a difference. That is not good.

 

[batsong]

6moons audio reviews: Auditorium 23 SoloVox

Here are some interesting comments from the original designer.

 

[cervelorider]

Hi guys. I'm happy to answer any questions you might have about the resonant style enclosure I used for the Betsy drivers.
The plans I used came from Troels Gravensen.
Greencones
They are a resonant cabinet. They are meant to impart their character on the sound. This isn't for everyone. Especially those who place a priority on measurements vs. listening pleasure. With that said, many of my non audiophile friends and my wife prefer them over some of my more "accurate" speakers.

 

[xrk971]

Thanks for the link Cervelorider - great details in there plus real measurements. OK, so give us the low-down: how much of a b!tch was it to bend and glue the curved side plywood panels? Are the cutouts directly behind the drivers meant to reduce reflections?

 

[cervelorider]

Bending the ply is very difficult. Not for the inexperienced. It does add significant tension to the sides and therefore effects the resonant frequency of the panels.The ports at the back vary from design to design. I imagine they affect both tuning and reflections.

 

[batsong]

I'd imagine one would want to come up with a flexible port design as the enclosures would have to be 'tuned' to their environment.

 

[talaerts]

Not exactly a copy of the Rondo but certainly inspired, this German design seems worth investigating:

Breezer

 

[xrk971]

Simulation of a Rondo-inspired design for Betsy K

Based on an 'open bottom' enclosure from the Rondo, I made a quick design using the Betsy K driver and sim'd it in AkAbak.

The baffle is 24 in wide and make the curved rear sections such that the CSA is 384 square inches x 60 in tall, with 4 in legs to allow a gap of 4 in clearance at the floor. The lower window brace is assumed to be 0.5 in thick plywood and provides 80% of the max CSA or 307 square inches. The driver is mounted at 25 in from the top, and the speaker is placed at 70 inches away from the back wall (measured to the front baffle). It requires quite a bit of BSC to get the rising response to go down level: 6 ohm and 1.5 mH in parallel before positive connection to driver.

Simulation with no stuffing or damping and 2.83 V of driver input gives the following frequency response and cone displacement plots:

 

[GM]

Hmm, 70" from rear wall, but measured distance [Lp] is 1 m?

GM