Jim Rogers JR149 DIY build

[Helen Bach]

hello Richard,

the 'sound' one gets when materials are hit is governed by a few things, how the material is made, what the exact composition is, what the dimensions are and how it is supported. Added to that is what you hit it with (impedance of each).

One of the major influences is what the critical frequency is. Pertinent to this reply is what happens below and above the critical frequency. Below the critical frequency, resonances begin to be radiated (into the environs surrounding the structure), at lower frequencies, radiation is small, but as one approaches the critical frequency, radiation increases, although the amount depends on the harmonic content. At the critical frequency, the radiation is amplified several fold. Above the critical frequency, all resonances are radiated 100%. So what one hears when the structure is hit is the sum of all the radiating resonances.

Hope that makes sense.

 

[AmadeusMozart]

It is actually the opposite: There are studies that show that you want to lower the resonant frequency of the materials (enclosure). That's why the LS3/5A uses bitumen damping on the panels. There have also been tests that the "stiffer" materials (e.g. very thick panels) have artifacts that are harder to get rid off. This is the opposite of popular beliefs.

Regarding my earlier remark on coils: the second page of the interview with AlChris mentions that inductors to close to each other introduce crosstalk. http://hifipig.com/wp-content/uploads/2021/09/HiFi-Pig-SUMMER-2021-Magazine.4.pdf

 

[lexi]

It's a nice project and hats off to you in tackling it. Having made ally bonnets and panels for small car projects, I can say that it is not easy, without proper formers and benders etc. ie a real metal fabricating workshop. Well done!

 

[Helen Bach]

the thicker the panel, the higher the resonance frequency.

resonance frequency ~ SQRT (bending stiffness) ~ thickness ³

Bituminous panels were there to aid damping, only.

What 'artifacts'? Bass frequencies are harder to damp than higher frequencies. That is because, in unit time, there are far more 'waves' at higher frequencies, so more damping can take place.

 

[grahamdocman]

Re: round speaker cabinets,a.k.a. JR149, I dimly remember a compact design by (I think) Dave Berriman, in one of the HiFi magazines in the 70's - possibly what HiFi - which used a clay chimney pot.

A friend made a pair and it actually sounded very good, the cabinet was very dead sounding when tapped, provided you didn't hit it too hard with a hammer.

The brief had been to design a "different" DIY budget speaker.

Does anyone remember this design and does anyone have a copy of the original article ?
if so I'd be temped to give it a go.

 

[AmadeusMozart]

the thicker the panel, the higher the resonance frequency.

resonance frequency ~ SQRT (bending stiffness) ~ thickness ³

Bituminous panels were there to aid damping, only.

What 'artifacts'? Bass frequencies are harder to damp than higher frequencies. That is because, in unit time, there are far more 'waves' at higher frequencies, so more damping can take place.

I rather go by the 1970's studies of the BBC (they spend over 100K GBP at the time) than by all the marketing crap that promoted a cheap build with MDF which is nothing but pressed cardboard that won't last the distance. Seen plenty of speakers made from MDF falling apart. Call me old fashioned.

 

[martinclan]

Interesting remark about MDF. It certainly isn't what it used to be. I used recycled MDF from a couple of old speakers I built 20 odd years ago. It's completely different to the modern stuff. Heavier ( higher density I guess) and with a much better surface finish. Fings ain't wot they used to be!

 

[AmadeusMozart]

Always the next step to make something cheaper - imho make it even crappier and hoping the public doesn't notice. Saw some unused KEF Q100 that had been stored in a garage for two years. One cabinet was literally bulging at a couple of the corners and falling apart.

 

[martinclan]

Well they are finished other than the grille. Mind you they look pretty good as they are, hmmm....
I did a brief test today with an original vinyl copy of Tubular Bells. The definition is amazing - I swear i could hear Mike Oldfield breathing on the section with classical guitar.
A couple of, not very good, pictures.
complete by Robin Martin, on Flickr
complete2 by Robin Martin, on Flickr

 

[a.palfreyman]

 

[Marra]

Very nice.

 

[martin clark]

I have thought about taking a section of plastic drain pipe (available in 200, 250 and 315mm diameter) and cutting vertically.
Soften in hot water and spread around a flat wood baffle for the drivers

Voice of exp: doesn't work... working with such extruded PVC is hard, requires more energy than you think, and just when you think its softened nearly enough - it all turns to custard. At the temps & effort required, you'd likely have better results achieving the shape you want casting a firm yorkshire pudding batter ... at least you can then eat the failure.