Morgan Jones "Arpeggio" Loudspeaker

[Variac]

This is a thread to discuss the Arpeggio loudspeaker designed by Morgan Jones and described in an article by him in the "Articles" section

[planet10]

Some page by page comments (most have already been seem on these pages by me or others) and some extensions & support for what is written.

I am very attracted to the concept & execution of this design. They look fantastic.

Page 6:

The slight blip at 1kHz is not a measurement error but is thought to be a dust cap/voice coil mechanical resonance being coupled back into the electrical impedance

Attached areimpedance plots of the same FE166e with and without a dustcap. Also note that the rise at high frequencies is about half what Morgan illustrates (meaning that you may need to play with the zobel).

Note: i have measures of some 20 other FE166 so i can check consistency.

Page 8:

Note that the analysis of edge diffraction ripple is only valid for on-axis listening, and the further off-axis you are the more the end result will move away.

Page 9:

A more generalized treatment of Passive Line Level Baffle Step Compensation by Paul Joppa (now at Bottlehead).

Page 10: Attached is a key diagram from Tappan's paper.


dave

[Scottmoose]

I could be misreading the notes on standing waves (I've got a squawking headache so I'm not at my best this morning) but they look to me to be related to the moving fibre notions largely discredited by Hersh & Walker, G. Augspurger, & M. King.

[planet10]

Continued, these are points i have been hammering away at for years.

Page 13: The brace is placed dead-centre. This is the worst possible place for it. Moving it over by a panel width even can make a differemce.

As anyone who follows my designs i like to brace the driver to the rest of the box, for this one i'd likely use 2 verticle brace, one right behind the driver.

Page 14: I strongly believe that MDF is not a suitable material for building loudspeakers out of. Use 18mm Baltic Birch (or similar) and you will end up with a better speaker with greater downward dynamic range.

dave

[Scottmoose]

I fear the minor queries raised thus far could seem depressingly negative -they're not meant that way of course, so I'll quickly get in at this point that irrespective of these, I still think it's a neat little box & should give decent results for anyone wanting something along these lines.

[planet10]

Page 15: Because it is so hard to compare 2 separate graphs i have created an overlay of Figure 19 (black) and figure 23 (blue) for easier comparison.

Morgan, how thick is the felt, and is it wool, corrom, or polyester felt?

As Toole has shown, on-axis FR is not a great indicator of sonic performance. It would be nice to see a set of 10 degree vertical & horizonatal plots (but i'll take the listening results as fine)

dave

[planet10]

A very good article, and nice to see Morgan do a sealed box that only goes to 85 Hz, This meshes well with Toole & Geddes suggesting that this kind of performance mated with multiple mono woofers for a full-range system.

This is also somewhat similar in concept (with added woofers) of the new Bottlehead system. Morgan's speaker has had a lot more thought put into it.

The basic configuration is also broadly similar to a quick-n-nasty break-in box we made for FE167 (quick-n-nasty hence the standard BR port) and the Classic GR Fonken so you can see why i am attracted to this design. Note that the GR when finally done had a bevel on the vertical edges.

In the spirit of articles being a stimulus for putting new twists on things -- Every designer has, at least, a slightly different take on things: these are things that i would at least consider changing.

I would build this from plywood, enhance the bracing, and use one of my fully treated FE166eN (or at least add phase plugs).

As well, from experiments we have conducted with FE126 + series R vrs FE127, i would consider executing something similar with FE167 so as to reduce the series R. And based on the very good results we have had with the high resistance ports in terms of getting away from the things i don't like about both sealed & ported enclosures, i'd would probably turn into a Classic GR Fonken167 allowing us to eliminate the series R completely (& possibly some of the BSC)

Very good article Morgan. Kudos.

dave

[planet10]

Originally Posted by Scottmoose

I fear the minor queries raised thus far could seem depressingly negative -they're not meant that way of course, so I'll quickly get in at this point that irrespective of these, I still think it's a neat little box & should give decent results for anyone wanting something along these lines.

Agreed. Think of the comments as polish on an excellent basic design.

dave

[SY]

They sounded very nice with the Scrapbox Challenge, even better with one of DHTRob's amps. The unfortunate part was that TheEyeLady saw them and immediately demanded that I make my speakers that small, nicely designed (visually), and unobtrusive. I tried to explain the realities of dynamic range and frequency response, but these fell on, errr, deaf ears.

[planet10]

If you subscribe to Toole & Geddes the mains need not be large... and the size of the woofers can be distributed thruout the room. If you sawed off the top of your NHT clones and optimally placed the woofers, yours would be even less intrusive

Unless of course if you have gotten the Acoustats back in action. No way to shrink those.

dave