Morgan Jones "Arpeggio" Loudspeaker

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
At the moment there are five cats 'round the house (two are black, one is yellowish, the avatar one is grey, plus the momma-cat who has the strange color mixture of black and yellow. Oh yes. And recently we adopted an orphan kitty, really cute, white-n-black. Dogs? My sister got a yellow retriever, but whenever she comes for visit we must ensure that he and the cats are kept at a safe distance from each other. :D

I'll stop here, don't want to turn this thread into cat-dog conversation :)
 
Really nice article with careful attention to detail which could apply across a range of projects. Reminds me of one by Peter Baxendale in the 60s where he took a straightforward driver and gave it the best box and equalisation to see how far he could take it.

It's all too easy to dismiss a simple design when actually executing it well, like this, can be anything but simple.

I'll chase up Dave's Tapin attachment when I'm back on the computer but a quick q. Morgan mentions the thin wall plus damping method. The original article said it moved resonance down to an area experienced listeners found hard to detect. Presumably panel bracing pushes them up, into an area we're more sensitive to?
 
Tricky isn't it. I guess the only way is to make and measure two boxes of the same internal volume, one using the BBC technique and one using the bracing. One loudspeaker manufacturer I spoke to said a colleague measured speaker cabinets in the 80s and came to the conclusion that they barely contributed at all, as long as they were well made - they were standard MDF (probably) boxes. No further details on that one, unfortunately.

Just caught up on Dave's jpegs. The first set show the frequency going up with bracing, so that matches the Beeb research. It's just a question of whether, as they said, the lower frequency resonances were less audible. It's an expensive way to build (for a commercial operation) so the fact that most manufacturers don't use it isn't a reliable sign.

Anyway, maybe a bit off-topic in a thread on Morgan's design, which clearly has its own balance of features.
 
Last edited:
Colin, he probably meant reduction of the amplitude of dissipated energy resulting from raising the panel's natural resonant frequency.

No Chris,

The BBC paper says it as Colin describes. Something i don't ascribe to. It will be interesting to compare Demis' LS3/5A when they are restored to the millis. The BC1s didn't do to bad, but were boxy compared to the units available for comparison.

dave


clearly, not having read the paper in question, I made an a$$ out of me - interpreting Colin's reference to mean that by using thin walls/selective damping (and bracing - not specifically mentioned) the result would be what we have experienced with our own work.

apparently I do need more than 5hrs sleep a night
 
Hi Chris - Here's a video showing the original research paper and Alan Shaw, of Harbeth, guiding the reader through it.

Harbeth thin wall cabinets - BBC research

The paper is available on the web (without the director's commentary). there's also a thread about it on Harbeth's own site - BBC-style thin-wall cabinets. Why so special?


thanks, Colin


You are getting sleeepppyyy....

dave


with my propensity for math any more complicated than the square root of 1, this could be more efficacious than a pill or couple of shots of bourbon :sleep:

certainly that was the case with the recent Toole text - I was lucky to keep my eyes open for more than 1/2 hr per session.
 
I spent years trying to figure out how to DIY speakers. Your article explained a lot very clearly. I just wish you had written this a few years ago, it would have saved me a lot of mistakes along the way. I had most of it down, but it was fuzzy, now it's not. One thing I had not figured out was how much delay a closed box roll off caused. You had that too.

I have some FE166E's in "storage". I'll make some of these.

PS: Is the felt a "wool felt", and how thick is it?

Thanks
Jim
 
A very good article Mr. Jones! Everything as very well explained as in your book on valve amplifiers.

I have a pair of Fostex Fe208 Sigma's and will make a pair of loudspeakers according to the same procedure as you described. Originally I used these in Jericho horns.

Besides that, I'm also working on an amplifier of Mr. Pass' design. (I'm stuck now at the chassis and the heat sinks) As mentioned in on of the earlier comments on the article, on the ESP-site adjusting the output impedance of an amplifier is explained. If I understand well, an Aleph type amplifier is easily adjusted to a certain output impedance by changing the feedback loop?

HJ
 
FE166ES-R/ Bottlehead/ Arpeggios

I own a pair of FE166ES-R, Bottlehead S.E.X. amp w/ iron supplement and C4S upgrade, Marchand XM1 crossover, and powered subs. I've been using the crossover and sub with a pair of CHR70 folded half towers which sound very nice! So nice that I barely listen to the fostex/bottlehead combo.
I would like to get rid of the Fostex BLHs and try the Arpeggios. This would allow me to have a nice A-B setup reminiscent of my old studio days.
I've studied Mr Morgan's great article and arrived at a volume of 17.32 L and Fe of 83.63hz.
I'm looking for some advice concerning the zobel and output impedance from the experts out there. It seems like i am on the right track?
Thanks in advance.
 
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

For sure a late very input to this thread, but can you please provide some drawings about the modification you did to this design. I'm willing to build this box but your small adjustments seem to improve it even.
Thanks in advance

Hans
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.