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Ergo Number Nine - Adventures in Micromonitor Design

James

James

Lord of the Erg\o/s
Spring is in the air, and what better time to think about another loudspeaker design. I have lots of ideas in mind, but unfortunately they don't quite match the amount of storage I have left in the house, nor the depth of my pockets. So my 15" 3-way will have to wait another day.

Instead, I will attempt to build my smallest design - based on the exact dimensions of the LS3/5a. But rather than simply replicating the design, I will attempt to make it my own. This means no B-110/T-27s, no 12mm birch ply, no veneer, etc. The driver complement that I have chosen are:

Scan-speak 15W/8530K-01: a 5-inch midwoofer that has very similar T/S parameters to the B-110 but features a doped paper cone and an ultralinear motor system with extraordinary excursion. This should be good for 40Hz in-room in a sealed 9L box, and extend cleanly to around 3kHz.

15W_8530K01.jpg


Morel MDT37: a horn-loaded 1" tweeter that has a usefully low fs of 700Hz. I'm using the bigger brother Supreme 110 in the E-VIIIs and continue to be delighted by what I hear. So, Morel promises much. The main reason for choosing the horn-loaded is not so much for the increased sensitivity, but to reduce the misalignment between acoustic centres.

MDT37.jpg


My initial thoughts are to use solid timber for the panels, and MDF for the baffle. Depending on how bulky the XO turns out to be (and therefore placing a premium on internal volume), it might be externalised like most of the Ergo designs to date. The two drivers chosen will present a very wide FR overlap, which suggests I could go for a low-order crossover, but that will depend also on how they measure on-baffle. A first-order system this won't be, but it's going to be either my preference 2nd order Linkwitz-Riley or 3rd order Butterworth.

The drivers should be here by next weekend. How exciting.

James
 
Smaller speakers you say, like for a second system?

That SS unit looks the bee knees on paper, 9L box, hmm small.

Good luck James.
 
Or third system, in my case. I already have two pairs of loudspeakers in storage, and two pairs on current rotation in the house. However, I do have a spare NAIT2 and Yamaha analogue tuner that could go into the bedroom.

Fancy a pair, Garf?

James
 
I think this sounds very interesting! I am on the lookout for a small box and this sounds very promising judging from the reviews on your other loudspeaker systems, nice!

/Magnus
 
James said:
Or third system, in my case. I already have two pairs of loudspeakers in storage, and two pairs on current rotation in the house. However, I do have a spare NAIT2 and Yamaha analogue tuner that could go into the bedroom.

Fancy a pair, Garf?

James
Click to expand...

You could always rotate them though my house...

I think I have the speaker building bug. Sadly my wife has just given up work to go back to college so we are a little skint at the moment. The Specials were probably the last big input to the hifi until she's back at work, unless I get a better paid job.

Is the front baffle going to be sloped for alignment, or straight flat (as the LS3s)?

And yes I would love a pair.
 
chiily said:
You could always rotate them though my house...
Click to expand...
I think it'd be cheaper for you to build them in England, Garf. The E-VIIIs with the twinned M26WRs have yet to leave my home for a trip around the neighbourhood. I don't think I can physically muster them down the stairs without hurting myself or denting a wall.

I think I have the speaker building bug. Sadly my wife has just given up work to go back to college so we are a little skint at the moment. The Specials were probably the last big input to the hifi until she's back at work, unless I get a better paid job.
Click to expand...
Do what I do and spend quality time thinking about the next design.

Is the front baffle going to be sloped for alignment, or straight flat (as the LS3s)?
Click to expand...
No, that's why I chose the MDT37 tweeter. The recessed dome brings the acoustic plane a lot closer to that of the midwoofer. I'll know for sure when I have the drivers in hand to take some measurement. A small amount of offset (less than 1/2-inch) won't do a lot of harm with 2rd order crossovers.

And yes I would love a pair.
Click to expand...
Better pay attention to this thread then. ;)

James
 
James,

I'm also considering building a micro monitor. I already have Linn Tukan mini woofers (I think it's actually a Vifa with a larger magnet) which I bought on eBay, and for the tweeters I think that I'll reuse the Fostex FT17 which I plan to remove from my main speakers (to be replaced by revelators).

Anyhow, have you considered a transmission line design? I'm thinking of something like the small PMCs here, if you look carefully on the first PDF you can see the internal layout of the ATL (on the right of the brochure). I already built a prototype and I'm quite impressed by the bass extension and clarity.
 
James, do you know how difficult they will be to drive and how much the parts will cost?. . . I'm always on the lookout for something better than my kans + sub
 
James,

What about the stands for these mini-Ergo? There a world of building and testing just in this subject.
 
teddy_pardo said:
... have you considered a transmission line design? I'm thinking of something like the small PMCs here, if you look carefully on the first PDF you can see the internal layout of the ATL (on the right of the brochure). I already built a prototype and I'm quite impressed by the bass extension and clarity.
Click to expand...
Hi Teddy, I am intrigued by TL designs and was mightily impressed by a close relative quarter-wave design (Castle Chester) that I test-drove at home some time ago. TL are inherently challenging because the tuning has to be spot-on, and the latitude for error much smaller compared to sealed boxes. The other thing I have noticed is that small drivers cleverly loaded can produce very deep bass extension, but the subjective quality of that bass is not nearly as convincing as a much bigger driver that doesn't go that low. Nonetheless, in my future adventures, I will most certainly try my hand in a TL - and it will be a design of my own making. How else will I learn? ;)

fatmarley said:
James, do you know how difficult they will be to drive and how much the parts will cost?. . . I'm always on the lookout for something better than my kans + sub
Click to expand...
I anticipate a very easy 8-ohm loudspeaker. The Scan-speak is rated for 60W continuous and so any competent amplifier will drive this easily. I'll know for sure when I design the XO. The Scan-speak midwoofer is US$202 each and the Morel tweeter is US$75 each. As for the rest of the parts, I've yet to determine what I need. Based on my guesstimate, I'd say you're looking at around US$1K + labour.

chiily said:
What about the stands for these mini-Ergo? There a world of building and testing just in this subject.
Click to expand...
I'm already on the lookout for Kan stands, Garf. That would be my preference. They come up for sale here from time to time.

James
 
Very interesting James. I was a long term user of the Linn Kan II and loved them including all their foibles, sadly I sold them on to a mate who doesn't really use them as much as they should be used. To be honest I wouldn't buy another pair, ...but would I build an ergo take on the theme? Oh yes.

By the way I have just bought a Woodrat, dovetailed box?
Ashley
 
G'day, Ashley.

AshleyD said:
dovetailed box?
Click to expand...
I almost died when presented with the bill for 5 Sapele (yes, again :rolleyes:) boards that I'm going to use to build a bookcase, hi-fi stand (for the shoe-box Naim system) and these micromonitors. I don't think I can afford to experiment with a new (to me) jointing technique. My faithful biscuit mitre-joints will have to do for now. But don't let me stop you. :D

James
 
My initial calculations for a standard LS3/5a sized box yields a maximum internal volume of around 6L, which would lead to a Qtc close to 1.0. I'm not sure how that would sound. The 8530K-01 needs 9L for a maximally flat bass response. I guess I can do this in one of three ways:

(1) Leave the dimensions at spec, and see how it sounds.

(2) Increase the depth of the enclosure to gain the extra 3L. This means a depth of 265mm against 165mm. From the front, it'll still look like an LS3/5a.

(3) Use an aperiodic vent at the back of the spec cabinet to increase apparent volume. I have never used one of these before. They are not a reflex vent and I'm comfortable that the sealed box 2nd order rolloff will be retained.

I can try options (1) and (3) on the same pair of enclosures with bolt-on backs. Option (2) will require a new pair of boxes. I'm not sure I have the inclination to try all three options. Which combination makes the most sense?

James
 
Since it's not going to BE an LS3/5a, or even a close replica, I don't see the point in sticking slavishly to that box size. Go for option 2.
 
I had intended it to be a visual replica - even down to the use of a grill, if not a sonic one. But your point is clear

James

P/S: Do you know anyone with a spare pair of ES11 stands?
 
I vote for option two.

I have a pair of EPOS open framed stands, swap ya for the Ergo VIIIs?
 
LOL! I think your EPOS stands have the wrong numbers on it, as does the shipping bill for the E-VIIIs, surely.

James
 
So the concensus is clear. Option 2 it is then. That will also give me more latitude to stuff the XO inside the box for a change. It'll still be a tiny box compared to what I've been building of late. Should be a breeze.

Given that it won't now look like a visual replica of the LS3/5a, would anyone care for naked drivers? It'd make managing edge diffraction so much easier. I was also thinking about offsetting the tweeter so that it is not equidistant from the baffle edge. Against a black background, the exposed drivers shouldn't look out of place.

Work starts this weekend.

James
 
It seems like this could be a project that's even easier to build than the PFM Specials and could get many followers. For this reason, consideration of the WAF / KFITS* should really be taken into account, meaning grilles would be a great bonus.

Of course, from a purist point of view then naked drivers are the way to go.

* Kid's Fingers In The Speakers
 
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