The Metronome

Metronomes! Just can get enough of 'em!

Had to build another pair for the Fostex FE103en drivers I bought early this year. I had tried them out in the Mets I built for the FE108eS and liked the sound. So here is the latest pair, adjusted slightly from the original formula used for the FE108eS, and with a different BSC as well.
L= 40"
Z(d)= 14"
S(0)= 1"x2.5"
S(l)= 4.5"x8"
port diameter= 2.2"
port L= 3.5"

BSC: 3 ohm Mills resistor & 0.6 mH inductor

Baffle is 3/4" ply that came with oak veneer (scraps from another project)
sides & back are 1/2" Baltic Birch ply (which I veneered with red oak, but with normal grain orientation)

Binding posts are artfully concealed on bottom by the port.

Photo below shows one of them next to my Pappa's TL (not that you wouldn't recognize the Met!)

They sound slightly different from the FE108eS, but rather similar. If you find the FE108eS a bit too peaky, then you might prefer the FE103en, which I find smoother. As always: YMMV.

Cheers, Jim
 

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Hi Larry,

Give the bipole Mets a try! I built a small pair of bipole Mets using Fostex FF85k--see post #997. (I mention this because this thread has gotten rather large and many folks may not have read through it all, much less memorized all the builds!)

After enjoying them for a while, I took them apart and moved the drivers back into their previous enclosures.

Cheers, Jim
 
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Interestingly, AmadeusMozart built a Met for the FF125WK and FF105WK. It seemed he may have slightly preferred the FF105WK but it was probably a close call. Look back at around 101.

I still prefer the FF105WK for sound and size. Top and bottom attached to enclosure and covered with upholstery cloth (slow drying water based contact glue)

The main differences between the 125 and 105 are that the 125 has a more noticeable peak and goes slightly lower (but hardly noticeable) in frequency. SPL wise they are much of the same since the 105 has a larger xMax than the 125. Prefer the mids on the 105. Should try out the FX120 in the 125 but recently have become locally hard to find. (plus more expensive)

I no longer have good use of my right hand - if I had I would try out a metronome with the FF165WK in it.
 

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Dave is correct: those are indeed the FE103en with Fostex grills --which may only be marketed for the FE108eS, but which I was pleasantly surprised to discover fit the 103. They do make the 103 look very different. Should have said that up front, but hey, I'm getting old & forgetful!

Cheers, Jim

The Fostex grills do fit the FF125WK except the little paper ring in the front has to be carefully removed to make it sit flush. One the 1FF05WK I made some grills.
 
Hi AM,

Sorry to hear that things are getting worse for you.

If you prefer the FF105wk to the FF125wk, then you probably would enjoy the FX120 and the F120A (which I have in Mets). I'm sure you would also like the FE103en, although the FF105wk will have an advantage in the low end. I think all of these are smother than the FF125wk...but as always, YMMV. And in the end, the differences may be too small to be worth the time/effort/cost.

Cheers, Jim
 
Hi AM,

...... And in the end, the differences may be too small to be worth the time/effort/cost.

Cost has held me back from putting in the FX120 (but have thought about it several times, now costs has shot up). Effort and size have held me back from making a pair with the FF165WK (appears not to have a pronounced peak).

There are tests that show that both high and low need to roll off in an equal manner in order to have a pleasant sound. In other words one does not want to have a speaker that is extended in the bass region and not on the top end.

This means that the FF165WK metronome needs a tweeter and I am solidly into single driver without crossovers.

I have often wanted try out the FE103En in the FE126En hybrid horn. Heard some clip on youtoob that sounded pretty decent and the (IIRC) Italian chap mentioned that it was lots better than with the FE126En. If you are into small desktop stuff then there is a small hybrid horn for the FF85WK (and the 3" bamboo TangBand) by "Korvi Blue*drop". So many things to try out ;).
 
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I am interested in building a Met for the FX120 or FX120A and I notice that the FF125WK appears to have similar dimensions.

Is it feasible and beneficial to try to arrive at a Met enclosure that could be used for either a FX120, FX120A, or FF125WK? They all appear to be about 120mm or 4.7" drivers.

I'm guessing that the published plans for the FE127E are the closest design for these drivers. I believe Jim mentioned he's adapted a plan for the FX120, but I could not find any dimensional plans.

Given the robustness of the Met design, I could modify the FE127E plans to fit or confirm fit to relieve the box for the large magnet cover of the F120A. A F120A enclosure might work for the series of 4.7" drivers with driver specific magnet braces.

Is this going down the right track? I can make some plans for review. If Jim would kindly share his dimensions for the "favorite" F120 I could draw them up.

Cheers,

Jamie
 
A small contribution to this question. From the Fostex documentation it appears that the FF125WK, FX120, and F120A all share the same baffle hole diameter, 104mm, and the mounting hole diameter of 126 mm.

Jim's listening opinions might suggest that there's a nice upgrade path where increasing price may correlate to improved performance such that someone could try a budget build with the FF125WK at $62.70 each, then onto the FX120 at $144.30, then the F120A at $290.00. Additionally the design might be compatible with a NOS or used FE127e?

Cheers,

Jamie
 
Okay, as usual, there's just about everything anyone needs to know in this forum.

Jim Shearer posted his F120A Met design, although in that thread he was less than wowed by the bang for buck of the F120A.

Reposting Jim's Met design parameters.

L= 52 inches
Z(driver)= 22 inches
S(0)= 2.5 x 2 inches
S(L)= 9.5 x 5.25 inches
Port Diameter = 3 inches
Port L = 4 inches

Also found further discussion of various drivers in this same enclosure plan. Enough for my meager theoretical needs. Just build it, right?

Jamie
 
And, oops, picked up the thread and Jim's tube discovery. F120A is hero again.

"Using tubes, the F120a sounds like a whole new driver--absolutely fabulous sound! Cymbals, brushes, piano, everything suddenly springs to life. Sound stage and imaging are excellent too."

I hate to re-invent wheels, so glad to have so much great knowledge shared.

Jamie
 
Hi Jamie,

Let me add a few more comments.

The FX120 should be a direct substitute for the F120A. I have never heard the FX120, but I have read comments from those who have; they claim that it provides 95% of the F120A’a performance at half the cost.

The F120A didn’t need any BSC. Not sure what the other drivers might need.

Also, for those who didn’t catch it before: The F120A sounded awful when run with direct coupled SS amps! The high frequencies just disappeared! It sounds best with tubes, but was pretty good with my vintage Sansui receivers (which are cap coupled output) and with T-amps.

I ran MJK MathCAD model of the FE127e in a Met with the dimensions of the F120A Met: it looked just fine.

Later, in another discussion: I ran MJK MathCAD models of the FF125wk Met using the dimensions for the FE127e. It does work, but can be improved with a little tweaking. AFAIK there is no single, absolute solution for cabinet dimensions--there is always some wiggle room and then you tailor the various compromises to suit your preferences. The dimensions I settled on look OK to me, but someone else may find a slightly better solution for their preferences.

Compared to Scott’s dimensions for the FE127e: I decreased the internal volume a bit, increased the length of the port, and increased Zd by 2". Changing Zd resulted in a bit less ripple in the SPL plot, but leaving Zd at 20" works OK--the ripple is then about what it is in the Mets I have built. So you can choose between higher driver placement and a little less ripple in the response.

L= 48"
So= 2 x 2"
Sl= 7 x 5"
Zd= 22"
port: D=2", L=3"

Hope this helps,
Jim
 
Jim,

Thanks so much for the reply. I thought I was sorted, but I tried to draw up by hand the dimensions I dug out from one of your posts in the long thread and I think I'm a bit turned around.

I thought you had posted these Met dimensions for the F120A driver.

L= 52 inches
Z(driver)= 22 inches
S(0)= 2.5 x 2 inches
S(L)= 9.5 x 5.25 inches
Port Diameter = 3 inches
Port L = 4 inches


I thought you had made the volume a bit LARGER and a bit LONGER which would appear to allow for the large magnet of the F120A and I guessed optimized the pipe response and damping. I couldn't really confirm whether the depth of the cabinet is enough for the magnet in my hand drawing.

If I use the FX120 I don't think there's a magnet clearance issue and I should save the money until I've learned more. A smaller cabinet helps me also a little bit if proceed with an ambitious construction technique I'm toying with.

Thanks for confirming the Met dimensions for these drivers, and it's an extra bonus to discover the bang for buck of the FX120. My idea is not serious enough to start a new design discussion, but serious enough that I want to make sure I've cribbed as much knowledge as is out there which is amazing in this forum.

I've been wanting to do something with the Met for some time now and the various feedback that you and others have provided regarding the 4.7" driver size and the Met have me very excited. I'll be sure to share what I come up with.

Jamie
 
Oh, and thanks so much for the tube amp and BSC information. I'm running tubes. It's great to know that I might not need BSC. I'm really quite stuck regarding bass response having woken up to room modes and boundary support. I plan to have a new room to use which I'd like to model and experiment with, otherwise I fear I have no way to "listen" to a speaker without listening to the room and not knowing which is which. I also have a Frugal MK3 I built and I'm reserving judgment on that one till I can really listen to it properly.