The Metronome

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#1,281
I tried something else last night, I turned on my subwoofer for the first time in 3 years. I set the cardboard mets to small, set the crossover to 200hz, and gave it a try. They have much more of a low end of course, but overall I didn't really care for the effect. With the xover setting so high the sound becomes directional so I could hear it from one side where the sub is. I never really liked the sound of the sub anyway. It is an older SVS.
 
#1,283
Jim Shearer said:
I have built Mets withFE108eSigma, F120A, and FE167e. All are very nice and I think you would be pleased with any of them.

That said, the F120A is my favorite--smoothest, best high freq and good enough low freq that I don't feel the need for a subwoofer; however, this driver doesn't sound good with direct coupled SS amps--the high freqs just die; with tubes it makes sweet, sweet music.

The FE108eS has great mids & highs, but the lows are limited enough that I like to use a sub with it.

The FE167e plays louder & sounds bigger with more authoritative bass. It gives up a bit of sound quality in the mids & highs, but is over-all quite pleasing.

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. The dimensions I settled on look OK to me, but someone else may find a slightly better solution.

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.

Plotted response is for enclosure dimensions:
L= 48"
So= 2 x 2"
Sl= 7 x 5"
Zd= 22"
port: D=2", L=3"
Click to expand...

On occasion I have epxressed my dislike for a foam surround . Some time ago I obtained three FE127e's and I applied the pre-treatment and then put these in the folded monopole. Big difference with the FF105WK and FF125WK metronomes. In the end I no longer could stand the monopoles and shortened the port on the FF125WK metronome to 2" and put the FE127e in there - MJK worksheets indicate it is not optimal but I like it a lot more than the folded monopoles - the bass is more noticeable than with the FF125WK but not unpleasant. (but not going as deep...).
 
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#1,284
I've had the Mets w/ subwoofer plugged in for a week now and after a few tweaks on the settings, mostly lowering the output of the sub, and a little break in of the ears (beyond softening of the surrounds and other moving parts, I don't believe in break in, it is mostly becoming accustomed to a sound IMHO), I hit a sweet spot. These are so nice sounding that I never want to turn them off.

My son came home from school tonight and he walked in and asked "what did you do to your system? That just sounds soooo good". When I explained the $5 drivers in cardboard he just wanted a pair. Then I mentioned the sub and he realized it was an illusion, but that doesn't take away from how nice this now sounds.

So now I still have to take it all apart so I can measure the drivers and build something else with them so they can stand alone without the sub.
 
#1,285
I'm hoping to build a pair of Metronomes using some Fountek FE83 3" drivers. Can anyone help me figure out the dimensions? If there's some sort of calculator out there that'd be great. I'd try to do it empirically but I wouldn't know where to begin making adjustments to the design.
 
#1,289
Can't run MathCad 2000 XP on Win7 Pro AFAIK, but this one in Hornresp doesn't look bad once damped to 'taste' [all dims i.d.]:

L = 121.92 cm
S0 = 1 cm^2
SL = 139 cm^2
Zd = 60.96 cm
Dv = 2.18 cm [assumes 18-19 mm thick bottom plate]

GM
 
#1,290
GM said:
Can't run MathCad 2000 XP on Win7 Pro AFAIK, but this one in Hornresp doesn't look bad once damped to 'taste' [all dims i.d.]:

L = 121.92 cm
S0 = 1 cm^2
SL = 139 cm^2
Zd = 60.96 cm
Dv = 2.18 cm [assumes 18-19 mm thick bottom plate]

GM
Click to expand...

GM

in Win 7 / 8 Pro you can use Hyper V to install XP as a virtual machine (free license from MS - I have not tried it recently but from memory it was a download). Then install Mathcad under that and it is all transparent.
 
#1,296
I'm liking this. 🙂 Big pipe for the little 'un. Damped out to taste, nice EBS style alignment with a bit of a flick at 50Hz to give a bit more presence. Vent velocity (forgot to add that one, apologies) would normally be a little high for my taste, but being downward firing, unlikely to be an issue here. Impedance pretty unreactive -similar to what I do with some of my over-sized MLTL alignments, but with a much lower damping density. 🙂 Pretty well controlled excursion too. For these, I assumed all faces lined to a couple of inches below the driver, then back & one sidewall to the bottom. Nice job (as always) Greg!
 

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#1,299
Scottmoose said:
Nice job (as always) Greg!
Click to expand...

Thanks!

Hmm, the vent is bigger than Small's formula based on Sd, Xmax, Fb for an inaudibly low vent mach, so curious why it would sim a bit high.

Regardless, the HR sim shows no under-damped Fb and a ~62 Hz excursion minima, so curious how it looks with modest stuffing all the down and increasing Dv to 2.54 cm or whatever is required to get the dip up to ~62 Hz.

TIA,

GM
 
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