When I did mine, I was sure to round over the corners and use closed cell foam for the gasket (the ones that come with fostex drivers are not great). They image really well and disappear. I agree with the others that they seem better on a hard surface. I place a piece of wood under them. I will send a pic soon.
I'll have a look for the F200a if I get time over the next few days. I seem to recall having done one before, so it might be buried somewhere in my archives.
As for whether AlNiCo magnets are worth the money, the F200a is a drive unit as a whole, not just an AlNiCo magnet, so you'd need to get hold of this driver with a different magnet type producing the same flux density in the VC gap for any comparison to be meaningful. Since Fostex have never produced such a unit, YMMV. Personally I have severe reservations about the assumption that using an AlNiCo magnet automatically results in superior performance. It doesn't work that way, not least because last I checked, we don't listen to magnetic fields. The magnet is just one element in the entire powertrain (VC, polepiece, front & back plates etc.) & it's almost impossible to isolate just one element, since to achieve (for example) the same flux density in the VC gap with other magnet materials, you'll almost certainly have to change other elements, thus violating the basic scientific method of only changing a single variable at at time.
With that said, AlNiCo can bring some advantages to the table in a quality unit, and the F200a is extremely good. Not cheap, but very well engineered & a solid performer for a driver of its type.
As for whether AlNiCo magnets are worth the money, the F200a is a drive unit as a whole, not just an AlNiCo magnet, so you'd need to get hold of this driver with a different magnet type producing the same flux density in the VC gap for any comparison to be meaningful. Since Fostex have never produced such a unit, YMMV. Personally I have severe reservations about the assumption that using an AlNiCo magnet automatically results in superior performance. It doesn't work that way, not least because last I checked, we don't listen to magnetic fields. The magnet is just one element in the entire powertrain (VC, polepiece, front & back plates etc.) & it's almost impossible to isolate just one element, since to achieve (for example) the same flux density in the VC gap with other magnet materials, you'll almost certainly have to change other elements, thus violating the basic scientific method of only changing a single variable at at time.
With that said, AlNiCo can bring some advantages to the table in a quality unit, and the F200a is extremely good. Not cheap, but very well engineered & a solid performer for a driver of its type.
thanks Scott - I hear what you are saying about the design of the entire unit. I guess the question came up because of the way Audio Nirvana positions there products, as costing more with various magnet configurations.
My real interest is not buying marketing hype but building a nice set of speakers with decent components, so I appreciate your comments. Maybe a better question is, is the F200 worth the extra money in the Metronome?
My real interest is not buying marketing hype but building a nice set of speakers with decent components, so I appreciate your comments. Maybe a better question is, is the F200 worth the extra money in the Metronome?
Ah, yes, AN. Possibly nice drivers for what they are (I've heard a handful), but the way they're presented... let's say I have reservations.
AlNiCo has some benefits, or I should say, it can bring them (a friend who wishes to remain nameless pointed this out in an email after reading my above post), and I'm no expert. I've probably become over-cynical due to far too many current / recent products clearly using it for marketing purposes rather than anything else. However. Re your question, whether the F200a is worth the extra over Fostex's cheaper products? IMO, if you can afford them, then emphatically 'yes.'
AlNiCo has some benefits, or I should say, it can bring them (a friend who wishes to remain nameless pointed this out in an email after reading my above post), and I'm no expert. I've probably become over-cynical due to far too many current / recent products clearly using it for marketing purposes rather than anything else. However. Re your question, whether the F200a is worth the extra over Fostex's cheaper products? IMO, if you can afford them, then emphatically 'yes.'
I am going to take a crack at designing a Metronome cabinet for the Vifa TC9FD using my Accidental MLTL technique and see how it works. http://www.diyaudio.com/forums/full-range/231951-accidental-mltl-technique.html
I am thinking that it will be close in length to the FE108Sigma version but a little fatter. Can someone tell me what the tuning freq of the Met is for the FE108Sigma? Is the fb around 60 to 65 Hz?
I am thinking that it will be close in length to the FE108Sigma version but a little fatter. Can someone tell me what the tuning freq of the Met is for the FE108Sigma? Is the fb around 60 to 65 Hz?
Just so you don't lead anyone up the garden path in attempting to do so. The connection of the Metronomes to typical BR volume alignments (or sealed box volume alignments) is roughly akin to the square root of jack. I'll also repeat my strong view: the Vifa, like all 3in drivers, is not suitable for resonant enclosures. You might be able to force it, but that doesn't make it a good idea. The 108 Metronome is not an especially good example to work from either from the POV that were I to choose a driver for such an enclosure, the 108 would not be anywhere near the head of the list. I modified Steve's original purely to kill some harmonic modes, not to provide LF output. That cabinet was always intended to be used with woofers.
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Scottmoose,
Yes, I have been warned by you on several occasions that the Vifa is not good for resonant enclosures but it seems to be good enough sounding for me and others, and given that I have a bunch of them and lots of foam core to play with, why not? Bjohannesen has simulated the TABAQ with the Vifa and it looks good. Jim Shearer has simulated a tapered tapped horn with constricted terminus with it and it looks good. These are all resonant enclosures are they not? Yes, maybe not as good as you would get with a MA Alpair or CHR or Fostex, but not ugly either. I would have to disagree with you that there is square root of jack (I like that term) in the alignment relationship. We will see once I get one built. Nice thing with the Met is that it is so slender and hardly requires any material at all, and all the cuts are straight. Should be a quick and easy build.
Yes, I have been warned by you on several occasions that the Vifa is not good for resonant enclosures but it seems to be good enough sounding for me and others, and given that I have a bunch of them and lots of foam core to play with, why not? Bjohannesen has simulated the TABAQ with the Vifa and it looks good. Jim Shearer has simulated a tapered tapped horn with constricted terminus with it and it looks good. These are all resonant enclosures are they not? Yes, maybe not as good as you would get with a MA Alpair or CHR or Fostex, but not ugly either. I would have to disagree with you that there is square root of jack (I like that term) in the alignment relationship. We will see once I get one built. Nice thing with the Met is that it is so slender and hardly requires any material at all, and all the cuts are straight. Should be a quick and easy build.
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We have a different view re the Vifa. It's a fine unit within its limits, but I couldn't give a toss what the FR looks like; the fact is, it's a 3in driver being forced to work to a low frequency, sending excursion & HD through the roof. For the same reason, irrespective of the pretty FR, I don't find the TABAQ or any similar box offers performance I regard as acceptable. The price for the LF extension isn't worth it IMO. To each their own of course.
As for the metronomes, since I designed them, I actually do know what I'm talking about. They were not designed with any direct corrolation to typical BR or sealed box Vb alignments. Sorry. You may be able to find a volume alignment that you feel gives repeatable results (indeed, you should be able to), but if you could possibly keep in mind that a/ this is just one alignment of many possible variations, and b/ the various metronomes were designed for different things and different purposes, whatever they might look like on an FR plot, I'd appreciate it. Generic alignments can often have utility, no question, but there are limits too (more's the pity
).
As for the metronomes, since I designed them, I actually do know what I'm talking about. They were not designed with any direct corrolation to typical BR or sealed box Vb alignments. Sorry. You may be able to find a volume alignment that you feel gives repeatable results (indeed, you should be able to), but if you could possibly keep in mind that a/ this is just one alignment of many possible variations, and b/ the various metronomes were designed for different things and different purposes, whatever they might look like on an FR plot, I'd appreciate it. Generic alignments can often have utility, no question, but there are limits too (more's the pity
).
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If I can't find it, I'll do an optimised one for you.
Re the brace, good question. Technically yes (and ditto for the volume taken by the driver for that matter) but in practice it's rarely an issue unless it's particularly extreme, in which case the box design can be adjusted to compensate. As a rule, I put a mild fudge-factor into most designs anyway for this & other considerations.
crap - I just double checked and realized the 200a is only 90db at 1 watt. I need at least 96 - 97 db for the SET. So that leaves me with the 206en in 8". or the 208esigma. I am sure it is in the thread but what is the need for the added resistance with the 208?
Apologies for my oversight.
Apologies for my oversight.
I think I got my question answered reading the posts. The 4 ohm resistor apparently helps with bass response by providing some additional DF for SS amps. Paul Joppa commented that since the 2a3 SET I am building has its own 3.5 ohms of output resistance, it would likely not be needed. sound right? so at this point, I am leaning towards the 208eZ, or maybe the 168eZ, mainly cabinet size trade off.
Spot on re whether any SR is required & needing to account for the output impedance / DF of the amplifier.
Glad you pointed it out while I was asleep; I was going to look into an F200a box this morning, but I'll shift it to an ESigma. FWIW, the 208 would be my pick, although it was designed to be used with a helper tweeter from ~10KHz upward. No bad thing; it does what it does well, the tweeter does what it does well, everyone happy. The 168 theoretically gets higher by itself, but the top end isn't much to write home about.
Glad you pointed it out while I was asleep; I was going to look into an F200a box this morning, but I'll shift it to an ESigma. FWIW, the 208 would be my pick, although it was designed to be used with a helper tweeter from ~10KHz upward. No bad thing; it does what it does well, the tweeter does what it does well, everyone happy.
The 168 theoretically gets higher by itself, but the top end isn't much to write home about.
everything seems to point to the 208eZ as the best choice for me, so at this point the plan is build Met with 208eZ - There are specs on the Metronome chart for it - are they accurate? or have you re-modeled it since? I assume the 0 measurement in S0 means the front and back just meet there. Could look cool if mitered well.
Thanks again for your help.
Thanks again for your help.
Assuming a high output impedance amplifier, revised Met. for the 208ESigma.
L = 68in
St = 4in x 3in
Sl = 12in x 10in
Zd = 34in
Vent = 4in diameter x 1in long.
Line top, back & one sidewall with 1in acoustic fiberglass or similar & adjust this & duct length to suit. Stock it's a flat alignment tuned to Fs as you can see. The downward firing vent will give some damping effect depending on how large you make the legs & the surface it's standing on.
L = 68in
St = 4in x 3in
Sl = 12in x 10in
Zd = 34in
Vent = 4in diameter x 1in long.
Line top, back & one sidewall with 1in acoustic fiberglass or similar & adjust this & duct length to suit. Stock it's a flat alignment tuned to Fs as you can see. The downward firing vent will give some damping effect depending on how large you make the legs & the surface it's standing on.
Attachments
Hi everyone, are there any suggestions for the dimensions of a Metronome to bipole with the ACR Swiss (Fostex) FE-103S (Sigma) driver?
I have 4 of these drivers and a Metronome bipole looks like a good project.
Driver parameters are:
Fs 79 Hz
Re 7.3 ohm
Z 8 ohm
Qms 2.8
Qes 0.29
Qts 0.26
Vas 6.2 litre
Mms 2.9 g
SPL (1W/1m) 92 dB
Sd 55 cm2
Rms 0.55 kg/s
Cms 1.43
Thanks if anyone can help or advise me.
I have 4 of these drivers and a Metronome bipole looks like a good project.
Driver parameters are:
Fs 79 Hz
Re 7.3 ohm
Z 8 ohm
Qms 2.8
Qes 0.29
Qts 0.26
Vas 6.2 litre
Mms 2.9 g
SPL (1W/1m) 92 dB
Sd 55 cm2
Rms 0.55 kg/s
Cms 1.43
Thanks if anyone can help or advise me.