Thank you GM for the reply.
I re-read the question about the building and dimensions, and I'm not even sure what I asked now...(wink) I'm not too concerned about that, It'll come out in the build anyway.
Your answer about the BSC filter, and output impedance lead me to Two conclusions, One, I need to do a bit more research about my Chinese amp, and Two I need to learn a bit more about output impedance, and how it will interact with the driver.
John
I re-read the question about the building and dimensions, and I'm not even sure what I asked now...(wink) I'm not too concerned about that, It'll come out in the build anyway.
Your answer about the BSC filter, and output impedance lead me to Two conclusions, One, I need to do a bit more research about my Chinese amp, and Two I need to learn a bit more about output impedance, and how it will interact with the driver.
John
You're welcome! Way back when, DIYers [at least here in the 'Deep South'] used most anything available free/cheap for cabs and since size, weight/WAF wasn't the 'big deals' they are today, both round and/or rectangular concrete, cast iron, ceramic tile or similar type pipe was fairly common, so learned about the need for various types of damping at an early age by noticing the huge difference in a speaker's 'tone' when swapped from a discarded tabletop radio, mono console or similar to rigid, massive ones.
Ditto the effects of floor coupling to suspended [floating] floors Vs concrete slab construction.
It’s really a pity many [most?] DIYers today aren’t able to enjoy the effortless, ‘open’ sound of large, heavy cabs [relative to driver specs] and tube electronics [or at least its SS current amp variants] that allows a wide BW/’FR’ driver to ‘be all it can be’ without the need for passive frequency shaping filters and complex XOs [if part of a multi-way].
GM
You're welcome! Sounds like a plan!
In the tube era it was normally part of the amp's specs, but nowadays the manufacturers apparently intentionally omit it for whatever reason, so one can ask them, though it seems that too often they don't provide it, leaving one to buy on faith and hope it plays 'nice' with one's speakers.
Missing Link in Speaker Operation
|| DHTRob - Tubefriendly loudspeakers? ||
The Importance Of Impedance
Amplifier Output Impedance
GM
Nick,
GM's explanation gets to the root of acoustic theory with respect to enclosure materials and design, not an empirical refinement of the basic model. It's probably one of the safest places to attempt to use straight up acoustic theory as it predicts behavior so easily and it's the easiest to understand, IMHO.
The acoustic models all start with the basic free body diagram of a mass suspended by a spring with a force acting on the mass. Several pages of differential equations later and you can pretty much encompass the entire set of T/S parameters and other derived models.
But for purposes of modeling the enclosure panels we only need very simple expressions. Just imagine how a very large mass on a spring responds to a very small force, and there's a small amount of dampening. Nothing happens, it's a non event and further modeling to determine exactly where the natural frequency occurs, etc. is not necessary. But, for what it's worth the configuration of the material changes amplitude not the resonant frequency, AFAIK.
To model the material's response we'd use Young's Modulus and the damping factor to predict impulse and harmonic response. What GM's trying to tell us is that even for cold rolled steel which has very little damping, the Young's Modulus is so high that you can't get the material to move with a speaker driver and resonance is just a non issue, with sufficient plate thickness, which wouldn't need to be much.
This also partly explains why birch ply is recommended by Planet10 folks instead of mdf. Birch ply has nearly 3X the rigidity of mdf using Modulus of Elasticity to model enclosure stiffness. Yes, mdf better dampen because it's not very stiff.
I'd like to think that cast iron or even cast aluminum might have some nice properties but I think even a very quick calculation by someone competent like GM would determine that welded cold rolled steel is equally good or even superior since it is about 5 to 10X more rigid.
Jamie
GM's explanation gets to the root of acoustic theory with respect to enclosure materials and design, not an empirical refinement of the basic model. It's probably one of the safest places to attempt to use straight up acoustic theory as it predicts behavior so easily and it's the easiest to understand, IMHO.
The acoustic models all start with the basic free body diagram of a mass suspended by a spring with a force acting on the mass. Several pages of differential equations later and you can pretty much encompass the entire set of T/S parameters and other derived models.
But for purposes of modeling the enclosure panels we only need very simple expressions. Just imagine how a very large mass on a spring responds to a very small force, and there's a small amount of dampening. Nothing happens, it's a non event and further modeling to determine exactly where the natural frequency occurs, etc. is not necessary. But, for what it's worth the configuration of the material changes amplitude not the resonant frequency, AFAIK.
To model the material's response we'd use Young's Modulus and the damping factor to predict impulse and harmonic response. What GM's trying to tell us is that even for cold rolled steel which has very little damping, the Young's Modulus is so high that you can't get the material to move with a speaker driver and resonance is just a non issue, with sufficient plate thickness, which wouldn't need to be much.
This also partly explains why birch ply is recommended by Planet10 folks instead of mdf. Birch ply has nearly 3X the rigidity of mdf using Modulus of Elasticity to model enclosure stiffness. Yes, mdf better dampen because it's not very stiff.
I'd like to think that cast iron or even cast aluminum might have some nice properties but I think even a very quick calculation by someone competent like GM would determine that welded cold rolled steel is equally good or even superior since it is about 5 to 10X more rigid.
Jamie
I am just wondering aloud (no offense intended) but all boxes colour the sound to some degree. (After all we can view the cone as being transparent to sound.)
Having said this then the ultimate would be to have no box whatsoever and then you'll finish up with planars, electrostatics and OB's. Unfortunately these take up more space than that we can accommodate in our home.
Which brings me back to the metronome - the FF125WK was just put together as cheap as possible to see what the fuss what it was all about. Later the FF105WK metronome was build and the outside was finished with upholstery material (imitation suede) and a grille was used to improve the HF. (Morgan's Arpeggio loudspeaker gave me the idea of putting this material on the outside. The LS3/5A showed me the importance of a grille, that had a metal one directly over the tweeter as well as a layer of felt around it). The difference is quite audible and this is not due to only the difference in height of the peak around 7/8 KHz which by the way seems to mellow over time. I did read stories from some Japanese audiophiles who measured it still lowering after 1000 hours.
The metronome is very rigid on its own, I am quite content with them the way they are. One improvement I can think of is instead of using spikes is to use a concrete slab or a heavy tile and have the four "legs" either glued, bolted or screwed against that. I do regret not getting the FX120 when I had the chance primarily for it having a better frame.
Only when the steel gets properly annealed after construction. Welding will set up a lot of stresses inside the material making it ring like a gong.
Errata: in my previous post I mentioned that "the FF105WK does not give much away to the FF125WK". What should have been clarified is that this is in the bass region (and mainly bass extension), in the mids and highs I regard the smaller metronome superior.
Having said this then the ultimate would be to have no box whatsoever and then you'll finish up with planars, electrostatics and OB's. Unfortunately these take up more space than that we can accommodate in our home.
Which brings me back to the metronome - the FF125WK was just put together as cheap as possible to see what the fuss what it was all about. Later the FF105WK metronome was build and the outside was finished with upholstery material (imitation suede) and a grille was used to improve the HF. (Morgan's Arpeggio loudspeaker gave me the idea of putting this material on the outside. The LS3/5A showed me the importance of a grille, that had a metal one directly over the tweeter as well as a layer of felt around it). The difference is quite audible and this is not due to only the difference in height of the peak around 7/8 KHz which by the way seems to mellow over time. I did read stories from some Japanese audiophiles who measured it still lowering after 1000 hours.
The metronome is very rigid on its own, I am quite content with them the way they are. One improvement I can think of is instead of using spikes is to use a concrete slab or a heavy tile and have the four "legs" either glued, bolted or screwed against that. I do regret not getting the FX120 when I had the chance primarily for it having a better frame.
Only when the steel gets properly annealed after construction. Welding will set up a lot of stresses inside the material making it ring like a gong.
Errata: in my previous post I mentioned that "the FF105WK does not give much away to the FF125WK". What should have been clarified is that this is in the bass region (and mainly bass extension), in the mids and highs I regard the smaller metronome superior.
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Material choice and weight has to be used intelligently. I am not saying this lightly, in my younger days I had telescopes and even build my own. You'll understand that when the optics vibrate then you will not see a lot sharply, this is not much different from sound, if the whole enclosure shakes then whatever you do to the enclosure is not going to be much good. Make it rigid and put a lot of weight at the right spots so the lot does not move on its own.
(apologies if I seem to be rambling, must be the meds I'm on, hopefully you'll get the gist)
Peace to all.
(apologies if I seem to be rambling, must be the meds I'm on, hopefully you'll get the gist)
Peace to all.
Amadeus,
I've been really curious to know how your builds turned out, I'm so glad to see you now on this thread talking about your results with the FF125WK and the FF105WK. I was thinking about those drivers and your feedback really helped fill that in.
The point about construction of the box is not that it would improve anything, just that given a sufficiently rigid material the resonance of the box becomes irrelevant and folks like me can make the box out of a material we fancy (like cast iron) without worry about "ringing" and that this is true for even non damped material like steel.
There's a lot of misunderstanding in forums about the fundamental relationship between rigidity and resonance where the influence of damping is exagerrated or intuitively employed. For example you said the weldment would ring. Yes it would but you're not considering the force required to put it into motion. You're thinking if you hit it with a hammer and it rings it would therefore not be suitable for an enclosure. A hammer and a paper cone driver acoustically coupled are quite different animals. We're talking butterfly wings and tsunamis here.
Jamie
I've been really curious to know how your builds turned out, I'm so glad to see you now on this thread talking about your results with the FF125WK and the FF105WK. I was thinking about those drivers and your feedback really helped fill that in.
The point about construction of the box is not that it would improve anything, just that given a sufficiently rigid material the resonance of the box becomes irrelevant and folks like me can make the box out of a material we fancy (like cast iron) without worry about "ringing" and that this is true for even non damped material like steel.
There's a lot of misunderstanding in forums about the fundamental relationship between rigidity and resonance where the influence of damping is exagerrated or intuitively employed. For example you said the weldment would ring. Yes it would but you're not considering the force required to put it into motion. You're thinking if you hit it with a hammer and it rings it would therefore not be suitable for an enclosure. A hammer and a paper cone driver acoustically coupled are quite different animals. We're talking butterfly wings and tsunamis here.
Jamie
thanks for that, at least someone profited from my rambling on a forum
Oh so true, plus over time information get regurgitated and eventually change totally. I just spent the better of four days trying to find the definitive answer if screen (g2) resistors are required with ultra linear implementation. In the end I found an article from the 1950's from Langford-Smith (of Radio Designer Handbook fame) that mentioned that they are especially required, even more so than when the screen is fed directly from B+. Additionally it is highly recommended to have a 1 - 2N capacitor between plate and screen.
The upshot of this that you'll always have to go back to the source (if you can) to verify.
http://frank.pocnet.net/other/AWV_Radiotronics/index.html
http://www.tubebooks.org/
last but not least: Sound Practices Magazine - CD bought on eBait
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Cool stuff! I'm always amazed at the technical documentation from the 50's and 60's, it's just consistently so well done. What a cool publication, Radiotronics. Makes me wish I understood circuits and had better than a "C" in diff q's. Have we really done anything new in analog circuits since that time?
Of course the new computer tools for modeling acoustics and even some new applied models like Martin King's make this a great time for taking the best of the old and the new tools. And to have the group here modeling and test building literally 100's of enclosures and validating those models is an incredible resource.
Of course the new computer tools for modeling acoustics and even some new applied models like Martin King's make this a great time for taking the best of the old and the new tools. And to have the group here modeling and test building literally 100's of enclosures and validating those models is an incredible resource.
I'm of the opinion that far more tube knowledge has been lost than that new stuff has been added (if any). However the modelling software has made making new designs a lot easier. I still have my slide ruler......
IIRC the UK is stopping teaching analog electronics this year.
That would be rather unfortunate as this was a key skills shortage identified in the Henley report
(Educating Engineers for the 21st Century:The Industry View Nigel Spinks, Nick Silburn and David Birchall, Henley Management College for The Royal Academy of Engineering 8 March 2006 )
I went to school with a calculator instead of a slide rule. I think that must be why I'm still struggling to wrap my brain around 6db being double the power or loudness. And, good grief how long did it take me to attempt to understand that gain and impedance should be considered when matching amplifier stages and how that might be more important than brand X versus brand Y.
I'm glad we have folks who learned engineering with a slide rule to help guide us back to fundamentals. Who's going to teach the next generation?
I'm glad we have folks who learned engineering with a slide rule to help guide us back to fundamentals. Who's going to teach the next generation?
The sons of those stubborn ones which think that prior to learn to use a calculator one must learn how it is done by hand.
The Metal Monster Metronome foundry pattern is in progress. I think Dave's moniker is going to be prescient as in iron they may be 100 lbs. each. Nicely svelte in Aluminum at 33 lbs., +/- some lbs.
Are the FX120 or F120A drivers available as eNable'd? Some nice hi freq ripples in those factory response graphs.
Jamie
Are the FX120 or F120A drivers available as eNable'd? Some nice hi freq ripples in those factory response graphs.
Jamie
I have done both Jamie. Contact me
Jeff can commenton his FX120 (but he is currently indisposed i understand)
dave
Here is a pic of my own FF225WK Mets.
These walnut veneered five footers, have been modified since I last talked about them three years ago.
The original Fostex FT17H horn supertweeter has been replaced to great effect by a Monacor RBT-95 planar/ribbon unit.
The treble performance is simply gorgeous.
The best mod I made however was to completely remove the stuffing from the top third.
The only damping they now have is courtesy of a layer of half inch thick wool felt from top to bottom of the inside back panel.
The improvement in overall performance gained by removal of said Dacron fibre stuffing is staggering.
Bass tone is wonderful, and even up and down the range. It is a pleasure to hear walking acoustic bass lines track up and down the fretboard, without emphasis of any particular frequency over another.
I have lived quite happily with these speakers over the three years since they were built, apart from a certain roughness at the top, which was enough to set me looking for an alternative HF unit. The Monacor ribbons fit the bill perfectly, with a sweet, clean and detailed sound that integrates far more easily with the Fostex widebander than the FT17H did.
I'm well pleased.
Amplification is provided by an EL34 balanced, push-pull amplifier built a couple of months ago. A nice push pull tube amp works great with the big Mets.
Crossover is a simple first order and uses a 1uF cap to the ribbon, relying on the efficiency of the tweeter, to compensate for the power drop off below the very high crossover point, rather than the L-Pad adjuster that could have been required If I had gone for a 12dB/octave 2nd order filter crossed lower down at 6KHz
Works beautifully, giving an even response up through the treble range, with no seams audible.
An externally hosted image should be here but it was not working when we last tested it.
These walnut veneered five footers, have been modified since I last talked about them three years ago.
The original Fostex FT17H horn supertweeter has been replaced to great effect by a Monacor RBT-95 planar/ribbon unit.
The treble performance is simply gorgeous.
The best mod I made however was to completely remove the stuffing from the top third.
The only damping they now have is courtesy of a layer of half inch thick wool felt from top to bottom of the inside back panel.
The improvement in overall performance gained by removal of said Dacron fibre stuffing is staggering.
Bass tone is wonderful, and even up and down the range. It is a pleasure to hear walking acoustic bass lines track up and down the fretboard, without emphasis of any particular frequency over another.
I have lived quite happily with these speakers over the three years since they were built, apart from a certain roughness at the top, which was enough to set me looking for an alternative HF unit. The Monacor ribbons fit the bill perfectly, with a sweet, clean and detailed sound that integrates far more easily with the Fostex widebander than the FT17H did.
I'm well pleased.
Amplification is provided by an EL34 balanced, push-pull amplifier built a couple of months ago. A nice push pull tube amp works great with the big Mets.
Crossover is a simple first order and uses a 1uF cap to the ribbon, relying on the efficiency of the tweeter, to compensate for the power drop off below the very high crossover point, rather than the L-Pad adjuster that could have been required If I had gone for a 12dB/octave 2nd order filter crossed lower down at 6KHz
Works beautifully, giving an even response up through the treble range, with no seams audible.
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Larry,
Thanks for the positive comments, I love these speakers, as you can tell from my purple prose.
They were a commission build, by a carpenter friend of mine; he did a great job.
Jim,
Yes, the FF225WK is a great driver, I think.
It does need help up top and its relationship with the FT17H blows hot and cold, at least in my experience.
It makes a far more consistent partner with a decent ribbon tweeter, I have found.
In a five foot Metronome it sings, providing it is not choked with too much damping, as it now seems it was in my cabinets.
A lovely driver for the price.
Steve.
Thanks for the positive comments, I love these speakers, as you can tell from my purple prose.
They were a commission build, by a carpenter friend of mine; he did a great job.
Jim,
Yes, the FF225WK is a great driver, I think.
It does need help up top and its relationship with the FT17H blows hot and cold, at least in my experience.
It makes a far more consistent partner with a decent ribbon tweeter, I have found.
In a five foot Metronome it sings, providing it is not choked with too much damping, as it now seems it was in my cabinets.
A lovely driver for the price.
Steve.
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