All New Metronomes.

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#16 Re: All New Metronomes.

Post by Cressy Snr »

Thanks for that Scott.
I was trying to say to Mark that a Met produces a broader band port output than an untapered pipe, so they are prime candidates for designing close-to-wall placement into them. Forgot about the tapped horn aspect of their performance.
A very useful hybrid is the tapered pipe, with the wide end open. Pity Ed is not doing Vofos any more. They sound very similar to Mets, IIRC
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#17 Re: All New Metronomes.

Post by pre65 »

I had Ed's prototype pair of VoFos for quite a while and liked what they did.

I'd be interested to hear if anyone builds the largest size that Steve has designed. :)
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#18 Re: All New Metronomes.

Post by Cressy Snr »

There are plenty of the five-foot version Scott designed, in the USA.
Apart from the Scott design I have that Colin built and I modded, I don't think there are any more big ones in the UK; not yet anyway :wink:
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#19 Re: All New Metronomes.

Post by IslandPink »

I must say I'm getting a bit confused about the terminology here. A tapped horn uses both the front and the rear outputs from the driver into an expanding line. The metronome doesn't do that as far as I can see. It's not really a horn in the sense a front-loaded horn is a horn, because although it expands, it finishes with a small-area vent at the end ( in the case of the Metronome the floor and the cut-outs around the sides ). It doesn't have the efficiency of a horn ( and it's a lot smaller ! ) . It's got to be an offset-driver transmission line hasn't it ? It's more sophisticated than a bass-reflex because of the length and the expanding line before the vent. On the other hand if you put a 92dB driver on it you only get a 92dB speaker, with more bass. If you have a front-loaded horn or a tapped horn you are going to get 100+ dB from mid-90's driver efficiencies. I suppose you could look at it in another way and say the rear driver output is a 'slot-loaded front horn' ? :D I mean, it's not a long enough line (even in the case of Steve's full-sized Mets ) to be horn-loaded at all below 100Hz , so it's functioning in a different way in the bass. Although it's not the same sort of case, most Back-Loaded Horns are not horns below about 150Hz because the mouth size is too small to support horn-loading - they become transmission lines, at a lower efficiency.
Anyway...
Confused of Denbigh

ps. It would be fun to simulate the Met on Hornresp and compare against a straight vented box, some time. Compared phase and group-delay in the bass. I have the model for me FE103 MLTL's - can just edit the details.
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#20 Re: All New Metronomes.

Post by Cressy Snr »

Tapped horn or quarter wave transmission line has been an argument over this design for years. My originals were a quarter wave horn firing at the floor and produced lots of bass ripple but a great deal of potential. Scott modelled them as a mass loaded tapered TL using MJK's worksheets and boom! :D
I stay out of it and just enjoy the music the Met makes these days.
My design methods are O Level physics, because that's all I'm capable of, but it works for me, especially now I know that O level quarter-wave calculations plus 15-20% added to the answer "just works" as Steve Jobs used to say.
I hit on a cosmetic twist of a 1930s concept 10 years ago working with hand tools in the basement and guess I got lucky.

If you want the gen on the design Mark, it's all here http://www.frugal-horn.com/metronome.html
Example designs by Scott and Dave D can be found here. http://www.frugal-horn.com/metronome-table.html

As I have said, it is a pretty mature concept these days.
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#21 Re: All New Metronomes.

Post by MJK »

Island Pink,

You are not confused, you are exactly correct. Almost all "BLH's" and "Tapped Horns" discussed on the Internet are just resonant quarter wave systems (TLs) due to small undersized mouth areas. There are no half wave systems if one end is closed and the other end open. If the SPL response and impedance trace exhibit ripples it is because of standing quarter wave resonances created by reflections at the too small mouth. A horn will have increased broad band and smooth efficiency created by a mouth that is large enough to be acoustically resistive at the frequencies being covered. The Metronome is another mass loaded (due to the port) quarter wave resonant system (TL).

There are a lot of non physics based sketchy terms being thrown around on the Internet when it comes to horns, a horn is not simply just an expanding geometry. This misuse of terms is very unfortunate, misleading, and hinders the real understanding of horn physics.

IslandPink wrote:I must say I'm getting a bit confused about the terminology here. A tapped horn uses both the front and the rear outputs from the driver into an expanding line. The metronome doesn't do that as far as I can see. It's not really a horn in the sense a front-loaded horn is a horn, because although it expands, it finishes with a small-area vent at the end ( in the case of the Metronome the floor and the cut-outs around the sides ). It doesn't have the efficiency of a horn ( and it's a lot smaller ! ) . It's got to be an offset-driver transmission line hasn't it ? It's more sophisticated than a bass-reflex because of the length and the expanding line before the vent. On the other hand if you put a 92dB driver on it you only get a 92dB speaker, with more bass. If you have a front-loaded horn or a tapped horn you are going to get 100+ dB from mid-90's driver efficiencies. I suppose you could look at it in another way and say the rear driver output is a 'slot-loaded front horn' ? :D I mean, it's not a long enough line (even in the case of Steve's full-sized Mets ) to be horn-loaded at all below 100Hz , so it's functioning in a different way in the bass. Although it's not the same sort of case, most Back-Loaded Horns are not horns below about 150Hz because the mouth size is too small to support horn-loading - they become transmission lines, at a lower efficiency.
Anyway...
Confused of Denbigh

ps. It would be fun to simulate the Met on Hornresp and compare against a straight vented box, some time. Compared phase and group-delay in the bass. I have the model for me FE103 MLTL's - can just edit the details.
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#22 Re: All New Metronomes.

Post by IslandPink »

Ah, this is what I need - a speaker expert to talk to ! ( 'course Scott sometime pops in, as well ) .

Thanks for the links above, Steve. I hadn't realised there was a special page for the Mets, so I'll read that in more detail later.
For Martin's benefit, I have built examples of Horns, Tapped horns and an MLTL in the last few years :
http://www.audio-talk.co.uk/phpBB2/view ... start=1770
http://www.diyaudio.com/forums/subwoofe ... orn-4.html
http://www.audio-talk.co.uk/phpBB2/viewtopic.php?t=5806

There's one specific thing - that might be contained within all your webpages, Martin - but seems easier to ask here.
When it comes to extending the bass of a given driver, there are many ways to do it, but they are all more or less a different set of compromises in three key areas :

Bass extension ( efficiency at the low end )
Phase response ( group delay )
Cabinet size, or horn size.

So.... I've often wondered , does the MLTL or Metronome manage to achieve a slightly better set of compromises in those three area, particularly bass extension vs. phase, than a conventional transmission line ? I'm thinking of the sort of TL I built way back in 2002 from an IPL kit - a driver that is either at the big end or slightly offset, then a tapering line to about 1/3 the Sd exhausting typically at the front. It seems the two options are both aiming to achieve a broader, less intrusive low-bass loading than a ported box, albeit with a larger cabinet.
I think the MLTL gets around one of the typical problems of TL's in that the offset driver kills the bad dip that often lurks in the lower-midrange on the old-school TLs. That was my understanding when playing around with the small MLTL design on Hornresp.

ps. I do like Steve's Mets by the way. The FF225WK is a driver I have my eye on for another project, too.
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#23 Re: All New Metronomes.

Post by MJK »

IslandPink wrote:There's one specific thing - that might be contained within all your webpages, Martin - but seems easier to ask here.
When it comes to extending the bass of a given driver, there are many ways to do it, but they are all more or less a different set of compromises in three key areas :

Bass extension ( efficiency at the low end )
Phase response ( group delay )
Cabinet size, or horn size.
Yes it is all about trade-offs and compromises. I do not believe there is an absolute best trade-off and there is always a counter proposal for any speaker design that can be perceived as better if looked at with a different end goal.
IslandPink wrote:So.... I've often wondered , does the MLTL or Metronome manage to achieve a slightly better set of compromises in those three area, particularly bass extension vs. phase, than a conventional transmission line ? I'm thinking of the sort of TL I built way back in 2002 from an IPL kit - a driver that is either at the big end or slightly offset, then a tapering line to about 1/3 the Sd exhausting typically at the front. It seems the two options are both aiming to achieve a broader, less intrusive low-bass loading than a ported box, albeit with a larger cabinet.
I think the MLTL gets around one of the typical problems of TL's in that the offset driver kills the bad dip that often lurks in the lower-midrange on the old-school TLs. That was my understanding when playing around with the small MLTL design on Hornresp.
Bass reflex, ML TL, or Metronome enclosures should all be capable of producing almost the same SPL response curve, the phase shifts should be similar since the bass is produced by two resonances (double humped electrical impedance curves) resulting in a pair of phase swings. Looking at the electrical impedance and SPL response for one of these speakers it is not obvious/clear which type of cabinet was used for the design. The addition of the port to the enclosure is what determines bass depth, shape of the knee at roll-off, and controls the higher harmonics more so than any stuffing. They all roll-off at 24 dB/octave. The differences between the calculated bass responses are small and none of them inherently produce significantly more bass output. The differences in performance are subtle.

A straight or tapered TL (closed end equal to or bigger than open end) will not produce any more bass gain but the knee is more rounded off and the transition to 24 dB/octave roll-off is more gradual, the same two phase shift will occur but due to stuffing will probably be less dramatic (not large swings) and more gradual. This is the big difference in the sound of a TL and if stuffed correctly the bass seems to be dryer or less resonant compared to one of the ported cabinets. The down side of a classic TL is size and the need to do something to mitigate the higher harmonics (3/4, 5/4, 7/4 ... standing waves) or learn to live with a lumpy SPL response.

In summary, the bass capability of a BR, ML TL, Metronome, or TL is about the same with subtle differences determined by trade-offs in the design. There is no magic solution and each represents a slightly different set of trade-offs. A bigger impact on the low frequency SPL response will be created by the layout of the driver and open end on the baffle, the baffle step, and the proximity of room boundaries. Most programs used by DIYers (including HornResp and Leonard Audio's TL) do not address any of these issues instead treating the driver and open end or port as coincidentally located on an infinite baffle.

For a summary of my thinking on TL's and BLH's take a look at the following link.

http://www.quarter-wave.com/Horns/TL_an ... hysics.pdf
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#24 Re: All New Metronomes.

Post by Scottmoose »

Oh aye, here we go again. ;) Martin and I have a periodic good natured ding-dong on this. At least, it's good natured at this end and I assume it is at the other. So, once more unto the breach and all that...
I must say I'm getting a bit confused about the terminology here. A tapped horn uses both the front and the rear outputs from the driver into an expanding line.
Ah, classic example of the dangers of abbreviation. You will note I placed the word 'single' in brackets. The term 'tapped horn' is generally used to refer to the type popularised by Tom Danley. But strictly speaking, TD's are double-tapped, i.e. the driver is mounted internally & excites the line at two physically different locations. The metronome, Voigt style horns / pipes etc. can be described as single-tapped horns, since the driver is tapped into the expansion at x distance from the throat (sealed small end), but excites it at that single location only.
It's not really a horn in the sense a front-loaded horn is a horn, because although it expands, it finishes with a small-area vent at the end ( in the case of the Metronome the floor and the cut-outs around the sides ). It doesn't have the efficiency of a horn ( and it's a lot smaller ! ) . It's got to be an offset-driver transmission line hasn't it ?
That rather depends on how you use the terminology, which is where things can get confused. People like TD, GM and mugs like me tend to use the word 'horn' as a shorthand catch-all for any pipe that expands toward the terminus, since at a very basic level they all share certain core features. Martin, as you can see, does not approve of this: as he says, he feels such abbreviations 'are very unfortunate, misleading, and hinders the real understanding of horn physics'. Unless I am reading Martin incorrectly, the word 'horn' in his view should only ever be used to describe full sized, 'optimal' horns that are impedance matched down to their QW cut-off frequency. Fair enough. I don't automatically subscribe to it though, since us heretics take the view that if our friends feel they are entitled to use the term 'transmission line' to describe resonant pipes that are functionally almost the opposite of a TL if that blighted phrase is to be strictly employed, then the rest of us are equally entitled to use the term 'horn' with similar flexibility. In truth, both terms are often used loosely, and for good or ill we're stuck with them. The issue is essentially one of clarity, which is not always easy on forums where time is limited. I'm typing this sentence at 0204 hours for e.g. and I quite fancy getting my head down. Be that as it may, a degree of care is necessary by everyone. However, it is only justice to ourselves to point out that those of us who use the term 'horn' to describe all pipes that expand toward the terminus are perfectly well aware that a proportion or even all the useful BW is produced (and ripples caused by the impedance mismatch at the terminus) via resonant action. We simply take it as a given for the sake of brevity and get on with it, although that can cause problems for people reading who either aren't familiar with horn design, or aware of the underlying assumptions / subtexts behind many of the posts. I'm rotten for riddling posts with acronyms for e.g., which can leave some wondering what I'm barking on about. But if I didn't use them as much as I did, I wouldn't have time to post much at all. Whether that would be a good or bad thing is open to question. ;)

Back OT, you can have a mass loaded horn (using the term in 'my' cavalier way) in exactly the same way as you can have a mass loaded straight pipe. Ultimately, you're working with enclosure gain to blend in with both room and driver responses. Expanding pipes typically provide gain over a slightly broader BW than a straight pipe of the same fundamental tuning frequency, which can be useful if the mass corner is too high for the output of a straight pipe to reach. GD, impedance, phase & FR tend to be implementation specific. As Martin notes, don't generally see large variations unless you start to move toward extremes; in most cases that isn't really necessary. Which is all a very lengthy way of saying the Metronomes and similar boxes are for practical purposes standing wave generators as Martin says (albeit operating over a somewhat wider BW than a straight pipe) and this applies to all similar types -Voigt pipes, Vofo, what you will. Detail differences due to the slightly different expansion profiles, but roughly akin.

Re driver surface area, it has almost no direct connection to any form of QW design. Multiples of Sd are sometimes used as a convenient way of expressing areas, which has had the unfortunate effect of prolonging the myth that they are connected. Worse fates could befall the nation, and this is starting to die out. End loading a pipe (driver at one end, terminus at the other) will provide maximum excitation of the fundamental and all relevant harmonic modes, so as a rule is best avoided, although with suitable drivers and dimensions it can work well enough, as the first wave of TLs from the 1960s & early 1970s proved. Not an approach I'd take given the option, but never rule anything out.
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#25 Re: All New Metronomes.

Post by MJK »

In most of the acoustics textbooks on my shelf, if you look at the derivation of the physics of horns one of the first cases solved is when the horn is infinitely long. For this case sound waves only travel away from the transducer and standing waves are not possible.

The next step is to assume a finite length horn where the mouth is large enough to not reflect a significant amount of the sound waves back into the horn avoiding generating standing waves and SPL ripples. So the finite horn behaves similar to an infinite horn.

For both of these horns, infinite and finite, the sound from the transducer is efficiently transferred into the listening room smoothly over a broad range of frequencies without reflections. That to me is a horn, it is easily defined by its function and acoustic performance.

An expanding geometry with a mouth that reflects a significant amount of the sound waves back into the enclosure, producing standing waves that are easily seen as large peaks and ripples in the SPL response and electrical impedance curve, is not consistent with the derivation and solution of the horn equations shown in classic acoustics textbooks. These are transmission lines or quarter wavelength lines, take you pick of terminology. Using relationships/equations derived in textbooks or technical papers for horns (which are based on the infinite horn solution or the finite length horn solution) is just a misuse of the math and physics. It implies physics conditions that do not exist for an expanding geometry and a small mouth. Using equations or sizing relationships derived from infinite or finite horns, as defined above, on any old expanding geometry is meaningless and misleading. The results will not be as implied or expected.

The phrase mass loaded horn makes absolutely no sense to me.
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#26 Re: All New Metronomes.

Post by Scottmoose »

Then we agree to disagree Martin, since it is purely a question of preferred use of terminology and how broadly or narrowly one wishes to apply it. You wish to apply it extremely narrowly for designs fully impedance matched down to the QW cut-off -fair enough. I, and many others prefer to use it more broadly as a convenient catch-all term for expanding pipes in general. Which as far as we are concerned is also fair enough, since it does not automatically imply ignorance of the resonant behaviour of expanding pipes that have their expansion compromised relative to the optimal. As noted, and (I stress -you may recall that I regard you as a friend, value that, and often go out of my way to support / defend your work) speaking with good-natured tongue partly in cheek, since the term 'transmission line' is freely bandied about as a similar convenient catch-all with little objection from yourself even when it is applied to relatively resonant enclosures (not exactly tightly aligned to the electrical TL definition from whence the term came, or its acoustic equivalent) I do not feel you are especially well placed to demand rigid adherence to highly specific definitions. We know what you mean, you self-evidently know what we mean -that really is 'it'. You're happy, we're happy, and we respectfully agree to differ over the boundaries of how a word or term is employed. I'm off to walk the greyhound, which also makes me happy. Have a good one.

Cheers
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#27 Re: All New Metronomes.

Post by Cressy Snr »

I'm the Mayor of Simpleton alongside all this.
BUT for my Engineering Science A level in 1976, I designed and built a pair of "acoustic labyrinth" speakers. They went a long way to getting me a B grade. The speakers themselves ended up in the sixth-form common room system and stayed there for years after I'd left. They looked fine with dark blue rexine covered cabinets and Vox diamond black and gold grilles.
That's where I got into quarter wave speakers in the first place, only reviving it thirty years later.
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#28 Re: All New Metronomes.

Post by IslandPink »

Looks like you were in this game long before me ! ( although my dad and I built a pair of Heathkit speakers in 1978 ) . Have you got a link to what an acoustic labrynth design looks like then ? - is it a way of making a resistive port ?
MJK wrote: The phrase mass loaded horn makes absolutely no sense to me.
:D my fingers were poised above the keyboard, but you got there before me !
I did find speakers very difficult to understand at first, perhaps this was caused by the various uses of the terminology by different 'camps' in speaker design ( bass reflex / horns/ MLTLs ). I'm going to come back on a couple of points when I've read through these posts in more detail again, there were a couple of areas where I wanted to delve a bit more into the comments.

Looks like we've really taken your thread off on a tangent Steve, is this OK ?
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#29 Re: All New Metronomes

Post by Cressy Snr »

No problem chaps. This is good thread drift.

Here is a pdf on Acoustic Labyrinth operation from 1937, courtesy of our friend Dave D on Planet10.

http://www.p10hifi.net/planet10/TLS/dow ... -Olney.pdf

The one I built was similar, but the principles were in an old textbook from the school library. Can't remember for the life of me what the book was now though, and the explanations were nowhere near as involved.
It had to be designed around the drivers the school had, (luckily a couple of 10" high Q Celestions) without the benefit of Thiele Small, and all the calcs had to be actually done. Quite rightly, I wasn't allowed to just copy somebody elses work, and the maths was all checked by external examiners. Scared the crap out of me :lol: I just used a cap to a cone tweeter for the HF. "Logarithmic and Other Tables for Schools" (F Castle) came in handy.

Steve S probably has something on Labyrinths I'll wager :wink:
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#30 Re: All New Metronomes.

Post by Scottmoose »

Per the link to Dave's site, the acoustical labyrinth was invented by Benjamin Olney of Stromberg-Carlson, and they marketed versions for about three decades, until the mid-late 1960s. His patent is available on-line as well as the article on Dave's site linked to above. Olney, like most of the teams at W.E. / Bell Labs., RCA etc. was an exceptional contemporary engineer. Money was largely in the 'no object' catagory & they built, tested & measured just about everything they could think of (and they could think of a lot). As I recall he was an RF engineer or had come out of that, so he knew he was dealing with acoustic equivalents to electrical circuits & approached them with that in mind. I like them. Variations are still quite effective; sufficiently so that I've been designing compact ones on & off for a couple of years for small wideband drivers. http://wodendesign.com/downloads/Woden- ... 081015.pdf Bit of fun. Can you theoretically obtain a smoother response with a more advanced / refined type of QW line? Yes, of course. I don't care. That wasn't the point; they're just my little nod to Olney & his contemporaries, and I'll continue to do new ones when Dave's back on his feet (he's currently recovering from medical issues) & able to draw them up. They actually sound rather good, within the contex of what they are (little boxes with small wideband drivers). I keep meaning to pay Colin to build me a pair of the Lances for some spare FF85wks I have.
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