All New Metronomes.

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Cressy Snr
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#1 All New Metronomes.

Post by Cressy Snr »

Over the past 9 months, I've been working on a range of three new Metronome TQWT speakers.

These don't use full-range drivers, but are conventional two-way setups that use a bass/mid unit with a high quality tweeter.
There is a 5ft, a 4ft and a 3ft 6" model, using 8", 6" and a 4" main drivers respectively. I've decided to build the middle one of the three for use in the living room.
The idea is to keep everything as simple as possible, with mechanical damping of the upper end of the bass/mid units, enabling them to be run wide-open with a natural, controlled upper end roll-off. HF will then be handled with a simple resistor/capacitor-fed tweeter to fill in the top.

Main driver is the 150W, Faital 6PR110, pro driver with cast aluminium frame and water proofed paper-pulp cone.
Tweeter is the SB Acoustics SB29RDNC-C000-4 ring driver.

As is usually the case with a pro driver of this size, the main driver Fs is 100Hz, which is a bit high, but the enclosure/port combination is configured to reinforce output below this and allow wall placement to boost the low bass. These speakers are designed for real rooms and maximum WAF. Qts is a very useful 0.5; spot-on for this type of cabinet. Driver sensitivity is 96dB/W and Vas is around 5L, again a good place to start from. FR looks nicely flat across the telephone band; just a slight rise but its even all the way.

The 6" driver Metronome is a further development of the one I designed for our Ant, that he is using in his set-up at home.

Since I'm no longer interested in going any further with valve amps, I'm going back to something I have loved and been doing since I was 14, namely speaker design and build. The Metronome is such a piece of form-follows-function design purity that it deserves to be developed to the max and I intend to do just that.

Drivers are on their way, from Blue Aran and Falcon and should be here by Friday. Just need to order the plywood for the cabs.
Wahey! here we go on the Christmas project.
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#2 Re: All New Metronomes.

Post by IslandPink »

Good luck - anyone needs luck with speaker designs !
Have you simmed that driver for a TQWT on something eg. Hornresp ? Qt of 0.5 is almost into OB territory, but maybe also on upper end of what a TQWT can handle.
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Cressy Snr
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#3 Re: All New Metronomes.

Post by Cressy Snr »

Nah!
I don't mess about with sims, never have done. I just use the maths and a pencil and paper. It has served me very well over the years and I can honestly say that I have never ended up with a bad speaker using the old fashioned methods. I have never had a truly outstanding speaker either but my speakers usually end up making a pleasing sound, which to be honest is perfectly fine by me.
Half the battle is getting a pleasing midrange sound, free of nasties, and that is my number one priority, when it comes to speakers. Speed and slam are for me very much secondary considerations until that all important midrange is sorted.

A Qts of 0.5 is actually ideal for a Metronome, which is a quadratic expanding line with the mass loading port at the wide end and the driver half way along the length. Something with a low qts such as for example a Fostex FE166 6 inch full-range driver will produce very little bass in a Metronome; too much motor control, and too early and steep rolloff, will not allow the line to work effectively. All you finish up with is a screecher.

As you raise the Qts, the line contributes more effectively and the line output is much broader and shelf-like. With the line output at the wide end, we make the line longer for the same tuning frequency than we would, if the output was at the narrow end. This can either be an advantage or disadvantage depending on what you want. A high qts driver also likes the line tuning to be 5-10% below its Fs, which in concert with the broader port output tends to sound more even in the bass when placed close to walls than does a lower qts driver, if the mass loading port is tuned nice and low. I tend to go further than this and tune the line 15- 20% lower than driver Fs if the port is at the wide end. It works for me.
Last edited by Cressy Snr on Thu Nov 24, 2016 8:28 am, edited 1 time in total.
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#4 Re: All New Metronomes.

Post by IslandPink »

Interesting.
I don't know how it works with length vs. volume in these sort of things. When I did the FE103E MLTL's, the driver was about the 1/3 the way down, but that was a constant cross-section from the closed to the open end. In a Metronome with the tapering shape, I suppose if you put the drive half way down, it'll be about 1/3 the volume to the closed end and 2/3rds to ported end.
Nice flat response on the driver.
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Cressy Snr
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#5 Re: All New Metronomes.

Post by Cressy Snr »

IslandPink wrote:Interesting.
In a Metronome with the tapering shape, I suppose if you put the drive half way down, it'll be about 1/3 the volume to the closed end and 2/3rds to ported end.
Nice flat response on the driver.
Aye, that's about the size of it.
About ten years ago now, Martin J King's software was used to sim my early Metronome against a tapered quarter wave pipe that tapered in only one direction as opposed to the two directions that the Met tapers. The results of those sims were that the Metronome works in the same way as a simple tapered pipe and the results are as near as dammit identical. What that means is that the quarter wave tube can be made into an elegant truncated pyramid form, without the maths being compromised. Having discovered this useful characteristic, it was not too big a leap for Scott with Dave Dlugos (Planet10) to work up a series of bigger Mets using a load of different full-range drivers. I've now diversified the range to include bass/mid/tweeter setups.
And yes, the half way positioning of the driver tends to result in a one third/two thirds volume ratio, the same as it does with a normal tapered pipe built into a conventional rectangular cabinet. Ed also exploited this with his Vofo speakers around 9 years ago, using the Fostex FE207E. These too were open at the wide end. Like the Metronome, the Vofo also sounded damned good near walls and were nice and even across the frequency range. The late Terry Cain's Abby TQWT was also of that ilk, but like the Met was a straight, rather than folded line. The Abby owed more to Voigt than King. There's a lot of prior art that I researched when designing the original Metronome. It's now a pretty mature concept, that has had plenty of input from guys on both sides of the pond.
Last edited by Cressy Snr on Wed Nov 23, 2016 10:45 pm, edited 1 time in total.
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#6 Re: All New Metronomes.

Post by IslandPink »

Thanks - that all make sense ! Tapered has advantages in killing typical box modes, of course.
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Cressy Snr
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#7 Re: All New Metronomes.

Post by Cressy Snr »

IslandPink wrote:Thanks - that all make sense ! Tapered has advantages in killing typical box modes, of course.
Oh yes,
There's a lot to like about the mass-loaded TQWT or QTQWT and not a great deal to dislike.
They are quick and extended in the bass but not awfully slammy at those frequencies; more jazz/blues/soul/latin/ classical than rock/dance. But as with everything to do with speakers, you have to choose the compromises that work for you.
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Cressy Snr
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#8 Re: All New Metronomes.

Post by Cressy Snr »

Bass/mid drivers have arrived from Blue Aran.
Ordered yesterday afternoon, arrived at 12:15 today; no complaints there :)

Image

I tested them out unmounted and they work fine. Performance is promising as even out of cabinets, vocals exhibit no nasality.
Next step is to test them in our Ant's cabinets, which although, in theory, are not quite right for the drivers, they should give an idea of the performance I can expect.
Last edited by Cressy Snr on Thu Nov 24, 2016 4:27 pm, edited 6 times in total.
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Cressy Snr
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#9 Re: All New Metronomes.

Post by Cressy Snr »

The bass/mid drivers are currently being tested in our Ant's Metronomes, using the crossover we developed between us, for the Faital 6FE100 to SB ring tweeter
Image

The sound is excellent; very promising indeed. Imaging is good, front to back, but overall width is constrained to the distance between the speakers, probably because the 6PR110 driver is more efficient than the 6FE100 that Ant is currently using. This means the tweeter level is slightly down in comparison to the rest of the frequency range. Bumping up the tweeter level a tad when I do the "proper" build should solve the width issue and get the image to stretch beyond the cabinet edges.

The midrange is shall we say ..er...lovely, as I predicted it would be. Through informed and careful choice of driver for cabinet type we have this vital part of the spectrum correct, so the rest of the frequency range can be tweaked up around it. This is how I tend to design speakers. YMMV but it certainly works for me.

The bottom end is clean, tight and controlled, with plenty of extension, not to the nth degree but great for a 6"driver.
Waffle is conspicuous by its absence. The line tuning is bang on the money, allowing the cabinets to be placed right next to the wall without a sign of boom. IOW the speaker works with the room and doesn't fight it. These are "plonk next to the wall, fire up and enjoy the music." This is how I believe a domestic speaker should work.

I'm now confident that the proper build is going to be good, so its now a matter of ordering the ply, veneer and crossover components. I'll detail the build once I get going on it.
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#10 Re: All New Metronomes.

Post by cressy »

I was rather surprised by the drivers, they haven't the guts of the 6fe100 in the same box with its crossover, but given they were fresh out of the box and the crossover was optimised for another driver, they are very close indeed.
With an added dash of resolution, and an added dash of air and space as the glossies say.
I reckon that with tweaked inductor values and a slight change in port volume they will make better speakers in the long run than mine.
They seem to start and stop faster than the 100s, probably due to the huge magnet assemblies that are almost twice the size of the 100s and the cast baskets that have bugger all flex in them.
Using the img power amp to give them a right kick up the arse, they were very good.
Handily, my crossover seems very close to what they are going to want, so there's a couple of weeks listening and tweaking saved there.
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#11 Re: All New Metronomes.

Post by Cressy Snr »

Tweeters arrive Monday morning, so I'll have all the drivers ready to go.
The SB Acoustics ring tweeters are one of the better sounding dome HF units, with a nice, smooth, sparkly presentation.
I've been spoiled in the HF department, by the Monacor isodynamic tweeters and these ring drivers actually come pretty close, which is a good thing as a normal bass/mid driver would struggle to get high enough to mate properly with a ribbon/isodynamic HF unit.
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#12 Re: All New Metronomes.

Post by SimonC »

I'm a fan of those SB ring tweeters. Been using some for about 6 months now and they are great to work with.
I'm running mine in a two way bookshelf design with audax carbon 4" drivers, again mechanical roll off on the audax with a cap cross over.
After reading Scott's thoughts on similar set-ups (DIY Audio threads) I'm going to try a low Q second order cross over to remove the HF from the audax and the LF from the tweeter. The thinking is that with a single cap/resistor set-up the tweeter is still dealing with a lot of LF due to the slow roll off. Removing some of that should give it an easier life and let it sparkle even more...
If you ever get round to experimenting with cross-overs I'd be interested to hear if you can hear any difference in the mets. )Part of my problem is that I've not got a stable reference system at the moment so its hard to tell where changes are coming from.)
Cheers
Simon C

PS: I love the mets, they are such an elegant looking speaker :)
Cressy Snr
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#13 Re: All New Metronomes.

Post by Cressy Snr »

Bit of a bonus, as the tweeters have arrived today.
Thanks for those thoughts on crossovers Simon.
I have a 2nd order crossover already designed and in my notes and drawings for these speakers, but was a bit loath to use it in the first instance, but I might as well build the crossover and see what happens. :)
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#14 Re: All New Metronomes.

Post by Cressy Snr »

Drawing to scale, with grille.

Image
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#15 Re: All New Metronomes.

Post by Scottmoose »

Metronome = a [single] tapped horn that may or may not be mass-loaded. Leaving mass-loading to one side, since it's a horn the basics of 1/2 wave behaviour come into play & it produces gain over a broader BW than a straight / untapered pipe with the same fundamental. Can be useful if the driver has a higher mass-corner than you can easily blend enclosure and room gain into with an untapered pipe (i.e. if you need more broadband gain than a straight pipe can provide).

Re Terry's Abbys, they were entirely cut & shut and tuned by ear factoring in room gain & the high output impedance amps Terry enjoyed most -as I recall, he had a pair of custom 2A3 monoblocks that looked like they came out of the same shop that used to do the interiors for TVR cars, and a David Berning ZH270. Some solid state gear too; he loved his First Watt F1.
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