Phobic

Design the perfect WAM speaker

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20 hours ago, ESK said:

Huge Maggies but without sounding as though the drummer is floating 6 feet up and all in a domestically suitable package.

Have you heard the larger maggies? 

Your comment is true about the 1.6/7 but interestingly I noticed that my 20.1 don't do that trick. Musicians and instruments sound normal size. Odd, given the enormous size.

I can't deny however that the 20 series isn't an entirely "domestically suitable package" and certainly wouldn't want mine in my living room!

Edited by Psilonaught

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On 24/10/2020 at 08:33, Phobic said:

Just for fun.

what would your perfect speaker look like? 3 way? Electrostatic? Horn? what size drivers? How big is the speaker?

let's see if we can agree on a WAM design :fight:

could be a nice event to try to build it at the next WAM hifi show :D

My perfect speaker would be active.

4-way if box with dynamic drivers in sealed compartments, concentric mid/tweeter.

5-way (4-way horn with subs) if horn. Perhaps a corner horn?

Narrow dispersion (to as low as possible), smooth off-axis.

Time coincident.

.

The Kef Muon looks good on paper: https://us.kef.com/pub/media/pdf/KEFMuon-ProductBrochure-2008.pdf

kVXwHOq.jpg

Edited by tuga

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17 hours ago, eddie-baby said:

Keith actually building one :) or two as it goes. 

They might just turn i to the Wam mascot you know ;)

13 hours ago, eddie-baby said:

I do have to admit tho as much as I love other designs, even sealed, the transmission line designs I have listened to over the years do give astonishing bass reproduction. 

Maybe some are astonishing.. I remember attending a meet quite a few years ago and we all agreed a pair of kef loaded ipl transmission lines was adding far to much to the bassline.

As ever, its not the topology, it's the implementation that's defines the quality 

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1 hour ago, steve 57 said:

Maybe some are astonishing.. I remember attending a meet quite a few years ago and we all agreed a pair of kef loaded ipl transmission lines was adding far to much to the bassline.

As ever, its not the topology, it's the implementation that's defines the quality 

Shouldn't the best transmission line be closed or at least heavily damped to the point of absorbing all rear radiation?

For example like Vivid's Giya or B&W's Nautilus?

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Wouldn’t a closed transmission line just be an infinite baffle ....or a pointless exercise.  The theory behind a t/l is a tapering long port which can also be ‘filled’ with longhair wool which acts as a secondary hf removal filter thus extending the bass far more than a std port.

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7 minutes ago, tuga said:

Shouldn't the best transmission line be closed or at least heavily damped to the point of absorbing all rear radiation?

For example like Vivid's Giya or B&W's Nautilus?

I may be wrong, but to me the term "transmission line" refers to a tapered tube that has an open terminus. I don't see that either of your examples match that description.

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1 hour ago, MF 1000 said:

Wouldn’t a closed transmission line just be an infinite baffle ....or a pointless exercise.  The theory behind a t/l is a tapering long port which can also be ‘filled’ with longhair wool which acts as a secondary hf removal filter thus extending the bass far more than a std port.

Why would you call a closed transmission line "a pointless exercise"?

If the goal is to achieve the most accurate transduction then as long as it does its job then I'd consider it very a meaningful and desirable effort.

In my opinion and experience attempts at producing sub-bass frequencies without the use of a transducer/driver are less accurate than using a dedicated driver and perhaps best avoided unless at really low frequencies (below 30Hz).

1 hour ago, Tony_J said:

I may be wrong, but to me the term "transmission line" refers to a tapered tube that has an open terminus. I don't see that either of your examples match that description.

I don't know if a transmission line has to be ported or not, hence my "?" at the end of the sentence.

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This is taken from Hi-Fi News' review of the Vivid Giya G1 Spirit:

https://www.hifinews.com/content/vivid-audio-giya-g1-spirit-loudspeaker-sidebar-horn-absorbers

Horn Absorbers

In every monopole loudspeaker, rear radiation from the drive units is contained within a cabinet, but designers need to engineer that containment without audible reflections and resonances within the enclosed air space. In 1965, Arthur Bailey of the Bradford Institute of Technology tackled this with an acoustic variant of an electrical transmission line. In electronics, transmission lines are used to convey high frequency signals with minimal degradation due to inductance and capacitance. Bailey's acoustic transmission line differed as its purpose was to absorb rear radiation down to low frequencies, but like the electrical line it still aimed to eliminate reflection and resonance.

Bailey's transmission line was like a folded horn in reverse, with the mouth immediately behind the driver and the narrower throat some distance away – at least a quarter of the acoustic wavelength of the lowest frequency handled. Long-fibre wool within the line gradually absorbed the rear-directed sound. When Laurence Dickie refined this idea for the B&W Nautilus, using continuously tapered horn absorbers of appropriate length behind each drive unit, B&W hoped to patent the idea. But they'd been beaten to it in 1976 by two (French and American) inventors whose patent, US3997020, describes something similar, albeit not in the context of loudspeakers. KH

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Kef has just come up with something of identical purpose (backwave absorption):

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Super Wammer

An ideal transmission line enclosure would be closed at one end, and extremely long! The idea is to absorb ALL of the rear wave, in a tapered pipe down to the lowest operating frequency. So 40Hz would be around 28ft, so not really practical.

This is why you have 1/4 wave 'tuned pipe' speakers, which are usually tuned to 1/4 wavelength of the desired size, most common around the natural resonant frequency of the bass driver, so which would be around 7ft (for 40Hz) much more manageable inside a reasonable sized cabinet.

These kind of enclosures help as they damp out a lot of the high frequency rear radiation from the driver, and in smaller tuned pipes, let only the low frequency information out of the 'vent'. They also dampen the impedance peak around the resonant frequency too, as well as the internal partitions making the pipe (or labrynth as it used to be called) helping to add a lot of extra mass and bracing to the cabinet.

Thats my limited understanding anyway...

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3 hours ago, HoopsOnToast said:

An ideal transmission line enclosure would be closed at one end, and extremely long! The idea is to absorb ALL of the rear wave, in a tapered pipe down to the lowest operating frequency. So 40Hz would be around 28ft, so not really practical.

This is why you have 1/4 wave 'tuned pipe' speakers, which are usually tuned to 1/4 wavelength of the desired size, most common around the natural resonant frequency of the bass driver, so which would be around 7ft (for 40Hz) much more manageable inside a reasonable sized cabinet.

These kind of enclosures help as they damp out a lot of the high frequency rear radiation from the driver, and in smaller tuned pipes, let only the low frequency information out of the 'vent'. They also dampen the impedance peak around the resonant frequency too, as well as the internal partitions making the pipe (or labrynth as it used to be called) helping to add a lot of extra mass and bracing to the cabinet.

Thats my limited understanding anyway...

Alan Shaw of Harbeth is fairly opinionated, so bearing that in mind, and that listening should be the ultimate test....here is what he has said about TL as a design:

"You have to ask yourself why, of all the design choices and the hundreds or even thousands of brands competing in an overcrowded market place all desperate for some Unique Selling Points, something to excite the reviewers, dealers and public why there are not even a handful (to my knowledge) of speakers/brands promoting 'transmission line' technology. The bold fact is, and this is the sad, depressing objective truth, that it is fundamentally wrong from an engineering and acoustic perspective to mount a bass/midrange loudspeaker drive unit on the end of a pipe, tube or tunnel. It could even be the world's finest drive unit, the result would be the same.

The issue is not (necessarily) the performance of the drive unit, the problem is the pipe, tube or tunnel itself. And since this woofer-on-a-pipe is the core element in the 'TL' speaker, the core is rotten and no amount of wishful thinking or brilliant marketing can airbrush out the truth. Pipes behave acoustically like pipes, whether they are made of metal, wood or plastic or concrete. Whether they are circular, oval, square, triangular or rectangular in cross section. Whether they are long and straight, or convoluted, bent or folded. None of that fools the sound wave in the pipe, and when the wavelength of the sound being reproduced by the woofer mounted on the pipe has a mathematical relationship with the length of the pipe, strange pressure aberrations occur in the pipe and at the two ends of the pipe.

That's really bad news, because what we call sound is nothing more than a pressure change, and anything that disturbs that pressure at our ears, as a sound generated at the end of a pipe will, will muck-up the pressure in the room. Very bad news indeed if high fidelity is the goal.

Whether or not the effect, in your real world living room is audible or not is not worth debating, since we know that domestic rooms screw up the response of the finest, flattest speaker. The issue is that using crude measuring equipment the grizzly reality of the 'TL' concept is laid bare, and that really is as far as we need to explore the concept after cross-referencing to 100+ years of understanding of the physical nature of pipes. The wheel has not and cannot be reinvented: a pipe is a pipe!

A 'TL' system has a realistic chance of working tolerably well if and only if no frequencies above about 100Hz (if the TL is a big box) are allowed to reach the woofer which is driving the pipe. This is an absolutely crucial point. All the serious issues with the TL are because upper bass/midrange frequencies should not - actually must not - be allowed through to the woofer that is driving the pipe. There must be a sharp electrical cut-off in the signal that reached the woofer (and is coupled to the pipe) to positively inhibit frequencies getting to that woofer which would stimulate nodes/anti-nodes along the pipe, which is most definitely not the case when a bass/midrange driver is coupled to a so-called TL pipe.

So there you have the beginning and end of the problem. In the deep bass, the TL is an expensive way of achieving the same result as a well executed sealed or vented box. In frequencies above deep bass, the pipe is a disastrously wrong approach, wrong in every conceivable way. But what do we see of commercial 'TL' systems in production now? Precisely the wrong approach; the single bass/midrange driver is working the pipe in frequencies far beyond the bass, and the result is, of course, a series of peaks and troughs. That's physics, nothing to do with drive units or marketing and sadly, there is no workaround.

The reason those pipe-speakers have not been taken up by industry is because industry, unlike the DIYer, has test and measurement equipment and all professional speaker designers know only too well what the issues are with mounting a drive unit on the end of a tube will be. After all, anyone who is familiar with church organs or wind or brass instruments, even as a listener if not a player, will be very familiar with the relationship between pushing air into the top of a tube and the sound that comes out.

Another issue is what I see as misuse of the term "transmission line". A transmission line is an electrical term which has been inappropriately hijacked. Electrically, a transmission line is a electrical circuit which performs very specific actions in conveying a signal from one end of he circuit to the other, and the only commonality with the loudspeaker so-called TL is that there are two ends to the pipe as there is an input and output end to the circuit. As I see it, the so-called 'TL' speaker is in actuality an acoustic labyrinth. It's not called an acoustic labyrinth presumably because transmission line sound so much more sexy and high tech, but what you can buy is really an AL.

What defines an acoustic labyrinth? Two things ...

1) The drive unit is mounted at the far end of a tunnel of near or actually constant cross sectional area and
2) the mouth of the tunnel at the other end of the pipe is permanently open and of similar or actual cross sectional area as the drive unit end of the tunnel or pipe

Here from The ABC of HiFi by John Earl (1975, definitely worth having) is a drawing of the acoustic labyrinth, the very same technology that is wrongly marketed as a 'transmission line'.

Sound waves cannot be fooled into behaving in a special way just because a speaker designer implores them to, so it matters not whether the tunnel runs up and down inside the cabinet, or front to back, or side to side or side to side and up and down and also top to bottom. A tunnel is a tunnel, and what primarily matters to its acoustic performance is its length and to a lesser extent, its cross sectional area.

So, we've seen what an acoustic labyrinth looks like. It's a tunnel or pipe or tube driven at one end (by the source, the bass unit) and is fully open at the other end. That's an absolutely critical point. The far end away from the source (the woofer) is called the mouth or as noted above, the exhaust, and like all motor exhaust systems must be open to the air or the engine will be strangled and cease normal operation.

What then is a transmission line? The fundamental character of the electrical transmission line is that the end opposite the source is completely sealed-off, an electrical dead end. Not a little bit sealed: completely sealed, air-tight as it were. We can see than that the product claims about the so-called 'transmission line' speaker are technically wrong from first principles: the 'TL' cabinet self-evidently features a gaping-open mouth at the far end of the tunnel, which means that by definition, it is not at all a 'transmission line' because if it was, the end of the line would be sealed.

If we look at the electrical world from which the term transmission line was lifted, we see that a properly designed electrical TL behaves like this here, animation where the input signal to the TL is on the left and the end of the TL and the load at the far end of the pipe is the rectangular vertical box (which symbolically is a resistor) on the right. The essence of the true TL concept is that it is a closed-system; all the power input to the line is fully absorbed in the line and load. The essence of the acoustic labyrinth is the opposite: it is self evidently and open-system, with energy flowing out of the mouth at the far end of the line and into the room or the room into the pipe.

And there we have the problem. If the so-called 'TL' speaker was really a transmission line system there would be no open mouth at the far end of the tunnel. Actually, if the pipe was truly a transmission line it wouldn't matter a jot if there was an open mouth or a completely sealed mouth because if there was perfect and progressive absorption of sound energy (not possible with existing materials or techniques) along the pipe there would be no energy left in the sound wave by the time it reached the far end. So open or not, no energy would flow into/out of the pipe.

But what we really have with so-called 'TL' speakers is a gaping hole at the end of a very short and poorly damped pipe (not that the damping can be much improved) and it's that open mouth combined with the nature of air column resonances in pipes - any pipes - that is the beginning and end of the insurmountable problems.

So you may well ask yourself, why not blank-off the open mouth and convert what is evidently an acoustic labyrinth into a true transmission line, assuming that is achievable to some degree or other? Or, sparing no expense or inconvenience, ramming the tunnel chock full of the most sound absorptive material known to NASA."


 

Edited by CnoEvil

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On 24/10/2020 at 17:46, Jules_S said:

How about... an active design using a 15" bass driver in a transmission-line enclosure, that lovely ATC dome midrange unit and a ribbon tweeter? Massive amounts of grunty Class-D amplification onboard for the bass driver and single-ended 300B for the mid and highs.

Oh and make it look pretty too, none of those tatty homebrew cabinets, and dear god PLEASE nothing like those horrendous WAMMs! 

Simples. Over to you DIY guys....

I appreciate the OP was intending to promote some jolly chat but given the wam show and a few with an interest in DIY a shared wam DIY design might have some legs if sufficient (actively involved) people can work towards an agreed spec. Taking the above as a starting point:

Several have expressed interest in large transmission lines (of whatever form) but how many people are able to accommodate such speakers? I cannot in my current home. Probably could squeeze in a medium sized one at a pinch but have no real interest in building such a speaker. Some interest in helping with the design.

15" drivers in the main speakers is a problem in terms of size for me in the current home. 2-4 x 8" or perhaps 2 x 10" is around the limit at the moment.

My preferred low frequency loading would be cardioid or sealed with distributed subs for reasons of sound quality. Not a requirement.

The ATC soft dome is no longer available and was ridiculously expensive but otherwise OK. A small midrange driver in a waveguide could control the directivity and narrow the beamwidth if we wished to go in this direction as mentioned by someone earlier.

Ribbon tweeters would not be my choice but likely not a stopper unless excessively expensive. Excessively expensive drivers would mean I wouldn't build the speaker but I may be interested in helping with some aspects of the design if a group project formed.

I have less than zero interest in valve amplifiers but substituting a conventional amplifier module within an active design would seem a very straightforward variation to accommodate.

Active, passive or both would be a significant decision. A likely superior active crossover could be substituted for a speaker design with a passive crossover but because of the flexibility of an active crossover when designing a speaker the reverse may not be practical/viable.

My preference in looks would be conservative and not too big due to a modest sized room at the moment. So long as the shape isn't ugly DIY speakers can usually be finished to taste. Or not finished at all.

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7 minutes ago, h.g. said:

The ATC soft dome is no longer available and was ridiculously expensive but otherwise OK. A small midrange driver in a waveguide could control the directivity and narrow the beamwidth if we wished to go in this direction as mentioned by someone ......

 Volt do a version of the ATC soft dome ...but it’s around £450 a pop !  I’ve had success with a Scanspeak soft dome midrange unit in my CM 30 monitors and at £85 each makes them far more cost effective ....

https://www.falconacoustics.co.uk/scanspeak-d7608-920010-midrange-discovery-range.html

mind you the itch to try the Volts will never go away 

Edited by MF 1000

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32 minutes ago, MF 1000 said:

 Volt do a version of the ATC soft dome ...but it’s around £450 a pop !  I’ve had success with a Scanspeak soft dome midrange unit in my CM 30 monitors and at £85 each makes them far more cost effective ....

https://www.falconacoustics.co.uk/scanspeak-d7608-920010-midrange-discovery-range.html

mind you the itch to try the Volts will never go away 

I don't think that it is "a version of the ATC soft dome".

Volt actually make two dome mids and they perform better on the test bench than the ATC:

https://audioxpress.com/article/test-bench-volt-loudspeakers-vm752-3-midrange-dome-driver

https://audioxpress.com/article/test-bench-volt-loudspeakers-vm527-midrange

Edited by tuga
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