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Evidence-based Speaker Designs

hollis

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"Most acoustically advanced audiophile loudspeaker available on earth today"

https://www.tektondesign.com/ulfberht-pmd-monitor.html

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a quite long article that ends up with a mini-review of these the PMD

https://audiophilestyle.com/ca/bits-and-bytes/what-is-accurate-sound-r923/
 

Rizzle

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MeroVinger released the Haberdasher Mk. II, I don't know how to read directivity graphs, but the frequency response seems nice to me. If anyone could interpret the results I'd be very interested. Got to say, I absolutely love the transparancy. Very few manufacturers that disclose the amplifiers & exact drivers. They're around € 5000.- per pair for if anyone is wondering. Scan-Speak Revelator mids & woofer, Wavecor tweeter, Pascal amplifiers & DSP (more on the amp plate) sounds like a great mix.

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Newman

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What evidence does Gradient provide that their designs are evidence-based?

Also, amir's review of the Kali IN-8 doesn't look like an evidence-based design to me... unless they attempted to be evidence-based, but failed.
 

Purité Audio

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They enjoy sewing and the ‘Matrix’.
Keith
 

Rollomoto

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MeroVinger released the Haberdasher Mk. II, I don't know how to read directivity graphs, but the frequency response seems nice to me. If anyone could interpret the results I'd be very interested.

It has some directivity errors in the horizontal plane (compare @+/- 60° 1.5 kHz vs. 2.5 kHz (almost 6 dB). Also they could have done better in the vertical plane since it's a 3-way design (errors in the crossing area @2,5 kHz). Overall it seems to be a fairly conventional design which has not been optimized for constant directivity. That's a pity because having 3-ways and especially a small midrange driver, that could have been easily achieved...
 

Rizzle

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It has some directivity errors in the horizontal plane (compare @+/- 60° 1.5 kHz vs. 2.5 kHz (almost 6 dB). Also they could have done better in the vertical plane since it's a 3-way design (errors in the crossing area @2,5 kHz). Overall it seems to be a fairly conventional design which has not been optimized for constant directivity. That's a pity because having 3-ways and especially a small midrange driver, that could have been easily achieved...
Thank you, now I know how to interpret the widening/narrowing @ the 2.5 kHz mark. Do you think this is very noticable, or could this still be a good loudspeaker for the money? I think I am going to try to audition these loudspeakers after I'm fully vaccinated.
 

Scgorg

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What evidence does Gradient provide that their designs are evidence-based?

Also, amir's review of the Kali IN-8 doesn't look like an evidence-based design to me... unless they attempted to be evidence-based, but failed.
While gradient doesn't show any measurements themselves, their excellence has been shown in third-party measurements. See for example stereophile's measurements of the original gradient revolution (an amazing feat of engineering more than 20 years ago).

Princeton university has also measured the gradient 1.5 helsinki, see image for horizontal directivity:
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Newman

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Yes I recall those graphs. More interested in the Five. IMO a worthy brand is consistently evidence-based.
 

witwald

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Output impedance profile (part of which can be realized with passive components after the amp, eg. series caps and coils) is a powerful additional degree of freedom available in active designs that should be exploited, alas only few manufacturers currently do this (though some don't advertise these features because the actual circuit designers implement this silenty... like I did in the ADAM F-Series).
The impedance of a passive loudspeaker can also be relatively easily equalised using passive components. The well-known Zobel network added to the tweeter serves to linearise a multi-way loudspeaker's high-frequency impedance quite well. Using a conjugate impedance network on the typical impedance hump that occurs around a crossover frequency is certainly not difficult either. Using a program like VituixCAD, one could easily come up with a suitable design, making a passive loudspeaker's impedance quite flat from 100 Hz or so upwards. This would essentially make that portion of the loudspeaker's impedance behave like a purely resistive load, albeit a lower impedance because the peaks and rising impedance responses have been equalised to now be flat.

Creating a suitable conjugate impedance network and adding it to a typical passive multi-way loudspeaker system would certainly affect the sound produced by the loudspeaker when driven by low-damping factor amplifiers, such as tube amplifiers. The improvements/changes in sound quality would be quite tangible. It's surprising that there are not kits on the market that do this already.

As for creating conjugate impedance networks for the twin low-frequency peaks of a vented system, or the single low-frequency peak of a sealed enclosure, although that's entirely possible, it might not be all that economical, owing to the large component values that would be needed. The results might also be sensitive to driver variations from one enclosure to the next.
 

Duke

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Creating a suitable conjugate impedance network and adding it to a typical passive multi-way loudspeaker system would certainly affect the sound produced by the loudspeaker when driven by low-damping factor amplifiers, such as tube amplifiers.


When impedance flattening is incorporated in a passive loudspeaker at the design stage, that speaker becomes relatively amplifier-agnostic, and can work as intended with a wide range of amplifier types. Such a speaker could be compatible with solid state amps, normal push-pull tube amps, and even specialty tube amps, such as single-ended triodes and output-transformerless tube amps.

As for creating conjugate impedance networks for the twin low-frequency peaks of a vented system, or the single low-frequency peak of a sealed enclosure, although that's entirely possible, it might not be all that economical, owing to the large component values that would be needed. The results might also be sensitive to driver variations from one enclosure to the next.


One really only need equalize the upper impedance peak of a vented system, as the lower peak will be below the system's passband. Equalizing the upper impedance peak can even be accomplished at the enclosure design stage, resulting in no need for a conjugate filter tuned to that frequency.
 
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witwald

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From https://en-de.neumann.com/product_files/1710/download:
"The 1” tweeter will become the new standard for all new monitors in the KH-series by Neumann. ... The final choice was a titanium sandwich cone. Developer Markus Wolff told us that the decision in favour of a metal cone instead of a pure fabric membrane was based on the significantly more pistonic motion of the metal cone. This usually comes with the disadvantage of a pronounced resonance, but this is above 30 kHz and in this case very well damped. Actually a resonance in this frequency range way above the audible spectrum would not be a problem anyhow. But if the resonance is started, it could lead to intermodulation distortion even within the audible frequency range, which makes suppression of the resonance worthwhile. A pure fabric tweeter cone does not have this problem, but would vibrate unevenly way below 20 kHz and therefore would lead to an uncontrollable dispersion behaviour."
This approach appears to be an excellent solution to the age-old problem of metal tweeters, which have pronounced, very high-Q resonances at higher frequencies in their passband. The use of the titanium sandwich membrane appears to be a good example of the application of constrained layer damping technology, which is discussed by Kumar and Behera (2019). An early reference to this technique was the journal paper by Kerwin (1959), Damping of Flexural Waves by a Constrained Viscoelastic Layer, so the method has been around for a long time. It would be interesting to see the raw frequency response of the tweeter used in the KH-series, so that we could better assess the efficacy of the damping system that's been added to the titanium dome.
 

witwald

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Equalizing the upper impedance peak can even be accomplished at the enclosure design stage...
How might that be done? Would it require adding considerable losses into the enclosure design?
 

witwald

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The measured vertical polar you describe above is just the result of non-concentric drivers through the crossover. The port isn't doing anything at 1–2 kHz.
One would certainly hope not! Undesirable port resonances are the bane of many a vented box loudspeaker, and any designer would try and avoid them at all costs. The ideal port simply produces a peak at its resonance, with the port's output rolling off smoothly and monotonically above and below the resonance frequency.
 

Duke

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How might that be done? Would it require adding considerable losses into the enclosure design?


The enclosure's internal shape targets the desired frequency region.
 
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bigjacko

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The enclosure's internal shape targets the desired frequency region.
Can you elaborate on that a bit more? I thought the shape of box does not change the tuning, but the volume does?
 

Duke

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Can you elaborate on that a bit more?

If I can find the technique adequately described online somewhere, then it's already in the public domain and yes I will elaborate a bit.

I'm pretty sure at least one company that I respect is using the technique and since they have never mentioned it (to the best of my knowledge), they presumably consider it to be a "trade secret". So if it's not already in the public domain, I'd rather not be the one to put it there.

(For the record, I had already developed the technique on my own and used it in a bass cab before noticing its apparent use by another manufacturer. I am not currently using it.)
 
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