As the schedule didn't allow sufficient time for Martin Colloms's pair of Thrax Sirens to be shipped to me for measurements, Thrax arranged for a different loudspeaker to be sent from their factory in Bulgaria. This sample had the serial number 211123. I used DRA Labs' MLSSA system with a calibrated DPA 4006 microphone to measure the speaker's behavior in the farfield and an Earthworks QTC-40 mike for the nearfield responses.
According to the manual, the Siren "is best heard with the tweeters at, or just below, ear height." I therefore started by examining the farfield frequency response on the tweeter axis and immediately ran into a problem. This sample had a severe suckout centered on 2.7kHz in its tweeter-axis response, while MC's measurements indicated that his Sirens didn't have this suckout. The loudspeaker's step response indicated that both drive units were connected in positive acoustic polarity, so I asked Thrax designer Rumen Artarski via email what the correct polarities should be. "The bass unit is 'normal' phase, meaning the cone will move outwards with a positive voltage on the red connector. For the tweeter it is the opposite," he responded. My sample must therefore have had its tweeter miswired at the factory. I removed the Siren's rear panel and internal stuffing and rewired its tweeter in the correct inverted polarity. (Much easier to write than do.)
I looked first at the repaired speaker's sensitivity. My B-weighted estimate was a little lower than the specified 87dB/2.83V/m, at 85.6dB(B)/2.83V/m. (MC also estimated the sensitivity; his estimate was slightly higher than mine, at 86.5dB.) The speaker's impedance is specified as 4 ohms. My sample's impedance magnitude (fig.1, solid trace), examined with Dayton Audio's DATS V2 system, lay between 4 ohms and 5.4 ohms for almost the entire audioband. While the minimum value is 4 ohms at 175Hz, the electrical phase angle (fig.1, dotted trace) is high in the bass and lower midrange, which will have an effect on the equivalent peak dissipation resistance, or EPDR (footnote 1). This lies below 3 ohms from 69Hz to 215Hz, with a minimum value of 1.76 ohms at 108Hz. Recorded music can have high energy in this region, meaning that the Siren is a demanding load for the partnering amplifier.
The impedance traces are free from the discontinuities in the midrange that would imply the presence of cabinet resonances, and the enclosure's panels did seem well-damped when I rapped them with my knuckles. Using a plastic-tape accelerometer, I found a single high-Q, low-level mode at 480Hz on the top and side panels (fig.2) and an even lower-level mode at 535Hz on the aluminum rear panel. It is safe to say that these modes will have no effect on sound quality.
The saddle centered on 36Hz lying between two low-frequency peaks in the impedance magnitude trace suggests that this is the tuning frequency of the Siren's reflex port. Measured in the nearfield, the woofer's response (fig.3, blue trace) has the expected minimum-motion notch at that frequency, the point at which the back pressure from the port resonance holds the diaphragm stationary. The port's nearfield response (red trace) peaks between 25Hz and 60Hz, in textbook fashion. Its upper-frequency rolloff is clean, with some low-level peaks between 400Hz and 900Hz. The low level of these peaks and the fact that the port fires to the speaker's rear will mitigate any audible consequences.
The complex sum of the Thrax's woofer and port outputs (fig.3, black trace below 312Hz) doesn't have the usual boost in the bass due to the nearfield measurement technique, which assumes that the drive units are placed on a baffle that extends to infinity in both vertical and horizontal planes. The Siren offers excellent low-frequency extension for a relatively small speaker, with an overdamped alignment. The black trace above 312Hz in fig.3 shows the Thrax's farfield output averaged across a 30° horizontal window centered on the tweeter axis. There is a slight excess of energy in the upper midrange and a small suckout just above 1kHz, but the response is otherwise even. The speaker's output rolls off rapidly above the small peak at 19kHz.
The Siren's radiation pattern on the tweeter axis (fig.4) is well-controlled, which implies stable, well-defined stereo imaging. As usual with a horn-loaded tweeter, the top-octave output starts to roll off at angles higher than 15° to the speaker's sides. In the vertical plane (fig.5), the tweeter-axis response is maintained 5° above the tweeter axis, as suggested by Rumen Artarski. A large suckout develops at 2.7kHz more than 10° below the tweeter axis and 15° above it.
In the time domain, the corrected Siren's step response (fig.6) indicates that the woofer is connected in positive acoustic polarity; the tweeter's output is now in inverted polarity. The start of the woofer's positive-going step arrives first at the microphone, followed by the start of the tweeter's negative-going step. The positive-going overshoot of the tweeter's step has a much higher amplitude than the start of its step, which nicely overlays the woofer's step.
The Thrax's cumulative spectral-decay, or waterfall, plot (fig.7) is perhaps the cleanest in the midrange and low-mid treble I have ever found!
With its very quiet enclosure, relatively even frequency response, extended, articulate lows, well-controlled horizontal dispersion, and that extraordinarily clean waterfall plot, the Thrax Siren's measured behavior is exemplary.—John Atkinson
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COMMENTS
Why not like with wines, and as German hifi reviewers do: "this is a 97 points speaker". Then we, the readers, your target group, have useful information. And we can compare this speaker with other 97 points speakers, which may be available for 6K or perhaps for 4K even.
Stereophile obviously doesn't want to. I'm not saying I don't mind it in some of their sister pubs or other UK mags, but I think Stereophile's writers are ... better friggin' writers! What is not covered by numerical rankings is covered by their descriptive writing, their emotional response to the reproduction of music or a conclusion where they this is a class A etc. Their writers are also all different. Back in the day, what Art D liked was different than what Fremer liked, That is what they do for the recommended components rankings. it will never be qualified w a number.
It's tough to take a subjective experience and then 'pretend rank' it as though it is something that can be reduced to two digits.
There are idiosyncratic things involved, as well: the room, the entire system, etc.
I take reviews as representing one person's opinion in one space during one period of time, so it wouldn't help me to associate a set numerical number to the whole thing.
I wine, a '97' rating doesn't mean that all '97' point wines taste the same, either.
The real rating is in the prose.
Law of large numbers reflects something of objectivity.
Most buy wine based on indeed one wine rating and then say "this is a 97 point wine".
Indeed, reviewers have personal tastes and commercial interests. The more professional the less you can expect. The more objective they are, testing on objective standards. At least we, the readers, hope that is what they do, try. Same for hi-fi stereo reviewers.
I buy wines based on the average of at least 8 professional ratings and then I apply the figure skating method, I do not include the lowest and highest ratings in the calculation. Then I have a reasonable average. Then at least 6 reviewers say, the average between them I mean "this is a 97 points wine". Then you know, but what is sure in life, it is a 97 points wine. Then it is up to me to decide whether it is also my kind of wine, I mean my taste. And yes, you are right, 97 points wines taste different, but I know what my taste is and I'm looking for the cheapest 97 point wine within my taste. The best wine I like in my budget. Btw for most dinners a good selected 94 points wine is already excellent, however at special occassions I prefer a 97 points wine.
I wonder why so many other wine buyers buy much more expensive wines with a much lower rating? (yes yes we know, they buy prestige, not quality - I see the same in hi-fi stereo, or fashion or cars, actually in a lot - people buy prestige out of ignorance and insecurity).
Oh boy... Another case where the review sample has a problem! (In case you didn't read the Measurements section: the tweeter wasn't wired properly.) At $13,600, this is simply unacceptable. Based on the number of manufacturing problems that are discovered when Stereophile measures pieces of equipement, you wonder how many of us have faulty gear in our system.
And in this case, what a shame it is! These look to be amazing loudspeakers. But I would hesitate to buy a pair given that Thrax may have some quality control issues (at least that's unfortunate impression I get from this silly wiring problem).
Apparently your comment is directed to me.
I gathered the evidence using my eyes and brain. I read the following bit of text written by John Atkinson in the article:
"This sample had a severe suckout centered on 2.7kHz in its tweeter-axis response, while MC's measurements indicated that his Sirens didn't have this suckout. The loudspeaker's step response indicated that both drive units were connected in positive acoustic polarity. [...] My sample must therefore have had its tweeter miswired at the factory. I removed the Siren's rear panel and internal stuffing and rewired its tweeter in the correct inverted polarity."
Based on these statements, I arrived at the conclusion that the speaker was wired incorrectly. I hope this evidence is sufficient.
The tested sample had no assembly error. Amplitude and time responses are superb. I directed my comments to this speaker, not a prior example.
Sample sent form measurement was pulled out of the lab in a rush as the review pair got stuck in the UK. The error is evident and we don't try to hide it. It is my mistake picking the first sample I saw without clearing QC.
JA measured a different sample of the speaker, due to logistical issues. The samples reviewed in the main text by MC were wired correctly.
Oh boy... Another case where the review sample has a problem! (In case you didn't read the Measurements section: the tweeter wasn't wired properly.)
Incidents like this have happened a number of time over the years. I conjectured in an As We See It essay a long time ago that this might be because the review sample had been assembled, not by the skilled workers on the production line, but by the designer or his colleagues.
At $13,600, this is simply unacceptable. Based on the number of manufacturing problems that are discovered when Stereophile measures pieces of equipment, you wonder how many of us have faulty gear in our system.
It should be noted by Martin's samples, which may well have been from regular production, were correctly assembled. And conscientious dealers do act as a further stage of quality control.
John Atkinson
Technical Editor, Stereophile
Thank you for your detailed reply.
I understand that Martin Colloms's pair was fine. And I'm sure most products that leave the Thrax factory are fine. But that doesn't change the fact that they shipped out a pair that was incorrectly wired. And this does look like the kind of problem that should have been picked up by a minimally diligent quality assurance process.
In the past, you might occasionally have received units that weren't assembled by the usual, skilled workers. However in this case, your unit apparently shipped at a later date than the one Martin Colloms got. A unit that shipped later more likely came from the normal production line than an earlier one. In other words, if a few "prototypical" units built by the designer left the company, they would be the earliest units produced and shipped.
Plus, I just had a look at the Thrax website and I saw the Sirens were launched in 2022. I should think a standard production process was in place by the time your unit shipped.
The last two paragraphs are rife with them. I think this is a forgivable error.
It's not a design flaw nor does this oversight negates the considerable high-level R&D and high-quality, custom parts this speaker sports. Martin was very thorough in how this product stands out in this section of the market and the considerable care that went into creating it.
I think I would care more about what you (auditor) would have to say if you put forth more productive discussion in this and other posts you have made. It would appear you haven't read the review, but just ran to the measurements with an axe to grind. Your communication does not extend to anything but this error.
It think most other understand this company is run by humans, not robots. Mistakes do happen. I don't think it negatively reflects on the company, as perhaps you intend.
Perhaps you see it as one mistake and the company should declare bankruptcy?
John suggested a possible explanation for the fact that situations like this are surprisingly frequent. If you go back through a couple years of Stereophile measurement sections, you'll find quite a few cases of review samples with manufacturing problems. John's explanation probably covers a few of these instances, but I was just saying that it seemed unlikely in this case. That's all. I wasn't indulging in idle assumptions for the fun of it.
I assure you I read the entire review carefully. It actually got me really interested in these speakers. They really do seem great. And I said it in one of my previous comments.
But they do cost $13,600. Which means this is definitely a high-end product. It's not a price a object to, though.
However, I would expect a product like this to be impeccably built. Mistakes can happen; I understand that. But when you build high-end products, you are supposed to have a rigorous verification and testing process to ensure that, if a mistake does happen, you'll catch it before the product goes to the customer. A lot of hi-fi manufacturers obviously have this kind of thorough quality control.
Lastly, each comment should be judged on its own merit. Be it negative or positive. No matter who wrote it.
It seems we're not allowed to voice critical opinions, as they appear to trigger/offend sir Glotz. I think that was a fair comment re: a $14K pair of small bookshelf speakers should not have wiring or any other problems. Feel free to just ignore him - he trolls the comments section looking to criticize people for having an opinion.
This would be a great time for that.
I admit to finding it off putting. If JA1 can't get one wired right....
in the print edition of the magazine. But even though he gives evidence of having read JA’s measurements, he chooses to completely ignore the wiring mistake, instead spending his time promoting his new factory, ongoing research, etc.
There actually is a manufacturer’s comment in the print edition of the magazine. But even though he gives evidence of having read JA’s measurements, he chooses to completely ignore the wiring mistake, instead spending his time promoting his new factory, ongoing research, etc.
See this essay by Robert Deutsch from 1992: How To Write Manufacturers' Comments.
John Atkinson
Technical Editor, Stereophile
An amusing little article!
Based on Robert Deutsch's detailed typology, I would say we have here something akin to psychoanalytic denial.
It's a shame that audio entrepreneurs don't understand the big competitive advantage they can achieve in a crowded, niche marketplace if they have competent media and public relations.
Competent PR isn't only about building a bigger foot. For startups, it can literally make the difference between surviving and folding.
You'd think more audio entrepreneurs would understand, given that most have been in the business previously and know the ecosystem. I'd guess that engineering types tend to see everything thru the prism of product ("If I build it, they will come. Because I built it. Me"). I don't know enough about marketing and sales guys to know whether they get the value of PR. Of course, it can be prohibitively expensive for very small companies. Decent, dedicated PR costs at least $3k/month.
They clearly will have rigorous verification and testing as the review attests. They will still make the occasional mistake despite ensuring 99% of every possible detail. And a lot of other hi-fi manufacturers are guilty of a mistake as well.
To assume Wilson or Magico or any other manufacturer hasn't made a mistake like this, is absurd. I won't offer conjecture as to why this issue happened. And I think it's offensive when someone pulls supposed answers out of thin air regardless of what JA used as past examples.
Your last statement is a bit leading, implying I want to censor you in some way. You here, rather are emphasizing to the deep degree this one minor oversight. It would seem to hold the utmost merit to you, but in reality would be reasonably forgivable for any reasonable human to understand Thrax's issue here.
I am quite sure the dealer and the manufacturer will be make it more than right. I have seen positive outcomes in many issues I have had in the past- PS Audio, NAD.. many others have risen well past their duty to give me something for my time, to the tune of thousands of dollars in my favor as well. That can also breed loyalty for that oversight or 'exception to perfection'.
I look forward to (perhaps) hearing these myself this year at AXPONA. I am interested in hearing where they lie in relation to the Magico A1's.
Kudos to Thrax in making one sexy speaker!
What manufacturer would be so incredibly lax in their quality control that they would send out their $13,000 ( $17,000 here in Canada ) speaker for review with the tweeter wired backwards ? Then , have the reviewer dismantle the speaker and rewire tweeter correctly so he could complete his review ? Definitely not a manufacturer I would ever want to deal with . If they don’t care enough to ensure their quality control is up to the highest standards for Stereophile , I doubt they would for their paying customers . I’ll pass
It seems to me that every few issues there is a review item that malfunctions. One of my many favorites was a $39,000 CD player (no SACD's, thank you). The release lever for the AES/EBU input was missing so the unit had to be sent back with Jason's cable still attached. I am not sure how the manufacturer was able to run their QA on the unit without noticing.
Doesn't Robert Schryer live in Montreal? I was hoping he would cover the Montreal show again.
Yeah, I noticed that too. It's a shame. It's a good show and Robert always did a good job covering it.
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