Coincident Speaker Technology Troubador loudspeaker Follow-Up Measurements

Sidebar 3: Follow-Up Measurements

Compared with the earlier sample (fig.1), the new Troubador's step response (fig.2) reveals that the tweeter and woofer are now connected with the same positive acoustic polarity. The tweeter output does lead that of the woofer by a fraction of a millisecond, however, meaning that the step response doesn't quite conform with the desired triangle shape that would indicate a true time-aligned design.

Fig.1 Coincident Troubador, WP sample, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).

Fig.2 Coincident Troubador, new sample, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).

Fig.3 shows the individual responses of the Troubador's tweeter, woofer, and port. The latter's classic bandpass output is centered on 57Hz, somewhat above the woofer's minimum-motion frequency of 50Hz. The woofer has a little bit of unevenness at the top of its passband but rolls off smoothly above 1600Hz with an approximate 18dB/octave slope. The tweeter's high-pass slope is also 18dB/octave, third-order, something that puzzled me considering the manufacturer's statement that the Troubador's crossover was first-order in nature. The tweeter's output suffers from some peaks and sharp dips throughout its passband, these due to the horn-loading offered by the woofer cone.

Fig.3 Coincident Troubador, new sample, acoustic crossover on tweeter axis at 50", corrected for microphone response, with nearfield woofer and port responses plotted below 300Hz and 600Hz, respectively.

The Troubador's response averaged across a 30° horizontal angle on the tweeter axis at a distance of 50" is shown in fig.4. On the left of this graph is the complex sum—accounting for magnitude, phase, and the physical separation—of the nearfield woofer and port responses. The measured –6dB point is 42Hz, the lowest note of the 4-string double-bass, which is lower than I expected from my auditioning. The upper bass is slightly elevated but the overall midrange is smooth.

Fig.4 Coincident Troubador, new sample, anechoic response on tweeter axis at 50", averaged across 30° horizontal window and corrected for microphone response, with complex sum of nearfield woofer and port responses plotted below 300Hz.

But look at the suckout in the low treble. The measured lack of energy in the crossover region in this graph correlates with the residual hollowness I noted in the speaker's perceived balance and the rather uninvolving nature of its sound. Because this character was similar to the original Troubador samples', I checked the second speaker. It was identical; in fact, the pair-matching of the two speakers was excellent.

The conventional wisdom regarding a symmetrical third-order crossover with in-phase drivers, which is what the Troubador appears now to have, is that the response is flat in the crossover region. However, with a conventional design in which the tweeter is mounted above the woofer, this type of crossover tilts the main response lobe up due to a 90° phase difference between the two drive-units. I suspect that in this coincident design, the 90° phase difference adds to the phase shift due to the residual time delay between the drivers to give something approaching an opposing-phase condition in a narrow band in the presence region (1–3kHz).

This lack of presence-region energy can also be seen in the spatially averaged response that I measured in my room (fig.5). The midrange is smooth, but with a slight rising trend apparent, while the mid-treble is also even. Over almost all the audioband, the Troubador's in-room response meets very close limits. However, the crossover region between the drive-units can be seen to be depressed.

Fig.5 Coincident Troubador, new sample, spatially averaged, 1/3-octave response in JA's room.

Finally, fig.6 shows the Troubador's on-axis response with the tweeter polarity inverted. Now the two drivers add in-phase through the crossover region, but the entire low- and mid-treble regions are elevated, giving rise to the hard-sounding, "megaphoney" tonal balance I noted with this condition.—John Atkinson

Fig.6 Coincident Troubador, new sample, anechoic response on tweeter axis at 50" with inverted tweeter polarity, corrected for microphone response, with complex sum of nearfield woofer and port responses plotted below 300Hz.
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COMMENTS
eugovector's picture

What's going on here?

mrplankton2u's picture

It's the token bad review that Stereophile feels it has to throw out to remind readers that on exceedingly rare occasions, it actually does take a break from the non stop advertising/promotional campaigns which help keep the lights on and pay for airfares for "journalists" to travel from show to show in which they endlessly kibitz with other "industry" figures in dining rooms and bars across the United States....lol!

[Possibly actionable defamation deleted by JA]

Now if only we could get these "journalists" to stop giving "very highly recommended" review summaries for products like a $6000 tube amp whose volume control gets too hot to touch... (eyeroll)

[More defamatory content deleted. If you continue to post defamatory and personal comments, we will have no option but to ban you from this site, mrplankton2u.-JA]

mrplankton2u's picture

I don't think you have a clue what the term "defamatory" actually means so I've cited a definition below:

 

"Defamation—also called calumnyvilificationtraducementslander (for transitory statements), and libel (for written, broadcast, or otherwise published words)—is the communication of a statement that makes a claim, expressly stated or implied to be factual, that may give an individualbusinessproductgroupgovernmentreligion, or nation a negative or inferior image. This can be also any disparaging statement made by one person about another, which is communicated or published, whether true or false, depending on legal state. In Common Law it is usually a requirement that this claim be false and that the publication is communicated to someone other than the person defamed (theclaimant).[1]"

 

Note, Mr. Atkinson, that under "common law", the requirement for defamation is that published claims are false. [Edited by John Atkinson]

GeorgeHolland's picture

It is pretty obvious that Mr Blume is clueless when it comes to speaker design. Even the "novices" on real audio forums know about the importance of acoustic phase.

junker's picture

Thanks for the honest review.

JohnnyR's picture

Well maybe more of a "Don't tell us the truth or you will be banned"attitude. When logic fails, just delete posts and call it "defaming". Lame.

tmsorosk's picture

You mean the truth as you see it JohnnyR ?

After reading many of your posts I would say there anything but true.

I'm usually agaist banning anyone, but I'll make an exception in your case. You contribute nothing to this great site and depict yourself as an unhappy and uneducated troll.   BEAT  IT.

JohnnyR's picture

......that MrPlankton2U spelled out what was going on and JA deleted it because? I'm glad you have no say so as to who should be banned. By the way it's "they're" NOT "there". Please be more civil in the future and perhaps you won't be making errors.

 Mr Blume obviously didn't bother to measure his finished speaker. I'm betting he used his "golden ears" to judge them. Ahhhhh the folly of relying upon "what he heard".

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