Stirling Broadcast BBC LS3/6 loudspeaker Measurements

Sidebar 3: Measurements

I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone to measure the Stirling Broadcast BBC LS3/6's frequency response in the farfield, and an Earthworks QTC-40 for the nearfield responses. (I measured S/N SB88019A.) The testing was primarily performed without the speaker's grille; I did repeat some of the farfield measurements with the grille in place. Stirling specifies the LS3/6's voltage sensitivity as 87dB/W/m; my estimate was significantly lower, at 84dB(B)/2.83V/m.

How the LS3/6's impedance magnitude and electrical phase angle vary with frequency is shown in fig.1. The Stirling is specified as a nominal 8 ohm design; its impedance can be seen to drop below 8 ohms only in the lower midrange, in the presence region, and above 35kHz. It is closer, therefore, to having a nominal impedance of 12 ohms, which will go some way to explaining the lower sensitivity—the speaker will be drawing less than 1W with a drive voltage of 2.83V. With a minimum value of 6.85 ohms at 3.6kHz and a phase angle that remains low except when the impedance magnitude is high, the LS3/6 will also be an easy load for the partnering amplifier.

214SLS36fig1.jpg

Fig.1 Stirling BBC LS3/6, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).

There is a discontinuity at 160Hz in the impedance traces. Investigating the vibrational behavior of the cabinet walls with a simple plastic-tape accelerometer, I did find a strong resonance at that frequency on the sidewalls (fig.2), as well as a mode at 145Hz on the rear panel. Given the large radiating areas of the affected panels, and the low frequencies and high amplitudes of these modes, I would have expected this behavior to produce some audible congestion. Art Dudley didn't remark on any such coloration, but I do wonder if his feeling that double bass lacked the "snap and temporal sharpness" he is used to hearing from his reference Altec Valencias was related to these modes.

214SLS36fig2.jpg

Fig.2 Stirling BBC LS3/6, cumulative spectral-decay plot calculated from output of accelerometer fastened to center of top panel (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).

The saddle centered on 40Hz in the impedance-magnitude trace (fig.1) suggests that the large-diameter reflex port on the front baffle is tuned to that frequency. The woofer's output, measured in the nearfield (fig.3, blue trace below 350Hz), does have the expected minimum-motion notch at 39Hz, and the port's output, again measured in the nearfield, peaks in textbook manner between 30 and 60Hz (red trace). The port also rolls off smoothly, disturbed only by a small, low-level peak in the midrange. The woofer's upper-bass response appears to be boosted in this graph. This will be due in part to the nearfield measurement technique, but it does suggest that the LS3/6 has a somewhat underdamped reflex.

Higher in frequency in fig.3, the woofer crosses over to the tweeters (green trace) at about 3.3kHz—slightly higher than the specified 3kHz—with high-order filter slopes. There is a very narrow and likely inaudible peak in the tweeters' output around 22kHz, which can also be seen in the Stirling's farfield response, averaged across a 30° horizontal window on the main tweeter axis (fig.4). (I chose this axis for measurement because that is the axis that is the standard 36" from the floor with the LS3/6 sitting on its 17"-high stand.) Other than the upper-bass prominence noted earlier, the LS3/6's overall response is remarkably flat and even. Repeating this measurement with the grille in place reduced the level of the mid-treble region by a couple of dB, but left untouched the levels of the top octave and low-treble regions.

214SLS36fig3.jpg

Fig.3 Stirling BBC LS3/6, acoustic crossover on lower tweeter axis at 50", corrected for microphone response, with nearfield responses of woofer (blue) and port (red), respectively plotted below 355Hz, 1kHz.

Below 300Hz, fig.4 shows the complex sum of the woofer and port outputs, weighting each in the ratio of its radiating diameter. As is usual with a reflex design, the Stirling rolls off with a steep 24dB/octave slope below the frequency of the port resonance. I suspect that this, together with the slightly higher-than-expected frequency of the port resonance for the speaker's size, correlates with AD's finding that the LS3/6's low frequencies did not sound as weighty as he would have liked.

214SLS36fig4.jpg

Fig.4 Stirling BBC LS3/6, anechoic response on lower tweeter axis at 50" without grille, averaged across 30° horizontal window and corrected for microphone response, with complex sum of nearfield responses plotted below 300Hz.

The LS3/6's horizontal dispersion, normalized to the response on the main tweeter axis, is shown in fig.5. The crossover frequency of 3.3kHz is on the high side for a woofer with a radiating diameter of 6.5", and the dispersion does indeed show a trough to the speaker's sides at the top of the woofer's passband. (This is because the woofer's size is now of the same order as the wavelengths of sound in this region.) As a result, the lower tweeter's wide dispersion at the bottom of its passband appears to produce an excess of off-axis energy in this region. All things being equal, this will render the Stirling's in-room balance somewhat bright, particularly in small, barely furnished rooms. However, things are rarely equal, and given the Stirling's flat on-axis response, this off-axis behavior may just add to the speaker's sense of articulation and detail, especially when the speaker's grille is left in place.

214SLS36fig5.jpg

Fig.5 Stirling BBC LS3/6, lateral response family at 50" without grille, normalized to response on lower tweeter axis, from back to front: differences in response 90–5° off axis, reference response, differences in response 5–90° off axis.

I was surprised to see that, with a small-diameter supertweeter taking over above 13kHz, the LS3/6's top-octave dispersion was not wider than it appears in fig.5. I suspect, however, that the dispersion is being affected by the wide baffle. In the vertical plane (fig.6), a suckout in the crossover region between the woofer and tweeters occurs more than 10° above or below the lower tweeter axis. In addition, a large suckout occurs in the crossover region between the two tweeters 5° above or below the reference axis. This behavior suggests that, to hear the flattest balance, the listener's ears should be level with the Stirling's lower, primary tweeter.

214SLS36fig6.jpg

Fig.6 Stirling BBC LS3/6, vertical response family at 50" without grille, normalized to response on lower tweeter axis, from back to front: differences in response 15–5° above axis, reference response, differences in response 5–15° below axis.

In the time domain, the LS3/6's step response on the lower tweeter axis (fig.7) suggests that the supertweeter is connected in inverted acoustic polarity, while the tweeter and woofer are connected in positive polarity. However, the decay of each drive-unit's step smoothly blends with the start of that of the next lower in frequency, which correlates with the excellent frequency-domain integration of their outputs seen in fig.4. There is a slight ripple in the decay of the woofer's step with a period of 1ms. However, there appears to be no significant delayed energy at 1kHz in the Stirling's cumulative spectral-decay plot (fig.8). Other than a small mode at 4.1kHz, and others just below and above 20kHz, the initial decay in this graph is commendably clean.

214SLS36fig7.jpg

Fig.7 Stirling BBC LS3/6, step response on lower tweeter axis at 50" (5ms time window, 30kHz bandwidth).

214SLS36fig8.jpg

Fig.8 Stirling BBC LS3/6, cumulative spectral-decay plot on lower tweeter axis at 50" (0.15ms risetime).

The Stirling Broadcast LS3/6's measured performance is what I would have expected from a classic BBC-inspired design updated for the 21st century.—John Atkinson

COMPANY INFO
Stirling Broadcast
US distributor: Fidelis Home Audio
460 Amherst Street (Route 101A)
Nashua, NH 03063
(603) 880-4434
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COMMENTS
Bill B's picture

Maybe it's just me, but Art over-uses italics in his reviews.  I don't care for the extra elbow in ribs tone.

Regadude's picture

Complain much? Geez, too much italics. Call the cops dude! no

tmsorosk's picture

I didn't see a problem either .

commsysman's picture

Is there anyone who actually thinks this ugly poorly-made speaker system is competetive with the excellent speakers you can buy now for $4500?

Why does the Stereophile staff keep trying to drag these old British monitors out of the grave, where they should remain buried?

While they may have been good in their day, we don't need a history lesson on them every few months. The reviews of various rebirths and iterations of the LS 3/6, SP 3/X,etc. etc, ad nausem seem to never end!

The description of how well the packing boxes are made is interesting; it sounds as if the packing boxes are made better than the speaker enclosures themselves. That is a new manufacturing strategy. Maybe they are designed to sound better if they are never unpacked.

Let's focus review articles on what is the best for the money in a given price range; that certainly does not apply here. This might be a mildly interesting speaker if it cost around $1500 or so, but the price is outlandish for what you get.

I would be interested in a comparison between these and a pair of Vandersteen 2C speakers, which cost half as much and almost certainly sound better, or one of the PSB or other popular modern speakers such as the Synchrony One.

It annoys the hell out of me when the only speakers the reviewer compares to the reviewed speaker are obscure rare models that less than 1% of the readers will ever have heard. How are such comparisons useful to the reader? It's like doing the review in French because that is the reviewer's favorite language.

It would be very helpful if Stereophile had a rule that revewers MUST compare a speaker to some recently reviewed or very well-known speakers so that the reader has some chance of interpreting the comparisons in a useful context.

Regadude's picture

D'accord, vous n'aimez pas ces hauts-parleurs. C'est votre opinion, et je la respecte. Mais, pourquoi ce cher Art ne pourra pas faire quelques test d'équipements en français? Son sens de la répartie se transmettrai très bien dans la langue de molière.  wink

John Atkinson's picture

commsysman wrote:
this ugly poorly-made speaker

Beauty is in the eye of the beholder, of course, but poorly made? I don't think so. Or, as Art would say, I don't think so, :-)

John Atkinson

Editor, Stereophile

RyanJL's picture

These speakers are beautiful.

Not everyone wants the now-ubiquitous 8" wide, 42" tall floorstander these would compete against. They certainly look better than some of the plasticy ones you mention.

Bill B's picture

Yes indeed, my comment about italics is kinda petty, but it's in the context of direct comments on his article, so it's in the right place at least. It goes to Art's tone in his columns, which is sometimes a bit condescending toward those who don't share his vintage preferences. But whatever. I essentially agree w commsysman above about art's tendency to just review and compare ultra-niche items to other ultra-niche items. 

corrective_unconscious's picture

I agree these sorts of speakers seem expensive for what you apparently get. I guess Spendor and Sterling and Harbeth really have some magic going on in their driver and diaphragm construction.

What is objectively more weird is going from about an 8" woofer to a 1" tweeter when there is a .75" tweeter present. Those three driver choices leaves a large dispersion discontinuity at the first crossover from the relatively big woofer to the first tweeter, when it could have been avoided.

Could have been avoided even if the design objective of these boxes is to get that first crossover happening above sensitive 3k or so. Does it really have to be above 5k or wherever?

tmsorosk's picture

I have to agree with commsysman for the most part . Because I'm a member of an audio club i get to hear many speaker incuding the above , and although there not my cup of tea there is something to be said for these units when listening to single instuments or small intimate ensembles . The midrange has an uncongested purity that many costlier speakers can't match . They may not do well in all sonic perimeters but for those that have specific music listening tastes they can be quite enjoyable . 

xyzip's picture

Wow, there is a reason that nobody reads these comment sections.

Doesn't seem too much a stretch to say that some of the comments here seem a little petty & trollish. 

Dudley talks about other fairly well known highend speakers, and other relatively classic speakers (something about harbeth, devore, spendor, altec, that are unheard of ? ..did he miss something you purchased lately? ).   The requests for specific comparisons ---  does anything suggest 'similar-to-vandersteen' about these? can't have been, say, the size of the baffle---  are kind of far fetched. 

The review's rundown on construction specifics may be grounds for further discussion:  does the lack of  threaded inserts indicate corner-cutting or does roughly doubling the metal content by doing so disrupt some other part of the strategy...  either way, the reviewer isn't saying these are poorly constructed.  ("Exceptionally well-crafted" doesn't seem equivocal.)  The commenters are sure they're not, though. 

Which brings up an interesting point;  the commenters seem to have pretty set objections to the methodology, as well as the actual equipment here.  For his part, Dudley says how he evaluated these speakers pretty succinctly.  The commenters aren't saying whether they have ever seen these speakers, let alone heard them or given them weeks worth of dedicated listening.  

All in all, good review, AD.  And commenters---  can't say for sure, but the general public might get the idea that audiophiles are ever-so-slightly more petulant than average people if you stick with this approach.  Italics? Writing in French? Freedom-fries, anyone? 

Let's all cringe along together:  the Audiophile Troll must be the most delicate troll on the internet.  Princesses of the practice, in fact. 

Carry on, everyone. 

 

Regadude's picture

Nobody reads the comments section. Well at the very least, there is me and you xyzip...

How is writing in french petty? It was a tongue in cheek, but sincere response to someone who was complaining. If you could actually read french, you would have realised my comment was not petty at all. 

Freedom fries? What's your point? 

"Carry on, everyone."

Carry on we shall.

SimplySpeaking's picture

The author writes "...garage with a brace of tools, including a hydraulic lift..."

A brace, in the sense I assume he somewhat intends, means two somethings. He might as well as shared the other item of garage equipment to spare us the agonizing guessing game of figuring out what additional item might make a humble garagiste envious. Perhaps an espresso machine?

..And veneer prevents warping? Seriously?

John Atkinson's picture

SimplySpeaking wrote:
veneer prevents warping? Seriously?

Yes. MDF that is veneered on only one side will warp. For long-term stability, the MDF sheet should be veneered on both sides.

John Atkinson

Editor, Stereophile

Doctor Fine's picture

In a world of over hyped super crispy annoying speakers here come the British with somewhat retro designed glorious open sounding actual classic speakers designed for the music lover.

In truth I am somewhat angry that the modern well educated over technical platoon have no offerings which do anything to move the soul the way these out of date conservative British relics seem to do.  And do consistently.

I recall John Atkinson and Art Dudley both drooling over the Harbeth mini BBC monitors which easily and eerily replicate an approach done well over a half century ago by Altec, JBL and other truth talkers..  Except the Harbeths were in miniature.

So here's the deal you modern marvel guys---cough up a design--even ONE that makes the soul juices of a gumbo crayfish cajun bayou lovin music sophisiticate go mad with lust.  Where in fact is LUST nowadays? Seems to me that LUST has gone a missing along with soul and cool and a lot of other words and concepts...

I would argue much has been  lost in time except for  these timeless "correct" speakers of great pedigree.  Pedigree is a word lost in a world that worships dumpster diving garbage encrusted late comers that wear gold encrusted gold teeth and tatoos.

Me and my brothers and sisters that love music do not need such tacked on congestion.   We prefer the open sound of the best of the best.

Try and compete you deaf modernists---we are all waiting with baited breath...

Regadude's picture

Doctor Fine wrote:

"So here's the deal you modern marvel guys"

Who you talking about? Iron man? Hulk? I am more DC. Gimme Batman and Superman anytime! 

Doctor Fine wrote:

"Where in fact is LUST nowadays?"

Where?! If you saw me watching a Katy Perry video, you would see a ton of lust in my eyes, on my face, in my pants...

Starbucked's picture

$4590 for these boxes with specs: 45 - 17k at 87 db.

I just bought new, German made Elac BS 53.2 bookshelves with a range of 46 - 25 k at 87 db.

They are smooth, transparent and image well. Look great too.

I paid $325. Once again: 325 dollars. I've heard stirling, and yes, they sound very nice. As do my $325 Elacs. Think the $4300 difference is just absurd

corrective_unconscious's picture

Even if these British box type speakers cost a lot and are curmudgeonly in various ways, and even if the Elacs you mention are fine for you, that was a preposterous deployment of "specs" to make your claimed point. Yours is not the worthiest troll I have encountered on the internetz in the past five minutes, or ten years, I am afraid.

JBLMVBC's picture

At this $4,500 price, one can truly design and build a DIY high efficiency studio monitor with real professional drivers that would blow this new old thing away: for instance 2226 JBL pro 15" bass driver, Compression Midrange 2426+2370 and a lovely Fostex T90A super tweeter...cool

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