LS3/5A - Tale of the curves

[Moz]

Here are some interesting response curves from Stereophile of different LS3/5A makes:

1977 BBC model.


BBC LS3/5a Specifications

Description: Two-way, sealed-box, stand-mounted loudspeaker. Drive-units: 0.75" (25mm) Mylar-dome tweeter, 4.5" (110mm) Bextrene-cone woofer. Crossover frequency: 3kHz. Crossover slopes: not specified. Frequency response: 80Hz-20kHz ±3dB at 1m with grilles on. Sensitivity: 82dB/W/m. Nominal impedance: 16 ohms (1977-1984); 10 ohms (1989 onward). Amplifier requirements: 50W maximum.

Dimensions: 12" H by 7.5" W by 6.25" D. Enclosure volume: 5 liters. Weight: 11.7 lbs each.



Subjective response curve



Note from Stereophile: Rogers LS3/5a, "subjective" frequency response. Stereophile's subjective frequency response curves show how the transducer under test sounded to us, rather than how it measured. The vertical scale on each curve is the same, and is scaled so that a barely perceptible audible deviation from flat frequency response is reflected in a barely perceptible visual deviation of the response curve.


Rogers LS3/5a, 1978 sample, anechoic response



Notes from Stereophile: The slight peak in the 1000-1250Hz region seems to be a consistent feature of the design, but according to Martin Colloms can vary in its height. Modern production is said to be well-behaved in this respect. The degree of upper-bass boom means that the '3/5a must not be placed near the rear wall in an attempt to add bass weight. The result will be thick and muddy.


KEF LS3/5a, 1996 sample



1993 Harbeth LS3/5a




Effect of Grille

Notes from Stereophile: Laterally, presumably because of the recessed baffle, the speaker develops a rather peaky mid-treble off-axis, which might be expected to make the room sound a little bright. Vertically, the outputs of the two drivers remain integrated as long as the listener is between the woofer axis and the top of the cabinet. Above and below that range a crossover suckout develops, but the severity of the suckout above the speaker implies that tall stands are best. It can be seen that using the speaker with the grille on, as recommended, gives the flattest overall response. The Harbeth pair had a little more brightness-region energy.


Stirling Broadcast LS3/5a V2



Response showing the Stirling V2 (Red) vs 1996 Kef (Blue) and 1978 Rogers (Green) samples.

Notes from Stereophile: How close does the Stirling V2's measured response get to that of true LS3/5as? The red trace is the Stirling's response. The slightly shelved-up treble can again be seen, as can the notch between 3.9kHz and 4.9kHz. The blue trace is the response of the 1996 KEF LS3/5a sample, again averaged across a 30° horizontal window on the tweeter axis. It is broadly similar in shape, but its T27 tweeter is a couple of dB less sensitive than that used by the Stirling, and the B110 woofer is flatter at the top of its passband. The green trace is the averaged tweeter-axis response of one of my 1978 Rogers LS3/5as. Its treble is flatter than that of both the KEF and Stirling speakers, but its LF is less extended, and the discontinuity between 1kHz and 2kHz gives rise to an audible nasal coloration compared with the other two.

[splendor]

Interesting. Where is the spendor graph? Based on the response curves and JO KI's observations on all three models that I heard/read, it is true (based on the energy output of the different makes) that the Harbeth to him gives out more treble energy, hence his suspicion it has a higher roll off character than most.

The Roger's curve which shows less extension quite explains to me the findings of Jo that it's more midrangy with less extensions in both extremes. Hence, this explains (at least to me) why the Rogers is reportedly favored as the most "neutral" sounding "because its treble is flatter than that of both Kef and Stirling speakers."

[Moz]

Unfortunately they didn't do any response tests when they reviewed the 1984 Spendor.
This also confirms the higher stands necessary to get the best integration between woofer and tweeter.

[splendor]

Moz we knew about the higher stands way back. Call it luck. I had no other stands that I could use on the LS saved those lovan 28s and the wooden (mdf) Atom speaker stands that were available to me. I can assure you there were some sleepless nights on the stand issue for me, whether it was the wooden Paradigm stands or the metal Lovans. I settled for the wooden planks. Light with no hernia inducing effects unlike those home brew foundations that were truly as heavy as boat anchors! Took this issue with Jo on height and weight of stands, and he too discovered that it's best to go with the lighter stands at a higher plane (height) than 24" to let the woof and tweet "integrate" better. The woofer will sound "leaner" and clearer on the hump when away from the floor and get blended better with the presence region that makes the LS a live presentor of music.

[Moz]

Yup this also validates the designed use of the Tyan grilles. The first time I got my Spendors I tried 'em with the grilles off and preferred the more linear response with them on.

[splendor]

Tygan in place was integral to the design I believe. Helps in the dispersion of sound. This is why the LS sounds more like a "point source" rather than a direct sounding speaker like many. Another good reason why the LS can be listened to nearfield! Just right in a small cubicle like the studio control room. Without realizing it, many direct radiating speakers can't be listened to nearfield. Too close for comfort and a good recipe to losing perspective. Ah, whatta about those horns?

[mossback]

Hmmm... my Harbeth did not show so well.

Good idea! I'll take the grills off and give a listen

[shushu]

Hi,

OK, I was ready to post these curves, but it is well done yet, thanks.

It is the response on axis, of course.

You will note that the 11 ohms version is a bit more linear than the 15 ohms version.

Very small changes in a amplitud/frequency response may change very much the perceived balance. I personnally made experiments making adjustements of the 11 ohms crossover.

Overall, the ls3/5a is a very detailed speaker, but not a very linear speaker; nevertheless, many like their tonal balance (I personnally prefer more linear).

Of course, the tonal balance may change a lot with the size of the room, its furnitures, and the listening distance.

[splendor]

I'm one of the "many like their tonal balance." Provided they are situated from all boundaries.

My listening distance is always at nearfield. The "point source" sound it produces is like the pattern a small stone produces when you drop it in a still pond. It's alck of directivity makes it somewhat omni directional, exactly as one might hear under live conditions.

[aaa11]

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