Alrighty then, here's a picture of the speaker ready for testing in the basement. Notice the foam ring around the tweeter removed; I actually measured with and without the ring to see what difference it made. As usual, the speaker was powered with my Emotiva XPA-1L amplifier. The DAC used for tone-generation is the Topping D10.
|With foam ring around tweeter removed.|
As passive speakers, it's good to start with impedance and sensitivity:
Impedance looks good and goes down to 7.6Ω at the lowest level, around 250Hz. Notice the EPDR (Equivalent Peak Dissipation Resistance) will dip down to 4.5Ω which is certainly not extremely low. There are 2 resonance peaks correlating with the 2 drivers at 66Hz and 1.3kHz. I don't see any discontinuities or irregularities in the impedance and phase curves at all! This suggests a well-dampened enclosure with minimal anomalous resonances.
Sensitivity calculated by average gated amplitude between 500Hz to 7kHz with a 2.83V sine sweep tone gives me a value of 85.4dB/2.83V/m. I believe these speakers were rated at 85dB/W/m so we're certainly in the ballpark. We can see from the +/-3dB red lines on the sensitivity calculation just how flat the frequency response appears.
Here's the CTA-2034A-inspired "qSpin" result:
Both tweeter and mid/woofer are arranged in positive acoustic polarity. The step response with its slight irregularity at 250µs suggests that the acoustic "center" is just below the tweeter axis and fits with the suggestion from the polar map that it might be best to listen to these speakers sitting with ear-level between the tweeter and mid/woofer.
The cumulative spectral decay "waterfall" graph looks good as well:
Dynamics-wise, here's the multitone burst test for linearity between 70dB SPL to 100dB SPL, normalized to 0 at 85dB SPL:
A couple of final measurements. First, here's the difference between having the grille on versus taking it off:
It looks like the grille will dampen that 13.5kHz accentuation a little bit but otherwise, it functions quite transparently at least straight on tweeter axis.
And how about that add-on foam ring "tweak" stuck around the tweeter I showed above? Here's the "qSpin" graph with "tweeter ring" in place:
Compared to the "stock" SA1, notice that the foam ring introduced a suck-out into 9kHz on the order of -6dB and we also see a concomitant distortion in the Directivity Index. Here's what happened to the polar maps:
I'm impressed! I don't think there's much more to say.
Spencer Hughes obviously knew what he was doing when he designed these back in the early 1970's and went into production by the mid-'70s. Given the vintage, I think it's natural to also think about the venerable BBC LS3/5A speakers of the day and the many fans of those speakers still (great site dedicated to LS3/5A). Remember that the LS3/5A is based on a smaller 5" mid/woofer; the SA1's 6" mid/woofer would/could/should achieve better bass extension. Maybe one of these days I'll have the opportunity to have one of those here at home for a listen and compare.
An inexpensive modern design similar to the Spendor SA1 might be something like the NHT SuperOne 2.1 speaker (<US$180 each) - 2-way, closed box, similar dimensions, slightly larger 6.5" mid/woofer. I've heard good things about these, again maybe something I can check out in the future.
With the reasonable <100Hz extension that the SA1 provides, I think it would not be too hard to match these with a nice subwoofer in the living room crossed over around 80Hz and achieve some remarkable full-range playback. With a sensitivity of 85dB/W/m and good impedance profile, amplifier matching should not be difficult. If fact, it sounded great on my desktop with the SMSL SA300 Class D amp with only 30W into 8Ω although I would advocate for a good 100W amp for the living room to achieve that extra dynamic extension. If you haven't tried, it's worth estimating your amplifier power needs.
Of note, the results here look different from what was found in the Stereophile measurement of the new Spendor SA1 released in 2009. Lots of differences in terms of materials used for the drivers, enclosure design, crossover is different, and even the dimensions are different. Other than name and sealed-box design, I'm not sure what is even similar about these speakers.
Thanks again to linnrd for giving me the opportunity to listen and test these speakers!
To end, I just wanted to spend a few minutes talking about that foam "diffraction ring" around the tweeter that was added by the original owner. Remember that over the years, people have used these in speaker designs, for example, here's a discussion of the application of this kind of "tweak" to the Acarian Alón Li'l Rascal Mk II speaker (see Addendum and also the Measurement changes) back in 2003.
Obviously the foam pad applied around the Spendor's tweeter resulted in profound effects which in my opinion were clearly undesirable.
If we were to talk to the previous owner who applied the tweak, he might have told us that the foam rings made a huge beneficial difference for him. While I would not be able to refute his subjective judgement or his experiential claims, to show you in the measurements what this tweak did to the sound I hope is a much more powerful disincentive to try doing such a thing knowing the effect regardless of what any one or more person(s) might testify! Again this is the power of taking an objective mindset and to seek facts rather than be satisfied with opinions.
An argument some audiophiles suggest is to "Listen for yourself!" to whatever tweak or supposed-beneficial products come our way. I obviously would not disagree either since personal experience counts for a lot on an individual level. But in practice, we obviously can't try everything the Industry produces or claims. Even if we were to buy a $1000 cable and likely return it due to lack of value, one would still have spent money at least on shipping costs assuming there were no international taxes or restocking fees. Better that we insist that companies come up with data and demonstrate the value of their products for us as consumers to consider first before anyone puts money down. Otherwise, the default position to take is that the product (and such companies) should be ignored if no evidence is forthcoming in my opinion.
Lastly for this week, reader Joe Pop sent me a link to this recent article by Brent Butterworth "The New Standard That Killed the Loudness War". It's reminiscent of this article by Ian Shepherd years ago in 2009 about loudness normalization with Spotify and the "end" of the Loudness War. Sadly, since 2009 there have been innumerable severely dynamically compressed new music for my liking. Well, let's hope it works out this time around. :-)
Take care and enjoy the music, audiophiles!