In much broader terms efficiency needs to be expressed in terms of bandwidth and resolution. I know that Altec specified frequency (e.g. 500-3000hz). We would expect to see reasonable resolution, such as +/- 3dB. I’m not saying Louis is incorrect, but my Super 3 Monitors with RS5 driver are rated as 94.5(!) dB/w/m. I am sure that number is accurate for some portion of the audio spectrum, but there is no way you can tell me this speaker is doing 94.5 (+/- 0.25dB?) from 60hz to >15khz. My ears tell me otherwise, especially when I compared the speakers side-by-side with Super Alnico monitors. To my ears, these drivers were pretty much the same efficiency from the mid band up, with the RS5 reaching a bit higher, or at least giving that impression. From the upper bass down, the smaller driver sounds considerably thinner, and I would estimate the midbass to be down at least 3-5 dB.
This is borne out in my experience with my Super 3HO monitors: the second driver is only active from 500hz down, adding an additional 3dB output from the upper bass and below. The balance of this speaker when driven by a tube amp is much fuller than the single driver model and is similar to the 6” Alnico driver. Speaking of tube amps...
Efficiency of the Super 3HO Monitor speakers:
This “1.5 way” speaker comprises two identical RS5 drivers in parallel. The lower helper driver has a single inductor in series for a 6dB low pass filter at 500hz. The total surface area below 500hz is about the same as a single 6” driver. The speaker is rated 97.5 dB efficiency. I do not agree with this rating.
The single driver speaker is rated at 94.5dB. The dual driver speaker is rated 3dB higher as we would expect by doubling the driver count. However, the second driver is only active below 500hz. From 500hz up there is only one driver playing, just as in the single driver speaker, producing 94.5dB. Below 500hz, the second driver comes in at 6dB/octave, adding 3dB in the midbass when driven by a tube amp.
However, if we drive the speakers with a typical solid state amp that doubles in power when we halve the impedance, we have a problem. The second driver in parallel below 500hz will not only double the acoustic power of the speaker for a given voltage, it will draw twice as much power from the amplifier. Driven by a SS amp, the second driver adds 6dB to the midbass rather than the 3dB added using a tube amp. The resulting sound is an overblown midbass that muddies the sound.
So how efficient are these speakers?
Based on memory and only my own ears, my seat of the pants opinion is:
1. Super 3 Monitor, single RS5 driver, wide baffle: This speaker started out as a 93dB Fostex model. It now features the 94.5dB RS5 driver. I would estimate that this is a 92-94 dB speaker from 150-15khz. The wide baffle helps in the lower midrange and upper bass. Corner or near wall placement really fleshes out the midbass and balances out the sound. Played in a small room with a small SET (I use a 4wpc 421A amp) this thing punches way above its weight. Ideal power is 3-5wpc. the driver can’t really use more than that and sounds compressed if you try to make it do more than it can. The tonal balance of this speaker reminds me of a higher-resolution Spica TC-50, with the lack of deep bass balanced by a slightly forgiving top end. I have these on Skylan 24” stands, but in my opinion the XRS version of this speaker may be the best all-around small room speaker Louis has ever made.
2. Super Alnico Monitor: I no longer own these as I have too many projects and couldn’t justify a largish Alnico monitor. I already had some Altec based 12” speakers so I needed to thin the herd (this was before the CAM came out). this speaker is now rated 95dB whereas the same speaker was previously rated at 93dB. My ears tell me this is again about a 92-94dB speaker, this time from probably 60hz -15khz. I had the SAM’s on 20” Skylan stands near corners. They could easily play four times as loud as the smaller speaker, with a much fuller midbass and ability to take more power. The RS5 driver has a better high end hands down. It extends higher and doesn’t have some of the challenges posed by the whizzer cone of the Alnico driver.
3. Super 3 HO Monitor: These are currently in my larger room, joined by a pair of Rhythmik F8 subwoofers. It is a powerful combo driven by 5-30wpc. As I stated before, I believe the dual driver speaker to be the same 92-94dB efficiency as the single driver model, but this time from 60-15khz. The second driver below 500hz really balances the speaker. It also allows it to play considerably louder than the single RS5 speaker as it can now absorb twice the power in the bass. I also found them to be able to more comfortably play louder than the SAM.
I listened to these speakers using one SS amp (Red Wine Audio Signature 16), an Oliver Sayes-built FI 421A, and two Dennis Has Inspire SEP amps (one of which as been on long-term loan to Louis for so long I am afraid to ask for it back). All amps were run from the 8 ohm tap of the 421A, and the single (6 ohm) tap of the Inspire amps (which as rated for full power at 2-20 ohms). In general, these speakers, even the dual driver model, are very easy to drive. Their impedance are benign and they have no (or very simple) crossovers. None of the speakers drew more or less power from the amps due to impedance.
What do these speakers do best?
1. Super 3 Monitor. Great small room speaker, fantastic on vocals. Will not really get down a boogie unless you relive them of the deepest notes. If you could high-pass before the amp at about 100hz and add subwoofers you could really cut loose.
2. SAM. If I were buying this speaker again I would buy the CAM or the Junior 6 (AKA Super Six XRS). These are a better naturally balanced speaker than the smaller RS5 speaker, can play a lot louder and work in larger rooms, but if you are looking for something to raise the roof you will still be disappointed. They do have a seductive wetness about them that is intoxicating, but do have their limitations. I couldn’t make these work for me, but they are a fantastic all-around grown-up speaker that will competently showcase much more expensive upstream equipment. They do require some care in system matching and setup to optimize bass.
3. Super 3 HO. Beautiful proportions (I have quartered ebony) and great balanced sound. At first glance they are a great high-efficiency replacement for speakers like the Harbeth P3 or KEF LS50. However, while they fill this high-resolution monitor role, they do require tube power (or careful matched SS, such as Pass or Firstwatt current amps that do not double into halved impedance) to sound acceptable. They can best run on 5-50 tube wpc, though a 45 SET would probably do ok at lower levels. They mostly sound like a bigger, more powerful Super 3 single driver speaker. Mostly. To my ears they do give up a small amount of the single driver magic. The two drivers in the larger speaker are 90 degrees out of phase (and about 6” apart in vertical displacement) so will likely only be completely coherent at a single point from the speaker at a single frequency. This is a far cry from the phase anomalies and driver spacing on conventional multi-driver speakers but to my ears makes the speaker very slightly less coherent than the single driver model. The balance of the single driver speaker features more forward (i.e., less balanced) midrange that gives female vocals a magical presence.
All of these speakers are special but all require careful system matching. Ironically, the amp that was the most universally successful with all the speakers was the Sayes/Fi 421A. 4.5 wpc is plenty with these speakers in my room. The amp is very high resolution and the 421A tube produces great bass. This is helped by the oversized Hashimoto output transformers. The Inspire amps (a KT88 HO at 12wpc and a PSE with 10-24 wpc depending on output tube) both had at least twice the power but couldn’t match the bass of the 421A. Admittedly Dennis used smaller custom outputs on his amps, but the 421A is really something special.