Unless I’m Missing Something... Speaker Efficiency

[James Edward]

Introduction:

I have Spatial M3 Turbo S speakers with an efficiency rating of 94 db per mfr.
I recently tried a pair of large 3-way bookshelves with 90 db spec per mfr.
I currently am trying a pair of floorstanders with 88 db spec per mfr.

My integrated amp has meters, and I used a RadioShack SPL meter to verify what I have found.
The 3-way bookshelves with 90 db spec came close to redlining my amp meters. I say ‘came close’, because things were fairly loud, and I don’t abuse any of my equipment.
At about the same volume level on my SPL meter, the Spatials were not close to the edge as indicated on the amp meters. Makes sense up to now...
Next up, the spec rated 88 db floorstander. At the same SPL level, my amp meters were, if anything, showing even less power output than when driving the Spatials.
The meters (SPL and amp meter) are analog, therefore none of this is exact.
In the world of db’s and speaker efficiency, 6db is A LOT.
**So, what exactly is my meter telling me?**
As an addendum- a Stereophile review/measurement of the 3-way bookshelf stated that it actually measured as 88 db efficient.
I’m also pretty certain that all three manufacturers used the standard 1 watt/1 meter metric.
This is just something I’m wondering about- please offer up any insights.
Thanks,
Jim

[Folsom]

Unfortunately impedance varies a lot with drivers and crossovers, totally screwing with actual sensitivity. There's a few more factors at play but in general the way we look at it now is a pretty piss poor way.

[James Edward]

Folsom, (and anyone else that cares to chime in...),

Which makes me wonder- what are my amp’s meters telling me? IF the specs are correct for both the 88 db efficient and the Spatials at 94 db, I would think the SPL output would be dramatically different. I don’t know a lot, but I do know that every 3 db increase in SPL needs double the amplifier power.

I am acutely aware of, or at least pay attention to, these things because I use a relatively low power (30 wpc) amplifier. According to those in the know, my amp will drive very low impedance loads. Could this in some way affect what I’m seeing on the amp meters?

Regarding the 3-way large bookshelf, Stereophile’s measurements indicated that there was an impedance dip that would indicate using an amp that was comfortable driving 4 ohm loads. That might explain the high meter output on the amp. However...

Another online site that performs measurements found the floorstander with 88 db sensitivity had an even more challenging impedance dip on a few levels. And yet, it performed admirably with my thoroughly unscientific SPL meter measurements vs amp output meters. MUCH more SPL output vs amp meter levels.

As I write this, I am realizing that I did not note the exact levels of the rotary volume knob on the amp. This probably also plays into this in some manner. An offhand observation at best- the 88db floorstander probably was a tick higher on the actual volume knob for a given SPL vs the Spatials, though I cannot verify that.

Lastly, I am being deliberately vague on speaker brands, as I hope to have a small get together for a listen, and the floorstanders I’m currently enjoying are decidedly NOT a brand that would garner audiophile approval. I’ve been auditioning a few speakers, since a redo of my living is decidedly unfriendly to the Spatial aesthetic. (Not it’s audio- not that there’s anything wrong with that!)

Jim

[dflee]

Wouldn't the Ohm of the speaker have something to do with it?

Don

[James Edward]

Yes Don, I would think so. I’m just throwing all this out there to better understand what my amp meters are representing. All speakers mentioned specify  6 or 8 ohm impedance. It’s just interesting and maybe too much for a Sunday afternoon! I will also say that many speaker companies spec a certain impedance, and testing usually reveals a lower number...

[HAL]

Unfortunately the impedance rating of a speaker is not a constant value.  It may be 8 ohms at bass frequencies and 30 ohms at treble frequencies and anywhere in between.  The highest impedance is usually at the system bass resonance. Depends on the drivers impedance response with the crossover impedance.  This means depending on frequency being reproduced, the power requirement can vary considerably. 

[rollo]

  Talk to Clayton and ask Him for Impedance range of that design. Some speakers do not vary much Others do. Old Apogees for example went down to a 2Ohm load. Difficult for most amplifiers. You need to ask each Manf. of a speaker you are considering. Your Luxman as well What is the lowest it can handle.

charles