Sunday Controversy: Cabinet sensitivity

Discussion in 'Amps [BG]' started by swamp_bass, Jan 5, 2014.


  1. swamp_bass

    swamp_bass I love it when a groove comes together Supporting Member

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    My last controversial discussion went over like a fart in Sunday school, with people accusing me of promoting something I was actually cautioning against:

    http://www.talkbass.com/forum/f15/car-subwoofer-sensitivity-1040006/

    Time for some more controversy by touching upon another divided subject from a scientific point of view: Cabinet sensitivity and its relation to actual usable volume!

    So right up front, I'm discussing:
    1. Cabinet specifications, not specifications on drivers
    2. Sensitivity in standard SPL @ 1W/1M, not some random contrived rating
    3. Passive cabinets, not combos

    Sensitivity ratings for a cabinet are an indication of how much volume will come out as measured from 1 meter away with one Watt applied.

    The ratio of amplification to output is approximately +3dB for every doubling of power. So if I have a horrifically inefficient cab with a sensitivity of 88 dB (my car subwoofer home practice cab), and a 125W amp, then the extrapolation is roughly:
    1 W 88dB​
    2 W 91dB​
    4 W 94dB​
    8 W 97dB​
    16 W 100dB​
    32 W 103dB​
    64 W 106dB​
    128 W 109dB​

    If you compare that to SPL levels necessary for a gig, such as those listed on the Greenboy Fearful page, you can see why this was built as a home practice amp with no further aspirations:

    http://greenboy.us/fEARful/faq.htm

    So another way of looking at amplifier power is in dB gain from 1W as measured from 1M away. Thus, a 125W amp gives you approximately 21dB gain potential, while a 500W amp gives you 27dB gain potential.

    This is all ideal calculations in an ideal world - in which we don't live. In fact, many folks here completely dismiss SPL sensitivity ratings and say they're meaningless. Why?

    While I don't believe in throwing the baby out with the bathwater, there are many reasons why folks are dismissive of sensitivity ratings, and why a cabinet rated at 104dB sensitivity and 500W capability might never come close to the calculated potential of 131 dB:
    • Power rating is not realistic for actual live music. That 500W is really an occasional peak, but only 150 useable Watts can be run before one or more speakers melt
    • The sensitivity rating is not guaranteed across the full range, and is likely just the highest peak somewhere at 2KHz.
    • Lowest frequencies are hardest to produce loud, and the cabinet is only good for 1/4 rated power below 100Hz
    • Volume rating at 1W/1M directly in front of the driver of choice gives no guarantees of off-axis response.

    So from the above, it's clear that the efficiency rating of a cabinet is no guarantee of how loud it will get in a specific application. It only tells you the volume produced at 1W from 1M away sitting in front of it.
  2. KJung

    KJung

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    Um, OK. Why in heavens would this be a controversy:confused:
  3. bgavin

    bgavin Supporting Member

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  4. swamp_bass

    swamp_bass I love it when a groove comes together Supporting Member

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    Just for clarification; the examples of why a particular 104 dB cab won't reach anywhere close to its rating was just a hypothetical example of the worst of the worst. If a 104dB cabinet is rated for 1000W and costs only $299 new, and it weighs only 40 lbs, it probably falls into all of these and then some.

    But a pricier cab that weighs more and is more conservatively rated will reach much closer to its calculated max potential.

    And multiple cabs being run less than their max will put out very close to the calculated max because you're not trying to load them fully.
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  6. swamp_bass

    swamp_bass I love it when a groove comes together Supporting Member

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    Because I'm actually a believer in the sensitivity ratings of a cabinet, and don't personally agree with the "ignore sensitivity ratings because they're not realistic" approach.

    Measuring the sensitivity of a cab at its most efficient frequency isn't much of a deal breaker. If the cabinet has a peak at say 3KHz, and I post my efficiency based on that highest peak, it's still close to the realistic efficiency. If the cab had a peak of much more than about 2dB at 3KHz, it's going to sound like *ss in the store and nobody's going to buy it.

    That leaves the other limitations of max power handling optimism on the part of the mfr.
  7. KJung

    KJung

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    Well, weight has nothing to do with anything, but otherwise, again, +1. All these specs trade-off due to the compromises any cab designer chooses. Basic stuff well known on TB.

    Given than many sensitivity ratings are calculated at 1K, sensitivity also often gives you an idea of the relatively ratio of midrange to low bass, which can be useful (a lot of bass extension is not necessarily a good thing by definition, depending on your tone goals, etc., etc., etc.).

    You might want to do a search on this. There are literally dozens of threads that discuss this, with very little controversy or drama.;)
  8. Mike Arnopol

    Mike Arnopol Supporting Member

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    one of the biggest problems is that sensitivity is typically measured at a much higher frequency---which gives little practical info for bassists. A cab may produce 102db at 1 meter at 1000 hz but may be 5db down from there at 100 hz.

    With my cabs I measure sensitivity at 50, 100, 200, etc.

    My sensitivity figures are usually based at 100hz.

    Power handling figures have little to do with real world music. They are typically thermal failure . As bassists we're more concerned with maximum excursion which will give more of a real world limitation for our needs.
  9. KJung

    KJung

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    Ah, OK. Per my above post, sensitivity will give you a rough estimate of upper midrange to deep bass (in general), but even that is a crapshoot, since different measures of sensitivity are used (i.e., average sensitivity through the usable range of the cab versus at 1K or whatever). Very 'unstandardized' spec that is usually poorly defined in the marketing specs available to the typical consumer.

    Best to use your ears if you can. If you can't try before buy, then TB reviews are a good way to get a feel for the relatively voicing of a cab.
  10. swamp_bass

    swamp_bass I love it when a groove comes together Supporting Member

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    This is where we disagree. Yes, they can eek out a little sensitivity boost from a peak, but to say that a 5dB peak at 1000Hz aint gonna sound harsh in the store is a bit of a stretch.
  11. KJung

    KJung

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    Hey Mike! Happy New Year!

    And yeah, everyone measures differently, and even full frequency plots don't really tell the consumer much about how the cab actually sounds (since distortion levels, etc. are never really included).
  12. KJung

    KJung

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    Again, if you can actually listen to the cab, all this doesn't matter. And there are some cabs that have a brutal peak at between 2K and 4K, and some seem to like them:D

    The key here is that without knowing at what frequency the sensitivity measure is based on, it is a relatively useless spec for sure. Even measured and defined accurately and usefully, it is just one basic measure among dozens of linear and non-linear interacting measures that define how a cabinet actually sounds.

    Better to pretty much ignore these sort of published specs for sure. Accurate or not, a single spec explains a very small amount of the variance in the tone of a cab.
  13. swamp_bass

    swamp_bass I love it when a groove comes together Supporting Member

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    It's my belief that power ratings and lack of bass extension at volume are the biggest factors in cabinets falling short of the potential promised by SPL ratings. Every subwoofer or woofer has lower output capabilities as frequencies drop. Cabinet design can help or exaxcerbate this.

    This means it's possible to use the sensitivity rating of the cabinet as real IF you can demo the cabinet loud playing your lowest string.

    In my case, the lowest I play is drop D tuning, and several commercially made cabs dropped out of the running at only moderate volumes.
  14. swamp_bass

    swamp_bass I love it when a groove comes together Supporting Member

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    Which again goes back to the controversy: I say SPL matters, provided the power rating is real, which is testable in a demo. To say that SPL is irrelevant is going too far in my opinion.
  15. swamp_bass

    swamp_bass I love it when a groove comes together Supporting Member

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    Actually, KJung, while we disagree on the specifics, we do agree on the basic premise: It's important to demo a cabinet before you buy!
  16. KJung

    KJung

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    Well, yes, but more importantly, once you demo a cab loudly in a full range situation, who cares about a limited, usually ill-defined number in a marketing brochure.

    So, +1, I guess. Of course, it also depends on how much fundamental versus first harmonic you have dialed into your amp, and also the hi passing start point and slope built into the amp.

    +1 though, once you try out a cab, you will know, and the marketing specs become blessedly moot!
  17. KJung

    KJung

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    +1 Always has been the case, and again, even with full frequency plots, xmax, xlim, thermal ratings, etc., it tells you very little about how a cab actually sounds.

    Short of trying, TB reviews are VERY helpful in at least reducing the risk in buying a cab on-line that won't work for a given player.

    Nothing particularly controversial about this again. Amazing how a slight change in cab tuning, and the quality of a crossover can literally make two cabs with otherwise identical components sound completely, utterly different.

    A good example of this is the Aguilar GS112 and DB112. Pretty much the same basic 'marketing specs', similar average sensitivity, -10db low end performance, etc., etc. Exactly the same driver and tweeter, and identical box size. Slight tuning differences, box material, etc. result in similar low end and high end performance, but significantly different midrange performance.
  18. swamp_bass

    swamp_bass I love it when a groove comes together Supporting Member

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    My point is this: rather than say published specs are worthless, I say they're meaningful with caveats:

    If you play mainly standard tuning 4 string, and prefer boosted mids with fewer lows, most SPL ratings will probably be close to actual provided you like the voicing in your demo.

    The other takeaway is that the less you plan to drive your cabinet near its max, the more accurate the SPL rating is to a wider range of applications and frequencies. Multiple cabinets help tremendously in reaching the potential published sensitivity.
  19. Passinwind

    Passinwind Charlie Escher Supporting Member

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    Power compression is extremely important too, and 1 watt SPL ratings tell you exactly nothing about power compression, unfortunately. ;)
  20. swamp_bass

    swamp_bass I love it when a groove comes together Supporting Member

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    Can you expand on this, Passinwind? (love the name, by the way)
  21. CL400Peavey

    CL400Peavey Supporting Member

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    All the single sensitivity specs you find are pretty meaningless. You dont know what frequency they were taken at, you dont know how they were taken, you dont have a full frequency response chart to compare them to.

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