How to interpret our specs
Rather than do the usual thing of letting the marketing department fabricate some unreal but typical specs we decided to let everyone see a complicated document which breaks down the differences in our cabs with accuracy and transparency. To keep things 'simple' we've divided the document into four sections:
1. Low frequency performance
2. Broadband performance
3. Amp matching
4. Response limits
Low frequency performance
Low frequency performance is essentially how our cabs would perform if they were used as pro-sound subwoofers. All of our cabs have enough depth and power in the lows to be used as band PA subs (something you cannot say about many bass cabs!) whilst the Big Series cabs perform better than most good PA subs. Once we release our PA models we will be selling a 1x12" and 2x12" PA sub, both of which will be Big Series cabs without the midrange, tweeter or crossover - same woofers, same tuning, etc.
LF 1W sensitivity (dB SPL)
This is the dB SPL (i.e. loudness) at 100Hz when 1W (or 2.83V into an 8 ohm cab / 2V into a 4 ohm cab). If you were purchasing a PA subwoofer this would tell you how loud a sub it was - and assuming equal low frequency extension (that's what the next bits deal with) the bigger the sub (the bigger the box that is, not the bigger the speakers) then the higher this number is. To increase this by 3dB you have to double the box size - this is the laws of physics, there is no wiggle room. NB: THIS IS NOTHING LIKE THE STANDARD BASS CAB SENSITIVITY SPEC EVERYONE ELSE QUOTES!!!
-3dB @ (Hz)
This is the frequency at which the sensitivity has dropped by 3dB from the 100Hz sensitivity figure above. This is also known as the "half power" point because your cab is putting out half as many acoustic watts. To match the loudness at this frequency to that at 100Hz you have to put twice as much power in, which you'd do by turning up the bass knob by 3dB. In the real world, once you figure in things like room gain and boundary reflections indoors, a bass cab that is 3dB down at a given frequency in a test lab will sound (and thus measure) flat at this frequency on the gig. NB: THIS IS NOT THE "FREQUENCY RANGE" SPEC OTHER MANUFACTURERS USE!!! Some of these other manufacturers have the audacity to claim their lower frequency range spec is -3dB (or even -2dB) when anyone with an understanding of loudspeaker physics would know that their claim is impossible in this universe - Eden, SWR, AccuGroove, I'm looking at you! Although Ampeg's blurb can be inaccurate or out of date their specs tend to be pretty fair and honest and are a good benchmark for what you can expect from a typical good quality bass cab. Acme are consistently honest with their specs - very low roll-off points which correlate with very low sensitivity - the only way to get both is to have a HUGE cab (to lower the -3dB point by an octave with no loss of sensitivity, you have to make the cab EIGHT times as big). Sorry, that's physics!
-6dB @ (Hz)
This is the frequency at which the sensitivity is now 6dB down from the LF sensitivity. Some manufacturers quote this figure as their "frequency range" spec but many don't! Boosting your lows by 6dB will flatten the response down to this point - but it requires FOUR TIMES AS MUCH POWER from your amplifier and the speaker has to be able to handle that extra power. The Midget is an excellent example of a cab where this kind of boost is often used without any problem - our larger cabs would get very bassy with this much boost - whilst most other small cabs will distort when you play low notes with that much LF power hitting them.
-10dB @ (Hz)
This is the frequency at which the sensitivity is now 10dB down from the LF sensitivity. This is also known as the "half loudness" point because when a sine wave is swept down from 100Hz to this point, this is when it sounds half as loud (you'd have to do this with the volume up high and your ear rather close to the speaker to avoid Fletcher-Munson issues, but this might cause deafness, so don't try it!) When other manufacturers actually use a real "frequency range" spec, this tends to be the the number they use. Note that some just pluck a random figure out of the air - if it looks right, who's going to check? It's not like a 0-60mph time with a car, which just requires a straight bit of dry road, no traffic and a stopwatch!
Peak LF power handling (W)
This one is a little complicated! Every octave you go descend, a woofer has to move four times as far to produce equal volume output. This means that at some point the woofer will run out of excursion (ability to move without noticeable distortion) which thus limits the power handling. However with a ported cab as the port begins to work it gradually takes over the task of moving air and the woofer excursion starts to decrease, reaching a minimum at the port tuning frequency, after which it starts to increase again - rather rapidly! So with a correctly tuned ported cab (some manufacturers tune too high in an attempt to fake more lows but this results in a boomier sound and more chance of unloading distortion when you hit lots notes) the point at which a cab runs out of excursion-limited power handling is below 100Hz but some distance above the tuning frequency. This spec is the peak power the cab can handle at that frequency with less than 10% THD (total harmonic distortion) - the cab can handle more power higher up, and within reason more power lower down (how low is indicated by another spec, which we'll address later). One of the really unique things about our Barefaced cabs is how extraordinarily high this rating is - which is why you can use a Midget on a rock gig - not many other 1x12"s can pull that off!
Volume displacement, Vd (cc)
This is very useful. It literally tells you how much air each of our models can move. The higher this number, the more low frequency output the cab can produce. As addressed in our technical piece on Vd, this number is very high for Barefaced cabs. The reason the Peak LF power handling for our cabs is so high is because the Volume displacement is so high. If you keep everything else the same but double the Vd, you quadruple the Peak LF power handling.
Maximum LF output (dB SPL)
This is the peak loudness in dB SPL at 100Hz if you apply the power in the peak LF power handling rating. It's a good guide to how much bottom each cab can bring on the gig. In reality it's rather more complicated than that but it does allow you to compare the different models. Note that the Big Series cabs will sound palpably deeper and bigger when producing similarly loud fat lows to the other cab - that's due to the lower roll-off points and this lower roll-off points mean you need more Vd to hit a given 100Hz SPL.