Sensitivity - marketing and over-simplified engineering

Keeping it short and sweet:

99% of the sensitivity specs you read are marketing department fabrications. There are no bass cabs currently on sale (August 2013) which have higher sensitivity than ours when comparing equal sized enclosures, fact.


Getting complicated:

Sensitivity is the measure of efficiency that the loudspeaker industry uses - it's the number of dB SPL output measured at 1m distance from the baffle, on-axis with the centre of the cone (or array), with an application of whatever voltage produces 1W through the nominal load (so 2V into a 4 ohm load, 2.83V into 8 ohm, etc). Unfortunately, it's a very commonly 'fudged' spec - possibly just plucked out of thin air by the marketing department because a big number sounds better - and has no basis in reality.

The value of accurate specs when you have a one month trial period

When we at Barefaced talk about sensitivity we talk in real numbers because what's the point of specs if they're made up? You might sell some more speakers in the short-term but they'll under-perform and you'll get your comeuppance in the long-term. With our old specs we gave low frequency (100Hz) and broadband (weighted average from 200Hz to the quoted treble roll-off point) sensitivity specs. We've decided to make things easier now and give you just the pistonic sensitivity specs (basically the 80-640Hz region) in half-space as, based on further research, testing and experience we've found they're most representative of real world use.

Old Model LF Broadband Pistonic New Model Pistonic

Midget   95   99 96 Super Midget  97

Compact   98 100 98 Super Compact 97

Super Twelve   98 101 99 Super Twin 100

Super Fifteen 101 103 101

Big Baby   94   95 94 Big Baby 2   97

Big Twin   96   98 97 Big Twin 2 100

How on-axis response variations affect your perception

The next obvious part of the sensitivity puzzle is the frequency response from high to low - peaks in response will help you cut through but rarely sound pretty whilst dips in response will mean lower sensitivity than in the pistonic bandwidth, and if those dips are just where your bass guitar speaks or where there's some sonic space in the mix, then you're going to have a loudness problem. Our cabs are designed to sound very even across their bandwidth with no significant peaks or dips in the on-axis response so the sensitivity we quote is the sensitivity you hear.

Thermal compression - your cab will always have less sensitivity at high power

But that doesn't tell the whole story by half! The whole point of the sensitivity spec is because it's the main indicator of how loud a speaker will play - the sensitivity matters more than the wattage (thermal power rating). But is the sensitivity when you apply 1W the same as the sensitivity with 100W? Sadly not! As the power through the voice coil increases, so the voice coil gets hotter, so the resistance of the voice coil increases, so the impedance of the cab increases and so the power the amp is delivering actually decreases. If a speaker's voice coil doubles in resistance then our 500W amp turns into a 250W amp, effectively taking 3dB off the sensitivity just when we need it most. Our latest models feature advanced thermal design which minimises power compression and helps you retain that sensitivity at those critical loud moments.

Magnetic and port compression - your cab will always have less sensitivity at high power

At the same point that our voice coil is getting hot and restricting current flow, that voice coil is also undergoing very high excursion fore and aft. A typical motor design exhibits the greatest magnetic flux when the voice coil is centred, with the flux diminishing a significant amount before over-excursion is clearly audible. Our motors have a very deep magnetic field and remain linear at far higher excursions than more conventional designs. This means the sensitivity stays high when the woofer is leaping back and forth, so giving you that loudness just when you need it most. Also conspiring against sensitivity is the port behaviour at high SPL, with the ports in most bass cabs compressing very early on which reduces your low frequency sensitivity once you're at gig loudness - again, we've focused on fully optimised port designs so you maintain as much sensitivity as possible.

How loud is it around the whole room? Isn't that what really matters?

The final point to consider is that sensitivity is merely an on-axis measurement. What happens if you're not standing with your ears right in line with the speaker? What happens if you're so far off from being in the firing line that much of what you're hearing is the reflected room sound? Well it stands to reason that the broader the dispersion of the cab, the closer they'll get to sounding as loud everywhere else in the room as being at the same distance but directly on-axis. Our cabs are designed to have the best polar response possible and that means their dispersion is far superior to the norm. This gives them very good power response, which is the sum of all the on- and off-axis response curves - the more even the power response, the more consistent a cab sounds when moving from a very dead (heavily furnished and full of punters) to a very live (bare walls and floor, one man and his dog) acoustic scenario.

Some real world comparisons

As an example, comparing old and new, the Compact has higher on-axis sensitivity than the Super Compact and Big Baby 2. But both those cabs have stronger off-axis response, particularly the Big Baby 2. Both those cabs are designed for better cooling and both those cabs have longer excursion motors whilst the Big Baby 2 also has more port area. The end result is that on the gig (i.e. at high power) the Super Compact is almost as sensitive as the Compact whilst the Big Baby 2 actually betters it, despite being slightly smaller.

The value of real and complete engineering design

To recap, we're starting with the highest possible pistonic sensitivity, ensuring that sensitivity is maintained across the operating bandwidth of the cab, reducing thermal power compression, reducing mechanical (over-excursion and port) power compression and ensuring that the dispersion is as broad as possible to give good 'power response' (the sum of on and off-axis response at many many positions off-axis ). When you buy a a Barefaced cab you know that it has been designed to be loud on the gig as opposed to merely loud in the shop!


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