SPL and Kevlar – A Sensitive Relationship

Sensitivity represents one of the most useful specifications published for any speaker. Sensitivity, measured in decibels, is a representation of the efficiency and volume you can expect from a device relative to the input power. This is important because it requires twice the power to increase the volume of a speaker by 3dB. For example, to increase the volume of a 350-watt bass amplifier 3dB (an audible, but relatively small amount), it would require 700-watts of power. To double the perceived volume (approximately 10 dB) you would need in excess of 2800 watts of power. A much more economical solution would be to replace the speaker with one with greater sensitivity. The following chart shows this concept well.

Competitor's Neo 210 cabinet
Sensitivity: 93db @ 1W/1M
1 watt 93 db
2 watts 96 db
4 watts 99 db
8 watts 102 db
16 watts 105 db
32 watts 108 db
64 watts 111 db
128 watts 114 db
256 watts 117 db
512 watts 120 db

EA NL-210
Sensitivity: 100db @ 1W/1M
1 watt 100 db
2 watts 103 db
4 watts 106 db
8 watts 109 db
16 watts 112 db
32 watts 115 db
64 watts 118 db
128 watts 121 db
256 watts 124 db
512 watts 127 db

What this chart shows is that our Competitor's neodymium 2 x 10” cabinet needs more than four times the power to achieve similar volume levels as EA's NL-210.

Most manufacturers determine sensitivity by putting the speaker in a baffle and measuring the sound pressure level at one meter, with 1 watt of input power across the frequency response curve. The sensitivity figure is the decibel (dB) reading at 1KHz (1,000Hz).The problem is that one manufacturer may place the microphone one meter from the dust cap of the speaker and gain a distinct advantage over the manufacturer who placed the microphone one meter from the baffle board. The EA method is to measure with the microphone one meter from the baffle board. We then take the frequency response curve and points across what we have specified as the usable frequency range to obtain the average sound pressure level (SPL). EA believes this method is extremely accurate and represents exactly what you can expect from the speaker.

Although sensitivity is important, until recently you had to be willing to compromise to get your ideal combination of low-frequency reproduction and sensitivity. Think of an automobile. If all you do with your car is drive a few miles to work each day, you can probably get by with a small, efficient compact car that has less than 100 horsepower. On the other hand, maybe you carpool and carry six other people to work with you. In that case, you need a larger, more powerful car. The end result is you gave up efficiency but you were doing much more work. If you have lots of power, you can have awesome low-frequency reproduction and maintain lots of volume from a speaker with lower sensitivity. On the other hand, you would have to sacrifice some low-frequency reproduction in order to maintain a higher sound pressure level if power is a consideration. That is until now.

About a year ago, I had a lengthy conversation with the Chief Engineer who makes our woofers and asked him if there was anything new on the scene. He told me that there was new Kevlar/pulp formulation that actually improved both the low and high end. This statement is somewhat contradictory. A 10" driver works in the piston mode up to about 1KHz and then goes into a breakup mode, which enables it to generate higher frequencies, generally up to about 2.5KHz. There are 10" drivers (vocal-PA type) that can go smoothly out to about 5KHz but they will distort when any substantial amount of bass is fed into it. If you want good bass, you need stiffness. If you want good high end from a large cone, you need flexibility. Alas, someone has found the ideal alchemy of paper pulp, Kevlar and binder that allow the cone to go into a nice controlled breakup in the high end and is stiff enough to do large excursions without distorting. This new cone goes to about 4KHz with very good off axis response to about 3KHz. We then cross over the tweeter electrically around 2KHz, which translates to about a 3KHz acoustic crossover with our horn/driver setup. So we have the tweeter kicking in with good off axis response before the woofer starts to beam excessively.