Interpreting the Technical Data
    At BESL we believe superior engineering leads to “Excellence in Acoustics”. Which is why we take pride in our measurements and gladly publish more technical data than our competitors. It is our hope that this information instills further confidence with our customers, allowing them to compare performance among our various products (as well as to our competitors’), and ultimately make more informed purchase decisions.
    You may be curious about objective performance, but less experienced on how to properly interpret the many forms of data. To preclude confusion, we offer this guide on how to properly interpret our published data.
    For more information on the highly refined BESL design and measurement methodology, see the Development Method page.

Specifications Page

Transducers
    Technical features and photos of the transducers [drivers].

Impedance (spec & graph)
    Impedance characterizes the electrical load that the speaker presents to the amplifier. It varies in amplitude and phase with frequency. The connection of the speaker drivers and crossover components with the amplifier makes the impedance change in reactance from capacitive to inductive to resistive.
    The bold purple curve represents the complex impedance magnitude, while the faint purple curve indicates the phase.

Amplitude response (spec & graph)
    This specification indicates the speaker’s ability to precisely reproduce the input signal loudness as tested in an echo-free environment. It is the difference between the measured response with the target curve. The lower the number, the more accurate the speaker in this regard.
Explanation of the plotted curves:
  1. Target curve (red)
    A modeled ideal curve whose title indicates speaker sensitivity, and bass alignment.
  2. Mid-High Sum (purple)
    SPL response of woofer and tweeter measured at 2 meters distance and 5.6 volts drive level.
  3. Mid-High Difference (faint gold)
    Response of woofer and tweeter, but with the tweeter connected in reverse polarity. A wide, symmetric, and deep null centered at the crossover frequency is indicative of excellent inter-driver phase coherency.
  4. Woofer (faint blue)
    Midrange and treble response of woofer measured at 2 meters distance and 5.6 volts drive level.
  5. Low (brown)
    Bass response of woofer measured at 1/2 meter distance and 1.4 volts drive level.
  6. Low w/ HPF2 @80Hz (faint brown)
    Bass response of woofer when an active high-pass filter (12dB/octave at 80Hz, 0.7Q) is used to filter out the low frequencies.
  7. Tweeter (faint green)
    Midrange and treble response of tweeter measured at 2 meters distance and 5.6 volts drive level.
  8. Top Octave (purple)
    Top octave response on axis to the tweeter.
Dispersion (graph)
    Dispersion is a measure of how the speaker performs at various angles from the front panel. For most conventional speakers the sound typically gets quieter in the treble as you move off to the sides or behind the speaker.
    Different philosophies abound as to how narrow or wide the dispersion pattern should be, and how to address the intricacies of varying dispersion through the crossover region.
At BESL, we believe
  • The 3D dispersion pattern should be as symmetric as possible around the Reference Axis.
  • While dispersion will narrow with increasing frequency as it must, the pattern should still change as smoothly as can be made possible.
  • The speaker should not be artificially "re-voiced" to overly compensate for the narrowing woofer and tweeter dispersion patterns. (Some competitor designs that attempt this exhibit a forward sounding presence band, or generally a slightly bright and ultimately fatiguing sound.) Instead we encourage the listener to acoustically treat front and sidewall first reflection points. Ultimately, this smoothes the response and improves image location and depth.
    Often call Polar Response, BESL elects to plot dispersion as a circular "radar" graph. Each graph line represents a constant frequency. By contrast to Amplitude graphs that display many closely-spaced frequencies, Polar charts display only frequencies spaced one-half octave apart, and above 200Hz. Otherwise the chart would be too dense to display.
Horizontal polar response:
  • Look for symmetry about the 0 to +10-degree line on the graph. This indicates the Reference Axis angles slightly off to the same side as the offset tweeter placement. In other words, BESL speakers are optimized for performance when seated slightly off axis.
  • Expect to see a gradual pulling in of the lines as the angle approaches the +/- 90-degree values.
  • No major dips or bumps should be seen in the horizontal dispersion pattern.
Vertical polar response:
  • Look for symmetry about the 0-degree line on the graph. This indicates the Reference Axis is level with the floor, i.e. it does not tilt up or down. In competitor’s designs, we often see the primary lobe tilt down for frequencies around the crossover region. Not so with BESL speakers, where the RA is kept horizontal for all frequencies. This makes speaker setup less tricky and more intuitive. The speaker does not change sound character as much whether the listener is seated or standing.
  • Expect to see dips along the +30 and –30 degree lines for the frequencies around crossover. This is typical of even order crossover performance.

Sensitivity
Sensitivity indicates how loud the speaker plays under three standard conditions:
  1. Voltage drive level = 2.83 volt (set at 300Hz).
  2. Distance from the speaker at which the measurement is taken = 1 meter.
  3. Acoustic environment configuration = 4-Pi (full space) and echo-free.
    Note that all too often you will see the third condition missing from competitors’ specs. This may be coincident with a higher sensitivity rating than for a similar BESL speaker. It is possible that their sensitivity rating corresponds to half-space conditions, which raises their sensitivity figure by 6dB.
    See the Development Method page for more information on how sensitivity is derived.

Inter-driver phase response
    See the Phase Compensation page for more details.

Maximum linear output
    This parameter indicates the maximum power input to the speaker and maximum sound output from the speaker.
    Maximum power as specified by most other manufacturers usually indicates the power level at which any part of their speaker fails either mechanically or electrically. This can be an extraordinarily high wattage rating, but it does not characterize how nonlinear or distorted the speaker’s output will be up to that point. Their max power limit is impressive, but useless to you.
    By contrast, BESL uses the max power spec to show what kind of output performance is to be expected under varying real-world conditions. Maximum output (without speaker failure) is usually limited by the excursion of the woofer cone at lower frequencies, thermal compression of the output at middle frequencies, or the onset of severe distortion.

    For monitors, the maximum output can be increased by reducing woofer cone excursion. This calls for filtering out the low bass via an electronic high-pass filter. When such a filter is combined with a suitable low-pass filter for the subwoofer, a proper crossover between monitor and sub is complete. Typically, the input power capacity to the monitor doubles with the HP filter, and maximum output increases by up to 3dB. This implementation is strongly recommended for all BESL monitor / subwoofer combinations. In fact, designing the active and passive crossover filters to gracefully hand off the load from monitor to subwoofer is one engineering accomplishment that sets BESL speakers apart from others. An active high-pass filter on the monitor should be considered mandatory for reaching maximum output with lowest distortion. See the BESL design philosophy for more insights.
    When the speaker no longer yields 3dB more output for each doubling of input power, it undergoes nonlinear compression due to voice coil heating.

    Subwoofers' output is generally limited by excursion of either the woofer or the drone. A gradual compression of the output is heard as a "softening" of the bass. BESL subwoofers are designed so that both woofer and drone reach their separate excursion limits at the same drive level. Rather than limit the 1st octave bass as a means to increase mid and upper bass max SPL, BESL subs’ SPL response tracks the same curve shape at all operating levels. We recommend the use of multiple subwoofers for systems requiring extra high output levels.
    Be wary also of claims for extraordinarily high output SPL and high input power for other manufacturers’ subwoofers. Often, their subwoofer is placed in a tri-corner, which boosts the output by about 10-15dB! The max power may be that of driver failure, or because of the use of drastic 1st octave electronic limiting. In other words, they don’t say that the SPL does not remain flat at all operating levels.
    Another claim to fame from manufacturers is that of subwoofer amplifier power. Such high power may be truly required for the radical EQ necessary to boost the 1st octave output from small, sealed subwoofers. This is a crude, and brute force approach to getting output from a poorly designed bass system.
    BESL designs drone-assisted subwoofers as a mean to boost low frequency output acoustically, and without requiring extraordinarily high amplifier power.
    Suffice it to say that to provide a truly meaningful set of specifications for subwoofer performance would take an entire page, and not just a few lines.

    Lastly, provided it is operated under the specified max power conditions, a BESL monitor or subwoofer will never produce severe distortion.
    For all these reasons, you may see up to three power levels specified. Consider your maximum output requirements carefully when choosing among the various monitors and subwoofers. See the FAQ page for a full guide on making this critical decision, or use the Speaker Selector wizard.

Bass alignment
    This parameter indicates the filter alignment of the woofer/box combination. (Any speaker enclosure acts as an acoustic high-pass filter to the woofer.)
    All BESL monitors are in sealed boxes. As such, they roll off in the bass at a rate of 12dB/octave (also referred to as second order). The Qtc indicates the shape of the knee where the rolloff begins. Ideally, Qtc should be 0.5 to 0.7, so as to combine properly with the additional electronic high-pass filter. BESL subwoofers utilize drone radiators to achieve low frequency extension with increased cone area while controlling woofer excursion, but without any of the ill effects presented by ports.
    The corner frequency is where the amplitude drops –3dB below the reference level (the flat, pass band at a level equal to the sensitivity figure), and is given in the Amplitude response section.

Crossover
    The passive crossover network transforms the raw in-cabinet SPL of the drivers to the smooth ideal target curves. The alignment parameters describe the acoustic slope of the target filters, and the precise cross frequency.
    The high parts count typical of BESL networks is no cause for concern. We always strive for minimal components in the series signal path. The remaining components are used to improve SPL amplitude accuracy and for phase compensation.