About Full Range Loudspeaker, Sound Stage, Phase Congruency and Goosebumps
- by Karl
When we say full range speakers, we really mean wide range single driver speakers. For one, loudspeakers that contain multiple drive units may well be full range. Second, full range must be defined as some range other than full, because no loudspeakers covers all frequencies. So for the purposes of this post, we will define full range as using only one drive unit and full as the frequency range expressed by real musical instruments. We also need to look at the loudness at which the loudspeakers can express the “full range” of frequencies.
Such full range speakers like the Sound Sommeliers are not for everyone. Single driver speakers are most suitable for the more intimate genre and at moderate volume levels. This includes solo voice, small group jazz and 18th century classical and chamber music as well as classical rock. Really anything expressed by real musical instruments and played no louder than would be considered just a little too loud for most people in an average sized listening environment. In technical terms we are talking about 80dB at the listening position. In non-technical terms this is the noise level of a freight train at a distance of about 15m. Anything louder than that, and a full range driver might not be for you. Now, if you are into very loud heavy metal, techno or Mahler symphonies at full concert volume, you may not be in the right place.
What are the advantages of single driver speakers? Well for one the completely unique sound that comes by the elimination of all electronics from the system after the amplifier. A speaker employing more than one driver uses a device called a cross over that divides the musical signal up between the different drive units. This crossover has two problems. One is it adds complexity and hence distortion. Second all but the rather difficult to design first order cross-overs, at the switching point, also called the crossover point, the phase between the neighboring drive units switches. This means that the membrane of one drive unit might rise while on the other drive unit it will fall. This is important because it leads to cancelations of frequencies making the listening position and speaker setup of such system a distinct art requiring constant tinkering. On the other hand, the human ear uses phase as a cue where a sound is coming from in the range of 300 to 3000 Hz frequency range and since a “normal” speaker has a crossover that operates in that point, phasing and thus the sound stage will become blurred and messy.
By not using a crossover the SoundSommeliers like select few other full range systems that are narrow enough to not need baffle step compensation, have no electronics at all. A high purity copper wire runs from the binding posts directly to the driver. This leads to reduced distortion, and provides a sound stage and a stereo image that is more precise and natural with depth that is not possible with speakers that have several drive units.
Another advantage of full range designs comes from the fact that in a multi driver set up, the sound around the crossover point which usually spans as much as an octave, actually comes from two different areas leading to interference patterns and a smeared stereo image.
And finally, well designed single driver speaker is that it is much more articulate and precise in the bass with better transient responses coming from a lighter cone and with a clever quarter wave design, these bass notes extend well bellow the capabilities of the drive unit itself and are always in phase with the sound coming from the tone. Congruency might not be something many have thought about, but there is something to be said about the bodily experience when the fundamental bass note of a musical instrument is in tune with its over tones. I describe this bodily experience as Goosebumps. Call it what you may, it is only a full range system like ours that can provide headphone-like soundstages and stereo imaging and the bodily experience of a deep congruent bass.
Now due to the intrinsic limitations of 3inch drivers to go to the very deep basses, compared to woofers, some “tricks” are necessary. First off: Consider that our tiny ear drums, aren´t really that good at picking up bass notes either and human hearing in the basses is terribly logarithmic. So the human brain uses an equalizer of sorts that lets us perceive loudness of lower notes in a similar way as we perceive the higher frequencies our ears are highly honed for. The way we do that is by comparing the loudness of a fundamental note to that of its overtones. The brain then adjusts the perceived loudness for both to match in the wondrous world of psychoacoustics. For this to work, a smooth bass roll of is required that keeps the overtones congruent with the bass. A well-designed quarter wave speaker can do just that and the results are outright surprising for many.
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When we say full range speakers, we really mean wide range single driver speakers. For one, loudspeakers that contain multiple drive units may well be full range. Second, full range must be defined as some range other than full, because no loudspeakers covers all frequencies. So for the purposes of this post, we will define…