Updated: Dec 10, 2019
point source loudspeakers
At the little audio company, we consider our loudspeaker choice very carefully. It is the loudspeaker that is interacting with the end user's listening room, not the electronics, so we like to be able to offer many different solutions for this all important system component.
The most common approach for the majority of the loudspeakers offered by manufacturers are two-way or three-way designs with the drivers mounted in a vertical line down the front of a box cabinet. The drawback here is that the frequency range has been split, and is coming from two different points on the front of the loudspeaker. When you listen to someone talking to you, the whole frequency range of their voice is coming from a single point. This is also true of musical instruments (ignoring room reflections for now). Cue the 'dual concentric' design, or 'point source' loudspeaker.
A perfect example of this dual concentric design is the Technics SB-C700 or KEF LS50. These models produce a wide frequency range that appears to come from a single point, overcoming many of the negative issues created by non coincident speakers, and bringing with it a lot of natural positives too. It's not all plain sailing though - the dual concentric brings its own issues, which is why the likes of Technics and KEF have been developing and perfecting the approach since the 1980s.
With coincident drivers, the 360 degree sound dispersion they create is more consistent and nigh on identical whether measured horizontal or vertically, or any which you you care to measure them. With this radially identical pattern, the speaker tends to behave better in any given listening space. Along with the profile of the mid/bass driver, this reduces high frequency reflection, and my general findings are that you hear more of the speakers and less of the room.
Because of the more consistent off axis performance, you don't have to sit in the sweet spot to fully appreciate them. Your horizontal and vertical elevation in relation to the speaker is less important - whether your ears are a foot above the speaker, level, or a foot below, will have far less bearing on the tonal balance when compared to many conventional loudspeakers.
It doesn't matter how close you sit to a dual concentric speaker. If you sit quite close to your speakers and move your head slowly up or down a few inches, you'll usually hear the tonal balance change. This is because the centre point of the treble unit is about 5/6" away from the centre point of the mid/bass driver (in a normal sized bookshelf speaker), so your ears are moving between the two and hearing more of the nearest driver. The lack of this effect makes coincident loudspeakers perfect for near field listening.
As coincident speakers measure more or less identically any which way, they can be used lying on their sides, making them easy to fit into more limited spaces without negatively impacting sound quality, which was how I used my KEF LS50s in my previous 5.1 home theatre system. These were chosen for my system because of their ability to gel together and produce a single soundfield, rather than sounding like five speakers producing individual noises. Again, my findings are that coincident speakers or speakers that create a more point source effect perform better in multi-channel home theatre (or hi-fi) systems.
As mentioned previously, if someone stands in front of you talking, their voice emanates from a single point - this has the same effect with musical instruments too. This is how we hear anything and everything, so it makes sense to reproduce sound this way too, and it can make quite a noticeable difference when listening to any genre of music. It is something that is easy to hear and appreciate when you listen for it, but very few do, so it's often overlooked when auditioning speakers.
Point source doesn't just apply to two-way speakers though. There are a number of full range, single driver loudspeakers available, which naturally produce a genuine point source experience. Heco's Direkt Einklang model, and the whole Eclipse loudspeaker range use a single driver to cover the full frequency range, without the need for a lossy crossover, allowing the user to enjoy all the benefits listed above, although frequency dispersion tends to be a little more narrow with this approach due to higher frequencies needing a little more direction.
There are some conventional loudspeakers that
mostly imitate the point source approach. Despite Amphion's loudspeaker ranges using separate HF and mid/bass drivers, they use an unusually low crossover point between them, so more of the directional frequencies you hear come from the HF unit, with the added benefit of utilising the speaker's bespoke waveguide to produce a certain frequency dispersion. This shaping of the speaker's dispersion controls the reflection points around the room, so you hear more of what you should, and less of what you shouldn't. Speakers that rely on the mid/bass driver to do more work are effectively creating more of a dual sound source effect, making it harder for more successful driver integration, and attracting negatives side effects.
So you may be asking yourself, "why aren't more manufacturers adopting this approach if it's superior?"
As mentioned earlier, the manufacturers who use this approach, and use it well, have been perfecting it for many decades - a manufacturer wanting to adopt it will have many decades of learning ahead of them - and unless taking the single driver route, it usually means designing and building your own bespoke drivers, rather than buying 'off the shelf' ones that many loudspeaker manufacturers use.
But don't take my word for it - have a listen for yourself to hear the benefits of point source loudspeakers. It can be an acquired taste initially as they may sound a little different to what you're used to, but once you appreciate what they do, it can sometimes be hard to revert back to more conventional loudspeakers...