AudioXpress's review of a Genelec Ones patent

[q3cpma]

https://audioxpress.com/article/patent-review-loudspeaker-with-a-wave-guide

Finally a pretty good explanation of how the slot loading provides increased LF directivity. I quote the relevant passage:

To extend vertical directivity, as disclosed in the patent (and the Genelec datasheet), the Genelec system adds an oval 215-mm by 100-mm woofer at each of the top and bottom ends of the enclosure, with the output of each of those woofers exiting out of a small (approximately 13 mm) slot running the width of the cabinet. This provides an additional pair of acoustic output sources at each end of the enclosure with a center-to-center separation of approximately 432 mm (17”). The woofers come in and extend down in frequency from 500 Hz to the lower limit of the system (claimed –6 dB at 32 Hz).

Besides providing the system’s low-frequency capability, the two slots interact with the waveguide over about half-octave, and then operate independently to maintain substantially constant directivity down to about 280 Hz. This type of spaced, dual source aperture can result in a simple and efficient means to enhanced directivity control. While a well-designed waveguide may maintain directivity down to about one-wavelength of its largest dimension, and a woofer, of the same active source diameter, can substantially match the directivity of a waveguide of the same dimension, a dual-point source, or slot source, can maintain the same level of directivity control to a frequency approximately 1-octave lower. At a plus-and-minus 90° angle from the zero-axis, a dual source will exhibit a cancellation null in the response at the frequency of which the center-to-center spacing is 0.5-wavelength, while exhibiting greater directivity between the 0.5-wavelength and one-wavelength frequency than a single source of the same dimension. So, in a small package that would normally only sustain directivity to a frequency at least an octave higher, this system can maintain very good constant directivity to a lower frequency, in one plane.

Really liking this "Patent review" serie, personally.

 

[stevenswall]

That is a nice series. I wish there were a diagram of how the sound interacts with the slot to control things lower.

 

[MrPeabody]

The effect described in the patent is not significantly different from what occurs in a center-channel speaker that uses two woofers and a concentric midrange-tweeter. The major difference in effect is that the two oval woofers are slightly larger than what you'll typically find in a center-channel speaker with dual woofers and a concentric in the middle. Of course the woofers are also pushed behind the concentric drivers so as to change the overall shape of the speaker, but this is only a "form factor" difference of sorts.

Perhaps it would be fitting to say "evolutionary, not revolutionary".

I recall reading somewhere that various people have found via measurements that the slot openings for the woofer are too restrictive. Considering how small they appear just from appearance, this isn't surprising.

 

[SIY]

Really liking this "Patent review" serie, personally.

#metoo
It's a terrific feature and really done well. Reminiscent of the old George Augsperger reviews.

 

[ctrl]

Besides providing the system’s low-frequency capability, the two slots interact with the waveguide over about half-octave, and then operate independently to maintain substantially constant directivity down to about 280 Hz. This type of spaced, dual source aperture can result in a simple and efficient means to enhanced directivity control.

I'm somewhat surprised that a patent has been granted. But I think in the US the patent concept is interpreted much more generously than in Germany, for example.

The use of a diffraction slot to control radiation and phase response is not new. An example of this would be the Ocean Way HR5 tested by @amirm.

What is new is the combination of two chassis with a diffraction slot and interference with the WG for better control of radiation.
But for example the D&D 8c uses lateral diffraction slots to control radiation.

The disadvantage is a significantly delayed decay in the range below 1kHz. It seems that the Genelec models with the diffraction slot, in the range 100-1000Hz, need about one oscillation period longer to decay than comparable speakers - more details here.
However, I cannot assess whether this slowed-down decay is audible.

 

[thewas]

But for example the D&D 8c uses lateral diffraction slots to control radiation.

By the way Geithain also uses similar for their cardiioid bass since 20 years or more?

 

[q3cpma]

The effect described in the patent is not significantly different from what occurs in a center-channel speaker that uses two woofers and a concentric midrange-tweeter.

Exactly, the first thought I had was "what's different from a d'Appolito design, then?". Guess the slot isn't a feature but a carefully mitigated downside to allow for a waveguide large enough.

But for example the D&D 8c uses lateral diffraction slots to control radiation.
View attachment 107747

I don't know if calling it "diffraction" slot is accurate, it's just an opening with some constant phase shift over the radiated bandwidth, like MEG does. Don't see where the diffraction comes in.

The disadvantage is a significantly delayed decay in the range below 1kHz. It seems that the Genelec models with the diffraction slot, in the range 100-1000Hz, need about one oscillation period longer to decay than comparable speakers - more details here.
However, I cannot assess whether this slowed-down decay is audible.

Indeed. Knowing Genelec, this was probably considered during design.

 

[stevenswall]

The major difference in effect is that the two oval woofers are slightly larger than what you'll typically find in a center-channel speaker with dual woofers and a concentric in the middle

I always though their drivers were smaller than similarly sized circular ones that would have more surface area (and fit in a taller cabinet.) Compared to some KEF speakers though, I suppose they might be close, and those are the only ones I know of that use coaxial drivers in an MTM (Or I think MMTMM, but I haven't seen that typed.)

 

[MrPeabody]

I always though their drivers were smaller than similarly sized circular ones that would have more surface area (and fit in a taller cabinet.) Compared to some KEF speakers though, I suppose they might be close, and those are the only ones I know of that use coaxial drivers in an MTM (Or I think MMTMM, but I haven't seen that typed.)

But what does "similarly sized" mean? To me it would mean the same effective diaphragm area. You mean (I think) circular drivers with diameter matching the larger diameter of the oval drivers. So yes, what you're saying is most certainly true in that sense. I had looked at the specs for the 8361A. The drivers are each 137 mm x 263 mm. I have no idea how strongly the corners are rounded, or whether their measurement is taken somewhere on the surround or all the way to the edge of the frame. If we assume that these measurements apply to the diaphragm, not the frame, then if the diaphragm were perfectly rectangular we'd get 36031 mm^2, or about 56 in^2. This would suggest it is roughly comparable to a woofer with actual diaphragm diameter of about 8.5", again with the assumption that Genelec's measurements are for the diaphragm itself. To compare this with the Kef R2c we have to make similar guesses, however with the Kef it is easier to make good estimates because we can see the woofer in the pictures and use the specs for the driver and for the enclosure and make comparisons. The 5.25" quoted by Kef does not seem to be the actual diaphragm diameter. Probably more like 4.5". It appears that the combined diaphragm area for both woofers in the R2c may be comparable to one of the two woofers in the 8361A if it happens that Genelec's specs are for the outer part of the frame. But of course the differences between these two speakers are so substantial that it makes little sense to even attempt a comparison of this sort. Suffice to say that the 8361A has the substantial advantage in this important metric. The R7 is potentially comparable to the 8361A in this respect, but probably not quite so.

I gave a little thought to the slot diffraction effect, i.e., the effect this has on directivity. Since the acoustic radiation pattern from the slot will be as though the radiation originated from the slot, the dispersion for each slot will likely be about as great at 500 Hz as at much lower frequency. This would presumably be beneficial in smooth directivity transition from woofer to midrange, if there were just one slot. But of course there are two slots, and the improved dispersion at the high end of the woofer's range likely is lost due to the interference/cancellation effect. So I doubt that the slot diffraction effect ends up being a significant effect when two slots are used this way. They may have intentionally wanted to use the D'Appolito effect to diminish dispersion at the upper end of the woofer range, but I'm inclined to doubt this as well, because the fundamental problem in getting smooth directivity match is that the woofer is generally too directional at the upper end of its range. I'm inclined to think that packaging is the true underlying motivation behind the design, and the reason that dual oval drivers are used is that this increases the total diaphragm surface area, as compared to a single circular driver that can fit on the same enclosure surface. Although, it does cause me to want to experiment with a speaker using a single woofer semi-enclosed in front using a tall slot with width maybe half the width of the woofer. Potentially this would make it possible to achieve good directivity match with a small-flange neo tweeter mounted directly on the slot opening.

 

[stevenswall]

^To clarify: Genelec's racetrack drivers are smaller than regular, circle shaped drivers with the same width/diameter. If one made a speaker with two circular drivers that were the same width of the Genelec, they would have about 40% more surface area. If a company used square drivers, they would an additional ~25% larger than the circular ones, totaling about 175% larger, with the same cabinet width.

I think the point is controlled directivity, not improving the bass vs one larger driver... If the goal was larger surface area drivers to improve the bass in a small package, they could put two 11" drivers on the sides, tilt two 8" drivers inside the cabinet, or have a massive racetrack driver on the back.