Technology

The development process behind the Ono Paka was rather unusual and has resulted in a number of innovations and a rather sharp departure from the “old school” way of reproducing stereo sound. Our primary design goal can be summed up as:

Build a speaker with the sound stage and imaging of a large planar speaker that also has the dynamic qualities of a small monitor.

Turns out, that is harder than it may seem. Starting from the groundbreaking work of Siegfried Linkwitz, to whom we owe a huge debt of gratitude, we relentlessly looked for fault in our design and pushed to create an entirely new type of speaker with unique capabilities. Below is an overview of how we met and exceeded our design goals.

Radiation Pattern

While most speaker companies have pushed towards having one and only one wavefront count towards soundstage and imaging, it turns out that our brain is not wired to easily recreate depth from a single wave front. Our internal audio processing engine (gray matter) relies heavily on secondary reflections to add depth and realism to a stereo image. The most effective way to trick our brains into hearing depth is with a strong second wavefront that arrives at least 6ms after the first one. We build that second wavefront by projecting as much energy to the rear as the front (with dipole and omni layouts), and using the wall behind the speakers to create the reflection.

Dipole Full Range

The full range, open baffle, driver is the most important player in creating a deep and clear image. We mount the driver to a stiff steel superstructure and back it with a tubular diffuser (a Linkwitz Innovation) that helps create a rear radiation pattern that maintains our image while allowing for flexible placement of the speakers.

Omni Woofer

Below 1500hz, a cone driver is effectively omnidirectional. Since our woofer’s pass-band is well below that point, we are able to mount the woofer vertically, allowing for closer placement of the full range and woofer, as well as a clean way to get our rear radiation pattern without using multiple drivers or a much larger open woofer baffle.

Haas Effect Omni Tweeter

The placement of the larger drivers gives us correct time alignment on the first wave front from 65hz to 23khz. We discovered that augmenting the full range driver with a silk dome tweeter gave us a very smooth way of filling in the fine detail about 6khz. However, we also found that the compromises of mounting the tweeter in line (above or to the side) with the main drivers were problematic. They either destroyed the transparency (single tweeter) or were too grainy and forward (back to back or dipole tweeters). We discovered that by taking advantage of one of the core principles of the Haas effect (the brain groups multiple signals less than 2ms apart into a single signal), we could mount the tweeter in an acoustic lens configuration behind the main drivers and achieve an omni radiation pattern with a very smooth response while maintaining correct perceptual time alignment.    

Crossoverless Main Driver

Crossovers have long been a necessary evil in speaker design. Without crossovers, we would still be listening to Victrolas and single driver cabinets. Sadly, they introduce phase and distortion problems regardless of the quality of the components. Even active crossovers can introduce phase related distortion, even when trying to correct a phase misalignment. While we are not able to throw the idea of a crossover completely out the door, we are able to run our main driver without any inductors or capacitors between the amplifier and the driver (crossoverless). This gives us an overall clarity and phase correctness that is difficult or impossible to match using traditional designs. Our low and high pass filters (for the woofer and tweeter) are phase aligned and help create a cohesive and correct wave front.

Size

There is an ideal cone driver size for various frequency ranges based on our current state of materials science. That size is 10-15” for subwoofers, 6-6.5” for mid-woofers, 4” for midrange (or full range), and 1” for tweeter. If you go above or below this ideal range, you will quickly end up compromising the driver’s ability to do what it does best. Larger high end speakers tend to obey this rule but have to use multiple drivers to get the dynamic impact they are looking for. Along the way, they have to figure out, usually compromising on several fronts, how to time align and combine the wave fronts of these multiple drivers in a coherent way. The more drivers you have, the more difficult the task becomes. We believe that the qualities you gain by having single small drivers (detail, accuracy, realism) far outweigh the ability pin your ears against your head. We tune our speakers to be able to play for distortion free for long periods at the maximum volume humans can withstand without hearing damage, which works out to 104-106db at the ear.

Low Mass High Power    

One of the benefits of using smaller drivers is the ability to combine very low mass cones with large and powerful motors. The ability to quickly and accurately change directions allows us to render inner detail in a way that has seldom been approached. The down side cannot be ignored, however, which is the ability to render distortion in the source exceptionally well. Poorly mastered and compressed tracks will be immediately obvious.

Cabinet

While we only have a single 6” driver to contain, we took the structure and stiffness of our cabinet very seriously. The end result is a stiff, inert bass cabinet that does not introduce spurious vibrations into the room. The variable curved exterior has two purposes: First, curves (arches) are exceptionally strong for their size and weight. Second, the curve allows our reflected waveform to slip around the cabinet without hitting sharp distortion inducing planes.

Sealed vs Ported

A small ported enclosure can generate a decent amount of bass, but has several problematic areas. Most importantly, a ported enclosure introduces both phase distortion and group delay. Since we have worked so hard to have a time aligned system, allowing our bass driver to get all muddy from phase shift defeats the point. We opt for less clean bass instead of more muddy bass. Secondly, it can introduce room modes which make the placement of the speakers more fiddly. Finally, a small ported system is exceptionally difficult to get to have a flat response from 65hz to 650hz. Almost every ported enclosure has a distinct bump in their pass band that colors instruments in this key range. Some people call it warm….we call it wrong. To extend the bass all the way down below 17hz, we recommend supplementing the Pakas with a pair of sealed subs in the 10-15” range with a crossover point of 75hz - 100hz. A fourth order active crossover is preferred as well as phase correct.

Baffle

One of the largest challenges when building an open baffle system is controlling how the front and rear waves interact. Nulling in certain frequency bands is very common, and a problem we struggled with in our original designs. We ended up turning to some very non traditional designs and created a quick change baffle system that allows us to carefully tune the front and rear wave interaction to tailor the sound to the exact tone and acoustic size required by the application.
 

The Paka radiation pattern is carefully designed to have the strongest reflected wave (red) arrive 6ms or more after the first direct wave (blue). With the wide dispersion pattern of an open baffle cone driver the resulting sweet spot is very large.

Typical planar speakers have a very direct radiation pattern with steep off axis dropoff. Since room reflections are minimal and the reflected wave (red) can achieve the desired 6ms delay if placed far enough into the room, the imaging and realism can be excellent. It can be very challenging to get placement correct and the resulting sweet spot is typically very small.