Conventional loudspeakers use uniform pistonic behavior, whether it is a ubiquitous cone or dome; or some form of planar magnetic or electrostatic device; usually a ribbon or an electrostatic driver. The primary goal of the transducer engineer using a conventional design is to make sure the diaphragm does not have any anomalies, i.e. that it does not “break up” in its pass band. However, diaphragm break up is inevitable. The secondary goal is then to move the frequency of this break up as high as possible so that when it does occur, the cross-over filter has significantly reduced its level.
Tectonic uses a distributed mode loudspeaker (DML) technology which is designed to break up and not just move as a uniform piston. This break up, i.e. “modal behavior”, is very intentional and highly engineered to produce a “diffuse sound source” which correlates at the human ear.
The acoustic differences, both the traits and the benefits, are also fundamental. Conventional drivers are either a point-source or a line-source with fixed size radiators, and as such they “beam” (exhibit a narrowing pattern at higher frequencies) and have strong (destructive and constructive) interactions with room boundaries. DMLs are a diffuse sound source and are highly resistant to disruptive room interactions, especially within the human vocal range, i.e. they are highly intelligible despite bad acoustic spaces.
The bending waves in a DML panel are “dispersive” meaning that the bending wave speed varies with frequency. This ensures that the primary radiation center automatically adjusts its size to provide wide angle output well beyond that of an equivalently sized piston driver.
There are many other benefits from DML applications including high-resistance to microphone feedback, very low distortion, higher relative acoustic efficiencies, low drop-off front to back, a flat-form-factor, and more.
How do Tectonic DMLs generate the Sound Pressure Levels (SPL) of cone and dome drivers from a rigid panel?
Tectonic DML’s are physically bigger in area than conventional drivers. As an example, the Tectonic DML has approximately 3 times the area of a 12″ driver, therefore the DML’s total movement need only be one third of that to shift the same amount of air.
Imagine a 12-inch bass driver being driven quite hard so that it moves +/- 5mm back and forth. This will produce high SPLs. So we can ask; how much does a DML need to move to shift the same amount of air?
A Bit Deeper –
The radiating area of a 12″ driver is about 0.07m^2. The radiating area of the Tectonic DML is 0.583m x 0.406m = 0.237m^2. If the 12″ driver is moving +/- 5mm, a DML only needs to move +/- 1.5mm to shift the same volume of air. For the DML to produce the same SPL as the 12″ driver it only needs to move 0.07 / 0.237 = 0.3; about a third as much.
However, the surface of a DML does not usually move as a rigid piston and the comparison shown above is only true for low frequency operation of the DML. At higher frequencies the surface of a DML is undergoing complex vibrations with multiple regions moving with different phases, so the total net radiating area is reduced. But remember we are now no longer comparing a DML with a 12” bass driver because a 12″cone cannot radiate above a few hundred Hertz. In the mid-range, a conventional speaker system is likely to use one or two 3” drivers, each having a radiating area of around 0.005m^2. (Compression drivers / horns take over from there.)
Comparing these drivers with the radiating area of a DML (0.237m^2) we can see that this is equivalent to 0.237/0.005 = 52 midrange drivers! So even if not all of the radiating area of a DML is contributing to the on-axis output, there’s easily enough area to provide sufficient output.
Tectonic Plate’s superior intelligibility is a combination of several technical and performance characteristics:
- Tectonic plates generate virtually no 3rd-order harmonic distortion. Pistonic-based transducer designs – cone drivers, compression drivers and horns – by nature of their design – produce odd-order harmonic frequencies (distortion) that are near and can even exceed the amplitude of the original signal source at sound reinforcement output levels. Odd-order harmonics are both unpleasant sounding and mask intelligibility. Tectonic Plate odd-order harmonic distortion is so far below the original input signal as to be nearly immeasurable.
- The Tectonic DML has a nominal bandwidth of 80Hz – 6kHz. (A large-format ribbon transducer/wave guide takes over from there to above 20kHz.) There are no passive or active cross-over points in the DMLs critical vocal / instrument range that could introduce phase, frequency or delay errors. No external DSP or signal processing is required throughout the pass-band of a DML.
- The random and diffuse acoustic radiation characteristics of Tectonic Plates are minimally interactive with reflective room boundaries, thus secondary acoustic arrival reflections are not a correlated secondary sound source and do not decrease intelligibility by way of echoes or slap-back.
- Tectonic Plates create an extremely wide coverage pattern and very long throw, providing stereo or surround imaging to nearly every location in a given venue for nearly the same audio experience to all areas.
Collectively, these attributes provide a superior level of intelligibility over existing loudspeaker systems.
For all speakers in rooms there is a measurement called the Critical Distance. This is the point where the level of direct sound equals the level of the reverberant sound in the room.
The more directional a speaker is, the further away from the speaker the critical distance occurs. The critical distance changes from about 30” (75cm) for an omnidirectional source to over 6.6’ (2m) for a more directional one.
Traditional sound reinforcement speakers have always tried to avoid sending too much energy off to the sides, top and/or bottom of a venue because the waves from these speakers are phase coherent and they create unwanted reflections bouncing off the walls, floor etc., which obscures intelligibility.
Focusing coverage increases the critical distance, meaning that more of the audience is in a region where the sound falls with the square of distance. Putting the audience in such a region means that those at the front will experience significantly higher sound levels than those at the rear – this is not ideal.
Line arrays and steerable column loudspeaker systems, by design direct the audio energy only at the audience, as much as possible. The way that these systems increase throw is by increasing the relative volume of the speaker elements that are aimed at the farthest locations, e.g. the top boxes in a line array are receiving more relative power than the boxes located in the lower part of the “J” array. This allows similar sound levels reach the front and back audiences.
This is the opposite of how real instruments radiate sound into a room, so the effect is not natural.
Enter the DML:
DMLs have wide directivity and therefore give a much reduced critical distance. This means that after the first 3’ (1m) or so, the drop-off in level is closer to a linear slope. Basically the balance between the direct and reverberant fields is much smoother with an omni-directional source such as a DML.
In other words, as you walk away from a DML you are already almost certainly in the reverberant field (after the first 3’/1m or so) and so will experience a much slower drop off. The initial region (direct sound field) is less intense because the DML is radiating its sound over a wide angle, not ‘firing’ it in a specific direction like a traditional system.
The near omni-directional nature of DMLs would cause significant intelligibility problems if it wasn’t for the fact that DMLs are predominantly diffuse sources. This means that all the energy going into driving the reverberant field is not bouncing around and causing interference. It is actually doing what the sound from real instruments does.
Absolutely Yes, Kind Of and No
YES – Tectonic plates are extremely forgiving when it comes to room placement and coverage, minimizing room interaction and the need for room acoustic treatment. Installation and rigging needs are significantly less than required for line arrays and trapezoidal flown or ground-stacked enclosures.
The Tectonic Plates’ inherent feedback resistance, full band-width frequency response from 80Hz – 20kHz (including HF ribbon driver) and no complex DSP needs makes for minimal processor requirements. We have found, from extensive use of the Tectonic systems in a wide array of settings, that there is little house EQ needed to accommodate specific venues.
We currently recommend the Symetrix Radius for simple cross-over, limiting and system EQ tasks. That’s all the Tectonic system needs. (Note: The Tectonic system requires our own factory-locked settings for cross-over points and power protection. By-passing these settings will void the Tectonic Warranty.)
KIND OF – Tectonic Plates are highly resistant to feedback and allow for fairly extreme speaker placements and the flexibility to add open mics in front of the Plates. That having been said, some feedback situations can occur, requiring adjustments in staging and level management.
NO – The Tectonic system is merciless in representing the rest of the signal chain and any problems that may exist that other speaker system do not reveal. (Verified at several demonstrations in major venues where poor electronics, bad microphones, unknown DSP plug-ins, internal routing errors, word-clock issues etc. were discovered.) Please note: This is not bragging. It is a reality of a low distortion, revealing speaker system.
Furthermore, the traditional cues to the sound operator that the system is being pushed too hard are not generated by the Tectonic Plates. Typical symptoms include excessive 3rd-order harmonic distortion and voice coil bottoming-out. The Tectonic system cannot produce these effects, so the system just goes until it doesn’t.
Pointing an SPL meter at the Tectonic Plates is not an accurate measurement of excessive system output, as the DMLs are not producing a pistonic audio energy wave into the room; ie. not producing ‘Sound Presssure’ that a meter is expecting to measure. SPL meter readings of the Tectonic Plates typically read about 7dB less than actual system output.
We provide processor files for Symetrix, Lake, Rane, etc… system controllers that include limiting parameters to keep excessive system drive from occurring. That having been said, operator orientation is strongly advised.