Lambda Labs professional acoustics


General questions General technical questions TX-1A TX-2A TX-3A CX-1A & CX-1B CX-2A CX-3A MF-15A DH-18

Which advantages do hornsubwoofers provide?

The first goal of a well developed horn loaded cabinet is a signifficantly larger power efficiency compared to a direct radiating loudspeaker. For a given amplifier power a higher acoustically output could be anticipated.

The vibrating cone and especially the resonant mechanical mass-spring system of the driver is acoustically loaded furthermore, which decreases the Q factor and leads to a highly accurate impulse reproduction.

For high and usual compression in the inside of a horn loaded subwoofer, non-linear distortion of second order (K2) occurs at high levels due to sound propagation in the adiabatic gas. This distortion factor is in the range of a single digit even on the maximum deliverable sound pressure level. The human ear can hardly percept second order distortions of this magnitude and is particularly impervious for low frequencies moreover. In addition to that, K2 isn’t rated as disadvantageous or unfavorable.

Concurrently, cone excursion is reduced due to the high acoustical load in the inside of the horn, and even more a higher sound pressure level could be achieved with a given cone displacement compared to a direct radiating system. With an ingenious choice of incorporating driver and horn enclosure a very high output can be obtained. Harmonic distortion of third order (K3) and disturbing higher order distortions as well as intermodulation distortion are reduced drastically. A natural and breathtaking dynamically sound reinforcement is the outcome of well developed horn loaded cabinets.

How do hornloaded subwoofers work?

Hornsubwoofers are engineered to maximize efficiency. That concludes a well energy conversion from the electrical into the acoustical domain and requires a high grade of acoustical adaptation between the vibrating diaphragm to the surrounding air. A direct radiating diaphragm for yielding an optimum power transfer without horn in this low frequency range would require a surface area that is difficult to manufacture and even worse to transport.

The radiation impedane of a flat isophase diaphragm mounted on an infinite baffle is approximately maximized for a value k * rm >= 1. The wave number k is derived from Lambda/2π and rm is given as the diaphragm radius. To achieve a very high efficiency for frequencies down to below 30Hz the cone diameter would need to have a diameter of 2 meters.

In the case of an acoustical transformator as a horn loaded loudspeaker represent, an provoked pressure on the horn throath emerges an acoustic wave, caused by eleoctromagnetic force coupled to the diaphragm. This wave is traveling along the horn path and is radiated reflexion free to the free space.

Only an ideal hornsubwoofer would have a perfect adaptation with reflexion free termination. An appropirate largely sized exponention horn comes close these requirements. But apart from several meters of horn path, the demand for the hornmouth is a diameter of 2 meters as well.

To gain a physically large horn mouth, several hornsubwoofers of the same type with small mouth could be stacked close to each other. Horn loaded cabinets which can deliver the full low end also in single mode operation are very well desired in practice. That is not the common case for most horn loaded subwoofer and not a matter of course. Especially for the usage in Cardioid, Tooth Gap or Phased Array application the performance of a single mode operation optimized hornloaded cabinet is vastly superior. It takes a lot of technical effort to tune and tweak a single compact size horn cabinet for the very low freqency transmission.

Which construction principle is behind the DH-18?

That is a complicated question and is maybe not to answer with a common textbook principle. The DH-18 takes advantage from both acoustically radiating sides of the diaphragm, and is in its general idea a rear loaded horn. Maybe not completely, because the general so called back loaded horn principle does not make use of discrete horn segments, nor would the horn mouth area for a flat frequency response down to below 30Hz be appropriately large enough.

The DH-18 makes extensive use of an effect, which is also used in transmission lines. It uses the acoustically Lambda/4 longitudinal wave, as organ pipes does as well. In larger stacks this effect decreases and gets substituted through an excellent reflection free acoustically radiation impedance. This approach guarantees the comprehensive usability with low corner frequency in single mode operation.

The rear of the driver is located in the inside of the enclosure, similar to a tapped horn. In this application with the essential goal to use the airflow as an efficient cooling mechanism for high power handling during operation. Furthermore this arrangement is demanded by mechanical needs to access both modes of operation easily. A tapped horn by theory makes use of sound traveling backward into the horn and requires a horn segment after the tap point. For the DH-18 the rear of the driver is located directly at the hornmoth indeed. Even for a textbook designed back loaded horn there is a reverse traveling wave. Simulations have shown, that this effect is neglectable for both a rear loaded horn and the Digitalhorn. Furthermore the backward traveling wave is reflected and prevented in its propagation to the inside of the horn by the discrete horn segments. This is to avoid excitation of resonances of undesired propagation paths.

The transflex principle from the mid of last century uses a transmission line effect with a very low corner frequency and a conjunction of both, direct sound and the horn path sound, directly at the horn mouth. For very low frequencies the transflex and the DH-18 are related to each other, because the discrete segments are seen as continous contour, as the spatial expansion of the resulting propagation wave is large enough. The transflex does not take advantage of discrete elements, thus the transmission bandwith is fairly restricted.

At this point the DH-18 comes into play with new ideas and contemporary nummerical simulation methods. For rising frequencies, the DH-18 has an exact and well controlled reflection pattern in the inside of the horn, which increases the upper frequency limit drastically. Due to specific suppression and spreading out longitudinal waves, the frequency response extends upwards resulting in a pass band of 2 full octaves. Because for a back loaded horn both diaphragm sides are acoustically radiating into space, destructive interferences occur at higher frequencies. It was the goal to fulfill performance specifications and not to subordinate to a certain design principle. By means of elaborated calculations, the frequency response was desired to be flat even outside the transmission band to about 200Hz. This optimization allows an easy and smooth crossover in the transition band to the high-mid range loudspakers.

The name Digitalhorn explains the principle of a back loaded horn with deliberated placed discontinuities inside the hornpath to supress interference phenomena and attain a flat response within the operational bandwidth and beyond. Even with still reduced bandwith compared to a proper designed front loaded horn, the outcome is extremely high efficiency down to the infasonic frequency range and in addition to that an extreme high power handling capability because of excellent heat dissipation.

Why did we choose the name Digitalhorn?

The naming describes the inner pathway of the horn construction quite well. The shape doesn’t follow a continuous and constant function as otherwise customary, but rather shows cross sectional discontinuities. These cross sections are calculated nummerical and placed in defined position to extend the transmission bandwidth of the horn loaded subwoofer and makes the upper frequency band easy to handle. Annoying resonances within the the operational range are consequently suppressed at their origin.

These exactly placed cross sectional discontinuities simplify equalization above the crossover frequency and guarantee a uniform maximum sound pressure level. Because of the systematically optimization and placement of discontinuities, the Digitalhorn achieve besides its very low corner frequency an incredible impulsive bass performance even in the upper frequency band.

Not least the type designation of the DH-18 accounts for the mechanical adaptability in one of two different operational modes.

Which mode of operation should I use with the DH-18?

Almost like a chameleon, the Digitalhorn adapts to mechanical and acoustical demands with just two clicks. With the switch of the changing flap, the hornpath and therefore the lower corner frequency changes. Depending on the choice, maximized Efficiency in the Directivity Mode (D-Mode) with a corner frequency of 30Hz and a pronounced sound steering or the Space Mode (S-Mode) with infra sonic experience down to 28Hz and that even in single mode operation.

In small stacks of 4 to 8 horns, the high directivity with long throw and desired rear attenuation in D-Mode is often a favorable argument. For high crossover frequencies in combination with larger arrays, it could be useful to change to S-Mode to avoid excessive directivity.

Why and when should I prefer basshorns over direct radiators?

Conventional direct radiating systems (especially vented and closed box) are the principles of choice for a compact transport size. High acoustic power densitiy can be reached even with these direct radiators, if the space requirement is on first priority. Horn loaded subwoofers requires a minimum size to incorporate the sophisticated horn pathway.

If one considers state of the art horns by Lambda Labs, a remarkable low corner frequency combined with particular high sensitivity can be found. The high efficiency saves valueable ressoures and above all expensive amplifier power.

The acoustical benefits are in our focus nonetheless. Horn loaded systems attain high radiation impedances, because of the velocity transformation principle. Due to this appropriate acoustic coupling the vibrating diaphragm is much better damped than in direct radiating systems. Acoustically low damped Helmholtz resonators does not find application in our horn subwoofers. Thus the resulting impulse response gains an incredible precision when reproducing transient music signals.