Low frequencies are often an issue for people. If you are using relatively small cabinets, getting enough sound pressure over a wide frequency range is often difficult without using stacks of speakers. Obviously, more or larger cabinets will give more output and potentially bass but how do you fit them in your Fiesta on the way to a gig? Do you want a single trip from the car to get playing or do you travel on public transport? Do you want light weight cabinets so your back is not at risk?
For the amateur “gigging” person, playing drums, keys or bass, it is often hard to get enough low end to be audible above the other players (guitars for instance often have very high efficiency speakers and huge midrange output but cannot push enough air to make effective bass).
With smaller cabinets you must have the following to generate low frequencies:
- A large cone area (Sd) to be relatively efficient and move enough air.
Multiple drivers can add significantly to cone area and two 8 Ohm drivers wired in parallel will give approximately 6 dB more output (3 dB from increased cone area and up to another 3 dB more due to the amplifier giving more output into 4 Ohms.
- A large X-max on the drivers so the volume of air moved can be large. This is the linear throw of the speaker cone combined with the Sd area gives the volume displaced, Vd. More air moved means more bass energy available. A single driver with twice the X-max of another driver of the same diameter could potentially mean using only a single driver instead of two, making boxes smaller, lighter and cheaper.
- Some form of porting such as a tube, slot, transmission line or passive radiator. (Horns too but not likely to be small!) All these methods use the rear wave of the speaker to enhance output over a certain frequency range and can add another 6 dB of output compared to an equivalent sealed box so mimicking two drivers. However, care needs to be taken on the tuning of the ports and their sizes if problems are to be avoided.
- A high enough power handling to cope with many Watts of power. This is because the bass level of a loudspeaker is often not directly related to the quoted sensitivity which is usually at 1 kHz. Ten times lower in frequency could mean ten times the power required…
So, what does LFS offer that is in addition to the above general rules?
LFS design cabinets for the specific frequency range required by the musician to maximise output and minimise distortion. The cabinets are designed with our CTL and CCL technology in mind, depending on application. Words to describe the cabinets character could be small, light, efficient, deep and powerful!
CTL (Compact Transmission Line) technology
CTL is incorporated in to most of our designs. This allows the rear wave of the loudspeaker to be emitted by a “port” over a wider frequency range than the usual single octave. If you port a speaker too high in frequency, it has punch but will have an excessive excursion at lower frequencies causing distortion and potentially mechanical damage. Tune the port too low and the upper bass causes the driver to move excessively and increases distortion.
The CTL technique combines two resonances on the rear side of the speaker drive unit via two different methods, one via the Helmholtz resonance like a reflex port (usually the lower frequency in smaller cabinets) and a quarter wave design as used in transmission lines for the higher resonance based on the path length from the rear of the driver to the box termination (but tapered). This can be achieved using only a single physical volume of air behind the driver (unlike double bass reflex designs which need at least two volumes) and mimic two different volumes depending on frequency as the inner part of the transmission line adapts to be “box volume” for the reflex resonance with the outer part being “port” but the entire line is used for the quarter wave resonance. Whilst the speaker impedance is kept relatively low due to the wide port output frequency range, it is more even and presents an easy amplifier load which is less reactive than most reflex designs.
Having the quarter wave resonance higher than usual, any potential cancellations are pushed up further in the frequency range where they are more easily controlled with light stuffing and don’t significantly affect the box output. The result is a much wider frequency range of cone control which minimises distortion and to some extent, reduces the need for such a large X max on the driver. They can therefore be made more efficient and obtained from suppliers more cheaply.
Thin walled construction makes for a light cabinet and the CTL internal baffling is not particularly complex but adds to the structural rigidity of the box significantly. Our prototype CTL10 cabinet was customised to hold a GK MB200 amplifier and uses a single Eminence Deltalite 10 speaker (or less expensive options) for an overall weight of well under 7 Kgs, a broadband sensitivity of 97 dB/W and 250W of power handling. (The weight is closer to 5.5 Kgs for the speaker without the built in amplifier). No other bass guitar cabinet “Ten” is as light or has this output and it can easily hang with a drummer.
CCL (Compact Cardioid Line) technology
The passive CCL technique maximises the front output compared to the rear. This “Cardioid” technique is ideal for Drummers who want the punch of the sound to be directed forward and minimising the rear radiation of the speaker. Bass tends to be “omni directional” from most passive loudspeakers and the mids are highs are directed forward. This often results in a boomy on stage sound which can become muddy and not clear. Sending the bass forwards and not backwards is an advantage which many top techs use in stage active systems to give the crowd the sound and not the musicians.
Not many people are using this as a passive technique so that no special amplification or digital processing is required. Just plug your speaker in as usual to your amplifier and more bass is sent forwards than backwards. The CCL effect can be optimised for a given frequency range as desired over at least an octave. Up to 10 dB difference between the front and rear radiation is achieved with similar low distortion as the CTL range due to multi-resonance control.
The method used in the CCL designs allow for a “delay” internally in the box through an acoustic low pass filter (tuned internal resistive port) so that the response of the rear passive radiator is delayed enough to match the sound travel time from the front loudspeaker to the rear of the box and reversed 180 degrees in phase. This creates a cancellation to the rear of the box and conversely, the output of the passive radiator over its frequency range then slightly assists the front output wave when projecting forwards. This type of speaker is also less likely to excite room modes offering a more even bass response and is less fussy about where it is placed.
The design is still currently under development but a working prototype with a single 8 inch driver has been made which is undergoing testing and weighs only 6 Kgs, 200 Watts power handling and 94 dB/W sensitivity. Where practicable, LFS will apply this technique to any speaker where it is desirable to have directional low frequencies.
CTL and CCL are patent pending and are published trademark designs to Low Frequency Solutions from 2011 and 2019 respectively. The CTL and CCL acronyms and design techniques belong to LFS and should not be used related to any other manufacturers product. However, if you are interested in using these techniques under a paid licence, please contact us click here.