At HH Acoustics we don’t regard a loudspeaker as a single item. Only by understanding the requirements and limitations of each part can we design the drive units that set our systems apart. Unlike most PA and MI companies, we have a long history of designing and building our own drivers, and working closely with component suppliers to get the very best from their process and our designs. A summary of the parts that make up a speaker, and some of the critical design issues is shown here.
the back of the loudspeaker. Not just an expensive and heavy lump of metal, the design of this part probably more than any other affects the efficiency and stability of the magnet assembly. It also has very significant effects in distortion mechanisms and voice coil temperature, which in turn affect thermal compression and power handling. The shape, the manufacture process used (and therefore the grain structure of the steel) all have affect how the yoke behaves. Using experience and Finite Element Analysis techniques we are able to optimise the flow of the magnetic circuit, avoiding saturation points and getting the best performance from the motor structure.
The driving force of the speaker, but magnets are available in a wide variety of specifications and sizes. Magnet weight alone (the most often quoted characteristic) has little meaning. We evaluate the sizes and material specifications to give the most efficient motor structure. This is also a situation where ‘more’ is not always better; we need a speaker to work perfectly in the size and type of cabinet we are designing, and every part is tailored to that application. Each type of magnetic material has different design requirements and ignorance of this leads to inefficient, wasteful assemblies, or inconvenient demagnetisation (or both !)
This (together with the yoke and magnet) completes the magnetic circuit. Too thin and it will saturate, losing efficiency and causing distortion. Too thick and the field will be too diffuse, with a loss of sensitivity and dynamics. The inside and outside diameters are critical too, with anything less than optimum compromising magnetic efficiency and stability, speaker sensitivity and power handling. A larger voice coil gap is much easier for production and quality control but it will not perform as well due to low magnetic field strength and poor heat dissipation. Make the gap too small however and the speaker will look great in the marketing spec, but will not last long in real world use.
Often these are chosen based on style and price. We choose chassis by more acoustic criteria. An inappropriate chassis will vibrate and flex in use, losing clarity and absorbing energy that should contribute to your sound. The shape of the chassis creates its own acoustic field too, like a cabinet or room. The wrong chassis will impose aspects of this field onto the loudspeakers own response, creating distortion and losing definition in your sound.
A coil is much more than wire wrapped around a former. If you cut through a coil and study it under a microscope (as we do) you find that consistency of winding tension, application of enamels and adhesives and wire composition can have very major effects on a coil performance. You can use the same specifications and wire but get coils that differ in efficiency and power rating by 50%, just by how you wind them and the choice of enamel and adhesive. We know how to wind coils, so we can work closely with our suppliers whether for round wire or flat (ribbon) wire coils to ensure we have a consistency and performance most companies cannot achieve. We also study the affect of different former materials, and select the best for any given application.
The suspension is often regarded as a pretty insignificant component, which serves only to keep the voice coil where it should be. Whilst this is its primary purpose, the suspension is a very significant part of the low frequency response and mechanical power handling of the speaker. Again, it’s easy to make a suspension that gives a great marketing spec, but if this adds distortion, has utterly changed its behaviour after a couple of hours of use and failed after a few more hours it is no good. The size, shape and material of a suspension are critical design factors to be balanced in design.
The cone is the biggest factor determining the frequency response and overall sound of the loudspeaker. It also suffers the greatest mechanical demands and so is a big influence on the power rating. The body of the cone can be made from an almost infinite variety of material and blends of materials, both man-made and natural, and then treated with a variety of resins and laquers in different concentrations. The combination of stiffness, weight, damping and resilience of these materials all need careful consideration in order to get the best acoustic performance. In addition to this, the shape or profile of the cone is also critical, For example a driver designed for a 2 way system will have a very different cone profile to a subwoofer.
Sometimes called the front suspension, the surround joins the cone to the chassis. Together with the suspension it controls the cone excursion, but also determines how energy travelling through the cone is absorbed, and how the speaker limits when it reaches the ends of its travel. Failing to get the surround right can lead to early mechanical failure, clearly audible distortion and unwanted peaks and dips in the response.
Although as the name suggests this keeps dust and dirt out of the voice coil, it becomes a part of the cone, having a direct effect on frequency response and cone behaviour. By bracing the cone it can encourage or discourage break up modes, which can cause the cone to tear if the wrong size or specification is used.
A huge variety of adhesives is available, with a vast range of prices and properties. Some require specialist application equipment or curing environments, some will work only in very specific applications. For any joint of a speaker, for example, cone neck fill or suspension neck fill shown above, we could name 3 or 4 glues that could be used, and tell you what the strengths and weaknesses of each are. We understand the effects of adhesives on acoustic performance as well as longevity, and we understand the costs and difficulties associated with using them in production.
Quality Control and Inspection
This starts as soon as the components arrive. Only by ensuring you have good components can you build good speakers, and only by ensuring your components always meet the design standards can you build consistently high performance speakers. Records are kept of every component delivery and trends monitored so supplier performance can be traced, tool wear can be seen and corrected before it affects performance, and potential problems spotted before they happen. Every driver is tested and inspected at the end of the production line before it goes to the cabinet line, and will be tested again in the final system.