What Is The Best Material For Speaker Enclosures?

Speaker enclosures play a critical role in the performance of a loudspeaker system. They are designed to prevent sound waves produced from the back of the speaker driver from cancelling out the sound waves from the front. Enclosures also help control the behavior of the driver and can modify the frequency response. A well-designed enclosure enhances the low frequency performance of the driver and prevents distortion.

The material used for speaker enclosures impacts several acoustic properties including density, stiffness, resonance and damping. These factors determine how well the enclosure controls unwanted vibrations and resonance. The ideal material will rigidly support the speaker driver while damping any unwanted cabinet vibrations. It should also be designed with the optimal volume and porting for the speaker driver. The right enclosure material paired with a properly designed cabinet ensures the speaker driver performs optimally.

Acoustic Properties

One of the most important acoustic properties to consider when choosing speaker enclosure materials is sound absorption. Sound absorption refers to how effectively a material can absorb sound energy rather than reflect it. Materials with good sound absorption properties help prevent unwanted reflections inside the speaker enclosure that can cause resonance and distortion. Some key factors that impact sound absorption are:

Density – Materials with higher density, like MDF or concrete, reflect more sound. Lower density materials, like wood or fiberboard, absorb more sound. According to a study by Song et al., sound absorption generally improves as density decreases (https://www.mdpi.com/1996-1944/16/18/6089).

Porosity – Materials with more open pores or perforations absorb sound better by allowing the sound waves to penetrate into the material. Adding custom perforations to panels is an effective way to increase porosity for absorption (https://www.mdpi.com/2071-1050/15/21/15230).

Thickness – Increasing the thickness of a material provides more opportunity for sound to be dissipated as it passes through. Thus, thicker materials generally have higher absorption coefficients.

In summary, lower density materials with porous, perforated, or irregular surfaces that have sufficient thickness will provide the best sound absorption inside speaker enclosures.

Density

The density of a material affects its vibration damping properties. Materials with higher density generally provide better damping, as the mass is more effective at absorbing vibrational energy. Metals like steel and lead tend to have high densities and make good damping materials (Chung, 2001).

Density relates to a material’s mass per unit volume. More mass means more inertia, which resists vibration. Denser materials require more energy to oscillate, and this energy gets dissipated as heat instead of sustaining vibrations (Ecomass, Technicon Acoustics). Materials with higher density can thus damp vibrations more effectively.

However, density alone does not determine damping ability. The material must also have good internal friction, or viscoelasticity, to convert the vibrational energy into heat. So both high density and high viscoelasticity make the best damping materials.

Stiffness

When choosing an enclosure material, stiffness is an essential property to consider. A speaker enclosure needs to be rigid enough to minimize vibrations and reduce unwanted resonances inside the box. Internal standing waves can be created when sound waves reflect off the walls of the enclosure. These standing waves can distort the speaker’s sound if the enclosure walls vibrate too much.

Rigid, stiff materials help reduce vibrations and ensure the enclosure holds its shape under the pressure of the speaker’s movement. Materials like MDF, birch plywood, and high-density plastics tend to have good stiffness properties for enclosures. According to one study, the stiffness of the enclosure material affects the deflection and performance of speaker components. Using sufficiently rigid materials can improve sound accuracy and definition.

Enclosure panels made of dense, stiff materials will have fewer issues with standing waves. The rigid walls limit resonances so the sound coming from the drivers and ports is cleaner and less colored. Stiffness is therefore a key acoustic property to evaluate when selecting speaker enclosure materials.

Cost

When building speaker enclosures, cost is an important consideration for many hobbyists and enthusiasts. The main material costs come from the wood used for the cabinet itself. Typical options like MDF, plywood, and solid wood can range greatly in price depending on thickness, quality, and type of wood. According to sources, basic materials for a single DIY speaker cabinet can be as low as $5-10 for cheaper plywood up to $50-100 for thicker, higher-grade MDF or more exotic wood species.

Other costs include damping materials, veneers, binding posts, wiring, and hardware, which can add $20-50+ to the total price. Ready-to-assemble flat pack cabinets are available which can reduce labor costs. Overall, building your own speaker boxes allows significant cost savings over pre-built commercial options. With smart design choices and budget-friendly materials, high quality, custom speaker enclosures are achievable at a fraction of the cost of retail speakers.

Workability

The ease of construction is an important consideration when choosing speaker enclosure materials. Hand building enclosures from wood panels requires carpentry skills and tools like saws, routers, drills, sanders, clamps etc. This can be time consuming and challenging to get precise joins and smooth surfaces. In contrast, using a CNC machine to construct wood or MDF enclosures is much easier and faster. The CNC can accurately cut panel pieces and joinery, eliminating the need for lots of manual labor. As discussed on the DIY Audio forum, “CNC milling entire periphery of each panel (and all joints, etc), certainly makes for well fitting assembly.” (source)

CNC also helps when working with more difficult materials like aluminum or acrylic. As noted by a speaker builder on Inventables, “Before my CNC-days I built a set of Line Source (LS) speakers utilizing decent quality drivers with a low price tag.” But without CNC, working with aluminum panels would have been “an absolute nightmare.” (source) So CNC makes complex and precision construction much more feasible.

Appearance

The visual aesthetics of speaker enclosures should not be overlooked, as they can have a significant impact on the overall look and feel of a home audio system. Many audiophiles prefer to have speakers that blend in seamlessly with their décor rather than stand out. The material, finish, and style of the enclosure all play a role in the appearance.

Wood remains the most popular enclosure material for aesthetics. Real wood veneers like cherry, walnut, and oak allow speakers to double as decorative furniture pieces. Wood can be stained, painted, or finished in a variety of ways to achieve the desired look. High-gloss piano finishes are prized for their luxurious shine. More rustic styles like bamboo or reclaimed wood offer an earthy character. According to discussions on AudioHeritage.org, speaker enclosure finishes can add to the overall aesthetic impact of a system when well matched.

However, wood is not the only option. Many manufacturers offer speakers with enclosures made of metal, plastic, glass, stone, concrete, and other materials that allow for eye-catching styles. Ultimately, the enclosure material and finish should complement the room’s décor.

Environmental Factors

The environment where the speakers will be used is an important consideration when selecting enclosure materials. Speakers used outdoors need to withstand heat, humidity, and potential water exposure from rain or sprinklers.

Wood enclosures can warp or crack when exposed to moisture and temperature swings. Marine-grade plywood is a good option for outdoor use as it is designed to resist rotting and withstand humidity. According to a thread on Reddit, marine grade plywood sealed with a shellac primer and protective outer finish makes a good outdoor speaker enclosure material (source).

Plastic composite materials like High Density Polyethylene (HDPE) are naturally waterproof and can stand up to outdoor conditions well. Aluminum is another enclosure option that resists rusting and withstands humidity and sprinklers.

Proper sealing and weatherproofing is important for any outdoor speaker enclosure to prevent water damage and mildew. Enclosure design should allow for drainage and include gaskets, sealed seams, and weather-resistant speaker components.

Weight

When choosing an enclosure material, weight is an important consideration especially when portability is a priority. Heavier enclosures can be cumbersome to move and transport. Using lighter materials can help reduce overall weight while still providing sufficient acoustic properties.

Some lighter weight options to consider are fiberboard, acrylic, and aircraft-grade plywood. These materials weigh less than traditional wood enclosures, with acrylic being one of the lightest options. According to one audiophile discussion, even a 100% birch plywood enclosure with two 12” drivers weighed around 90 lbs, quite heavy for portability.

The tradeoff with lighter materials is potentially less rigidity and natural damping. Extra bracing or strategically placed mass weights can help improve stiffness without overly increasing weight. The enclosure design, size, bracing, and drivers themselves also factor into the overall heft.

When using lighter materials, it’s recommended to focus enclosure design on the mid and high frequencies which are less affected. The low end may lose some impact, but the improved portability can make lightweight enclosures worthwhile for many applications.

Conclusion

In summary, the key factors to consider when choosing the best material for speaker enclosures are acoustic properties like density and stiffness, cost, workability, appearance, and environmental factors like weight. Based on weighing all of these factors, the best overall material for most speaker enclosure applications is 18mm plywood. Plywood offers a good balance of acoustic properties like density and stiffness, while also being cost-effective, easy to work with, and relatively lightweight compared to materials like MDF or concrete. While other exotic materials like aluminum and composites can provide benefits, standard plywood delivers the best combination of acoustic performance, cost, workability and practicality for typical speaker box fabrication.