Let’s talk about speakers and cabinets
For the purposes of this discussion, I want to focus on the speakers and cabinets that we encounter as guitarists and bassists as opposed to high fidelity equipment. A speaker, at this most basic level, accepts an electric current where this current is directed into a coil of wire in the presence of a magnetic field.
Speakers
The primary and most visible element is the diaphragm, a thin, usually cone-shaped membrane, often made from materials like paper, plastic, or metal. Attached to the diaphragm is the coil of wire known as the voice coil. This coil is positioned within the magnetic field created by a permanent magnet affixed to chassis that holds the diaphragm and voice coil.
When an electric current passes through the voice coil, it becomes an electromagnet. This coil interacts with the permanent magnet's field, generating a force according to Fleming's right-hand rule. John Fleming was an English electrical engineer who in addition to defining the right hand rule for electromagnetism in physics was also the designer of the first thermionic valve, what we call a vacuum tube. If you are a fan of tube based amplifiers, a word of thanks to Mr. Fleming is in order. As a result of this electromagnetic field generation, the voice coil experiences an upward or downward force, depending on the direction of the current. This movement of the voice coil causes the attached diaphragm to vibrate. Now you know why you can see the speaker’s diaphragm or cone move.
As the diaphragm vibrates, it compresses and rarifies the surrounding air, producing sound waves that we hear. The frequency of the electrical signal determines the frequency of the vibration, which in turn determines the pitch of the sound produced.
The diaphragm materials, the type and size of the magnet and the wire used in the voice coil all come together to define the sound characteristics of the speaker. The physical size of the speaker also impacts the sound. A speaker with a larger diaphragm does a better job at low frequencies while a speaker with a small diaphragm does a better job with high frequencies. If we step sideways and consider the traditional 3 way stereo loudspeaker, the big speaker we called the woofer and was focused on the bass. The middle sized speaker that we called the midrange focused on the midrange frequencies and the small speaker that we called the tweeter focused on the higher frequencies. A circuit called a crossover separated the incoming signal by frequency band and sent the appropriate signal to the appropriate speaker.
In a typical guitar or bass cabinet, we find one or more speakers, commonly of the same size, where the speaker is designed to deliver a specific frequency response from a low frequency to a higher frequency specified within a range of +- dB. As time has passed, technology has become more involved, including computational audio that can deliver improved frequency response out of smaller diagphragms.
In guitar speakers, we find traditional designs as small as 8 inches across to up to 12 inches across. In bass speakers, we typically saw a range between 10 inches across to 15 inches across. Musicians and sound engineers might mix different sized speakers or different design speakers to deliver a particular sound field.
With the advent of technology we can now get incredible sound out of very small speakers that in the past would have been considered horrible. Large companies such as MarkBass make bass speaker cabinets with smaller speakers that sound terrific and with computational audio, tools like the Spark GO deliver incredible sound from single very small speakers.
For the moment though, let’s constrain ourselves to the more traditional speaker implementations. For the purpose of examples only, I will use speakers from Celestion but we know the Electrovoice, Jensen and others are popular choices in speakers as well as those made for branding by cabinet makers from independent makers.
One way to increase loudness in a speaker is to increase the size of the magnet, but the size of the magnet is not the only thing that determines how much power a speaker can handle. Power handling is the composite of voice coil design, diaphragm material in addition to the mass of the magnet. A larger magnet simply increases the size of the magnetic field, which can be a very good thing. Magnets are commonly made of Alnico (an aluminum nickel cobalt alloy), Ceramic or the more recent Neodymium. Each magnet material influences the nature of the magnetic field. Neodymium is increasingly popular because it can generate a suitable field strength from a physically lighter magnet reducing the overall mass of the speaker.
The diaphragm’s job is to move air. While most diaphragms in guitar and bass speakers take the shape of a cone, planar speakers also do this. However because they look different, some people erroneously assume that they do not work as well. Different diaphragm materials also impact the sound. The diaphragm can be made of paper, metal, plastic or some combination thereof.
The voice coii size can influence how much power the speaker can handle as well as the frequency response. Thus we see that is the combination of the parts that determines a speaker’s sound. Much is made of the documented efficiency of a speaker. An inefficient speaker produces less volume measured at a distance of one meter with a specific input level than a more efficient speaker. Some pundits say that efficiency is critically important however physics teaches us that speaker efficiency is only about 1% of how power is used in a speaker as most of the incoming power is dissipated as heat.
Efficiency will be more important in terms of the volume heard than anything else as well as having impact on how we hear the sound. For example, the venerated Celestion Creamback has an efficiency of 96 dB while the Celestion Blue and Celestion Ruby speakers have an efficiency of 100 dB. This means it takes nearly 4 times the input on a Creamback to achieve the same value as in a Blue or Ruby. Higher efficiency speakers get louder, but may be difficult to control when lower volume levels are needed.
Speakers also are measured by impedance. Impedance is measured in ohms, the same as resistance. Both reflect the restriction on input of the signal to the device. However resistance is the methodology for measuring impact on DC current whereas impedance is the methodology for measuring impact on AC current. (Yes I know those phrases have redundancy - bear with me). The lower the impedance, the less resistant to input a speaker is. The critical thing here is to match the impedance of the speaker to the load that the amplifier output is expecting. Impedance mismatches can result in distortion to the destruction of the equipment. A Fender Twin Reverb has an effective impedance of 4 ohms, and this makes it louder than an amp delivering the same output into an 8 ohm speaker system.
Speaker Cabinets
Now let’s move on to the cabinet that contains the speaker or speakers. Cabinet design has massive impact on what you hear.
Loudspeakers are designed with enclosures to enhance performance. Enclosures provide a controlled environment for the movement of the diaphragm and help in managing the sound waves produced. They can be sealed or ported, each design affecting the speaker's bass response and overall efficiency.
A fundamental principle in cabinet design is enclosure type. Different enclosure designs, such as sealed, ported (or bass reflex), bandpass, transmission line, and horn-loaded cabinets, significantly impact the speaker's performance. Each type has its advantages and trade-offs in terms of bass response, efficiency, size, and frequency response. For instance, sealed enclosures provide accurate and tight bass but might lack efficiency compared to ported designs, which can produce louder bass at the expense of some accuracy.
The size and shape of the cabinet also influence sound reproduction. Larger cabinets tend to produce deeper bass due to increased internal air volume, while smaller cabinets might excel in midrange and high-frequency reproduction. This consideration shows why a 4x12 cabinet will sound quite different from a 1x12 cabinet even if the same speaker is used in each. Additionally, the shape and internal bracing of the cabinet can minimize unwanted vibrations and resonances that distort sound, ensuring cleaner audio output. Consider for example a speaker cabinet that uses internal baffles to manage sound reflections inside the cabinet
Material selection is another critical aspect. The choice of materials, such as solid wood, MDF (medium-density fiberboard), plywood, or specialized composites, affects the cabinet's structural integrity and acoustic properties. High-quality materials and proper construction techniques can minimize sound coloration caused by cabinet vibrations, resulting in more accurate sound reproduction. To make this simple, you don’t want the cabinet to be able to vibrate. You want it to remain immoveable.
Furthermore, cabinet damping and insulation play essential roles in controlling internal reflections and resonances. Strategic placement of damping materials like foam or fiberglass inside the cabinet helps absorb unwanted sound waves, reducing distortions and improving overall clarity. Take apart a really high end cabinet and you will find baffling and insulation although due to the limited frequency response requirements of guitar and bass cabinets, these additions tend to be rare.
The design should also consider the speaker's placement within the cabinet. Proper positioning and alignment of the drivers (woofers, tweeters, midrange) relative to each other and the cabinet walls impact phase coherence and dispersion characteristics, affecting the soundstage and imaging. This is particularly critical in bass cabinets that use different sized drivers to manipulate the sound stage effectively. Guitar cabinets tend to be simpler designs.
Moreover, advancements in computer modeling and simulation have revolutionized cabinet design. Engineers now utilize sophisticated software to optimize enclosure dimensions, port configurations, and internal acoustic treatments to achieve desired frequency responses and minimize distortions, ensuring a more accurate and enjoyable listening experience. These design considerations are felt more dramatically in high fidelity speaker systems but go a long way into building great sounding speaker cabinets in conjunction with computational audio.
Summary
So what do we learn from this? First that the speaker design and the cabinet design matter. They matter a lot. It also tells us that not all 2x12 cabinets are created equal, and that it is to our advantage to pair match the speaker to the cabinet. This is of course true for 1x12, 1x10, 4x12 and any other speaker and cabinet design. You choose the speaker system that best serves your desired tone, and that includes both the speaker(s) used and the cabinet design.
Buyers often wonder why separate heads and cabs are so much more expensive than a combo. A combo has to be a compromise by design. This does not mean that combos cannot sound great. The Fender Deluxe Reverb remains the most popular studio amplifier in the world and we are seeing more and more of these lower powered amps on stages as the volume delivery demands move from the amps to the PA systems. Indeed, it’s getting harder to sell big heavy 4x12 cabs every day. I look forward to the day when I can get an Ampeg 8x10 bass cabinet because the owner has decided the darn thing is just too big and heavy and will be happy to have me remove it at no charge. However, I am, in so many ways, an anomaly. The demands for separate heads and cabinets is often more an emotional thing than anything else, however there are prominent studio players who have racks of heads to achieve certain tones, where the cabinets are in sealed quiet locations. Look to videos by Tim Pierce or Pete Thorn to see examples of this.
The best way to buy an amp and speaker system is to audition it yourself, preferably in conditions like where you will play it. If you are playing in your furnished and carpeted living room or bedroom it’s going to sound way different than in a large open rehearsal hall with hard floors or in your unfinished basement. All that said, you cannot ignore the speaker system itself. I recently bought a small 1x8 Orange speaker cabinet to use with my Dave Kowalski 0.5 watt tube amp. The Kowalski had been used exclusively with a PRS 2x12 Stealth and sounded magnificent. That is a great speaker cabinet system. However, when I plugged it into the Orange cabinet, which I bought because it was very small, and because it was very cheap in a post Christmas sale, it sounded horrible. As I had destroyed the packaging, I could not return the cabinet so I opened it up. It contained the specified “Orange designed” 8 inch speaker. I removed that speaker that had a very small magnet and replaced it with a Celestion 8 inch speaker. The Celestion magnet was easily twice the mass of the original speaker. It’s still a too small wooden box with little room for air to move, but a different speaker has changed that system from being what I will politely call shit, into something that is usable. It’s still several light years away from an excellent 2x12, but I no longer want to puke if I use it.
Don’t like the sound of your combo? Consider changing the speakers. Don’t like the sound of your cabinet? Consider changing the speakers. It’s going to be cheaper than buying a replacement and might actually get you to where you want to be. Sadly the availability of speaker comparisons is limited in terms of ones that you can hear yourself, although Andertons Music Co, has done this a few times on their YouTube channel and you might find that content illuminating, although be aware that Youtube does massive audio compression and you should listen with good headphones or through proper hifi speakers.
Thank you as always for reading and your support. If you have not yet subscribed, please do so to be notified of new content. Please submit a comment or send in a question, I read and respond to all. I’m Ross Chevalier, and I wish you peace and good health.
