We're approaching the end of this series of articles. I know that it seems very tedious - musicians tend to be the type of people who want to plug in and get a perfect sound. Sadly, it takes a lot of work to get the exact sound you are looking for. That's what this series was meant to do - explain some things while letting you experiment and find what works for you. If you've followed the series we've seen the differences between solid state and tube amplification, a more in depth look in amplifier tubes and their audio properties, new developments in solid state amplification, and now we're going to complete the picture with speakers and cabinets.
OK there are a few things we need to cover. A speaker basically converts an electrical signal into movement of a speaker cone to produce sound. The materials that make up an instrument speaker can definitely affect how it sounds. Often just changing the speakers in a cabinet will really change the sound as some are designed to produce more distortion and others are designed to be very clean and tight. In order to swap speakers you'll need to know what size speaker you have now as well as the impedance. Impedance is measured in ohms. General sizes for guitar speakers are 10" and 12" but speakers as small as 8" can be used and speakers as large as 15" can be found in a bass cabinet.
Finding Those Speakers
This is completely subjective. Its what sounds good to you that matters. Rather than just spending top dollar to copy your favorite guitarists sounds I suggest you go to a big box music store and try several cabinets. Often there is an area with used cabinets from different manufacturers - a great setup to try lots of different speakers. Take your smartphone with you and search the specs for each one. When you hit upon a cabinet you really like now its time to decide whether you should buy or perhaps you can upgrade a cabinet you already own with these speakers you like. I own a couple of cabinets - one more rock oriented and the other for clean sounds. The expense of buying new speakers actually surpassed finding the cleaner sounding cabinet used. Buying a used cabinet is as easy as playing sound through it to see if the speaker cones are good.
But what if you come across a deal on used speakers? Take a 9v battery with you. To test each speaker touch the terminals on the speakers with the battery terminals - you'll hear a sound and can even see the cone move on the speakers. If the cone is no good you'll hear a fluttering sound - a loose flap. Often the cone can separate from the magnet in a way that isn't visible. This isn't all doom though - speakers with bad cones can be had for a deal and then re-coned by pro. If you are very handy there are kits available to re-cone a speaker.
What Makes Speakers Different?
The basics on speaker design are the magnet, the cage or spider, and the cone. Different speaker magnet materials can create different qualities of sound. Alnico speakers tend to have a smoother less defined sound while other materials such as ceramic are preferred for a tighter sound. As long as a cage is straight and of sturdy design you won't see much change in sound - but often low end speakers skimp in cage design. Although very critical, the cone itself does not make as much of a difference in sound as the magnet. Cones can be thicker to handle higher power levels but often high power speakers' cones don't look different than low power speakers. This brings up the last design point - efficiency. The more efficient a speaker the cleaner its sound - less efficiency is a bonus for someone looking for more of a rock and roll tone. The classic rock sounds of the 60's and 70's were made with less efficient speakers like the Celestion V30 Greenback. As more distortion came on tap from newer amp designs less speaker distortion became desirable (actually these amps would drive the speakers into huge speaker distortion).
Does this mean speaker distortion is bad? Not at all - it all depends on what you are looking for. In the early days amps produced so little gain that guitarists would often resort to damaging their speakers on purpose by punching holes in them with pencils to get more speaker distortion. I don't recommend this - and imagine if those guys had any idea what those speakers would be worth today with complete cones? If you play a majority of clean sound you need a more efficient speaker - that is a higher dB rating. Want a looser warm sound - a lower dB rating is where you should start your search. Remember, even speakers of the same type and rating can sound a little different - its all part of the manufacturing process. Speaker size also plays a role. Smaller speakers tend to have faster response - that is why a 15" speaker can work well for bass - loose with slow response. But often bassists add a 4x10 cabinet to add fast response and clarity. One of the best cabinets I ever had used a 10" and 12" speaker. These two speakers really complemented each other well. The smaller speaker was a vintage design that drove into speaker distortion easily while the larger modern design cleaned up the overall sound.
Lets move onto cone materials. Older speakers are often referred to as paper speakers - their materials didn't change much since the first speaker designs. Later, as more powerful amps were built artificial materials that have a resemblance to rigid foam were used. One new trend is hemp cones - something pioneered by Tone Tubby. I saw an Eminence Canabis Rex speaker this last weekend which is also hemp. I'm very interested in hemp as it is a much thinner material that can handle high levels of shock. Tone Tubby swears by this material and I'm interested in picking one up soon to try out. That said I won't endorse any particular speaker brand. Celestion is the big brand in this market and they have several different offerings. But Eminence, Jensen, Sheffield, Electro Voice and many small manufacturers like Tone Tubby build great speakers also. Its all about what you are looking for in your sound.
Ideally, shopping for instrument speakers would be like shopping for car speakers. You'd go to a wall with different speakers installed, press a button to activate a different set, and pick the ones you like at the price point that works for you. Something like the picture I found on the internet I included in the article. Nothing could be further from this in the instrument world. There is a certain mystique manufacturers guard - often insisting that stores not place competing brands of speakers side by side. Hopefully knowing the size and efficiency you are looking for will get you started. You may have to visit a few different stores as often you'll find that stores will only carry one or two brands of competing speakers. This is when listening to YouTube videos can get you an idea what a speaker can do.
The most basic way to break down cabinets is whether they are open back or closed back. Closed cabinets tend to have more bass and more projection forward - they are louder if all other specs are the same than open back cabinets. Open back cabinets allow some of the sound to escape out the rear. This can create a smoother sound - less punchy. Volume levels can be lower but again this is a bonus if you want to raise your volume control up to get to the sweet sound in your tubes. Generally the more speakers in a cabinet the higher power rating it carries. As we are used to seeing walls of cabinets behind an artist at a concert we assume that is the best setup. Often, the best sounding cabinets are single speaker cabinets but again that's my ear talking. BTW - most of those cabinets you see in that concert situation are dummies - they aren't hooked up. Some bands don't even have speakers in those cabs - they are just for looks. The type of material used can change a cabinet's tone - solid pine vs. pine plywood vs. solid birch vs. birch ply. Birch ply is what is popular in higher end cabinets but pine cabs have a unique sound all their own. This is why I recommend you try a lot of different cabs and cab designs to see what you like. I don't recommend MDF cabs unless this is all your budget allows. Although very rigid MDF does not hold up to being dropped or exposed to moisture. In the end you may decide you like a cabinet but not the speakers in it. Unloaded cabinets can also be found if you find yourself in this predicament.
Hopefully this last step will help you get to that last bit of sound you were looking for. You should spend as much effort finding the right speakers/cabinet as you did your amp head. A great amp played through poorly picked speakers is a recipe for dissatisfaction. I've played lower end amps through a high end speaker setup and was blown away how good they can sound - if you are going to err I'd say err this way. You can hold onto that great cabinet as you upgrade your amp head. Another last idea is that you can mix different speakers in a cabinet - a popular mix is to put two modern speakers in a cabinet with two vintage style speakers. Another is one modern and one vintage speaker. Often the sum of the sound is better than the sound that each speaker can make on its own.