Understanding and Calibrating Your System: Monitor Speakers
Welcome back my friends for another round of system calibration! In our last tutorial we covered basic acoustics, what goes into a good system, and good general system calibration that can work on any system. But now we need to take everything another step further. In today's tutorial we are going to look at a specific part of the system chain, the speaker.
Also available in this series:
- Understanding and Calibrating Your System: An Understanding
- Understanding and Calibrating Your System: Monitor Speakers
- Understanding and Calibrating Your System: Amplifiers
- Understanding and Calibrating Your System: Convertors
Our monitors are unarguably the most defining piece of gear for an audio engineer and we need to really understand how they work. In addition, we particularly need to understand how they handle the bass frequencies, as that range tends to be the most troublesome for most engineers.
So with all of that in mind, get ready to dive into the world of speakers and deep into the deep reaches of bass!
There are many ways in which speakers can be designed, and each design has their own pros and cons. If you have the luxury to do a shootout and compare speakers side by side then by all means you should do just that. However, while we as audio engineers and musicians normally only care about how they sound, having a working knowledge of speaker design can help us figure out, roughly, the sound of a speaker before even hearing it. This is particularly useful if you are looking for new speakers but have no way to 'try before you buy.'
Also keep in mind that while a particular speaker design may have certain characteristics, a little change here or there in design could lead to a huge change in sound; again nothing beats hearing the speaker for yourself! So with that in mind lets start by taking a look at a few typical speaker cabinet designs...
This type of basic speaker cabinet is what most other designs are based around. These designs at the most basic level are a box (either square or rectangular) with a driver (speaker cone) mounted in a hole in the box. The benefit of this type of speaker design comes in the ease of design, cheaper cost (most of the time) and predictability of frequency response.
Generally speaking, a closed style speaker cabinet will have an increased bass response as the size of the cabinet becomes larger and the driver (speaker cone) becomes larger; however there are practical limitations to this. The drawbacks of a typical closed cabinet however are that the frequency response tends to be irregular and not as accurate as one may think. If you remember the acoustics section of the previous tutorial, we discussed the frequency response issues of a square or rectangular room and these issues extend directly to a box style closed speaker cabinet.
One way to help alleviate some of the inherent issues in a closed speaker design is to add a vent or port to the box. The addition of a port primarily extends the bass response of the speaker cabinet by minimizing the inherent phase cancelations of bass frequencies (just like our square room). On small speakers and near field studio monitors you will almost always find a porthole to achieve that extend bass response you always see advertised by little 6-inch woofers.
However, some argue that by adding the port you risk skewing the frequency response and smoothing over transients creating a duller sound. There are however very high end ported speakers so take everything with a grain of salt!
Where most designs concern themselves with bass response, a horned system is most often concerned with the high end and high-mid range. While they do not directly amplify the output of the driver, a horned enclosure will create a greater efficiency between the driver and the air while at the same time controlling the dispersion of the sound.
While the horned system is perfectly applicable to the lower frequency ranges, the construction of such a system would require almost a whole wall in a room to properly effect bass frequencies.
While there are of course other designs and variations on these cabinets, you will most often come across these styles of speaker cabinet. There are other considerations however that should be taken into account with any of these cabinet designs. Here are some other things to keep in mind when analyzing a speaker cabinet.
- Rounded corners - The reason the box shaped speaker tends to have an inaccurate response is due to the flat parallel walls of the speaker itself. By rounding off the speaker you begin to minimize this effect. This is why some monitors go as a far as to severely round the speaker as much as possible. A great example of this comes from the SE Munro Egg 150 which is in fact egg shaped!
- Port Location - A common design practice to look for in ported speakers is where the port is located. While some argue nothing but a push of air comes out of the port, others say that it produces a subtle tone. Because of this possibility of a resonance at the port some argue that you should not have a rear facing port to avoid having the walls boost the resonance.
- Passive Radiators - A passive radiator system is essentially a modified ported speaker with a passive driver put in place of the port. Instead of acting from the amplifier, the passive radiator will react based on the air pressure changes inside the cabinet from the primary driver. This scheme, just like the ported, is used primarily to extend bass response.
- Internal Enclosures - Anther very important feature to look for is whether the drivers are internally enclosed from one another. As you add more than one driver to a given cabinet you start to induce phase cancellations and inter-modulation distortion from the drivers fighting one another for control of the air pressure; usually you end up with the lower pitched more powerful driver controlling the higher driver. To compensate for this, larger speaker towers will have internal enclosures for each driver to separate them from the other drivers. If you are unsure whether or not a cabinet is internally enclosed, gently press in the lower driver and see if the smaller driver moves from the air pressure changes.
While in the last section we covered basic speaker designs and cabinet enclosures, we did not directly analyze how these concepts play into full range systems. A full range system can take on many different shapes and sizes and varying levels of complexity. Assuming all the systems are full range (roughly 20 Hz - 25 kHz) and produce a frequency response that is as linear as possible, then there is nothing directly wrong with any of these systems. However certain systems will work better in certain rooms, under certain situations, etc.
So with that in mind let's take a look at some typical systems you will see for audio engineering...
These setups involve the use of two speaker towers that at bear minimum have at least three drivers each. The advantage to these large towers are that when they are properly designed, you will get a full range sound that is perfectly in phase and requires minimal fuss. Simply plug in your amplifier, make sure your stereo field is centered and you are good to go.
However, they can be expensive, heavy, take up a lot of space and hard to change around. In addition, you need enough space to be able to sit back away from them at a proper distance. But for those with minimalistic ideals and a medium sized room, a quality tower speaker systems provides full range sound with minimal fuss.
Nearfield and Sub
As we have discussed before most nearfield monitors usually will not provide true full range sound on their own but provide good sound in a small form factor. But one way to get the very bottom end of these systems is to include a subwoofer. This combination provides a big sound, a lower price point, and with minimal initial fuss.
However, the initial minimal fuss usually gives way to full on headaches as you begin to notice phase issues in the bass range. Despite what many say, bass frequencies are in fact directional and can be very prone to phasing problems when trying to align a sub and a pair of monitors.
Ideally you would in fact have two separate subs for stereo just like the tower system but using only one will still work. For those with smaller rooms and budgets the Nearfield and sub will work wonders.
While sometimes a combination of the above, there are some speakers specifically designed to be soffit mounted. Soffit mounted speakers that are mounted physically inside a wall and effectively mimic the idea of a speaker floating in space called an infinite baffle. They tend to be extremely accurate and are always full range.
However, they are very expensive, usually very large, and require you to modify or in most cases build a whole new wall which means they are here to stay. But if price and room size do not bother you, but hi fidelity does, these are the end alls.
So by now you should have a good idea of what goes into various speaker systems and hopefully have a nice full range system. However, managing the bass, even in a full system can be tricky to get right. Worse yet, trying to get it right in a system that doesn't have full range! But fear not there are some tricks to help yourself along for managing the bass in your mixes...
- The easiest way to handle the bass in any system is to listen to as much music on it as you can and learn the sound of the system itself and use that as your reference. When you know the sound of your system well, you should be able to mix on it, put on a comparable (same genre) hit song, and the two should sound very close to one another. The drawback then becomes that you will have a harder time adjusting when you move to a better system but beggars cannot be choosers!
- Some speaker systems simply do not have the bottom end required for accurate mixing. Generally there are two ways to obtain this extra bottom end. The first and most obvious way is to add an equalizer before the power amplifier in your system. You can then add the necessary bass or better yet, subtract level from the high end and then turn up the overall gain (subtractive equalizing). Your other option would be to place the speakers in the corner of a room as this will add significant bottom end build up.
However keep in mind you will probably induce major resonances at certain frequencies and can very easily skew your image. For those desperate to get some bass out of their system and do not have the funds to acquire more gear, this is probably your only option. With both of these tricks, keep in mind that you simply will not get that chest shaking bottom end of a kick on smaller speakers. You might get a very low tone, but to get that air moving sound you need drivers big enough to move that much air!
- Related to the above trick, if you find your mixes lacking bass seemingly every time you take a mix to a familiar place such as a car or friends house, turn down the bass on your system. Remember the name of the game as an audio engineer is translation. We need our mixes to translate well to any system and if time and time again your mix is lacking bass then your system has way too much. Vise verse if your mixes come out way too bass heavy then you need to add more bass to your system.
- Sometimes our systems are actually fairly accurate but the room we mix in is not. The issues you can have with standing waves and cancellations with bass frequencies in a square or rectangular room can be staggering; particularly in the corners of a room. A simple way to see how the bass is being distributed in your room is to play a simple sine wave sweep from your speakers and listen for a resonance build up. Every time you hear a build up then you know you need a bass trap that covers that frequency. While they can be expensive, they are worth the while. For those on a budget, I recommend looking up DIY IKEA bass traps.
Conclusion for Now
So where do we stand now after two tutorials? By now you should have a decent grasp of what goes into a good system, what different types of speakers designs we have to work with, and some tips for bass management in your mixes.
Next time we are going to take a good hard look at power amplifiers and convertors to round off our system so when the time is right you can put together a really top notch system! Thanks for reading.