There really was not a large amount of lab work to be done with this project. The things that I did that I would consider lab work was testing 5 speaker systems and going to a place that uses speakers and testing it's system. I also didn't learn a tremendous amount of new physics. I did however learn how physics that we have learned about applies in the realm of speakers. So although I didn't learn a lot of new physics, it was very interesting to see how it works with the speakers in things like the movement of the voice coil.

In my opinion, there was really 3 main goals. The first was to learn how speakers work. I had no knowledge of this going into the project and found some very interesting information. The second goal was to learn how to test speakers, and then doing it myself. This also proved interesting as I found out the quality of my speakers and the quality of the system at my church. Finally the third goal was to build quality speakers. This was my personal favorite part. I think that these three goals make up a fantastic audio project and the only thing that I would change is the tests. Possibly add a different test and give a choice between them, because the sound level test on 5 speakers gave me a very large headache.

The outside of the classroom component of this project was the building of the speakers. I went out to Meniscus Audio along with many of my classmates and we built our speakers there with the guidance of the guys who own it. I enjoyed this part immensely. The guys at Meniscus were extremely helpful, they were fun to be around and they stopped us from making any stupid mistakes, while not taking over the project and doing it themselves. The outside of class portion of this project is great.

I think that I deserve a 500/500 on this project. I spent a great deal of time taking notes on the books in class, and testing speakers out of class. I also worked my tail off building the highest quality speakers that I could in the price range that I had. I'm really happy with the way the speakers turned out, and I'm proud of the amount of work that I did on my notes. I did everything the project asked me to do, and I'm proud of the level of quality that I did it at, therefore I think that I deserve 100%

 

As you can see from the graph, the 3 best speakers were the JBL Creatures, the Ihome and the Bose SoundDock. They have the most consistently flat lines throughout the entire graph, meaning that they are the highest quality speakers. I knew that the Bose would be good because Bose makes all around good speakers. I wasn't sure about my JBL speakers because they seem like they might have been built aesthetically first and quality second, but I'm not surprised that they were good either. I was surprised however by how flat the Ihome line is. It doesn't even waver from 1,000 to 10,000 Hz. I was surprised because these speakers are built in to an alarm clock, and I assumed that they would be average because of that, but they proved themselves and are actually great speakers. The portable Sony speakers aren't a surprise because they are cheap little plastic things, so I had no expectations for those, and the Yamaha speakers are desktop computer speakers that are close to 15 years old, so frankly I'm surprised that they still even work.

My procedure for this test was very straightforward

1. Place decibel meter about a meter from the speakers

2. Play the 315 Hz tone and move the decibel meter or control the volume until it reads 85 Decibels

3. Start with 50 Hz and move up through each level on the CD

4. Record the Decibel level for each set

5. Repeat steps 1-4 for 5 sets of speakers

6. Graph the information

7. Email the chart and graph to my posterous

The first 3 pictures in the set show how the speaker are arranged at park church. There is 3 main speakers that are flying. Each one is aimed at a certain seating section. The next 3 pictures are looking out off of the stage just to give an idea of the size of the room. We drew a rough map of the sanctuary and then filled in decibel readings from a number of different spots around the room. This is how we found our dead spots. There is 4 main dead spots, the 2 hallways next to the stage, and 2 spots along the back walls, one on either side. The picture of the hallway shows that it is mainly used for storage of instruments and cases, so I wouldn't change anything there because nobody really uses it. The other dead spots are in the back as the pictures show. If I could change anything I would put some speakers up along the back wall and use them at lower volumes so that they improve the volume level in the back, but are not so loud that they are distracting.

A speaker works by setting up a magnetic field in the speaker in which the coil sits in, the current running through it makes the field build up and collapse in correlation with the frequency, making the cone move, which moves the air molecules, which creates sound waves.

Speaker selection is very important because it can greatly improve the quality of the music. It is more important to have a smoother response through a smaller range, than a peaked response in a greater range. In order to get good response from a frequency over 10,000 Hz, the speaker needs a cone lighter 5 grams, but it is not strong enough to move the amount of air required to get good bass, so it ends up bending and not working.

A good speaker also has a good transient response. This is the ability of the speaker to start moving the moment it gets the signal and stop moving the moment that the signal stops. The hangover of a speaker is how much it still moves after the signal stops.

The higher the frequency of a signal, the less dispersed the sound is. General rules are the a 12 inch speaker is omnidirectional to 1300 Hz, 8 inch to 2000 Hz, and 4 inch to 4000 Hz. This can be remedied by using whizzer cones.

The impedance of a speaker is the voice coil's resistance to current flow.

It is important to pay attention to the power rating of your system. This rating is the amount of power your speaker can handle without being damaged. In general, it is better to have a higher powered system.

It is also important to get the speaker polarity correct when connecting more than one speaker covering the same frequency in the same room. It is important to connect the positive lead to the positive terminal and vice versa. If the two speakers are not working correctly and canceling each other out, try switching the leads on one of the speakers.

A small system should consist of at least a woofer and a tweeter in order to cover the higher and lower range well, as opposed to a single driver system where it is designed to cover all ranges. This is because these single speaker systems do a poor job of covering the highs and lows, making a lower quality speaker.

When one is going to build speakers, the type of speaker enclosure that will be used is important. There is 2 major types of speaker enclosures. Closed Box enclosures are completely sealed and are simple to design and build. They have a purer "upper bass" and they tend to not overshoot as much. Ported boxes on the other hand have a hole in the back. This reduces the pressure on the box and gains a greater bass range. It is slightly more challenging but will be better if you are thinking long term and don't want to submit your box to a lot of pressure like the closed box system does. I plan on building a ported enclosure for mine, to reduce the pressure on the box and to get a greater range out of my woofer.

Crossovers are very important in a multi-speaker system, so that the drivers don't get fed the wrong frequencies and try to match them and then fail. They also assist when a combination of the woofer and tweeter is needed to match a middle frequency. They must work together to do this and the crossover also helps achieve this with little or no distortion.

Choosing speakers is mainly based upon the size of the room that you are using them in. Choosing speakers that are too big can be just as bad as choosing speakers that are too small. A general rule of thumb is that if the speakers look like the right size for the room you are using them in, then they probably are. Also, when choosing a position for your speakers, you should experiment to find the best areas. This is another reason for correctly sized speakers. Speakers that are too big limit the amount of places that they can go, and therefore ruin the acoustical potential that the speakers could have if they were correctly sized.

The most obvious way to test ones speakers is to listen to them. If they sound good then there's no need to mess with them. The test that we will be doing for this class is to check the sound level. The goal is to get as flat of a response line as possible. Other tests include polarity tests and damping tests.

For my project, I am going to somewhat follow the ported mini speaker project in the book. I am also planning on going to Meniscus Audio and using some of their expertise and advice in the area of speaker building in order to build the best possible speakers.

The piezoelectric effect is that some crystals can generate electricity when they are manipulated. As a driver they transmit high frequency ranges well but not well for mid to low frequency.

Electromagnetic motors are a motor with a diaphragm attached. When a direct current passes through the magnetic field created, it causes the coil to move and subsequently move the diaphragm, matching the audio signal waves and transferring them into sound.

Cone drivers are what most people associate with being a speaker. In a cone speaker, as the coil moves back and forth in the electromagnetic field, it moves the large flexible, usually paper diaphragm that in turn sets the molecule in motion. A cone driver is made of an electromagnetic motor, the diaphragm, the frame and basket, the spider and the surround. The surround is the folds around the outside of the speaker that allow the diaphragm to move. The gap in the middle is covered by a dome or dust cap, and the leads run from the connection terminals to the coil behind the dome.

Loudspeakers are more omnidirectional the larger the diameter of the speaker is. Also, as frequency rises, the directional ability narrows. This means that many people can hear the low bass, but only a few will hear the higher frequencies. Because of this, speakers must be tailored for their specific purpose.

Compression drivers are used more as a high frequency pitches because they have low mass and minimal movement.

Overlap of speaker waves is very important to consider when thinking about placement, especially in large concert settings. The idea is to get the largest audience coverage with the least amount of overlap. A 30° vertical angle of coverage works well, and 90° or 2 60° angles work well horizontally.

Speakers and subwoofers are always put in enclosures so that the sound only goes out the front and is blocked when the sound waves try to travel out the back. Sealed speakers are a problem because they create wasted energy that can knock the coil out of place, and the only way to remedy it is to make a heavier coil, making a heavier speaker.

Bass reflex speakers solve this problem by making putting a hole in the enclosure to allow the air to move out as the speaker cone moves. This hole also creates a tone of sorts when air moves across it, allowing it to be tuned.

Band pass speakers are like 2 bass reflex speakers put together. There is two ports, allowing them to be tuned to different tones, making it a louder speaker in a wider range. Because of this, it's louder and lighter. In order to create a full range system in a large scale, it will require several speakers to cover the entire range.

Basic Types of Equipment

There are essentially two types of audio equipment, transducers and signal processors.

Transducers change mechanical energy (audio) into electrical energy or the other way around. The human ear is an example of a transducer. In the audio world, examples of transducers are guitar pickups, mics, phono pickups that convert physical changes on a vinyl record onto electrical signals.

Output transducers work at the other end. An example of this is a loudspeaker.

Signal processors are anything that alter the electrical signal. Mixers are a big part of this, and an important part of any large concert or event.

Amplifiers transform the line level signals of a mixer and make them into the high level power that is need to drive the speakers.

  What is Sound?

Sound waves are translated into electrical waves when they are converted. We may alter the wave in some form but it is essentially the same wave. The electrical current fluctuates and is proportionate to the original sound wave.

Voltage is the force that causes the current to flow through and electrical circuit. Current is the flow of electrons. DC currents move in one single direction whereas AC currents switch directions of flow several times a second.

Power is the voltage multiplied by current and power measures the amount of work done.

Resistance allows us to use electrical current by impeding the flow when the voltage is too high for the thing being used.

There is 3 standard operating levels in audio. Mic level goes from no signal to -20 dBu (.0774 V). This level needs to be raised before it is workable. Some mics put out more but usually it stays around there. Line level begins at -20 dBu and goes to +30 dBu (24.5 V). It includes things such as synthesizers, keyboards etc. Speaker level is everything above +30 dBu, this is generally from speaker outputs of power amps.

sound is radiated in acoustical energy. It can be measured in acoustic watts but it is not a good measure because 1 acoustic watt is painful to hear but .000000000001 acoustic watts.

Sound pressure level measure the difference between the power of the sound at the source and the perceived loudness. 3 dB is the smallest change that most people can hear. 6 dB SPL is the first noticeable change in the perception of sound. 10 dB SPL most people hear as a doubling of loudness. to increase by 10 dB SPL you need to increase the power of your amp 10 times.

Volume is a very vague term. It describes the different ratios in sound, but you must be careful to specify which one your talking about. When talking about gain, most people assume that you are talking about transmission gain, the power increase of an audio signal. But gain can also be used to describe voltage gain. Gain is not volume however...a singer can sing louder and the volume will rise, but the gain will have not increased.

Loudness is generally the term that most people refer to as volume.

The dynamic range is the difference between the loudest and softest part of a program.

Sound is affected by factors such as where you are located and the temperature where you are. The hotter it is, the faster sound travels. Also, the more humid it is, the farther and faster sound travels.

If wind affects sound waves just like it affects a plane, a tailwind makes it move faster whereas a headwind slows it down. Wind can bend sound waves up or down, making them less perceptible from farther away.

When you are inside, there is all different things to deal with. Boundaries like walls floors and ceilings all absorb, reflect and even transmit sound in certain cases. Dr. Wallace Sabine developed the table of absorption coefficients. Sound reflects and reverberates around the enclosed space, combining which can lead to problems or a complete balance of sound in the room.

Critical distance is the spot at which the SPL of direct sound equals the SPL of the reverberant field at which point you get a 3 dB bump in SPL.

Spots in which parallel waves that are moving in opposite directions interact and create low and high areas known as nodes and antinodes.

The Sound Matrix

A vibration is the starting point of all sound. There must be a vibration in order for there to be sound. These vibrations set the air in motion allowing sound to travel to our ears

A transmission system is the system through which sound is output. All transmission system consist of a signal input, signal transfer/processing, and signal output.

Signal input is the point where one kind of energy (acoustic in the case of an electric guitar) is changed into another (electrical energy) in a process known as transduction. Microphones, pickups, etc. are examples of transducers.

Signal transfer/processing occurs once the sound has been converted into electrical energy. At this point it can be manipulated by electrical devices like mixers and amplifiers.

Signal output is transduction at the end, but this time converting the electrical energy back to acoustic energy.

The room in which you will be placing your speakers affects placement of speakers and even what mixers and amps one might use.

The audience at a concert is very important to take into consideration because they absorb sound and have an opinion about it. They can also affect where one should place the speakers and the volume one should play them at.

Air and its movement due to location, wind etc. will affect sound because sound travels through air.

The Purpose of a Sound System

The intended specific use of a sound system will dictate how it is put together.

Gain is what makes the sound louder.

Articulation through your sound system is very important because in every case, be it a song or a preacher, you must be able to hear their words clearly.

Effective Audio Distance (EAD) is the perceived distance between the man at the mic, and the audience member listening. Increasing sound level decreases perceived distance.

Sound level greatly effects the impact of the sound.

Special effects are a key component of a sound system.