tbrattspeakers's posterous http://tbrattspeakers.posterous.com Most recent posts at tbrattspeakers's posterous posterous.com Tue, 18 May 2010 16:57:00 -0700 Speaker Building Part I http://tbrattspeakers.posterous.com/speaker-building-part-i http://tbrattspeakers.posterous.com/speaker-building-part-i

As you already know, the speakers that I am building are a pair of ported box speakers that consist of a woofer, a tweeter, and a crossover system. As I mentioned below, I am getting some help from the experts at Meniscus Audio in Grand Rapids. Today was the first of two or three days that I will be in the process of completing this speaker system. Today we got very many vital steps done in the building process.

After much confusion and frustration with traffic and construction in Grand Rapids, I finally was able to find this small company amidst about 15 other businesses in a large building. Upon arrival, I was given a quick tour of their building, and we began the process. To begin with, the first man that was helping me (I won't mention his name) told me which parts we would need in order to build the crossover, and then we went around collecting them from various trays around the room. Second, he taught me how to wind the inductors to use in our crossovers, and we each did one of them. We tested our inductors to make sure they were correct, and then assembly began. He showed me a diagram of how these crossovers needed to be wired up, and we completed the crossovers for the woofers and the tweeters together. After that, we needed to cut small wood panels to glue the cross overs to. After watching him complete one and explain to me why different parts went in different places, we carefully glued the crossovers together. Once the leads were attached and the sodering was done to short the negative leads, the crossovers were complete and had to dry overnight.

Because my work with the first man (the one who works more with the electronics aspect) was as far along as it could be, I met with the other man at Meniscus and began the process of building and assembling the boxes. He already had a wood (cherry) box/cabinet previously made, so all we had to do was cut the holes for the woofer and the tweeter. He first told me how far to measure in from the sides to mark with pencil where the wood needed to be drilled. After completing this task, he used a specifically designed tool to cut out the holes the exact size that I would need for my specific drivers. Because he didn't want me to use power tools, he did most of the cutting. Once he was done cutting, I sanded the inside of the holes and measured them to make sure they were correct, which they were. This was as far as we got during the first day. Because of school, I am not able to get to Meniscus until about 3:45 so I really only had about an hour and a half to work on it. We are waiting for the various glues to dry, and will be finishing the box/cabinet assembly as well as installing the crossovers next time I go in! All in all, a very successful first day.

 

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Mon, 17 May 2010 13:55:00 -0700 Speaker Test of a Public Place (Park Church) http://tbrattspeakers.posterous.com/18831147 http://tbrattspeakers.posterous.com/18831147

The goal of this experiment/test was to to go a public place that uses speakers, note where the speakers are, use a decibal meter to find dead spots, and think of what you would do to fix these dead spots. Because there are a not of easily accessible places for me to test, I went to Park Church with a friend of mine who knows how to run their system. I brought along with me the test CD and a decibal meter, and our procedure was very simple.

1. I played the 1,000 hertz frequency over the speakers

2. I placed the decibal meter about waist height and toward the stage of the sanctuary

3. I adjusted the decibal meter until I got an accurate reading

4. Repeated Steps 1-3 for about 25 locations around the sanctuary

Park Church was an ideal place for me to conduct this test because it is a perfect size room, not to big and not to small. Basically, there are three main speakers suspended from the ceiling above the stage, as shown in pictures 1-3. Because I couldn't take a picture of the entire sanctuary, I decided to drap a map and write down the decibal readings from the different locations I tested (the map is the last picture.) Quite honestly, the dead spots that I found didn't surprise me very much. The four main dead spots were along the walls far off to the side/back of the sanctuary and the two hallways that connect to the stage (there are pictures of the back walls and hallways posted above). It doesn't surprise me because with the way the sanctuary is shaped, they would need more speakers at different angles to convey the sound thoroughly. To fix the dead spots in the side/back walls of the church, I would maybe put two smaller speakers in the back corners. If they were angled correctly and not played very loud, they could easily fill those spots without interfeering with the speakers already in place. And as for the two hallways,  they are dead spots simply because they don't need sound in these hallways. They are for getting on and off the stage and those who are listening can't sit there anyway, so I wouldn't even worry about fixing them. One other dead spot that I did find interesting was a spot in the pews near a corner in the back of the sanctuary. The decibal readings in front and behind this spot were good, but I think I have a reason. I think that the reason the decibal reading further behind the dead spot is good only because it is near a corner where the sound can be somewhat tunnled downward.

My conclusion for the test is that Park Church has a very good audio system. The decibal readings around the church are very consistent in 95% of the places I tested, and the only dead spots were far off to the sides or back of the church where people wouldn't sit unless the rest of the sanctuary was full. One main thing I have learned from this test is how important the placement of speakers really is. This church was able to cover their entire sanctuary using only 3 (large, but still only 3) speakers! They get good sound almost everywhere and save money because they are aware of their speaker placement. Well done Park Church.

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Mon, 10 May 2010 07:16:00 -0700 Untitled http://tbrattspeakers.posterous.com/18397415 http://tbrattspeakers.posterous.com/18397415

Speaker Test.ods Download this file

 

This is a small addition to my latest post. I didn't change my procedure at all, I simply tested two more sets of speakers from two different vehicles at my house; my mom's Dodge Durange and my Mazda 3. The conclusions I made about the other three speaker systems still apply, so I will evaluate and compare the two systems from the cars to those tested in my house. To be honest, the results did not surprise me at all. All of the systems that I tested in my house consisted of only 2 speakers while the speaker systems in the car consist of 6 or mroe speakers. Because of the surround sound in the cars, the car speakers performed the best on the decibal test. They have the most consistently flat lines throughout the entire test. One thing that interested me was that both car systems had good results on the 50 Hz, I think that is because the systems have a lot mroe bass than those in my house. Also, the dodge durango had lower decibal readings than those taken in the Mazda, but I think that is because there is so much more open space in the durango. So all in all, the car speaker systems win, but that shouldn't really come as a surprise. They really should almost be in a different category.

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Sun, 09 May 2010 12:55:00 -0700 Untitled http://tbrattspeakers.posterous.com/18359080 http://tbrattspeakers.posterous.com/18359080

Speaker Test.ods Download this file

This was my home speaker test during which I learned how to use a decibal meter. I tested three kinds of speakers that I had at my house: A pair of Bose speakers that were connected to my home computer, an older pair of Aiwa speakers that my brother has, and my iHome. The goal of this test was to take decibal readings from the speakers when different tones were played. After graphing the speakers, the one with the flattest line will resemble the best speaker because you want a consistent decibal readings at different frequencies. Of the three that I tested, I had one pair of speakers that really surprised me and two that didn't at all. I knew that the Bose speakers would be good because they are top quality and expensive speakers. I also knew that they Aiwa speakers probably wouldn't be very good because they are cheaper and have been in my brothers room for atleast 5 years. However, I was somewhat surprised by my iHome speakers. These speakers are speakers put into an alarm clock that has an iPod dock. I didn't expect a whole lot from these speakers but they actually did a great job. If I had to rate the speakers after my test based on how consistently flat their lines are, it would be Bose at number one, followed by the iHome, and then the Aiwa speakers.

The procedure for my test was:

1. Start with the decibal meter about 1 meter from the speakers, then play the 315 hertz tone and adjust the volume until it read about 85 Db.

2. I started with 50 Hertz and played all of the tracks through 18,000 hertz, recording the Db reading for each.

3. I did these steps for all three of the systems.

4. I graphed my data.

5. I sent my graph to my posterous

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Thu, 06 May 2010 05:24:00 -0700 Speaker Construction plans http://tbrattspeakers.posterous.com/speaker-construction-plans http://tbrattspeakers.posterous.com/speaker-construction-plans

The requirements for this project state that I have to make my own set of speakers at the end of the semester. This couldn't be a better project requirement if you ask me. I get to put all of my learning into action, build awesome speakers that I will get to keep (and most likely use in college), and get credit for it! For the final part of my project, I have decided that I will follow Project 3 from the book "Designing, building, and testing your own speaker system." It is a ported-box mini speaker that is very similar to the one I had in mind. They are small but still produce a good amount of sound. They will be very portable and will not cost as much for me to build because the drivers and box are smaller. It is also nice bcause the drivers that the book suggests I use can be purchased from Meniscus Audio which is the company I plan on asking for help in my construction. Their vast knowledge on the topic of speakers will help me make mine much higher quality. And with the money I'm going to be spending on this project, I want the speakers to be the best possible.

I also need to do one other thing for this project, a speaker test of a public facility. I am taking the decibal meter and test CD home with me today and will have results and a post of my test on posterous soon!

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Fri, 30 Apr 2010 08:49:00 -0700 The Electrical Representation of Sound http://tbrattspeakers.posterous.com/the-electrical-representation-of-sound http://tbrattspeakers.posterous.com/the-electrical-representation-of-sound

Sound waves are converted from waves of air pressure to waves of electricity, and eventually back to acoustical energy. An audio signal is an electrical representation of a sound in the form of a fluctuating current. When a sound wave is translated from acoustical energy to electrical energy, it still is the same wave. The signal voltage/current fluctuates at the same rate as the acoustical energy and the signal level is proportionate to the amplitude of the original sound wave.

Four properties of electricity: Voltage, current, resistance, and power.

Voltage: Basically electrical pressure, it is hte force that causes the current to flow the the electronic circuit. Voltage is measured in volts (imagine that)

Current: Current is the flow of electrons from one atom to another. Metals and other materials with loosely bound electrons are called conductors, where as materials like rubber are called insulators. Current is measured in Amps. In a DC (Direct current) current, the electrons flow in only one direction; from negative to positive. AC (alternating current) current switches back from positive to negative many times a second. This current is very helpful in audio because the up and down behavior resembles the nature of the alternating compressions and rarefractions in sound waves.

Power: Power is voltage*current, and is measured in watts. It is the measurement of the amound of energy expended.

Resistance: Resistance allows us to use electrical current. It is how much material resists the flow when voltage is applied to the current. Conductors have little resistance, insulators have a lot. It is measured in Ohms.

 

 

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Tue, 27 Apr 2010 07:01:00 -0700 Designing, Building, and Testing Your Own Speaker System http://tbrattspeakers.posterous.com/designing-building-and-testing-your-own-speak-1 http://tbrattspeakers.posterous.com/designing-building-and-testing-your-own-speak-1

How a Speaker Works

There are many factors that go into selecting speakers for a speaker system. The first thing to take into consideration would be the frequency response. The biggest thing to remember about frequency response is that a system with a smoother response within a smaller range is better than one that has a larger range but peaks at certain frequency within its range. If you want to get good performance about 10,000 hertz, the cone has to be light. You don't want the mass to be greater than 5 grams, but as you get lower in the frequency range, the cone will bend. The key is that the cone needs to be big enough to produce good bass sound at lower frequencies, but it must be small for good dispersion at high frequencies. A heavier cone will have poorer tansient response and won't perform as well as the range gets higher. However, you can add a secondary cone to help solve this problem, and it is called a whizzer. It is driven by the same magnet and voice coil as the main cone.

Another factor to take into consideration is the speakers transient response. Transient response is a speakers ability to start moving right when it receives the signal from the amplifier, and then stop right when the signal ends. The extra movement of a speaker after the signal ends is called hangover.

"A speaker is omnidirectional only up to the frequency at which the effective cone diameter is equal to the wavelength of the sound. A speaker that is fully omnidirectional when: For a 12 inch speaker, to about 1,300 hertz, for an 8 inch speaker, to about 2,000 hertz, and for a 4 inch speaker, to about 4,000 hertz. If you want your speaker to perform at higher frequencies, you can use a whizzer cone. Sound is more directional at the upper end of their range of frequency.

The opposition of the voice coil to the current flow is called impedance. The restistance of a speakers voice coil is generally about 75% of it's impedance.

A speaker's efficiency is its ability to convert electrical energy into sound energy. Efficiency is sound power output (acousticl watts)/electrical power input(electrical watts). If youw ant to increase the efficiency of a speaker, you can reduce the cones resistance to movement, or you can increase the force of the voice coil. To make a cone less resistant to movement, the best thing to do is to make it lighter. If you divide it's mass in two, the speaker will be 4 times more efficent.

You will also want to take into consideration the power rating assigned to your speakers. Power rating is the amount of power the speaker can take without being damaged. Power ratings rise as the voice coils diameter rises. An amp or receiver with a high power rating is often safer because they can handle more power without being damaged. You have to be very considerate of it's power rating because if you biuld the speakers wrong and exceed the power they can handle, you will damage the speakers, and no one wants that.

Next is speaker polarity. If you are only using one speaker, it doesn't matter which lead goes to which terminal. However, if you have two speakers in the same room that cover the same frequencey range, they can cancel each other's sound. You want to make sure that the leads from the positive terminal go to the positive reciever, and the negative to the negative. You may have the problem of two speakers cancelling each other out. You will want to reverse the leads to one speaker and then test them by facing them. You only have to change the leads on one of the speakers.

A speaker system is made up of direct radiator speakers called drivers. Because single cone drivers struggle to cover large frequency ranges, a good speaker system often consists of two drivers, a woofer and a tweeter. The woofer is for lower frequencies and the tweeter is for higher frequencies. A woofer generally has a limited high frequency response, so the tweeter is added to cover the higher range, making a better quality speaker system. However, there is not a simple cut off line where it will switch from the woofer to the tweeter, there are mid-range frequencies that require a combination of both, so a crossover system is need. Crossover systems are very important because you don't want a driver to recieve the wrong frequencies and fail. If you want a good quality system, a crossover system is used with a woofer and a tweeter.

Kinds of Speaker Enclosures

There are really two types of speaker enclosures that are generally used for most stereo speaker systems, closed-box enclosures and ported-box enclosures. A closed-box speaker is when the speaker is installed and inclosed inside of a closed box. This type of enclosure is generally easy to build. The air in the box acts as a type of air spring. The air, because it is enclosed, acts like a spring against the cone. Closed box systems tend to have poor efficiency, but they do have a a higher bass range. Ported box enclosures are similar to closed-box enclosures, but they have a hole in the back of them. This hole provides somewhat of an air piston which reinforces and increases the range and sound of the bass output. There are other types of speaker enclosures you can make (labyrinths, horns, flat baffle), but considering the cost to build many of them, the complexity of them, and my limited knowledge/budget, closed-box enclosures and ported-box enclosures are the most appealing to me. I think that the closed-box enclosure would be easier for me to make, I think that the ported-box enclosure is the right one for me. It is easy enough for me to make but challenging enough that I will really have to think about what I am doing. The ported-box enclosure, in some cases, costs the same or less to build, and I think with less pressure in the box, the speakers will last longer.

 

 

 

 

 

 

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Tue, 20 Apr 2010 07:05:00 -0700 Learning Audio Basics http://tbrattspeakers.posterous.com/learning-audio-basics http://tbrattspeakers.posterous.com/learning-audio-basics

Audio is the range of acoustic vibrations that humans can hear as sound

Humans can generally hear a frequency range from 20 Hz to 20 kHz (1 Hz is 1 cycle per second)

Loudspeakers:

"An excellent loudspeaker will reproduce all musical pitches at the same loudness and with no significant differences in delay among the component frequencies."

SPL: Sound Pressure Level: Measure of the percieved loudness of a sound

3 Way Speaker: Uses a woofer, a midrange, and a tweeter. Divide audio energy into the system into 3 different frequency components, lows, mids, and highs

How a Speaker works:

Working parts of a dynamic speaker:

- Cone and its suspension

- Voice Coil

- Magnet

How it works:

"When an electric current flows through a wire, it sets up a magnetic field around that wire, and for a coiled wire the field is increased. If the coil of wire is located in an external magnetic field, provided by a magnet, the field of the coil interacts with that of the magnet to apply force to the coil. If the current is an alternating current, the field around the coil builds up and collapses in response to the frequencies of the current. In a speaker, this changing field interacts with the constand field of the magnet, causing the coil to move in response to the current. As the voice coil moves, it moves the cone, which creates pressure waves in the air near the cone. These pressure waves are heard as sound."

Sound Basics

All sound begins with a vibration. Vibrations set the air in motion. Every sound system is made up of three basic components, signal input, signal transfer and/or processing, and signal output. All of these components involve conversion points where energy is converted into another form of energy. With a sound system, the energy is generally converted from acoustical energy to electrical energy, and eventually back to acoustical energy. This is called transduction. All sound travels in waves. A sound wave is a chain of vibrating molecules. Energy waves must be transfered through matter, but it is only the energy that moves, not the matter. The molecules pass on the energy from one to another. A wave consists of a rise and fall of energy. Particles recieve the vibrations, and collide with other particles. After colliding, due to elasticity and inertia, the particles move back the same distance in the opposite direction; this is called rarefraction. The entire process creates a wave graph that looks like the sine graph. The amplitude is the height and depth of a sound wave. Sounds of higher amplitude are louder, compressing the air molecules more than those of lower amplitudes, softer sounds, do. Wavelength=Speed of sound/Frequency. Frequency is how many cycles pass a given point in one second. Generally, the higher the frequency of the sound waves, the higher the pitch.

 

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