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   freds sound advice newsletterg

 Tweak Your System 
 Keeping Power Amps Cool 
 Sound Pressure Meter 
 Room Tuning 
 Home Theater Surround Speaker Design 

 Why Speakers Fail 

 The Speaker Audition 

 The Speaker Break-in 
 Home Theater Speaker Set-Up 
 Stereo System Set-up 

 

 

Tweek Your System, Small Things To Improve Sound

 

Update your speaker wire and inter-connect cables. Remember, thicker is not always better! Quality not quantity. Also, bi-wire your speakers whenever possible.

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Spike your speakers, it will tighten the bass and improve imaging. Use of speaker stands for small speakers to position them closer to ear level will greatly improve clarity.

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Test your stereo or home theater system for proper phasing. We can help you with that.

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Reduce vibration, cushion those components that react to vibration such as disc players and turntables. You can also isolate the entire audio cabinet or rack.

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Turntables, To many of us, our favorite component, is the ever lasting turntable and with a little attention your turntable will still be the favorite component in your system. So check the tonearm for proper weight. Check the stylus for wear. Keep your needle and records clean. Basic adjustments to your tonearm are complimentary at our store and we carry all the supplies for your audio video system including cleaners, cables, cartridges and needles.

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Clean your compact discs. The optical system in your CD and DVD player will not make up for dirt and scratches so take care of those discs. Soft cloth and mild non-abrasive liquid cleaner should do the job.

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Optimum speaker balance of all speakers. Using a sound pressure meter like the one described in this newsletter will do wonders for best sound positioning and precision stage pin-pointing for stereo and home theater systems. We offer a free loaner of a sound level pressure meter for your system at home. Please see Fred's Sound Of Music for details, read information below and view the PDF for further information.

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Sound meter radio shack 33-2050

 

Sound Pressure Level Meter

View information on our free Sound Meter rental at Fred's (pdf) and details of what the sound meter will do for you

 

 

The sound pressure level meter from Radio Shack 33-2050 is an awesome tool for measuring sound levels in your listening room. It is an indispensable aid when optimizing loudspeaker and listening positions and it allows audiophiles to quickly measure sound levels to ensure they are within safe levels. It is truly an essential audiophile accessory. Instruction Manual.
The Radio Shack sound pressure level meter is a small hand-held device for measuring the pressure level of a sound wave in an acoustic environment such as your listening room. The meter can be used to measure sound pressures in the range 50-126dB. This is accomplished through the use of an analogue display which ranges from -10dB to +6dB and a rotary dial that allows you to select one of seven ranges centered at 60dB, 70dB, 80dB, 90dB, 100dB, 110dB and 120dB. The dial also has a setting called 'BATT' that can be used for testing the meter's internal 9V battery.
Aside from a dial for range selection and an analogue display, the meter consists of a front-mounted microphone and two switches for changing the meter's frequency response or "weighting", and the speed of its response to sound pressure changes. The weighting switch allows for switching between the standard 'A' and 'C' weightings. Choosing the 'C' weighting will make the meter respond more-or-less uniformly over the frequency range from 32 - 10,000 Hz, and the 'A' weighting will make the meter more sensitive to frequencies in the range 500-10,000 Hz. The response switch allows for changing the speed of the meter's response from 'SLOW' to 'FAST'. Finally, the meter is equipped with a phono-type output jack for connection to other measuring equipment, and a standard threaded socket for tripod mounting. Mounting the meter atop a tripod is recommended in order to avoid reflections off of your body which can alter measurements by more than 2dB.
When setting up loudspeakers in a listening room, the ultimate goal is to choose loudspeaker and listener positions such that sound pressure levels are fairly constant over the audible frequency range. The first step in using the meter for loudspeaker placement is to pick a starting location for your loudspeakers and listening seat. Don't worry about the initial placement too much since you'll most likely be changing it radically once you start measuring. Pick initial locations such that your speakers are equidistant from the side walls, and your listening position is centered between the loudspeakers. If you're not using a tripod, try to stand to the side of the meter to reduce reflections from your body that might affect your measurements. Play pink noise and adjust the volume of your system so that the meter reads 0dB (which means that the sound pressure level at the meter's location is 80dB since the meter's dial is set to 80dB). Be sure to leave your system's volume control at this level so that subsequent measurements can be meaningfully compared to the pressure at this volume level as you rotate the sound meter. For each test tone, jot down the tone's frequency and the meter's reading at that frequency. When you're done measuring the sound pressure level for each test tone, you will have a set of measurements of frequency vs. sound pressure level. In other words, you will have the data for a frequency response graph of your room, given the current loudspeaker and listener locations. Fred's Sound Of Music has one of these meters for you to rent.

   
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 Why Speakers Fail:

 

Despite the best of engineering, the selection of the best drivers and the most careful production and quality control techniques, loudspeakers can still fail.  The purpose of this article is to identify some of the causes of such problems so that they can be avoided and your loudspeaker system can continue to deliver the quality sonic performance that was intended.     Fewer than 1% of high-end speakers in the field ever fail or cause trouble for their owners.  There are two reasons for this excellent record.  Quality loudspeakers have always used relatively “high-order” crossovers.  This improves the crossover’s control over the drivers’ performance within each operating range, turning each driver off quickly outside of its band.  This control keeps a tweeter from attempting to reproduce midrange frequencies, and a midrange from trying to handle lower frequencies (tasks which neither driver is designed to perform).  Gentle or “low order” crossovers, a current audio fad, place extreme demands on the power handling capabilities of drivers, and sharply increase distortion, a sign of protest from the drivers.  Consequently, these two deficiencies sharply increase the prospect of the driver eventually degrading or failing.  Most high quality speakers protect against these problems even further by always choosing crossover frequencies very carefully, and using only the highest quality drivers.

Speaker Misuse #1: Too Much Power
The first reason for speaker failure is the most obvious: playing any speaker at excessive levels can damage it.  If any distortion is audible, the volume is too loud and likely to cause damage.  But in some cases distortion may not be noticeable before damage occurs.  For example, home loudspeakers can easily reproduce the real dynamic range of live acoustic music; but no high quality speakers can reproduce the brutal levels of a rock concert.  Low fidelity PA speakers should be used if this is your goal.
Caution: prolonged exposure to high sound pressure levels can permanently damage your hearing.  Moreover, your hearing adapts to high volumes, allowing you to incorrectly feel that potentially damaging volumes are normal.  Protect your hearing as well as your investment in high quality loudspeakers by avoiding excessive playback levels.
The average audiophile mistakenly believes that the position of the volume control provides some indication of the percentage of output power the amplifier is delivering at the time.  This is not true; in fact, most systems are clipping with the volume control set around “one o’clock.”  Preamp/receiver designers probably set these levels so that less sophisticated buyers will be impressed by their product’s power (I’ve only got the control set half-way and it plays this loud.”)  Additionally, and not surprising, many audiophiles believe that the “power meters” on their amplifiers or receivers can be used to avoid clipping.  Unfortunately this is not so.  The meters used on amps are only decorative and cannot show actual power levels since they can only be calibrated to one impedance.  Actual speaker impedance varies with frequency, it might be 20 ohm at 40 HZ and 4 ohm at 150 HZ, and yet be rated at 8 ohm!  A very small number of power amplifiers have clipping indicators that actually do what they say.  If your amplifier has this capacity, it will be made clear in the instruction manual.  To guard against clipping, ask your dealer for guidance, or keep your volume control below “twelve o’clock” on the dial.
 

  

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The effects of too much power are either burned voice coils, deformed voice coil formers, loose voice coil windings, or lead-in wire fatigue.  The first three effects are the result of excessive heat.  More than 95% of the amplifier’s power is converted to heat in the voice coils.  A burned voice coil results when the wire has actually melted. click

Most voice coils are wound on aluminum bobbins to improve heat dissipation and cooling.  Unfortunately, when aluminum is heated to the point of deforming, it does not return to exactly its original shape.  The result can be a “rubbing driver” where the former touches the “pole piece” during its operation.  (The pole piece is a cylindrical piece of metal which, together with the magnet of the speaker, forms the magnetic gap in which the voice coil moves.)  While most high-end drivers use high temperature adhesives, excessive heat can still melt the adhesive enough to free turns of the coil.  This results in a rattling sound as these loose turns hit the pole piece.  Stop by our store, we’ll show you these parts.

We are all familiar with the concept of metal fatigue.  This occurs when a piece of metal is bent back and forth so far and so many times that it eventually breaks.  This can also occur in drivers which are overpowered.  Since woofers and midranges use “tinsel leads” or special heavy-duty wires attached to the voice coil, they don’t fail this way.  But tweeters use a very thin voice coil wire to attach the voice coil to the terminals.  Excessive power can break those leads.  This is one of the causes for the “after-the-party syndrome,” where the speaker was working at high volume levels, and then quit the next day at low levels.  The actual damage was done at the high levels, but then the wire finally broke at levels that would not normally cause any damage.

Speaker Misuse #2: Too Little Power
The second cause of speaker failure may be surprising: too little power can destroy drivers, especially tweeters.  To see why, we can look at two musical waveforms below:

Non-Clipping Sine Waves On Left         And Sine Waves With Amplifier Clipping
If we take music and reproduce it at a level greater than the amplifier is capable of, we get something like the one on the right with the amplifier clipping.  Now the signal is looking more like a group of square waves rather than smooth rolling sine waves.  Square waves contain large amounts of high frequency information, and can destroy tweeters.  In this situation, clipping in the midrange creates large amounts of high frequency energy which damages the tweeter.  This is one of the reasons we look for high maximum amplifier power ratings: they will assure that musical peaks are not clipped and so turned into potentially damaging square waves. 

 

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Speaker Misuse #3: Defective Sources 
Some tweeter failures are also caused by defective associated components.  CD players, tuners, tape decks, preamps, receivers, or power amplifiers  can “oscillate,” or produce inaudible high frequency signals that can destroy tweeters  These same components can also produce direct current (DC), which is especially damaging to woofers.  Not even the most expensive and exotic components are immune to these potential defects.  If your speaker has become damaged for no apparent reason, it may be that a piece of associated equipment is at fault.  Enlist the assistance of your dealer in troubleshooting your system.  Most audio dealers can easily test your components for these two problems.

Summary: Your high-end loudspeaker has been carefully designed to provide years of consistent, superior  performance.  In the unlikely event that you do require service, you can give us a call directly or by email.  We are unique in the world in providing this level of service.  Our goal is your continued satisfaction, and we work hard to make this happen. To maximize your enjoyment of these speakers over the years and, even more significantly, to avoid damaging them, please implement the cautionary suggestions outlined in our newsletter.  Be sure to use an amplifier sufficiently powerful to reach the volume level you desire.  Feel confident to reproduce live acoustic levels (given a powerful enough amplifier), but avoid live rock concert levels.  If you have any doubt as to whether your current amplifier is sufficiently powerful, or would like to learn more about this subject, we encourage you to contact us, Fred’s Sound Of Music (503)234-5341

 

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HOME THEATER SURROUNDS: BIPOLAR & DIPOLAR

Emerging to the forefront of stereo and home theater surround speaker technology have been two diverse designs of speaker systems called bipolar and dipolar.  These speakers look similar from the outside with two complete sets of drivers, one set on the front and the other set on the rear.  But each speaker system functions differently.
The BIPOLAR speakers front and back drivers move at the same time with the music and are used as your main speakers in stereo and your front right/left speakers in a home theater system.  The front output sound provides direct information that is crucial to detail, focus and localization.  The radiated output from the rear of the speakers provide reflected information that creates added spatial realism.  A well designed bipolar speaker will give you a 3-D sound without losing the main focus of exact placement of the sound of instruments, singing, dialogue and movie sound track pin pointing.

The DIPOLAR speakers on the other hand have come into existence primarily within the home theater realm.  Surround speakers have slowly moved from the back or rear of the seating area to directly on the sides of the listener.  At the same time, the sound of the surround speakers has been diffused and non-focused using dipolar speakers.  Unlike the bipolar speaker, the dipole surround speaker fires information both to the front and back at opposing times of each other, reflecting off the walls and into the room.  Since the front and back of this speaker are out of phase of each other, the surround speaker has a null or cancellation zone within the movie viewing area.  Thus, the focus of sound transcends forward to the movie screen with the surround speakers enveloping the listening area.

  

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ROOM TUNING:

Sound is vibration and in a room these vibrations will tend to gather against, and move along the large, uninterrupted flat surfaces such as the walls and ceilings.  When these wall and ceiling surfaces meet at the corners and seams of the room, acoustic pressure builds.
The most important of these “pressure zones” are the upper corners of the room, where three of these flat surfaces will build pressure, which is then reflected back into the room with a horn-loading effect. Usage of acoustic treatments can be demonstrated in our sound rooms.  And at the same time we can help you with your own room at home so you can achieve the best sound possible from your stereo or home theater system.Home Theater systems’ sound performance is not just placing the speakers at the proper position and angle.  Reducing or eliminating reflective sounds in the room for pin-point sound accuracy is most critical for the “Best Theater Performance”.

 

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HOW TO SET-UP A STEREO SYSTEM:

Buying the correct components for your individual needs is just the first step in reaching your goal of owning a fine stereo system.

Speaker placement:

This is probably the most important aspect of setup. Without optimizing the speaker's position in relation to the room and your seating area, it will never perform to its full potential. Both speakers should be placed along the same wall, facing your listening position. Ideally, they should be separated from one another by at least six feet, and probably no more than ten. Speakers too close together can sound "cramped," too far apart and they lose a tight center image. If your floor is carpeted and spikes were included with your floorstanding speakers, they should most definitely be used. The spikes (points go down) will couple the speakers to the floor, making them more stable and generally improve the quality of bass. This is one of the easiest ways to improve the sound of any speaker. Smaller speakers need to be elevated so that the top of the speaker is 30 to 40 inches from the floor. Solid speaker stands (with spikes) are recommended. The room boundaries are an important consideration. Your speakers should be positioned out from the rear and side walls at least 12 to 18 inches. If the speakers are too close to the side walls, imaging will suffer. Moving a speaker closer to the rear wall reinforces bass, but soundstage depth will probably be hindered. Speakers like to have some breathing room around them .  If you stuff your speakers into a tight spot between pieces of furniture, their imaging and sound quality will suffer. The optimum position for a speaker's placement is rarely in the first spot they're placed. Trial and error is the only way to determine where the speakers will sound the best, but the rewards are well worth the effort.

 

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Component placement:
The equipment stand is a surprisingly important part of any home stereo system. Beyond aesthetics alone, there is performance and convenience to consider. "Open-air" cabinets with no doors, sides, or backs are generally the best choice. Because there are no sides to interfere with the sound waves these cabinets are nearly "invisible" to your speakers. The open-air design lets the equipment run cooler and allows very easy access to the rear of components. Metal stands, with their weight and density, tend to perform better than wooden stands. Large wood entertainment centers look good and are very popular but they severely compromise the system. These wall-units reflect a large portion of your speakers sound, restrict ventilation and cable access, and totally ignore vibration. Remember, vibration is detrimental to sound reproduction. The more vibration you can control, the better. Many of the open-air cabinets use floor spikes and shelf spikes to reduce vibration.

Cables:

Interconnect cables are used to transfer audio (and video) signals between components. It is extremely important to use good quality brand name interconnects if you want your system to sound as good as it can. The free cables that came with your CD player, VCR, or amplifier should not be used but replaced with a cable that matches the quality of your components. The difference in picture and sound can be substantial. We can recommend cables that are appropriate for your system. As a general rule, your system will be properly balanced if your speaker and interconnect cables total 5% to 10% of the cost of your stereo system. Your system will only sound as good as its weakest link, and for many people, that is their speaker cables. If you are using cheap or thrown-in speaker cables, replace them with a brand name audiophile cable. These speaker cables come in two basic types, one of which should be well suited to your system. The first type is braided (multiple-stranded) cable. A heavy braided cable made with hundreds of strands of oxygen-free copper will be a large improvement over the thin "lamp cord" you may be using.The second type of speaker cable is a design called single strand. These cables are made of solid core copper or silver, and each strand may be individually insulated to prevent interference from adjoining strands. These designs tend to be a little more expensive and are very popular with audiophiles. AUDIOQUEST is a highly respected manufacturer of this type of cable. Compared to the braided cables, you can usually expect better high frequency response, midrange clarity, bass definition, and imaging. If your front speakers are capable of being "bi-wired" you should do so. We will help you select the bi-wire speaker cable that is right for your system. Look for four (or more) speaker wire connectors on the back of your speakers instead of the usual two.

 

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Surge suppression:

Just like computers, audio systems are highly susceptible to damage from power surges, voltage fluctuations, and lightning. At the very least you should protect your valuable system with a high quality surge protector. Be prepared to spend a little money for this. The truth is, the cheap $20 models at discount stores are nowhere near adequate. Depending on your individual system, you may be vulnerable to surges from electrical outlets, roof antennas, cable TV lines, satellite dishes, and phone lines. If what you want is a good basic surge protector, we will be happy to recommend a great brand or model that is right for your system. Beyond simple surge protection there is line conditioning. A line conditioner purifies the electricity that runs your system. Electrical power leaves the plant clean but becomes polluted (with electro-magnetic and radio frequency interference) along the way to your house. The result is a dramatic drop off in the picture quality of your television, and a serious reduction in the sound quality of your stereo system. Line conditioners remove this interference and improve the performance of every TV and every audio system. They also protect your valuable system from harmful power surges and voltage spikes.


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HOME THEATER SPEAKER SET-UP:

A home theater needs at least six speakers: left front, right front, center front, two surrounds, and a subwoofer or bass module. For a Dolby Digital system, all speakers except the subwoofer should be capable of a full range of sound and be fairly equal in quality and performance.The left front, right front and center speakers carry the bulk of the music and sound effects in a home theater. These speakers should be high quality and able to handle a wide range of sounds. The center speaker is the primary carrier of dialogue and should therefore be the same quality as the left and right front speakers. Ideally, it should be the exact same speaker, or at least matched in quality and power.  Placement of this speaker may be best right on top or directly below the video screen. For some home theater systems, the surround speakers can be smaller in size because they do not need to carry the booming bass. The surround speakers should be as close as possible in sound quality and balance as the front speakers for an even sound.  We do recommend the same speaker driver ensemble as the fronts for Dolby Digital.  Subwoofers reproduce the low bass sounds that make movie effects like explosions, sonic booms, crashes, and dinosaur footsteps seem realistic. These are the sounds that really pull you into the experience.  A good subwoofer, preferably a powered subwoofer, is needed for a full effect.Any speaker placed within 2' of the conventional crt television needs to be magnetically shielded to avoid video signal breakups and picture distortion not to mention picture tube damage.  In most cases flat screen TV’s do not have this problem.

 

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THE SPEAKER AUDITION:

When auditioning speakers you should always listen to music even if you are going to use them in a home theater system. Music is a much better measure of quality than movies. Music is harder to accurately reproduce and much easier to focus on. We know of many speakers that sound good for movies and sound terrible for music. Visa-Versa, we don't know of any that sound good for music and terrible for movies. When you are shopping for speakers for home theater, audition front speakers only. Find the fronts you like the best and then match them with a center and rear. Almost all front speakers made today have matching front and rear speakers from the same manufacturer. Speaker manufacturers will have timbre matched front, center and rear speakers. They will generally use the same style of enclosure, crossover components, and most importantly the same drivers. This insures they will be timbre matched (same tonal balance). If you don't have speakers that are timbre matched you have a chance of having a mismatched system. For instance a car panning across the front speakers. The car sounds like a Ferrari in the left front, and then it moves across to the center speaker. It now sounds like a Porsche 911 in the center speaker. Then it moves back to the right speaker and the sound changes back to the original Ferrari. When shopping for any component it is best to bring a few CD's that you are familiar with.  If you are shopping for Home Theater equipment you might want to think about bringing in your favorite DVD or LD discs. Also, listen to more expensive systems than what you are looking for. Most of the time it will show you how much better of a sound more money can buy.

 

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THE SPEAKER BREAK-IN:

There's really only one piece of gear in a home theater system that almost every audio/video expert agrees can benefit from “break-in“, and that is speakers!  Dynamic speaker drivers (the cone woofers and dome tweeters found in almost all speakers) have moving parts that are generally rather stiff when they come out of the factory.  One of these parts is called the surround; it's the rounded piece of rubber or foam that connects the outer edge of the cone or dome to the speaker basket.  The other is called the spider; it's the part that connects the center of a woofer cone to the back part of the speaker basket, and that keeps the woofer's voice coil centered in the voice-coil gap. Surrounds and spiders are kind of like shoes, they're not very flexible at first but with use, they become much more flexible.  And as the surrounds and spiders in your speakers become more flexible, your speakers will sound better.  Some speakers sound just a little better after break-in.  Some go from sounding horrible out of the box to sounding glorious after 24 hours of break-in. Should you break in your speakers?  Absolutely, if you want to get great sound from them right away.  There are a couple of easy ways to do it.  If your receiver or preamp has a test tone that automatically circulates from speaker to speaker, you can just leave the test tone on for a day or two while you're at work.  You could also find a particularly action scene on a DVD, such as the canal chase scene from Terminator 2, and set your player for chapter repeat, then turn up the system (not too high) and leave the house for several hours. With audio electronics, the need for break-in is nowhere near as acute.  Once they're warmed up the first time, after about 15 minutes of use, solid-state electronics will almost always sound 95 percent as good as they'll ever sound.  Break-in of audio electronics does make sense.  However, for those who use tube amplifiers in your stereo or home theater systems, or for high-end, high-resolution audiophile sound systems, break-in time is of the utmost importance. One last suggestion:  Be sure to give your speakers a listen right out of the box, before they're broken in.  That way you'll really appreciate how good they sound once those flexible surrounds and spiders stretch out.

 

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KEEPING POWER AMPS COOL:

A cooling fan for use with power-amplifiers, receivers, integrated amplifiers or any other equipment that runs hotter than it should is a must. Just center it over the heat sinks and plug the wall-type power supply into a switched outlet on your receiver or preamp or any switched AC outlet. The Cool-it will send a quiet stream of room temperature air down the heat sink fins to the power transistors in your amp or receiver, ensuring that they operate many degrees cooler than they would normally.
An exhaust fan may be ideal for amps and receivers which must operate with limited ventilation, such as inside partial enclosures, cabinets or enclosed A/V component racks.  Ask for “ The Cool It 2 ” By Active Thermal Management when you come to visit our store.

 

 

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