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SA-3052A

Owner’s Manual

6-4

Chapter 6 - Getting the Last ¼ dB

The Meaning of Signal-to-Noise Ratio

Signal-to-noise ratio is a common term used on spec sheets. As common as it is,

many people (both learned and not) misunderstand or misuse it. Signal-to-noise ratio

is the relationship between a device’s normal operating level, the noise floor, and peak

clipping.

The noise floor, or the Ultimate noise

All electronic equipment operating above absolute zero generates noise. Fortunate-

ly, modern electronic design techniques can identify each noise source, all the way from

the tape head in a cassette machine, to each stage in the amplifiers following it on the way

to the speakers. Careful design minimizes each potential sources, resulting in optimum

performance. Of course, cost is a limiting factor in the overall design process at least

if most of us are to be able to purchase the device. The bottom line is the thermal noise

generated by the electrical resistance of the source. In the case of a cassette machine,

the source is the tape head itself. Even if the amplifiers following it were noiseless, they

would still amplify the thermal noise of the head itself. This source unit noise then is the

Ultimate noise.

The normal, residual noise output of any electronic device is known as its noise

floor. Again it is the product of the thermal noise of the source, plus the noise contribu

tions of each succeeding amplifier stage.

Peak clipping, or the peak ceiling

At the other end of the scale is peak clipping. Peak clipping occurs when an ampli-

fier’s output signal can no longer rise as directed by the input signal. Typically, it occurs

when the peak value of the output signal attempts to exceed the value of the power supply

voltages supplied to the amplifier stage.

Figure 6.2 Clipping

Figure 6.2 shows this graphically. The amplifier supply voltages are + and - 12 volts.

The signal can vary around ground (zero volts). up to 12 volts positive (above ground) or

12 volts negative (below ground). If the signal were to try to exceed this limit, clipping

occurs as the instantaneous signal level reaches 12 volts. At this time, the output signal

can go no further, and the signal peak is truncated or flattened until the signal level falls

below 12 volts. The signal level at which clipping occurs is known as the peak ceiling.

Содержание SA-3052A

Страница 1: ... Autosound Analyzer SPL Meter 22410 70th Avenue West Mountlake Terrace WA 98043 Phone 425 775 8461 Fax 425 778 3166 Internet http www audiocontrol com 2014 AudioControl All rights reserved Operation Manual P N 9021100 SA 3052 ...

Страница 2: ...SA 3052A Owner s Manual ...

Страница 3: ...g extreme at 175dB SPL 3 6 Chapter 4 Acoustical Testing with the SA 3052A Overview 4 1 Basic Procedure 4 2 Body Effects 4 3 Sound Pressure Level and Hearing Loss 4 3 Chapter 5 A Primer on Car Acoustics 5 1 Chapter 6 Getting the Last dB Getting the Last 1 4 db 6 1 Setting Gain Levels 6 12 Chapter 7 Contest Scoring IASCA Scoring 7 1 USAC Scoring 7 1 Chapter 8 Other SA 3052A Applications Sound System...

Страница 4: ...SA 3052A Owner s Manual ...

Страница 5: ...nd system equalization and analysis Chapter 5 Car Acoustics looks at the research and specifics of automobile acoustics Chapter 6 Last dB describes some advanced topics Chapter 7 Contest Scoring explains the special programming built into the SA 3052A for car stereo contests Chapter 8 SA 3052A Applications describes a few other applications for the SA 3052A besides equalizing sound systems Chapter...

Страница 6: ...r emphasis Words printed in boldface convey more em phasis than those printed in italics Notes Cautions and Warnings Some of the text in this manual is set apart by the headings Note Caution or Warning These terms are used to denote varying degrees of awareness required by the user during installation operation or maintenance of the SA 3052A ii NOTE conveys information that may be helpful to the u...

Страница 7: ...resolution Six non volatile memories with lithium battery backup Frequency response averaging for up to six stored response curves 20 second temporal averaging Peak hold Balanced XLR microphone balanced TRS phone jack and unbalanced RCA connector inputs 175 dB sound pressure level measurement optional Test Instruments vs Toys There is a fundamental difference between the many real time analyzers c...

Страница 8: ...est to design and manufacture and are usually only found on the most expensive read unaffordable analyzers Class II filters are easier not easy just easier to design and manufacture than Class III filters Any real time analyzer intended for serious measurement work will use filters that at least meet Class II standards The filters used in the SA 3052A analyzer meet or exceed the standards specifie...

Страница 9: ... cable is a standard PC type parallel printer cable also not provided The printed output is a form with suitable blank spaces for recording the time and place of the measurement and other data followed by the a printed representation of the real time spectrum display on the analyzer On screen score display For quick check ups in the shop when you don t have a printer handy the SA 3052A will displa...

Страница 10: ...le designed to be inserted inline with the microphone The AC 10 applies the standard A or C weighting function to the microphone signal Very High SPL option The high SPL option allows sound pressure level measurements over 170 dB This option includes a high SPL microphone and software upgrades External SPL Display Designed for SPL contests this option includes a large very bright SPL display which...

Страница 11: ...g the SA 3052A on the optional internal rechargeable batter ies a flashing green LED indicates that the batteries need recharging Once the Low Batt LED has begun flashing there is approximately hour of battery life remaining The SA 3052A has a sense circuit that prevents operation of the instrument below critical battery cell voltage This prevents total battery discharge which shortens the cell li...

Страница 12: ...h per second Memory The SA 3052A can store up to six different frequency response curves including the SPL bar graph display in its internal non volatile memory These memories are stored at the highest resolution of the SA 3052A so you can scale the display with the dB Step switch during memory recall Any combination of the memories can also be averaged Look in the Operation section of this manual...

Страница 13: ...ut 3 A tip ring sleeve phone jack is used for connecting to balanced and unbalanced sources Connect unbalanced sources by using a tip sleeve 2 conductor plug inserted into this jack This input has an impedance of 10 kohms and is suitable for signal levels from 56dBu to 36dBu An input signal of 0dBu represents 100dB SPL Input 2 This is a standard audio RCA connector with an input impedance of 1 Moh...

Страница 14: ...lt the AudioControl factory for power supply conversion information n 120 VAC 60 Hz n 220 240 VAC 50 60 Hz Power Fuse The correct fuse is listed next to the power input receptacle Printer Interface printing function no longer supported This is a female 25 pin connector DB 25F used for connection to an external PC type printer not supplied The connector is wired for a parallel interface printer A d...

Страница 15: ...play by pressing the push button switch adjacent to the Fast Med or Slow LEDs The Fast setting is suitable for viewing transients The Med setting is suited to signal monitoring and the Slow setting works well for pink noise measurements 7 You can determine the sound pressure level at the microphone by pressing and holding the SPL push button for one second until the display changes to the digital ...

Страница 16: ... locations to be averaged press and hold the Store Freeze button for one second The Memory 6 LED will come on solid and the average will be displayed on the screen and written into memory location 6 6 The contents of memory location 6 are lost when the average is calculated The result of the averaging operation is overwritten into memory location 6 Peak Hold The Peak Hold mode allows you to accumu...

Страница 17: ...ed for logging the time and date of the job as well as any other data A sample is shown in figure 3 1 The SA 3052A prints special output formats when in IASCA or USAC scoring modes Printers Supported The SA 3052A printer interface is designed to connect to any Centronics type paral lel interface compatible printer dot matrix ink jet laser etc No special printer control codes or emulations are requ...

Страница 18: ..._ _ _ _ Units _ _ _ _ _ _ _ _ _ Bass _ _ _ _ _ _ _ _ _ _ Crossover _ _ _ _ _ _ _ Subwoofer _ _ _ _ _ _ _ _ Amplifiers _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Suggested System Improvements _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Performance Match Technician _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 25 50 100 200 400 800 1 6k 3 15k 6 3k 12 5k...

Страница 19: ...charge the battery Charging the Internal Battery Pack 1 Plug the SA 3052A into a suitable source of AC power 2 Set the front panel Power switch to Off 3 Leave the SA 3052A for a period of 8 to 10 hours twice the discharge time 4 The battery charger automatically adjusts the rate of charge as the battery reaches full charge The Power Charge LED will glow red then flash slowly when a full charge is ...

Страница 20: ...position Leave the instrument plugged in for at least two hours and look for the red battery charging LED to glow continuously If this revives the instrument simply continue charging the batteries for another six to eight hours If not consult the factory for additional information NOTE The low voltage cutout could make the instrument appear to be totally dead If the SA 3052A appears dead plug it i...

Страница 21: ...C Weighted Measurements optional The AC 10 in line weighting filter provides A or C weighting to the microphone input of the SA 3052A Without the AC 10 the SA 3052A s measurements are unweight ed The AC 10 uses active filters to create the two weighting curves Power for the filter is supplied by the phantom power supply on the microphone input of the SA 3052A figure 3 4 AC 10 weighting filter Figu...

Страница 22: ...on t use the High SPL microphone for RTA measurements Selecting the SPL operating mode is very simple 1 Press and hold the SPL button to enter the digital SPL mode 2 The display will alternate HI and LO Release the SPL button when the appropri ate mode is displayed 3 When the digital SPL mode is in the HI range a single LED will stay lit at the left edge of the display Figure 3 6 SA 3052A display ...

Страница 23: ...eal time analyzer with a calibrated micro phone is one of the most popular methods of measuring the frequency response of a sound system within an acoustical space In a nutshell a pink noise source excites the space a microphone picks up the acous tical signal and converts it to an electrical signal The real time analyzer RTA breaks the signal up into equal octave percentage bands and displays the...

Страница 24: ...u should do is to set these controls for the best overall response curve Setting crossover level controls properly before starting is very important 1 Connect a pink noise source to the sound system This could be the output of the SA 3052As pink noise generator a tape or a CD with prerecorded pink noise on it 2 Place the microphone at the listening position It helps to position the microphone away...

Страница 25: ...e highest peak show ing on the display When you ve pulled this down to the level of the surrounding terrain find the next highest peak and pull it down Repeat this process as necessary Adjust the output gain control of the equalizer to make up for equalizer s loss If the peak straddles two equalizer controls then split the difference between them Unless the system and or space are really poor you ...

Страница 26: ...mea surements points and taking an average of all of them Sound Pressure Level and Hearing Loss Although it s great to have a sound system that will achieve levels of 130 dB SPL it s also great to be able to hear it for a while It s proven fact that one of the causes of hearing loss is prolonged exposure to excessive sound levels Research has shown that prolonged exposure to average levels under 9...

Страница 27: ... Next consider the problem of the ambient noise level present in the car Figure 5 1 shows the interior of a typical car at freeway speeds as viewed on a real time analyzer Notice the rather high noise level at the low frequencies as compared to the higher fre quencies If you want to listen to music in that environment you ll need a fair amount of low frequency boost just to overcome the ambient no...

Страница 28: ...nefit from some judicious equalization For the home listener there are a few options that should be exercised before using any sort of equalization Change the placement of the speakers within the room to vary the bass response You can increase the bass response by setting the speaker directly on the floor or into a corner You can decrease the bass response by moving the speaker away from a wall or...

Страница 29: ... isn t an easy way for the listener to return to this starting point unless you physically mark each control setting on the equalizer Bi amplified systems have a slight advantage in this discussion Typically you can adjust the level of the high frequency channel in relation to the low frequency channel just like at home If the system crossover point is low enough then you can fudge the crossover p...

Страница 30: ...SA 3052A Owner s Manual 5 4 ...

Страница 31: ... old problem of noise in its various forms to rear its ugly head Even if the manufacturer has done their engineering homework it s still really easy to forget some detail during installation and make even the quietest components seem noisy Consider A head unit with an integral power amplifier An outboard equalizer with input and output level controls An outboard power amplifier with high and low l...

Страница 32: ... to the engine speed Although the voltage is relatively low the alternator wiring carries fairly high cur rents Passing an electrical current through a wire is a sure fire way to generate a mag netic field Higher currents generate higher strength fields Now if you put two wires in close proximity to each other and one of them is carrying an electric current you can generate electricity in the othe...

Страница 33: ... be created between various points in the car body The alternator in the battery charging system makes things worse because the fre quency of it s AC output alternating current that s why it s called an alternator not a generator is easily within the audible range The low impedances involved high avail able current means low impedances make filtering out alternator noise even more diffi cult Anywa...

Страница 34: ...he amplifiers following it were noiseless they would still amplify the thermal noise of the head itself This source unit noise then is the Ultimate noise The normal residual noise output of any electronic device is known as its noise floor Again it is the product of the thermal noise of the source plus the noise contribu tions of each succeeding amplifier stage Peak clipping or the peak ceiling At...

Страница 35: ...o a signal level of around 0 1 volt a normal listening level on many source units At 20 dB the working signal to noise ratio is 50 dB 70 20 which is okay but not spectacular At this same level we have 30 dB of headroom 10 20 Now let s push the operating level up to 10 dB about 0 3 volt See if you can do the math yourself The working signal to noise ratio is 60 dB and we have 20 dB of headroom As y...

Страница 36: ...as 1 volt It s important to remember that low sensitivity means a higher voltage is necessary to drive the unit while high sensitivity means less voltage is re quired Note that sensitivity has nothing to do with power output POWER OUTPUT Power represents energy which can do work like moving a loud speaker cone Power is always measured in watts Power has nothing directly in common with sensitivity ...

Страница 37: ... full power output from the power output from the power amplifier Since most volume controls are followed by gain to make interfacing varied signal sources easier the average system reaches full power long before 100 rotation is reached Thus the amount of volume control rota tion required to drive the system to full output depends on 1 The signal level present at the input of the volume control 2 ...

Страница 38: ...nator output with a capacitor may help IGNITION Noise is a ticking sound that changes with engine speed the clicks get closer together It can be caused by poor or careless grounding ground loops poor wiring practices or bad level matching Resistor spark plugs may help especially when tuners are affected TURN SIGNAL Noise is a clicking sound synchronized with the turn signals Make sure that the aut...

Страница 39: ...ure 6 4 shows how to bypass the alternator output It s important to put the bypass capacitor as close as possible to the source of the interference Bypassing other electrical devices is very similar Make sure that the ground connection the vehicle body is the place to use to the capacitor is solid and clean If you have an ohmmeter measure the resistance between the capacitor and the vehicle body I...

Страница 40: ...ends to amplify any noise present in the ground system The net result is noise Here s some heh heh ground rules 1 There should be one and only one path to the negative side of the vehicle elec trical system If you elect to use the vehicle body as this point scrape the paint from under the contact point and use an internal star lockwasher on both sides of the terminal lug This grounding method is k...

Страница 41: ... depends on the distance of the run and the current demands of the amplifiers You can t err by making the wire too big For really high powered systems or if the run to the amplifier location is particularly long you may want to run separate power wiring for the power amplifiers high current drain and for everything else relatively low current drain High powered amplifiers usually have a DC DC inve...

Страница 42: ...ts in a car stereo system The answer is as close at hand as your trusty real time spectrum analyzer How to Use the SA 3052A to Set Levels 1 Connect SA 3052A as shown Diagram 2 with one channel of the output of the unit you are setting plugged into Input 2 Note you will need to unplug the microphone or any other inputs 2 Put the SA 3052A on digital SPL hold the SPL button in for 2 seconds with inpu...

Страница 43: ...above 4 or 5 volts If you run any unit in the signal chain into clipping you will defeat the advantages of the higher signal to noise in the other components 2 Don t drive the SA 3052A with a source impedance higher than 2k ohms This should not be a big problem as almost all car stereo components have output impedances below 2k ohms the Audio Control components output impedance is usually a wonder...

Страница 44: ...component with the lowest output capability is the head unit Since the system is only as quiet as the least quiet piece also known as the weakest link theory carefully select all your components See the tables below for more on the importance of this 6 Turn your amplifier sensitivities down where the volume is the lowest Then drive a higher voltage signal into them The result will be the same SPL ...

Страница 45: ...f competitions were scored by hand The amount of effort required to score even 50 cars was phenomenal Something had to be done Necessity or at least dislike of work has always been one of human kind s greatest sources of innovation The AudioControl SA 3052A makes computerized scoring easy and affordable All you need is a SA 3052A and a parallel type printer The SA 3052A measures the frequen cy res...

Страница 46: ...t set on 3 you will get the error message of 3dB on the display Frequency response scoring NOTE The unit must be in either IASCA or USAC mode for the scoring to work Few things are simpler than using the frequency response scoring in the SA 3052A analyzer There are just two steps 1 Press the STORE FREEZE button or recall a memory 2 Press the PRINT button on the rear of the SA 3052A Presto a comple...

Страница 47: ...input sensitivity control to 80dB Make certain the display speed is on MED 6 Adjust the fine 10dB sensitivity control on the RTA until the top of the dis played curve is just flickering below the top LED row 7 Set the RTA display speed to Slow If the curve runs off the top of the display reduce the 10dB control slightly 8 Freeze and store the curve into memory 9 Print the score sheet and log the s...

Страница 48: ...el at reading between the lines In this example there are a couple of possible explanations for the missing octave 1 Low input level the missing bands could be lurking just off the bottom of the screen Try adjusting the 10dB fine input control up to see if more of the curve can be brought onto the display without any of the bands going off the top 2 System failure A gap in the frequency response c...

Страница 49: ...SA 3052A If all else fails try another printer cable or try using the cable on a PC type com puter Cables can go bad once in a while THERE IS NO SCORING ON THE PRINTOUT The SA 3052A is not in the competition scoring mode Turn the analyzer OFF While turning the SA 3052A back on press hold the PRINT switch Release the PRINT switch when IASCA or USAC is displayed on the analyzer OTHER GOODIES FROM AU...

Страница 50: ...SA 3052A Owner s Manual 7 6 ...

Страница 51: ...ystem Whether you re equalizing a home stereo or a 100 000 watt concert sound system the basic technique is the same 1 Listen 2 Measure 3 Balance speaker components and equalize 4 Listen 5 Trim equalization settings Hi Fi Equalization Before attempting any corrective equalization use the SA 3052A to make a prelim inary assessment of the situation Use several microphone positions finally drawing a ...

Страница 52: ...e hear most sounds at a distance This causes high frequency loss because of the friction between the sound wave and the air as well as other losses due to absorption caused by walls and other surfaces As a starting point try 1 to 3 dB per octave starting somewhere between 1 and 8 kHz Experiment let your ears be your guide and the SA 3052A be your compass Sound System Equalization Equalizing a larg...

Страница 53: ...ur end product could be bass shy As you can see the speakers really do have an inverse effect on your end product Careful equalization of your monitor system using the SA 3052A and a good equal izer can give your studio the ability to make tapes that sound good anywhere The process and pitfalls are very similar to equalizing a home hi fi system Additionally you should be aware of the following You...

Страница 54: ... the screen This even works during performance Now find the frequency on your equalizer and dial in some cut at that frequency Once more bring the system slowly into feedback Repeat the squeal and notch technique until two or more frequencies feed back simultaneously Component Checkout You can use the SA 3052A to check out the frequency response of any component that you can get pink noise into or...

Страница 55: ...ng to figure out how another engineer equalized a certain instrument Likewise if the mix is starting to sound cluttered a glance at the RTA can tell if the problem is energy build up in some portion of the frequency spectrum Conversely the RTA can identify a portion of the spectrum that is perhaps under used The engineer may elect to equalize an instrument to place the dominant portion of its ener...

Страница 56: ...llowing items 1 Two load resistors resistance equal to the impedance rating of the crossover 1 Watt power rating is sufficient You can also use the speakers that will be connected to the crossover as a load If you re checking an active crossover you don t need the load resis tors Use the setup shown in Figure 5 6 2 The SA 3052A SA 3052 SA 3052 SA 3052 SA 3052 Figure 5 5 Checking a passive crossove...

Страница 57: ...ap proximate crossover frequency Store this reading in one of the memories Now repeat the operation for the other crossover output Store this reading also Now toggle between the two memories The two curves should look reasonably sym metrical mirror images of each other Beware however some crossover designs are deliberately asymmetrical If you re using load resistors for testing note that the load ...

Страница 58: ...SA 3052A Owner s Manual 8 8 ...

Страница 59: ...eamplifiers are then summed together The gain of the summing amplifier is also set by the dB Input switch The last stage of the input cir cuit is another variable gain stage The gain of this stage is also controlled by the 10dB control Lastly the signal is scaled to the correct level by the dB Step switch One Third Octave Filters After the input circuitry the signal drives the inputs of thirty one...

Страница 60: ...ve the display and or memory Once the µP has the data from the A D converter it performs some math on it decibel conversion sends it to the display and stores it in the temporary display memory When told to store a reading the µP transfers the contents of the temporary display memory to another RAM location for safekeeping On recall the µP does the opposite moving the data from RAM to the temporar...

Страница 61: ... but you do need a copy of the original sales slip 4 You cannot let anybody who isn t A the AudioControl factory or B somebody authorized in writing by AudioControl to service the SA 3052A equalizer If anyone other than A or B messes with the SA 3052A equalizer that voids your warranty 5 The warranty is also void if the serial number is altered or removed or if the SA 3052A equalizer has been used...

Страница 62: ...f there is anything wrong that you can fix yourself or arrange to have it sent back to our factory for repair Please include the following items with the returning unit 1 A copy of your proof of purchase that sales receipt we ve been harping about No originals please We cannot guarantee returning them to you 2 A brief explanation of the trouble you are having with the SA 3052A You d be surprised h...

Страница 63: ...cteristic Fourth order bandpass Meets or exceeds ANSI S1 11 1986 ClassII Type E specifications Frequency Range 30 1 3 octave bands from 25 to 20 kHz on ISO preferred 1 3 octave center frequencies Center Frequency Accuracy 2 of design center Band Center Frequencies 25 31 5 40 50 63 80 100 125 160 200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 6300 8000 10000 12500 16000 20000 H...

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