III A police car sounding a siren with a frequency of Hz is traveling at What two frequencies are heard in this car? III The Doppler effect using ultrasonic waves of frequency 2. A maximum beat frequency of Hz is observed. What is the speed of sound at that altitude? What is the speed of the boat? II An airplane travels at Mach 2. Determine the shock wave angle it produces a in the air just before entering the ocean, and b in the water just after entering.
III You look directly overhead and see a plane exactly 1. By the time you hear the sonic boom, the plane has traveled a horizontal distance of 2. III A supersonic jet traveling at Mach 2. Where will the plane be relative to the observer when the latter hears the sonic boom?
General Problems A fish finder uses a sonar device that sends 20,Hz sound pulses downward from the bottom of the boat, and then detects echoes. If the maximum depth for which it is designed to work is 85 m, what is the minimum time between pulses in fresh water? A single mosquito 5. What will be the sound level of such mosquitoes?
What is the resultant sound level when an dB sound and an dB sound are heard simultaneously? The sound level 8. What is the acoustic power output W of the speaker, assuming it radiates equally in all directions? A stereo amplifier is rated at W output at Hz. The power output drops by 12 dB at 15 kHz. What is the power output in watts at 15 kHz?
Workers around jet aircraft typically wear protective devices over their ears. Assume that the sound level of a jet airplane engine, at a distance of 30 m, is dB, and that the average human ear has an effective radius of 2. What would be the power intercepted by an unprotected ear at a distance of 30 m from a jet airplane engine?
What is its gain in dB? Manufacturers typically offer a particular guitar string in a choice of diameters so that players can tune their instruments with a preferred string tension. For example, a nylon high-E string is available in a low- and high-tension model with diameter 0. A tuning fork is set into vibration above a vertical open tube filled with water Fig.
The water level is allowed to drop slowly. As it does so, the air in the tube above the water level is heard to resonate with the tuning fork when the distance from the tube opening to the water level is 0. What is the frequency of the tuning fork? Two identical tubes, each closed at one end, have a fundamental frequency of Hz at The air temperature is increased to If the two pipes are now sounded together, what beat frequency results?
The four equal-length strings are to be placed under the same tension; what must be the mass per unit length of each string relative to that of the lowest string? A particular whistle produces sound by setting up the fundamental standing wave in an air column 7. The tube is closed at one end. What frequency do you hear? The diameter D of a tube does affect the node at the open end of a tube.
For a closed tube of length 0. The frequency of a steam train whistle as it approaches you is Hz. After it passes you, its frequency is measured as Hz. How fast was the train moving assume constant velocity? Two trains emit Hz whistles. One train is stationary. The conductor on the stationary train hears a 3. What is the speed of the moving train? Two loudspeakers are at opposite ends of a railroad car as it moves past a stationary observer at If the speakers have identical sound frequencies of Hz, what is the beat frequency heard by the observer when a he listens from position A, in front of the car, b he is between the speakers, at B, and c he hears the speakers after they have passed him, at C?
Two open organ pipes, sounding together, produce a beat frequency of 6. Thanks again for the help. It seems to me that it makes more sense to filter the liquid entering the TXV than to filter the gas entering the compressor. What am I missing? I purchased the compressor on eBay. The gaspack contained what I assume was an earlier equivalent part. Doug we see filter dryers installed at both sides of the compressor.
It depends Fan never starts turning. Fan started running on its on, but at a very low speed, nothing like it normally does. Any suggestions? Inside unit seems to work normally. Our Apt complex told me " well if they're blowing cold were not gonna replace them. I just noticed tonight sitting here with no TV on nothing on around me when the outside unit kicks on I hear a loud and it kinda sounds harsh BUZZZZ like Electricity telling it to come on.
Is it just the electricity hitting the fan motor and thats the fan coming on? Sounds like a failing relay or control in the unit. I suspect repair or replacement is in the near future. It sounds electrical in nature to me, like a transformer or maybe something short circuiting.
There are four indoor units running off one outdoor unit. Only one of the indoor units is making this noise. The system is new, only six months old, in a new house. The unit will make this noise even when it is powered off. I can't figure out a pattern to it, sometimes I'll hear it several times in an hour, sometimes I won't hear it for a couple of hours. They were telling me there's basically nothing in the unit that could cause such a noise and suggested that it was that maybe just a grill rattling or the sound of refrigerant flowing through the pipes but I don't believe that, it's far too loud and besides it happens when the unit is powered off.
They are coming back Friday and I would love to tell them what to look for. Thanks very much! Joe Greaney jfgreaney gmail. I'm puzzled too. Even if we had an odd problem such as a late-releasing torqued motor component, refrigerant, relief valve, or fan motor, the sound ought to occur once, not repeatedly. And refrigerant doesn't keep flowing through pipes when a unit is off. Certainly not several times an hour. I have a Pioneer minisplit and it ran fine for several days after install but then the outside unit started to buzz.
This is 12, BTU unit and the heat produced is the same as before but the unit is using about W more energy to produce it. Energy consumption tested with the heat setting as high as it would go for several hours. Outside temp about 50 inside about Comparing it to the energy used for my 2. I have permanently installed kWh meters on the heat pump and the minisplit. Thank you for an excellent question. We've written only a little about the use of variable speed motors inverter drives, pulse motors, varible-frequency-drive motors in air conditioners and heat pumps.
For other readers, an inverter drive air conditioner system uses a variable-speed electronically controlled motor or motors: synonyms: inverter drive, pulse motor, variable frequency drive or VFD. VFD motors are also called adjustable-frequency drive, variable speed drive, AC drive, micro drive and adjustable speed drive motor systems.
These motors use an electronic variable frequency controller to vary motor speed and in some designs to vary motor torque. For example a bad relay will buzz horribly but the repair is much less onerous than a motor that's failing. However when you see the energy consumption rise, and thinking rather generally, after ruling out intermittent shorts and bad wiring, I do suspect a failing motor or fan bearing.
I'm not expert on this but I speculate that any binding moving parts can increase the current draw in an electric motor. I have read that noise complaints are not a surprise and in fact inverter type HVAC equipment manuals for some Carrier and other brand equipment has a "silence" feature: quoting:. When the Silence function is activated, the compressor running frequency will keep lower than F2 and the indoor unit will bring faint breeze, which will reduce the noise to the lowest level and create a quiet and comfortable room for you.
Some of these can result in impalanced motor operation and vibration noise. Sorry I can't offer a smarter guess. Please do keep me informed as what you learn will certainly help other readers. The switching rates of modern power semiconductors can lead to voltage overshoots. If you can do so without getting your fingers chopped off from a moving fan blade, try a mechanics stethoscope to see if you can pinpoint the component that is making the buzzing sound.
That would be the most useful diagnostic. Thank you for your reply! Love this place. I like doing these things myself because I learn so much, but I do have a VERY healthy respect for the deadly power of electricity. That being said I took a closer look at the wiring. There is no aluminum wiring anywhere around here, except to the residence from the power company. I noticed some green corrosion on the ground wire to the compressor.
Had to cut it back about 4" to get to clean wire under the insulation. Put a new spade on and wired up. These dB ratings, being logarithmic, cannot be added directly. The easiest way to combine them is with the chart in the next column. After the total radiated power has been determined, then follow the method of Paragraph 3 to find the pressure level produced at a specified distance.
Because of the way dB pressure and dB power are defined, any change in dB power at the source such as adding additional pumps will cause the same change in dB pressure level at any distance from the pump location.
If a second pump or power unit is to be installed, either at the same or a different location than the existing power unit, its effect on the dB pressure level at a listening location where an operator is working can be determined by the method in Paragraph 6.
Example: If noise from Pump 1 is 85 dB, and Pump 2 is added with 90 dB, what will be the new noise level? Use the chart: Add 1.
In combining several noise sources, combine the two highest first. Combine this total with the next highest level, etc. Pump Added to a Noisy Background To find the additional noise which will be contributed by a pump added to an already noisy background, first measure the existing noise level at the listening location.
Then, using the manufacturer's dB rating for the pump to be added, calculate what its dB pressure level would be at the listening location if run by itself. Finally, combine the two noise level by using the chart above. Finding the dB Power Level Use this method to find the dB power level when the output power, in watts, is known. This conversion would be used more often in electronics than in acoustics. Example: Assume a watt power level. What is this in dB? Glass or Jonathan can help you with that problem more then I can since I have never had that problem.
Oh and heres a site for both of you idiots to educate yourselves a little about car audio. Something has to be making interference with something. Industrial noise d. Flicker noise. Low frequency noise b. High frequency noise c. Due to random behavior of carrier charges d. Due to increase in reverse current in the device. Ratio of output signal to noise ratio to input signal to noise ratio b. Ratio of input signal to noise ratio to output signal to noise ratio c. Ratio of output signal to input signal to a system d.the relationship between ventricular pressure and volume measured when the myocardium is contracting (depends on preload and afterload) upper left boundary of the pressure-volume loop represents the maximum pressure that the ventricle can develop at any volume, assuming constant contractility (decreases with ventricular volume).