Anemometer & Sound-level instruments
1) Anemometer . . .bought one of these a few weeks ago and found I agreed with "comments" left by others . . . which I ignored as being picky. However, the cheap-one I bought had an excellent screen display and Hold function.... but when stationary if you rotate the instrument, the vanes should rotate also, delayed by the friction naturally. But this one showed signs that the vanes were bottom-heavy- as soon as they tried to move they drop-back. Unfortunately there is no way of identifying any vane as a drop of paint would invalidate the Returns Policy.Next test was to blow gently and determine the wind-speed... several strengths were shown and I have no reason to doubt they are about right.
Don't know but presume holding it outside a car (no-one about!) should show the speed in MPH similar to the car speedometer ( although care with slip-streams. etc).
Using local "Weather reports would be fraught with error, unless a friendly weather-station allowed access to the tower, for real-time comparison.
The reason I returned it was, finally, the inability to achieve a low-reading. The spec suggests down to 0.4m/S but try as I might the lowest it would rotate for showed 2m/s( although achieving the right placement wasn't easy ). Any lower and the vane would stall after some erratic movement.
Whilst this might be "like a magnetic vane"... I'm fairly sure it is Optical, although viewing it in the dark with my camcorder( as IR detector)showed no light-leaks - although the Zoom lens might be filtering IR.
Another odd fault was that when stalled the display would show 38, or 44m/S and this was quite repeatable . . . very confusing when only a light breeze is present.... i.e when/if Out and About.Zero m/s was sometimes shown, but it was quite random, it seems.
Does anyone have similar experience . . .or suggestions for Re-tests?
This was a cheapo-model, so I wasn't expecting great accuracy... but the out-of-balance and stall-speed struck me as a faulty product. Oddly one of the even-cheaper models offered shows 30m/s as the lowest spec, but then suggests 40 is practical....eh?
I tried to avoid any that use 9v batteries, or CR2032 cells - these are too fiddly and Iremove my batteries ( like AAA), when not in use.
Any thoughts on making one's own?I watched a schools-YT which used paper cups . . . but this is suitable for a mast "Weather-Station" experiment.... very difficult to use for air-duct checking.
2) Audio-meter.
Sadly, this cheapo Audio meters was a real failure.
Whilst I cannot comment on "loud" setting, ( jackhammers, Jets take-off ) it would flash as I screwed the lid on a glass "Kilner Jar" - which in a quiet setting should IMHO be about as close to zero as you can get. The spec is not up to the very loudest sounds, so it is intended for comparison in offices, trains, etc. "for interest" - I guess.
The Kilner-Jar experiment showed 40dB . . . the same as going outside after an aircraft had flown away. The snag for me was the spec starts from 30dB - and I would expect lower levels to be inaccurate . . .but NOT unavailable.
The Jar was in my basement, which I know from SDHC recorders is very quiet . . . indeed approaching the point where noise in their preamp is looking at you.( you have to boost the Volume by40dB to see anything - I used Sound Forge, but Audacity has similar features.).
----Anyone had similar experiences . . . was my experiment at fault?
The reason for buying was to assess low-levels of audio in a forest, so I might replicate that noise in my basement ( using a playback device, suitably muffled ), for microphone (amplifier) experiments. It being far more convenient than moving the workshop into the woods.
It's such a shame that Manufacturers over-spec. their products, when for many uses their limits would be unnoticed . . .
BTW. Using a reasonably strong fan, the impeller was "run-in"for several hours; face-in and face-out, to give the bearings a preliminary polish.No improvement was discerned!
Thoughts...? Bear in mind that the air is compressed by the windscreen and would probably be moving faster by the time it gets to the side window. Aerofoil effect?
What worries me more is you driving with your hand stuck out of the window.//static.avforums.com/styles/avf/smilies/facepalm.gif Now that they have banned using mobiles at the wheel will anemometers be next.data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7
Why not just sit in the forest and, using your Zoom (or whatever), record an hour or so of forest sound to use in your editor. 1) Anemometer:
I wouldn't be able to drive and watch the LCD display.... you were joking? I'd hope to find someone that would have a suitable vehicle for such experiment...and as I wrote "....although care withslipstreams...."
2) Audio-Level
I wanted to be able to create the same ambient level as in the said Forest... so the Video-Editor would not do, ( and neither would playing back from a Zoom, for example ) - since there is no "Calibration"- it was using the audio-meter that would/should provide the correct level, by replicating the ambient-level witnessed on the LCD.
I would record this as well, but my suspicion is that at such levels the pre-amps in the Recorder are likely to be having difficulty.
Some out-of-the-way places can be very quiet ( between aircraft flights ), so there is no problem recording...except the Recorder-amplifiers are a significant part of the noise. I proposed building a super-low-noise amplifier - and using a moving-coil microphone, so the noise-level could be kept low.However, without any "Standard" I'm left using somewhat cruder methods... like making it as quiet as possible... that means selecting the OPamps for noise and maybe applying coolant spray too, -as freezer spray is about -55 DegC. that should lower the front-end noise.
I read somewhere, that a very expensive OPamp was so quiet the gain-setting resistors were the likely source of noise...Yikes.But sadly, they were rather pricey. ( but maybe cheaper than a useless Instrument?)
The whole point of the exercise is to record low-noise situations ( such as "Forest" ), with a reasonable level on the Recorder - this means the recording is "clean", having very little noise-floor, due to the recorder's preamp.It would be artificially "too loud" but a simple drop in level on playback would fix that . . .and that's quite easy to achieve.A noise-calibration at 30dB is probably not available with El-Cheapo instruments.
If anyone has a £200-instrument, can they tell me how quiet it can read? ( along with how they are measuring this.).
Was what you suggested somewhat different from my interpretation....?
Cheers. Joking ME?data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7 No seriously the airspeed around a car's window would not reflect the car's actual speed. You would need to get a selfie stick to locate the anemometer well outside the direct slipstream to get a more accurate reading. You may do better to go to the coast because the windspeed is not so affected by terrain. If there are some local yachties about you could compare your unit with their masthead anemometers.
Might try my own experiment with my Tascam DR-60D which is reputed to have good microphone pre-amps. The jets from RAF Valley don't fly on a Sunday (unless they need to practice for another Middle East hot spot.data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7) We still have some decent deciduous forests around this area. Mind you the back garden is well sheltered and, in the early morning, can be very quiet, except for the dawn chorus.data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7 In doors is much quieter than outside...Those pesky birds chirping and cawing, the wind rustling the leaves, the distant train, the nearer road ,Not to mention the sea 400 metres away.. Indoorsturn off the water, the electricand central heating and what noises are there?. .. if you were to cool your amplifer to -50degrees C , it simply will not function. Anyway you are looking at this the wrong way around. Rather than making your electronics quieter, you should be seeking to make the microphone more sensitive. The larger the acceptance area, the more acoustic power intercepted. .. think in terms of a parabolic reflector or horn. If it's a really low noise floor recording you're after, then a moving coil mic is not a good choice. ... you could improve on that by a factor of 10dB- or maybe even more? - by using a high quality low noise preamp together with a low noise condenser mic - like the Rode NT1 for example .
That mic has a very low self noise (around 4.5dB).If I use my NT1 in conjunction with the low noise preamp in my Tascam DR100Mk3 - which has a signal to noise ratio of over 100dB - I can expect to be able to capture a dynamic range of around 75 to 80dB referred to a 0dB full scale figure.
You might be able to improve on that slightly by using a high pass filter on the input, as at very low levels to noise tends to be dominated by low frequency background ambient 'rumble'-
But at these levels you're very much in the realms of the law of diminishing returns anyway......
However, the big downside of using condenser mic outdoors is moisture.With the exception of the Sennheiser or Rode RF modulated mics( expensive!) all condenser mics - even electrets - can be seriously affected by moisture.When they are, they can get very noisy, very quickly...
The mics in many SPL metersare usually not that good, noise wise.
Most are electrets, and if capable of accepting high maximum SPL levels, will often have quitea high noise floor.You're unlikely to get any accuracy with readings below around 30dB ... which is pretty quiet anyway..
Those who like to experiment with low noise recordings will often try using the Primo EM172capsule ( which you can find HERE for around £11). Using that - together with a decent preamp - can produce pretty good results...( the noise figure for that mic is quoted as 14dBA - so only around 10dB worse than the very low noise Rode NT1)
A dynamic mic will have a much lower output level, and thus require more gain from the mic preamp.Using an SM58 or an AKG202 for example - in conjunction with the same Tascam preamp - results in much higher noise floor for the same output level (around 15dB worse than the Rode NT1 mentioned above)....
So, it's a dilemma for outdoor use:
• Dynamic mics- no moisture problems - but worse noise figures.
• Condenser mics- lower noise -- except when damp (excluding RF mics)
Or you could start saving for a Sennheiser MKH 416(or perhaps a Rode NTG3if you're on a 'tighter' budget?) data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7 Thanks folks for yr inputs.
dannnielll - parabolic is on the "to-do" list for birdsong. But there would be no more sound for a forest, since it is then pointing at a smaller region.The point of the Test Instrument is to know what level I'm recording from ( i.e the forest itself, so I can replicate this indoors)...I don't understand yr comments re -55 DegC as military spec amplifiers work OK at these levels and are "sorted" chips...not a different part. However -55DegC spray is rather short-term and component temp would soon rise due to ambient and internal power. It would only be a "test" to determine if it helped reduce noise in the chips.
Interestingly, one phono pre-amp used six NE5534 in parallel, the idea being their noise would cancel - but I wasn't convinced it was worth the effort.
Re indoors - you are right, under night-time(& away from the city) in a soft-furnished room ( I use my basement ), the greatest source of noise is one's heart-beat breathing.
rogs - will try that IoW mic-source you mentioned. I thought "m/c" since they contain only copper ( electrets will have a booster amp), so I can apply the extra amplification myself. I don't wish to buy commercial mics for what is a hobby-horse / crackpot line of development ( er, some might say ).
30dB is shown as "Wispered sound" in charts I've seen - which isn't that low AND if a Test-Meter claims it can indicate this level, I do expect it to display lower, when in a silent-situation, such as inside a glass jar.... which is also in a quiet place.
Cheers All. I think you'd need to go for a class 1 meter to get any accuracy below 25dB. That is the lowest specified figure for Quest 1900, using their standard 1/2"electret mic. You can get down to 10dB using their externally 200V polarised condenser capsule, but I hate to think how much that costs....
(Those figuresare from page 49 of the 1900 manual - see HERE)
Even Quest's class 2 model 2900 is around £1500... and I've never found a purchase price for the class 1 model 1900 ....serious money I suspect?..
Unless you get into truly lab quality class 1 or class 0 sound level meters- with specialised professional mics and preamps you're not going to get anything useful below about 30dB, IMHO.
The lowest noise floor I've ever had to deal with personally was when I was trying to help someone record the sound of a needle and thread passing through fabric....and the sound of scissors cutting cloth.
For that I used a Primo EM172 connected to my Sony PCM M10 recorder (which had a nice quiet mic preamp).
You can hear the results of that experiment HERE Thanks rogs, I'm nowhere near to spending that sort of money.
I was hoping others had some experience of El-Cheapo sound meters and could suggest something that behaves a little closer to what I'd expect.
For the money, the device I had looked brilliant - until you do some checking; then the whole low-end spec comes under question . . . if it's internal noise, then they need to alter the Spec - but if I have a faulty unit, I'd expect the Supplier to come back with profuse apologies, Offers, Etc.
Yr link to micbooster is of interest, which I'll follow-up after my summer hols.
Cheers.
BTW . . . . can you, or anyone suggest some "standard which we can all use with some reliability? My thought is a British housefly, temporally in a 1lb glass jar. snag is it won't accept a Zoom recorder and as soon as different mics are involved, they are difficult/impossible to cross-calibrate.
For low-noise amplifier Tests I was planning in making a long quiet-box ( like a show-box), out of carpet tiles ( double thickness, maybe with O-ring suspension to something likea wooden box outside.).
By placing a mechanical wristwatch at a set distance from the mic I have a repeatable sound-source . . . .by interposing screens, made from cloth, card, carpet, etc different levels of attenuation can be provided. Then after the amplifiers are connected ( their Gain is easy to determine).... it should be relatively easy to work-out what the attenuated source is [ Although not it's Absolute level, naturally.].
This scheme when conducted in a quiet-room ( like my basement), should enable me to approach the noise-level in the pre-amp - and of course compare microphone sensitivity - as I suspect some are not going to respond at all to low-level sounds. Those that are designed for high SPL are unlikely to have High-sensitivity on the Spec.
Cheers All.
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