The threshold of hearing is generally reported as the RMS sound pressure of 20 micropascals, or 0.98 pW/m2 It is approximately the quietest sound a young human with undamaged hearing can detect at 1,000 Hz. The standard threshold of hearing at 1000 Hz is nominally taken to be 0 dB.
The first research on the topic human ear was Fletcher and Munson in 1933
https://en.wikipedia.org/wiki/Fletcher%E2%80%93Munson_curves
International Standard The IEC 61672-1:2013 mandates the inclusion of an “A”-frequency-weighting filter in all sound level meters. In almost all countries, the use of “A”-frequency-weighting is mandated to be used for the protection of workers.
“C”-frequency-weighting is for music. (Flat over a large frequency range.)
dB must be reported at a distance When distance doubles is a -6 dB change.
1. Background Noise If the level difference between the absence and presence of the sound is 10 dB or more the influence of the ground noise may be disregarded.
2. Reflection The microphone should be placed well away from reflected surfaces. Hold meter at arm’s length. This will help to avoid reflections from your body.
3. Exposure to 85 decibels or more for 8 hours is hazardous.
U.S. Department of Transportation Federal Railroad Administration
The Use of Locomotive Horns https://www.fra.dot.gov/ Page/P0105
Under the Train Horn Rule (49 CFR Part 222), locomotive engineers must begin to sound train horns at least 15 seconds, and no more than 20 seconds, in advance of all public grade crossings. If a train is traveling faster than 60 mph, engineers will not sound the horn until it is within ¼ mile of the crossing
Sound of train horns compliance
Title 49 → Subtitle B → Chapter II → Part 229 → Subpart C → §229.129 Locomotive horn
Each lead locomotive shall be equipped with a locomotive horn that produces a minimum sound level of 96 dB(A) and a maximum sound level of 110 dB(A) at 100 feet……..
(3) Each remanufactured locomotive shall be tested in compliance with paragraph (a).
(8) Background noise shall be minimal: the sound level at the test site immediately before and after each horn sounding event shall be at least 10 dB(A) below the level measured during the horn sounding.
(9) Measurement procedures. The sound level meter shall be set for A-weighting with slow exponential response ……..at least six such 10-second duration readings shall be used to determine compliance.
http://atsf.railfan.net/airhorns
The Prime Manufacturing Corp. of Oak Creek, WI produced a horn identical to the S-3L which they called the PM-920. Factory tuning for both was: B inverted 7th (B, D#, A) or 493, 633, 880 Hz tones.
At ¼ mile to the crossing, the minimum horn sound is 74 dB(A)
I have now reported what you should hear standing at a railroad crossing. Sound can be measured and reported by you. http://www.amazon.com sound level meters
Enjoy, it took me some time to find all this information.
Bob Frey
Website: http://bobfrey.auclair.com
I'd keep the sound volume low or in the middle.
That way it's not super loud.
The club I belong to has an accoustic meter and sound standards. Most locos are at or below the max sound sandard out of the box. However knowing what your whistle/air horn sounds like is a quick way to find out where your train has run off to. We have a lot of visitors with a lot of questions. Our layout is loosely based on EsPee's Donner Pass line. We have more varities of cab forwards than any other steam locomotives. Although we run just about anything on occasison. Bet ya didn't know G-1's ran on Donner didja?
With a walk-around railroad, I've always felt that the loco should only be as loud as to be heard when you are near it. I really don't want to hear a locomotive on the opposite side of the railroad room.
Our club, Pacific Southern, Rocky Hill NJ, is about to set some sound parameters, using a small sound meter, so your figures are quite valuable. Our proposed approach is to test a variety of locos running on the RR with the meter at a 3' distance for chuff/prime mover, bell snd horn/whistle. Once the values are recorded, we would select units that displayed an "acceptable" volume level and use those sound levels as our reference. The owner would need to tone down the louder units before they could be run further. We are mostly interested in steady state noise; the louder chuff of a steam loco at startup would not count. A steady rod clank would.
Should be a challenging endeavour.
pocovalleyI really don't want to hear a locomotive on the opposite side of the railroad room.
i believe this is an unrealistic expectation. The physics of sound does not "compress" way that we model our layouts.
In general, I think the measure of a sound being too loud at some distance is if at that distance someone would need to speak louder for the type of sound being generated.
Background noise above 71 dB SPL cause people to start speaking louder. This is 3 dB lower that the average talker level of 74.
Based on the noise level of a coal train I previously posted, this would be between 1 and 2 ft. Assuming this noise level is the same for steam chuffs and prime mover, it means that you would not need to talk louder if you stood next to the engine and were more than 2 feet away from it.
However, a prototype whistle could be 30 dB higher. I don't think it's realistic to model this, but it suggests that a whistle might disrupt someone speaking (~)10 ft away. This translates to 77 dB at 5', 83 at 2.5' and 89 at 1.25'.
at 3 ft, whistle/horn would be ~85 dB SPL and steam chuffs/ prime mover 65 dB SPL
i recently measured the background noise level of ~~55 dB SPL in a layout room about 20 ft from some people talking. So while the prime mover level of 65 may seem low, it should be noticable 12 ft away, 12 dB lower level of 53.
i think using the disruption of someone talking 3 ft away from you as a measure is reasonable starting point for evaluation.
greg - Philadelphia & Reading / Reading
In a 3 three deck layout room, you can operate with a diesel horn about 1 Ft. from your face. I am more of a 70 dB(A) at 2 ft. type of person. I think it should be more general as to how far is your Diesel horn from your visitors’ ear?
I am 5’ 6” My layout in places is 4’ high. Horn say 6” from the edge. I walk with my arm about 6” from the edge. This comes out to about two feet from the horn to me ear for me. Your visitor could be further back to say 3 feet?
Set sound parameters, based on feet?
I don't know about others but loud horns and bells really annoy me. Our club meets in an old bookstore in a mall and some members locomotives can be heard from one end to the other. I set mine so that the sound carries about 10' or so. This is plenty if you follow your train around. Keep the smokey side up.
“Loud horns and bells really annoy me. Our club …… some members locomotives can be heard from one end to the other side of a store.” (40 Feet?)
Based on the dB sound at 10 Feet then 40 Feet is a factor of 2 at 20 feet (+6) ,and another factor of 2 at 40 feet (+6). This a +12 dB difference when measured at the same distance.
Horn= 66 dB(A)@3' "annoy"= 82 dB(A)@3'
Ft. dB(A) Ft. dB(A)
1 75.5 1 87.5
1.5 72 1.5 84
2 69.5 2 81.5
3 66 3 82
4 63.5 4 75.5
6 60 6 72
8 57.5 8 69.5
12 54 12 66
16 51.5 16 63.5
20 50 20 62
24 48 24 60
32 45.5 32 58
40 44 40 56
I like a maximum horn of 66 dB(A)@3’ Some of my operators think it is just a little on the high side. (I am retired.) The thing is, all my sound locomotives are adjusted to the same limit. The idling sound lever of 6 diesel in the yard becomes noise, this may be the next dB limit. Most dB sound meters start at 40, so if your room ambient is 45 dB, a readings of 55 dB or higher is acceptable.
On Athearn Genesis and Atlas Locomotives that are equipped with sound, can the sound system be turned down or adjusted in any way on the club layout?
What a neat topic!
Two observations:
I have a sweet little gas-electric that I added sound to. Since gas-electrics aren't big, I thought the sound shouldn't be, either. Sounded great at home. I took it to a Free-mo setup, and I could hardly hear it. And I'm not saying it was drowned out by other trains. So, next time I bring it, I'll kick up the sound a bit.
Other thing I've noticed: sound QUALITY seems to go up when volume goes down. A lot of my stuff sounds, when I first start the as-delivered sound up, like the sound's coming out of a plastic box (duh!). Turning it down, that nasty effect lessens. For me, a real incentive to lower the volume. That, and glowering club members.
Oh, yeah. Third thing: UP turbine sound gets REAL old REAL fast.
Ed
On Athearn Genesis and Atlas Locomotives can the sound system be turned down? http://www.athearn.com/ Athearn Genesis Sound uses a Tsunami2 Sound. DecoderCommon CVs on the Tsumam2 for volume are:
Horn Select CV 120 (0-36)
Bell Select CV 122 (1-48)
Prime Mover Select CV 124 (0-30)
CVs 128-160 Control the volume levels of individual sounds These CVs can be set from (0-255) with 0 being muted and 255 being the max volume.
Quick Start Guide may be down loaded from http://www.atlasrr.com/ by going first to Support, then to DCC Support, and finally to the Atlas Quick Start Guide for your particular locomotive, which is listed on the website under the heading Atlas Quick Start for Locomotives with QSI Quantum Titan Sound-Decoders. ( See Controlling Individual Sound Volumes, in your particular locomotive sound manual. )
http://www.bachmanntrains.com/home-usa/ Bachmann DCC Sound-Equipped Locomotives use Technology by SoundTraxx. http://www.soundtraxx.com/ Look for Manuals See: Tsunami2 Steam User's Guide or Tsunami2 Diesel User's Guide. Look for Volume Levels CV
Sound QUALITY seems to go up when volume goes down? Sound quality depends on the amount of information in the sound wave. https://en.wikipedia.org/wiki/Sound_quality When you increase your sound volume generally above the factory CV setting, you generally start running into clipping (audio). All Amplifiers have a voltage limit where clipping begins. This is the point where Sound QUALITY does go down, with the increasing the volume above the factory setting. https://en.wikipedia.org/wiki/Clipping_(audio)
With Digitrax the factory setting is 09 with ( 0-15 ) My estimate is that clipping starts at about a setting of 12 when you blow the diesel horn. (The peak-to-peak at the speaker is limited to about 5 volts because of a 5 Vdc voltage regulator. This makes for a 2.5 Vac square wave max, into a 8 ohm speaker, which now will never burn out.) Digitrax SoundFX® decoders come "ready to run" The SDXH166D decoder has 16 Bit Premium Sound. http://www.digitrax.com/tsd/product/SDXH166D/
CV# Used For Range (Default Value)
58 Master Volume (F8 used for Mute) 1=min 0=max 0-15 ( 09 )
135 Mute Volume 00-64 ( 00 )
140 Prime Mover / Chuff Volume 00-64 ( 60 )
141 Bell Volume 00-64 ( 25 )
142 Horn/Whistle Volume 00-64 ( 60 )
145 Misc Volume Levels 00-64 ( 40 )
I tend to agree with Hornblower. Fortunately, I do not belong to a club, (not much NG stuff around here to make a club), I "lone wolf" a small narrow gauge layout.
Regardless of room size or background noise, I set my sound levels to what pleases me and only me. After all, they are my sounds. I paid the $ 350.00-$400.00 per NG loco. In spite of all the really fine technical answers here about "realistic" scale levels, etc.,having to please a myriad of others with my loco sound seems ridiculous.
Many do crave the attention and respect of other MRs and are willing to bow to the general conscensus in a club layout situation. This, I respect, of course.
Do I raise the sounds to loud or out of proportionate levels? No. Do I attempt to match the sound to some proper scaling factor? No. I match the sound of each component to my delight and desire. Then, and only then, am I happy and glad I layed out the bucks and am getting my money's worth.
Richard Hull
Richard
If I can't fix it, I can fix it so it can't be fixed
How loud should it be? "I'll know it when I hear it." Some sounds seem louder than others because of the speaker. Most speakers reproduce different frequencies at different levels at the same volume level. What I mean is some locos with turbos really scream while the low rumble is barely heard. If a decoder has an EQ (equalizer) that lets you adjust the levels of frequency ranges, you might want to turn down the range that seems loud and turn up the ones that are too quiet. What you're shooting for is a flat sound curve with no spikes in volume at certain frequencies. I'm sure someone can explain it better than I can, but I hope you know what I mean.
I use JMRI (for the most part) and once I get things to sound 'right' to me, while in my quiet basement, I save that profile (and put 'HOME' at the end of the name). Then I duplicate that profile, turn all the sound levels up and save it again (and put 'CLUB' at the end of the name). This way, I can quickly set the volume depending on where I plan on running the loco; pretty quiet when I'm switching alone in my 10'x27' basement, or loud when I'm at a Free-Mo venue.
If possible, go to the prototype and listen to what it sounds like. The horn is unbelievably loud, the engine is relatively quiet (once again, this depends on the location and time of day. During the day, in a city with cars, trucks and airplanes, the loco will seem kind of quiet but in the middle of the night in the suburbs, the loco seems much louder (at night I can clearly hear Amtrak blowing it's horn from several miles away but during the day, I strain to hear it from a half mile or so away).
If you can't get to the prototype, go to youtube. One video I found has good examples of geeps switching; nice video but I like it for the sound (there is no narration and I can really hear the different sound levels. It also is a good example of how the RPM's equate to the speed and number of cars being moved.
I really wish small speaker manufacturers would test the freq response of their speakers and publish the results...it would let me know how speakers will reproduce certain sounds (some tend to be real tinny an others seem to reproduce low bass better). Some mfg's do publish such graphs, and those are the ones I usually buy (to encourage other mfg's to do the same).
http://delray1967.shutterfly.com/pictures/5
SEMI Free-Mo@groups.io
“I really wish small speaker manufacturers would test the freq response of their speakers and publish the results”
All speaker manufacturers do have test the freq response of their speakers! The problem is you must know the manufactures name and the part number of the speaker they are selling. Example of one speaker Mfg. (dB, Microphone distance, enclosure, and type of test wave are important.)
delray1967I really wish small speaker manufacturers would test the freq response of their speakers and publish the results...it would let me know how speakers will reproduce certain sounds (some tend to be real tinny an others seem to reproduce low bass better).
the response of loudspeaker depends on the encloser. The same loudspeaker can have different responses in enclosures with different volumes.
A loudspeaker (outside an enclosure) will sound significantly different placed down on a table top and held up in the air.
Yes, the effect of the enclosure can be a +3dB increase of the sound volume. The air pressure behind the speaker increases, when the cone moves into a sealed enclosure. Then the sound wave pressure going out can be doubled, when the cone moves in the other direction. (Say 60dB@3’ is now 63dB@3’ for a 1000 Hz sine wave into your 8 ohm enclosed micro speaker.)
Bob Frey.
Robert FreyThe air pressure behind the speaker increases, when the cone moves into a sealed enclosure. Then the sound wave pressure going out can be doubled, when the cone moves in the other direction.
i didn't think the pressure inside the enclosure was significant. The same argument can be made that the partial vacuum created when the cone moves foward degrades the movement.
with an enclosure, when the code moves forward, the air has nowhere to go except away from the enclosure. Without an enclosure, the forward movement of the cone displaces the air in front of the cone while there is a vacuum created behind the code with minimal net movement or pressure wave away from the spreaker.
I think one way to make things work without a sealed enclosure (bass reflex) is to increase the path distance between the front and rear of the cone.
https://en.wikipedia.org/wiki/Loudspeaker See: “Most loudspeaker systems consist of drivers mounted in an enclosure, or cabinet. The role of the enclosure is to prevent sound waves emanating from the back of a driver from interfering destructively with those from the front. The sound waves emitted from the back are 180° out of phase with those emitted forward, so without an enclosure they typically cause cancellations which significantly degrade the level and quality of sound at low frequencies”.
The energy of the sound wave out the front gets to your ear. The energy of the sound wave into the sealed chamber is returned, and also gets to your ear. A +3dB increase of the sound volume is the most you can get.
https://en.wikipedia.org/wiki/Bass_reflex#Explanation A bass reflex system uses a port (hole) or vent cut into the cabinet. (This is not a sealed enclosure.) The design approach enhances the reproduction of the lowest frequencies .
I would estimate a +1dB or a +2dB increase of the sound volume
https://en.wikipedia.org/wiki/Main_Page the free encyclopedia that anyone can edit.
Greg, what is a realistic sound level at some distance? A horn of 55dB at 1 foot in a 45 dB room, I would consider this horn as very low.
Robert FreyThe energy of the sound wave out the front gets to your ear. The energy of the sound wave into the sealed chamber is returned, and also gets to your ear. A +3dB increase of the sound volume is the most you can get.
not sure why you describe this in terms of energy. The wavefronts from the two sources can cancel or add depending on wavelength (freq) and distance (angle) between the sources. The most they can add is 6 dB. But they cancel far greater (e.g. -10) and significantly depends on frequency. An enclosure minimizes the loss at all frequencies, maintaining the freq response of the loudspeaker.
Robert FreyGreg, what is a realistic sound level at some distance? A horn of 55dB at 1 foot in a 45 dB room, I would consider this horn as very low.
not sure what you're asking. Any sound can be annoying if you can't get away from it. There's some max level at some distance such that the sound is not annoying beyond this distance. I've suggested an annoyance level being at 71 dB SPL where the nominal talker level 1 meter from the person is 74 dB SPL. So at what distance do you want some sound to be at 71 dB?
Part of the distance determination depends on other sounds. Chuffs may be ok at 71 dB at 10' but horns/whistles would be higher depending on the difference between prototypical chuff and horn levels.
yes, 55 dB SPL would be low.
A quick note about enclosures (correct me if I'm wrong):
Putting a poor enclosure around a speaker is just as bad as not using an enclosure at all. If you build an air tight enclosure out of 0.005" (super thin) styrene, the action of the speaker moving in and out will cause pressure/vacuum to build inside the box; if the enclosure is weak, it will simply flex and therefore move the air surrounding it, not really stopping the pressure waves from the rear of the speaker meeting (and affecting) the pressure waves from the front of the speaker. The enclosure must be rigid (or dense) enough to completely keep the pressure inside the enclosure and keep it from affecting the outside air. The small speakers don't create a lot of pressure, but in our application where we're trying to get the most out of our speakers, every little bit helps (or hurts). I've built a handful of enclosures out of 0.060" or 0.080" styrene and it seems to work well (I typically set my decoders to a low volume, which lowers the pressure a bit).
The bass reflex port isn't just a hole cut into a speaker enclosure but rather the end of a tube that starts some distance inside the box. The length of this tube 'tunes' the enclosure.
Back in the days I was building subwoofer boxes for cars, there were these things called (passive) radiators. As far as I can tell, they are basically a speaker cone without a magnet or speaker coil (and wiring). I don't know the science behind it, but when one speaker and one radiator was installed in a enclosure, pushing the speaker in (using my fingers) would visually make the radiator push out...if the box was completely sealed. I think it acted like an air spring, delaying the two pressure fronts enough to enhance the sound. This was all for deeper or louder bass, not for full range (all frequencies) speakers...I doubt radiators would work on our small speakers (but correct me if I'm wrong).
The volume of the enclosure was very important too, as was the kind of speaker. Some speakers needed a sealed box and others were known (to me) as free-air speakers. Free-air speakers could be mounted to a board that was leaned against the back of the rear seat and used the trunk of the car as a non-airtight enclosure; my understanding was these speakers needed to move farther (and more freely) than speakers designed to be used in a sealed box (which used the inside air pressure as a spring) to make the speaker sound 'tighter'. I don't know if this was to improve speaker response when (relatively) high and low sounds were played right after one another, or for some other reason (to change impedance, limit the frequencies being created or just because of the design of the speaker).
Our speakers do a lot in the small spaces of a locomotive shell; to me, tuning our small speakers to get the most out of the decoder is similar to tuning a race car to get that extra 1/2 horsepower needed to win a race. I'm not exactly a sound 'tuner', I'm happy with any kind of sound...as long as it's not too loud, or too annoying. :)
Speakers (and sound engineering) are quite complex, I've give up trying to comprehend it all, but I am a little familiar with the science behind it so I know where I can and can't cut corners in my sound installs. If my information is wrong, feel free to correct it...I just wanted to mention the importance of enclosure strength, size and design. :)
Every speaker has a natural resonance. When it is receiving input that includes the frequencies near the natural resonance, those frequencies are emitted at a much higher volume than those in the rest of the range. That is a form of distortion.
One way to lessen that distortion is to use a speaker enclosure. With an enclosure, when the speaker is forced to move, it has to compress (or decompress) the air in the enclosure. The farther the cone moves, the more resistance it feels. So the natural resonant frequencies are damped more than the others. Thus there is less distortion--an improvement in sound quality.
Generally, when you have ducted port speakers, the design is adding a new natural resonace above or below the natural resonance of the speaker itself. This modifies the speaker/enclosure emissions. For example, if a designer has an 8" speaker with a natural resonance of 60 cps, he might add a port that has a resonance of 45 cps. This will increase bass response.
I once built a speaker enclosure that had TWO natural resonances: one above the speaker and one below. This made a rather flat response curve from about 30 cps up to maybe 120 cps.
The natural frequency of a speaker is generally related to its size. Bigger is lower. The natural frequencies of the speakers we use in our model locomotives must be awfully high, such that installing them in a ducted port enclosure would be nearly meaningless. But putting them in a closed enclosure should lessen the distortion based on speaker natural resonance.
As far as needing an enclosure so that the emissions from the rear of the speaker don't cancel those from the front: I used to have a radio that just had a 6 x 9 speaker sitting on its top. No enclosure. I assure you, there was no noticeable canceling. I could listen to the Rock and the Roll quite nicely. I DID have a volume knob, and it worked well. There was, of course, some sort of distortion. But you do recall what I was listening to, don't you? So, who knew?
Oh, yes. A flimsy enclosure will not be as effective as a sturdy one, because the walls are flexing instead of working to constrain speaker movement. How flimsy is too flimsy? Beyond the obvious, it's hard for me to say. For example, is an enclosure built of .020" styrene a disaster compared to one built of .060"? Don't know. I do have a not-so-secret yearning (I'm telling you, aren't I?) to build an enclosure by milling it out of the lead weight in the locomotive. THAT will be flex-free!
Thank you Greg for your reply.
Energy can be converted in form, transferred to an object by the work of moving it a distance (The moving of the speaker cone in and out.) The rate of doing work is measured in Watts. One half the energy goes out the front, and one half goes out the back. But, the back energy is returned like a spring. (Sealed chamber) Therefore, +3 dB.Max. if no energy loss in the enclosure. But, double the Voltage on the speaker, it is +6 dB or double the distance is then -6 dB on my sound meter.
My problem is, I am a 80 year Electrical Engineer, and use a dB(A) sound meter to help me adjust my horns and diesel idling sounds to be similar. Horn= 66 dB(A)@3' Max. is acceptable in a 45 dB(A) basemen, Idling -6 dB or more. (or Horn= 67 dB(A)@1 meter Max.) To lose 12 dB you must be 12 feet away. This is near the 55 dB SPL.
See; Posted by Robert Frey on Wednesday, August 16, 2017 7:57 PM Horn= 66 dB(A)@3'
7j43kAs far as needing an enclosure so that the emissions from the rear of the speaker don't cancel those from the front: I used to have a radio that just had a 6 x 9 speaker sitting on its top. No enclosure. I assure you, there was no noticeable canceling.
some frequencies will be partially supressed due to destructive interference and some frequencies will be enhanced due to constructive interference. You can imagine what this does to the flatness of the response.
cancelling certainly doesn't mean very low or no sound.
The response of a loudspeaker without an enclosure will be much better if the cone is face down on a flat surface, which creates a small partial enclosure, than if both sides of the cone are unenclosed. Of course response will be more optimal if the enclosure is of proper size.
Robert Frey Energy can be converted in form, transferred to an object by the work of moving it a distance (The moving of the speaker cone in and out.) The rate of doing work is measured in Watts. One half the energy goes out the front, and one half goes out the back. But, the back energy is returned like a spring.
If energy is stored and returned when the cone moves into the enclosure, the reverse is also true when it moves away from the enclosure, the movement is inhibited by the partial vacuum which then sucks the cone back. the net result is zero. If anything, this mechanism distorts the signal not amplifies it.
A properly sized enclosure minimizes this effect.
what i don't understand about energy is where is goes when there is destructive interference due to the addition of uncorrelated waves.
I have laser beam (coherent single wavelength light). If they combine in phase, the amplitude increases. If it combines out of phase, the amplitude shinks. Where does the energy go? The physicist I worked with on the Bell Lab optical transmission system didn't know the answer.
Robert FreyAnd open speaker hanging by its wires and the wall 6 feet away, horn measured 63 dB at 3 feet. With layout panel 1 inch away.it was near 66 dB at 3 feet no enclosure.
of course it's an improvement. (bear in mind double is 6 dB. sound level is a measure of amplitude, not power)
how does this compare to a speaker with a proper enclosure?
When I worked on speakerphones, the microphone port is located on the bottom of the housing. The housing has feet and the bottom of the housing is slightly above the table top. This is by design. There is ~6 dB gain because the microphone sees both the free field wave and a reflection off the table-top that is nearly in phase and therefore constructive.
the plate behind the hanging speaker provides a reflective surface for the sound eminating from the loudspeaker. This can both enhance and supress a signal and again depends on the measurement point.
sound travels approx ~1000 ft/sec or ~1ft/msec. The wavelength at 1 kHz is therefore ~1 ft. or ~12 in. A reflecting surface 3" away results in a reflected waveform 180 deg out of phase at the speaker which will significantly degrade the output from the speaker when measured directly in front of the speaker.
a reflecting surface 1" away results in a reflected path distance of 2" which is half the wavelength at 6522 Hz. Maximum supression occurs at this freq, less so as freq decreases and enhancement will probably begin below 5 kHz.
i thought we were discussing sound pressure level, not the power required to produce it.
Now I say helloooooooooooooo for more than 1 second.. I can very easily get 60 dB(A)@18” on my sound meter. I also have an Apple ipod, an can go to the App Store. Look for: Categories, Productivity, Search by typing in “Decibel 10” OPEN “Decibel 10” and download this App.
With an open speaker hanging by its wires, and the wall is more than 4 feet away, horn measured 63 dB at 3 feet. With the layout panel 1 inch away, it was near 66 dB at 3 feet, no enclosure. This is near a 3 dB change. (But 3.0 is a small number, and 6.0 is a much easier change to measure.). Look In the SUMMARY REPORT, just use the Avg/leg: number reported for each test.