Hi I need to model PA system for a train station with EASE.
I got this doubt, while a speaker makes announcement, sound from it have all frequencies or it will be at one particular frequency.
Because in EASE, it divides electric power equally among all frequencies.
If there are 21 frequencies, and electric power provided is 0.75W, then for each frequency the power is (0.75/21). We use pink noise.
Since the power gets distrbuted we are not getting the desired SPL.
It depends on the speaker - some are designed to reproduce the full human audio spectrum of 20 Hz to 20 kHz - others have a smaller range e.g. small diameter speakers tend to be used for high frequencies and larger diameter speakers tend to be used for low frequencies.
Speaker systems usually feature two or more speakers so that the full range of 20 Hz to 20 kHz may be reproduced.
As Keith mentioned, the response of a speaker varies. It depends upon the speaker and on the audio chamber that the speaker is in. All speakers have a response curve of amplitude (or air pressure) vs. the frequency of the input signal. There will be "resonant" frequencies that the speaker/chamber respond louder at and some frequencies where the audio output is diminished somewhat. When possible, the input signal can be adjusted (via an EQ or audio filtering) to flatten the resulting output of the speaker/chamber.
From the point of view of frequency response a speaker is a filter and depending on its size and shape it emits sound only in a given band of frequencies. In the speaker data sheet there should be reported its frequency response or at least the range of frequencies in which it can operate.
All frequencies in its pass-band are usually present in the output signal (accordingly with its frequency response some frequencies are more attenuated).
If input signal is suitably filtered is possible to limit the output spectrum to a desired one.
For what is concerning your issue notice that you can pre-filter the sound with an electronic filter (such as an equalizer) to suitably modify (e.g. eliminate superfluous frequencies) the spectrum of the input signal to compensate undesired shapes in speaker frequency response. The same can be done by software by digitally filtering the source signal (lower cost).
Notice that human voice (for your application, i.e. spoken human voice) does not need all frequencies in the range 20Hz-20kHz to be accurately reproduced but just in the range around 300 Hz - 3400 Hz and frequencies outside this band are usually filtered away (usually an adult male has fundamental frequency around 85-180 Hz ; adult female 165-255 Hz; even if fundamental is outside the above mentioned interval it is possible to well understand voice beacuse of harmonics). Finally notice that intelligibility can be improved with filtering the signal e.g. with a vocoder and messages can be well understood even if output SPL is a bit lower of expected one.
Be careful to relative position of speakers in order to avoid dark regions (destructive interference).
I hope it helps, best of luck!
As Fabrizio above has correctly mentioned, you need to consider just the frequency range for human voice in your application, which is much more limited than the hearing frequency range. In addition to the acoustical response of the room you are interested in to model (a train station), an important detail is to consider the background noise as accurate as possible. This will also affect the total required sound power of your PA system in order to get an appropriate intelligibility level.
Best
Hi;
For audible frequencies, traditionally between 20 and 20,000 Hz, the sensitivity of the ear depends heavily on the intensity. The response is linear - that is, as sensitive in bass, midrange and high-pitched - only from a level of 90 dB and up to 110.
With my best regards
As mentioned by others, the frequency response of speakers differs. If you can find a frequency response graph for the speakers you are using, that would be excellent; however, those can be difficult to find. You may be able to ask the manufacturer. Filtering the sound itself to adjust for the frequency response of the speakers would be pretty difficult to do with much accuracy, but in the case that you are unable to choose the speakers it may be your best course of action. You should also consider that the environment will have an effect on the frequencies that arrive at the ear as well. Just as speakers respond to different frequency input differently, so too does the environment.
Dear all, all apologies for my late response. Thank you so much for your replies.
yes we do consider the background noise in our analysis.
My speaker data base says @1w, 1000Hz, SPL at 1m is 100.1dB. While importing the speaker EASE model provided, EASE suggest to use PINK noise and it distributes the power to all frequencies and hence SPL at 1W, 1000 Hz is lower around 87dB. So I'm confused, I need to provide power only to that particular frequency or all frequencies listed in EASE.
Unqualified Comments :
Repititive counts, classes and class marks, in spread measure sense has nothing to do with loudness. Joules expended in a unit time do not alter the inherent charactersic modes or response, extraneous to or beyond receptivity are automatically arrested, as it effects loudness only. You have to determine the appropriate counts per unit time along the wave number line. Determine equipotent ( any watts) "performance characterstic" output counts lines envelope of the speaker. This appears a must.
Does the speaker develops sound in all frequencies or only particular frequency? Speaker chassi develop sound in the frequency range for which it is designed. Commercial speaker drivers are divided into classes as, subwoofer, woofers, mid range and tweeters, respectively, for low (up to 250 Hz) , mid low, mid and high frequencies (up to 20 kHz). The speaker drivers curves, SPL ( sound pressure level) and Z (impedance) are found installing it on a open baffle inside a anechoic chamber. See: https://www.jensentone.com/what-is-frequency-response-chart . Inside the box, the response can be optimized to suit particular need. There are a lot of box shapes as sealed, bass reflex, bandpass, transmission line,TQWT, H/W frame. Boxes are developed using software which employs the Thiele Small parameters. Thiele Small parameters has one (n%) to calculate the speaker box efficiency as the ratio between the acoustical and electric power. For special applications, there is a speaker class called HSS- Hypersonic Sound which uses two sonars transducers operating in the 250 KHz range, one with audio modulated and the other without modulation, when the two 250 kHz beams intercept the air, a de-modulated sound is generated from scratch like a miracle, very useful as domes for cars where each person inside the car can listen a particular music. Inside a hall, the box behavior shaw be computed using free and commercial software.
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