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We are considering the 3000 series scope

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We are considering the 3000 series scope

Postby Lynn Blakely » Fri Jun 30, 2017 9:10 pm

We are wanting to discover a way to analyze a room, that is any venue, from a seating capacity of 100 to several hundred. This would be using a pulse generator, and a scope to trigger on the initial pulse, and measure the time, between the speaker, and the measuring mic. We will want to know the levels of the direct sound and the reflective sound. The purpose is to determine the critical listening distance in the venue, and the proper installation of any and all speakers involved in covering the area of the listeners.
Respectfully submitted Lynn Blakely
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Re: We are considering the 3000 series scope

Postby Gerry » Tue Jul 04, 2017 5:06 pm

Hi Lynn,

First of all, Acoustics is a complex subject, and this is probably not the best forum to raise acoustic specific queries. However, we prefer to guide customers in achieving their measurement goals, rather than just responding with the technicalities of a measurement that may not be so relevant to their goals. So, I will give you my take on this (based upon years of recording and PA experience) with references to various material on the internet, in the hope that you will fully research this to optimize your intended measurement and analysis methods.

My understanding of 'critical listening distance' is that it is a point in a room where the direct sound is at the same sound pressure level as any reverberant sound. However, basing your speaker choice/positioning purely on this is not the best thing to do, in order to approach the optimum audio experience for as many listeners as possible from a large audience. The Image created by the sound stage is of vital importance for orchestras or groups of musicians, and the actual decay rate of the reverberation (known as RT60) also has an impact on both music and the spoken word, as it is a direct way of quantifying the amount of room ambience perceived by the listener, which is also vital if you want to include the richness of the room ambience. A good starting point in understanding this is the video here: https://www.youtube.com/watch?v=YH0o6InRYeQ. The following article talks about auditorium acoustics, which is a different application to a concert hall, but the auditorium requires clear intelligibility of the spoken word, while the concert hall requires good crisp imaging of the sound stage (as well as good ambience) which are similar goals (e.g. regarding reverberation): http://www.acousticsciences.com/media/a ... s-clean-it.

There are other quantitative factors that can significantly influence the quality of the audio experience, such as the timing between the direct sound and early reflections, which has a bearing on the coherence of the sound stage from the speakers, as do the effects of absorption, reflection and diffusion of spectral components. The type of material being replayed through the speakers is also very relevant (are you expecting to add room ambience to quite dead sounding material, e.g. just amplifying the sound from live performers on a stage, or are you expecting to faithfully reproduce material already containing all the room ambience that is needed, e.g. recreating the audio from films, or are you using speakers for something else?).

In addition, there are critical subjective factors that also impact the listeners perception of the audio. There is a good video here: http://www.akustiks.com/tuning-the-new- ... cert-hall/, and a great summary here: http://manager.sfwebs.co.uk/assets/nger ... 202015.pdf describing the importance of the subjective analysis that is required (although specific to acoustic instruments in an orchestra, it is still relevant to pre-recorded material, as recordings are typically trying to recreate the sound-field from a group of instruments being played on a stage) The video emphasizes the fact that different musical instruments, and compositions, have different dynamics, frequency content, and phase relationships, which affect the optimum listening positions.

Finally, it's quite straightforward to gauge critical listening distances in a small room, (with few, or even one position being most prominent) but in a concert hall there is likely to be be many seated positions that are impossible to 'dial in' to optimum listening positions with pure speaker choice and placement. When you couple that with the fact that the listening position is significantly affected by the number of people and their positioning in the auditorium, and that you are looking at a variation of one hundred to several hundred seated listeners, you can appreciate the complexity of what you're trying to do. Ultimately, unless the room already has it, you need to consider acoustic material added to the room in order to control the reverberation and create many more optimum listening positions.

To return to details that are more relevant to this forum, you can use a PicoScope with a microphone and suitable amplification (with the right signal source) to accurately determine the RT60 positions in a room, the timing and level of early reflections relative to direct sound, and the relative levels of spectral components. However the ideal PicoScope for this application and audio in general is the PicoScope 4262, because it has low noise, and large resolution (you need at least 12-bits of resolution to measure RT60, which the 3000 series PicoScopes don't have).

I hope this helpful.

Regards,

Gerry
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