Martin Poulin
There’s really no point in me writing about a topic, when a quality article or a good video is already available.
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The links below are not endorsements, nor do I have any affiliations whatsoever with them.
I consider them as "areas to explore". I'll try to share links that are off the beaten path.
Often, I may link a product for it's novel idea or different thinking, mostly for inspiration and never as a recommendation.
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1- An explanation about a topic the average HiFi employee showcasing a sound system demonstration, might not have any clue about.
The Schroeder frequency:
https://www.soundandvision.com/content/schroeder-frequency-show-and-tell-part-1
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2- Bass, bass and more bass. Most sub-woofers do not deliver, as people don’t realize their limited output. THX Reference level is 115 dB at listening position. A small 10" sealed sub can't achieve this sound output, and never will.
A great website for sub-woofer learning and measurement. You may want to buy a pair of 18" drivers after spending time here. And for sub-woofers, sealed cabinets are often the best compromise. Simply buy more of them if it doesn't reach your SPL target, and then benefit from the multiple sub approach.
https://data-bass.com/data?page=home
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3- Not an endorsement, but rather an alternative to coupling loudspeakers to floors.
Isolate instead of spiking them! Doesn't work every-time, but worth replicating and trying out.
Note: The mathematics about decibel loss in the video isn’t accurate, as it omits "air mass" but the rest of video should be very informative.
https://www.youtube.com/watch?v=dW9-r83IvhI&t=14s
4- How much power does one actually need from an amplifier? (a must for solid state, whilst tubes require less, due to different clipping behaviors)
Required power is often more than one would think. Mcintosh Labs also understands this and offers 150 watts/channel in their solid-state entry-level amplifier line. Ever wonder why serious companies like Krell, Mark Levinson or Classe Audio don’t do "small high quality" 25 watts amplifiers?
The main three parameters for calculation are present and the fourth one (headroom) is provided as a bonus. A default of 3 dB is a good value to use.
https://geoffthegreygeek.com/calculator-amp-speaker-spl/
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5- Beaming in loudspeakers is often misunderstood, and yet so important. Directivity of speakers must be a smooth transition from the highest focused treble, to the omni-directional bass. (save for omni directional speakers, but they also have flaws)
The link below provides a good ballpark value for popular driver sizes.
Absolute beaming of a driver will change depending on the specific cone profile used by the manufacturer. The chart is a great and accurate reference source.
If your driver plays higher than the frequency noted in the table, you're asking for trouble.
http://greenboy.us/fEARful/frequencytables.htm
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6- Piston Excursion Calculator. How loud can a given speaker can play without reaching Xmax? For bass, room gain will be added, but it’s rarely as much as one would expect. If you think that your 10" sealed sub-woofer can do 115 dB @ 30 Hz, I’ve got bad news for you. If it could do 115 dB @ 30 Hz, then it would require ~70mm of Xmax (or around 3" one way). This just isn’t happening :) The only feasible way, would be to use four of them. However, this is only 30 Hz at 1 meter, not 20 Hz at 2 or 3 meters...
http://www.baudline.com/erik/bass/xmaxer.html
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7- Cancellation from ceiling and floor reflection is real. Here’s a simple page to calculate your situation. Absorbency is great idea for ceilings, but for the floors, one doesn't have much choice.
https://mehlau.net/audio/floorbounce/
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8- Various calculators all in one location. I use this page quite often for quick verifications. It even provides DIY acoustic panel ratios.
http://www.mh-audio.nl/spk_calc.asp
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9- Excellent general description of Sound System Design by JBL…105 pages...
http://www.jblpro.com/pub/manuals/jbl_ssdm.pdf
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10-Multiple sub-woofer advantages. A classic read with good information on the subject. (I'll never use less than four sub-woofers)
https://pdfs.semanticscholar.org/00da/51387c572cfd27c0256cb15e44e976a1a72e.pdf
https://www.harman.com/sites/default/files/multsubs_0.pdf
http://seriousaudioblog.blogspot.com/2012/05/two-great-articles-on-multiple.html
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11-A great video from an acoustician on room acoustics.
https://www.youtube.com/watch?v=cTnituQu8ig
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12- The Doppler effect.
A- a video that make you understand exactly what it is
https://www.youtube.com/watch?v=h4OnBYrbCjY&ab_channel=ScienceABC
B- is a complete text specifically for Doppler effect in loudspeakers