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Bass Guide Discussion

This post is where you can post questions that may have arisen from reading our Bass Optimization eBook! Please use the “add a comment” function below to ask your question.

Haven’t downloaded our Bass Optimization eBook yet? You should! It’s packed with information about how to optimize your bass. The guide covers the room, equipment, placement, acoustic treatment and set-up aspects of good bass. Download it now!

10 thoughts on “Bass Guide Discussion”

  1. Hi guys,

    just finished reading your Bass Guide – it’s very insightful, thanks!
    I built a home theater/music listening room recently. It’s my first experience with surround sound, for now I have a 5.1 setup with floor stand speakers and large center in front, 2 bookshelf boxes for surround and a SVS SB-12 as the subwoofer. All powered by a Yamaha RX-V781. I have some absorbers in place on the side walls and ceiling and I am already quite happy with mid/high frequency. However, still wondering how I can optimize bass frequencies – at the moment only the big sofa (really large) in the room can be considered as a natural absorber. Measurements with REQ showed very uneven frequency distribution below 200 Hz and results massively vary depending on the position of mic and sub. the room is a siple squared room with dimension of 5.5m x 3.85m x 2.16m so lowest mode is at about 30Hz.

    I am now considering the purchase of 2 second sub (same model) since I read about the improvements it brings confirmed by your bass guide. WHat I am wondering about is how to to use the auto calibration of the AVR in such kind of a setup. The AVR has 2 sub-outs, however, both yield exactly the same signal so the AVR cannot apply different level or phase settings on it. So how to handle the subwoofers when using the built-in calibration of the AVR – which level and phase should be set on the subs during the calibration? Do I have to manually tweak it after the AVR calibration e.b. with REW? If yes, how?

    Many thanks for your help in advance!

    1. Yes, with your AVR you would need to manually integrate the two subs before running the automated room correction. Typically this would mean running a pink noise PN signal through both subs simultaneously and then adjusting the positioning, phase, polarity and level of the 2nd sub for flattest response. You can use the signal generator function in REW to generate the pink noise PN signal and then the RTA function to view the frequency response.

  2. I just wanted to know what your thoughts are about the relevance of room dimension ratios in the design of a new control room.

    I’ve just been reading this article:

    And they mention that lately the room dimension ratio theory is somewhat irrelevant when it comes to low frequencies…

    If my understanding is correct, apart from first reflections the main issue that most rooms need addressing is in the low end (sub ~250Hz)? If so, then would you still design a room with splayed walls and minimize parallel surfaces even if these don’t change much in the low end response of a room?

    1. Splayed side walls and ceiling can allow you to more easily create a reflection free zone by redirecting the reflections towards the back wall. They also prevent flutter echo. The article is right in that they don’t do anything for room modes – room modes will always exist. As soon as you get away from a rectangular room you need to use techniques like boundary element modeling (BEM) to determine room mode frequency and spatial distribution.

      I do not agree that room dimensions are irrelevant, but I do agree that the formulas out there that recommend room ratios are only part of the puzzle. I hope this is clear from the bass optimization guide, since in there we also talk about room construction, multi-subs, EQ, acoustic treatment, etc. In the “old days” dimensional optimization was about the only thing acousticians did when planning a new room. Now we know better. The dimensional ratio recommendations are an overly simplistic representation of reality as they do not account for where in the room the speakers and listeners are located. If you understand about room modes you’ll understand that location within the room for source and receiver plays a huge role in the frequency response.

      1. Thank you so much for getting back to me and explaining this.

        So for example if I am building a new room (drywall within a larger room) and the design only lets me adjust one of the dimensions, the length. How can I determine the best length for the room. The height is fixed at 4m and the width at 2.8m The maximum length I can have is around 4.2m. I’ve looked at multiple different ratios but not sure how to use them under this circumstance..?

  3. I’m in the process of finishing the interior of a 20 x 16.5 x (9 to 13 cathedral) listening room. I’m considering resilient channel and two ply drywall with a dampener in between. I’ve also seen other specialty sheet goods which state higher STC performance. My main consideration is room performance not soundproofing. Would I have better bass management with resilient channel or should I save my money for interior bass traps.

    1. Best internal acoustic performance would be factory damped gypsum board such as Soundbreak XP supported as minimally as possible (e.g. using clips and hat channel or resilient channel). Gypsum board walls and ceilings function as bass absorbers, with the primary tuning frequency related to mass of the gypsum board layer, the depth of the airgap and whether the cavity is insulated. A gypsum board wall can also function as a “plate resonator”, in which case the mass, stiffness and size of the unsupported area of each “segment” (e.g. the gypsum board piece between two vertical studs) are the primary determinants of performance.

  4. Hello, nobles. Good afternoon from Brazil.

    I’m talking from Brazil and I bring some stupid questions, but that leaves me in doubt and confused. I apologize for the many questions. I have tried and studied the principles of acoustics a lot, I have already downloaded the ebook on bass and bought many books besides reading many articles on the internet, but there is this knot in my thinking.

    Question 1: If a 20 Hz hertz has 56.50 feets at the speed of sound at 1130 feets / second, does that mean that the maximum air compression in relation to atmospheric pressure occurs every 28.25 feets? As the 20-hertz wave will compress and become rarefied over the distance of 56.50 feets, am I correct? Or the compression will occur every 56.50 feets?

    Question 2: Another question, after completing a cycle, does the 20 hertz wave lose strength considerably? I mean, in a room of 56.50 h X 56.50 l X 56.50 w feets, the wave of 20 herts would be compressed once and would be thinned until completing the 56.50 feets and the reflection generated by it would be negligible , I mean, would there be no reflection, or would he be weak enough to require no treatment, regardless of the surface of the walls?

    Question 3: In a small room, after the speaker creates the first compression just in front of the speaker, this compression will “travel” through the air and hit the walls and be reflected (assuming a hard surface like concrete) the number of times necessary to complete the cycle (after traversing 56.50 feets), and then start a new cycle that will also have the same size of 56.50 feets until you lose the power and lower 60 dB, is that it? Will we hear the sound the instant it squeezes in front of the speaker and then again after it bounces on the walls, traversing 56.50 feets and compressing again? Was that the logic? That’s speaking in 20 Hz hertz pulses.

    Question 4: Last question. Did we hear the sound below atmospheric pressure? I mean, during rarefaction, do we hear the sound? Or is it only felt (heard) in moments of air compression (pressure above atmospheric pressure)?

    I ended up using it as an unfortunate example, just a frequency that many people do not even hear but wanted to use it as an example only because its wavelength is absurd and I still do not understand if that length is the distance between each compression of the air above of atmospheric pressure. Ignore the fact that it is a frequency that many people did not have, it will serve as an example for me to understand what is happening.

  5. I’ve downloaded the guide. It is well written, it gives a good overview of the elements to take in care building a listening room for hi-fi/HT. But the title is a bit misleading… it is an “Introduction”, not a “Guide”: there are missing a lot of useful details about the topic to be considered a guide.

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