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Heeman's Dynaudio C1 + DIY Scan-Speak 13" Woofer Cabinet

Discussion in 'Speakers' started by Flint, Oct 13, 2018.

  1. Flint

    Flint "Do you know who I am?" Superstar

    Sure. I'll work on it.
  2. Flint

    Flint "Do you know who I am?" Superstar

    Why is Heeman's HT bass the best ever? Well, it is a multitude of things, but aside from the amazing 13" woofer cabinets and well tuned system, it is about acoustics.

    Heeman did many things to deal with the limitations of every small listening room, and by small I mean any room where the distance between any two walls is less than the wavelength of the lowest frequency being produced - that means any room with any set of parallel (or near parallel) walls which are less than 56 feet apart (the wavelength of 20Hz) is considered a small room with small room acoustical issues. In every practical room, the reflections off large surfaces have a massive impact on the bass performance.

    Assuming the walls are 100% reflective (which most are not), every wall adds 3dB of gain at frequencies below the frequency where the distance between the sound source and the wall has a wavelength of greater than 1/4 the wavelength. With two parallel walls, that means the distance between the walls will determine the frequency where the acoustic energy will be 6dB louder than higher frequencies where the walls are not reflecting pressures and thus "pressurizing" the room. So, if the ceiling is 8 feet above the floor and both are 100% reflective at all frequencies (which is rarely the case), then at frequencies below 35Hz, or 1/4 the 8 foot wavelength of 141Hz, the energy will simply be a pressurized chamber and not a waveform.

    But, in the frequencies between 35Hz and 141Hz there will be standing waves where the acoustical energy will resonate as it decays through absorption or leakage somewhere in the room. Above 141Hz there can still be resonating standing wave at specific frequencies, but since the signal from the source will start acting more like a ray and less like a wave (for those of you who have studied the characteristics of light) that standing wave will be limited to angled of reflection which repeat for multiple periods before decaying from absorption, diffusion, or leakage.

    Thus, sound in the bass in any practical listening room is going to either be in the form of a pressure chamber, a resonant standing wave, or a reflective ray. In the case of pressurizing the room, having a well tuned room where no two dimensions have perfect denominators or multiples (such as a 8 x 16 x 32 ft room) is a bonus. I believe Heeman did his best to address that issue and no two reflective surfaces are exact multiples or have common denominators of each other. That spreads the pressure and standing wave characteristics more evening across the frequency spectrum being used in the room.

    Second, standing waves only stand when the reflective surfaces are exactly parallel, so if one wall is askew of another and the angle of reflection of the standing wave is not perfectly perpendicular, as the wave reflects back and forth it will reflect and an angle away from the narrower side towards the wider side with increasing non-perpendicular angles with each reflection. Heeman made his side walls non-parallel which improves the bass performance of the frequencies where the distance between side walls would setup standing waves. It doesn't completely eliminate the initial room tuning standing wave issue, but it drastically reduces the resonating energy at those frequencies. So, if the walls are, on average, 15 feet wide, there will be a standing wave initially setting up at 150Hz, 75Hz, and 38Hz where below that the bass will more pressurized than resonating. Those standing waves will still impact the in-room amplitude response, but then the decay to acoustic silence will happen more quickly and thus the mental perception of a room mode will be almost eliminated.

    Thirdly, Heeman build absolutely massive bass traps in the room, including using the proven adjacent chamber technique and the corner "superchunk" bass traps. These bass trapping techniques demand incredible amounts of absorption material which Heeman did not spare on when building them. By absorbing huge amounts of bass, the room will experience bass decay at a higher rate than otherwise and this the dynamic performance will be more comparable to a much larger and well dampened room. Basically, while reflections still exist, and should, the resonances will decay extremely rapidly and the common characteristic often discussed as room bass decay is far superior than most can accomplish in a room that small, or in nearly any room which isn't huge or also treated with such an extensive amount of absorption material.

    So, the pressurization will still occur, but it will be absorbed the same way a shock absorber keeps the bouncing to a minimum in a car's suspension. Likewise, the affects of the mathematically definable standing waves will still be present, they will be reduced to a near minimum because the standing wave will decay very quickly and the acoustic energy being sustained in the room will be reduced significantly through losses and absorption. Finally, because the side walls are not parallel, the standing waves from side to side will be immediately present, but decay faster than one's ears can perceive them as room resonance.

    So, the bass in Heeman's room will hit the listener as in any room, but within a few milliseconds of the sound entering the room from the speaker, it will be down to nearly inaudible levels.

    Now, it isn't perfect. A system in a more perfect room which is larger, aggressive bass trapping, and absent any parallel surfaces will be better. But to be ideal all the reflective surfaces need to be at least 28 feet apart and not parallel to any other surface.

    So, how does it sound? Well, I've struggled to find words as this is not a characteristic which is discussed on audio fanatic forums or in magazines because almost no enthusiasts are willing to make the effort to get the bass right, and when you do you need more power and output from your bass speakers to make up for the reduction in room reinforcement. But, I like to talk about the dynamics more than anything. With real life instruments, bass doesn't just suddenly stop - it decays. Even with a hand damped bass drum hit in an orchestra, it takes a few milliseconds before the huge bass drum head stops making audible sound. Same for tympany, rock drum set bass drums, and bass guitars. They don't naturally go from generating loud bass sound to total silence instantaneously. But, they can exhibit great control and cutoff speed which most of us have never heard. So, while a good Punch from a woofer can be easily appreciated anywhere, the suddenly decay to silence after the punch of a bass drum or tap of an electric bass guitar has rarely been heard in a home. Heeman can go from chest vibrating bass to dead silence almost instantaneously.

    This is what I have been praising. Yes, because of initial standing waves his measured frequency response is not as "smooth" as mine or others' might be. But, his bass range dynamic performance is unmatched in my experience. Very impressive.

    Can it be measured? Yes! I have testing tools which can measure bass decay and RT60 and other time based acoustic performance. But the results are hard to understand for a layman. And, to make them truly understandable, I would need to use the exact same gear and same SPLs to make the same tests in dozens of rooms so we could compare them to each other. Even better, if I could measure each of your rooms the same way I do Heeman's, you could see how your's is different from his.

    But, it is a great sounding system and I hope one day to get similar or better performance in the bass range in my listening room.
    team_tsp, TKoP, heeman and 4 others like this.
  3. Zing

    Zing Retired Admin Famous

    In case anyone is not willing to read the lengthy, detailed and technical explanation Flint just wrote, allow me to give you a succinct summation; Heeman sucks.
    TKoP, Randy, heeman and 3 others like this.
  4. heeman

    heeman Well-Known Member Famous

    I will accept only the highest rating of suckery...............when it comes to great bass performance in my awesome HT!!!

    The rest of the sound isn't quite bad either.

    Randy likes this.
  5. team_tsp

    team_tsp Active Member

    I think in another thread you mentioned how you couldn't match heeman's bass performance, and I know I asked about the woofers you chose for your own speaker build, but this answered a lot of questions -- good info!

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