HT subwoofer is done; anyone remember "The Wrong ... [message #34348] |
Thu, 06 December 2001 20:01 ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
BillEpstein
Messages: 886 Registered: May 2009
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Illuminati (2nd Degree) |
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....Box"? I ordered the surplus Klipsch 10" woof with an Fs of 32 and built the 1.62 cu ft box. Got the woof and decided I should have ordered the Dayton Titanic 12" in the first place. Back went the Klipsch, Titanic sailed in to port today. Fs is 16 but I put it in the box anyway. Both Boxplot and WinSD say 10 cu. ft. Kinda critically under done, right Wayne? But I don't want another 36X24X20 box in the tv room unless it's a TV stand and the little (!) 22X16X13 fits in the corner real nice. Data sheet says the Kevlar spider takes forever to break in but right away the Titanic goes deep and loud on the explosions. You can really feel it in the chestal region. The $79 plate amp is a treat, too. Feeds 150 watts to the 4ohm Titanic with polarity switch, 40 to 160 Hz crossover and the usual line and speaker connections. So I've got $240 in this thing and it's cooking. Maybe I should get 2 more and have them fire out the sides of the Theatre 4 Pi's! 3dB down= 16.5 Hz! Yowza!
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A bit small, yes? [message #34352 is a reply to message #34348] |
Fri, 07 December 2001 05:52 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
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Wayne Parham
Messages: 18758 Registered: January 2001
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Illuminati (33rd Degree) |
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It does sound like that box is a little too small. However, there are a lot of alignments that work well, and some can be shoehorned into small boxes. Generally speaking, subs need to be large but you can make use of a small box if you're willing to make certain compromises. Speakers in small boxes can be made to have response that is reasonably flat and low, as long as the box is tuned appropriately. Check out the alignment called "Underdamped Ported Alignment, tuned low". That particular response curve was made with a rather large box, but you can get a similar response curve in a small box with appropriate tuning. More likely is the case shown as "EBS Stepped Response from ported cabinet with specific peaking", which is attractive since your Dayton motor will be used fundamentally in its lower stepped region, which is flat. You can crossover before the edge of the step where response rises. Granted, this is a lesser efficient part of the curve, but it is a way to get flat response over the intended range from a very small box. For that matter, you can generate an "Overdamped Ported Alignment" using certain tuning in a undersized box. This isn't what you would want for a subwoofer that would be used in large rooms or outdoors, but it is perfect for home hifi use, for subs that will be used in small to medium sized rooms or when corner loaded. Room lift tends to boost the lowest frequencies, and this kind of response prevents room gain from forming a peak.
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Re: A little more help, Wayne? [message #34360 is a reply to message #34358] |
Sat, 08 December 2001 08:14 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
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Wayne Parham
Messages: 18758 Registered: January 2001
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Illuminati (33rd Degree) |
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PiAlign suggests 4.0 cubic feet tuned to 15Hz with a 3.3" long x 1.6" dia cylindrical port or a 3" x 1.8" x 3.3" long rectangular port. This makes a nice flat response curve with -3dB at 25Hz, -6dB at 20Hz and -12dB at 15Hz. A 3.5 cubic foot sealed is very similar, having -3dB at 30Hz, -6dB at 24Hz and -12dB at 17Hz. Your proposed 2 cubic foot box is too small for sealed because it becomes underdamped. Not too badly though, so I wouldn't consider it to be unacceptable. A sealed 2 cubic foot box gives a -3dB point of 30Hz, so it is similar to the larger 3.5 cubic foot box but underdamped. My suggestion is that you build the PiAlign recommended cabinet, and that you consider 3.5 cubic feet a minimum chamber volume. If you must run the system in a 2 cubic foot cabinet, you should tune it as low as possible or just leave it sealed. In a cabinet this small, there is nothing you can do to prevent the system from being underdamped.
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Pneumatic damping [message #34367 is a reply to message #34362] |
Sat, 08 December 2001 18:39 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
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Wayne Parham
Messages: 18758 Registered: January 2001
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Illuminati (33rd Degree) |
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A system at resonance oscillates at maxiumum intensity. This can be a mass and a spring, a Helmholtz chamber or an electrical tuned circuit. At the resonant frequency, even just a little energy input creates large amplitude output. Notice that the examples of resonators each have two reactive elements. The mass and the spring are two reactive elements, the electrical circuit has an inductor and capacitor and the Helmholtz resonator has mass of the air and its compressibility, just like a mass and spring. If you add a resistance, you are providing damping. A shock absorber of a car is a damper, and it prevents the car from bouncing wildly at resonance. Likewise, the acoustic/pneumatic properties of a loudspeaker cabinet control the resonance of the speaker.
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