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#41
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Seeking advice for buying home audio equipment
On Nov 20, 11:16 pm, Chris Hornbeck
wrote: Also to be noted is that the 3 dB efficiency gain of ported systems is really only applicable in the narrow range of the port's output. Not correct. Most importantly, the port does not ADD to the woofer's output over the narrow range, it REPLACES the driver's output over this narrow raange. But, more importantly, the 3 dB increase in efficiency is oft cited and equally often misunderstood. Taking any give driver and putting in a ported enclosure WILL NOT increase the efficiency of the system by 3 dB. The 3 dB results because, for a given enclosure volume and bandwidth, the driver used for a ported version CAN BE as much as 3 dB more efficient in the optimum case (maximum efficiency C2 sealed alignment vs maximum efficiency lossless B4 alignment results in a 3 dB increase in system efficuency). If you have a specific driver, your system efficiency is set, no matter WHAT enclosure you put it in. The issue is what type of enclosure, how big and what's the bandwidth that results. |
#42
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Seeking advice for buying home audio equipment
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#43
Posted to rec.audio.tech
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Seeking advice for buying home audio equipment
In article , Doug McDonald wrote:
wrote: Where it DOES have factor is like this: suppose you want to design a subwoofer with a small volume. Indeed, the acoustic compliance of such a volume is small. You find that when you put a high-efficiency woofer with a litght- weight cone in it, the resulting system resonance is too high to be a "sub"woofer. So, you add mass to the cone. This does three things: 1. Lowers the resonant frequency of the system, 2. raises the Qt of the system, 3. lowers the system efficiency. So, yes, the small, closed box system has a lower efficiency for a given bandpass, but NOT because the air is stiff, it's because the moving mass of the cone has to be high to get the resonant frequency down there. I've wondered what would happen if you left the mass alone and simply boosted the bass signal so you get the same speaker movement. Does this screw up relative phase? If so, what happens if you use a digital filter before the power amp so as to fix that up? Would the low bass efficiency be the same as if you had weighted the cone? Doug McDonald I would think efficiency would go down with mass vs watts/equalization, but just a guess. I give an example of extreme equalization, the Bose 901 with about 18 dB boost at 30 Hz. greg |
#44
Posted to rec.audio.tech
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Seeking advice for buying home audio equipment
"Doug McDonald" wrote in
message I've wondered what would happen if you left the mass alone and simply boosted the bass signal so you get the same speaker movement. Does this screw up relative phase? Relative to what? If so, what happens if you use a digital filter before the power amp so as to fix that up? In general, bass equalization works, as long as you don't exceed the dynamic range of the driver. Would the low bass efficiency be the same as if you had weighted the cone? Weighting the cone just cuts the efficiency of the driver in its mass-loaded range. |
#45
Posted to rec.audio.tech
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Seeking advice for buying home audio equipment
On Nov 21, 1:28 pm, Doug McDonald
wrote: I've wondered what would happen if you left the mass alone and simply boosted the bass signal so you get the same speaker movement. You have to stop boosting at some point, so your equalization has to have a pole or two at some low frequency. That adds an order or two to the ultimate transfer function. Does this screw up relative phase? No. the natural rolloff of the system is minimum phase so adding a complementary minimum phase equalizer has no overall phase penalty. If so, what happens if you use a digital filter before the power amp so as to fix that up? There's no need to. Would the low bass efficiency be the same as if you had weighted the cone? "low bass efficiency" is a somewhat curious, misleading and, overall, meaningless term. Your goal is to achieve a certain frequency response over a specific bandpass. The efficiency of the system is specifically defined to be the passband efficiency. Below and above the passband, the efficiency drops. That's why the response rolls off. Changing the amount of power you apply via an equalizer doesn't change the efficiency at all. Now, if what you mean is how does one compare the efficiency using mass loading vs equalization at some low frequency, that's a different question. In essence, if you want to go down an octave, below the normal cutoff, you either have to add enough mass (in this case, by quadrupling the mass) or you have to put 4 times as much power into the system at that low frequency. The effect is at that low frequency, you have to put that same power in to get the desired sound pressure at that very low frequency. |
#46
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Seeking advice for buying home audio equipment
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#47
Posted to rec.audio.tech
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Seeking advice for buying home audio equipment
On Wed, 21 Nov 2007 14:57:45 -0800 (PST), wrote:
On Nov 21, 1:28 pm, Doug McDonald wrote: I've wondered what would happen if you left the mass alone and simply boosted the bass signal so you get the same speaker movement. You have to stop boosting at some point, so your equalization has to have a pole or two at some low frequency. That adds an order or two to the ultimate transfer function. You might enjoy this: http://www.linkwitzlab.com/publicati...nd%20Crossover for an elegant single-stage solution for a two pole resonant system. Look in the third section, IIRC. Timeless. Much thanks, as always, Chris Hornbeck |
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