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Silver Member Username: CheapskatePost Number: 291 Registered: Mar-04 | while trying to find reviews of silver flute drivers, i came across a forum thread that claims every time you double your number of drivers, you gain 3 free decibles of output. that's the equivilent of doubling your amplifier output. it's obvious that you'll have the POTENTIAL to move twice as air, but it just sounds like voodoo science to me. if it were true, you'd think someone would build a big speaker out of 20 or so full range drivers for fans of SET amps, or even stack 4 bookshelf speakers on their sides for each channel. is this stat REALLY true? i just can't see rocking an auditorium with just 2 watts if you have enough drivers. those huge stacks of cabinets are also driven by tens of thousands of watts. maybe they were confusing the doubling of amplifier power one can get when loading it with four ohms instead of eight. THEN you really could get an honest 3dB gain. if anyone knows the REAL math behind this claim, please do share it. it just doesn't sound right. |
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Gold Member Username: Jan_b_vigneDallas, TX Post Number: 5456 Registered: May-04 | Of course, it's true. But you cannot "rock" an auditorium with a mere two watts as every time you double the distance from the speakers you loose 6dB. http://www.myhometheater.homestead.com/splcalculator.html |
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Silver Member Username: CheapskatePost Number: 293 Registered: Mar-04 | ahhh... very informative. thanks JV. your audio knowledge is truly prodigious. so it's a matter of the law of diminishing returns. if you have 1024 small full range drivers rated at 90dB, you could get 123 dB out of a two watt amp, but ONLY at 1 meter. this is the difference between audible volume and moving alot of air? all that power isn't for loudness... it's to project the wavefront greater distance right? so, why hasn't anyone built 8 full range fostex driver towers then for home use? not caring one bit for the sound of klipsch horns, i would think that alot of baffle mounted drivers would sound more natural than horns. along similar lines, why does my subwoofer NOT gain 3 dB when i connect another amp channel to it's other coil effectively doubling it's power flow? does the extra power offer any benefit eg. better controlling the driver? i don't want to use it in 4 ohm mode as i've read that it's harder for an amp to control lower impedences and that 8 ohm loads are tighter. if i had my way... i'd have an 8 inch sub instead of my 12 inch. |
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Gold Member Username: Jan_b_vigneDallas, TX Post Number: 5460 Registered: May-04 | Too many questions! Your sub should gain 6dB if you hook both channels through it. But that's just relative to the position of the gain control not the total wattage of the amplifier. It sounds like you're running it at speaker level and then I have to get into how much extra wattage any one amplifier delivers into a lower impedance and how impedance is not constant. That doesn't touch on the room gain of additional speakers. Why no one has put eight Fostex drivers in a box? I don't know that they haven't. It might not sell since single drivers are a tough sell in the first place. Then there's still the issue of inefficiencies in the drivers and adding more in a parallel/series hook up doesn't really get you the gains you think. Projecting a greater distance is a function of controlling the wavefront. That's something most home speakers don't do in the same fashion as a speaker designed for filling an auditorium. Power handling ... now that's something to consider! |
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Silver Member Username: Timn8terSeattle, WA USA Post Number: 501 Registered: Dec-03 | "why hasn't anyone built 8 full range fostex driver towers then for home use?" I'll accept the branding as a reference to someone using a line of full-range drivers. With that caveat the answer is; lots of people have built mini-line arrays of full range drivers for home use. A true home line array will reach from floor to ceiling to take advantage of the reflected sound wave from those surfaces. In this situation the SPL drop off is only 3db per meter and sensitivity gains can be substantial. If you're looking for HUGE sound in a LARGE room this is one way to do it. The challenges can be many. Cost is a big one. There is also the potential for comb filtering at the upper frequencies. This is why you'll see many of these line arrays with a row of woofers and a row of tweeters. The woofers will typically be rolled off at a frequency below the wavelength equivalent to the center to center distance between the woofers. Another challenge is that with a line this size the listening position is going to be closer to the middle drivers than the drivers at each end of the line. To compensate, power tapering is used. This is accomplished by alternating between series and parallel wiring of the drivers to allow more power to the drivers at the end of the line. Personally, I think line arrays have their place as sound reinforcement equipment and perhaps home theater since you have several channels you can use to control the soundstage. Otherwise, give me a single point source or something close to it for music (just my opinion). Shorter line arrays of full range drivers have been created with good success. The downside is that the wavefront tends to be cylindrical rather than spherical. The result is if you stand up while listening you lose high frequency response. The typical solution to this is to add a tweeter to create something like a D'Appolito arrangement (lower frequency drivers surrounding a central high frequency driver) or depending on the design adding a tweeter to the top of the line. Dr. Jim Griffin wrote a white paper on the subject if you care to read more. http://www.audiodiycentral.com/resource/pdf/nflawp.pdf |
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Silver Member Username: AudioholicPost Number: 120 Registered: Apr-05 | Budget minded, you asked "why hasn't anyone built 8 full range fostex driver towers then for home use?" Think about damping factor and also the distortions passed on, for a start. Then look into cost for each driver. |
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Bronze Member Username: QuinnPost Number: 48 Registered: Aug-05 | A 3-6dB increase is hardly doubling your sound output. Here is a link to a sound ramp that decends at 6dB then at 3dB. http://www.sfu.ca/sonic-studio/handbook/Sound/Decibel_Ramp.aiff |
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Silver Member Username: Devils_advocatePost Number: 298 Registered: Jul-05 | AFAIK 3dB is a doubling of acoustic power (6dB is 4X); 10dB is perceived doubling of loudness. |
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Bronze Member Username: QuinnPost Number: 50 Registered: Aug-05 | It takes doubling the power to the speakers for every 3dB volume increase. I think that is what you mean. |
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Silver Member Username: Devils_advocatePost Number: 299 Registered: Jul-05 | Doesn't really matter. Both ways of saying it work. 3dB is a doubling of acoustic power and as a result, requires double the power from the amplifier. However, as our hearing follows a logarithmic as opposed to linear scale, it takes a 10dB increase for us to perceive a doubling of volume. |
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Gold Member Username: Jan_b_vigneDallas, TX Post Number: 5547 Registered: May-04 | Steady state signal only. Don't forget the variables that enter the picture. |