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Old 8th January 2002, 06:11 PM   #1
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Default High Efficiency Speakers

I am interested in building a pair of speakers that would be highly efficient. Something like the klipsch reference line. Thier floor standing loudspeakers have efficiency ratings of 98 dB/1 watt or greater. But they also have a fairly wide response range and are shielded for home theater use.

I don't seem to be able to find any drivers that would give me this capability. Tweeters are no problem, but the only way I can think of to get this kind of efficiency would be to wire together two sets of in series wired drivers and then connect the two pairs in parrales. This shoudl theoretically get me the impedance of 8 ohms and an efficiency of about 98 dB/ 1 watt.

This approuch seems liek overkill though, klipsch does it with two drivers and a horn tweeter. Could someone shed some light on this problem.

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Mark
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Old 8th January 2002, 07:32 PM   #2
subwo1 is offline subwo1  United States
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I am still trying to understand the math invloved with the concept efficiency increasing with more drivers. Non of my calculations seem to support the idea. Admittedly, I am not the best at math, but it seems that if more drivers are used, the power is simply redistributed, and each speaker emits according to the amout of power it receives. If it receives less, its emits less. So 4 speakers configured as two series pairs in parallel, should distribute the power so 1/4 goes to each one, and each emits 1/4 what it would have. I used to think the efficiency went up with more drivers, though.

Now if they are all in parallel, then the power input goes up, causing an increase in total SPL, in fact 4 times more energy output since there is 4 times more input (assuming they are not driven to the point of power compression in any case, and the amp can drive the load without voltage drop). Am i still wrong about this thing?
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Old 8th January 2002, 10:02 PM   #3
PassFan is offline PassFan  United States
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Default DB vs SPL

You guys are close. Wiring up speakers in parallel or series deals with the resistance the output of the amp sees. The resistance the amp sees determines how much power the amp puts out. This is known as load. When you double your speakers and double your power you gain 3 db. That is going from 1 speaker to 2 to 4 to 8 to 16. Now each speaker has a rating of 90 db at 1w/1m, and if you had 16 speakers driven by a 16 watt amp you would figure 90 db + 12 more db because we doubled 4 times. 4 x 3db = 12 db. If a speaker is 90db at 1w/1m and it can handle 100 watts, then at 100 watts its db gain would be determined by watts = log x 10 = 20db . 20db + our original 90db = 110db at 1 meter. Now if we hook up 8 amps at 100 watts per channel to 16 of these speakers we gain 12 more db to give us 122 db at 1 meter. Now for every doubling of distance away from our speaker we are we lose 6 db. From 1m to 2m to 4m to 8m to 16m we just lost 24db. Seems unfair to pay so much for 3db and then lose more by stepping back a little bit. This is the reason for those monster pas at the concerts. How you would apply this to multiple drivers in a cabinet with a crossover must be answered by someone else. I don't have the design background that other members do.

As far as parallel, 4 8 ohm drivers in parallel would give you 2 ohms. This is going to make the amp attempt to output more power if it can. If it can't your shopping for another amp. Ideally, you would balance an output with a driver of the same rating. If the amp puts out 200 watts a channel into 8 ohms match it with a 200 watt, 8 ohm driver. If an amp puts out 300 watts into 4 ohms match it with two 150 watt 8 ohm drivers wired in parallel. Series and parallel are circuits that help us match drivers to amplifier outputs to more efficiently utilize our money.
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Old 8th January 2002, 11:02 PM   #4
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Thanks for your reply PassFan.

I know understand why my idea wouldn't work as expected. I was sort of thinking that logically it didn't make sense. However some information I had acquired in the past made me think it might work. I suppose that information wasn't the whole story.

Now I would like to ask if anyone has any insight into how klipsch produces such high efficiency speakers. Thier ratings for the whole box are upwards of 98 dB at one watt. In my personal browsing of audio sites I have never seen any high efficiency designs for home audio that weren't some kind of horn loaded design.

Basically I know why my design won't work, now I need to know what will.


Thanks,
Mark
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Old 8th January 2002, 11:08 PM   #5
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Default Re: DB vs SPL

Quote:
Originally posted by PassFan
When you double your speakers and double your power you gain 3 db. That is going from 1 speaker to 2 to 4 to 8 to 16.
not quite .... if you double your speakers and keep power the same the radiating area has doubled so you gain 3dB if you double the power you get another 3dB.
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Old 8th January 2002, 11:40 PM   #6
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PassFan, I think you are incorrect.

speakers are linear with voltage, not power.

doubling the # of drivers and doubling the power would give you a theoretical on axis 6dB increase in output.

example, an 8 ohm speaker with a sensitivity of 92dB/2.83V/1m aka 92dB/1W/1m.

If your amplifier can output say 11.32Vrms(16W) into 8 ohms, a single driver connected would play at 104dB.

Now lets add a second identical speaker on its own identical amplifer. it too can play at 104dB by its lonesome. If the speakers play in phase, at a point, that is equidistant, and one meter away from the center of both cones the RMS air pressure at that point will double. similar to voltage, a doubling of pressure correlates to a 6dB rise in SPL. (to test this for yourself, 20 log (1/2E-5) = ~94. 20 log (2/2E-5) = 100. so double the power, and double the drivers gives an increase of 6dB. Two drivers with a total of 32 watts will give an output of 110dB.

now lets keep the same overall power as the first example.

Each amplifier now is going to output 8 watts(8Vrms) into 8 ohms. each speaker will play at 101dB alone, summing the on axis outputs at a point equidistant from both cones will yield an SPL of 107dB's. which is 3dB more efficient than a single speaker, even though the overall power is the same.

You do have to be mindful when adding more speakers changes the final load impedance, which is why I used two amplifiers instead of one in my example. When you have a final load rating that differs from 8 ohms, the power sensitivity (dB/1W/1m) will be different than the voltage sensitivity (dB/2.83V/1m).

I prefer to work with voltages since its easier for me to think of amplifiers as voltage controlled voltage sources and you can skip a step and just work with the basic ohms law, instead of converting back and forth to power all the time.

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Old 9th January 2002, 01:45 AM   #7
PassFan is offline PassFan  United States
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Default DB

I love this forumn. I learn alot everytime I come here. Power is proportional to the square of the voltage. The db relation to voltage is therefore doubled that of the relation to power. A doubling of wattage gives a 3db increase and a doubling of voltage gives a 6db increase. It is much easier for a novice to use wattage over voltage. Now if you double your wattage from 200 to 400 you will naturally need another driver. I'm not saying anybody is wrong, I think its more a case that we're using two different methods to arrive at the same conclusion. Now given db/spl=20log(p1/p0) where p0 and p1 are the sound pressures in Newtons per square meter, Then if one spl is twice another it is 6 db greater if 10 times another it is 20 db greater. Anyway, I've gone a little deeper into this than I wanted but that is good. I stand by my earlier statements. This is the formula used by the large Concert Sound companies to size their rigs for different venues given a target db rating.
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Old 9th January 2002, 02:06 AM   #8
PassFan is offline PassFan  United States
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Default jteef

Explain to me your math on your speaker example. If 8 ohm at 92 db 1w/1m, then at 16 watts why only 101 db ( I calculate 104. In keeping with the same driver for your second example you give each speaker half the power yet you deducted 3 db. When you sum the on axis output this would have to double the single spl to gain 6 db to reach 104 db, which is what I calculated the original spl to be as opposed to your 101 db. Are you saying the spl will double with two speakers. Also I've never heard of rms applied to sound pressure before, could you explain this.
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Old 9th January 2002, 02:08 AM   #9
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Default Re: DB

Quote:
Originally posted by PassFan
I stand by my earlier statements.
Well just one point about your earlier statements ...

doubling power will give you 3dB, doubling the number of drivers will give you 3dB so if you do both you'll get 6dB extra.

also 92dB/1W/1M @ 16W gives 104dB
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Old 9th January 2002, 02:11 AM   #10
PassFan is offline PassFan  United States
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If you double the drivers without the power then you half the power to each speaker which causes a 3db loss per speaker. Naturally if I am driving my speakers to their max eff. then if I double my power I must add more drivers. My example was not a typical case of driving 100 watt speaker with a SE tube amp. I'm assuming a perfect output match; amplifier to driver.
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