CJ1965 4-20-2018
Wrong again. You cannot simply substitute the electrical power ratio into the sound power formula and call it a day.
The ratio of measured sound power to reference sound power is 1/2 - not 1/4.
I posted the following in this thread, into which this debate had spilled over: Almarg 4-21-2018
Regarding the debate about the relation between SPL and speaker input
power, I found the following sub-page at the site which provided the
calculators that were referred to earlier:
http://www.sengpielaudio.com/calculator-efficiency.htm
Entering
various parameters into either of the two calculators closest to the
bottom of that page (one entitled "Sound Pressure Level and Amplifier
Power" and the other in the section entitled "Electro-Acoustic
Sensitivity") clearly confirms what Atmasphere, Erik_Squires and I have
all said on this subject. Namely that if the input power to a speaker is
changed by a given number of db, SPL at a given listening distance will
change by the same number of db. (As previously stated, this of course
assumes that the speaker is not being driven hard enough to cause
thermal compression in the drivers to become significant).
I also
found the following writeup at PSB’s site, which provides additional
confirmation. About 2/3 of the way down the page a table is provided
showing power vs. volume for an unnamed 87 db speaker used as an
example. Note that 40 watts results in a volume of 103 db, while a 6 db
reduction in that power level (to 10 watts) results in a volume that is 6
db less (97 db). While a 3 db change in power, from 1 watt to 2 watts,
changes the volume by 3 db, from 87 db to 90 db. And a 20 db change in
power, from 1 watt to 100 watts, changes the volume by 20 db, from 87 db
to 107 db.
http://www.psbspeakers.com/articles/Guide-to-Speaker-Specifications
Regards, -- Al |
Assuming that a speaker is operating in a reasonably linear manner, meaning for example that it is not being over-driven to the point that thermal compression becomes significant, it seems to me that the relation between acoustic power out and electrical power in will remain constant to a close approximation. And electrical power in will be proportional to the square of the applied voltage.
Therefore it would seem to me (and I believe also to Erik, Atmasphere, and Kijanki) that since a 50% reduction in applied voltage will result in a 75% reduction in electrical power in, which corresponds to a 6 db reduction in electrical power in, the result will be a 6 db reduction in acoustic power out.
Regards,
-- Al
|
... not 20 X log 10(P/Po) db as you [Erik] suggested above. CJ1965, Erik did not say that or suggest that. He said 20 x the logarithm of the ratio of applied voltage, not 20 x the logarithm of the ratio of power. If half the voltage is applied power will be reduced to 1/4 of the original amount, resulting in a 6 db reduction in SPL according to your own 10log(P/Po) formula, which is correct. And that is what Kijanki was implicitly pointing out when he quoted your erroneous original comment on the matter. Also, and more significantly, +1 to the very well said comments above by Peter (Ptss), which together with the earlier comments by Timlub I suggest that you (CJ1965) would be well advised to take to heart. Regards, -- Al |
Thanks, Kijanki. Here's another interesting quote, this one from the thread Tim referred to above:
CJ1965 4-19-2018
For some people, "results" means using antiquated 80 year old technology
that is highly vulnerable to changes in performance depending on what
it's connected to. And for some folks, the lack of bass and exaggerated
highs, coupled with increased harmonic distortion when using this
ancient "technology" is "pleasing" or "desirable". Similarly, others see
the pops and ticks, rapid wear, uneven high frequency performance,
limited dynamic range, increased distortion, wow, and flutter associated
with ancient vinyl technology as "more authentic". Unfortunately, we
can't confine such individuals who promote and buy this junk to padded
cells. We pretty much have to create invisible "padded cells" that
effectively allow ourselves to ignore them.
Best regards, -- Al |
As quoted by CJ1965: " So if you have a 97 db 1 watt/1 meter 8 ohm driver, two in series will have the same efficiency (since each is absorbing 1/2 watt) while the sensitivity is 94 db " - atmashpere [sic] Given that efficiency is defined as the SPL produced at 1 meter in response to 1 watt, when he said "since each is absorbing 1/2 watt" he clearly meant "since each is absorbing 1/2 watt if a total of 1 watt is being provided." Also, the paragraph in which that statement appeared certainly made no reference to 2.83 volts. If that was not clear then it certainly should have become clear during the course of the subsequent posts, especially mine. ... you can double the input drive voltage to 5.7v and then the series arrangement will have each woofer dissipating 1/2 watt. You can also multiply the input voltage by 10,000 - it won’t tell us anything about the effect placing two identical drivers in series has. Specifying the efficiency of a series combination of speakers, defining efficiency as the SPL produced at 1 meter in response to 1 watt, will tell us whatever can be told by an efficiency spec. As Ralph alluded to earlier, efficiency specs tend to be especially relevant in the case of tube amps, since for example in the case of an amp providing 4 and 8 ohm output taps maximum power ratings (in watts) will typically be the same or similar when an 8 ohm load is connected to the 8 ohm tap as when a 4 ohm load is connected to the 4 ohm tap. Regards, -- Al |
CJ1965 4-18-2018
...
the erroneous statement atmasphere made and you [Almarg] supported which
suggested two 8 ohm speakers in series would each dissipate 1/2 watt
with a total of 2.83V applied as input.
Neither I nor Ralph (Atmasphere) said or even implied that.
You can't apply or "provide a watt". All you can do is apply a voltage
and the load draws whatever current it draws based on its resistance.
What we were referring to is applying whatever voltage is necessary to result in a total of 1 watt being consumed by the two speakers, whether they are connected in series or in parallel. Which is what is relevant if what is being referred to is the overall efficiency of the speaker combination, and if efficiency is defined as the SPL produced at 1 meter in response to 1 watt. I'm not sure how that can not be clear, after all that has been said. Regards, -- Al
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CJ1965, re your last post that was directed to me, your math is of course correct. However, once again, if efficiency is defined as the SPL produced at 1 meter in response to an input of 1 watt, if that 1 watt is provided to two speakers connected either in series or in parallel each speaker will absorb half of a watt. So when efficiency is referred to, and defined as the SPL produced at 1 meter in response to 1 watt, the results of your calculation need to be normalized to 1 watt of supplied power. Which in turn makes Ralph’s statement that you alleged to have "blown it" entirely correct. You [Kijanki] could know something that no one else on the planet knows and we’re all in for a new, amazing discovery. But then again, you just might be another clueless individual trolling around on the internet in search of a pointless argument.... For someone who has only been participating in this forum for a couple of months you certainly are quick to direct insulting comments at some of the forum’s most knowledgeable and widely respected members. And that certainly includes Kijanki, as well as Atmasphere. I suggest that some modification to your manner would result in your contributions being better received, and discussions in which you participate being more constructive. Regards, -- Al |
CJ1965 4-17-2018
"So if you have a 97 db 1 watt/1 meter 8 ohm driver, two in series will have the same efficiency (since each is absorbing 1/2 watt) while the sensitivity is 94 db. If you put the two drivers in parallel for a 4 ohm load, the efficiency is the same as 1/2 is absorbed by each driver if 1 watt is applied. However the sensitivity is now 100db. " - atmasphere
With that, you clearly blew it. Ralph’s (Atmasphere’s) statement is entirely correct, if (as he is assuming, consistently with commonly seen usage) efficiency is defined on a 1 watt basis. And if sensitivity is defined on the basis of 2.83 volts. Strictly speaking, I would define speaker efficiency as being the ratio of acoustic power out to electrical power in. But that definition would have little practical use, and the term is widely (and IMO very reasonably) used to refer to the SPL produced at 1 meter in response to an input of 1 watt. Regards, -- Al |
CJ1965, I believe that what your analysis about phase differences between voltage and current in reactive circuit elements may not be taking into account is that the motion of a dynamic driver results from the current it is conducting, rather than from the voltage that is applied to it. And the current in a series circuit is of course identical at all points in the circuit, aside from the consequences of the propagation delay that will exist along that path. Which in turn will be completely negligible for path lengths that would be present in a home environment, putting aside reflection effects for which timing may have relevance in digital applications.
Regards,
-- Al
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CJ1965 4-17-2018
If you [Atmasphere] had any experience designing or building amplifiers, you’d know that every energy storing element within a circuit contributes to phase lead or lag between voltage and current. Loudspeaker coils are no different. FYI, "Atmasphere" is the designer and owner of Atma-Sphere Music Systems, Inc., which for more than 40 years has produced some of the world’s most unique and highly regarded amplifiers and preamplifiers. Also, my belief and my perception has been that his frequent contributions to this forum are more highly valued and more widely respected than those of any other designer or manufacturer who participates here.
A little humility goes a long way
.... +1 Regards, -- Al |
