I haven't grasped your reasoning behind the extra 10db. Anyways, speakers sporting at least one driver with a 87,5db rating would probably be < 87,5 overall.
Unless you're thinking of s/thing else? Cheers
In many cases, when you load a speaker into a proper cabinet, it can increase the efficiency level by about 1-2db.
To get more efficiency than that, you would need to go to a horn loading system which can increase the efficiency of the system.
Twl is correct.
Though, one should question the heck out of companies who use drivers of 88 db/2.83 V sensitivity and then claim the speakers are 94 db/2.83 V sensitive. I know of one famous one that plays this game egregiously.
You can't measure the efficiency of a bare driver. It needs to be in some sort of test enclosure. The test enclosure is not the same as the final system enclosure, and may yield a lower efficiency measurement. This is not a problem if your objective is just to compare different drivers (all tested in the same box).
If you connect two drivers in an MTM configuration,the impedence will be halved,drawing twice the current, but about 6 dbs will be added. So,it is possible to wire two 88db,8 ohm speakers so that the final result is 94db sensitive into 4 ohms.
Sorry , I meant 87.5db. It was a typo. I was looking at various Vifa and Scan Speak mid-range drivers and almost all of them has an efficiency rating of 87db or less. So I was wondering how one can build a speaker using those driver but can achieve an efficiency rating of 90db or larger.
Pragmatist, if more current is drawn to achieve a higher sound level, the efficiency hasn't increased. Or am I making a mistake here? A higher efficiency means more output with teh same cuurent.
Satch...Efficiency is stated as dB per VOLT (not current). Of course the current will be more with a 4 ohm load, but that's the power amp's problem.
I'm not an expert,so allow me to quote my source:http://www.northcreekmusic.com
If you link through to the page that describes their rhythm speaker,in the fine print,it talks about an mtm set-up and its effects.(It's the paragraph labeled "Sensitivity and Impedance".)
Are they just going to give more sound-per watt, or will they also communiate more texture (micro-dynamics?) of the sound, along with the extra dB?
Here we go again. One thing we modern folk oft do is to use the WRONG terminology. 'Efficiency' is different than 'sensitivity'. Speaker-system efficiency normally is measured 1 meter from the speaker/driver when driven with exactly 1 watt of power measured into the speaker's rated impedance. IOW, a '4-ohm' speaker system's output is measured while being driven by TWO volts into 4 ohms (which equals ONE WATT). Decades ago, with the increasing popularity of solidstate amps*, the audio industry started publishing sensitivity ratings, and not all of them do it correctly.
Sensitivity is measured with a signal created by driving an 8-Ohm load resistor with 2.83 volts. That does happen to be 1 watt into 8 ohms, but it's not 1 watt into 6 or 4 or 3 or 2 ohms. The correct way to state this is 'sensitivity at 1M using 2.83v. into 8 Ohms' or something like that. And BTW, it's not PER meter, it's at 1 meter.
*--Solidstate amplifiers are constant-voltage devices and not constant-current devices are as most tubed amps. That is, because a SS amp's output impedance is so low, it will maintain its output voltage into decreasing loads until it reaches its maximum current output. A tubed amp generally will NOT increase its current output much as the load impedance decreases.
"Efficiency"???...The only thing I see quoted in specs is SPL in units of dB at 1 meter for 2.83 volts. This is 1 watt for an 8 ohm load.
Power = Volts squared divided by ohms.
(2.83 * 2.83) / 8
For 4 ohms it's 2 watts.
""Efficiency"???...The only thing I see quoted in specs is SPL in units of dB at 1 meter for 2.83 volts. This is 1 watt for an 8 ohm load.
Power = Volts squared divided by ohms.
(2.83 * 2.83) / 8
For 4 ohms it's 2 watts."
What's your point? I already did that math.
My point is that there's a difference between the 2 terms, and those of us who aren't aware and careful, including several members who posted above, tend to mix them.
Jeffreybehr....My points are:
1. The term "Efficiency" is just confusing. I don't see it quoted by manufacturers.
2. You gave the answer, but did not "do the math" so that others could understand where you are coming from. I am not disagreeing with you. Just making a clarification.
Okay, so "efficiency" deals ONLY with how much volume a speaker can put out? And has nothing to do with the quality of sound reproduced?
I'm learning here... ;-)
When it comes to speakers, "efficiency" is the % of electrical energy that the transducer converts into sound pressure -- the rest being converted into heat, etc...i.e., lost to our ears.
Sometimes this word is used by manufacturers to underline how loud their speakers/drivers can go when fed with a reasonable amount of W (i.e. energy). It sounds "marketing" to me...
Plus you have other manufacturers sporting interesting performance levels, to quote Trelja
who use drivers of 88 db/2.83 V sensitivity and then claim the speakers are 94 db/2.83 V sensitive
Would that be 94db @1M, both speakers fed a 1kHz sine wave, the mic on axis, 2ms gate / or is it that they have two drivers in parallel for each pass band / or?
You are correct about the definition of efficiency, Gregm. The term we are actually discussing in this thread is sensitivity, but I didn't want to interject it until you so wisely brought up what efficiency actually is.
My perspective is that the box should add maybe a couple dB to the sensitivity of a driver. And, that is the best you can do, using a driver such as a Lowther. When you begin adding crossover components, the senstitivity goes down, and the impedance curve begins to dance around, both of which make the speaker more difficult to drive. Think of crossover components as speed bumps for your amplifier.
Trelja...What if the "box" includes a passive radiator? Of course the PR draws its power from the driver, but I think it does the electrical-to-acoustic conversion more efficiently (because cone excurion is less) than if the audio all came from the driver cone.
I am talking about SPL. Audio quality is another matter.