With any panel speaker the measurement is done the same way as it is with a point source speaker.
What happens is most of the sound made by the speaker is not picked up by the microphone. Examples of this are the Magnaplanars, Martin-Logans, and also mbls (which are omnis instead of planars).
Its possible to correct for this and create a number that is the equivalent of 1 watt/ 1 meter or 2.83V/i meter. But usually the single-mic number is stated.
This causes the speaker to look about 6 db less efficient or sensitive on paper than it really is. It sounds like Martin-Logan has corrected for the fact of their speakers being panels per the example given in the opening post. The adjusted number of 92 db is actually about right, although if you do the traditional measurement you get something more like 87db (which suggests that ML was being conservative).
|
What bugs the crap out of me is that amplifier manufacturers used to do
the same thing with power ratings.I don't know how this was changed but
IMO it's high time the same pressure was brought to bear on speaker
mans.to provide honest & accurate specs!
that would certainly help but.............. i dont think there is a IEEE or AES or similar standard instituted by an industry institution. That leaves the door open to fudge specs. You confront the speaker manuf & he'll tell you that his speaker spec is correct because (for example) his spec sheets quotes in-room spec (but he's not obligated to put that in the spec notes so you are left guessing). There's nobody to enforce this spec. What we can do is educate ourselves & ask the right questions during purchasing. That'll let manuf know that they cant pull wool over our eyes. I still remember the marketing slogan from Syms Mens Clothing "
An educated consumer is our best customer" - that's what we have to become.... |
What bugs the crap out of me is that amplifier manufacturers used to do the same thing with power ratings.I don't know how this was changed but IMO it's high time the same pressure was brought to bear on speaker mans.to provide honest & accurate specs! |
Yep, well known that several manufacturers bump up their ratings from what they really are. The other trick is to leave off the +/-db in the frequency response. However, there are many that tell the truth (ex. Revel, Paradigm, PSB). You just have to learn which ones or have enough experience in speaker design to know what's achievable. |
Hey, you guys earned it.
I need to bookmark this thread. |
thanks for the kind words nonoise :-) |
I've been offered to be encased in concrete Tim |
Well aww shucks!! No ones ever offered to carve my words in stone before.
Im flattered.
Erik
|
I have a website. I have a frequency response section. I come right out and tell everyone: if your stupid enough to believe these figures, I won't sell you a pair of speakers.
We've all been lied to for so long, we actually want to read it, and believe it.
A day will come, when we let our 'EARS' determine how good a speaker is, and not the shite a marketing department exhales. Don't get me started on 'reviewers', and there single minded endeavor (endeavour for us Canadians) to garner more advertising dollars. We're a long way away.
Listen to the speakers. If they don't put the performers in the room with you, cross them off your list. Marketing garbage.
I agree with nonoise. |
These last posts from timlub, erik_squires and bombaywalla should be carved in stone.
|
I am very guilty of using the term sensitivity and efficiency interchangeably and really they are, a more efficient speaker will play louder than a less efficient speaker, but in the truest sense... Loudspeaker efficiency is defined as the sound flux or sound power at output divided by the electrical power input... Sensitivity is how loud a speaker plays with a given input. I defer back to 1 watt of power measured 1 meter away anechoic. Tim |
freediver, i'm looking at the M-L 35XT speaker manual & on the last page, the specs read: Sensitivity = 92dB @ 2.83V / meter. You can find the manual here: http://www.martinlogan.com/pdf/manuals/manual_motion_35xt.pdf The speaker is clearly noted as a 4 Ohms speaker. If you input 2.83V into 4 Ohms (after you calculated V^2/R) you get an input of 2W. Usually the standard is to input 1W into an 8 Ohm speaker. So, for the M-L Motion 35XT we have to compensate/normalize to bring Sensitivity number to an equivalent 8 Ohms so you can do an apples-apples comparison with other speakers. We need to halve the number of input watts to 1W Or double the input speaker impedance to 8 Ohms (which will also yield an input of 1W). In either case, the output SPL should drop by 3dB (assuming the speaker SPL response is linear in this region & is being fed by power well within its handling capacity. This should be the case as 1W is well within the power handling capacity of the speaker which also means its not distorting hence response should be linear). So, in effect the M-L Motion 35XT Sensitivity is 92-3 = 89dB. You say it's measuring 87dB ( I could not find a review that said this. Can you please provide a link? Thanks). it's not out of the ordinary to lose 2dB due to measurement setup issues. And, like others wrote, the spec could be in-room & the measurement could be in an anechoic chamber. Anyway, you should view the M-L Motion 35XT as an 89dB sensitivity speaker; not 92dB. |
FYI, sensitivity and efficiency are two different things, and is rarely the same for any given speaker.
Efficiency is measured at 1 Watt, and is also called "Power Efficiency." Sensitivity is measured at 2.82 Volts and is also called "Voltage Sensitivity." If the speaker is purely resistive and measures exactly 8 Ohms, then these two figures will be the same.
Efficiency explains how much work is required to produce a certain volume level, while voltage sensitivity cares nothing for the amount of work, and only thinks about what happens when a certain voltage is applied. Take for instance a 1 Ohm speaker, remember the old Apogees?
At 2.83 Volts, an 8 Ohm speaker draws 1 Watt, a 4 Ohm speaker 2 Watts, 2 Ohm speaker 4 Watts, and a 1 Ohm speaker draws 8 watts.
Sensitivity could be accurately called 85 dB, but at 1 Ohm it would actually be drawing 8 Watts, so the efficiency is actually a lot lower, probably around 78 dB or so. I've gotten quite forgetful about the precise math, but you get the idea.
This matters more to tube amplifiers, which have the same power output regardless of the transformer taps. For those with reasonably beefy solid state amplifiers, and speakers with impedance curves at 3 Ohms or higher voltage sensitivity matters more.
Best,
Erik
|
The only fairly accurate way to measure is 1 watt 1 meter anechoic... even then, many speakers are not adequately impedance compensated. As posted above... 1 watt @ 8 ohms is 2.83 volts, 1 watt @ 4 ohms is 2.00 volts.... a big difference in power for rating a speaker... Many speakers are called 8 ohm that stray down to even 3 or 4 ohms and those measurements can be quite flawed....
Plus when put in them in a room setting, you know deal with peaks in the room, so someone could easily rate at its highest peak rather than 1k or over average frequency response. Not sure that there is anyway to win here. These are just a few of the problems when quoting sensitivity... If they are using off the shelf parts, like a seas, scan speak, audax, etc, you could take a look of individual drivers and go from there... If manufactures are truly trying to give you a flat response, the lowest sensitivity of any single driver should be very close to the sensitivity of the entire speaker, but even that is flawed... Tough call. Tim
|
If the sensitivity is measured in a room instead of an anechoic chamber, it will be 2-3db higher. Some manufacturers have been known to spec room sensitivity. Also, some specifications say 1 watt and others say 2.83v. If the speaker is 8 ohms, it doesn't matter, they are the same. They are not the same with a 4 ohm speaker. If the spec says 2.83v, that is 2 watts with a 4 ohm speaker, and the 1 watt spec will be 3db lower.
|
Measurement techniques perhaps? Did yours match the manufacturers? |
are any of them made by Volkswagon?
...
;^) |
When I got my Clearwave Duet 6 monitors, I questioned the lowish sensitivity (85db) and was told by the designer that lots of speaker makers fudge the specs. He also told me that they are actually closer to 87db in a real room. At least he was honest and I've never regretted buying them.
Yes, it takes more volume to get things cooking but what a meal they serve up.
All the best,
Nonoise
|
|
