AES, RMS, and Program Oh My!

[gafftaper]

As you know I'm involved in this issue with a subwoofer and amp. A side branch of that discussion is what is the deal with all the speaker ratings stuff?

We've got:RMS, AES, Program, and then my sub lists "long term system power". What's the deal with these terms? Why are there so many? I tried to read about AES vs RMS and just got confused. Is there a reason we can't just have one standard rating for speakers?

Help! I want to understand.

[mbenonis]

I've never hears of AES in the context of speaker power - AES stands for Audio Engineering Society, and it commonly is used to describe a digital audio output (AES/EBU). Can you perhaps provide some context for the "AES" rating of your speaker?

[cutlunch]

For a start ignore "program" as this seems to be manufacturer dependant also you don't know what there "program" source consists of.

RMS is normaly the one to go by.

RMS - Root Mean Square is basically used to compare the AC power to the equivalent DC power needed to provide the same heating capacity into the load. In amps and speakers they usally measure this with a 1KHz frequency sinewave input. This is measured as a constant input signal. But in real sound the levels change all the time so this where some people quote peak power. But this refers to only short bursts of input causing large outputs. The amplifier couldn't maintain this peak output constantly because of power supply, and overheating problems. You might see an 6 Inch computer speaker rated as a 1000W Peak music Power Output (PmPo) but you try and put even 50 W RMS through it and you will cook it.

I am not sure about AES so will stay away from it.

I had a quick look at QSC amplifiers speakers. I take it when they talk about so many watts output for so many hours. I am not sure if there is a defintion on their site but I would take this to be the length of time you can run the amplifier at this load before components start over heating and damage occurs. Their ratings look pretty good because it is unlikely you would run an amplifier for over 100 Hours at maximum load constantly.

[gafftaper]

Originally Posted by mbenonis

I've never hears of AES in the context of speaker power - AES stands for Audio Engineering Society, and it commonly is used to describe a digital audio output (AES/EBU). Can you perhaps provide some context for the "AES" rating of your speaker?

My JBL Sub is rated as follows:
Transducer (AES) Power Rating: 1200 W (4800 W peak), 2 hrs
Long-Term System Power Rating: 800 W (3200 W peak), 100 hrs

I'm guessing that they are basically saying you can run it for two hours between 1200 and 4800 watts OR you can run it for up to 100 hours if you keep it in the 800-3200 range.

There is no mention of RMS on their website.

[BackEMF]

Originally Posted by mbenonis

I've never hears of AES in the context of speaker power - AES stands for Audio Engineering Society, and it commonly is used to describe a digital audio output (AES/EBU). Can you perhaps provide some context for the "AES" rating of your speaker?

AES power handling is perhaps one of the best defined ratings for loudspeakers.

It is simply pink noise filtered between 125Hz and 8kHz with a peak to average ratio of 6dB and applied over a period of two hours. It is one of the better indicators of both the thermal and mechanical aspects of power handling.

[gafftaper]

So is AES essentially a more accurate measurement of RMS?

[museav]

I believe that RMS power is a misnomer, it has become commonly used but it really is a meaningless value and is actually the calculated power based on RMS voltage and current measurements. Also realize that Program and Peak ratings are calculated rather than measured values, the AES test signal used has a 6dB crest factor, the peaks are 6dB above the average, so the "peak" power is 6dB (4X) the continuous power while "Program" is essentially a made up rating to reflect that the test signal is not the same as a typical program source such as music and it is typically simply 3dB (2X) above the continuous rating.

There are numerous different speaker power rating schemes, some intended for individual drivers and some for full range devices. AES ratings are quite common and you might see IEC/EIA ratings as well. A few manufacturers use their own proprietary hybrid or modifications of some of the standard test methods. Many of the differences relate to the driving signal applied (bandwidth, filter slopes, crest factor, etc.) and the time the signal is applied. There are pros and cons to each method. And do not think that marketing is not a factor in this, how many people really understand or even notice the differences in the test methods or specifics of the ratings versus those that simply look at the numbers? So if your competition changes the test methods used or how the information is reported then from a sales perspective there is definitely some pressure to do the same.

As the specs for gaff's sub show, the length of test is a factor can also be a factor as longer test times can start to reveal long term issues, typically thermal, when the speaker is driven continuously for long periods. Not necessarily applicable for your 2 hour show with live music but perhaps relevant to the all night DJ with heavily compressed source material.

One of the limitations with current power ratings is that a speaker could have a noticeable change in response before reaching the rated power and that would not be identified. There are also a lot of calculated vlaues reported for both speakers and amplifiers. There is a move within AES and by some of the independent speaker testing labs to develop new speaker and amplifier rating systems that are based on the actual voltage and current measurements rather than calculated power levels and that for speakers define the power limit as when an audible (3dB) change occurs in the frequency response. This makes a lot of sense to me as it means you are really looking at when the power starts to affect what is heard and it is also a condition from which most speakers could recover.

[gafftaper]

Thanks again to the noise boys. I've been learning a lot lately in this forum.

[mixmaster]

.....and if that's not complicated enough, as you compare speakers, don't just get hung up on the Watts rating. The rating for power handling (watts) are exactly that, how much power is this speaker capable of handling before the speaker quits working with spec. It says little about how loud a speaker will get given a specific amount of power (efficiency), or how loud the speaker gets at full power (max spl). When comparing speakers one should look at all the numbers. I would rather have a speaker rated at 400 watts with an efficiency of 104 db 1watt/meter than a 500 watt speaker that is only rated at 90 db 1 watt/meter.
I have often found that the amount of information and the availability of specs indicate the quality of manufacture. The better quality manufactures, like JBL, EV, and EAW tend to provide more information on the specs for their speakers. These reputable companies are not afraid to tell you how you can expect the equipment to perform and are willing to stand behind anything that comes up short.
If OTOH, the specs for speakers are vague or missing, it raises a red flag that maybe the numbers aren't something that the manufacture is proud of, or didn't bother to test, or that the marketing department has cherry picked only the best numbers to advertise. (maybe the rest of the specs aren't nearly as good).
You can't have too much information.
Matt