What Do I Use To Determine How Loud A Speaker Is?

Question

I am interested in a new surround sound system, and I am interested in PA systems. I need to know what number represents how loud a speaker is. Some say that its the watts, or the ohms, or the decibles per 1 watt... I really need to know how to decide what PA system I want for my band, and what home theater system I want for my room. I would also like to know if ohms effect what frequencies of the spectrum a speaker can produce. Because I have heard that a subwoofer that has 8 ohms can't produce as "deep" of a sound that a subwoofer with 2 ohms can produce. Plz HELP!!!!!!! Thanx!!!

Answer 1

Well, it can be a bit baffling. No pun intended.

There are a number of ways to measure this.

For speaker efficiency DB's per Watt is good, normally shown as DbA, which is the sound level produced by the speaker measured at a distance of 1 meter from it while a signal is inputted into the speaker using 1 Watt RMS of power.

Now we get to power measurement, this can also be done in several ways. The only REAL true power measurement is in RMS (root, mean, squared). This is measured as 0.707 of the peak power output of the half cycle of the measured waveform into a load (speaker 8 Ohm 4 Ohm 2 Ohm). This is normally 1KHz into a 4 or 8 Ohm load. Peak music power or total power is c**p! So normally from any quality manufacturer they would represent the amp output as;

2 x 85W rms into 8Ohms (thats for stereo), or 5 x 85W rms into 8Ohms (for 5.1 ch surround) with pre out for the subby (this is the 0.1 of 5.1ch). Hope I didnt blow your mind with this.

So to cut it short, Peavy or Marshal for the band (cant go wrong), Onkyo, Sony, Bose for the surround. Live life, Have fun!!

Answer 2

At high frequencies the maximum SPL a driver can produce without burning the voice coil is the Sensitivity in dB for 1 Watt at 1 meter added to the lesser of: amplifier power in dBw at the rated impedance, or speaker system Power handling in dBw.

MaxSPL = dB@1W@1m + dBw

dBw = 10*log(Power)

so 50 Watts is 17dBw, 100Watts is 20dBw,

and 200Watts is 23 dBw

If your speaker has a sensitivity of 90dB@1W@1m handles 200w and your amplifier puts out 100W, your maxSPL is 90+20 or 110 dB at one meter.  If you got a 200W amplifier it would put out 113dB.

The Ohm rating has nothing to do with how "deep" a speaker plays, but it has something to do with sensitivity.  A speaker with a 2 ohm rating will have a rating of 6dB more voltage sensitivity than an 8 ohm woofer with the same specs and input voltage, but it takes 4 times as much power (6dB) to run a 2 ohm speaker, so the speaker is really producing the same amount of sound "per watt".  Hopefully that makes sense to you.

At low frequencies, what matters is the size of the woofers and the distance they can move in and out (called the excursion)  IF you multiply cone area and excursion, you get a value called the volume displacement of the cone as it travels.  The higher this value, the more bass you can get without breaking something ;).

For the PA system or the Home theater system, you would need to indicate a price range before a recommendation can be made.

There are more important things than Loudness or SPL.  You want low distortion, you want flat frequency response, you want controlled directivity, and many other things...

Answer 3

If your looking to measure how loud a speaker is, I would say use a decibel (db) meter which I found they sell at Radio Shack for $50.

As for ohms or impedance, a lower ohm/lower impedance speaker will drive and amplifier harder meaning more power output.  Some amps can run at 2 ohm stable meaning that you will get more wattage out from the amp at that impedance then you would at 8 ohms or more.  As for PA speakers,  there are many brands to choose from,  I like JBL, EV, EAW but I don't like Yamaha, Peavey or any of the real cheap brands.