Google for an SPL calculator, that should give you a good idea.

 

I agree with the other response. Just use an SPL calculator and you’ll be fine. Most cheap meters/oscilloscopes aren’t going to be fast enough to display current peaks, at least in my experience. Nicer meters can probably store the peak (kind of like an RTA graph for sound). But those get expensive quickly.

The max power rating of your speakers is based on thermal or physical limits. You won’t need anything near that to achieve ear-splitting levels of sound.

 

Use an o-scope to get the most accurate readings

Another option is you can rent a pro amp from many musical instrument vendors for a weekend. Most professional amps have power output lights to inform you of actual power output, clipping and/or limiting of the amplifier. Plenty of pro sound amps also have DSP and can be connected to your computer to give you a ton of information on your TV screen. Input signals, output signals and so on.

My garage speakers use a pro amp to drive them with full DSP, parametric EQ and adjustable limiters and crossover filters along with output lights. I've connected it to some frends systems so they can get an idea in real time how much power they require until the sound level becomes painful or their speakers start wildly distorting. Also connected that amp to my pre-amp outs on my AVR to see how much power was required at reference (40 watt peaks) so no worries about outboard amps required with my high efficiency speakers. Very entertaining to go rockstar mode and tap the adjustable limiters at my speakers max power (around 300 watts) and know they keep their composure even at ear bleeding levels for the win.

True, I did all those calculations and measurements before I built the latest rig and my calculations were very close to actual power required. This is a hobby so I found it entertaining to see if my calculations agreed with actual power outputs from the pro amp on screen display. All depends on how far you want to geek out with your rig, your mileage will vary.

Extra tip, don't buy amplfiers that have no power output or limiter/clip lights--at the minimum a clip light gives you a visual warning to turn it down to both protect your ears and prevent damage to your equipment. No indicators is like driving a manual transmission sports car without a tachometer--going by ear with engines will get you into trouble.

 

First, you are way over complicating this. Nobody does this kind of analysis. Amp power is more about headroom than straight usage. If you find that your speakers distort at a certain level, then you need a more powerful amp. Rarely does anybody with out some really hard to drive speakers need more than 200wpc.

 

The real issue is the efficiency of your speakers. Highly efficient speakers need very little power. Many can play very, very loud with only 10 to 20 watts of amplifier power. Even average speakers don't need as much power as you think they might. Most of the time at moderate levels, even these average speakers are only drawing a few watts. Just because your speakers are capable of handling a particular amplifier wattage doesn't mean they need that wattage to perform well. Only some exotic designs (usually with very low impedance) or highly inefficient speakers need massive wattage.

 

Thanks for all the info. I pulled up an SPL calculator (Peak SPL Calculator) and punched in my info. If I'm understanding this right, 33 watts (with an 11 channel system sitting 14' away) would result at reference level SPL (105 dB).

At this wattage, I would think two of the "new" Emotiva BasX amplifiers (BasX A7 Seven-Channel Power Amplifier) would suffice. This would save me $1600 over the other amps I was looking at. These Emotiva's could push SPL up to 109 dB if needed.

Is there any reason I should spend the extra money on the larger amps (the other amps output 180 watts/channel which could achieve 112 dB)?

That being said, I'm not sure if the Emotiva amps have limiter/clip lights so I would need to look into that.

 

Change the number of speakers from 11 to 1 speaker,

Reference is 105dB from each speaker--not all of them together. A sound rolls out from the extreme right, the right speaker has to provide the SPL..not all of the speakers. D'oh!

The SPL calculators are valuable but not exactly precise but a good starting point. Doing the math, 89dB at one watt at 4 meters distance would be a 12dB drop then add +3dB for being near a wall. You'll get 80dB so.... carry the six.... you'll need 25dB of gain from the amps or 320 watts of power.

Typically, you'll need less than that depending on the reflectivity, size and lunar phase of the moon not to mention how accurate the manufacturer makes their specs.

The accurate way to measure is to measure the output of your speaker with a 2.83V signal, be it 1KHz, pink noise or whatever. Measure what your actual SPL reads then go back to where your ears are located and measure again. That is the actual drop in SPL with distance in your room. If you get a 10dB drop from one meter to your ear location, now you know how to more accurately figure out future designs. If you like, you can also do the 2.83V signal test on one speaker outside on a ladder at one meter. Then compare the difference from the speaker actually located in the. For even higher accuracy, you can gate the measuring microphone to not allow the reflections of the ground to reach the microphone while the speaker sits on the ladder up in the air.

Depends on how OCD you are, the gated measurements with an SPL mic using REW measureing and tone sweep software is common in DIY Audio--it really matters when tweaking passive crossover filters to get even response.

Enjoy!

 

Change the number of speakers from 11 to 1 speaker,

Reference is 105dB from each speaker--not all of them together. A sound rolls out from the extreme right, the right speaker has to provide the SPL..not all of the speakers. D'oh!

The SPL calculators are valuable but not exactly precise but a good starting point. Doing the math, 89dB at one watt at 4 meters distance would be a 12dB drop then add +3dB for being near a wall. You'll get 80dB so.... carry the six.... you'll need 25dB of gain from the amps or 320 watts of power.

Typically, you'll need less than that depending on the reflectivity, size and lunar phase of the moon not to mention how accurate the manufacturer makes their specs.

The accurate way to measure is to measure the output of your speaker with a 2.83V signal, be it 1KHz, pink noise or whatever. Measure what your actual SPL reads then go back to where your ears are located and measure again. That is the actual drop in SPL with distance in your room. If you get a 10dB drop from one meter to your ear location, now you know how to more accurately figure out future designs. If you like, you can also do the 2.83V signal test on one speaker outside on a ladder at one meter. Then compare the difference from the speaker actually located in the. For even higher accuracy, you can gate the measuring microphone to not allow the reflections of the ground to reach the microphone while the speaker sits on the ladder up in the air.

Depends on how OCD you are, the gated measurements with an SPL mic using REW measureing and tone sweep software is common in DIY Audio--it really matters when tweaking passive crossover filters to get even response.

Enjoy!

That makes more sense. I haven't played with REW yet but do plan on buying the UMIK and playing around with it. But sounds like I may need to go with the larger amps and only watch movies during a full moon 😉. Thanks for all your help.

 

It is not proportional. It is logarithmic. You need to double your power for each 3db SPL gain. 500W may sound a lot compared to 250W but it really is 3db difference.

 

Get a digital oscilloscope app for your smartphone and purchase the necessary interface for it.

A Windows freeware scope application can use the Line In direct for measurements.

You're really looking for flat-topped signal voltages, not power.

 

For example, if my speakers have a max wattage rating of 500 watts, but an uncomfortable listening volume occurs around 128 watts, there is no reason for me to spend the money on a 500 watt (per channel) amplifier when a 200-300 will do.

The difference between 250W (split 200-300W) and 500W is only 3dB and barely noticeable. The difference in price often isn't that much anyway.

Google for an SPL calculator, that should give you a good idea.

They're not accurate as they make assumptions that don't occur in the real world. Out in a field SPL drops 6dB for every doubling of distance but it doesn't in a room as reflections from walls and floor etc will add to the apparent SPL. 3-4dB per doubling is more appropriate.

In the real world, unless you listen to extremely inefficient speakers really loud, 200W is enough for most people.