Re: JBL SRX / QSC PL236 underpowered?
It doesn't have to be difficult to factor what you should be powering a speaker with. Take the information given and run with it. If the speaker says it will handle X amount of continuous, program and peak power that is all you can go by. The manufacturers will sometimes divulge what they feel is an appropriate amp. In general it is usually an amp that is rated right about where the program power is for said speaker. Others ( people ) will say to simply double the continuous power rating and there you have it. I prefer a slightly different approach, but then again I prefer to run my equipment at around 70-75% of what it can do.
The more scientific way ( the way I like to do it ) is to factor the speakers sensitivity and my desired SPL level. I want some room left over, so I spec for equipment that will acquire the desired results and still be within a reasonable safety margin. The peak SPL listed by manufacturers is not going to happen. So I rely more on the continuous SPL listed ( if it is ), if it is not listed then I subtract 6db from the peak as a safety margin. I want the continuous SPL to be above my desired SPL. Next I do the math. Speaker sensitivity is rated at 1W/ 1 meter. Easy enough, I just start doubling the wattage over and over till I reach the desired amount of gain needed, relying on the old adage that every doubling of power is = to 3db of possible gain. 1w, 2w, 4w, 8w, 16w etc. until the desired SPL at distance is achieved. You will run into one of two things? You will either reach your desired SPL, or you will run out of speaker/amplification...... Don't forget to factor distance for your desired SPL level....... The SPL that will be reached based on the 1 watt/ 1meter rule will be the SPL at 1 meter! So at 50-100' it will be of course much lower by 6db for every doubling of distance. Inside an indoor venue you will not loose as much energy, but that is another issue all together.
If you have more than 1 sub you can add 3db for every doubling thereof. But this is really only true if they are side by side. Placing the subs on the ground will net another 1-3db to that total. I don't rely heavily on half space loading addition, so I add 2db as it is a safe addition to the figures. This should give you a rough idea of what your capable of providing if you do the math on your current rig. It's not an exact science, but it can give you general idea of what you can provide. As long as you intend to work below the factored max ratings you can provide, you should get the results you desire. Once you want to go above the factored potential, your on borrowed time. This is why I shoot to run at 70-75% of potential. My amps, speakers and everything related to it should be able to provide what I need with a good margin left over for the unknown........
If you have done the math and you factor you need X power to get the desired SPL result, the next step is finding an amp with at least that amount of power and not exceeding the speakers peak power rating. I find that the optimal amp power rating usually exists somewhere between the program and peak power rating. Power compression is tough to calculate, but wattage loss over X cable distance is another thing to consider. This should be factored into your decision as well. Just when you thought you had it nailed......... You will more than likely need an amp rated for higher than the manufactures recommended amp power, but that is dependent upon your needs? I prefer to run on the high end and use DSP/ speaker management to reduce speaker damage. So now comes the next issue.
Diminishing returns......... At some point you will either get to where there is no appreciable amp that will provide the exact needed power and stay within budget. To get that last 3db and still be within the speakers peak power rating may cost more than that 3db is worth? You have to spec within a margin that will also appease a budget. You may find that getting that last 3db of desired SPL may cost you more than the speaker your powering? So you may end up having to run with an amp that is running near it's limit if you have to run your system that hot? It's something to consider. What you need, what you can acquire and what you can afford are all part of the big picture. So is your 1K watt amp enough for your current speakers? That depends on if you already have enough to get there and if not, will getting there cost you more than it's worth? If getting the last 3db is not possible then you will have to settle for the next best thing that you can afford. This difference may only result in a couple db loss in potential, but you will be working the system that much harder for more time. If you spec your system to have more than the needed levels you will have little to worry about. The goal is to spec a system that can easily achieve what is needed and within budget.
It's not very black and white, but it's also not very difficult. Simple math will give you an idea and reasoning will finish the job. I prefer to run at 70-75%, but on occasion I have to run beyond that. It's all about needs, not what is truly right, or wrong. Is your amp under-powered? Only if it doesn't meet your current demands.......
