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Author Topic: Advice: PRX612m/ VRX918s / SRX818sp DJ Setup  (Read 4310 times)

Mike Sircee

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Re: Advice: PRX612m/ VRX918s / SRX818sp DJ Setup
« Reply #20 on: July 26, 2021, 03:55:15 AM »

Peak or continuous, it doesn't matter. If you have an amp that will provide 3,000 watts to two subs regardless of their wattage rating, and you have the same 3,000 watts going to your mains, you will need at the very least to double the amount of subs and the power you have for them.

Going down the powered road: Let's assume you buy a pair of SRX-828 subs and a pair of SRX-815 mains. They have the same total power each. Each model touts a 2,000-watt peak amplifier. So if the one pair of 828's do not do it for you, you will need yet another pair, or possibly 4X as many of them.

Watts do not = Volume. The difference between 2,000 watts and 1,500 watts with the same speaker is about 1db.

Eluding to the question Matthias asked, there is a way to mathematically guesstimate how much amplifier power you need based on the speaker specs you have to come to a potential peak SPL level ( volume ) and at what distance you can achieve a desired SPL. If you don't know what volume you want at X distance, then looking at watts, speaker sensitivity, and a number of subs or speakers is of little use. Most " sound guys " go by gut if you will. They use X gear once, twice, several times and get an idea of what it will do. They then use that experience to guess if what they have will do the task they are asked to do. This is often what gets them into trouble. They can bring too much and waste time, energy and destroy the aesthetics of an event, or they can bring too little and not make anyone happy either way.

Doing sound is more about physics more so than " I think I can ". A good system designer can tell you pretty much exactly what you can or can't do with what is available, and integrate a system to perform to an above-average standard without doing much work at all. Doing a lot of the math and planning ahead of time can save you money on purchases, setup time, labor, storage, and transportation costs. Heck, even insurance costs can be reduced by smart purchases and more methodical systems design.

I can't tell you if you need 2X or 4X more subs and if adding X sub to your current setup will achieve what you desire. I can tell you that if what you currently have isn't enough for you, then you will need more. How much more? Well, that depends on what your target is. Knowing the goal is a large part of the equation. If you don't know what the goal is, then it becomes a moving target. And what you feel today may not be what you feel tomorrow.

So to shorthand this. You can do a couple of things. If you don't have the amount of bass you want, you can reduce the level of the mains to acquire the balance/ratio of bass you desire, but your volume limit will be dependent upon what the subs will allow. If the subs start clipping, you have no more volume to give. Or you can throw more subs at the problem. Ideally, you want the same brand and model, but that isn't always in the budget. Having different brands and models of speakers makes calculating the actual gains a little more challenging, but you can come to a reasonable expectation.

Thank you for the thorough explanation, this makes a lot of sense and as I said in my last replay, I gained a lot of knowledge over the past few days and it's amazing how many guys are out there, like me, who were just listening to people who really don't have a clue.  This whole topic has given me a lot to think about. Appreciate it!
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Matthias McCready

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Re: Advice: PRX612m/ VRX918s / SRX818sp DJ Setup
« Reply #21 on: July 26, 2021, 03:31:13 PM »

that's a loaded question for a guy who's not a sound engineer.


Thanks I will be here all day  ;) ;D 8)

Joking aside, perhaps get an SPL meter? And measure what feels good to you. Note you may want to measure C weighted so you can get an idea of how much subbage your are liking.


There was a lot of talk about comb filtering, yet I may have an untrained ear and have a bit of tinitus from years working in the nightclub industry,  after a lot of reading on comb filtering I haven't really noticed it. We will be setting up the system this week and will run several tests to now that I have a better understanding.

If you are not hearing the comb filtering, play some pink noise through the system, and walk the coverage area. You will hear it!  ;D

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The bottom line is that more top boxes don't net much of increase in volume, but they do make things sound much worse.

Subs when placed together can work together. Hence why more is helpful.

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This all comes down to physics.

The higher the frequency the shorter the wavelength and the lower the frequency the longer the wavelength.

I suggested doing some searching for frequency, wavelength, and com filtering.

Homework questions for you  ;)

1) Why is a subwoofer just as loud 10ft behind it as in front of it? What does this have to do with wavelength?
2) How does the horn size of a speaker affect its pattern control, as relates to frequency?

If you figure out and can answer these questions I think things will start to click into place for you.  :) :)

Have fun!
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Luke Geis

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Re: Advice: PRX612m/ VRX918s / SRX818sp DJ Setup
« Reply #22 on: July 28, 2021, 12:31:57 AM »

The only reason to need more mains is to increase the coverage area. A 30' X 40' area will be covered perfectly fine by two mains. You have the volume from the mains you want, you just want more lows. So yes, start by adding more subs. Knowing how much your subs are lacking by would help in factoring in how much more sub-power you need. If you feel you need +10db more subwoofer output ( that would be twice the current perceived output, or twice as loud ) then you would know you need at least 4X the number of subs. If you feel you only need +6db more sub output, then you would only need twice as many as you currently have to get real darn close to that.

With subs, you get a +3db boost in output for the doubling of power and another +3db for doubling the number of elements moving air. In theory, you should have about a +6db increase in output if you double the number of subs and if you double the number of amps you use. In practice, I feel you gain a solid +4 - 5db, but that is close enough really.

You have to know your target though. If you double the number of subs and that still isn't enough, then adding a third pair may not finish the job, and adding even a full quad more may only just get you where you want at the expense of a TON of space and power needs. Often it is best to know what your target is and do the math to find a speaker and amp combination that gets you closest to your goal utilizing the least number of amp channels and speakers.
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Re: Advice: PRX612m/ VRX918s / SRX818sp DJ Setup
« Reply #22 on: July 28, 2021, 12:31:57 AM »


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