I want to setup a PA system (in my new barn/playhouse that will never move) to drive 6-8 speakers, with each speaker rated at 75 watts RMS @8 ohms and 92 db sensitivity. I will use a 750 watt or 1000 watt amp in an 8 Ohm bridged mode (that means a 500 watt@8ohms amp with 2 channels, but will configure it as bridged and get 1000 watt@8ohms). I am new to all of this, so please be patient.
Please see attached pictures for the specifications and possible configuration. One of my pictures shows one possible “parallel” configuration, but I am just not sure of my ohms understanding.
I am building a barn/playhouse in Thailand, and it is 15meters x 15 meters inside (50 feet x 50 feet). This system is for the inside. Thai’s like it loud. See attached picture.
My primary question is getting the resistance/ohms correct with so many speakers, and what is a decent strategy for getting it done. I can see some of the first decisions is wiring parallel or serial. I watched YouTube and read websites to understand this. I focused on Parallel, as the wiring is simpler for me.
- Do I add resistors to the circuit, so at the end, the amp is presented with something around 8 Ohms? I included a picture of adding a 100 watt@50 Ohm resistor to each speaker, in order to get back to roughly 8 ohms. If I add a 50 ohm resistor to 8 ohm speaker, I get 58 ohm speaker. If I have 8 speakers, I assume I take 58 ohms/8 speakers to get around 7 ohms total resistance?
- For a system with 75 watt speakers, driven by a 1000 watt@8Ohms bridge mono amp, so I use 100 watt resistors? I hope so, as they seem easy to get. Bigger ones are harder to get and get expensive? I have attached a picture from China on the type of resistors I can easily get.
- What happens if my overall ohm presentation to the amp is much lower, like 4 or even 1 ohm? Seems to me if I had 2 speakers in parallel @8 ohms, it would present to the amp only 4 ohms. Is this bad? Is there a range of allowable ohm tolerance?
- Or am I thinking about this all wrong?
I will add a separate amp for some subwoofers. I was thinking 4 subwoofers that are 150 watt RMS @8 Ohms, and use a similar amp and use the low cut filter option on the amp. So your advice on my 8 speaker main system on how to get the correct impedance, will also apply to this separate subwoofer system.
I bought a pair of these speakers already, and hooked them to an existing stereo so hear how they sounded. To me, they are perfect. I also bought 1 sub-woofer for testing – and I love it too. I just need to get the resistance and wiring correct.
If you come to Thailand, please visit. I like beer.
Thanks - Pat
PS: I tried to upload more than 1 picture, but it only allows 1 tiny picture, so I chose the one with the parallel wiring diagram. Maybe I can add more later, but this one picture does some up what I am trying to achieve.
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