2X subs @ 8 or bridged @ 4 (parallel)

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9 years 7 months ago #22004 by keith
Major newbie question,

I have a Mackie M1400 amplifier feeding two 12" Electro-Voice "subs".

What are the comparative pros and cons between feeding each 8 ohm speaker with each side of the stereo amp (300 watts X2 @ 8 ohms) and feeding the two speakers in parallel with the amp bridged to mono (1000 watts X1 @ 4 ohms mono)?

Also, I have a fairly regular gig at this place where I hang my speakers. Hanging the speakers is easy but wiring them is difficult. The owner has a large spool of single strand solid core copper wire, the kind used in commercial construction 20 amp AC wiring. I am currently re-hanging my 16m wires each gig but he said I could have the wire to string up in a (semi) permanent way with boxes on each end for speaker connectors.

My second quesion is this, is it better to use my 14 gauge speaker wires directly from amp to speaker (without any additional connections) or is it better to string the solid core (unknown guage but MUCH thicker than my 14 gauge wires) and connect the first 3m and the last 3m each time, creating two more connections between the amp and each speaker? By the way, this is a covered outdoor venue.

Thanks in advance.

Take care, Keith

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9 years 6 months ago #22038 by bjm362
Replied by bjm362 on topic 2X subs @ 8 or bridged @ 4 (parallel)

keith wrote: Major newbie question,

I have a Mackie M1400 amplifier feeding two 12" Electro-Voice "subs".

What are the comparative pros and cons between feeding each 8 ohm speaker with each side of the stereo amp (300 watts X2 @ 8 ohms) and feeding the two speakers in with the amp bridged to mono (1000 watts X1 @ 4 ohms mono)?

Also, I have a fairly regular gig at this place where I hang my speakers. Hanging the speakers is easy but wiring them is difficult. The owner has a large spool of single strand solid core copper wire, the kind used in commercial construction 20 amp AC wiring. I am currently re-hanging my 16m wires each gig but he said I could have the wire to string up in a (semi) permanent way with boxes on each end for speaker connectors.

My second quesion is this, is it better to use my 14 gauge speaker wires directly from amp to speaker (without any additional connections) or is it better to string the solid core (unknown guage but MUCH thicker than my 14 gauge wires) and connect the first 3m and the last 3m each time, creating two more connections between the amp and each speaker? By the way, this is a covered outdoor venue.

Thanks in advance.

Take care, Keith


Mackie rates that amp
1400 watts @ 4 ohms bridged
1000 watts @ 8 ohms bridged
700 + 700 watts @ 2 ohms stereo
500 + 500 watts @ 4 ohms stereo
300 + 300 watts @ 8 ohms stereo
If you are talking about a pair of those EV subs wired in parallel, that is a 4ohm load. 1400 watts. While they rate the amp down to a 4 ohm load in bridge mode, what is its life expectancy really under heavy use at that load?
They also don't specify if that is peak or continuous. I looked up some EV 12 inch subs that are rated at 800 watts...also not specified if it is peak or continuous.
If that is a continuous rating from the amp, and a peak rating from the cabs, you are inviting destruction! Even if that is a peak rating from the amp and a continuous rating from the cabs it is still in the seriously likely to self destruct area!
Presuming that is a peak rating on the amp, adding a matched amp to run each sub in bridged mono, with a really good "brick wall" limiter could help you quite a bit! Your mismatch becomes safe to dial in!

As to the wires, the question can't be answered accurately without more info, Stranded wires do conduct better than the same gauge solid core due to the surface area. Your 14 gauge may be OK depending on the length of the runs. The solid cores may actually be better, depending on how much bigger they really are.
I don't know if that helps you or not!

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9 years 6 months ago - 9 years 6 months ago #22045 by keith
Replied by keith on topic 2X subs @ 8 or bridged @ 4 (parallel)
Thank you so much for your response. Your answer was very helpful.

While your answer is helpful, I would love to understand the issue better generally. Would you be so kind as to explain the general pros and cons of:
Using amps in bridge mode vs. dual mono
Running amps at various impedances
Running speakers in series/parallel
What is the power rating of 2 X 100 watt @ 8 ohm speakers when run in parallel, yielding a 4 ohm load? In series at 16 ohms? Sound any different?

I see the obvious reciprocity occurring as one (more or less) halves impedance and doubles wattage. I get why impedance mismatches between amp and speaker are a no-no. I dont get why someone would chose to run at a given impedance if more than one option is available. Why have I heard of people searching for gear specifically to run at low impedances? I just don't understand the overall issue and would like to so any insight you are willing to share is greatly appreciated.

If you are talking about a pair of those EV subs wired in parallel, that is a 4ohm load. 1400 watts. While they rate the amp down to a 4 ohm load in bridge mode, what is its life expectancy really under heavy use at that load?
They also don't specify if that is peak or continuous. I looked up some EV 12 inch subs that are rated at 800 watts...also not specified if it is peak or continuous.
If that is a continuous rating from the amp, and a peak rating from the cabs, you are inviting destruction! Even if that is a peak rating from the amp and a continuous rating from the cabs it is still in the seriously likely to self destruct area!
Presuming that is a peak rating on the amp, adding a matched amp to run each sub in bridged mono, with a really good "brick wall" limiter could help you quite a bit! Your mismatch becomes safe to dial in!


So I believe the EV Sb120s are rated at 300 watts. Don't know if that's peak or continuous. I hope to God that's continuous. These can hardly be called "subs". They are really more of a low-mid. I plan to re-cab the drivers in a couple of Cubo-12s this fall. Also, I'm using a DriveRack+ for these, my FOH. The limiter will be set for safety per the dbx manual.

Thanks again for your help.

Take care, Keith
Last edit: 9 years 6 months ago by keith.

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9 years 6 months ago - 9 years 6 months ago #22047 by bjm362
Replied by bjm362 on topic 2X subs @ 8 or bridged @ 4 (parallel)
Here are some real basics that might help.
Most of us are accustomed to old school power ratings, each given in RMS at a specified impedance. advertisers have founs a way around established industry standards and can essentially rate their power amps at whatever they want by saying it is peak.
Continuous and peak are both numbers you need to know to match needs with both amps and speakers.
Actual peak as a standard rating is rms times 1.415
Sometimes speakers are rated with continuous, program and peak...largely to confuse you more IMHO (so they can give you bigger numbers. Amps that are rated rms have worked well with speakers in the same number range as program in my experience!
Square waves (clipping) will destroy drivers really fast, in order to prevent that most people prefer to have a little more peak power than required (headroom)!
Overpowering speakers to much makes it easy to blow them even with a clean signal.
There electronics that can help with some of those scenarios, internal protection as well as additional devices such as limiters.
A stereo amp that will pump out 1000 watts per side each into an 8 ohm load costs a lot more than two amps that will each in bridged mono pump out 1000 watts into 8 ohms.
The term Subwoofer is used very loosely, a great deal of commercial "subs" won't produce anything musical near the true subwoofer range.
Horns are way more potent if you use them in the range they were designed for...an 80hz horn can sound like a bullfrog on crack trying to produce a bass players E let alone the B from a 5 string!
Nobody on the internet is going to replace your gear if it blows, so it is up to you to take advice with appropriate grains of salt, and do your research!!!!
That is all pretty generalized, and really basic....but maybe I was able to help you a little !
Edit: There are some Engineers that sometimes participate in this forum that can probably give you some very accurate answers to a lot of your questions. I am not an Engineer, I am a DJ/Musician, but hopefully some of my brief answers really can at least get you headed the right way. Some of the really accurate answers an engineer might write would inherently be an entire article in length!
Last edit: 9 years 6 months ago by bjm362.

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