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PostPosted: Thu Sep 13, 2018 5:48 am 
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Joined: Sat Apr 19, 2014 6:06 pm
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Location: Chilliwack, BC, CA
Hi folks,

I got this incredible JBL subwoofer, a real legend actually. W15GTi mkii. It is an oddball however with dual 6 ohm voice coils.

So parallel, it's 3 ohms. Series it's 12. Most amps only specify ratings for either 4 or 8 ohms.

The amp I have chosen for my needs is the Paradigm X-850, but they very specifically say it's only warranted to power their proprietary subs which are 8 ohms.

Now I'm not an idiot so I know right away not to parallel the coils as it will run 3 ohms and I'm guessing the amp isn't designed to throw that much current down to the sub, based on their technical service advisors blankly telling me not to do it as it may permanently damage the amp.

But if it's connected in 12 ohms, it should limit the current below the rated 850 watt value based on their 8 ohm design, right? Maybe it'll only throw 550 watts RMS down to the sub?

I'm an electrician but not an electronics expert.

The only other sub amps I've looked at for this are the Dayton Audio amps and Crown rack amplifiers. But again nothing seems to have info for 3 or 12 ohm loads.

I picked the paradigm because it looks amazing and found it for 75% off :D


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PostPosted: Thu Sep 13, 2018 6:20 am 
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Joined: Mon Feb 03, 2014 7:21 am
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Location: Grimsby, ON, CA
Hi.

Check out the Crown xls series. They rate outputs at 2 ohms so I assume relative stability. I use one with a 4 ohm Tekton Speaker
in a 2 channel system and it works very well.


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PostPosted: Thu Sep 13, 2018 6:35 am 
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Joined: Wed Feb 27, 2013 8:43 am
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Location: Stratford, ON, CA
Hi,

The ratings for amps are usually into a nominal 8 ohm load - sometimes 4 ohms to bump up the power ratings in watts. You are right not to push that amp into a 3 ohm load. But the impedance load that a loudspeaker presents to an amp varies quite widely depending on the frequency(cies) being reproduced. Wiring the sub so it presents a 12 ohm load is safe and will only reduce the potential output power of that amp by a fraction - likely not even noticeable.

Cheers,
David Neice

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PostPosted: Thu Sep 13, 2018 7:53 am 
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Joined: Mon Apr 26, 2004 2:33 pm
Posts: 3222
Location: Toronto, ON, CA
Any power amp with an adequate 4-ohm rating will work fine:

Crown, QSC, MC2 and Lab Gruppen are a few of the many pro audio brands that would work, though there you usually have to accept some degree of fan noise.

There's any number of inexpensive, Class D plate amp modules made for subwoofers, though I generally find these to be of inferior quality.

And any relatively high powered solid-state consumer amp should also work well: Bryston, older McCormacks, SimAudio, etc., etc.


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PostPosted: Thu Sep 13, 2018 10:23 am 
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Joined: Sun Apr 05, 2009 7:06 pm
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Location: hawkesbury, ON, CA
just bought a crown macroteck 1200 for $300. it sound great with my tc sounds axis 15 inches.it deliver just a few watt under 1200 watt bridge at 4 ohms.


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PostPosted: Thu Sep 13, 2018 10:32 am 
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Joined: Fri Dec 02, 2011 8:49 am
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Location: Saint-Augustin-de-Desmaures, QC, CA
Masama wrote:
Hi.

Check out the Crown xls series. They rate outputs at 2 ohms so I assume relative stability. I use one with a 4 ohm Tekton Speaker
in a 2 channel system and it works very well.

+1 and easy to find used. Behringer can do also but you will likely want to change the fans: https://www.youtube.com/watch?v=zG1WJA4Nux4

Also, plan your crossover before buying your amp as many pro amps have crossovers and often DSP. The DSP can be used to flatten room response based on measurements at your listening position if you want to get into fixing room modes.

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PostPosted: Thu Sep 13, 2018 10:45 pm 
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Joined: Sat Apr 19, 2014 6:06 pm
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Location: Chilliwack, BC, CA
zon001 wrote:
just bought a crown macroteck 1200 for $300. it sound great with my tc sounds axis 15 inches.it deliver just a few watt under 1200 watt bridge at 4 ohms.


Thanks for the input from everyone.

I looked at Crowns a bit futher and as far as being used for subwoofers, they don't offer control for frequency cutoff and gain, phase etc. Some of them have gain, sure, and phase in my experience doesn't really matter much unless there is distance or stereo subs being used.

But to those that have set up a power amp that didn't have the subwoofer controls built in, what do you use? My receiver already has digital cutoff settings just like any other when addressing LPF / LFE details.. so do I necessarily need a physical knob or not?


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PostPosted: Fri Sep 14, 2018 3:03 am 
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Location: hawkesbury, ON, CA
BSavvy wrote:
zon001 wrote:
just bought a crown macroteck 1200 for $300. it sound great with my tc sounds axis 15 inches.it deliver just a few watt under 1200 watt bridge at 4 ohms.


Thanks for the input from everyone.

I looked at Crowns a bit futher and as far as being used for subwoofers, they don't offer control for frequency cutoff and gain, phase etc. Some of them have gain, sure, and phase in my experience doesn't really matter much unless there is distance or stereo subs being used.

But to those that have set up a power amp that didn't have the subwoofer controls built in, what do you use? My receiver already has digital cutoff settings just like any other when addressing LPF / LFE details.. so do I necessarily need a physical knob or not?

if driving your sub amp , from processor or av receiver, lfe output, your processor is dealing with frequency cut off and level. so no need for the amp to do those things. but if feed from just a pre amp out, then you need a cross over.the newer crown amp , some of them have built in xover, equalizer, and limiters.


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