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wiring a D4 sub to a 2ohm stable amp


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nyguy4u 
Copper - Posts: 148
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Joined: December 31, 2003
Location: New York, United States
Posted: June 15, 2005 at 11:51 PM / IP Logged  

What's up guys. I have an issue, and everyone I talk to is giving me different answers, and maybe you guys can help me out.

I have 3 15" JL W3V2 D4's. I also have 3 Kenwood KAC-929's, one running to each sub. Also, I have a Audio Control Matrix Line Driver to properly split the RCA 3 ways. I hate Y adapters.

Here are the specs for my amp...

Two-channel power amplifiers such as the 150 watt x 2 channel KAC-929 2-Channel Power Amplifier are hard to beat.The bridged rating of this amp is 460 watts and the maximum output rating is 1000 watts. Included Features are tri-mode operation, a variable low-pass crossover, selectable bass boost, a dynamic expander, and 2-ohm stability. Also included are speaker level inputs, speaker relay protection circuitry, and a Quiet Turn-On circuit.

  • stereo or bridged mono output
  • Tri-Way capable
  • 460 watts x 1 in bridged mode
  • 230 watts x 2 at 2 ohms
  • 50-200 Hz low-pass crossover, 18 dB/octave
  • selectable 0/+6/+12 dB bass boost at 90 Hz
  • speaker-level inputs
  • 4-way protection circuitry
  • cooling fan
  • signal-to-noise ratio 100 dB

I'll just use one sub as an example being it'll be the same for the other 2.

Currently the sub is wired for 8ohms. I think. Right now, on the sub.. I have a wire going from the +, to the -, on the other side of the speaker. And, the + of the amp to the remaining + on the sub, and the same for the -. When I had it installed, this is what they did. He also bridged the amp.

Now, in talking to people, they are saying to wire it in 2ohn not 8, by taking 2 short wires.. and on the speaker, run the - to the -, and the + to the +, and take the + and - from the amp, and run them to the + and the - on the sub. That's a parralel set up I believe?. Then I was told after that is complete, to lower the gain on the amp a good amount, and use the Matrix to adjust the gain.

Now, in reading the specs for the amp, it's saying it's 2 ohm stable, but not in bridged mode. I am into SPL, and I want to get every bit out of the amp as I can. But, I don't know how to wire it. I really don't know.

As I said, right now the sub is wired at 8ohm, from my understanding. But, people are telling me to wire the sub in 2ohms, and not bridge the amp.

What should I do?, and if I did wire the subs in 2ohm, and not bridge the amp, will I hear a noticable difference then what i'm hearing now??. Because right now, the bass is really clean, deep, and loud. But of course, i'd like to get even more SPL if i'm able to, safely.. with the equipment I already have.

Please tell me what route I should go, and the pro's and con's of each. And if all possible, where I should have the gains/lp crossover/bassboost etc on the amp properly set at.

Any help will be appreciated.

DukeDuke 
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Joined: November 01, 2003
Location: United States
Posted: June 15, 2005 at 11:55 PM / IP Logged  
Wiring Option #1
wiring a D4 sub to a 2ohm stable amp -- posted image.
Duke Duke
nyguy4u 
Copper - Posts: 148
Copper spacespace
Joined: December 31, 2003
Location: New York, United States
Posted: June 16, 2005 at 12:07 AM / IP Logged  

ok thanks. So basically when the guy installed my equipment, he wired it in 8ohm, and what everyone is telling me, regarding wiring it in 2ohm is correct.

Now comes the amp, the amp is not 2 ohm stable in bridged mode, to my understanding. So, how should I run my amp?. Set the selector to "mono", and run out of one channel?.

Am I going to hear that noticable of a difference?, because myself being a newbie.. I see running it at 2ohm would drop the wattage. So, that leaves me alittle confused.

DukeDuke 
Silver - Posts: 206
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Posted: June 16, 2005 at 12:10 AM / IP Logged  
Wiring Option #2
wiring a D4 sub to a 2ohm stable amp -- posted image.
Duke Duke
nyguy4u 
Copper - Posts: 148
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Joined: December 31, 2003
Location: New York, United States
Posted: June 16, 2005 at 12:13 AM / IP Logged  
That second diagram is how it's wired currently.
stevdart 
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Joined: January 24, 2004
Location: Pennsylvania, United States
Posted: June 16, 2005 at 5:15 AM / IP Logged  

nyguy4u wrote:
 I am into SPL, and I want to get every bit out of the amp as I can.

That second diagram, at 8 ohms per sub/amp, is correct.  But  your original selection of equipment is where you went wrong if you want to wring the maximum out of everything.  You should change either the subs or the amps...

...if you change the subs, use the D2 model instead of the D4's.  You can then wire them to 4 ohms each.

...if you change the amps, use mono amps instead of two channel amps.  With your current subs, the final 2 ohms loads will indeed work if the amps were mono.

With the change will come twice (or more) draw upon your car's electrical system, so an upgrade in alternator, wiring and batteries will most likely be necessary.  And, sound damping of the vehicle will have to be increased.  So, in reality, the trade-out will cost you.

nyguy4u wrote:
I see running it at 2ohm would drop the wattage. So, that leaves me alittle confused.

You have it backwards.  A lower impedance load on the amp will cause the amp to produce higher output.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
oonikfraleyoo 
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Posted: June 16, 2005 at 8:55 AM / IP Logged  

nyguy4u wrote:

Am I going to hear that noticable of a difference?

The difference will be heard when your amp dies from running it at 2ohms.

Nik
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Drewt 
Copper - Posts: 183
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Posted: June 16, 2005 at 9:32 AM / IP Logged  
yeah, you need either D2 subs or mono amps.
-Drew
nyguy4u 
Copper - Posts: 148
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Joined: December 31, 2003
Location: New York, United States
Posted: June 16, 2005 at 10:20 AM / IP Logged  

Yeah, I know I should either have mono amps, or D2's.. but right now, my financial situation won't allow me to do that.

I'm not sure how running my amps at 2ohms would make them "die", if the amp is 2 ohm stable. Please explain?.

So, until I buy different amps and/or subs.. I should just keep my setup the way it is?. Wired in 8ohm. And, my installer was incorrect then?.

I'd like to keep these subs, so if I did do something.. i'd buy different amps. I like an amp to a sub setup, so i'd buy 3 mono amps. With my subs, what's the highest wattage mono amp i'd be able to go?. 2ohm stable of course :)

stevdart 
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Posted: June 16, 2005 at 10:55 AM / IP Logged  

I agree with keeping the subs and changing amps, the main reason being that a mono class D amp is much more efficient in powering subs than a two channel class A/B amp.  So the load on your car's electrical system when changing won't be such a drastic difference.

Yes, you will have to keep the setup the way it is.  To explain why it doesn't make sense to you that the amp is 2 ohm stable but you can't bridge a 2 ohm load onto it:  the amp is 2 ohm stable per channel.  Bridging is across both channels, and the load is split between the two, making each channel get a load of 1 ohm.  The amp will shut down or burn up in that scenario.

Your subs are rated at 500 watts RMS.  Right now they receive about 230 watts each.  The mono amps you eventually switch to should be rated at 500 watts RMS output into a 2 ohm load. 

And...when you switch amps you will also have the opportunity to change to a single amp to power the three subs, which will result in less load on the alternator.  You could shop for a mono amp capable of 2000 watts into a combined 2.67 ohm load.  (..and save the extra cost of buying three amps...)

wiring a D4 sub to a 2ohm stable amp -- posted image.

Here's a good buy and a good example:  http://www.cardomain.com/item/JBLBPX22001Z

With the use of just one amp, you can sell the line driver and get it out of the signal path.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
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