PDA

View Full Version : 2 ohms or 4 ohms????



morgan040
07-01-2011, 12:24 AM
Its a long story on why and how I have these options but here is the senerio, What would you do???

I have a kicker 2500.1 and have the opportunitiy to run it with a 12" Massive DMX and it would be wired at 4 ohms because it is a quad 1 ohm Speaker. so my amp would only be putting out 1250 watts at 4 ohms.....

OR

I can run it with a Memphis Mojo D4, so It would be wired at 2 ohms allowing me to run my amp at full power 2500 watts at 2 ohms.

At 4 ohms the amp will run much cooler than running it at 2 ohms, being tucked away in that cubby I think this is a good idea but am I wasting all that power I could be using if I run it at 2 ohms with the MOJO.

How much louder would it really get?? or would it get louder?

Retail the Memphis Mojo is $599 and the Massive DMX is $799.

Right now I have the Massive DMX in there and it is WAY LOUD. Should I swap it for the MOJO? if I do I cant swap it back, so ......... tough question

I was hoping some of you Stereo genius' would give me a good idea as what you would do.

My box is a down firing 3 cubic feet ported box with 2, 4" ports

ian ashton
07-01-2011, 11:01 AM
I would personally wire for higher impedance - sure, you can get more power with lower, but being in a boat chances are you are going to be pounding it for long periods of time, on hot days. Lower loads generate more heat and draw more current. Either option is going to be loud, build for longevity.

EarmarkMarine
07-01-2011, 11:27 AM
morgan,
A difference of 1250 watts is a major increase when going from 125 watts to 1500 watts, at least a 10 dB increase in fact which is perceived as twice as loud. However, going from 1250 watts to 2500 watts is no more than an additional 3 dB in a perfect world. And, 1 dB is the smallest increment that you can discern. Other factors will come into play that will somewhat reduce the expected increase at that type of power level including power supply voltage sag, speaker compression as the voice coil heats up and as the voice coil travels out of the sweet spot. So that theoretical 3 dB increase will never be completely realized.
I look at it like this. If I'm doubling my power by using an amplifier that is twice the power at the same impedance then I'm going to hear a difference in control and dynamics because I have twice the reserves. In my opinion the system that is run most conservatively will always sound the best. If I am having to drop the impedance in half in order to double my rated power then in reality I am not getting double the power. Two many other negatives are brought into play.
Specifications can be difficult to compare from brand to brand too.
Usually the amplifier efficiency drops as you lower the impedance. So another concern that I have is do I really want to more than double my current draw for less than a 3 dB increase. Where will those dominoes fall? The true power of an unregulated amplifier will drop like a rock as your battery voltage falls.
If you can enlist Phil from Kicker in this discussion, he is very knowledgable about this subject and may have some valuable perspective and contrasting language to offer. He states things very well.

David
Earmark Marine

philwsailz
07-01-2011, 12:31 PM
Hey Morgan, Phil here-


On the amp - woofer interface: You are debating the impedance. David is right, 3dB is 3 dB but it is only 3 dB A measuring device sees 3 dB as doubling of amplitude, but our ears barely hear it. It is not a lot.

The box: we know it is 3 cu. ft. vented, but we don't know how long the two 4" ports are. At this point, without going and looking up the two woofers and modelling them in the enclosure we don't know what the change will be. We also need to know what length your ports are to know for sure what you have currently.

Is the Massive woofer 3db more efficient than the Memphis? It is possible, and all other things being equal if the Massive is more efficeient than the Memphis you for sure will not hear the difference.




You say the Massive is WAY LOUD. Is that what you want? If so, it seems to make sense to leave it alone. If it is not what you want, can you verbalize or explain what you are missing at your ears? Do you want it even louder?

If your goal is WAY louder, swapping woofers is not going to do it. What you are suggesting in a car analogy is swapping out a GMC V8 for a Chevy V8. Okay maybe more like swapping out a Brand-X V8 for a Brand Y V-8, (to keep the Ford, Dodge and Chevy guys off of my neck). We can get into woofer brand arguments all day, and many folks here do, but physiscs is physics and we all gotta play by the same rules. It is highly unlikely that you will be able to hear any volume difference. You may think you hear it, but that is your ear-brain system trying to rationalize it for you and make you think it souds better. Emperor's New Clothes...


If you want it WAY louder, you need to add another woofer and enclosure.... Then the analogy turns into swapping out a 4-cylinder for a V8.
With two woofers, two enclosures and a 2-ohm load you have twice the cone area, and almost twice the power... that is going to be close to 6 dB which IS noticeable

Can't go two woofers? Well, you are back to the current question as asked. I will restate what I did above. While 3 dB is 3 dB it is only 3 dB. If you put 3 dB more into the same woofer, you are not going to really notice much of a difference. Your amp will though. It will work twice as hard, drawing twice as much current, getting at least a little warmer, (the amp you have is a Class D amp, so there is some efficiency built in) while not quite delivering twice the power as David points out.


Tell us more what youi perceive is lacking with the current system, and then we can make some recommendations; some that might be better than simply wishing on the hopes of a woofer swap...

Sorry, I have rambled, but I think what I shared is going to help put your head better around your question.

Let us know!
Phil
Kicker

EarmarkMarine
07-01-2011, 12:47 PM
Here is a way to more objectively clarify what you will hear as a 3 dB increase. Sit in your boat with only the in-boat speakers playing. No sub. Balance from one channel only to both channels set in the middle. That change in amplitude is the maximum and probably more than you would discern as a difference.

David
Earmark Marine

bergermaister
07-01-2011, 03:58 PM
My .02/experience regarding heat-

My cabins run 4ohm, 12" sub runs 4ohm, both those amps stay reasonably cool. Tower runs 2ohm and that amp definitely gets noticeably warmer than the other ones do.

morgan040
07-02-2011, 05:22 AM
Wow, This is really good info!

I think I am going to just keep the woofer that is in there so I can leave it at 4 ohms, I like the idea of keeping the amps cooler and I agree, I wasnt sure I would even notice the difference in sound.

I wish I could add another woofer but I just dont have enough space!!! I guess I know I can always upgrade when I get another boat and know this amp can handle running 2 12s down the road.

Thanks again for your input guys!!!

New Guy
07-02-2011, 10:45 AM
Morgan how about some pictures of this setup??