Playing with my Polk DB651s set up - 2 ohm vs 4 ohm question

[swatski]

I'm playing with my DB651s set up and wondering about the following.
What would be a best/most efficient configuration given:

1. 10 speakers - Polk DB651s (RMS: 120 watts per pair)
   
2. 2 micro amps - Clarion 1410 (RMS Power Rating: 4 ohms: 50 watts x 4 chan. / 2 ohms: 75 watts x 4 chan.)

Currently, I have those set up as the most simple install:

1. bow/mid/mid/rear (1 pair each) cockpit speakers (4 pairs) powered by 2 amps (2 pairs per amp, running at 4 ohms)
   
2. the swim platform speakers are on the factory HU - those speakers sound a bit subdued (by comparison to the ones powered by the amps in the cockpit)

I am considering pairing all 4 of my mid cabin speakers (mid/mid) to run off of 2 channels (2 speakers per channel in parallel - 2 ohms) leaving the other 6 (bow, rear, swim) speakers at 4 ohms (1 per channel - 4 ohms).

Would this be an issue - running one of the amps as "4 speakers/2 chan. // 2 speakers/2 chan."?

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[Bruce]

The wattage available to each of the 4 cabin speakers would be reduced from 50 to 37.5. The increase in power to the swim deck speakers would likely be substantial.

I suggest trying it and if you do not like it add another amp.

 

[swatski]

The wattage available to each of the 4 cabin speakers would be reduced from 50 to 37.5. The increase in power to the swim deck speakers would likely be substantial.

I suggest trying it and if you do not like it add another amp.

Will do. That whole ohms business is out of my comfort zone. I needed someone to confirm I wasn't missing something obvious - thank you!
The amps are said to be "2 ohms stable", but I have never before played with impedance. (I mean - knowingly, lol)
I love how efficient this little system is with two micro amps, and trying to squeeze everything I can out of it.

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[maboat]

OR...

Power the bow speakers from the HU and then run the Mid/Mid/Rear/Swim off the two 4-channel amps.

 

[swatski]

I guess the question is - if there are any long term disadvantages associated with running an amp/speakers like that at 2 ohms? Would it be pushing the limits and asking for failure? I can't tell.
(kind of want to set it up and be DONE, not have to worry)

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[Bruce]

Ohms are similar to the load you are pushing up a hill. The higher the number the more work required to push it. When you wire two matching speakers in parallel half of the available watts go to each and the ohm rating halves. The reduction in ohms (resistance) allows the same amp to push out more watts.

I believe you already have the amps. If you did not I would suggest the JL MHX280/4 which appears to be a very similar product. I am sure the JL is 2 ohm stable. Your amps are rated to handle 2 ohm loads so you should be fine.

 

[robert843]

@swatski Do you have any pics in a thread somewhere I would like to see where you added the mid speakers?

 

[swatski]

@swatski Do you have any pics in a thread somewhere I would like to see where you added the mid speakers?

I spent months debating where to place the extra DBs, finally decided on this (don't have the pics with speakers in, but these are the new/extra locations - in addition to 4 factory speakers)

Mid-ship strdb side

Port:

And swim deck:

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[swatski]

@robert843 Those extra mids make a huge difference, as you know. With two pairs there, that's when I started thinking of spreading it out a bit more, it is a lot of sound in the mid cabin. But I am convinced that is the way to go - if you want the most efficient system.

 

[swatski]

I believe you already have the amps. If you did not I would suggest the JL MHX280/4 which appears to be a very similar product. I am sure the JL is 2 ohm stable. Your amps are rated to handle 2 ohm loads so you should be fine.

Oh, those JLs are nice, of course.
I mounted the amps to start testing the setup, and now is the time to change anything. Can't wait to be done, but still waiting on my distribution blocks and couple other things.


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[robert843]

@swatski I agree I think speakers mid cabin will help with sound at speed I only plan to add two should I go with your upper or lower mount were there any issues with either? That upper mount looks tight.

 

[swatski]

@swatski I agree I think speakers mid cabin will help with sound at speed I only plan to add two should I go with your upper or lower mount were there any issues with either? That upper mount looks tight.

The upper mount is @fraserjr baby. It is awesome, IMO. Plenty of room if going with DBs, but I think @Julian or soemone else managed to squeeze JL 6.5"s there as well - without any spacers.

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[swatski]

were there any issues with either?

No real issues, but running the speaker wires from the port-mid is a bit of a pain. I don't have pics but can take some over the weekend if you want - ran mine across/around the ski locker (under the floor), I found out those boats are pretty tightly sealed under the fuel hatch, that was a surprise to me.

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[Julian]

Yup...I got JLs to fit fine....they sound so good I'm thinking of replacing all my polks with JL!

 

[swatski]

Yup...I got JLs to fit fine....they sound so good I'm thinking of replacing all my polks with JL!

Oh, don't burst my bubble, @Julian !!! LOL

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[Julian]

Oh, don't burst my bubble, @Julian !!! LOL

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Sorry........I thought I'd be fine with Polks....but when I plugged these JLs in they were noticeably better.....<BOAT-Break Out Another Thousand> LOL

 

[Mainah]

Be careful with the Polks. I am not recalling if it is the db series or the mm series or both but the true impedance on them is 3.7 ohms which when split in two gets dodgy for the amp. @Bruce made a good comparison to pushing things uphill. Impedance is resistance and I like to compare it to deadlifting. If you think you have 400 lbs on the bar but only have 200 lbs then exert 400 lbs worth of power that bar is going to come up with much more energy (watts in this comparison). Doing this multiple times as a human means you can do it quicker and your heart rate goes up quicker so you heat up. If an amp is not 2 amp and stable or there is too much load on a 2 ohm stable amp it will overheat or clip the signal.

 

[fraserjr]

@swatski I agree I think speakers mid cabin will help with sound at speed I only plan to add two should I go with your upper or lower mount were there any issues with either? That upper mount looks tight.

What boat do you have? Running the port speaker wires for me was actually pretty easy since I mounted the amp near the batteries. The starboard run was a bit longer and I ran it through the engine compartment along the front edge of the hatch.

 

[maboat]

Be careful with the Polks. I am not recalling if it is the db series or the mm series or both but the true impedance on them is 3.7 ohms

That statement is true of ALL speakers. No "4-ohm" speaker is fixed at 4 ohms. Impedance changes with frequency. Speakers are labeled with "nominal" impedance which is an approximate average resistance over the frequency range of the speaker. Any speaker's resistance in ohms is lower at lower frequencies and higher at higher frequencies with the nominal impedance being the approximate middle.

 

[swatski]

Be careful with the Polks. I am not recalling if it is the db series or the mm series or both but the true impedance on them is 3.7 ohms which when split in two gets dodgy for the amp. @Bruce made a good comparison to pushing things uphill. Impedance is resistance and I like to compare it to deadlifting. If you think you have 400 lbs on the bar but only have 200 lbs then exert 400 lbs worth of power that bar is going to come up with much more energy (watts in this comparison). Doing this multiple times as a human means you can do it quicker and your heart rate goes up quicker so you heat up. If an amp is not 2 amp and stable or there is too much load on a 2 ohm stable amp it will overheat or clip the signal.

That is exactly why I was asking here about it. Even though this is a decidedly "budget" upgrade, I would like to configure the system to stay healthy for a long time, alleviating unnecessary risks of amp heart attack!

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