Boat Audio

[Legacy]

Im in search of an expert in audio. I am installing a 4 channel amp with 7 speakers on the boat. One of those is a sub that im looking to add to the rear channels. What the proper way to add it using this diagram. Unless of course you have a better solution all together. I wouldnt be opposed to adding a separate amp for the sub on a switch to have the abilty to turn on/off. Thanks!

 

[Chas0218]

What I would do is bridge the rear channel for the sub and install inline speaker crossover for the sub to only allow the low range frequencies to the sub. only thing you will end up loosing is the ability to turn the sub off. If you wanted you could also add a quality inline switch to allow you to turn off the sub when needed.

 

Can you list some of the specs for the amp?

 

Here is an example of a crossover I'm referring to.

http://www.parts-express.com/parts-express-80-hz-low-pass-8-ohm-crossover--266-442?utm_source=google&utm_medium=cpc&utm_campaign=pla

Edited March 14, 2016 by Chas0218

[Legacy]

heres my other thought and just add a switch to the sub amp to power on/off.

 

[Chas0218]

Here is a photo of what I meant. How big of a subwoofer? Why dont you want to power your speakers from your radio and run only an amp for your subwoofer?

Edited March 14, 2016 by Chas0218

[hermit]

If you start bridging things you will have to make sure the impedance (ohms) work out and your amp can support the lowered resistance.   This actually applies to anything you're trying to do here since you're running either 6 or 7 speakers on 4 channels.

 

Do you have a line-level out you can run to a powered sub?  Like in the wiring diagram above (Legacy's), with the sub-out from the receiver and before the amp.  That would be easiest I think.

Edited March 14, 2016 by hermit

[SylvanTroller]

I think running the sub off the amp and the speakers of the radio is the way to go. Straight forward and that way you shouldn't over power your speakers. At least that's how we used to do it back in the run dmc days.

[muskiedreams]

heres my other thought and just add a switch to the sub amp to power on/off.

 

 

This diagram looks like it is showing a head unit with line outputs (like preamp outputs) for the main amp(s) and sub. With a separate sub amp, there is usually an electronic crossover involved which splits the audio so everything from mid base and up goes to the main speakers and only low base goes to the sub.

 

If the receiver has actual speaker outputs that go to the power amps, the power amps must be able to accommodate that type of input. In this type of system, the crossover is usually in the 4 channel amp.

 

If you add two speakers to the front channels you will be lowering the load impedance on those channels. If the amp is not rated to operate at the lower impedance, you could blow the amp. When you wire two speakers in parallel like in the diagram Chas0218 posted, the load impedance on the amp will be half that of one of the speakers. If both speakers are 8 ohms, the impedance will be 4 ohms. Most mobile audio systems are rated to handle that and the power output will be higher with a 4 ohm load. But many of the speakers are 4 ohms and if you put two 4 ohm speakers in parallel, the load on the amp will be 2 ohms which may overload, overheat and possibly burn out the amp. You must check the specification for the minimum load impedance rating of the amp.

 

Funny it doesn't show a power lead going to the receiver. I think each electronic component should have it's own fuse also.

[Chas0218]

This diagram looks like it is showing a head unit with line outputs (like preamp outputs) for the main amp(s) and sub. With a separate sub amp, there is usually an electronic crossover involved which splits the audio so everything from mid base and up goes to the main speakers and only low base goes to the sub.

 

If the receiver has actual speaker outputs that go to the power amps, the power amps must be able to accommodate that type of input. In this type of system, the crossover is usually in the 4 channel amp.

 

If you add two speakers to the front channels you will be lowering the load impedance on those channels. If the amp is not rated to operate at the lower impedance, you could blow the amp. When you wire two speakers in parallel like in the diagram Chas0218 posted, the load impedance on the amp will be half that of one of the speakers. If both speakers are 8 ohms, the impedance will be 4 ohms. Most mobile audio systems are rated to handle that and the power output will be higher with a 4 ohm load. But many of the speakers are 4 ohms and if you put two 4 ohm speakers in parallel, the load on the amp will be 2 ohms which may overload, overheat and possibly burn out the amp. You must check the specification for the minimum load impedance rating of the amp.

 

Funny it doesn't show a power lead going to the receiver. I think each electronic component should have it's own fuse also.

If wired in parallel he won't lower the impedance. a 4 channel amp should handle anything down to 4 ohm and most of your 3 way speakers are 8 ohm so it shouldn't be a problem even in series. The sub on the other hand could be an issue unless it is a 4 ohm dual voice coil-over.

[muskiedreams]

Ohms divide in parallel and add in series.  Two 8 ohm speaker in parallel would be 4 ohms and in series they would be 16 ohms. But also when you use two in parallel as opposed to one, you will increase the wattage substantially (almost doubled) because the amp puts out more power into a lower impedance. I was just saying before that if they are four ohm speakers, you shouldn't wire them in parallel because you will have only 2 ohms which will probably blow the amp.

[GAMBLER]

PM the runner up from the WHI sound off!

[Big Water]

Ohms divide in parallel and add in series. Two 8 ohm speaker in parallel would be 4 ohms and in series they would be 16 ohms. But also when you use two in parallel as opposed to one, you will increase the wattage substantially (almost doubled) because the amp puts out more power into a lower impedance. I was just saying before that if they are four ohm speakers, you shouldn't wire them in parallel because you will have only 2 ohms which will probably blow the amp.

Correct

[Legacy]

PM the runner up from the WHI sound off!

[Chas0218]

Ohms divide in parallel and add in series. Two 8 ohm speaker in parallel would be 4 ohms and in series they would be 16 ohms. But also when you use two in parallel as opposed to one, you will increase the wattage substantially (almost doubled) because the amp puts out more power into a lower impedance. I was just saying before that if they are four ohm speakers, you shouldn't wire them in parallel because you will have only 2 ohms which will probably blow the amp.

You aren't taking into consideration it is dual voice coils that means (2) 4 ohm voice coils and when wired in series is 8 ohms total.

[muskiedreams]

You aren't taking into consideration it is dual voice coils that means (2) 4 ohm voice coils and when wired in series is 8 ohms total.

The purpose of a dual voice coil subwoofer is not to connect them in series.  It is to be able to connect right channel to one voice coil and left channel to the other. This is after you filter all but low frequencies either through an active electronic crossover (for a biamp configuration) or a passive crossover. So you then have a mono woofer that is more robust because of the two voice coils and you get the best efficiency from the power amp.

[Chas0218]

The purpose of a dual voice coil subwoofer is not to connect them in series.  It is to be able to connect right channel to one voice coil and left channel to the other. This is after you filter all but low frequencies either through an active electronic crossover (for a biamp configuration) or a passive crossover. So you then have a mono woofer that is more robust because of the two voice coils and you get the best efficiency from the power amp.

What you are describing is considered bad practice in car audio. If he is considering buying a sub woofer he should buy a dual voice coil 2 ohm sub. This would allow him to run the 2 voice coils in series (4 ohms) while bridging the amp (2 wires) and running 1 crossover some amps actually have built in crossover on their bridged connection so he wouldn't need to buy a separate crossover. Instead of running 4 wires and 2 crossovers.