[autoart]

My car has a 4ohm sub. logic 7 I believe. Can I install a 2ohm sub? will it damage the amp.? or sound bad? Can I add a resister to it?
I am almost getting it for free that's why I'm asking. Thanks.

[sk1939]

A 2 Ohm sub will be louder than a 4 Ohm sub, and will demand more power due to a lower resistance. If your replacing the stock under-seat sub using the integrated amp I wouldn't recommend it.

[rbryantaz]

Originally Posted by sk1939

A 2 Ohm sub will be louder than a 4 Ohm sub, and will demand more power due to a lower resistance. If your replacing the stock under-seat sub using the integrated amp I wouldn't recommend it.

Some amplifiers are also not stable with 2 ohm loads especially if they are using a BTL (bridged) configuration.

In general you can always put in higher resistance speakers on an amplifier but lower can create problems.

2 ohm speakers draw twice the current so therefore twice the power at a given voltage so the amp has to be able to handle it. I am how the BMW amplifier is designed.

The sensitivity (efficiency) of the speaker also plays an equal role. If you have an 91db sensitivity 4 ohm speaker it will be roughly the same SPL (sound pressure level) which is essentially volume that you would get with a 2Ohm 88db speaker. Power and SPL doubles every 3db.

Car speakers are usually lower ohm (impedence) than home audio speakers because cars run at 12-14volts which really limits the amplifiers. Home amplifiers usually run 30-70V at the amplifier rails depending on the power requirements.

-Rich

[ctuna]

There was a thread in here someplace where people substituted
other stuff for the underseats, it was a long way back.

The following thread has some info about the output chips

https://www.e90post.com/forums/showthread.php?t=1144129

https://www.e90post.com/forums/attac...2&d=1435788287

pretty underwhelming at BMW specs the power a 10 percent distortion.

[mweisdorfer]

Originally Posted by autoart

My car has a 4ohm sub. logic 7 I believe. Can I install a 2ohm sub? will it damage the amp.? or sound bad? Can I add a resister to it?
I am almost getting it for free that's why I'm asking. Thanks.

Generally speaking, you want the RMS of the amp & the RMS of the sub or speaker to match or be very close. You also want to ensure the ohm at the proper RMS matches as well.

A lot of amps will list 2 RMS values

Like :

250 RMS @ 2ohm
150 RMS @ 4ohm

So, for example you have underneath subs that that have a 150 RMS @ 2ohm value with a peak of 500watts

You would want to have the amp be 150 RMS @ 2ohm.

The stock logic 7 amp might be around 60 watts per channel. The logic 7 subs are 4ohm. I don't know the RMS of the logic 7 amp.