[SXX360]

A few months back I purchased an LC2i and harness from Tecnic to install an amp and sub in the trunk to gain back some of the low bass the OEM woofers lack. I am extremely happy with the results at moderate listening levels and the sub really added in well after a little crossover tuning.

Now what I'm noticing is that at high volumes you can hear the underseat woofers start to distort from playing notes that they just can't play. Would it be easiest to add a high power crossover to the underseat woofers at 50-80Hz or would I be better off getting another amp to power the underseat woofers?

I have a feeling that getting another amp is going to sound better and I know it would give me more adjust-ability on the crossover point...which leads into the next question...Does anyone know what the rated power is to the undeseat woofers? Or recommendations of amps that can power them adequately?

[Billfitz]

You definitely want to high pass filter the under seats, not only to take out content that they can't handle, but also to prevent phase sourced interactions that can cause them and the trunk sub to fight each other. The problem is that the BMW amp configuration doesn't make it an easy job to accomplish. You may have to replace the stock amp.

[SXX360]

I think I forgot to mention I have the HK sound system, but I could very easily setup to drive the underseats by an aftermarket amp with the harness from Tecnic.
And I was thinking I would have to get another amp...was just hoping I could avoid it

[Billfitz]

Originally Posted by SXX360

I could very easily setup to drive the underseats by an aftermarket amp with the harness from Tecnic.

You could do that, using a crossover to send below, say, 60Hz to the trunk sub amp, above 60Hz to the under seat woofers amp.

[SXX360]

I figured it would be the best way.... So what kind of power would I need to drive the OEM under seat subs?
I'm not interested in replacing them. I believe they are 8 ohm speakers? If so, I'm going to need a decent amp to push them

[Billfitz]

50w/channel would suffice if you use a two channel amp. I believe they're 4 ohm, so if you go mono use 100w/2 ohm rated. You can go more powerful if you want, but the trunk sub will be doing all the heavy lifting. If your trunk sub amp has a low pass filter it would be a simpler arrangement to get an amp with a high pass filter rather than add a separate crossover.

[SXX360]

If I remember correctly from what I read before I think they are actually something like 7ohms. Which is why if you aren't replacing the factory amp you have to put an 8 ohm woofer back in. If you're going to use an aftermarket amp to drive new woofers then you can pick whatever woofer will fit...but it's been a few months since I had done that research.

So I guess I need an amp that's capable of something more than 100W at 4 ohms...not hard to find but more expensive for sure

[Billfitz]

Originally Posted by SXX360

If I remember correctly from what I read before I think they are actually something like 7ohms.

I can't say, but it would be the exception to the rule. 4 ohms is the standard for auto sound, and you'll find far more 2 ohm drivers used than 8. About the only time you see 8 ohm drivers is when a pair of them are wired parallel for a 4 ohm load.

[SXX360]

I believe the HK stuff is completely different from the standard HiFi found in most BMW's in the states. I will get out the multimeter after my trip this weekend to verify.

[Billfitz]

Originally Posted by SXX360

I believe the HK stuff is completely different from the standard HiFi found in most BMW's in the states.

Probably not all that different. When I pulled my control panel to so some wrapping of the dash I noticed that the head unit is made by H-K, so it's a safe bet the amp is as well.

[Encanto]

HK OEM woofers are 7ohms.