[SlowX6M]

Anyone know if our HK subwoofers are 8" or 6"?

[chris719]

8", not sure I would call them subs, though.

[3t3p]

Mid bass units I've seen them referred to! 8 I believe also

[SlowX6M]

Tried to replace the HK subwoofers in the M2 with Bowers & Wilkins subwoofers. I have previously done so successfully in my E70 - replaced the Logic 7 subs with newest Bowers & Wilkins, and the difference is night and day.

Didn't get so lucky in the M2, the B&W subs fit perfect, direct replacement, but they do not punch as hard as the stock HK subs. I guess this is due to the different resistance across them, Logic 7 subs were 8ohm, B&W are 6ohm, and the HK are 2ohm. I guess the stock amp is not able to drive the B&W to the full extent.

I wonder if replacing the amp with Bavsound amp will help.

In the pictures below, the B&W sub is the one with the yellow cone and shallow magnet.

[WagonR]

The factory amp is tuned for a 2 ohm "sub" so 6 ohms is basically going to play at 1/3 the volume. Replacing with the Bavsound amp will probably not help, because they tune for either their speakers, or the factory speakers, either way, their tune will expect to be driving a 2ohm "sub".

The Bimmertech or Audiotec Fisher Match PP 86DSP or Match Up 7 would allow you to up the input to match the 6ohm "sub". The Bimmertech amp is just a rebranded AF Match PP 86DSP, as a FYI.

[SlowX6M]

Originally Posted by WagonR

The factory amp is tuned for a 2 ohm "sub" so 6 ohms is basically going to play at 1/3 the volume. Replacing with the Bavsound amp will probably not help, because they tune for either their speakers, or the factory speakers, either way, their tune will expect to be driving a 2ohm "sub".

The Bimmertech or Audiotec Fisher Match PP 86DSP or Match Up 7 would allow you to up the input to match the 6ohm "sub". The Bimmertech amp is just a rebranded AF Match PP 86DSP, as a FYI.

Yep, it looks like most of BMW's subs are either 8ohm or 2ohm. The B&W is probably nominal 8, but in reality closer to 6.

Thank you for the advice on the amp, I will contact Bimmertech and consult with them. I would really love to use these B&W subs, I have them from factory in my F96 and I swapped them into my E70, and they are awesome.

One more question - is there a risk of damaging the amp or the subwoofer while they are mismatched? If I decide to go with the bimmertech amp, I'd like to leave the B&W subwoofer installed for now.

[SlowX6M]

Is the bimmertech amp plug and play? Any issues with it?

[WagonR]

I think 2, 4, and 8ohm is what I've seen for replacement "subs", but I wouldn't be surprised if there were some 6ohm ones too.

No issues with the bimmertech amp, but again, it's just a Audiotec Fisher Match PP86DSP amp. All of those amps are Digital Sound Processing (DSP) amps. You can change everything in them, each speaker output is 100% customizable with software you can load on a laptop. To be honest, it's a bit overwhelming how much you can do.

The nice thing with the bimmertech version is that they've created tunes for individual models that you can either just load their file into the amp, or you can load their file as a base and customize the tune from there. However, you can find those baseline tune files on the forums, so you don't necessarily need bimmertech. That said, I think they do provide some service if you buy the amp form them. If you took the standard M2 file from bimmertech you could adjust the "sub" settings to up the output by 3x to make it the equivalent of going form 2ohm to 6ohm.

The Match Up7 has more watts per "sub" channel, so if you're starting form scratch I'd go with that, but any of them are really good options. They usually are for sale on the forums, so you can get into one for around $600ish. Plug and play harness, so easy to reverse if you want.

[WagonR]

Your current setup shouldn't damage anything. The sub is just being under-driven by the amp. I think the risk would be you had an amp putting out power for a 6ohm speaker and you plugged in a 2ohm speaker - you'd be overpowering the speaker and could blow it. You're in the opposite situation here.

[SlowX6M]

Nice, thank you so much. I think I will go with bimmertech just for the support, maybe they can even help me set it up. I am not an expert in audio, just want to get a bit of an upgrade over my stock system.

[chris719]

Originally Posted by SlowX6M

Nice, thank you so much. I think I will go with bimmertech just for the support, maybe they can even help me set it up. I am not an expert in audio, just want to get a bit of an upgrade over my stock system.

The impedance in this context is just telling you what ratio of voltage/current you need to achieve a specific power. Essentially Ohm’s Law even though we are taking impedance not DC resistance. V = I*R, so R or Z = V/I, P = V*I, etc. The sensitivity is usually expressed in dB SPL @ 1W at 1 meter at a certain frequency.

Anyway, what has been said is correct basically. The HK system doesn’t have an internal boost converter from what I’m told, so it must operate internally on 12V alone. That means it can’t swing any more than that at its outputs. To get a system that can play loud with those kinds of low voltages, you need very low impedance speakers. That means more current and less voltage needed for the same output. Usually this is a pretty crappy tradeoff, which is why you see good home speakers mostly around 8 ohms. It won’t hurt your speaker or the amp, but you’ll get less output most likely as you noticed, unless the driver was super efficient.

In fact, if I were designing a brand new automotive system, I would go for higher voltages and higher impedances. I’m going to guess that soon the declining cost of DC-DC converters will make this happen since the OEM can then save weight with thinner wiring for the same amount of loss and possibly even lighter voice coils on the drivers themselves. Driving 2 ohms is no fun for most amplifiers, so they will be a lot lower distortion and cooler closer to 8. If they are paralleling outputs for current for 2 ohms they can save money there too.

As others have said, the DSP in the amp is tailored to the stock speakers, so upgrading the amp is unfortunately required unless you’re lucky and arrive at something listenable anyway.

[SlowX6M]

It is weird how BMW designs their audio systems. All their speakers and subs are the same size, and interchangeable between systems/models, but with different specs. I'm pretty sure they are all made by HK, and brand labels such as B&W, B&O, etc are just licenses.

For the 2 series in particular, the HK system uses 2ohm subs, but the base system in the 2 series uses 8ohm subs. But in a F30 3 series, its exactly the opposite - standard system uses 2ohm subs, while HK subs are 8ohm.

[SlowX6M]

By the way, these B&W subwoofers are sweet when paired with proper amp. I have swapped B&W mids and subwoofers into my E70 that came with Logic 7 originally, and they are awesome. Much better than stock Logic 7, or the bavsound that I had in it for a whole. This is why I'm trying to do the same in the M2.

[JSebF1]

Hello
So all m2 including m2 competition are with 2ohm subs? Im thinking upgrading to Focal ISUB BMW2.

[chris719]

Originally Posted by JSebF1

Hello
So all m2 including m2 competition are with 2ohm subs? Im thinking upgrading to Focal ISUB BMW2.

As far as I know, yes. Let me know what you think if you do. I actually think that most aftermarket 8" woofers will not be an upgrade over the stock given the constraints of the enclosure. The Focal is possibly better given the specs, but not sure. If you are using the stock amp it probably isn't going to be better, might even end up with less output.

[MR RIZK]

Originally Posted by chris719

As far as I know, yes. Let me know what you think if you do. I actually think that most aftermarket 8" woofers will not be an upgrade over the stock given the constraints of the enclosure. The Focal is possibly better given the specs, but not sure. If you are using the stock amp it probably isn't going to be better, might even end up with less output.

I tend to agree. Had a listen to a fully upgraded system that was running a pair of stegs under seat drivers. There was a difference but not to the extent that most would hope for at the price point.

At the end of the day we all know the enclosure volume is quite small so if you are hoping for a dramatic difference or thinking will it be good enough most will be disappointed.

For me I'm running a custom setup of AVI's, Match AMP and oem subs. The only reason I would change the subs is cause I'm bored.

But hey, each to their own choices