BMW 135is Speaker Size

Rear Side Panel Speaker

Front Door Panel Speaker

Rear Deck Lid Speaker

Below Seats Speaker

BMW 135is Speaker FAQ

What speakers should I upgrade first in my BMW 135is for the biggest sound improvement?

Replace the front door 4-inch component speakers first. These handle most of your mid-range frequencies and vocals - they're doing the heavy lifting for sound quality. The BMW 135is uses a component setup up front, so you're already getting dedicated tweeters. Look for speakers rated around 50-75 watts RMS with 4-ohm impedance. The front stage creates your stereo imaging, so this upgrade delivers the most noticeable improvement. After that, consider the 8-inch subwoofer below the seats if you want more bass impact.

Can I replace just the tweeters in my BMW 135is without changing the main speakers?

You could replace the 1-inch tweeters independently, but it's not ideal. The BMW 135is has tweeters in three locations - front doors, rear side panels, and rear deck. However, tweeters are voiced to match their paired drivers. Mismatched frequency response between new tweeters and old main speakers often sounds... off. Plus you're looking at six separate tweeter replacements. Better approach might be replacing complete component sets in the front doors first, then evaluate if the rear tweeters still need attention.

What's the difference between the rear deck and rear side panel speakers in the BMW 135is?

Both locations use 4-inch coaxial full-range speakers with 1-inch tweeters, but they serve different purposes. Rear side panel speakers provide rear passenger audio and some ambient fill. The rear deck speakers add width to the soundstage and help with rear imaging. Since they're both full-range coaxials rather than components, they're easier to replace as single units. Look for coaxials with frequency response around 60Hz-20kHz and sensitivity ratings of 87-90dB. The rear deck position typically gets better bass response due to the larger mounting surface.

How much power do the BMW 135is speakers need for proper performance?

The 4-inch speakers should handle 25-50 watts RMS comfortably, though most factory systems probably push around 15-20 watts. The 8-inch subwoofer below the seats can take more power - maybe 75-150 watts RMS depending on the specific driver design. Don't get too caught up in peak power ratings; they're mostly marketing. Focus on RMS power handling and make sure your amplifier doesn't exceed the speaker's thermal limits. The 1-inch tweeters typically handle 10-25 watts, but they're usually protected by crossovers anyway.

Should I keep the factory 8-inch subwoofer in my BMW 135is or replace it?

Depends on your bass expectations. The factory 8-inch under-seat subwoofer provides decent low-end extension, probably down to around 40-50Hz. It's positioned well for even bass distribution throughout the cabin. If you're satisfied with moderate bass levels, upgrading to a higher-quality 8-inch driver in the same location works well. For serious bass, you'd need to add a separate powered subwoofer system. The under-seat location limits displacement, so there's only so much output you can achieve regardless of the driver quality.