BMW 128i Rear Side Panel Speaker Size
The BMW 128i rear side panel accommodates a 0.75 inch speaker size and 1 inch speakers, along with 4 inch units. Compatible audio types for the system include tweeters and midrange replacement units. The specifications cover a range of years from 2008 to 2013.
| Year | Type | Size (inch) |
|---|---|---|
| 2013 | Tweeter | 1 |
| 2013 | Midrange | 4 |
| 2012 | Tweeter | 1 |
| 2012 | Midrange | 4 |
| 2011 | Tweeter | 1 |
| 2011 | Midrange | 4 |
| 2010 | Tweeter | 0.75 |
| 2010 | Midrange | 4 |
| 2009 | Tweeter | 0.75 |
| 2009 | Midrange | 4 |
| 2008 | Tweeter | 0.75 |
| 2008 | Midrange | 4 |
Speaker Types
| Type | Description |
|---|---|
| Tweeter | A small driver built for high frequencies, typically from about 2,000 Hz to 20,000 Hz. It adds treble detail and clarity and is usually mounted near ear level or aimed at the listener. |
| Midrange | A driver for the middle of the audible range, typically from about 300 Hz to 5,000 Hz, where vocals and most instruments sit. It is often paired with a tweeter and a woofer. |
Additional Notes
- The rear side panel location of the BMW 128i accommodates a 2-speaker configuration per position, pairing a small-diameter tweeter with a 4 inch midrange driver across all listed model years.
- The 4 inch midrange driver handles the middle frequency band, roughly covering vocals, instruments, and upper bass detail, a range well-suited to a rear side panel placement where the speaker fires into the cabin passenger area.
- A 4 inch cone diameter produces a relatively directional midrange dispersion pattern, meaning rear side panel positioning angles the sound toward seated occupants rather than diffusing it broadly across the cabin.
- The tweeter sizes specified across all listed years are either 0.75 inch or 1 inch, both of which reproduce high frequencies, generally above 3,500 Hz, where wavelengths are short and highly directional.
- The 1 inch tweeter, listed for 2011 through 2013, has a slightly larger radiating surface than the 0.75 inch unit, which corresponds to marginally lower high-frequency extension before off-axis dispersion narrows significantly.
- The 0.75 inch tweeter, listed for 2008 through 2010, has a smaller diaphragm that extends into upper treble frequencies but narrows its dispersion cone more quickly, affecting how high-frequency energy spreads from the rear side panel position.
- The BMW 128i rear side panel transitioned from a 0.75 inch tweeter to a 1 inch tweeter between the 2010 and 2011 model years, representing a dimensional compatibility distinction relevant to replacement fitting.
- Rear side panel installations typically involve enclosed or semi-enclosed mounting cavities within the vehicle body structure, which can influence the low-frequency output of a 4 inch midrange driver through internal volume resonance.
- The physical proximity of the tweeter and midrange within the rear side panel unit means crossover frequency alignment between the 2 driver sizes affects how smoothly the frequency response transitions from the midrange band to the high-frequency band at the listening position.
- A rear side panel location places both drivers behind and to the side of seated occupants, a geometry that can introduce time-delay differences relative to front-mounted speakers, affecting perceived stereo imaging.