In the spirit of sharing, I'm posting my findings as I dive into the world of in-car measurement w/ a laptop & microphone data acquisition system. I hope others can benefit as I learn the ins and outs of using this tool, and I continue to move forward in that never ending quest for better sound.
- I've always wanted to better understand my car's acoustics.
- I already had a laptop, so buying a mic and setting up a measurement system was both inexpensive and easy.
- What measurable differences in frequency response will we actually see when speakers (raw drivers) are put in the "harsh" automotive environment?
- Does a "car-audio" specific driver really work that much better than a "home" driver in a car door?
- What impact does sound deadening and install effort have on the frequency response of a car door loudspeaker?
Figure 1: Measurement Setup
- Acer "Ferrari" Laptop
- M-Audio MobilePRE USB
- Behringer ECM8000 Measurement Microphone
- Associated connection cables
- ARTA Software
- My 1999 Honda Accord LX 4 Dr., Phoenix Gold XS6600 Amplifier "rear" channels driving the door speakers
- Seas W15LY-001 loudspeakers
- Seas Lotus Reference RW165 loudspeakers
Figure 2: Microphone Placement (those are shadows, my car isn't that dirty! )
- Hardware was set up per manufacturer's recommendations.
- Microphone placement per Figure 2.
- Sound output was input directly into the car amplifier, bypassing the processor completely. Only one channel measured at a time.
- Impulse response measurement (MLS), 1/3 octave smoothing.
- First round of measurements were done with two pairs of speakers: Seas Excel W15LY-001 and Seas Lotus Reference RW165. No modification or additions to the car door accept for the attachment of MDF mounting/spacer rings.
Figure 3: Left Door, W15LY-001
Figure 4: Left Door, RW165
Figure 5: Right Door, W15LY-001
Figure 6: Right Door, RW165
- Cone breakup is readily seen (just under 5 KHz) in the RW165 on figures 4 and 6.
- No surprise: left and right side response are quite different, note the poor bass response on left side.
- As expected, the magnitude of the swings in frequency response are quite astounding over the speaker's usable range when placed in a car door.
I exported the data from ARTA and graphed/overlaid the W15 with the RW165 so that a more direct (in door) driver-to-driver comparison could be made. The results are shown below.
Figure 7: Comparison of the the W15LY-001 to RW165, Left Door
Figure 8: Comparison of the the W15LY-001 to RW165, Right Door
Key Takeaways: (however obvious they may be)
- The vehicle's transfer function (environment) has far more impact on frequency response than any other variable. Differences between drivers are relatively small in comparison.
- Differences in driver performance (frequency response) are quite measurable. These drivers to me sound different, particularly in the midrange, and the differences in response from ~1KHz and up correlate well with my subjective evaluations.
- I was surprised that the lower frequency response of the two drivers didn't differ more, but there does seem to be a small measurable difference nonetheless. It's not much though, and error in accurate gain setting and in measurement repeatability renders that point completely moot.
- If smooth frequency response is your goal, there's no way of getting there without having separate left/right EQ, AND alot of control via parametric or NUMEROUS graphic bands.
- Deadening/sealing the doors to see how that impacts speaker frequency response. I myself have experienced enormous subjective differences with installs in the past, and I'd now like to see how that measures.
- Testing ensolite and/or other treatments behind the speaker to see how they impact frequency response. (How effective they are at killing "midrange echo"?)
- If I'm ambitious, I may try to measure differences using clay as a door "decoupler", etc... We'll see.
- If there's something interesting you want me to look at, throw your ideas my way.