18. Screen Readability

Figure 97: Measuring Screen Readability

In order to test the 755T's screen brightness, I used a Mastech Digital 4-range luxmeter (LX1330B), capable of accurately measuring from 0 up to 200,000 lux. A luxmeter is used for checking the level of illuminance, defined as: 'the density of the luminous flux incident on a surface'. It is the quotient of the luminous flux by the area of the surface when the latter is uniformly illuminated. - (E = df / dA). This luxmeter has a rated accuracy of ±3% ±10 digits.

The nüvi 755T was placed in a controlled lighting area, inside a light tent illuminated by daylight balanced (5500° K) fluorescent lamps (the lamps are positioned on both sides of the GPS, as well as directly above it.

The luxmeter's sensor was held 1-inch away from the LCD display, with the light sensor horizontally facing the screen. The GPS was set to the Main Menu during the light reading, and the screen brightness was set to 100%. Measurements were taken three times, and the average was used.

In order to accurately compare screen readability between models, I have established Garmin's nüvi 660 as the baseline reference model. At the time of its release, the nüvi 660 sold for around $1,000, and was Garmin's most expensive automotive GPS at that time. The nüvi 660's LCD display was generally considered to have the best display of any GPS at that the. Other GPS displays may have come close, but none were better. In fact, the 660 at the time of its release was as close to a spare-no-expense GPS as had been seen.

The nüvi 755T's display measured almost identical brightness to the reference nüvi 660. The average reading for the nüvi 755T was 302, while the nüvi 660 scored 305 - a negligible difference that's within the margin of error for the luxmeter's rated accuracy.

In other words, the nüvi 755T has a bright, high contrast* display that's on par with the nüvi 660 reference display.

* The ability of a display designed into an electronic device to produce and maintain a viewable image with discernable differences between the lightest and darkest parts of the image when subjected to varying external and/or ambient lighting conditions.

19. Speaker Volume & Quality

Figure 98: Measuring Speaker Volume

Like most GPS units, the nüvi 755T has a rear-facing internal loudspeaker.

An Extech Type 2 digital sound level meter was used to measure the sound level at maximum volume. This type 2 sound level meter meets ANSI and IEC 651 Type 2 standards, and has a rated accuracy of ±1.5dB.

The sound meter was setup on a tripod spaced 12-inches (measured horizontally from the face of the LCD display to the tip of the sound meter) from the GPS.

The volume was set to maximum on each GPS tested, and the sound level meter was set to capture the peak level over a 2 minute period while the GPS simulated a route.

Although the nüvi 265WT registered slightly "louder" than the 755T, the speaker was tinny and distorted at maximum volume. The nüvi 755T wasn't quite as loud as the nüvi 660, and I did, at times, find it difficult to hear the GPS when driving at highway speeds.

20. Playing Audio Through Your Vehicle's Speakers

The nüvi 755T has an internal FM transmitter that lets you broadcast the nüvi's audio over FM to your vehicle stereo system. Set the nüvi and your car's radio to the same, unused, FM frequency, and the nüvi's audio is heard through your car's much better, louder speaker system rather than the nüvi's internal speaker.

Figure 99: Main Menu

To switch the audio output from the internal speaker to the FM transmitter, touch Main Menu > Volume > Audio Output > FM Transmitter.

Figure 100: Audio Output

Touch Audio Output.

Figure 101: Current FM Frequency

Touch the large blue frequency button to change the FM frequency, if needed.

Figure 102: Adjust FM Frequency

Find an unused spot on the FM dial using your car's stereo, then use the Plus and Minus buttons to tune the nüvi to the same frequency. Once both the nüvi and your car's radio are set to the same channel, you'll hear the nüvi's audio output via the car's speaker system.

Figure 103: Mixer

It's also possible to adjust the volume levels for navigation prompts and media (music, Audiobooks) separately via the Mixer.

The ability to hear the nüvi's audio on your car's speaker system is a potentially powerful feature that can turn the GPS into a full fledged a media hub, linking cell phone, navigation, and music all into one seamless combined system.

Unfortunately, the nüvi 755T's fatally underpowered FM transmitter remains totally inadequate, just as it has been on previous Garmin nüvi models. Even the weakest FM interference causes static, and the nüvi isn't powerful enough to broadcast over other FM frequencies. The result is an endless hunt for unused FM frequencies that must be re-adjusted every 10 miles or so.

I became so fond of using the car's speaker system instead of the nüvi's internal speaker for hands-free calling, mp3 playback, and navigation prompts, that I ended up working around the poor FM transmitter and using a cassette adapter (one that's designed for use with mp3 players) instead, plugging the cassette adapter into the car's tape player and the other end into the headphone jack on the nüvi.

Garmin says the poor FM transmitter performance is the result of FCC regulations that limit the power output of the transmitter. However, I've tested GPS units from Alpine and TomTom where the FM Transmitter works very well.

Simply put, the FM transmitter is so underpowered that it's almost useless.