Samsung HW-D550 HT Sound Bar

Audio|Video|Misc
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TESTS IN THE ANECHOIC CHAMBER

SPCR is a couple of big steps ahead of other PC hardware review sites in acoustics metrology. We have...

  • our own home-built, hemi-anechoic chamber, an environment that is extremely quiet and almost completely without reverberation above ~150 Hz.
  • a lab-reference, calibrated, ultra-low noise microphone with ruler-straight frequency response that cost over $2,000
  • a sophisticated PC-based sound measurement system

Our audio measurement / spectrum analyzer system consists of...

For testing loudspeakers, a signal generator is needed to drive the speakers. As the speakers have built-in amplifiers, this was provided with software via the integrated sound card of a second PC, a silent PC with no moving parts, inside the anechoic chamber.

NOTES on MEASUREMENTS and TEST CONDITIONS

1. SPL: The sound pressure level at which measurements are done is extremely important. A common procedure is to provide the sensitivity with 1W input, and also test the frequency response at the same power input. For a typical passive speaker (one that does not have a dedicated amplifier built into it), this might be something like 90 dB/W, which means when driven with 1W input at, say, 1 kHz or with white noise, the speaker output measures 90 dB SPL one meter away. In fact, 90 dB@1m is a fairly common level for frequency response measurements.

Two considerations:

What is the right baseline SPL? I have already tested some other speakers in the chamber using 85 dB SPL at 1m as a reference, so it makes sense to continued using this level. It's 5 dB lower than the usual 90 dB used for hi-fi speakers. 90 dB is much louder than you might think: Typical SPL scales suggest that 90 dB is about what you hear from a diesel truck 10m away, inside a moving subway train, or from a food processor directly in front of you.

What is a realistic volume for actual use? A check of SPL levels was done at the listening position with movies and other video material in the small media room, with seated position 6' from the speakers. The results are summarized below.

SPL @ 1m, Typical Use in Media Room
HT/TV Drama 70~85 dB
Action 75~95 dB
Documentary 75~85 dB

The SPL @1m in the TV room averaged about 80~85 dB, with some peaks reaching 95 dB or higher. Spot checks with other family members, friends and visitors confirmed that this is fairly typical: It is not likely that many people actually watch videos on their TV with higher SPL than indicated above. There are always exceptions; remember, I am just trying to establish a reasonable baseline.

2. Frequency Response: This is the single most widely cited specification in audio, especially with mechanical devices like loudspeakers, which traditionally have the greatest deviations from flat frequency response. It is best shown in a frequency vs sound pressure level graph. In the simplest terms, frequency response tells the ability of an audio device to reproduce sounds of different frequencies at the correct relative levels (loudness). (Here is a good primer on the topic.) A perfect device has a frequency response that looks like a ruler straight line; hence the term "flat" (not flat as in B-minor flat.) Alas, there are many complex issues around this much-cited parameter.

It is highly dependent on the acoustics of the room, the position of the speaker(s) in the room, and the position of the microphone. If this test is performed in a live room, then sophisticated calculations must be used to remove the effect of room reflections (echoes). Otherwise, it must be performed in an anechoic chamber.

Frequency response of a loudspeaker generally does not stay constant with loudness level. Typically, there is a range of SPL in which a speaker is most frequency-linear; go outside this range, especially above it, and the speaker will exhibit frequency non-linearities that lower fidelity.

Frequency response also changes with the angle of perception, both vertically and horizontally. How smoothly the frequency response changes as one moves off axis is a key to better sound loudspeakers.

Given the complexities, dozens of frequency response graphs could be plotted and posted... but their usefulness would be questionable for most readers. So... this is the procedure established for frequency response testing:

  • Place the speaker at the front edge of the 28.5" (72cm) tall table in anechoic chamber.
  • Place the microphone 1m directly in front, at the same height.
  • Set the output level to 85 dB@1m SPL using white noise.
  • Capture the frequency response graph at 1m distance, on axis, and at 30 degrees laterally off axis
  • Treat one satellite + subwoofer as a single speaker, with bass unit directly under the satellite.

NOTE: Normally, only a single speaker (or single speaker + center woofer) is tested, as there are many complications that arise when trying to measure a stereo pair together at the same time. In the case of the Samsung HW-D550, testing was done with the left channel speakers plus sub as well as all speakers.

3. Harmonic Distortion: This is a relatively easy parameter to measure. A pure sine wave tone is fed into the speaker, and the spectrum analyzer sums up all the aspects of the signal that are not this pure tone, expressed in a percentage of the total signal. Harmonic distortion is not particularly important, however, as it occurs naturally in music and is thus difficult to perceive. Even 10% THD at 50 Hz is probably not audible to most people if it occurs in the context of music — and I am not talking here only about a heavy fuzz bass guitar. Amplifiers and other electronics are capable of minuscule levels of harmonic distortion (say 0.01%), but it is much higher in mechanical devices like speakers, especially when large cone excursions are involved (necessary for high volume at low frequencies). Again, the SPL at which HD is measured has a serious impact on the result, as does the frequency. Simply put, the louder and lower the test tone, the harder a speaker has to work to reproduce it. Longer cone excursions almost always result in greater signal anomalies.

After much experimentation, this is the procedure established to test for harmonic distortion:

  • Place the speaker at the front edge of the 28.5" (72cm) tall table in anechoic chamber.
  • Place the microphone 1m directly in front, at the same height.
  • Set the output level to 85 dB@1m SPL using white noise.
  • Leave the gain unchanged while running test tones at the following frequencies: 10kHz, 5kHz, 2.5kHz, 1kHz, 500Hz, 250Hz, 100Hz — and lower, to the lowest frequencies where distortion does not exceed 20%.
  • Tests were kept as short as possible: It is easy to damage speaker drivers with steady state pure tones, even at low power levels!

ANECHOIC CHAMBER AUDIO ANALYSIS

1. Frequency Response


The three lines represent the maximum, normal, and minimum (+6, 0, -6) settings for the sub volume available on the remote control

  • As predicted, the bass response is not impressive. There's hardly anything below about 60 Hz. An illusion of more bass is provided by the peak around 90~130 Hz.
  • The dip at ~200 Hz is likely a combination of...
    • 1) cancellations due to floor reflections, and
    • 2) crossover effects between the woofer and sound bar.
  • The above dip and a second significant dip at 400~500 Hz contribute to the unevenness of the subjective sound.
  • The broad trough at 3~8 kHz and the sharp dip at 11~15 kHz contribute to the "closed-in" aspect of the sound.

How do these frequency response test results compare with those on other speakers we've tested? None of the other speakers tested thus far are sound bars. Still, for a laugh, here are the other curves. The closest comparable is the Soundscience Rockus 3D | 2.1, which has a slightly better extended bass (just 10~12 dB down at 40 Hz, compared to ~15 dB down in the Samsung) and similar dips in the high bass and midrange. Its treble is much more prominent, which gives the Rockus a livelier, more open sound. The tiny AudioEngine A2 without sub obviously cannot compete in the bass, but its overall response is smoother, and it sounds that way, too. The Paradigm Millenia speakers obviously extend much deeper into the bass and higher in the treble, and generally appear smoother throughout (but you cannot tell by these curves the real difference in sonic performance between the Millenia and the other speakers, which are completely outclassed in listening comparisons).

Click for large view
Frequency response graph of the Rockus 3D | 2.1.

Click for large view
Frequency response graph of the AudioEngine A2.


Frequency response graph of the Paradigm MilleniaOne + Sub.

2. Harmonic Distortion

As with all the other tests, the SPL level was set to 85 dB@1m with white noise. Sine wave tones were then run, for harmonic distortion to be measured with our SpectraPLUS audio analyzer. Results from previous speaker tests are also presented.

Samsung HW-D550 Measured Harmonic Distortion
Test Tone
Samsung
HW-D550
Paradigm
MilleniaOne/Sub
Soundscienc
Rockus 3D | 2.1
AudioEngine A2
SPL (dB)
THD
SPL (dB)
THD
SPL (dB)
THD
SPL (dB)
THD
10 kHz
79
0.21%
83
0.03%
78
0.38%
78
0.15%
5 kHz
83
0.55%
83
0.14%
84
0.64%
84
0.36%
2.5 kHz
84
0.58%
83
0.07%
77
0.21%
77
0.28%
1 kHz
83
1.6%
83
0.55%
78
0.68%
78
0.39%
500 Hz
81
3.5%
85
0.92%
81
1.20%
81
0.60%
250 Hz
72
3.3%
88
0.24%
70
4.80%
78
0.76%
100 Hz
85
8.6%
84
0.42%
85
4.90%
79
5.90%
80 Hz
83
17.8%
86
0.50%
88
16.40%
72
8.10%
70 Hz
70
12.8%
72
0.92%
72
13.20%
69
12.40%
60 Hz
66
17.8%
86
2.90%
n/a
n/a
n/a
n/a
50 Hz
60
36.0%
72
*27.0%
n/a
n/a
n/a
n/a

*This is an anomalous measurement, believed to be incorrect.

The Samsung HW-D550 has low harmonic distortion only in the treble. Its THD rise steadily as frequency dropped, running 1.6% at 1 kHz and rising to over 8% by 100 Hz. The bass distortion was about equal to the Rockus, running in the teens through its useful range.



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