2019-08-13_TAB_PC_SPKR_CABLE_CONNECTED | 13.08.2019 11:26:21
Distances [cm]	Mic - L | Mic - R	L - R	Positions (x, y, h) if changed
1     L_1	93 | 101	121	Mic: (86, 102, 120) L: (31, 176, 120) α=90 R: (151, 179, 120) α=90
2     L_2	143 | 83	121	Mic: (149, 97, 120)
1     R_1	93 | 101	121	Mic: (86, 102, 120) L: (31, 176, 120) R: (151, 179, 120)
2     R_2	143 | 83	121	Mic: (149, 97, 120)
Specification	2 Places
Device	MEDION P1040X Release: 7.1.1No frequency response correction has been used for this device.
Microphone	Default
Logsweep	20 - 20000 Hz, 2 s

1a 2019-08-13_TAB_PC_SPKR_CABLE_CONNECTED L_1 L_2

1b 2019-08-13_TAB_PC_SPKR_CABLE_CONNECTED R_1 R_2

Sound quality at the individual listening positions:

This is the summary of the scores described in detail below. Each loudspeaker arrangement is evaluated separately. If more than one listening position resp. microphone placement is measured, the average rating is displayed. Technical Background

Especially in the bass range, the sound quality depends strongly on the interaction between loudspeakers and room. Reflections on walls or large objects can cause amplification and cancellation at certain frequencies. This results in a ripple in the frequency response, its strength is shown in the tables. By the interaction of several reflections the amplifications can build up to room modes, similar to the water in a bathtub when it is moved back and forth in the appropriate frequency. The algorithm finds the three most prominent frequencies, which are most likely room modes, and outputs them as well. The first table contains the summary of all measurements of the respective measurement series, the second table shows the individual measurements.

Considered Frequency Range	20 - 180 Hz
Avg. Ripple in Frequency Response	11 dB	A
Avg. Deviation Seat to Seat	2.3 dB	A++
Worst Room Modes	5, 4, 4 dB at 144, 132, 119 Hz

	Room Modes			Ripple
Frequency	144 Hz	132 Hz	119 Hz	20 - 180 Hz
Wavelength	2.4 m	2.6 m	2.9 m
Wavelength / 4	0.6 m	0.6 m	0.7 m
L_1	-	4 dB	1 dB	11 dB
L_2	-	4 dB	-	11 dB
R_1	5 dB	-	7 dB	11 dB
R_2	6 dB	-	6 dB	11 dB

Suggestions for Improvement

By comparing several measurements with different loudspeaker and listening position arrangements, the optimum should first be found in this respect. If a listening test was carried out at the end of the measurement, the notes should also be taken into account. Only after this should damping measures or electronic corrections be taken. This is dealt with in the chapter "Suggestions for improvement".

No fluctuations were detected that were significantly dependent on the position of the listening places. However, no listening places were investigated that were far apart in relation to the dimension of the "wavelength / 4" values. No fluctuations were detected that were significantly dependent on the placement of the speakers. Admittedly, the examined arrangements are in relation to the dimension of the "wavelength / 4" values very close to each other.

The use of bass absorbers does not seem to be necessary - depending on the position of the speakers. The most favourable positioning can be found in the respective ratings. Because relatively few places were examined in relation to the dimension of the "wavelength / 4" values, the result may change if more listening places are added.

Absorbers
Helmholtz resonators are specifically proposed for the absorption of a) narrow-band, b) isolated, c) low-frequency room modes.
Here too many peaks in the frequency resopnse were found. Therefore, no resonance absorbers are proposed. Instead, broadband membrane (or limp mass) absorbers could be used.

Important for the locatability of the instruments is the equality of both stereo channels. The average deviation of the Frequency responses are displayed in the first table.

The second table shows the calculated and measured values of the so-called floor bounce: During the measurement the locations of the loudspeaker and microphone were noted. From this, the detour of the sound reflected on the floor was calculated in comparison to the direct sound. The value is displayed as "Deviation". f↓ and f↑ are the frequencies calculated from these values, at which a weakening or amplification is to be expected. In the next column these are compared with the measured frequency response. The weaker the values, the better the evaluation.

The third table gives an overview of possible colorations caused by all reflections occurring in the room. The average fluctuation of the frequency response due to comb filter effects is used as a measure. The area with the strongest fluctuations is displayed in a separate column.

	Calculated from Geometry			Measured Amplitude Fluctuation
Floor Bounce	Deviation	f ↓	f ↑	Peak_1 - Dip_1	Grade
L_1	165 cm	104 Hz 313 Hz	208 Hz 417 Hz	-6 dB	A++
L_2	136 cm	126 Hz 377 Hz	251 Hz 503 Hz	Not applicable*
R_1	159 cm	108 Hz 323 Hz	215 Hz 430 Hz	-6 dB	A++
R_2	171 cm	100 Hz 300 Hz	200 Hz 401 Hz	1 dB	A++

* The calculated frequency is outside the specified interval 80 - 220 Hz. Go to CONF for revision.

Coloration	Average fluctuation at 220 - 7000 Hz, 0 - 10 ms	Most significant	Grade
L_1	22 dB	43 dB at 2311 Hz	D
L_2	30 dB	54 dB at 1029 Hz	D
R_1	18 dB	42 dB at 4117 Hz	D
R_2	19 dB	44 dB at 3639 Hz	D

Suggestions for Improvement

The channel equality is rated as : UNDEFINED.
Anyway: For Improvements it should first be examined whether differences are caused by the room or by the inequality of the speakers. For this purpose, the speakers should first be placed directly next to each other and checked (eg. with white noise), if still differences are audible. Only if not, the cause is to be found in the room. Otherwise, check the polarity of the connections first. If the asymmetry of the room can not be removed, the speakers can be placed closer together for a better stereo image.

Reflections from the floor and ceiling usually worsen the sound, while reflections from the side walls may be desirable. We can tell this apart thanks to our lateral ears. With a measuring microphone, on the other hand, this is not directly possible. Instead, the expected frequencies for floor reflections are derived from the measured distances between loudspeakers, Microphone and floor are calculated and compared with the measured frequency response. For a reliable result, it is important that the stored positions are are accurate enough (39 cm ) and a sufficient number of measurements have been made. This measurement includes too few usable measurements.

The average sound coloration is rated as D. Therefore absorbers could be useful. Average frequency response below 140 Hz appears 5 dB stronger, which can increase with the use of (further) absorbers and must therefore be balanced if necessary. **


** The measurement was done with an uncalibrated microphone. Therefore, this can rather be used as a guide, provided that the characteristics of the microphone can be estimated by comparison measurements.

Not all reflections are bad. Not even recording studios are designed as completely "dead" rooms. Lateral diffuse reflections can create a pleasant, enveloping impression for the listener. The listener does not look at the music as if through a window, but feels "in" the music. The prerequisite for this is an appropriate for T_60 (reverberation time) and that the decay of the reverb is as uniform as possible. The table therefore shows the most obvious irregularity, i.e. the moment after a sound event at which the reverberation decays least evenly. In addition to discoloration of the sound and deterioration of the localization, such irregularities can produce an unpleasant flutter echo. This is usually caused by reflections on walls or objects in the room. The table shows the difference in transit time between the direct sound from the loudspeaker and the reflected sound is in ms. and cm together with the strength in dB. In the chapter "Suggestions for Improvement" this serves as a basis to eliminate the causes.

Reverbration	T60	Most obvious irregularity	Grade
L_1	1171 ms	342 cm (10 ms): 15 dB	best
L_2	1098 ms	320 cm (9 ms): 17 dB	best
R_1	1094 ms	365 cm (11 ms): 12 dB	best
R_2	1198 ms	365 cm (11 ms): 12 dB	best
Avg. uniformity of decay in first 15 ms			C

* microphone uncalibrated.

Suggestions for Improvement

The measured reverbration time T_60 is on average1.1 sec. This fits perfectly into the preferred interval of 0.8 ... 2.0 s. From this perspective, no further acoustic treatment is required. Only individual resonances should be targeted if necessary. Check: Clap your hands and estimate the duration of the audible reverberation. This should be comparable with the measured value.
The reverberation in the room is not optimally uniform. This can be caused by reflections. The most prominent reflection is listed in the table. In order to find its cause, the surface that reflects the sound from the loudspeaker to the listening position must be found. For this purpose, a cord can be stretched between the loudspeaker and the listening position, which is then extended by the amount shown in the table. The ends of the extended cord must be attached to the loudspeaker and listening position. Hard, smooth surfaces that can just be touched with the stretched cord (to an accuracy of a few centimeters) may be the cause. First cover them experimentally with at least 20 cm of sound absorbing material (if not available bedding, clothing or mattresses). Then check improvements by measurement and listening test.

Start the optimization with the room! It's a kind of foundation for everything coming! The simplest and cheapest step is positioning. Even changes of 20 cm in the placement of speakers and / or listening positions can have a significant impact on the listening experience. Get an overview of the changes in measurements and listening experience at different positions before taking any further action.

• The distance of the speakers is 1.21 m, which is below the specifications of ITU-R BS1116-1. However, a small distance can be justified if a high direct sound component is desired, e.g. in acoustically bad rooms.
• Avoid placing items directly in front of your speakers.
• Most speakers are designed to sound best when they are in level with your ears.
• Listening places should be placed nearer the middle of the room (not too close to the back wall).
• Speakers on a desk or shelf should be placed on a layer absorptive material like foam.

In the Bass range reflections and standing waves in the room (so-called room modes) are a decisive factor. Both can't be eliminated electronically, as they emerge after the playback chain and thus are different in each place of the room. On the other hand the reflections on the wall behind the loudspeaker hardly depend on the listening position. If the path to the wall and back to the sound source is equal to the wavelength of the sound, both components match which causes an increase in volume. If it is half as long, they attenuate which causes a decreased volume. Since the exact propagation of the sound depends on the respective loudspeaker construction, the associated values can only be used for orientation to find suspicious spots in the frequency response. Some example values are

Speaker (Front) - Wall Distance [cm]	30	50	100	150
Attenuation at [Hz]	286	172	86	57
Amplification at [Hz]	572	343	172	114

Electronic corrections should therefore not be categorically rejected, but should be applied with the necessary background knowledge: Even if only one room position has been optimized, the result can be disappointing. The measuring microphone could not process the directions of direct sound and reflections in the same way as the individual sense of hearing.

Here you can see the expected effect of the equalizer settings EQ [dB] on the frequency response. If the curve in EQ is flat, the right side shows the measured values at the individual listening positions and "Avg" on the left shows their average.
- Tap on "Avg" to see the situation if equalizer is set
- Tap on "EQ" for the situation without equalizer
Equalization can correct audible peaks that occur equally at all listening positions. Narrow peaks and dips often have little effect can often be ignored. Never try to boost narrow dips: They are caused by cancellations - it would be wasting of speaker’s headroom. It can be an acceptable compromise "to taken the energy" from very disturbing room modes if a reorganization of the room is not possible.

f [Hz]: 50 63 80 100 125 160 200 250 315 400 500 630 800 1k 1k25 1k6 2k 2k5 3k15 4k