Jbl bs 602 service manual
This is the 13 pages manual for jbl bs 602 service manual.
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Extracted text from jbl bs 602 service manual (Ocr-read)
Page 1
To enable long impulses to be measured, auto-EQ uses a lower sample rate than the normal audio sample rate. This is not a limiting factor for room equalisation, which rarely extends beyond 500Hz. Specification Auto-EQ sample rate: 6kHz MLS sequence length: 4095 Number of averaged sequences: 8 Maximum impulse response length: 682ms FFT length: 4096 FFT window type: Raised cosine bell Log-frequency domain resolution: 1/50 th Octave Number of EQ filters: 12 Main LF Compensation Level Matching Level matching is carried out prior to the first AEQ measurement. It is essential that the average level of the sub is accurately matched to the level of the main system so that the combined LF response curve lies within the limits set by the maximum allowed eq cut and boost . The process is carried out in 4 steps: - 1. The DSP is loaded with a patch to realize the system in Fig.1. The main system gain is ramped to a fixed level. The level from the Microphone meter is used to adjust the output gain so as to achieve a reference level at the Mic (-12dBFS). This gain ( MainGainRef )is saved for later calculations, as is the difference between the final meter reading and the desired target level(MainRefDiff). An FFT of the main system is then taken. The average FFT level across a range of frequencies, not affected by room response, is measured (MainZeroLine ). Main Amplifier preAmp LineIn SubOut Sub Amplifier MainAmp PRBS CalGain Cal Out Mic In Level Matching Configuration SubGain SubAmp Figure 1
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2. The Sub LP crossover is temporarily extended from 100Hz to 500Hz. The sub output gain is then ramped to a pre-determined level. The Output gain is then adjusted as before, to achieve a reference level at the Mic. This gain (SubGainRef) is stored, as is the difference between the final meter reading and the desired target level(SubRefDiff). An FFT is then carried out on the Sub and the average level is stored (SubZeroLine). 3. Pink noise is passed through 20Hz to 100Hz crossovers and into the main system amplifier. The Cal output gains are ramped to the level stored in Step 1. The difference between the level measured at the input (Fed from main amp Sub Out) and the output level is stored as MainSysGain and is a measure of the position of the Volume control on the users amplifier. The signal is band-limited to ensure that an amplifier with a band-limited sub output will read the same as an amplifier that does not band-limit its sub output. 4. W hen the above steps are complete, enough data has been obtained to set the final output gain for the sub so that when both systems are excited from the main amplifier, (fig. 3) the mean sub level is at the same amplitude as the reference level in the main response. Main Amplifier preAmp LineIn SubOut Sub Amplifier MainAmp PRBS CalGain Cal Out Mic In AEQ Measuring Configuration SubGain SubAmp Figure 2