DOWNLOAD JBL TiK Master Sub Service Manual ↓ Size: 1.45 MB | Pages: 13 in PDF or view online for FREE

Model
TiK Master Sub
Pages
13
Size
1.45 MB
Type
PDF
Document
Service Manual
Brand
Device
Audio
File
tik-master-sub.pdf
Date

JBL TiK Master Sub Service Manual ▷ View online

Specification - BS602 Automatic Equalisation 
Iss 2 
23
th
 Jan 2001 
Paul Williams 
Rob Belcham 
 
General Description 
Maximal Length Sequence (MLS) analysis allows us to measure the magnitude response for 
auto-EQ. 
 
MLS benefits from good tolerance of poor SNR, so a high level stimulus is not required. MLS 
analysis uses a Pseudo Random Binary Sequence (PRBS) which is pink-filtered so as to 
adequately stimulate the LF end of the spectrum without over-driving HF drivers. The stimulus 
sounds just like pink noise.  
 
The stimulus is ‘played’ over the system, and is synchronously recorded via the measurement 
microphone into memory on the DSP card.  
 
At the first (primary) microphone position, the main system and the sub system are independently 
stimulated, and their levels and magnitude responses are measured (see Level Matching). A gain 
factor is then calculated for the sub system to match the level of the main system. The rest of the 
auto-EQ process is carried out with both the main system and the sub system active. 
 
Several sequences are repeated, and the result averaged. The recorded sequence is then 
correlated with the original stimulus in such a way as to derive an impulse response for the 
system. With knowledge of the parameters of the pink filter etc, an impulse response for the room 
can be calculated from which the magnitude response parameters can be obtained using an FFT 
with a window function. The linear-frequency domain FFT data is converted to log-spaced 'bands' 
for EQ response fitting. 
 
At the first (primary) microphone position, the magnitude response is evaluated (see below) firstly 
with normal polarity, and then with reverse polarity. The responses are then compared over the 
range to be EQ’d, and whichever polarity setting has fewer points beyond the Max Boost / Max 
Cut limits is used for the rest of the auto-EQ process, and is retained for normal operation. If both 
responses lie within this range, the response with the smallest absolute error is chosen. 
 
The remaining microphone positions are then measured in a similar way, and their magnitude 
responses averaged. 
 
The resulting response is then inverted to obtain a required EQ response, and smoothed to take 
out noise and narrow peaks or dips, using moving average filtering. A target curve is then 
subtracted to compensate (where possible) for the LF response of the Main speakers. The 
parameters of a bank of Parametric equalisers are then manipulated to give a best-fit to the 
required response. The mapping of the required response to EQ parameters is done by looking 
for the frequencies with the worst error, assigning an EQ with the appropriate amount to boost to 
cancel the error at that frequency, then widening the bandwidth until the error within the range of 
the filter changes sign (when the skirts of the EQ bell tend to go over the target line). The errors 
are then reassessed and further filters assigned etc until all filters are used up. 
 
 
 
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: 
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 
 
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 it’s sub output.  
 
4.  When 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 
 
 
 
 
 
 
Main Amplifier
preAmp
LineIn
SubOut
Sub Amplifier
MainAmp
Nomal Configuration
SubGain
SubAmp
CD PLAYER
Figure 3 
Page of 13
Display

JBL TiK Master Sub Service Manual ▷ Download

  • DOWNLOAD JBL TiK Master Sub Service Manual ↓ Size: 1.45 MB | Pages: 13 in PDF or view online for FREE
  • Here you can View online or download the Service Manual for the JBL TiK Master Sub in PDF for free, which will help you to disassemble, recover, fix and repair JBL TiK Master Sub Audio. Information contained in JBL TiK Master Sub Service Manual (repair manual) includes:
  • Disassembly, troubleshooting, maintenance, adjustment, installation and setup instructions.
  • Schematics, Circuit, Wiring and Block diagrams.
  • Printed wiring boards (PWB) and printed circuit boards (PCB).
  • Exploded View and Parts List.