Lyngdorf Audio Room Perfect TDAI 2200 - Manual (Page 11)

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In a case like this the RoomCorrection index will also be quite high since correction in the bass
region is needed. However, the index number is not high because you have a ‘poor’ system –
it’s high just because you have chosen a loudspeaker position that improves the impulse
response but then requires compensation for the increased efficiency in the bass region.
Try it out and see what works for you – near wall or ‘free space’ placement - RoomPerfect™
works in both cases.
Test signal and measuring techniques
To be able to get the necessary room knowledge for our ambitious goals, we also had to invent
new ways of measuring.
Using traditional test signals e.g. pink noise, normally means a trade-off between S/N (signal
to noise) ratio and frequency resolution. Long analysis windows lead to high frequency
resolution but poor S/N due to the low number of averages. But using multiple pure tones
means long analysis windows (5.5 sec. for low frequency test signal) leading to both high
frequency resolution (0.2 Hz) AND an excellent S/N ratio due to very narrow analysis
bandwidth in the frequency domain, something which is almost insensitive to normal
broadband background noise. Another way of describing the advantage of this measurement
signal is that we only generate energy at the very same frequencies, where the analysis takes
place, i.e. we don’t waste energy and S/N ratio measuring the spaces in-between the analysis
frequencies. We have found that the usual frequency resolution in acoustic measurements of
1/3 octave (3 frequencies for each doubling of frequency) is not sufficient for room correction.
Many years of experience with many different loudspeakers in numerous listening rooms have
shown that 1/12 octave is what is required – this corresponds to no less than 121 pure tone
for covering the range from 20 Hz to 20 kHz.
To put this in perspective, we have taken the
above frequency responses and used 1/3
rd
octave band smoothing – and as can be seen
this is – even though very commonly used –
not very useful for making serious room
correction.
The first 50 tones (covering from 20 Hz to 350 Hz) forms the “low frequency test signal” while
the remaining 71 pure tones form the “high frequency test signal”. The first 50 tones are on
for approximately 25 sec. in each loudspeaker and the 71 tones are on for approximately 5 sec
in each loudspeaker due to lower background noise levels at higher frequencies.
RoomPerfect™ implementation in TDAI-2200
In versions with RoomPerfect™ the menu system for the TDAI-2200 has been changed to allow
it to act as a stand-alone product. With the implementation of RoomPerfect
TM , which can be
fully operated without any PC connection, we also wanted to be able to control set-up of the
TDAI-2200 via its display menu. Consequently, master/slave, channel routing, delay and
crossover can now be set directly on TDAI-2200, thus eliminating the need for PC connection
and control for setting up a master/slave system and a 2+2 system.