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1. TWOTHINGS A ROOM CORRECTION
PRODUCT MUST DO
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2. ROOM CORRECTION
My research has led me the conclusion that there are a number of basic functional
elements that ALL room correction devices should possess.These conclusions
derive from a room acoustics design viewpoint rather than a sound quality
perspective. It is interesting that there are many devices on the market that do not
meet these two basic criteria…

3. Must not apply correction filters
above the transition frequency OR
must allow the user to switch off
room correction above the transition
frequency

4. THINGS A ROOM CORRECTION PRODUCT
MUST DO
When a measurement microphone is placed at the listening position(s) and the
source is a reasonable distance away (e.g. 8ft) what we see on a frequency
response chart above around 300Hz (the transition frequency) is a combination of
the direct sound from the speakers and the reflected sound from the surfaces of
our room.The contribution of the reflected sound from the room to the measured
frequency response can be as much as 60%.The measured response, as seen on
the chart, is often termed the ‘power response’ of our speakers.The shape of the
line normally ‘droops’ towards high frequencies; this is due to the increasing
directivity of our tweeters as 20kHz is approached.

5. THINGS A ROOM CORRECTION PRODUCT
MUST DO
Each line on the graph represents a
measurement at a different angle off axis.
The chart shows 0,30,60 and 90 degree off-
axis measurements.The red line is an
estimation of the ‘power response’, or what
the listener hears.These speakers maintain
very good off axis response through 75
degrees off axis.

6. THINGS A ROOM CORRECTION PRODUCT
MUST DO
Above the transition frequency room correction products are actually correcting
the power response of our speakers i.e. they are applying speaker correction. In
some cases this can be a good thing, for example with lower quality speakers that
possess variable on-axis frequency response.

7. THINGS A ROOM CORRECTION PRODUCT
MUST DO
In most cases however, and especially with audiophile quality speakers, one should
be hesitant about allowing a room correction product free reign to determine and
apply correction filters above the transition frequency. Some reasons for this are
listed below:
 Equalizing the power response will typically cause the direct frequency
response to rise towards 20kHz; your nice speakers that measure flat on-axis at
1m will now exhibit a rising frequency response!
 Many speaker designers purposely engineer in some minor deviations in the
frequency response.This is often a subjective voicing of the sound but is also
sometimes required to control the sound quality impact of a driver breakup
mode. An example of this is the BBC or ‘Gundry’ dip.

8. THINGS A ROOM CORRECTION PRODUCT
MUST DO
These examples illustrate why any room correction product should either:
 Only apply correction to bass frequencies like Meridian.
OR
 Allow the end user to select which the frequency range to which room
correction is applied likeTacT.

9. Must allow the user to choose a
target frequency response

10. THINGS A ROOM CORRECTION PRODUCT
MUST DO
Room correction devices aim to fit the measured frequency response to a nominal
target frequency response by applying correction filters.There is an element of
preference in the shape of the target curve, some people preferring a ruler flat
response whilst others prefer a rising response in the bass which adds a little more
weight to music.To some extent this preference is informed by the volume at
which a person listens to music and the sound level dependent nature of our
hearing.Those who listen at lower volumes (e.g. 70dB) may prefer a lift of up to
10dB at 30Hz. See this information on the Fletcher Munson curves for more
information.

11. THINGS A ROOM CORRECTION PRODUCT
MUST DO
In any event any room correction device should either:
 Allow the user a wide choice of target frequency responses
Or
 Allow the user to manually ‘draw’ their target frequency response.Any system
that requires the user to specify the correction filters (e.g. Rives Audio PARC, Z-
Systems RDP-1) is effectively providing a limited version of this capability.

12. THINGS A ROOM CORRECTION PRODUCT
MUST DO
There are three additional
criteria that a room correction
product should have:
-not performing a needless
analog to digital conversion
-providing measurement
capabilities
-providing filter generation
capabilities

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