Is My REW Result Good? Benchmarks for Room Graphs

You’ve measured your room and you can read the graphs. This guide gives you numbers to judge them against, from listening-room standards and published research, with what a problem looks like on each graph.

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Check your results, graph by graph

Beginner

The standards below come from reference listening rooms used for critical listening. A home cinema or living room doesn’t have to meet them. Use them as a guide to what “good” means, not a pass or fail.

1. Frequency response

Illustration of a poor and a good in-room frequency response against a target curve — Illustration: a poor response (orange) and a good one (green) against a target curve.

	Good	OK	Poor
Overall shape	Smooth, with a gentle downward tilt of about 2 to 3 dB per decade from 100 Hz to 10 kHz	Mostly smooth with a few broad bumps	Flat or rising treble, or big steps between regions
Bass (below about 300 Hz)	Peaks and dips within a few dB of the target, except narrow dips	Some broad peaks left	Peaks of 10 dB or more; a gap at the crossover
Narrow dips	Left alone		Boosted by EQ (they rarely fill, and waste headroom)

Sources: Toole’s in-room research, as summarised by audioXpress; ITU-R BS.1116 for reference rooms.

2. Bass decay (waterfall and spectrogram)

Illustration of bass decay at one frequency, poor and good, with the audibility threshold — Illustration: a frequency that rings for about 1 second (orange) and one that dies away in 0.3 s (green).

Research by Fazenda and colleagues found the point at which listeners start to hear a room mode ringing on. Below these decay times, a longer decay wasn’t noticed.

Frequency	Audible above, with music	Audible above, with test signals
32 Hz	Not tested	0.9 s
63 Hz	0.51 s
200 Hz		0.17 s
250 Hz	0.12 s

	Good	OK	Poor
Decay at each bass frequency	Below the thresholds above	Close to them, with no single frequency standing out	Individual ridges clearly outlasting their neighbours

How to read decay time on a waterfall: a frequency that takes 0.5 s to fall 60 dB falls 30 dB in about 0.25 s. Source: Fazenda, Stephenson and Goldberg, Journal of the Acoustical Society of America, 2015.

3. RT60

Illustration of RT60 per octave, poor and good, against the ITU target band — Illustration: uneven RT60 (orange) and an even one close to target (green), for a 60 cubic metre room.

The listening-room standard ITU-R BS.1116 sets a target reverberation time from the room’s volume: Tm = 0.25 × (V / 100)^1/3 seconds, where V is the volume in cubic metres. EBU Tech 3276 keeps it between 0.2 and 0.4 s. REW’s own guidance is about 0.3 s for rooms under 50 m³ and 0.4 to 0.6 s for rooms up to 200 m³.

Room volume	Target Tm (ITU-R BS.1116)
40 m³	0.18 s
60 m³	0.21 s
80 m³	0.23 s
100 m³	0.25 s
150 m³	0.29 s

	Good	OK	Poor
RT60 from 250 Hz to 4 kHz	Within about 0.05 s of the target, similar in every band	Within 0.1 s, fairly even	Far above target (lively, blurred dialogue), or treble much lower than the mids (dull, over-damped)

Volume is length × width × height in metres. The ±0.05 s tolerance applies through the midrange; the standard allows more at low frequencies and at 8 kHz.

4. Early reflections (impulse and ETC)

Illustration of early reflections in the ETC, poor and good, with the 10 dB and 15 ms guide — Illustration: strong early reflections (left) and reflections kept below -10 dB in the first 15 ms (right).

	Good	Poor
Reflections in the first 15 ms	At least 10 dB below the direct sound	Within 10 dB of the direct sound

This is the ITU-R BS.1116 and EBU Tech 3276 rule for reference rooms, measured from 1 to 8 kHz. Floyd Toole’s research found that reflections in small rooms can be neutral or even positive, so treat it as a guide, not a must.

5. Group delay

Published audibility thresholds (Blauert and Laws) are about 3.2 ms at 500 Hz, 2 ms at 1 kHz, 1 ms at 2 kHz, 1.5 ms at 4 kHz and 2 ms at 8 kHz. Later research found smaller thresholds with some test signals. There are no well-researched thresholds for the bass: there, group delay peaks come from room modes, so fix the modes and use the waterfall to judge.

6. Distortion

There’s no standard for in-room distortion. For subwoofers at their maximum output, the CTA-2010 test allows the 2nd harmonic up to -10 dB, the 3rd up to -15 dB and higher harmonics lower still, relative to the fundamental. Research on bass (Fielder and Benjamin) found low bass masks 2nd harmonic distortion far better than 5th, so odd, high harmonics matter most. Treat a sudden jump at one frequency or level as a sign of a rattle or overdriven driver.

Spectrogram: there’s no numeric standard. Read decay times against the bass decay thresholds above.

Next step

Guide 7: Share Your REW Results

Want a second opinion? Export your measurements so others can open them and check your graphs.

Continue: Guide 7: Share Your REW Results

Back: Guide 5: Before and After Checks

Using the benchmarks well

Advanced

Compare like with like: same mic position, level, smoothing and graph limits for every measurement.
Judge the bass on several seats, not one. An average across positions shows what most listeners hear.
A result can miss a benchmark and still sound good. Listen as well as measure.
Fix big problems first: speaker and sub placement, then treatment, then room correction.

Is My Result Good?