Room Target Curves - then, now, and options to try...

Be it resolved that there is no such thing as achieving sonic perfection - technically at least based on objective ideals, but "perfect" can also be a subjective state of mind.

In domestic homes, we're simply not going to be able to achieve near-perfect rooms. Likewise, no sound system will be absolutely transparent although the digital electronics side will get much closer to "perfect" than analogue playback and loudspeakers. Furthermore, beyond what we can say about our domestic playback systems, despite all the care and detail-orientedness put into a recording studio, they're not identical even if they followed published standards (like ITU-R BS.1116, or EBU Tech 3276), and besides, is there ever such a thing as a perfectly engineered recording? Or a perfect performance from our favorite artists for that matter?

While perfection might be out of reach, let's not turn away from the pursuit of what is reasonably accurate which is something we can all do to some extent whether it's choosing better-engineered gear, working on small room acoustics, or using DSP to improve frequency response and/or time-domain performance at our listening position. Regarding the specifics of DSP room correction, let me refer you to previous articles covering various methods here, here, here, here, and here.

The intent of this post is to focus on the topic of Room Target Curves which we define and apply when doing EQ and DSP correction. Let's explore a little history, what they are, what they look like and considerations for what to try at home.

[I know there are people who want to instill fear in audiophiles against the use of DSP but know not what they speak of nor provide evidence - like this fellow, who prefers to have his customers waste time and money on Synergistic Research stuff instead of doing something useful. He sells the stuff of course so is financially incentivized.

Modern reputable DSPs including EQ are done at very high quality/precision. Assuming you already have high quality gear and a good room, when set properly within reason, they can improve clarity and restore neutrality, enhancing subjective enjoyment without distortion. 

I suspect most audiophiles can benefit from good DSP correction. You just needs to know what you're doing; apparently not that guy! 🤣]

1. What Is a Target Curve?

A target curve (or "house curve") is a specified frequency response that defines what the combined output of a loudspeaker system should look/sound like when measured at the listening position in a room. It describes the end result of the entire chain: the electronics, the loudspeaker's inherent response, its directivity, the room's acoustic properties, and any equalization applied.

The key insight is simple but profound: an "ideal" loudspeaker that measures perfectly flat in an anechoic chamber will not sound or measure flat in a real room. As discussed previously, in a typical small room, boundaries reinforce bass, reflecting surfaces add midrange energy, air absorption and furnishings attenuate high frequencies. The net result is a downward slope from low to high frequencies. Research consistently shows most listeners prefer this natural slope over truly flat in-room response which would sound overly "thin" or harsh.

Fig. 1: Simulated anechoically flat speaker down to 40Hz (blue) produces a tilted in-room response (red) due to room gain, along with modal behavior, SBIR, and HF absorption. The exact amount of room effect of course will vary depending on the space, speaker positioning, furniture, seating position, etc.

Therefore, from the perspective of human experience inside rooms enjoying music, whether it's a small room at home, a cinema, or the local concert hall, what sounds "natural" in our listening rooms is not a perfectly flat frequency response.

So, while we generally do want our DACs and amplifiers to be capable of flat frequency response and not impart their own "color" to the sound, and want loudspeaker anechoic response to be reasonably flat, we generally do not want our room frequency response at the listening position to be ruler-flat.

2. Why Do We Use Target Curves?

Well, it allows us to control what kind of tonal quality we want our sound systems to have in the room. The shape of the target curve acts as room correction guidance for DSP systems such as Dirac Live, Audyssey, Audiolense, Acourate, etc. Since a flat response would be unnatural as discussed above, we therefore would want the shape of the target curve to correlate with a euphonic, "natural" experience.

[Even without using these DSP systems listed above, you can measure your existing frequency response in REW and compare what you're getting with the research over the years in psychoacoustics we'll be talking about.

REW is very capable. With the measured frequency response, you can still define the "house curve" you want to aim for and have the program calculate the appropriate correction EQ parameters to apply. These can then be programmed into hardware options from manufacturers like miniDSP, Behringer (discussed awhile back, also here) or plug into playback software like foobar, Roon, and Audirvāna.]

To summarize, here are 3 main reasons to use a target curve:

• Standardization: Ensures recordings translate predictably (not necessarily perfectly) between calibrated rooms. This is important especially in studio control rooms to ensure that they're at least listening to the music "accurately". Sonarworks SoundID is a good example of a calibration and virtual monitoring system targeted to sound creators for speaker and headphone monitoring.

• Preference optimization: Just because we have typical target curves that most people seem to like doesn't mean you have to follow them! Target curves allow us to have some power over the tonality we subjectively prefer. As discussed previously, you can be your own "tonmeister".

• Compensating for deficiencies: Beyond the overall shape of the frequency response, applying DSP (multi-thousand-tap FIR filters much more precise than a handful of parametric EQs) provides us with the opportunity to smooth out the frequency response, taming bass room modes, while adjusting speaker tonality. In a typical small room that's not extensively treated, 15-20 dB range between modal peaks-to-nulls is to be expected, and usually we can tame that down to ~10dB total range, with ±3dB through most of the frequency range using DSP/EQ. This is audibly significant.

Implied in the points above, there is no single universally correct target curve. What is "best" could depend on room properties, listening distance, and to a very large extent, personal preferences. The various target curves we'll be talking about below provide for us scientifically, typically empirically, informed starting points.

3. A History of (Potential) Target Curves

3.1 Bruel & Kjaer Measurements (1974)

Among the earliest systematic measurements, B&K documented what they called the "optimum curve for HiFi equipment measured in the actual listening room" using their pink noise QR 2011 test record and 1/3-octave analysis. The curve ends up being flat from 20 Hz to approximately 160 Hz, then begins a gradual downward slope reaching roughly -6 dB by 20 kHz. This gentle, continuous roll-off starting in the upper bass/lower midrange region rather than a sharp knee at any single frequency would later be echoed in the shape of the Toole/Harman research findings and Dolby Atmos Music curve.

Fig. 2: The B&K (1974) "optimum curve for HiFi equipment" traced from the original paper.

3.2 The SMPTE X-Curve for Cinema (1975)

The first standardized "electroacoustic response guideline" target is SMPTE ST202 (see review article - note some earlier work described from back in 1948) also referred to as the "Academy Curve", first proposed in 1975. This curve was derived also from analysis of pink noise averaged over 1/3-octave. Instead of a hi-fi room, this curve was for the cinema venue with typical 1970's era projection and sound systems; typically 35mm reels with a mono soundtrack along with all kinds of compromises and difficulties in measuring the frequency response as documented in that review.

It served as the EQ standard for cinema "B-chain" playback including the amps, speakers, and room effects, measured at 2/3 of the distance from screen to back wall, at the lateral midpoint of the room. A microphone array (at least 4) would be used, clustered around that target position.

The X-Curve specified flat response to 2 kHz, then -3 dB/octave roll-off above, compensating for low and mid-frequency accumulated energy in large cinema spaces. This -3dB/octave roll-off would be too aggressive for small rooms where it would sound too "dull".

A compensation for small rooms (<150m³ or 5300ft³) that I've seen, which can be applied in home theaters, is to reduce the roll-off to -1.5dB/octave as plotted below:

Fig. 3: The SMPTE X-Curve: flat to 2 kHz, -3 dB/octave for large cinemas, and -1.5dB/octave for small rooms.

3.3 Floyd Toole and the NRC/Harman Research (1986–2015)

Through decades of research, Toole established that listeners in typical domestic listening rooms preferred speakers with flat, smooth anechoic response and directivity. A key contribution was demonstrating how room reflectivity determines the steady-state in-room response when the loudspeaker itself has flat direct-sound output.

The figure below, traced from Toole's paper, shows estimated steady-state curves for home and professional-monitor loudspeakers in three acoustic environments. The highly reflective small room curve shows a steep downward slope of roughly 8 dB from bass to treble, driven by a bass-heavy reverberant sound field that's stronger than the direct sound. Bass frequencies are radiated omnidirectionally where it strikes walls and reflects as opposed to the progressively more directional high frequencies as drivers start to beam.

A typically reflective small room curve (like an untreated living room with furniture and carpet) with a bit more absorption shows a more moderate slope of approximately 5-6 dB; and an acoustically dead space shows essentially flat response since without reflections, only the flat direct sound is measured.

Real rooms and real speakers will fall within the shaded region between these extremes in this graph:

Fig. 4: Estimated steady-state sound in small rooms, traced from Toole's published figure. All loudspeakers have flat direct-sound response. The slope of the steady-state curve is determined primarily by room reflectivity and the speaker's directivity characteristics.

3.4 Olive, Welti & McMullin: The "Harman In-Room Loudspeaker Curve" (2013)

In this study from 2013 (AES Convention Paper 8994) which I've seen referred to a bit, the authors ran an experiment with 11 listeners (8 trained with Harman How To Listen software achieving level 8+, 3 untrained - obviously small sample size) allowing them to adjust the bass and treble dial of a calibrated system to their subjective preference. This test was using Revel Performa F208 speakers, 24' x 21' x 9' treated reference listening room, RT60 at 0.4s constant above 125Hz, with selections from Jennifer Warnes' "Bird On A Wire", Steely Dan's "Cousin Dupree", and Estelle & Ye's "American Boy". Already, I think we can imagine the limits of this experiment and how it might or might not reflect the context of our own sound rooms, equipment, and choice of music.

On average, these 11 listeners liked a room curve with +6.6 dB bass (below 105 Hz), and -2.4 dB treble (above 2.5 kHz) - a spread of 9dB. As you might imagine, there was a wide range found between individual preferences: 17dB range for bass and 11dB for treble!

What's most interesting I think is that the 8 trained listeners preferred a more gradual slope whereas the untrained (only 3 listeners!) preferred a steeper bass-heavy shelf.

Naturally, dear audiophiles, the question then becomes, what kind of listener are you? 🤔

Fig. 5: The Olive/Harman (2013) preferred in-room loudspeaker response. The bass shelf transitions smoothly from the low-frequency plateau through the 80–250 Hz region into the midrange as defined by their experimental procedure where they used a 2nd order filter at 105Hz.

3.5 The Dolby Atmos Music Target Curve (2020s)

A recent addition to the target curve landscape is the Dolby Atmos Music Target Curve, documented in Dolby's Best Practices for Dolby Atmos Music Studios. This curve evolved from the Cinema X-Curve heritage but was specifically refined for music production in smaller, controlled studio environments. (Dolby still recommends using the X-Curve for large rooms >125m³ - Section 2.7.2.)

The curve's key specifications are:

• Bass: +1 dB shelf below approximately 160 Hz
• Midrange: Flat reference region from 160 Hz to 1.6 kHz
• Upper treble roll-off: -1.5 dB/octave from 1.6 kHz to 10 kHz
• High treble roll-off: -3 dB/octave above 10 kHz (steepening)
• Tolerance: Speakers should extend 40 Hz to 18 kHz within ±3 dB

The Dolby specification does not explicitly define the response below 40 Hz, but as I previously discussed, a smooth sub-bass extension is desirable for systems with capable subwoofers. The graph below uses the sub-bass extension, which smoothly rolls the +1 dB bass shelf, reaching approximately -3 dB at 20 Hz. I believe this provides a realistic and pleasant target for audiophile systems with full-range bass capability that rhymes with the X-Curve sub-bass roll-off.

Fig. 6: The Dolby Atmos Music Target Curve with sub-bass extension to 20 Hz. SMPTE X-Curve is overlaid for historical comparison.

The Dolby Atmos Music Curve I think matters for audiophile listeners for several reasons these days as we're seeing more Atmos 'spatial' streaming content from sites like Apple Music, Tidal, and Amazon Music:

1. Standardization benefits translation: if Atmos-certified studios mix to this target, home systems calibrated similarly should reproduce the intended tonal balance. There would still be variation of course since there is ±3 dB tolerance, but at least higher end studios and home systems can seek to tighten the system's accuracy. 

If you believe there is such a thing as sound quality "as the artist intended", then this is probably as close as you can get.

2. The curve addresses intra-system consistency: in a multichannel Atmos layout, all speakers should match the same timbral target so that audio objects moving through space do not change tonality as they pan between speakers around and also vertically.

Some studio professionals have expressed a preference for more bass emphasis (around +3 dB instead of +1 dB below 160 Hz). This echoes Harman's finding that many listeners prefer more bass. For home listeners, I think the Dolby Atmos Music Curve can serve as a very reasonable starting point that may benefit from a modest additional bass shelf of +2–4 dB seasoned to taste. As I noted above, there's nothing locking us hobbyists into a specific curve although I think it would be important for professional studios to calibrate to the Dolby standards tightly.

Software tools like Sonarworks SoundID Reference already include the Dolby Atmos Music Target as a built-in calibration option.

[As far as I can tell, point 2 above about intra-speaker consistency and using the same target across all speakers, has been a recommendation across the documents I have seen for doing DSP/EQ. This is why I don't quite understand all this stuff from Magic Beans Audio and their claims about a unique "True Target" - see videos such as this - with target for each speaker in a system based on measurements (also see the per-channel filters video here). 

Hmmm... Doesn't doing that and not using a specified target, same for each speaker, potentially result in some wild tonal variability between the speakers? For example if we have small surround channels vs. large front mains, or if we mix and match speakers of different brands in a surround system?! 

This discussion video with Erin remaining almost silent through it all seems awkward and I find even more confusing. 🤔 For example, when it comes to nomenclature, my understanding is that the "correction curve" (which can vary by magnitude depending on deviance from the target), is not the "target curve". The correction curve is referring to the inverse adjustments to be applied to the channel in the room in order to achieve the target response (in practice, represented by "8. Room Macro 3: Inversion" step in this post).

From my perspective, the "Target Curve" is something we set, there is an act of will here that determines the shape of this, not something we just measure to find; thus there is no such thing as a "true", single, target. 

To be clear, I'm not saying that we don't respect the natural frequency response of the speaker. We should try not to design target curves that push the hardware in ways that it cannot handle. For example, here's what a target curve design in Dirac Live looks like for me overlaid on the natural measured frequency response of my speakers:

I'm also not saying that in a dynamic system playing music that the sound itself wouldn't be different than the steady-state sweep. However, I don't get the sense that what's being done by this Magic Beans system clearly makes the correction "better" sounding, and probably would lead to more tonal irregularities. 

Let me know if you've tried Magic Beans and found it worthwhile or have a better explanation for why there's such a thing as a "true" target curve, or even how it's supposed to work!]

 

4. Comparing Target Curves

From the curves above, published across five decades, they all share the same fundamental principle: the preferred in-room response slopes downward from bass to treble. They differ in steepness, breakpoint frequencies, and intended application.

The Toole "typically reflective room" curve provides a physical reference for the slope that arises naturally from speaker-room interactions in a room that's not specially treated. Another point of interest is the fact that the black Olive/Harman 2013 curve based on the average preference of all 11 subjects tested has quite a notable bass bump which I think is telling of what "average" listeners in-the-wild prefer - an accentuated bass (like Beats headphones back in the day 🫣)! This could be quite different from the preferences of "trained listeners" and I suspect experienced audiophiles who like a more neutral sound.

The Dolby Atmos Music curve as a recent evolution inherits a bit of the X-Curve's cinematic lineage while incorporating small-room characteristics for music production plus a small bass bump which is typically empirically preferred by listeners.

5. Applying Target Curves in Home Hi-Fi; some practical ideas...

Assuming you have the pre-requisite system to apply room correction (eg. computer playback with convolution engine like Audirvāna or JRiver; plug-in like Hang Loose Convolver; server-side DSP like Roon; built-in Dirac capabilities in your receiver, etc.), here are some general points to keep in mind when designing and applying your target curve.

5.1 Start with good speakers and hopefully a good room

No target curve can fix a fundamentally flawed loudspeaker in horrible echoic and noisy rooms! We want transducers capable of "accurate" sound reproduction, characteristics of which would include a flat, smooth anechoic frequency response with smooth, gradually narrowing directivity as we get into the higher frequencies. Speakers with severe directivity errors (eg. off-axis tonality grossly different from on-axis) cannot be fixed by just a change in the electrical frequency response (what we're doing with EQ or more precise FIR DSP filter) because what amounts to a improvement in the direct sound will not be beneficial to the off-axis energy.

Another characteristic of the loudspeakers we should consider is that it's capable of good dynamic range while maintaining low distortion - at least loud enough for sound to fill the room size. This is dependent on the room noise floor and how loud you want to play. For example, let's aim for a quiet room with 30dB SPL noise floor and usable dynamic range of 70dB. This means it'll be nice when you're sitting at the sweet spot to be able to hear 30+70 = 100dB SPL peaks. Due to the inverse-square law, if we sit something like 9' (3m) away, this would mean that the loudspeaker would have to play up to 110dB SPL measured at 1m hopefully with low distortion (<5% THD at those 100dB transient peaks probably would not be objectionable). How well you achieve this will of course be a combination of your loudspeaker capability with amplifier of adequate power and low distortion - it should not be difficult to achieve this with decent modern amps.

5.2 Correct more aggressively in the Modal and Transition Zones

Below ~150–300 Hz (Schroeder Frequency), room modes dominate. Focus on reducing peaks. Deep nulls cannot be EQ'ed, and if you do want to add some correction gain, I would limit this to +6dB for the correction curve or EQ setting. If nulls are a major problem, consider: adjusting speaker +/- listening position, add bass traps/absorption at antinodes (reduce Q, dampen standing wave energy), try using more than one subwoofer.

You might want to be less aggressive in the Transition Zone (from Schroeder to ~2 octaves up) where things like physical room treatments such as first-reflection point absorption should be prioritized.

Target a gentle downward slope from bass to treble, reflecting natural room gain in the bass as you see in the curves above while smoothing out roller-coaster bass response.

5.3 Be more gentle above the Transition Zone

If the speaker has good directivity, the natural speaker-room interaction should already produce a gentle slope without much intervention as we enter the Quasi-Diffuse Zone. Many would recommend just applying partial frequency correction DSP (such as doing this) to affect lower frequencies only such as below 500-750Hz.

For me, I have not had any audible concern with modern DSPs applying full-bandwidth correction (ie. 20Hz to 20kHz). The correction systems I've been using (Acourate, Audiolense, Dirac) utilize Frequency Dependent Windowing (FDW), a sliding window technique that scales the analysis and correction progressively across the frequency range. For example, low frequencies having longer wavelengths, require the analysis window to be longer like say 750ms at 20Hz compared to only 15ms at 1kHz. Doing this correlates with how our ears/brain integrate frequencies based on the time window needed to perceive, mask, or extract for directional cues. These modern DSP applications also provide excess phase (time domain) correction to improve driver integration at the listening position.

Note that some other AV receiver correction systems such as Yamaha's YPAO, stock Audyssey, and Pioneer's MCACC are built on simpler parametric EQ techniques that do not implement FDW nor excess phase correction.

6. Summary

From B&K's empirical results in the 1970s through Dolby's specification, the science of loudspeaker target curves has converged on a consistent finding: listeners prefer an in-room response that slopes gently downward from bass to treble. The cinema X-Curve formalized this for large venues; Toole and Olive quantified the preferred slope in domestic settings; and the Dolby Atmos Music curve provides a modern, standardized reference for immersive music production that bridges the gap between studio and home.

I would argue that as hobbyists, these target curves can be considered as starting points - pick a foundation; then adjust to your own ears/brain.

To end, let me suggest a couple of target curves I've been using for the last 6 months which I've found enjoyable. The first is what I'll just call the General Audiophile Target Curve. It's orthodox, nothing extreme. It acknowledges the importance of the bass boost as enjoyable for most of us and doesn't accentuate the 200-500Hz mid-range which can get congested and "muddy" with some albums.

If you've never played around with room curves, I think you'll be in good shape starting with this simple one and it'll likely satisfy most audiophile tastes across a wide range of music including modern EDM and pop with deep bass content. Trained listeners should also find this reasonably satisfying:

• Start -1dB @ 20Hz then up to +2dB @ 35Hz
• Flat accentuated bass: 35Hz to 80Hz
• Gentle downward slope from 80Hz: ~2 dB decline from 80Hz to 250Hz. (Reduce energy by the 200-500Hz midrange "Mud Zone".)
• Flat midrange region: ~250 Hz to 1.5 kHz
• Gentle HF roll-off: ~5 dB from 1.5 kHz to 20 kHz
• Total bass-to-treble difference: ~7 dB

General Audiophile Target Curve: I've been using this one in place of the Harman Trained Listener curve in my system for the last few months. Quite enjoyable for a wide range of music. 😊
Of course if you don't have much sub-bass, obviously don't force it, just let it roll-off below 60Hz.

[Implementation Note: I'm not a "bass-head". While I can certainly enjoy the deep vibrations especially in movies, I find that a lot of modern music production accentuates the sub-bass too much which is why I like to attenuate the frequency response down by 20Hz, otherwise it's just unpleasantly "rumbly" for my taste. 

A target curve like the average preference curve from Olive, 2013 with +6.6dB at 20Hz (0dB at 1kHz) would be unpleasantly bass-heavy for my taste! Yuck.]

Another target curve you might want to try reflects my attitude that these curves are also determined by subjective preference and there's no "true" target - just a combination of knowing what is "natural" sounding and what one prefers.

I will often use this one for playback of acoustic albums and vocal tracks. This is what I'll call the Vocal Bloom Target Curve:

Again, we don't overload the 200-500Hz zone so as to reduce "mud". And roll-off above 3kHz (especially 3-6kHz) to reduce vocal harshness.  

As you can see, it's a bit unorthodox. But it's a fun sound that can work well with acoustic recordings and audiophile-fave female vocalists like Diana Krall, Anette Askvik, Norah Jones, Eva Cassidy, Jennifer Warnes, Alison Krauss, and the like.

See, an "objectivist" like myself can enjoy "colored" and intentionally inaccurate sound? 😏

Specific data points for implementation:

# Frequency    Level  Description

1 20 Hz        0.0 dB  Sub-bass roll-off
2 35 Hz       +2.0 dB  Sub-bass rise
3 60 Hz       +3.0 dB  Bass shelf
4 100 Hz      +2.5 dB  Mid-bass warmth
5 200 Hz      +0.8 dB  Upper bass
6 300 Hz      +0.1 dB  Low midrange transition
7 500 Hz      +0.5 dB  Lower midrange body
8 700 Hz      +1.5 dB  Male vocal fundamental
9 1000 Hz     +2.0 dB Vocal bloom peak
10 2000 Hz     +1.25dB  Vocal presence
11 3000 Hz      0.0 dB  Upper presence / articulation
12 4000 Hz     -1.0 dB  Presence taper
13 12000 Hz    -3.5 dB  Upper treble roll-off
14 20000 Hz    -5.0 dB  HF limit

In my Integra receiver these days, I have three Dirac Live Bass Control target settings to toggle between:

1. General Audiophile Target (most music)

2. Dolby Atmos Music Target (Dolby Atmos studio standard for music and movies)

3. Vocal Bloom Target (acoustic & vocals, warmer, dare I say "more analogue" sound)

I can switch between these easily depending on the music and mood. And yes, switching between them results in clearly noticeable changes in tonality as you can imagine if we overlay the three curves:

"General Audiophile" curve has IMO pleasant punchier, controlled, bass (AC/DC's "Thunderstruck" comes alive) and the "Vocal Bloom" warmer. I'll use the Dolby Atmos Music target for the more neutral "studio" sound. 

Addendum:

Thanks to Mitch Barnett for his comment with a couple of links to consider:

Sean Olive's post: "The Subjective and Objective Evaluation of Room Correction Products" from 2009 showing preference for room correction being applied compared to no EQ for a majority of the products 3/5 (one of them rated about the same as no-EQ so 4/5 at least better or equivalent to no correction), double blind, 8 trained listeners.

And here's Slide 24 from the PDF slide-set showing the simple tilt "curve" (arrow and annotation added):

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Some parting music: let's start with retro badass Joan Jett & The Blackhearts - "I Love Rock 'N Roll" (1981):

Recently the Joan Jett Essentials (2026, DR12 multichannel) compilation has been released in surround/spatial audio on Apple Music (I think the Atmos mix currently is an exclusive to Apple, not on Tidal or others). Pretty good remixes - turn it up!

As for new music, Ludwig Göransson's soundtrack for The Odyssey (2026, DR6 stereo mix) is pretty interesting. Here's "Zeus's Law":

Very strong deep bass if you're using sub(s). I heard that Christopher Nolan didn't want a symphonic suite like they did for the movie Troy (2004, DR15) because there were no orchestras back in those day. But did they have such strong dynamic range compression back in ~1200BC during the Trojan War? 🤔

Track 2, "Ithaca" is an interesting mix of menacing sweetness:

I hope you're having a great season, dear audiophiles! And having fun with your music and audio systems.