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Speaker Engineer Questions Home Theater Equalization Process

Paul Hales, founder of Pro Audio Technology, wonders why installers tune home theaters with unreliable microphones and measurement techniques, adding that musicians don’t tune Steinway pianos to suit the room.


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Digital Projection showed off its new HIGHlite 330-3D three-chip DLP projector as part of a system demo at Sapphire Marketing’s Boston RoadShow.

Sapphire Marketing is a large, N.J.-based manufacturers’ representative that handles high-profile companies such as Crestron, Digital Projection (DP), Middle Atlantic, Pro Audio Technology and Leon Speakers in the Northeast.

Sapphire invited its brands to exhibit at its Boston RoadShow, putting together an impressive home theater demo that included DP’s new HIGHlite 330-3D three-chip DLP projector and a multichannel audio system from Pro Audio Technology.

Pro Audio Technology and founder Paul Hales have a growing legacy of producing well engineered products that can withstand the rigors of high-demand home theater playback, with systems capable of producing more than 130dB of volume.

Highlighting Pro Audio Technology’s ability to reproduce high SPLs is its demo that features Cream’s 2005 reunion show Blu-ray disc and legendary drummer Ginger Baker’s drum solo.

The key to the wide dynamics of this demonstration, Hales contends, is the use of minimal equalization (EQ) in home theaters above the standing wave/modal region. Hales says the industry has become too reliant on automatic room EQ, and he questions the quality of the microphones and techniques used to gather the data used to measure home theaters.

Hales says the best way to get quality sound in a home theater is to make an accurate speaker and treat the room. He adds that if there is something between the listener and the speakers, such as an acoustically transparent screen, installers should then look at compensation tools to correct the problem.

The bottom line when thinking about equalizing a home theater: approach it from a musician’s perspective. “No one tunes a Steinway [piano] to compensate for the room,” he asserts. “People are designing with their eyes [a reference to using plotted graphs] and are not listening to what their ears are telling them.”

The following videos feature Hales explaining his perspective on room equalization and a clip from Pro Audio Technology’s popular Cream system demo.

 

 





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About the Author

Robert Archer, Senior Editor, CE Pro
Bob is an audio enthusiast who has written about consumer electronics for various publications within Massachusetts before joining the staff of CE Pro in 2000. Bob is THX Level I certified, and he's also taken classes from the Imaging Science Foundation (ISF) and Home Acoustics Alliance (HAA). In addition, he's studied guitar and music theory at Sarrin Music Studios in Wakefield, Mass.

30 Comments (displayed in order by date/time)

Posted by Jeremy R. Kipnis  on  03/22  at  10:26 AM

I totally agree! When creating any listening room or home theater, the necessity is to first start with flat response speakers, and then to make sure that the speaker orientation aligns with the room architecture and that acoustic treatments are benign to the overall sound produced. However, pianos, harpsichords, and organs are in fact Voiced for the specific performance venue they will be heard in. Although this is more work, it is a necessity particularly with top performers!

Posted by Robert Archer  on  03/22  at  10:47 AM

Pianos are typically tuned to A440, guitars are also tuned to A440 and are tuned to the key of E. It’s much easier to re-tune a guitar than piano and that’s why many guitar players will tune to Eb and they include Jimi Hendrix, Eddie Van Halen for the DLR era stuff, and today many metal bands will tune down to D or even C. An 88-key piano is tuned to the key of C and it provides nine octaves of C that run from about 16Hz to 20kHz.

Posted by Ed Houck  on  03/22  at  01:05 PM

The logic of the Steinway doesn’t really stand up as an analogy. Pipe organs are tuned to the room, which is if you think about it an ‘EQ’, each pipe a different fundamental frequency. Live sound is mixed with each instrument to the room and each live professional sound system uses ‘speaker management’ systems or DSP time alignment and equalization to tune to the room. Add to that, the problems with small living spaces in homes are much more problematic than the larger live sound venues, with multiple room modes, especially from 300 Hz on down. While it may be true that there is an overuse of DSP before properly situating speakers and setting levels, the Steinway title grabbed me because it just is a faulty analogy.

Posted by Gerry Lemay  on  03/22  at  03:06 PM

Just a few points.

1) Performance spaces are very different than reproduction spaces.  Frequency response (ala EQ) is not generally a factor as the larger the room, the less frequency response distortion is present.  Thus EQ in performance spaces is highly uncommon and a bit silly. This is also potentially true in large home theaters but most folks don’t own a large home theater.
2) Small rooms, as most home theaters are in, produce resonances which are audible and do change the perceived sound of the speaker.  Many clients are opposed to the kind of radical subwoofer placement that would reduce this distortion.  EQ offers a powerful solution.
3) Speakers with a higher directivity (Martin Logan stators, Magnaplanars, horn loaded, waveguides, etc) are less susceptible to response distortions since they present a higher direct sound level.  It’s up to the consumer on what they prefer.  Listening primarily to direct sound reduces the need for EQ but does not eliminate it because of resonance in small rooms.
4) Use of an RTA or FFT to measure response is not an attempt to see what listeners are hearing but rather to identify resonances and boundary effects in low frequency range.  Some might use binaural microphones mounted in a dummy head but there’s little point since the measurement goal is much simpler.
5) Equalization should be limited to the lower portion of the frequency range typically below 300 Hz in a small room and never above 1000 Hz.  EQ at higher frequencies serves only to distort the true response of the speaker.
6) Choosing to hear primarily direct sound by high speaker directivity or moving closer to their speakers is a consumer’s choice but it’s not always chosen.

Posted by Robert Archer  on  03/22  at  04:33 PM

Thanks for your comments Gerry.

To address the point about the tuning of an instrument, it doesn’t matter if it’s a guitar, pipe organ or piano, they are all tuned to a standard pitch (typically A440) regardless of whether they are in a small practice space or in a large arena like Boston Garden. They are tuned in a standard manner to ensure when a piano player or guitar player plays a “C” chord the notes C, E, G ring out. Any attempt to tune an instrument to a room would alter the pitch of those notes which then in turn not allow the musician to play that “C” chord. This also ensures when the bass player, and other musicians all hit that “C” chord they are all in step together and playing as a band.

Posted by Paul Hales  on  03/22  at  08:19 PM

Gerry,

Thanks for the thoughtful reply.  Yours is exactly the kind of dialog I was hoping to open with the video.

I agree with mostly everything you said, with the following comments.

What Bob points out in his copy, but which I failed to mention in the video, is I am skeptical of system EQ based upon in-room measurements in the frequency range *above the standing wave/modal region*, which I take to be approximately 200Hz and below (in typical North American rooms).  Your value of 300Hz certainly also reasonable. 

Above that frequency, though, moving a well-designed loudspeaker further away from flat amplitude response, which by definition, such EQ does, is not benefitial, in our opinion.

To each point you made:

1 - I was referring to musical instruments in small spaces, not performance spaces.  If you place a Steinway in your living room, you still don’t attempt to alter it’s output based upon in-room acoustical analysis.
2- I agree with you entirely since I believe you’re referring to room resonances (modes) and these generally occur below the 200-300Hz transition frequency.
3 - Great point and our speakers are horn designs with high directivity.  That said, you make reference to “resonances” which occur at low frequencies.  Higher than that, the measured room-response irregularities that EQ schemes seek to correct are caused by destructive and constructive interference due to reflections.
4 - Again, your comment is about the LF. The good news here is that human hearing is essentially omni directional at these frequencies and therefore we do pervceive the sound similarly to the small omnidirectional mics used.  At frequencies above about 1kHz or so, this is no longer true.  Omni directional mic response no longer correlates to what we hear.
5 - I don’t believe we “chose” to hear the direct sound though any technique, but rather, it is our natural tendency to do so, all the time, independent of the directionality of our speakers or where we sit in the room.  We, as Floyd Toole puts it in his book Sound Reproduction, “have a remarkable ability to listen through rooms to hear the essence of sound sources; that is, after all, the basis of live performances.”  He makes many references to this phenomena throughout his very complete look at the topic of sound systems.

Another quote from his book that I particularly like because I think it offers very valuable insight into this topic is:

“In some ways, our problems with rooms, especially small rooms, began when we started to take measurements.  Our eyes were offended by the things seen in the measurements, but our ears and brain heard nothing wrong with the audible reality”

At low frequencies, most of the EQ methodology used today and its objectives are valid; such endeavors, though still challenging, have a chance to improve things.  And I know your courses, having taken one myself, offer very valuable instruction in this regard.

Above the modal region though, there are many sources of error in the EQ schemes out there, whether executed manually (by a person) or automatically (by an algorithm).

Two last comments:

I wish more folks in our industry would read Floyd’s book as he does a great job of identifying those things that matter and those that do not matter, and why(!),  in sound reproduction systems.  The knowlege in his book can help put an end to a lot of the incorrect dogma that is out there in our industry.

I appologize if there are typos or mispellings - I typed this on an iDevice.

Posted by Paul Hales  on  03/22  at  08:37 PM

To Ed:

I refer you to Bob’s comment as to how musical instruments are tuned.  And your comment about “live sound” doesn’t apply here; I’m talking exclusively about acoustic instruments listened to live, without sound reinforcement.

I don’t believe my Steinway analogy is faulty for reasons explained in my reply to Gerry.  If you put a Steinway in your living room, no one, to my knowledge, attempts to modulate the output of the piano over its bandwidth (its “amplitude response”, if-you-will) to compensate for the acoustic signature of the room.

And yet we routinely enjoy the sound of pianos in just such environments.

Can we at least agree on that?

Posted by Rick Murphy  on  03/23  at  02:57 AM

Mr. Archer,
Not tuning as in correcting pitch.  You are a musician, you always tune to the least tunable instrument on stage, the organ or piano is the

In this case, ‘tuning’ was used in the context of adjusting the location of the pipes (just as we choose locations for subwoofers) and then reducing or increasing the pressure at each pipe to get that individual pipe’s register to be similar in amplitude to the next note directly above of below it.

If a room’s transfer function has a peak at 27 Hz vs the surrounding frequencies, then the air pressure in the ‘Low A’ pipe may be lowered to create a reduction in output.

This is the same basic thing as tuning a speaker system to a room electronically with an equalizer, which was Gerry’s point.

Posted by Rick Murphy  on  03/23  at  03:06 AM

“minimal equalization (EQ) in home theaters above the standing wave/modal region.”

This is a good practice.  Always listen first, follow the steps in setup and adjust everything else to get the best result, and use the EQ as sparingly as possible.  Manipulation of crossover points and levels can often smooth out some peaks and valley’s before EQ is applied.  Cascading the sub amp’s crossover behind the processor’s crossover and/or using asymmetric crossover points to leave a slight gap between the high pass and low pass can also tune a peak in the mid-bass if a system is too boomy and bloated sounding.  Gerry is obviously all about treatment through bass traps, absorption panels and diffusion panels, since his company is one of the premier providers of those products for out channel.

I don’t know where Archer came up with his pitch tuning analogy, as it has no bearing on the conversation in any way.  Archer, you are a little flat.  smile

Posted by montvilleguy  on  03/23  at  07:24 AM

I agree that room treatment is vastly superior to any EQ solutions.  That said, room modes are notoriously hard to manage, especially when room dimensions are sub-optimal.  High quality bass absorbers (e.g., various RPG products) are expensive and generally take up space.  One this basis, room EQ in the modal range is a good Band-Aid, with the understanding that an optimal solution for one listening position is not necessarily going to have the desired effect at other listening positions.  Regarding the rest of the frequency range, I think the answers are not quite black and white.  In a recording studio, flat response (with a bit of a “house curve”, i.e., gentle roll off of higher frequencies) is desirable, so that the resultant mix is not inadvertently equalized to compensate for speaker inaccuracies.  In a home listening environment, it can be reasonably assumed that the content one is hearing was mixed a mixing theater/studio that was designed to be as flat as possible.  I accept the point that the ear has the ability to focus on direct sources, but in a home theater with multiple sources and diffuse surrounds, this localization ability may be somewhat limited.  Since no speaker is perfectly flat, and non-modal room effects can be quite extreme, I think judicious use of EQ can make a playback system better.  To me, “judicious” means less is more, and it means using your ears as the final judge as opposed to obsessing on a nice-looking graph.

Posted by montvilleguy  on  03/23  at  07:29 AM

Sorry for the typo above.  It should be “In a home listening environment, it can be reasonably assumed that the content one is hearing was mixed IN a mixing theater/studio that was designed to be as flat as possible.”

Posted by Robert Archer  on  03/23  at  08:54 AM

I think, without speaking for Paul, his general point is that maybe these auto room calibration programs go too far, and that given the compromises with them, which include cheap microphones and the practice of averaging measurements less is more when it comes to applying EQ.

I think we have all experienced using these auto EQ modes and found that some are unreliable in terms of accuracy.

Posted by montvilleguy  on  03/23  at  09:16 AM

I agree

Posted by Gerry Lemay  on  03/23  at  11:31 AM

Good discussion, but it’s hard to state in a short comment the full depth of understanding on a topic. I’ll add a couple more bullets to clarify my position.

- I’ll join with Paul on this: Read Floyd Toole’s book on Sound Reproduction.
- Audiophiles of the world unite and kick the full-range speaker habit. 
- Near-field and/or high direct to reverberant ratio listening is intoxicating but not all reverberant sound is bad.  In fact, I find it a serious enhancement over pure direct sound listening.  For example, do your speakers sound better in the backyard or in your house?  During numerous HAA workshops students have been given a chance to absorb, modify or keep reflections; 90% of the time strategically absorbing some reflections while keeping other reflections is the winner.  Of course, you have to determine the good reflections from the bad ones.  A scientifically engineered treatment strategy can be amazing.  However, if your speakers or listening position causes you to primarily listen to direct sound the room acoustics become less of a factor.  But it’s a different sound lacking full envelopment than my preference which includes reflections.  It’s a personal choice.
- Great speakers will sound good in most rooms if set up properly without any acoustical treatment. No amount of EQ or room treatment can solve the problem of a poorly designed speaker.  Great speakers make it easier to have multiple good listening locations and great speakers are seriously enhanced by an engineered environment.
- Its relatively easy to make one location in a room sound good.  Great calibrators/designers work on sound quality for many seats in a small room. High directivity speakers or near field listening make this a much harder problem to solve (in a small room).
- Bass traps work well if you use good smelly cheese and set your bait near the bottom, but they are not reliable tools to deal with the room modes.  Use equalization hand tuned by someone who’s done it before.  But first, use mechanical equalization; translation intelligent subwoofer/LCR placement.  Nothing works better than engineered speaker positioning on pesky resonance issues.
- This discussion has been about low frequencies but it’s been my observation that smooth low frequency sound makes everything (cymbals, flutes, voices, etc) sound better.

Posted by Paul Hales  on  03/24  at  04:42 PM

Gerry - all great insight.  Thanks.

I especially like your comment that great loudspeakers will sound good in most rooms if set up properly without any acoustical treatment. Along that line of reasoning, I could float the notion that most listeners would be better served by steering their room treatment budget towards buying better loudspeakers instead, but as a speaker manufacturer that would be selfish of me. So I won’t!

While I wouldn’t go quite so far as to say “smooth bass makes cymbals (etc.) sound better”, I do agree that smooth (non-resonant) LF response does allow us to hear non-bass content in greater detail and in the proper perspective to the bass content creating the subjective perception that “it all got better”, just as you suggest.

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