A Broad Discussion of Speakers with Major Audio Luminaries

[Keith_W]

How small is "small?"

In acoustics, "small room" means "any room where the low frequencies are dominated by room modes". This means ALL domestic listening rooms and ALL rooms smaller than a stadium or auditorium or a very large church.

But if you are asking "what is the largest room where spatial bass can be heard", I suggest you read the other thread, specifically posts by @Thomas Lund . This post implies that the dimensions of the room affect the perceptual limit below which "stereo bass" is inaudible. The larger the room, the lower the frequency where "spatial bass" can be appreciated. A paper was posted which I analysed here. The problem with that paper was that the room dimensions were not stated, although later posts showing photos of the lab they used suggests it is about the same dimensions as a large domestic listening room, about 6-7m width and length.

At the moment, the evidence suggests that "spatial bass" down to 20Hz is not achievable, but you may be able to obtain it down to 40-50Hz depending on the dimensions of your room and if you deploy your subwoofers in an advantageous way. However, setting up your system for stereo bass by necessity means you have to sacrifice timbral accuracy. If you feed your subs decorrelated signal, as required for spatial bass, they will no longer be timbrally accurate due to the nature of room modes.

Dr. Toole seems to think that the benefits of timbrally accurate bass outweigh spatial bass. Dr. Lund seems to think the opposite. I guess the most reasonable course for us ants is to try both configurations and decide for ourselves

 

[EL_PW]

Yes, because we now have very robust, reliable, repeatable, and effective measurements. So when people make extraordinary claims based on sighted listening, claims that are at odds with measurements but for which no blind listening data exists, a scientific-minded person will naturally dismiss them, because we know a great deal about how unreliable sighted listening is.

That's all good and well but how will these speakers sound in my space? Is my ceiling the same height as the store space, or wider, or narrower? Most people have smaller (i.e. more reflective) listening spaces than the stores do and that can lead to big disappointment despite how nice the specs look. That's why a great a return policy is key because I think most people actually need smaller speakers for their smaller rooms. But they have to figure that out themselves. If they even bother to think about it. Meh. :/

 

[RexrothPigeon]

That's all good and well but how will these speakers sound in my space? Is my ceiling the same height as the store space, or wider, or narrower? Most people have smaller (i.e. more reflective) listening spaces than the stores do and that can lead to big disappointment despite how nice the specs look. That's why a great a return policy is key because I think most people actually need smaller speakers for their smaller rooms. But they have to figure that out themselves. If they even bother to think about it. Meh. :/

I'm not sure what your point is. It's not remotely controversial that in-home auditioning is the gold standard, and all consumers prefer vendors with good return policies. But the perfect is not a suitable enemy for the good, and a huge, huge number of people want performant speakers but lack access to in-home auditioning or easy return policies, especially at budget levels. And nowadays performant speakers can be had at budget levels.

 

[MayI]

Dr. Toole seems to think that the benefits of timbrally accurate bass outweigh spatial bass.

When Dr Toole returns, hopefully he can explain why multisub EQ smoothing can't be used on the L and R sides of rooms and/or reference the blind listening tests vs monophonic where mono is still preferred. I have his wonderful 4th edition.

 

[Floyd Toole]

Dr. Toole seems to think that the benefits of timbrally accurate bass outweigh spatial bass. Dr. Lund seems to think the opposite. I guess the most reasonable course for us ants is to try both configurations and decide for ourselves

Not so. I think I have explained my position on the "spatial bass" thread, but to repeat:

First, two ears and a brain should have no problem hearing it if it exists. I hear it in live concerts and it is a pleasant embellishment, but for me the dominant sense of envelopment is delivered by higher frequencies, as the traditionalists have claimed for decades. In my research I have focused on sound quality because that was the principal issue with loudspeakers, and by extension, the room. That alone was a challenge and I think we have succeeded quite well.

At Harman, David Griesinger introduced the topic of spatial bass, and set up a demonstration of it for a collection of engineers and researchers - all very experienced listeners - in a large, acoustically well damped, home theater room used by Revel for dealer demonstrations. It was quite thorough, involving music excerpts as well as synthesized signals aimed at illustrating the effect. It was subtle, but audible, and after a long session of playing with the electronic and acoustical variables, the interesting conclusion was that there was nothing much convincingly audible below about 80 Hz. This is the common bass-management crossover frequency, so it was apparent that in normal systems the "spatial bass" would be delivered by the surround channels, not the subs. Life went on.

Now, enthusiasts of the effect claim that lower frequencies are involved. I can't argue against that, my research days are over, but if as claimed by some, that it is audible down to 60 Hz - we are talking about a narrow band of frequencies, 60 to 80 Hz, needing special attention. If, as others claim, it is 40 Hz, then it is an octave needing that attention.

I have said only that, if this is true, someone needs to do some "real" research to determine the relative perceptual merits of spatial bass IF it means sacrificing bass sound quality. Multiple sub schemes will be needed for both spatial and good sounding bass. The multiple sub schemes developed at Harman aim to deliver improved bass quality to multiple listeners. A single listener can use EQ only, and be quite happy. The most successful scheme, Sound Field Management, employs delay, gain and one parametric filter in the signal paths to each sub to achieve quite impressive seat-to-seat uniformity, after which global EQ is applied. The room resonances substantially disappear over a large listening area. This has been very successful where multiple listeners are involved, and many (most?) people spend at least some time sharing an entertaining experience - not just for home theater.

Spatial bass is a subtle effect, and arguably one that might be of less importance to the home theater, movie crowd. So, if the requirement is just to satisfy a single classical music loving listener, the setup requirements change, and are much less demanding.

So, Thomas Lund and I are not on separate sides of an argument. Ideally, a system should satisfy us both. Both goals might be achievable, but again, someone needs to do something resembling research. Me, I'm on vacation

 

[myHRTF]

Head motion tracking is needed for persuasive externalization, although some say that custom HRTFs help - in my limited experiences it was not a problem solver - moving the head destroyed any advantage.

I have had the same experience with HRTFs (ie. reflection-free). However, in my experience with custom / personalized BRIR (binaural room impulse responses, including reflections) about 80% of the users don't need head tracking, and they can move their head without the externalization being destroyed.

This finding is also supported by the fact that some users of the Smyth Realiser don't use the head tracker that is included and don't seem to miss anything.

 

[MayI]

At Harman, David Griesinger introduced the topic of spatial bass, and set up a demonstration of it for a collection of engineers and researchers - all very experienced listeners - in a large, acoustically well damped, home theater room used by Revel for dealer demonstrations.

Hi Floyd, do you recall how that Revel room was acoustically well damped in the 40-90Hz range? The MLL room showed rising RT below 125Hz (Fig 2) https://pearl-hifi.com/06_Lit_Archive/15_Mfrs_Publications/Harman_Int'l/White_Papers/Harmon_Lab_for_Components_Systems.pdf

 

[Floyd Toole]

Hi Floyd, do you recall how that Revel room was acoustically well damped in the 40-90Hz range?

In an airport lounge between flights.
The MLL has nothing to do with the Revel room. It was in Kevin Voecks' (manager of Revel at the time) home theater, in his private home. It was used to demo Revel products to dealers and distributors who sat in rows of cushy fabric upholstered sofas which provided a lot of mid/high frequency absorption - it was noticeably on the "dead" side. Low frequency absorption was provided by two monster sliding single glazed (it was California) patio doors and "economy" single drywall walls. It was enough to attenuate standing waves so the sometimes large audience heard something similar. No hard data, but I spent a fair amount of time there. It was selected because it was large enough and dead enough to be a reasonable demo space. If spatial bass is to be a commercial success it should have worked well in this room - IMHO - but I was not at all involved with the setup and running of the evaluation - I was one of the listeners.

I have heard it said that one should expect to spend serious money on bass traps in order to enjoy spatial bass.

This is why somebody needs to do a proper, unbiased, scientifically controlled test. It may cost some money, and I know at least one significant manufacturer is represented in the discussion, so-o-o-o. Harman has done its share, and the research group is gone. But there has to be either altruism or a profit motive to make that happen.

 

[ADU]

I only use headphones when there is no alternative, so I have not been motivated to chase the details. Sean Olive has done that and his summary in Chapter 15 is pretty thorough. .

Many thanks for the reply, Dr. Toole. My copy of Sound Reproduction arrived yesterday! And I've only thumbed though the chapter on headphones. There's alot in there!

I read the first and last chapters of the book though to get my bearings. And really enjoying it so far. It's technical, but not so technical that a somewhat audio literate person like myself can't understand most of it, which I very much appreciate.

Since I haven't designed any speakers (or headphones) myself, it sometimes takes a little longer for me to grasp some of the concepts associated with their engineering. It took about 10 viewings of the CIRMMT video before I really felt that I understood what directivity was all about, for example. So I'm still learning about all of this stuff.

I've spent many years looking at and reading about headphone measurements as well, and still have quite a bit to learn and understand there too. For those who may be interested, these are the headphones I'm currently trying out. They are very similar in appearance, and to some extent in sound. I think I'm leaning toward the less expensive one though (the post-2022 HD560S) for both comfort and sound. Still listening though...

 

[john61ct]

I have the ebook

Sound Reproduction 4th edition | 9781032761978, 9781040426937 | VitalSource

Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers, Rooms and Headphones 4th Edition is written by Floyd E. Toole; Sean Olive; Todd Welti and published by Focal Press. The Digital and eTextbook ISBNs for Sound Reproduction are 9781040426937, 104042693X and the print ISBNs are...

www.vitalsource.com

and Fig. 2.6 is mangled with text overlays.

Could someone please decode the relevant text, or even better post a corrected image?

 

[kyuu]

I have the ebook

Sound Reproduction 4th edition | 9781032761978, 9781040426937 | VitalSource

Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers, Rooms and Headphones 4th Edition is written by Floyd E. Toole; Sean Olive; Todd Welti and published by Focal Press. The Digital and eTextbook ISBNs for Sound Reproduction are 9781040426937, 104042693X and the print ISBNs are...

www.vitalsource.com

and Fig. 2.6 is mangled with text overlays.

Could someone please decode the relevant text, or even better post a corrected image?

Just looked in my printed copy and that figure is mangled there as well. The publisher unfortunately has really not done justice to Dr. Toole's fine work with this and other issues.

Plainly the Y-axis on all those graphs is "Relative Level (dB)". The bottom bar on 2.6(d) is supposed to simply read "Reflections", I believe?

 

[olieb]

The bottom bar on 2.6(d) is supposed to simply read "Reflections", I believe?

"REFLECTIONS" is what is underneath. And the correct text is "Sound Power". (Which is the dominant thing in bass.)

Plainly the Y-axis on all those graphs is "Relative Level (dB)"

Yep.

This diagram became very ugly indeed, but still readable, as everything in it is explained in the text several times.

 

[Floyd Toole]

I have the ebook

Sound Reproduction 4th edition | 9781032761978, 9781040426937 | VitalSource

Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers, Rooms and Headphones 4th Edition is written by Floyd E. Toole; Sean Olive; Todd Welti and published by Focal Press. The Digital and eTextbook ISBNs for Sound Reproduction are 9781040426937, 104042693X and the print ISBNs are...

www.vitalsource.com

and Fig. 2.6 is mangled with text overlays.

Could someone please decode the relevant text, or even better post a corrected image?

This is the figure I submitted - weird things happen with digital files. Sorry.

 

[RickS]

Also Slide 50 or 51 in the Toole presentation I just posted...

 

[john61ct]

This is the figure I submitted - weird things happen with digital files.

Thanks SO much!

> Sorry

You sir have NOTHING to apologize for.

My close parsing is yielding great advances in my understanding.

 

[Jaxx1138]

Concerning "spatial bass" discussion; some of the latest inovations in loudspeaker engineering may assist in shedding some new clues on any possible perception thresholds on this. TRINNOV has bass managent that now includes the possibility of subwoofer arrays on two opposing walls where the second wall absorbs the waves of the first wall. Thereby reducing some room modes and reducing the RT in the low frequencies as well. The other technology is the use of cardiod woofer patern control which can greatly reduce the back wall bounce and eliminating much of the constructive and destructive interference from out of phase lower frequency content. The real question becomes , how much of the room transfer function are part of the way sound recordings and sound reproduction at home is currently baked into what we are accustomed too? It would seem intuitive that low bass in relatively small rooms would be difficult to create a stereo image due to the fact that the wavelengths get larger than the room dimentions and below the Shroeder frequency the room begins to dominate how bass sounds. These type of innovations mostly reduce the rooms effects on the bass. Although at the same time there are no standards in the recordig industry calling for a specific directivity index or further , one that calls for directivity control down to 100 hertz (utilizing cardiod woofer radiation patern). I clearly do not know the answer and may be conflating some things that may not be related to each other. Controlled experiments are required to confirm or dispell any hypoythesis.

 

[john61ct]

I am no expert, but from my reading here, this rings true as a summary of the "spatial bass" issue.

From @Keith_W

The quick answer is: you need stereo subwoofers if you want envelopment, but if you have stereo subs you will lose the benefits of the smoothing the room response if you use mono subs. With a mono sub approach, subs are used to fill in dips created by other subs. And if you want to maximize the envelopment effect, the stereo subs have very specific placement requirements: they MUST be to the left/right of the main speakers, preferably on either side of the listener.
https://www.audiosciencereview.com/...ool-measurement-fir-export.70372/post-2564661

 

[john61ct]

Rather than an either / or tradeoff, I want to try for the best of both, combining Stereo subs to way down deep, and additional Mono-fed subs for taming room modes

Understanding subwoofers

Or you can have full range mains with cardioid down to 40Hz, monopole to 20Hz, side (of MLP) cardioid subs to 40Hz, dual monopole ULF to 15ish Hz directly behind MLP. Finish it off with center tower with cardioid to 40Hz … sounds real good to my ears ;) More than one way to skin the...

www.audiosciencereview.com

All feedback welcome, please, here or there would be fine.

 

[Blueprint]

There have been examples posted here of successful mono bass using just one subwoofer on each of the front and back wall. Therefore, to me, yes, it does make sense that Trinnov WaveForming and DIRAC ART can achieve both goals, summing to a signal in each channel that contains decorrelated information. What is the downside? You may forgo a little bit more mono perfection, but it is likely to still be acceptable. I’m curious about the experiences of people with such a system, particularly with DIRAC ART which tends to be deployed in somewhat smaller rooms.