The "audio reference" idea and/or music reproduction, what is your opinion?

[Cosmik]

I think I find it useful. No harm done that I can find, and both measureable and audible improvements.

Maybe "room" correction is a poor choice for an identifier.

It's pretty good at "boom" correction in here, though.

Makes the step response look more like the ideal.

Minor things like that. Maybe the results are variable with different sytems and methods of execution.

What's the downside for you?

The way I see it, the delayed reflections from the room constitute a system that cannot be inverted by manipulating the signal from the speaker.

It may be possible to achieve a true inversion at a single point in space (but that is not guaranteed) but in doing so we make every other point in the room arbitrarily 'weird' - and render the sound at the inverted singularity the sound of the signal in an anechoic chamber - is that what we want?

Such an inversion is more than getting the 'frequency response' flat: as you say, the step response would have to be correct too. It isn't just a graphic equaliser, or even a graphic equaliser with phase control. The true inversion of the room's impulse response (at that single position) may require effectively sending out anti-phase impulses to neutralise delayed reflections at the listening point, then further impulses to neutralise the reflections of those impulses, ad infinitum.

If we couple this mathematically ill-posed problem to that the idea that humans are automatically 'doing the inversion' dynamically as they move around the room, separating the original sound from the 'ambience' effortlessly, it seems to me that the only correct sound is the uncorrected sound. Sure, bass in rooms is thought to be an issue - but I don't seem to have too much problem from that myself. Could this be because I'm listening in comfortable domestic rooms that are carpeted, have furniture, bookshelves etc. in them? Or that I am using sealed boxes, not ports, which helps marry the roll off to the room gain?

The Kii Three approach is to increase the proportion of bass that reaches the listener directly. It is not an attempt to 'correct' the room. As a result, people cannot get enough of the sound. It is a neutral speaker playing into the room unmolested and it sounds magnificent.

 

[amirm]

The way I see it, the delayed reflections from the room constitute a system that cannot be inverted by manipulating the signal from the speaker.

It may be possible to achieve a true inversion at a single point in space (but that is not guaranteed) but in doing so we make every other point in the room arbitrarily 'weird' - and render the sound at the inverted singularity the sound of the signal in an anechoic chamber - is that what we want?

Having bass sound like anechoic chamber is just fine. Indeed it is perfect. It is near clone of bass outdoors which sounds tight and excellent (but takes huge amount of power).

As for correction everywhere, we don't need that of course. We can for example completely dismiss all the volume above our ears. No one sits on our head. . Likewise, we don't need to optimize for front or back of the room. Only optimization needed is for the seating location (s). For stereo and single sweet spot, that is not much of an issue but even then you are right that we want it for more than in inch. To that end, spatially averaged responses across a few feet and optimizing that gives up a bit of top performance in exchange for wider sweet spot.

Take a look at this actual measurement in a theater across 6 seats: http://audiosciencereview.com/forum/index.php?threads/computer-optimization-of-room-acoustics.12/

There is a peak near 50 Hz that is shared between multiple seats. There, the decision is easy to pull that one down. For the rest, we can make a choice (heuristics) to use the average or some biased version (in favor of sweet spot).

Now, that is just relying on equalization. We can do a lot more than that with signal processing. Using multiple subs and filtering/delaying/adjusting levels on those alone can provide much more smoothed response even without EQ. See the graphs in that article.

All in all, no system in a domestic environment is going to have ideal response without signal processing/equalization. It just can't be done.

 

[RayDunzl]

The Kii Three approach is to increase the proportion of bass that reaches the listener directly.

I see so many references to these, but I'm still sitting here completely surrounded by no measurements.

Except one, well, two, the second of which bothers me a little with its distortion levels.

Actually three including this slightly odd looking step response from the same source:

Wait, that's 4, including the waterfall. Truncated to -20db. What's with the flat-top on the step?

Still, no in-situ measurements from unrestrained goobers like me out in the wild.

 

[Fitzcaraldo215]

Time and amplitude and HRTF and...?

My room first shows up at 7ms (dipole bounce) and 20dB down from the direct sound.

From my research on this over the years, I believe there is a time threshold below which the ear cannot separate direct from reflected sound. Only above that threshold does it start to be discernible as echo or reverb. So, I believe much reflected energy affects the sound, but we are unconscious of that explicitly as reflected energy. For example, bass modes which are due to reflective cancellation/reinforcement, I believe are perceived first as non-linear alterations of net perceived speaker plus room frequency response. That may be followed by the decay of the ringing, echo, reverb associated with a modal peak.

But, then it gets complicated because music is continuous. So, notes subsequent to an initial impulse may partially mask the original residual ringing, echo, reverb, etc. in the time domain, again making the explicit presence of the reflected energy difficult to identify or discern as delayed reflections.

I think we agree that this happens even with excellent, linear speakers, because it is the room that is doing it. Some, like me, agree that cleaning this up in the room works wonders in improving clarity, reducing bass boominess and hangover, etc. Analytically and intellectually from acoustic science, we know reflected energy is the cause of this, but the reflections themselves are usually not perceivable by ear alone, just their resultant net impact on the overall sound.

When I sit in a concert hall, as I did last night to Carmina Burana with the Philadelphia Orchestra, except for some slight delayed reverb when the music stopped, I was unaware of the considerable amount of diffuse reflected energy that was there with every note of the music throughout the concert. I know that reflected energy is there, of course, in huge amounts. That has been proven empirically many times. I am not surprised at how many audiophiles are unaware of it, because it is not directly obvious to the unaided ear. And, our eyes fool us into thinking the sound is all coming from performers up front, which it is not.

It is also true that we humans tend to prefer the sound of music in a reflective, reverberant hall. Yes, some are better, more "ideal" than others. But, to me classical music outdoors where there are few reflections sounds washed out, threadbare, lacking in warmth, dynamics, envelopment, etc. to the point of not being enjoyable at all to nearly the same degree.

 

[Thomas savage]

I see so many references to these, but I'm still sitting here completely surrounded by no measurements.

Except one, well, two, the second of which bothers me a little with its distortion levels.

View attachment 3955

Actually three including this slightly odd looking step response from the same source:

View attachment 3956

Wait, that's 4, including the waterfall. Truncated to -20db. What's with the flat-top on the step?

Still, no in-situ measurements from unrestrained goobers like me out in the wild.

Sadly we don't have any members who own a pair... Hang on

That Keith guy who used to beat up guys on WBF because they never had measurments, turns out he don't like measurments either

' the best bass iv ever heard' 'completely eliminates the room'

 

[fas42]

Still obsessed with measurements, and bass... . When I hear a system get the subjective impact of a pipe organ going for it right then I might be interested what in the "measurements" say; otherwise, continue playing around in the sandpit, out in the backyard ...

Agree with Ray about the distortion readings of the Kii - look at the great wads of the stuff, below 200Hz, - and it still hasn't hit 100dB! Anyone for some 'false' bass ... ?

 

[amirm]

From my research on this over the years, I believe there is a time threshold below which the ear cannot separate direct from reflected sound.

There is indeed and nicely shown on this graph from Dr. Toole's book:

The bottom solid line is the threshold of detection for the reflection. At 10 feet reflection path for example (10 millisecond), the reflected sound needs to be louder than -15 db relative to the direct sound to be perceptible.

 

[RayDunzl]

So... by my meticulous calculations using my rule and my thumb, my reflections are below threshold.

1 ms - top of couch with short mic stand on top - 7.6% of impulse = -22dB
7ms - dipole bounce off wall behind speakers - 3.9% = -28dB
27ms - room length and back bounce - 4.7% = -26dB .. or the negative side 6.4% = -23dB
General diffusion level - about 1.5% or -36dB

Q: So why do I think hear the room?

A: HAL 9000: Well I don't think there is any question about it. It can only be attributable to human error. This sort of thing has cropped up before, and it has always been due to human error.

 

[fas42]

Just came across this ... http://www.6moons.com/industryfeatures/nagra2014/1.html. This nails the subjective behaviour one's after in quite some detail - and looking at the mods in progress pics reminded me of the sort of carry on I get up to - quite funny, really ... .

It's pleasing that a well known and regarded manufacturer has got a sharp handle on what the target is - good progress is being made!

 

[amirm]

I can't read your graph Ray. The red cursor line obscures the starting impulse level.

 

[RayDunzl]

the starting impulse level.

100% - "Plot responses normalized" under "Controls"

(zoomed)

(more zoom - 48kHz sample points)

 

[Blumlein 88]

So... by my meticulous calculations using my rule and my thumb, my reflections are below threshold.

1 ms - top of couch with short mic stand on top - 7.6% of impulse = -22dB
7ms - dipole bounce off wall behind speakers - 3.9% = -28dB
27ms - room length and back bounce - 4.7% = -26dB .. or the negative side 6.4% = -23dB
General diffusion level - about 1.5% or -36dB

View attachment 3960

Q: So why do I think hear the room?

A: HAL 9000: Well I don't think there is any question about it. It can only be attributable to human error. This sort of thing has cropped up before, and it has always been due to human error.

Yes Dave/Ray, you are human and in error.

Perhaps Dave/Ray, the threshold for a single lateral reflection is insufficient in a space with multiple reflections in gauging total room audibility.

 

[amirm]

Thanks but which display are you using in REW? Impulse response already shows these values in dB.

 

[RayDunzl]

That's the DBFS display. The sweep was an indicated 75dB for further reference. Toggle with a little control in the top left of the IR window when the mouse is there.

Zoomed out.

 

[RayDunzl]

Perhaps Dave/Ray, the threshold for a single lateral reflection is insufficient in a space with multiple reflections in gauging total room audibility.

Perhaps, Dr Chandra. But I don't see a lot of lateral reflections here with the Martin Logans.

I think I did when I had a pair of Infinity P-363 set up right in front of them. Somewhat but not guaranteed comparable Impulse Response. Martin Logan top, about a 75dB sweep, Infinity P-363 bottom, about 80dB sweep.

 

[Cosmik]

What's with the flat-top on the step?

What shape should a real step be? We are so used to the behaviour of normal speakers that we forget that a real step has a flat top. The Kii Three is actually behaving so well that it manages to give you some real step response.

A measurement so good you have never seen it before, and possibly a sound you have never heard before.

 

[tomelex]

Sort of curious what the point of the video is - is it to point out that one can emphasise poor reproduction quality, and make it sound like it's coming out of a small box, by adding room treatments everywhere?

Tsk, tsk, tsk. Really now, it is obvious to show you how your "reference" is a lot to do with your room. Dinking around with electronics is not enough by a country mile, Sir.

 

[RayDunzl]

What shape should a real step be? We are so used to the behaviour of normal speakers that we forget that a real step has a flat top.

The shape would be a 'step'. An abrupt change from one static pressure level in the "room" to another level.

However, outside a sealed pressure vessel a step doesn't occur, unless you know of a case I don't. You're a smart guy, you might surprise me.

A measurement so good you have never seen it before, and possibly a sound you have never heard before.

I'd suppose it could sound like a "click" (depending on the rapidity and amplitude of the pressure change), maybe with a little "whumpf", along with possible discomfort due to the pressure change, but no sound, afterwards.

 

[fas42]

The shape would be a 'step'. An abrupt change from one static pressure level in the "room" to another level.

A sound "step" can always be broken down into a set of sine waves - you know, Fourier, and all that ... . If it was a "perfect" step then it would mean a FR which was ridiculously beyond any speaker, so there will always be curves to it, so some degree. And that's how it should be ...

 

[Cosmik]

The shape would be a 'step'. An abrupt change from one static pressure level in the "room" to another level.

However, outside a sealed pressure vessel a step doesn't occur, unless you know of a case I don't.

I would guess that the only reason the step with a flat top doesn't occur - for a short time - is that the phase and timing of the drivers isn't correct (at least, not all the way down in frequency). If they are, then you must get the flat top - just like reproducing a square(ish) wave, which some people use as a test for their setups.

There is the concept of the rotary woofer. This feathers the blades of a fan in response to the signal. Presumably even in a leaky room, it could create a static pressure increase..? I read somewhere that pipe organs actually do this, and if we really wanted to reproduce the experience perfectly, we would need to go down to DC. What do you reckon?