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Step Response: Does It Really Matter?

Cosmik

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#81
As has been described, a ‘perfect’ step response indicates a transducer that behaves perfectly in the frequency and time domains i.e. it duplicates the signal in terms of sound pressure; it is neutral. But with this simple statement comes a number of qualifiers:
  1. the step may only be valid at a single point in space. If so, is this any great achievement?
  2. most audio people don’t believe that the time domain matters anyway.
  3. most DSP people don’t believe that a neutral speaker sounds good in a real room – if ‘room correction’ is applied, the step will be modified in some way.
  4. a good step derived from a sine sweep may not show how the speaker behaves with a real step (although Ray has demonstrated a good match with one of his tests), or at different volume levels
  5. the step cannot be expected to remain uncontaminated once room reflections reach the listening/measurement position. If step-iness is valued literally at the listener’s ears, reflections must be eliminated as much as possible:
  • acoustic treatments = anechoic chamber
  • use of headphones
  • sit close to the speakers
  • use a phased array to produce a directional beam of sound to the listener
  • a desperate measure would be to kill the reflections at the listening position using DSP from the speaker but this would be very unstable, not possible in some rooms, and only valid at a single point in space.
All very confusing and rather tenuous.

But as I ranted on about earlier, I think the significance of the step can be appreciated logically as long as the designer knows what they want to achieve. In my case it is: a neutral, moderately directional speaker in a real room; if the combined output of the drive units stays reasonably time-aligned off axis and at different distances then that will be a bonus (another one of your tests as I recall, Ray). There’s not much point in my measuring this, though: my speakers already have the drive units in a vertical line as close together as possible on a baffle. Their geometry defines what they are going to do off-axis in a predictable way, and I can’t change that very much with DSP.

However, I am reasonably sure that this configuration is the best compromise for me in terms of the interaction with the room: it is moderately directional thus keeping reflections down to some extent; but it is small so I feel it will sound reasonably ‘natural’ in a real room. As such I won’t be investigating panel speakers, or phased arrays (unless it’s German-style bass cardioid), or truly omni-directional speakers, and any DSP room compensation I apply will be minimal. For me, I think I do want a real step i.e. time-aligned output from the direct sound at the listening position and I am happy that I will hear past any reflections to that, even if the in-room (non-anechoic) measurements look messy because of the reflections.
 

RayDunzl

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#82
if the combined output of the drive units stays reasonably time-aligned off axis
It doesn't, if considering two speakers...

A nice step or impulse on-axis (stereo) becomes two (nice) steps or impulses off axis. Left end of the couch, you get the Left, the Right + some Left residual:

upload_2017-10-18_4-59-59.png



upload_2017-10-18_5-0-24.png



I am happy that I will hear past any reflections
My "directional" panels spatial sound is much different from the JBL. My room is not treated on the sidewall, other than some CD rackage.

The JBL reflects from numerous unknown locations, the panel from the wall behind the speaker (7ms) and the room length bounce (27 ms).

The spatial difference makes the JBL sound wide - which is what it is - the panels seem to project a much narrower sound when you first switch to them, more distant, but, in the end, much more satisfying (to me) when critically listening.

A comparison of extended impulse response, JBL red and MartinLogan black.

Not "normalized"

upload_2017-10-18_5-22-10.png


Normalized, and zoomed out a little:

upload_2017-10-18_5-40-39.png


They are about the same level (80dB) in the room here, the JBL slightly lower in SPL (maybe 2dB), I should do a more controlled test, the panel a hair louder (old measurements), but the results are always the relatively the same - panels quiet except for dipole (7ms) and room length (27ms) reflections (maybe some 4ms floor bounce in this zoomed-in perspective), JBL gives all sorts of reflective hash off walls ceiling who knows where. Spatially "enhanced", but artificial. I hear it - things aren't nearly as focused (I prefer focused).

As such I won’t be investigating panel speakers
I still like mine (19 years old now). I don't promote them as they are a bit of an idiosyncratic choice, and the same size panel is $25k now (I paid $4k in 1998).

For casual lower volume listening, I have no audible preference between the two (JBL much more economical here and in use right now), but critical/loud/beer Saturday listening, I always go back to the panels.
 

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Cosmik

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#83
The spatial difference makes the JBL sound wide - which is what it is - the panels seem to project a much narrower sound when you first switch to them, more distant, but, in the end, much more satisfying (to me) when critically listening.
Have you tried some of the floor-to-ceiling type line arrays. The Keele CBT? I would be interested in how you find the sound of these. They presumably are directional in the vertical but much less so in the horizontal. Do they sound 'natural'?
 

RayDunzl

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#84
Have you tried some of the floor-to-ceiling type line arrays.
No. My audio past is somewhat limited. I didn't buy LPs. A handful only.

1959~73, Dad's stereo
1973~92, car stereo, other people's systems
1980~81, ran a nice rocking teen combo triamped pro setup. Audio buddy had some AR-3 and a receiver.
1983~2002, working Telecom, travelling a lot, homeless (literally) for years.
1992~94, Bose 301 and Harman Kardon receiver (and the big amp from the pro setup). Started CD collection
1995~1998, ML SL3, CP player, passive attenuator, Acurus A250 amp
1998~2011, ML reQuest speakers
2011~now, added Krell and DSP and TV and HDRadio and cheap subs here at the Neverland East Retirement Home and Audio Sanitarium
2015~ Infinity P363 ($200/pr)for mother's room. My panel buddy didn't guess "speakers" when he came over and we played the "Something's Different" game and they were playing in this room but invisible.
2016~ added the little JBL (for the garage, but they've remained in here)

I suppose I heard some 1995 vintage B&W and Wilson and Magnepan (which I don't remember) and McIntosh and Carver and Definitive and ??? when shopping. I don't go out listening to things...

Don't go out much at all... My time in Japan spoiled me for having any interest in that here.

Mr O'Hanlon is coming to demo at the local Audiophile Society later this year with some Vivids and ???, might go to that with A.J. (http://www.soundfieldaudio.net/) since he is a member and can have a guest. I haven't heard what he has to offer, except one example at a club meeting. I don't think it was his best effort.

Never heard horns (maybe a Klipsch in 1994 maybe, and, of course, the PA horns on top of the speaker cabs, would be interested in hearing the M2. Don't feel like driving across town (assuming they even have any, haven't called).

---

My initial MartinLogan demo was in the big back room of a Sound Advice store in Tampa with a pair of SL3 powered with a Krell KAV-250 (500w 4 ohm), maybe 25 x 50 x 16, strip mall architecture. The sales guy got paged and handed me the remote and left.

I cranked it. All the way, eventually, It was good. I said something like "Wow." Brought my audio buddy (he was in the band). He said something like "Wow." That's standing back 30 feet. "Wow." They really had a "right" sound to them. Bought a pair a couple of months later (was living near Houston). They're in the bedroom now.

Bought the reQuests without hearing them. Bigger panel and woofers, what could go wrong?

In fact, there is nothing in my system right now that I "heard" before buying. Nothing bought has been returned, either. Maybe I'm easily amused.
 

watchnerd

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#85
---

My initial MartinLogan demo was in the big back room of a Sound Advice store in Tampa with a pair of SL3 powered with a Krell KAV-250 (500w 4 ohm), maybe 25 x 50 x 16, strip mall architecture. The sales guy got paged and handed me the remote and left.

I cranked it. All the way, eventually, It was good. I said something like "Wow." Brought my audio buddy (he was in the band). He said something like "Wow." That's standing back 30 feet. "Wow." They really had a "right" sound to them. Bought a pair a couple of months later (was living near Houston). They're in the bedroom now.

Bought the reQuests without hearing them. Bigger panel and woofers, what could go wrong?

In fact, there is nothing in my system right now that I "heard" before buying. Nothing bought has been returned, either. Maybe I'm easily amused.
Wait, what?

You have a pair of ReQuests in your living room and another pair of SL3's in your bedroom?

Nothing against having 2 pairs of ML's (my old pair are some SL3 upgrade to a Sequel)....but I would have never thought of putting them in a bedroom.
 

watchnerd

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#86
If step-iness is valued literally at the listener’s ears, reflections must be eliminated as much as possible
It seems the corollary of this is:

If good step response at the listener's ears matters the most, then good step response at the speaker itself doesn't matter.
 

Cosmik

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#87
If good step response at the listener's ears matters the most, then good step response at the speaker itself doesn't matter.
At the speaker it may not be a step response, but it needs to be a specific 'something'. All the drive units need to combine correctly to produce the step response at the measurement/listening position, hence the use of sloping baffles or delays for time alignment.

However, if the speaker is always subject to floor bounce, say, then you won't get an uncontaminated step at the listening position even if the speaker behaves perfectly in free space. Your choice would be to modify the signal to the woofer in order to get a step at the listener's ears, or accept it on the grounds that it is 'natural'. Linkwitz says:
The brain operates both in frequency and time domains when interpreting the summation of sound streams at each ear drum. A floor reflection, which probably causes the dip at 250 Hz is a natural phenomenon that we have grown up with. The frequency of the notch has changed as we grew taller and I suppose that we interpret the delayed reflection versus the direct sound from a source as an indication of source height over the floor.

The room response is used as the basis for room equalization to an empirically derived target. I am highly skeptical of this practice. It should only be applied to one or two most dominant low frequency room modes. Our brain has evolved to deal with sound in reverberant environments and gets tired when having to compensate for unnatural processes from a DSP room equalizer.
 
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Krunok

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#88
I don't pay attention to them. But JA does and hence the reason he measures them in stereophile. Maybe we can j_j to comment on it. :)
I didn't really understand that John Atkinson pays that much attention to step response.

Here is what he said:

Acoustic Phase Responses
Does a loudspeaker's time coherence matter? A "perfect" speaker, of course, would have both a perfect impulse response and a perfect frequency response (at one point in space). Another way of looking at a loudspeaker's time-domain performance is to examine its acoustic phase response, the phase angle between the pressure and velocity components of the sound plotted against frequency.
Again, this is an aspect of loudspeaker behavior that has proved controversial. One school of thought holds that it is very important to perceived quality; another, which includes almost all loudspeaker engineers, finds it unimportant. Floyd Toole, now with Harman International but then with Canada's National Research Council, in his summary of research at the NRC into loudspeaker performance that is described in two classic 1986 papers [32, 33], concluded thusly: "The advocates of accurate waveform reproduction, implying both accurate amplitude and phase responses, are in a particularly awkward situation. In spite of the considerable engineering appeal of this concept, practical tests have yielded little evidence of listener sensitivity to this factor...the limited results lend support for the popular view that the effects of phase are clearly subordinate to amplitude response."

This is also my view. Of the 350 or so loudspeakers I have measured, there is no correlation between whether or not they are time-coherent and whether or not they are recommended by a Stereophile reviewer.

https://www.stereophile.com/content/measuring-loudspeakers-part-two-page-4
 

RayDunzl

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#89
Another way of looking at a loudspeaker's time-domain performance is to examine its acoustic phase response, the phase angle between the pressure and velocity components of the sound plotted against frequency.
I wonder how you do that.
 

sergeauckland

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#90
Acoustic Phase Responses
Does a loudspeaker's time coherence matter? A "perfect" speaker, of course, would have both a perfect impulse response and a perfect frequency response (at one point in space). Another way of looking at a loudspeaker's time-domain performance is to examine its acoustic phase response, the phase angle between the pressure and velocity components of the sound plotted against frequency.
Again, this is an aspect of loudspeaker behavior that has proved controversial. One school of thought holds that it is very important to perceived quality; another, which includes almost all loudspeaker engineers, finds it unimportant. Floyd Toole, now with Harman International but then with Canada's National Research Council, in his summary of research at the NRC into loudspeaker performance that is described in two classic 1986 papers [32, 33], concluded thusly: "The advocates of accurate waveform reproduction, implying both accurate amplitude and phase responses, are in a particularly awkward situation. In spite of the considerable engineering appeal of this concept, practical tests have yielded little evidence of listener sensitivity to this factor...the limited results lend support for the popular view that the effects of phase are clearly subordinate to amplitude response."

This is also my view. Of the 350 or so loudspeakers I have measured, there is no correlation between whether or not they are time-coherent and whether or not they are recommended by a Stereophile reviewer.

https://www.stereophile.com/content/measuring-loudspeakers-part-two-page-4
I did some tests back in the 1980s which had the tweeter of a two-way loudspeaker on a sliding carriage so it could be moved fore and aft from about 6" 150mm in front of the main baffle to 6" 150mm behind. Moving the tweeter over that distance made no difference whatsoever to the sound when listened to blind at a distance of around 2.5m. I can imagine that if the tweeter was, say, 3 kilometres behind the woofer, then level apart, the time delay would be very noticeable. So what about 300m or 3m behind? At what point would the tweeter's sound be heard as a distinctly different source compared with the tweeter in line with the woofer?

I don't know, but my experiments led me to the view that time alignment of a few cm really doesn't matter.

When I built my active versions of the B&W 801, which are nominally mechanically time aligned, I used my DSP crossover's time alignment facility to fine-tune the alignment, and again, I couldn't hear any difference before and after.

Whilst there clearly isn't anything against time-alignment, in my view it's nothing to be concerned about.

S.
 

Krunok

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#91
I wonder how you do that.
Well, my guess is as good as yours, but once you apply gating you loose resolution at LF so your amplitude graph won't be looking as good as it was without gating. And, of course, if you don't apply gating your phase graph won't be as good as it was with gating. So, it looks a little bit like "mission impossible" to me. :D
 
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Krunok

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#94
With a pressure mic and velocity mic. Omni and figure 8.
Exactly. Accordinng to Enterpirse captains log we will acquire that technology at stardate 2312.18 from Borg. A bunch of folks will be assimilated in the process but that is the price you pay when getting Borg technology. :D
 

RayDunzl

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#95

Krunok

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#96
"Microphones work on the principle of pressure, pressure gradient, or velocity. If you don't know the difference, then you can't yet call yourself a sound engineer."

Whoa, dodged that bullet...

More at https://www.audiomasterclass.com/ne...re-pressure-gradient-and-velocity-microphones
Ok, I'm definitely not a sound engineer but as far as I remember microphone measures only pressure on its membrane and that pressure is a direct result of a bunch of air molecules hitting the membrane with some velocity. :D:p

I can even make a car analogy: in cylinder combustion chamber a number of particles generated after ignition is hitting the piston with some velocity, that generates pressure and engine torque is a direct result of that pressure. ;)
 

Blumlein 88

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#97
Ok, I'm definitely not a sound engineer but as far as I remember microphone measures only pressure on its membrane and that pressure is a direct result of a bunch of air molecules hitting the membrane with some velocity. :D:p

I can even make a car analogy: in cylinder combustion chamber a number of particles generated after ignition is hitting the piston with some velocity, that generates pressure and engine torque is a direct result of that pressure. ;)
Now ribbons approach being velocity microphones. The output is proportional to the velocity of the ribbon and the ribbon is moved by the air. Since some pressure is needed to move the ribbon (it isn't a massless ribbon) it is more accurately a pressure gradient microphone, but close enough for some purposes. Some figure 8 microphones are actually a pair of cardioid condensers front to back which can be combined for any pattern (all microphone patterns are combinations of omni and figure 8). Figure 8 or pressure gradient patterns are combining the two diaphragms so they have opposite polarity.

I have one multi-pattern mic that lets me record both diaphragms separately. So I can record once and decide after the fact which microphone pattern I want out of all the possible patterns. I suppose you could measure a sweep with it and switch between omni and figure 8 (pressure gradient) to get pressure and velocity results that way.

I have combined it with a sideways figure 8 microphone and you can get not only all patterns, but any directionality after the recording is done. The Calrec Soundfield mics and clones can do this in a more elegant manner.
 
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RayDunzl

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#98
can even make a car analogy
I can too:

Mount your piston so the top surface of it is parallel to the bore instead of the head.

Create combustion. It blows right on past.

That, to illustrate the velocity mic, which ignores "pressure" from its edges.
 

Krunok

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#99
Huh.. Guys, I'm having my 2nd bottle of wine so this discussion has gone in all posible aspects over my head. I remember that some pistons are not flat and that they have inflections (dips) to deal with that, but I would really need extended help from @Frank Dernie to continue with my car analogy. :D
 

Blumlein 88

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