Kvalsvoll

Seems I have posted too much, there is a limit to attachment uploads so I can not post the graphs. Solved by hosting images on my web.

System 2 with subwoofers units located behind - spl is more flat, it does not extend very low, velocity is very different.

V6030 is tuned much higher, so it is limited to around 25hz, and the placement is very bad for low bass.

We see the v at low freq is much better, overall the v is higher in the bass range. This is expected, the units are quite large acoustically, so you are actually in nearfield in the listening position.

We observe the same vertical 70hz resonance, so moving the subwoofers did not change the room. Some effects are due to the room-listening position interaction - will not change, others are caused by speaker boundary - changes when speakers/subs are moved.

100-200hz there is a dip in v, this would have to be investigated further to make this into a resonably good sounding system. First would be to find out what cause this, a new meas with fronts off would reveal if it is the interaction between front and subs causing the problem. It is not spl, phase, timing related (which you would see if you have the .mdat).

This system does not sound good. You can easily hear bass coming from behind, and even though the tactile is quite strong, it does not feel right, something is missing, and it does not sound well integrated and coherent.

Can you hear direction of bass? No, not below around 100hz, but the subs on cf 120hz will emit sound much higher up in frequency.

Can you feel direction of sound? No, and yes. Very close to the sound source you can feel it, and I conclude due to the velocity and intensity being higher on the side of your body facing the sound source - now we are talking about sound that has so large velocity that it actually feels like wind on your body. Direction in itself is not perceivable, and once you get reasonably far from the source, you can not detect direction.

(image hosted on my web)

Looking at v in 0 (on-axis), 90 (sideways) and h (vertical) directions gives information about the direction of the sound.

Direction reveals where reflections come from, and indicates the intensity of the sound. High intensity sound is directive.

Here we can see that the 70hz spl dip is caused by reflection from the ceiling, because h direction v has a top in this same range.

Up through lower midrange the sound field becomes more directional and resembles the outdoor free-field situation.

Above 1K the measurement device is no longer valid.

At low freqs the velocity drops, and that is not a good thing. But there is not much that can be done with that, unless one is prepared to do structural changes to the listening room - moving walls, closing off the open side wall door. For music it does not matter that much, and the low bass (<20-30hz) is experienced as airy, powerful, tactile. Sound intensity is the vector product of velocity and pressure, and there is plenty of energy to move the floor enough to create the necessary tactile feel.

Sound intensity is what drives tactile feel, and vibration of objects. If we eq this spl response to flat - such as removing the 70hz dip, it will not sound more flat and balanced, because we induce too much velocity and intensity in the sound field in the range that already has a velocity resonance.

What can we see from the velocity measurements.

In addition to the normal spl we can get more information about what is going on when measuring the velocity. We can see the direction of the sound, resonances that does not appear on spl, cancellations of sound intensity.

Ideally, the v should match the spl across the whole frequency range. If we measure outdoor, we see that this is the case when there are no reflections or standing waves or room modes present.

In a room and with multiple sound sources, this changes dramatically. Here are 2 examples from the same room, 2 FL FR + bass system cf 120hz.

System with 2 V80 bass horns up front, spl and velocity in on-axis direction:

System with 2x V6030 behind, almost nearfield:

We can see that the velocity does not follow spl at low and low-mid frequencies. This is caused by room acoustics and subwoofer locations.

The 2. has better v at very low freqs, and there is less v around 100-200hz. This may actually be due to the sound waves from the front main speakers meeting the same phase sound from the subwoofers located behind, causing v to cancel out while spl looks good.

Wanted to see Titanic, never saw it before.

Watching the opening scenes reveals something is missing, and from what I can hear - such a pity. Can this be improved..

And it can. There is a steep 25hz high-pass, and doing the bass-eq magic retrieves some of the weight and natural balance that was lost in the studio because they had mediocre monitoring speakers.

The exact numbers are on a different computer, but something like this:

L,C,R:

2x sfm 22hz q=2.2 gain=+9dB, + eq to adjust for the inevitable midbass dip.

LFE:

2x sfm 22hz q=2.2 gain=+9dB, 1x sfm 22hz q=2.2 gain +6dB + eq to adjust for the inevitable midbass dip.

Much better, the helicopter in an early scene now sounds great, you can sense your hair moving as it comes around to land.

One day I may elaborate some more on the velocity measurements - what is it useful for, what can you see and what is still missing.

... a velocity measurement kit to build or device ...

@dgage, I sent you a pm several days ago with this, I saw today you may not have read it yet, you should be able to see it in your Inbox.

Sorry to take it off topic with the sound velocity meter but I really didn't as I've noticed what you described above as well. Why does a 12" midbass have more impact than a 6"/8" midbass when played back at the exact same sound pressure level? I've asked multiple times, at least on AVS and I haven't ever received a satisfactory answer. I was hoping measuring the velocity would help point me in the right direction so I can understand this phenomena better. If you have ideas on the physics, I'd love to hear it.

 

And I'd love a pointer to a thread (couldn't find the one you referred to) on a velocity measurement kit to build or device to buy. Purchase depends on cost as well as if that will help me understand this size difference better. Thanks.

Exactly. The question is not IF the larger driver sound different, the question is WHY. Once that is established, we can move on and try to learn and find out what is going on.

I think there is at least two different causes at play here.

One is size of radiating area - the larger couples better to the air and creates sound with more intensity.

But capacity is also important. Even if they play at same spl, the smaller driver can be at its limits, causing dynamic compression of transients. This will not be audible as distortion before you turn it up much , much louder. But the peak level of the transients are missing.

I believe size is important from mid-bass and up into the midrange. At very low frequencies the size of one radiator is very small whether it is a 6" or a 24". But if you have 2 subwoofer units, they combine, and create a very large radiator together. If each of those units are very small, that does not matter.

And I'd love a pointer to a thread (couldn't find the one you referred to) on a velocity measurement kit to build or device to buy.

http://data-bass.ipbhost.com/index.php?/topic/404-understanding-and-optimizing-tactile-feedback/

I can send you a description on pm, the one that several others already have received. I just do not want to put it out in the open.

Don't worry about OT, that decent audio forums are dying is far worse. And this is on-topic enough, just today I have set up, calibrated, measured and listened to 4 different bass system configurations in Room2.

Sound velocity meter? I'd love to measure sound velocity as well as pressure. Tell me more please.

There is a thread about sub calibration & setup, actually two, search for the one with "tactile" in the title.

You already have pressure measurement, but of course you already knew that.

Velocity measurements are useful to see what you ended up with, if you have sub units both up front and back, it is also possible - to some degree - to change things with calibration.

8 sealed units makes a much larger radiator compared to 2 horns, it also depends on the horn, the drivers. Differences in capacity will also affect preception of the bass, and often at lower volume levels than you first assume.

What you definitely can measure with the v meter is the direction of the sound - when everything is perfect, the direction will be along the normal axis from the front speaker system. At low freq the level has significance, but higher up in the mid and upper bass, intensity may be more important. v measurement can give you an idea of intensity because the intensity will be highest in a directional sound field. 

Timing and phase response also has significance.

If I understand you correct - adding bass traps improved, and moving all sub units to the front wall improved.

The bass traps improves everything, and especially the time domain, so that makes sense.

Having all subs up front, close to the main speakers, should make it easier to integrate properly. And easier to achieve a good transient response. Subs all over the place has some very real problems with achieving a good time impulse response, and at the same time preserve sound field velocity and intensity.

Much of this is already known - "it is known".

We know delay and crossover must be right, we have an idea for how to do this, we know the frequency response must be reasonable.

The interesting parts start after all this is roughly adjusted.

Such as the character of the bass - a big system sounds better, even at low volume. How is that - certainly more than capacity comes to play here, because the difference is present at low volume, when a small 8" sealed sub should sound similar - according to simple theory. It does not. 

The difference is transient response and sound field properties - how the bass couples to the air. A large radiating surface couples better, and creates a sound field with more power and tactile feel, for the same spl. We have also experienced that a ported box has more impact than a sealed.

In the new subwoofers I created a larger radiating surface, with high velocity output. It is narrow in one direction - giving the high velocity - and long in the other direction - acoustically large radiator. The horn loading makes it possible to make this in a practical subwoofer.

A horn is different from a direct radiator, in that the sound has a higher velocity at the output, and kind of already has turned into a sound wave inside the horn path. The port in a ported box works in a similar way, the difference is in the tuning and that the horn port outputs sound across a much wider frequency range. The horn output works better even when the radiating area is smaller. This means it is possible to make a smaller subwoofer with the large sound.

The smallest of the new designs measures 22cm x 22cm x 68cm (divide by 30 to get feet). Very small, and output capacity is also limited.

At reasonable listening levels, you get that lively, realistic punchy character of the bass. Which of course makes you want more, so you turn it up, but that doesn't work so well, because you soon reach the capacity limit, the bass does not sound distorted or bad, but you don't get more of that addictive, powerful punch.

Jøkleba - album Nu Jøk!, track Popcorn (Can be found on Tidal).

When the bass drum comes in, it hits with a massive, powerful impact. Of course, at low volume you don't experience a hard, physical impact, but you can hear it is there. On the larger horns it certainly is very real and present when you turn up the volume, because they have more than 10dB more output, and wider frequency range.

One of the largest surprises was the V6030 unit - a larger horn tuned to 30hz, for massive output. Here, the bass drum on Popcorn is very dynamic and powerful, and it does not fade off when you turn it up - loud.

I have used this room to test a new series of compact horn subwoofers for some time now.

Several new designs and many configurations, from very small subwoofer systems up to something that approaches the real thing.

Part from the fun in testing and listening to all-new designs, here are some more general thoughts around bass in small rooms:

- Subwoofers do not sound the same. Even with same type - horn - and the same driver, the tuning affects sound character.

- Calibrating for a perfect and smooth frequency response is not the most important to get decent bass, time related problems are far worse. 

- Tactile feel is different from different subwoofers. Placement and calibration also affects this, but the subwoofer itself has huge significance. 

- A very small subwoofer can have a sound similar to a larger system if they are designed properly and the volume is kept reasonably low.

- Subwoofers both up front and in the back (4 or more) gives much more flexibility for calibration, but is difficult to set up properly, it is easy to end up with worse performance compared to 2 up front only, and just forget doing this without measurements. 

- When you think you have heard it all, and think there is no more to achieve, you set up a new design and realize you were wrong.

Wow!  This is first rate.  Thank you!

...

Still have not watched SW-RO, your comments make me look forward to this one. With Bass-EQ and a decent reproduction system all other reviews on sound quality usually becomes mooth..

Is this your own BEQ solution for Rogue One?  What does sfm mean?  How much content do you lose with "hard limiter -10dB" in your chain?  FWIW, my BEQ implementation has no headroom limitation aside from what the equipment can do. 

This is the quick-fix-BassEQ, the one JSS presented is the state-of-the-art.

Perhaps a bit too quick with the copy-paste:

sfm = shelf filter min = Low Shelf

sfm hs = High Shelf

The effect of the hard limiter remains to be verified, I did not get to those scenes in my brief testing. The reason for this is that I ended up getting some heavy ulf peaks in some very few scenes, the 12hz high-pass fixed most, and the hard limiter does the rest. This is on the lfe channel, it should not introduce audible distortion and no content is lost. Doing the same on any other channel would destroy the sound, as the limiter would distort and remove all other higher frequency content when the signal is limited.

Doing the hard limiter in the signal processing makes no difference compared to letting the bass system dsp limit the signal during playback - the result is the same.

The ulf boost is a bit heavy - JSS uses only 8dB where i put in a +12dB boost with a much higher q on the filter, making for much more level in the 5hz - 20hz range.

I wanted to test a simpler filtering scheme, more suitable for bass system dsp presets. If that works, it becomes so easy to play back a movie with BassEQ that anyone with a similar dsp can do it simply by looking up the movie on data-bass and select the most suitable preset.

Remember that the alternative is NO EQ, with too low ulf level and too much 30hz boom. Even if it isn't perfect, the improvement will be very significant, to the extent that the experience is lifted to a different level.

SW-RO BassEQ filters:

lcr:

sfm 16hz 2.0 +10dB


lfe:

gain -10dB

sfm 16hz 2.6 +12dB
sfm hs 32hz 1.6 +1.6dB

hpf 12hz 24dB/oct
hard limiter -10dB

gain +10dB
 

Spectrum for fixed LFE:

In this scene (from the opening) you can now feel the spacecraft passing by:

Rogue One: A Star Wars Story

 

BEQ Solution:

 

LFE:

 

Gain: -7dB

Low Shelf: 20Hz, Slope 1.2, Q 0.776, +8dB

High Shelf: 50Hz, Slope 1.5, Q 0.873, +8.5dB

 

 

LCR:

 

Gain: -7dB

Low Shelf: 20Hz, Slope 1.75, Q 0.943, +8dB (2 filters for total gain of 16dB)

Low Shelf: 40Hz, Slope 0.5, Q 0.5, +2dB

 

 

Surrounds:

 

Gain: -7dB

Low Shelf: 20Hz, Slope 1.5, Q of 0.872, +8dB (3 filters for gain of 24dB)

Low Shelf: 40Hz, Slope 0.5, Q of 0.5, +3.5dB

 

 

Playback for equivalent dialog level will be +7dB.  No scene is louder than 126dB if played back at equivalent reference.

 

Let me know what you guys think.  The high shelf is OK on LFE as the very steep DTS filter is in place on the original LFE track.

 

 

JSS

Fixed SW-RO yesterday, briefly saw some scenes earlier today - huge improvement, and I found the sound to be quite good, despite all the negative comments. This movie has great dynamic range, the loudness varies between scenes, some are softer and some are loud.

Removed the 30hz-boom and may have ended up with quite high level below 20hz, added only a moderate midbass-lift.

Sounded quite balanced on the scenes I saw - the beginning and some later. I will post a spectrum and the filters later.

Lots of movies has this 30hz boom-boost and falls off below - question is, are they similar enough to allow for one simple predefined filter solution.

BassEQ with several filters for each channel is fine, and will give the best results. However, if I just want to watch a movie - NOW - this is not a practical solution. It takes to much time and effort to implement either you are doing it in dsp for playback or remastering the soundtrack.

Since many movies share similar frequency balance defects, one or a small selection of predefined filters could improve things a lot - actually improving the overall sound quality by magnitudes - and it would be easy to select if predefined in the bass system dsp.

A bass-system dsp with option for presets could be configured with a few filters, covering most of the movies:

1: Default - flat response (flat ref to chosen target).

2: ULF boost - +10dB < 25hz.

3: ULF boost + boomfix - +10dB < 25hz, -3dB at 30hz.

Example #3:

When I want to watch SW-RO, I go to data-bass, observe the frequency spectrum chart, and choose preset #3. Done, start the movie.

This is something that could work for a lot of people.

For new readers:

Now, of course, the soundtrack should be played "as intended", but that will have to wait until they actually present a soundtrack with decent sound quality having reasonable full frequency range balance, and this will not happen until they install proper sound systems in their studios.

When "as intended" is boomy bass with lack of realism and dynamics and refinement there is huge potential for improvement, and if you really believe there is no significant difference to balanced, full frequency range sound, you are lucky because you can look forward to having a new experience for what sound reproduction actually can be like.

@minnjd, great job posting those reviews, 

Nice, @maxmercy.

How is your impression of the improved lf, does it sound good?

Some movies improve a lot in the fr graph, but not so much in terms of sound quality.

With very high boost at low freqs you often end up amplifying just noise.

Star Trek: Beyond - Dolby ATMOS

 

Level - 4 Stars (110.16dB composite)

Extension -  0 Stars (33Hz)

Dynamics - 5 Stars (28.55dB)

Execution - TBD

Overall - TBD

 

Comments - Wow, what a rolloff.  But the good news is only clips occasionally in the LFE channel, LCRS are clean, no flat-tops.  This one will probably need a BEQ correction.

 

 

JSS

I have pretty much given up movies, I find I rarely see a movie these days, and it is a long time since I bought a new movie.

When I sit down in the media room I end up listening to music instead, other entertainment can be anything streamed from the net, just as good to watch something on youtube when this is the current level for sound quality in movies.

A combination of ignorance and incompetence has destroyed what could have been a great business opportunity for the whole supply chain - from content providers to equipment manufacturers - and a great experience for movie enthusiasts.

@Ricci, I find it generous of you to share this data, very useful information.

I'm still a major skeptic that sound intensity of the sound field in the room (without your body in it) impacts tactile feel.  In my room, I have a very obvious standing wave room resonance at around 62 Hz.  Theoretically, a standing wave has zero sound intensity.  They are also sometimes called stationary waves for a reason: no energy moves.  But I feel plenty of tactile stuff at 62 Hz or so.  My MBMs are close but not exactly near-field, and the room resonance is impossible to miss in their responses.  IIRC, I've got like a -12 dB or higher PEQ there.  The reality is that sound intensity is only zero far away from my body.  Sound intensity is actually non-zero at the interface between the air in the room and my body because my body is literally absorbing that energy.  People flesh does work fairly well as a bass trap.

 

Tactile sensation is about impedance matching, and the impedance of air is probably closer to that of the human body high pressure regions of the room.  Hence, high SPL regions of standing waves in small rooms may offer even greater tactile sensation compared to anechoic / ground-plane or near-field.

Sound field properties does matter, a lot.

In the standing wave situation you have lost of velocity, and can actually have more tactile feel than audible sound, if you are in a pressure null, where the velocity is at the maximum.

...

Don't horns have their share of response non-itineraries as well?  I guess they aren't as bad, or maybe it's just that you get so much output from a horn that you're less likely to hit non-linear output levels.  The same may apply for the M.A.U.L. in practice, even though it certainly doesn't quit at 5 m/s port velocity. 

Mouth area usually ends up so large, it is not a problem anymore.

At the throat you have a very different pressure situation, you will not get flow separation to the extent you do when a horn mouth or port radiates into free space.

But there will be physical limits to how loud a horn can get, and this relates to size.

Most of my horns are so small they would not perform much better with a driver with more excursion, simply due to excessive pressure and velocity levels inside the horn.

I am way behind on the PVL / TR discussion you guys have over at AVS but it does seem like the consensus now is that particle velocity should be as high as possible. However a 1" port will always have higher velocity than a 6" vent which will have higher velocities than a 16" square horn mouth. This is opposed to the age old problem of trying to get enough vent or mouth area to avoid severe compression and noise. Also is there any thought being given to other considerations such as the total area of the high speed particles? For example a 4" port firing into the back of a couch versus a 21" driver surface area. One is a higher intensity but much more localized effect versus a more diffuse effect over a larger area.

A port which is acoustically small will - which is the case for all normal reflex ports, and even bass horns - will be the same as any small point source  when you get some distance to it.

To be sure, I did an experiment once and measured it; a sealed box measures exactly the same as a ported.

The relationship between pressure and velocity is the same for both.

However, if you get close enough to the sound source, the situation will be different.

Also, if you drive the port hard enough to get very high air velocity, the nonlinear effects of the flow and flow separation will affect the situation and create something different from the small point source model.