Wanted: Proof of multiple subs and sub EQ

[RayDunzl]

It may better to buy Acourate first

I want the convolver in hardware - so that it also works on the Oppo, TV, Cablebox, Roku, and HDRadio.

So, that's what I have.

 

[dallasjustice]

Geese Amir! Give the man a break. He's just describing his background. The whole point of the book is to help folks get accurate reproduction without needing to resort to using too many room treatments or building some scientific laboratory for music listening. All of the examples are taken from Mitch's living room which has very few room treatments and is not purpose built for playback.

The concepts and recommendations he uses are very universal.

OK, read through the first chapter and had to take a pause when I got to this:

"LEDE is state-of-the-art in acoustic control room design.

Barnett, Mitch. Accurate Sound Reproduction Using DSP (Kindle Locations 220-221). Kindle Edition. "

He is completely wrong here. LEDE is old school and nothing about it is state of the art. It came about in the age of broken studio monitor designs and assumptions about sound reproduction with no controlled testing. Decades of research since has shown the approach to be improper. Dr. D'Antonio who is the founder of RGP (largest manufacturers of acoustic product) puts all of this in great context in one of his presentations:

View attachment 1973

There it is: 1979 when LEDE (live end, dead end) was invented. Then came formal studies at NRC as highlighted below:

View attachment 1974

RFZ became the other buzz word as was NE Room as mentioned above. Just as with LEDE, improper methodologies with no controlled testing to validate them.

Then came enlightenment:

View attachment 1975

To the pinnacle of what we know about sound reproduction in rooms:
View attachment 1976
View attachment 1977

The author is old school, having done pro work years back when concepts like LEDE were the rage. As with many people of that era and domain, they still talk about these old approaches as being valid even though it is trivial to show that they are not.

Anyway I will read through the rest of the text but so far, it is not a good thesis for home listeners to follow.

 

[amirm]

Geese Amir! Give the man a break. He's just describing his background. The whole point of the book is to help folks get accurate reproduction without needing to resort to using too many room treatments or building some scientific laboratory for music listening. All of the examples are taken from Mitch's living room which has very few room treatments and is not purpose built for playback.

The concepts and recommendations he uses are very universal.

I don't know Michael. It doesn't appear to me that he has a proper grasp of the topic. Take this for example halfway through the book:

"Group delay is typically introduced by loudspeakers and multi-way loudspeaker cross-over networks. So it is important to know the threshold of audibility of group delay with respect to frequency. As far as I can tell, the best thresholds of group delay audibility versus frequency is provided by "Blauert, J.; Laws, P. (May 1978), "Group Delay Distortions in Electroacoustical Systems", Journal of the Acoustical Society of America 63 (5): 1478– 1483."

Barnett, Mitch. Accurate Sound Reproduction Using DSP (Kindle Locations 1421-1424). Kindle Edition. "

Here is the conclusion from that paper:

Yet the author goes on to say that the paper says these things are audible and gives the thresholds heard in headphone listening. Headphones eliminate the room. Room reflections substantially change these characteristics. It is clear to me the author has not read the above paper and as such, providing misleading advice.

 

[h.g.]

I just dont see PSI introducing a product that does not work, their monitors are highly thought of.

You can see the product works but it is only an active version of a passive absorber. Just like a passive absorber you need lots of surface area to achieve large reductions in a whole room rather than just near the absorber. How much sound reduction do you get if you open a window? So how many absorbers were used to get the 1-2dB reduction and how large was the room? PSI are recommending 4-8 are used.

Now dallasjustice's active version of something like LEDE doesn't seek to create a small zone of silence in a region in front of the absorber sub but to absorb all the sound in the room created by the source sub a short time earlier. That is a great deal more sound absorption which can be seen in his plot. However, if he was to plot what the sound in his room actually is rather than an averaged version of it and at a few more spatial locations it would provide a bit more information on what is going on. Clearly things have improved greatly at the main listening location despite LEDE being an improper methodology. However, I suspect there is more to know about the sound emitted by the absorber sub that doesn't cancel with the source sub. My suspicion is that it is possibly more good than bad given a 100% dry bass is almost certainly not optimum even if it is preferable to what would be heard in an uncontrolled room.

 

[Purité Audio]

Bob appears to like the absorber well enough from this quote,
http://www.psiaudio.com/en/our-products/avaa-c20/
Is there a link to a copy of the review, June's Stereophile ?

Keith

 

[dallasjustice]

I don't know Michael. It doesn't appear to me that he has a proper grasp of the topic. Take this for example halfway through the book:

"Group delay is typically introduced by loudspeakers and multi-way loudspeaker cross-over networks. So it is important to know the threshold of audibility of group delay with respect to frequency. As far as I can tell, the best thresholds of group delay audibility versus frequency is provided by "Blauert, J.; Laws, P. (May 1978), "Group Delay Distortions in Electroacoustical Systems", Journal of the Acoustical Society of America 63 (5): 1478– 1483."

Barnett, Mitch. Accurate Sound Reproduction Using DSP (Kindle Locations 1421-1424). Kindle Edition. "

Here is the conclusion from that paper:

View attachment 1983

Yet the author goes on to say that the paper says these things are audible and gives the thresholds heard in headphone listening. Headphones eliminate the room. Room reflections substantially change these characteristics. It is clear to me the author has not read the above paper and as such, providing misleading advice.

He simply wants the reader to know how much group delay is audible and he links to a Wikipedia page which references basic science by Blauert on thresholds.
https://en.m.wikipedia.org/wiki/Group_delay_and_phase_delay#Group_delay_in_audio

Amir, Acourate is not just a minimum phase EQ generator. It works in both time and frequency domains using very long FIR filters. So it's important for the user to read and comprehend a group delay measurement as well as step response. Amplitude isn't the only factor. For example, different filter settings will change the group delay and the user should know whether those changes may be audible.

 

[h.g.]

Bob appears to like the absorber well enough from this quote,
http://www.psiaudio.com/en/our-products/avaa-c20/

That is worth what do you think given the likely relationships between Bob Katz, Stereophile and PSI? Is Bob Katz like Steve Hoffmann? If not, and I have no idea how he uses his name, it maybe reasonable to assume it is not a poor product but probably unwise to assume much more such as it being a good product. It is certainly expensive but appears to be based on established principles and so should work if competently implemented. To me it looks like a nice product if someone else pays for (4-8 of) them.

Is there a link to a copy of the review, June's Stereophile ?

I think someone posted a link earlier to a pdf but I didn't look at it at the time and couldn't find it when I wanted to get the context of the posted figure.

 

[Purité Audio]

Yes not suggesting one should automatically believe anything one reads, but I can't recollect a 'pro audio' product from a reputable manufacturer that hasn't met its specs.
PSI for example have their own anechoic chamber, and apparently worked with a University department and government funding to develop the product.
I don't believe it is a 'box of dirt' design.
Keith

 

[amirm]

Here is some data from PSI's web site: http://www.psiaudio.com/en/wp-content/uploads/sites/2/2015/09/PSI-Audio_AVAA-Presentation.pdf

 

[dallasjustice]

Here is some data from PSI's web site: http://www.psiaudio.com/en/wp-content/uploads/sites/2/2015/09/PSI-Audio_AVAA-Presentation.pdf

View attachment 1985

View attachment 1984

It looks like that's 4 AVAAs. I bet Bob measured only one of them. Maybe it takes several of them to make a big difference. That looks impressive but it's $8,000 to get that result. Of course, room treatments could never produce a result like that so its a good thing. I would image they are more effective in rooms where axial length modes need to be reduced.

 

[amirm]

The one thing I worry about is feedback. It has a microphone that controls what comes out of the sub and therefore it has a loop. If they filtered the loop frequency then it won't be effective in that region.

Wish they were not so expensive so that I could buy one to try. The cost has been the reason people don't use them because you can buy a sub for the same price or less.

 

[dallasjustice]

The one thing I worry about is feedback. It has a microphone that controls what comes out of the sub and therefore it has a loop. If they filtered the loop frequency then it won't be effective in that region.

Wish they were not so expensive so that I could buy one to try. The cost has been the reason people don't use them because you can buy a sub for the same price or less.

I could see them maybe being a good solution for someone who doesn't want to use subs, EQ or any DSP. But it would be a real roll of the dice if they didn't work. If I was a dealer, I'd make sure they work well before deploying them or you could have some unhappy customers.

Compared to RPG modex plates, they seem reasonably priced and may work better in a narrow low frequency range.

It's always a good thing to find a low frequency absorption solution which doesn't also eat up too much mid/high decay time from the room.

 

[h.g.]

Of course, room treatments could never produce a result like that so its a good thing.

I suspect serious attention to the wall construction could do a great deal if that counts as room treatment. Another approach I have seen work well is covering large sections of wall with Helmholtz resonators inside diffusers. But I would agree that rolls of fibreglass in the corners is not likely to work well.

I would image they are more effective in rooms where axial length modes need to be reduced.

Not really. They seek to absorb all the incident sound and so will reduce all the modes picked up at their location.

If I was a dealer, I'd make sure they work well before deploying them or you could have some unhappy customers.

The principle on which they operate is fine. They absorb sound but don't emit any and so they are safe in that respect but their effect may not be strong enough to achieve what is desired. Like all active control systems they are limited by how fast they can respond and so there is an upper frequency limit. There is also an upper frequency limit following from avoiding a significant gradient over the active surface since the moving cone will be controlling a single average quantity over its surface.

 

[Ethan Winer]

If I was a dealer, I'd make sure they work well before deploying them or you could have some unhappy customers.

If that were true, every high-end audio dealer that sells $2,000 speaker or power wires on the premise that they improve sound quality would have "some unhappy customers." Yet every high-end dealer sells such bullshit, and they're all still in business. Or if they do go out of business, it's not because of selling placebo-based products.

Just stirring the pot a little.

--Ethan

 

[dallasjustice]

If that were true, every high-end audio dealer that sells $2,000 speaker or power wires on the premise that they improve sound quality would have "some unhappy customers." Yet every high-end dealer sells such bullshit, and they're all still in business. Or if they do go out of business, it's not because of selling placebo-based products.

Just stirring the pot a little.

--Ethan

That's exactly right, except when it comes to room acoustics. Audiophiles are willing to accept anything their dealers tells them is happening inside some magic box. But when it comes to someone telling them what's happening in their room and how to fix it, they immediately become skeptics.

 

[Thomas savage]

If that were true, every high-end audio dealer that sells $2,000 speaker or power wires on the premise that they improve sound quality would have "some unhappy customers." Yet every high-end dealer sells such bullshit, and they're all still in business. Or if they do go out of business, it's not because of selling placebo-based products.

Just stirring the pot a little.

--Ethan

For a guy like you Ethan it's hard to find a spoon big enough

Always yearning for a stirring..

 

[Ethan Winer]

That's exactly right, except when it comes to room acoustics. Audiophiles are willing to accept anything their dealers tells them is happening inside some magic box. But when it comes to someone telling them what's happening in their room and how to fix it, they immediately become skeptics.

If only. You confuse educated, sensible, and knowledgeable audiophiles like yourself with the typical customer for those stores.

 

[Fitzcaraldo215]

If that were true, every high-end audio dealer that sells $2,000 speaker or power wires on the premise that they improve sound quality would have "some unhappy customers." Yet every high-end dealer sells such bullshit, and they're all still in business. Or if they do go out of business, it's not because of selling placebo-based products.

Just stirring the pot a little.

--Ethan

In the Bridge column the other day:

"Just because there are not a lot of complaints doesn't mean that they folded all the parachutes correctly."

 

[FrantzM]

In the Bridge column the other day:

"Just because there are not a lot of complaints doesn't mean that they folded all the parachutes correctly."

I love this quote!!!

 

[Fitzcaraldo215]

I love this quote!!!

Thanks, it was from Frank Stewart's nationally syndicated bridge column, daily reading for me.