Totem Acoustics Rainmaker Speaker Review

[Duke]

I read a famous multi-sub proponent (the one who built large waveguide two-ways) say multi-subs OR decorrelation filters.

I'm under the impression that he never actually came out with the decorrelation filters he was working on at one time. That would have been very interesting. Did I miss something?

 

[Floyd Toole]

I read a famous multi-sub proponent (the one who built large waveguide two-ways) say multi-subs OR decorrelation filters. I'm not sure what decorrelation filters are but I think it might be reverb applied to the low frequency band. If that's accurate - maybe I totally misunderstood him - and digital processing power is increasing are we going to see a day where we can add decorrelation filters to our mains and get closer to multi-sub approaches?

I'd still want multi-subs for the output but if you only have two mains it would be nice if a signal processor could tame room resonances.

Decorrelation is disorder - i.e. each source of low frequencies is in a random time sequence with others. It almost certainly will reduce coherent coupling to room modes which is good, but it will change the time domain structure of the bass. The purpose of multiple subs is to coherently couple energy to modes but in a fashion that attenuates specific sets of room resonances. With these attenuated, the recorded bass is heard without the detrimental effects of standing waves. Using subs means that the main speakers can play louder with lower distortion. For a single listener or a small number, near-field subwoofing is an alternative or an addition.

 

[Heinrich]

Decorrelation is disorder ...

Was it Dr Griesinger who attempted to use bass as a subjective indicator for big rooms? Phase, hence a manipulated (made up) reflection pattern would suggest spacial qualities?

 

[Floyd Toole]

Was it Dr Griesinger who attempted to use bass as a subjective indicator for big rooms? Phase, hence a manipulated (made up) reflection pattern would suggest spacial qualities?

David was most interested in concert halls, and in such large spaces even long bass wavelengths have space to propagate and be reflected from large surfaces. The delays generally responsible for impressions of envelopment are of the order of 80 ms and more. Small rooms are in a different category entirely. In the 3rd edition of my book, the topic of "stereo bass" is discussed, as this is the closest one can get to replicating something that might resemble events in a concert hall. David was among others who promoted the idea that stereo bass was a requirement, and at Harman (where he worked, as I did) a demonstration was set up to test the notion. I titled the section in my book "Stereo Bass: Little Ado about Even Less" with apologies to Shakespeare. That about sums it up, because substantial effort, including generating special signals to reveal differences showed that any audible spatial differences attributable to stereo bass occurs at frequencies above about 80 Hz. Others have found similar results - so bass managed subwoofers sacrifice nothing spatial, but multiple subs are huge advantages to the timbral quality of bass when room modes are tamed. Todd Welti wrote a paper summarizing the topic: Welti, T. (2004), “Subjective comparison of single channel versus two channel subwoofer reproduction”, 117thConvention, Audio Eng. Soc., Preprint 6322.

 

[JPA]

David was most interested in concert halls, and in such large spaces even long bass wavelengths have space to propagate and be reflected from large surfaces. The delays generally responsible for impressions of envelopment are of the order of 80 ms and more. Small rooms are in a different category entirely. In the 3rd edition of my book, the topic of "stereo bass" is discussed, as this is the closest one can get to replicating something that might resemble events in a concert hall. David was among others who promoted the idea that stereo bass was a requirement, and at Harman (where he worked, as I did) a demonstration was set up to test the notion. I titled the section in my book "Stereo Bass: Little Ado about Even Less" with apologies to Shakespeare. That about sums it up, because substantial effort, including generating special signals to reveal differences showed that any audible spatial differences attributable to stereo bass occurs at frequencies above about 80 Hz. Others have found similar results - so bass managed subwoofers sacrifice nothing spatial, but multiple subs are huge advantages to the timbral quality of bass when room modes are tamed. Todd Welti wrote a paper summarizing the topic: Welti, T. (2004), “Subjective comparison of single channel versus two channel subwoofer reproduction”, 117thConvention, Audio Eng. Soc., Preprint 6322.

Do you have an opinion on Double Bass Arrays, where multiple subwoofers on one wall of a room generate a bass signal, and other multiple subwoofers on the opposite wall absorb the signal? It appears to work well in theory and simulations, but I wonder if home theater seating (especially 2nd row seating on a riser) in the real world would disrupt the smooth flow of sound waves enough to reduce its effectiveness.

 

[Floyd Toole]

Do you have an opinion on Double Bass Arrays, where multiple subwoofers on one wall of a room generate a bass signal, and other multiple subwoofers on the opposite wall absorb the signal? It appears to work well in theory and simulations, but I wonder if home theater seating (especially 2nd row seating on a riser) in the real world would disrupt the smooth flow of sound waves enough to reduce its effectiveness.

These systems work, ideally best in perfectly rectangular, acoustically symmetrical, rooms. In the real world there will be deficiencies (risers would be a disruptor), but the principle is logical. It is discussed in Chapter 14 of the upcoming 4th edition of my book, co-authored with Todd Welti. The scheme is only practical for custom installations and requires at least four loudspeakers strategically located in/on each of the front and back walls. Since energy is created and then absorbed, the efficiency is not high, but in such installations cost is not likely to be a consideration. There are more cost effective, less disruptive, solutions that work in ordinary rooms, and that increase overall efficiency - more subwoofers are needed but they can be smaller. Having experienced such systems over many years in different rooms it is difficult to find fault with any of them - the bass is just as one wants, clean, deep and tight, and shared among multiple listeners. Massive single subs are illogical knowing what we now do.

 

[tktran303]

Dear Floyd,

What do you mean by absorbing? Are the woofers on the opposite side of the room out of phase with the ones on the front?

Have you used software, like Treble Technologies, to simulate/model the room, and it's floor, walls, furnishings etc, with the speaker(s) and the listener(s)?

BR,
Thanh

 

[Floyd Toole]

Dear Floyd,

What do you mean by absorbing? Are the woofers on the opposite side of the room out of phase with the ones on the front?

Have you used software, like Treble Technologies, to simulate/model the room, and it's floor, walls, furnishings etc, with the speaker(s) and the listener(s)?

BR,
Thanh

Yes, the idea is that the energy arriving at the wall is not allowed to reflect - it must be cancelled/absorbed to prevent standing waves from developing.

As I understand that model, it is another of the idealized/simplified simulations of direct and reflected sounds arriving at the listening position or area from loudspeakers. The belief is that the sum of all sound components is the key metric to sound quality. Proof of their success is how closely the calculated and measured steady-state sound fields compare. The assumption is that this metric is a reliable indicator of perceived sound quality. It isn't. Two ears and a brain interpret a complex sound field very differently from an omnidirectional microphone. Binaural hearing separates the direct sound from later arrivals allowing for directional perception - localization - and for key indications of sound quality. In addition there are various spatial effects including image size and the very important sensations of envelopment. All these perceptual dimensions combine in complex ways. Only at frequencies below the transition/Schroeder frequency is a steady-state room curve reliably indicative of sound quality. I have discussed this more than once in this forum, and it is all well explained in my books, especially in the upcoming 4th edition. Todd Welti has used room simulation models in developing his multi-subwoofer solutions, which he describes in detail in AES papers and in the 4th edition of my book where we share a chapter.

 

[tktran303]

Yes, the idea is that the energy arriving at the wall is not allowed to reflect - it must be cancelled/absorbed to prevent standing waves from developing.

This was done at least 20 years ago, IIRC.

It results in bass response that is similar to a dipole woofers at the MLP,

I'll speak to someone and see if I can some data to share...

 

[Floyd Toole]

This was done at least 20 years ago, IIRC.

It results in bass response that is similar to a dipole woofers at the MLP,

I'll speak to someone and see if I can some data to share...

"similar to a dipole woofers at the MLP" - not possible. Dipole sources radiate opposite polarity on each side simultaneously - they are "velocity" sources, so they couple energy into the room standing waves best at the null locations, where they are sensitive to orientation. Used intelligently, this can be used to attenuate specific room modes by varying the energy coupled into them. This is, of course, fundamentally different from conventional "pressure" sources. These too can be positioned to vary coupling into modes, but at the high pressure regions of standing waves.

The subwoofer scheme being discussed here radiates sound from one wall, and an inverted version of that sound is radiated at the opposite wall delayed by the propagation time across the room. The theory is that the sound travels only one direction across the room and then disappears. It has no resemblance to the behaviour of a dipole source.

 

[olieb]

I found this discussion coming from a thread on diyaudio.
But these answers got me a bit confused.

These systems work, ideally best in perfectly rectangular, acoustically symmetrical, rooms. In the real world there will be deficiencies (risers would be a disruptor), but the principle is logical.

As I understand that model, it is another of the idealized/simplified simulations of direct and reflected sounds arriving at the listening position or area from loudspeakers. The belief is that the sum of all sound components is the key metric to sound quality. Proof of their success is how closely the calculated and measured steady-state sound fields compare. The assumption is that this metric is a reliable indicator of perceived sound quality. It isn't.
....
Only at frequencies below the transition/Schroeder frequency is a steady-state room curve reliably indicative of sound quality.

Now, does these special kind of source-sink models (DBA-subwoofers) work as intended or are they simplified simulations that do not?
Are they chasing a wrong metric or is the metric not so wrong for subwoofers below Schroeder frequency?
I understand the limitations in terms of room layout, but why would the characteristics of directional hearing play a role here for the performance of sound reproduction in the subwoofer range? If I understand correctly, you just explained that spatial hearing below 80Hz is so limited that bass management does not sacrifice anything in that regard.

 

[Juhazi]

Large speakers with good low extension will help to smooth out bass response, compared to a single sub.
Stereo low bass in music recordings is irrelevant despite it is in the recording, harmonics will make the localization.

My setup is in no way optimized for the room, speaker location is dictated by general interior design ot the living room. Speakers are symmetrically along the long wall. Here you can also see the effect of mic moved 80cm front-back. There is no way to correct that by dsp or multisub. I have tested/measured 1, 2 and 3 diststributed subs in my small HT room and definitely 3 was best in every way without any dsp. Sadly that was just a test and helper "subs" didn't go below 40Hz

 

[Floyd Toole]

I found this discussion coming from a thread on diyaudio.
But these answers got me a bit confused.



Now, does these special kind of source-sink models (DBA-subwoofers) work as intended or are they simplified simulations that do not?
Are they chasing a wrong metric or is the metric not so wrong for subwoofers below Schroeder frequency?
I understand the limitations in terms of room layout, but why would the characteristics of directional hearing play a role here for the performance of sound reproduction in the subwoofer range? If I understand correctly, you just explained that spatial hearing below 80Hz is so limited that bass management does not sacrifice anything in that regard.

Below 80 Hz two phenomena combine to dominate our perceptions, it seems. One is that our binaural systems fail badly at localizing sound at such low frequencies/long wavelengths (our ears are too close together). We do not hear a distinct "direct" sound, so "time alignment" of individual subwoofers is not required. Instead, in small listening rooms resonances/standing waves absolutely dominate bass sound quality, strongly accentuating and attenuating specific bass frequencies and resulting in no two listeners hearing the same sound. The traditional solution has been to use large areas of low-frequency absorbers (bass traps). I may have been the first to publish results of deliberate mode manipulation using multiple subwoofers (AES 1990). Since then Todd Welti and numerous others have offered variations on active and passive schemes using multiple subwoofers to manipulate the energy in specific room modes to optimize performance at specific locations or over specific areas. The source/sink method being discussed is one of them. They all are beneficial, and none of them rely on bass traps, although low-frequency absorption is always an asset if it can be aesthetically achieved. Steady-state measurements are adequate to describe performance at very low frequencies, and because strong room resonances behave as minimum-phase phenomena, the time domain (ringing) is also corrected when peaks in the frequency response are attenuated. There is a generous amount of misunderstanding about this in the audio industry. It has been discussed in earlier editions of my book, and in the literature. Todd Welti and I share a chapter in the 4th edition discussing the subject. Bass in small rooms can be managed, and it must because low frequency performance accounts for about 30% of our overall assessment of sound quality. We all listen in small rooms. This problem is sufficient to invalidate, or at least cast doubt on most casual subjective evaluations.

 

[olieb]

Thank you for the reply.
So this is what I take away:
Below ≈80Hz

• we „hear“ only the spl presented at the ear(s) [no spatial cues]
• room modes can be described by steady-state terms and measurements
• they are minimum phase phenomena and can be EQed correcting the time domain in the process
• multiple-subwoofer schemes work and that includes DBA

But would you agree/disagree that this bass array idea is different from most other „mode manipulation“ concepts as it tries to „erase“ the effect of low frequency modes altogether?
If it works (and that is a big IF of course) the sound would not propagate by means of low frequency modes but would transform the rectangular room into a duct with more or less fully absorptive termination.
One difference would be that the sound field is position independent to a high degree and mode decay would be nearly absent.

 

[Floyd Toole]

Thank you for the reply.
So this is what I take away:
Below ≈80Hz

• we „hear“ only the spl presented at the ear(s) [no spatial cues]
• room modes can be described by steady-state terms and measurements
• they are minimum phase phenomena and can be EQed correcting the time domain in the process
• multiple-subwoofer schemes work and that includes DBA

But would you agree/disagree that this bass array idea is different from most other „mode manipulation“ concepts as it tries to „erase“ the effect of low frequency modes altogether?
If it works (and that is a big IF of course) the sound would not propagate by means of low frequency modes but would transform the rectangular room into a duct with more or less fully absorptive termination.
One difference would be that the sound field is position independent to a high degree and mode decay would be nearly absent.

The propagating "wave front" attempts to eliminate length modes only, but the initiating subwoofers do not launch a plane wave. The width and height modes are separate issues, and in their installations they are attenuated, not eliminated, by locating the subwoofers at locations 25% in from the floor, ceiling and side walls. Oblique modes might sneak in, but if all others are attenuated, they are likely to be negligible. Todd Welti's Sound Field Management calculation would recognize it as a desirable option. Having lived with and experienced several versions of SFM, they all can provide superb bass entertainment for multiple listeners. There are multiple desirable physical configurations if signal processing of individual subs is involved.

 

[celroid]

The propagating "wave front" attempts to eliminate length modes only, but the initiating subwoofers do not launch a plane wave. The width and height modes are separate issues, and in their installations they are attenuated, not eliminated, by locating the subwoofers at locations 25% in from the floor, ceiling and side walls. Oblique modes might sneak in, but if all others are attenuated, they are likely to be negligible. Todd Welti's Sound Field Management calculation would recognize it as a desirable option. Having lived with and experienced several versions of SFM, they all can provide superb bass entertainment for multiple listeners. There are multiple desirable physical configurations if signal processing of individual subs is involved.

Is there software that does Sound Field Management for multiple subwoofers more available now or still just JBL? i have an SVS sub and I planned to add more and hoped for SFM to be available.

Edit: There's a software called MSO and if I understood correctly it can import measurements done with REW (I will need to measure the transfer function as written in your book). Sounds ideal. I'm wondering if I'll be able to manually adjust each subwoofer through Bluetooth config that the svs pro provides, so no individual DSP device will be even necessary.

 

[DanielT]

Also add the interior design challenge of having multiple subwoofers in a combined living room, listening room.

Subwoofer cubes are not particularly beautiful. Which can be exemplified by the thread linked below. Currently; 227 pages with 4537 posts:

Most beautiful speakers in the world ?

audiosciencereview.com

But there is no thread on ASR called: Most beautiful sbwoofer in the world?

 

[celroid]

Also add the interior design challenge of having multiple subwoofers in a combined living room, listening room.

Subwoofer cubes are not particularly beautiful. Which can be exemplified by the thread linked below. Currently; 227 pages with 4537 posts:

Most beautiful speakers in the world ?

audiosciencereview.com

But there is no thread on ASR called: Most beautiful sbwoofer in the world?

One possibility is to put them behind fabric, like the fabric covered doors Toole has shown here:

The Ultimate "Real World" Home Theater and Listening Room

By Dr. Floyd Toole, introduction by John Schuermann So, if you are literally one of the world's foremost authorities on loudspeakers, rooms, and acoustics - and have literally written the industry accepted book on the subject -- what components and speakers do you chose for your own personal...

www.thescreeningroomav.com

 

[DanielT]

One possibility is to put them behind fabric, like the fabric covered doors Toole has shown here:

The Ultimate "Real World" Home Theater and Listening Room

By Dr. Floyd Toole, introduction by John Schuermann So, if you are literally one of the world's foremost authorities on loudspeakers, rooms, and acoustics - and have literally written the industry accepted book on the subject -- what components and speakers do you chose for your own personal...

www.thescreeningroomav.com

Absolutely. I fully understand hiding HiFi as much as possible. It should be added that for those who can and have the opportunity to DIY a subwoofer, it also increases the possibility of tailor-made solutions. Hidden or integrated subwoofer solutions, that is.

Which brings me to this. Not hidden but made to blend in. In general, I think that, for example, Sonos' ability to adapt to modern furnishing ideals is a big explanation for their success. My belief is that Sonos' fingertip feel and adaptability is a big reason why many people have replaced their "old" outdated in appearance HiFi. People want something that blends in nicely. In addition, it is possible to get fairly good sound these days with these tailor-made lifestyle interior-adapted HiFi solutions, so I fully understand that they are popular. Speakers that are examples of that for example:

Ikea SYMFONISK Picture Frame Speaker Review

This is a review and detailed measurements of the Ikea SYMFONISK picture frame speaker designed by Sonos. I purchased it a couple of days ago from Ikea store for US $199. Their website said they had 42 in stock so they are planning to sell a lot of them. That said, there was not a single...

audiosciencereview.com

Low SPL but measures ok (in relation to price):

Google Nest Audio Speaker Review

This is a review, teardown, detailed measurements, listening tests and EQ of Google Audio Nest "smart" streaming speaker. It was kindly drop shipped to me by a member. List price is US $99.99 but I see it as low as US $65. While not very unique in its looks, the Nest Audio nicely fits in the...

audiosciencereview.com

Edit:
Then we have the exception, vintage lovers, but then we are talking more about enthusiasts with understanding wives who accept that, for example, over half a century old tube amplifiers are placed in the living room. Not so common, but there are probably a few enthusiasts left who renovate and fix one, for example:

And have it in use..

Classic Marantz and Citation vs modern

How do classic Marantz and Citation compare to modern equipment for roughly the same price? Asking in other fora as well

audiosciencereview.com

 

[Flaesh]

the interior design challenge of having multiple subwoofers in a combined living room

Buchardt Audio SUB10

Like it has been abused in start-ups, kickstarter and the video game industry for years. The ICO boom was the absolute apotheosis of this concept - pay in advance for…nothing at all, other than the hope that a greater fool will pay more.

www.audiosciencereview.com