Best Acoustic Products for First Reflection Points

[caliaripaolo]

+1

Except that I use helmholtz resonators for the bass but that is another discussion.

Yes, this is the right solution!!!

 

[Argonaut]

Ron......You might find this series of YouTubes rather illuminating, you might even recognise the Transducers, similar principle topology to your Griffins

#5 and 6 deal with built in wall Helmholtz Resonator's

[video]https://m.youtube.com/watch?v=rsroD57FZnA[/video]

Should you feel like a trip out to Boulder Colorado I believe that one may arrange to demo this system/room by appointment.

 

[flyer]

Ron......You might find this series of YouTubes rather illuminating, you might even recognise the Transducers, similar principle topology to your Griffins

#5 and 6 deal with built in wall Helmholtz Resonator's

[video]https://m.youtube.com/watch?v=rsroD57FZnA[/video]

Should you feel like a trip out to Boulder Colorado I believe that one may arrange to demo this system/room by appointment.

Very interesting video, hadn't seen that before! When looking (rather rapidly skipping) at the various episodes, I was already wondering how they would make the - otherwise wonderful - space for the helmholtz function properly.
I found the answer in the last video (7), where basically Paul explains that he is disappointed by the effect despite all the effort.

Seeing how they implemented these resonators, they have actually not built resonators nor real bass traps, it is a hybrid that serves not one nor the other's purpose, hence the mere 2 dB drop he talks about. The good news is that it would be very easy to remedy that but that is another subject again.

The fact he then explains that he gets a good bass response only at his listening space is another testament of the fact that room still has a severe standing wave issue. In my room, with all my resonators (and a big one on the back wall containing 3 m³ empty space), I can go where I want and not experience the nodes as they used to be. Of course, it is still not perfect but I like to think 80% is covered through a good implementation of the HH resonator principle.

Conclusion: as with everything else, the poison is in the detail (of the implementation). As Calliaropolo said, take it step by step carefully considering what you do. Of course you can go for a full pre-engineered solution, but make sure the guy(s) knows what he is doing. If someone thinks he can and therefore should fill up a big empty space with absorbing foam, then he can ruin a good design.

 

[Argonaut]

Quite flyer....It just goes to show that no matter how much diligence one puts into crunching theory, that in the end, an efficacious in room audio response is nor always a given.

 

[Bjorn]

What is your recommendation for acoustic treatment products to absorb or diffuse the sound from the loudspeakers hitting the first reflection points?

ASC, for example, makes sound-absorbing rectangles, around 1" to 3" thick, that can be mounted on the wall or just leaned against a wall at the points of the first reflection.

RPG has a bewildering array of products. What is the best RPG product for absorption and for diffusion at the first reflection points? Abfusor? BAD Panel? Absorbor? Broadsorbor? Diffractal? Diviewsor? Modfractal? Modfusor? Omniffusor? Skyline?

What about the Vicoustic Multifusor Wood 64 diffusor? How does this product compare to the RPG Skyline?

Do any products combine characteristics of absorption with characteristics of diffusion?

What acoustic product do you use at the first reflection points in your listening room?

The better treatment depends on areas like distance (time of flight) and that acoustic principle one is following. However, there are some areas which are important to consider when treating early arriving reflections which I've pointed out to some degree here:
http://www.lydogakustikk.no/?p=2281

I will also recommend to read the link below that describes the difference between scattering and diffusion. Many so called diffusers in the market are simple scattering units and doesn't offer proper diffusion.
http://www.lydogakustikk.no/?p=2137

 

[Mark Seaton]

Thank you very much, Mark! This is all terrific advice!

For low frequency absorption I will first try in the corners the ASC Tube Traps I already have. I will not be installing a whole acoustic treatment built-in from the get go. I will start with a couple of things I know I want to do, and then I will get a couple of pairs of RPG Modfractals and a couple of pairs of SMT V-wings and play around with different combinations in different locations.

Maybe I will try a pair of SMTs at the first reflection points and maybe flank each pair of SMTs with a Modfractal. Each of these can be made 8' high and 2' wide. Together these would cover about 8' of horizontal space of each side wall.

The ribbon panels go inside of the bass towers. Each base tower will only be about 2 feet or maybe a little more from the side wall. This puts the ribbon drivers about 4' from the sidewalls. Like Mike's MM7s, the bass tower blocks some of the side reflection from each ribbon panel.

I also have 8' X 4' absorption panels. It will be interesting to hear the difference between the absorption panels and the diffusors at the first reflection points.

Hi Ron,

One key difference with your speakers vs Mike's are that the ribbon and AMT columns are both dipoles. Dipoles have a cancellation/reduction in output in the plane of the speaker's face with the sound radiating in a pattern that would look like a figure 8 if observed overhead. Here is an over simplification of the situation:

Here you can find some great info regarding dipole speaker operation and listening rooms from one of the experts on the matter, Siegfried Linkwitz. It is admittedly heavy on the math and a very technical approach to the issues at hand. Here is another great graphic I found from Linkwitz showing how reality deviates from theory with different types of dipole implementations:

For a better understanding of dipoles scan through this page from Linkwitz as well where I pulled this image which clarifies many of the differences between conventional, front firing speakers vs dipoles when set up in the room:
[IMG]http://www.linkwitzlab.com/images/graphics/reflections-3s.png[/IMG]

The point here is that the speaker's dipole operation above ~250Hz means there isn't much of an early lateral reflection for the woofer towers to block. Also important is that for the listening distance I suspect you will be at, the first side wall reflection will be well forward of the area shadowed by the woofer tower.

Could you give us a general recap of the size and openings to the space you are setting up in?

 

[Ron Resnick]

I will not state here that one is better than the other by themselves, i do think that each panel has to be used in the best setting.

For the QRD-panels this is in rooms that are wide and deep enough to avoid the lobing effect (hence the relatively large distance you have to be from the panel for the lobing to become sufficiently attenuated). Also, the QRD's are determined in bandwith by their pattern and maximum depth. Some panels are quite shallow and hence will have limited bandwidth effect, others are quite deep, so you will have a lot wider effect (compared to the shallow ones) but loose a lot of space at the same time.

For the SMT wings this distance requirement is not applicable as you can literally sit or position them as close as 40-50 cms from your ears or speakers. Now, the effect of the wings, by the way they are built, is further improved by positioning them one next to the other as they connect in the time delay propagation. Positioning one single of them at first reflection points is already very good, but more is better. Is it worth to put multiple of them? I would just recommend to order a few of them and see (hear) if you like them, if so, putting more will only make your joy greater.

Having had QRD panels in my small room and having done a direct comparison, I clearly favour the SMT wings, reason also why I became a kind of audition point for them. So that is my disclaimer.

Your room is considerably larger than mine, I understand if you hesitate and get drawn in different directions... I am afraid, to make this particular choice, no measurement will help you, reason why I didn't mention it.

This was very understandable, flyer, thank you.

 

[Ron Resnick]

Hi Ron,

One key difference with your speakers vs Mike's are that the ribbon and AMT columns are both dipoles. Dipoles have a cancellation/reduction in output in the plane of the speaker's face with the sound radiating in a pattern that would look like a figure 8 if observed overhead. Here is an over simplification of the situation:

Here you can find some great info regarding dipole speaker operation and listening rooms from one of the experts on the matter, Siegfried Linkwitz. It is admittedly heavy on the math and a very technical approach to the issues at hand. Here is another great graphic I found from Linkwitz showing how reality deviates from theory with different types of dipole implementations:

For a better understanding of dipoles scan through this page from Linkwitz as well where I pulled this image which clarifies many of the differences between conventional, front firing speakers vs dipoles when set up in the room:
[IMG]http://www.linkwitzlab.com/images/graphics/reflections-3s.png[/IMG]

The point here is that the speaker's dipole operation above ~250Hz means there isn't much of an early lateral reflection for the woofer towers to block. Also important is that for the listening distance I suspect you will be at, the first side wall reflection will be well forward of the area shadowed by the woofer tower.

Could you give us a general recap of the size and openings to the space you are setting up in?

Dear Mark,

Thank you for these links.

When you write "the speaker's dipole operation above ~250Hz means there isn't much of an early lateral reflection for the woofer towers to block" are you implying that I do not have to worry much about first reflections and I should not put any acoustic panel at the first reflection points? Are you implying that diffusion at the first reflection points is likely to be better for me than absorption at the first reflection points?

Since you are kind enough to discuss these issues as they relate to my particular room, may I ask that we pick this up on my system thread here: http://www.whatsbestforum.com/showt...d-Room-Treatment-Upgrades&p=476857#post476857

 

[Mark Seaton]

Dear Mark,

Thank you for these links.

When you write "the speaker's dipole operation above ~250Hz means there isn't much of an early lateral reflection for the woofer towers to block" are you implying that I do not have to worry much about first reflections and I should not put any acoustic panel at the first reflection points? Are you implying that diffusion at the first reflection points is likely to be better for me than absorption at the first reflection points?

Since you are kind enough to discuss these issues as they relate to my particular room, may I ask that we pick this up on my system thread here: http://www.whatsbestforum.com/showt...d-Room-Treatment-Upgrades&p=476857#post476857

I found that thread soon after making the previous post here. We can certainly continue there. Related to the thread topic here, the answer to your question is entirely dependent on your room/speaker/listener positioning and geometry, along with the exact aiming of the mid/high frequency columns. Based on your description, I expect the 90 deg off axis null from the main columns to mostly point at the bass column location. We can't know if the bass tower will shadow the first reflection point without knowing approximate speaker locations, room width, and listening distance. What's equal or more important to understand is that with the dipole ribbon/AMT columns, while much wider in dispersion than your Monoliths, will still have a significant reduction in energy 90 deg to the speaker's aim. In many rooms this means you can adjust how much energy arrives at the first reflection area.

 

[caesar]

...
caliaripaolo, In my particular set-up I place no treatment behind the speakers. I want a clean, unadulterated rear wave bouncing off the front wall. This is one reason I am inclined to use absorption at the first reflection points rather than diffusion -- I want an unadulterated reflected back wave so I want to make sure no first reflection mixes with that back wave...
...

Hi Ron,

Hate to harp on the same point over and over, but experts are not very good at predicting what will sound good to you and get that "we are there" experience you are looking for... On the other hand, experts are very good at explaining things after the fact...

So just because you read something from Yates, doesn't mean it will work for you... YOU will have to try!

And why stop at a potentially incomplete point?

Heck, go for 4 (or more) SMT wings (or rpg equivalents ) on both the front wall and back wall. As you start placing these things, you may just find out that you are re-creating more and more of the original acoustic space in your room. And if didn't work out, at least you tried!

I don't know about rpg, but if smt doesn't work out you can sell it on the used market. It'll be snapped up by some lucky guy who will celebrate Hanukkah in the spring or summer, whenever your construction is done.

Good Luck!

 

[microstrip]

Very interesting video, hadn't seen that before! When looking (rather rapidly skipping) at the various episodes, I was already wondering how they would make the - otherwise wonderful - space for the helmholtz function properly.

I found the answer in the last video (7), where basically Paul explains that he is disappointed by the effect despite all the effort. (...)

Triggered by your comment I watched the video - but I really found it a loss of time. . It can be summarized at minute 7'30" - "But our experiment did not work, it was a lot of fun.". I have to say that probably my definition of fun is different from Paul's one and I find that such experiences and comments only create disbelief in our hobby. I did not watch the whole series, but flashed through them. Paul designs great electronics, he should have remembered an old saying "Let the shoemaker meddle with his slipper, the smith with his anvil, and the priests with their prayers."

IMHO his electronics and such great Genesis speakers deserved better.

 

[Mark Seaton]

Triggered by your comment I watched the video - but I really found it a loss of time. . It can be summarized at minute 7'30" - "But our experiment did not work, it was a lot of fun.". I have to say that probably my definition of fun is different from Paul's one and I find that such experiences and comments only create disbelief in our hobby. I did not watch the whole series, but flashed through them. Paul designs great electronics, he should have remembered an old saying "Let the shoemaker meddle with his slipper, the smith with his anvil, and the priests with their prayers."

IMHO his electronics and such great Genesis speakers deserved better.

It does show just how much empirical work and/or experience is needed to make devices like Helmholtz resonators work as desired. That said, the measured intensity reduction of "only 2dB" likely made a significant difference in the time domain of the room, and I wonder if covering over the traps might be more audible in the room than the magnitude measurements suggest. Based on devices I've observed successfully and unsuccessfully working, I believe they had way to small an opening area giving a very short "port" length, and had way too much stuffing blown into the bass trap cavity. The balance can often be a matter of sucking up enough energy while damping it sufficiently that it won't regurgitate bass energy back into the room when the devices get very large. Ultimately the best way to deploy such resonant traps is to have scaled or otherwise similar devices you can measure as a base line to adjust and scale from with some flexibility designed into the traps for final tuning in room.