The perfect speaker is room dependent - wide vs. narrow directivity and more

[Kvalsvoll]

Only way I know would be subs fully in the corners....?

Exactly, and there is no need for several options to solve this. Subwoofers/bass-units placed close to at least 2 boundaries, and the result is as good as it gets, and that is a lot better than a speaker placed into the room.

But it isn't perfect? Because the other surfaces will reflect bass and create resonances and nulls. Yes, and this problem can not really be eliminated completely, at least not within practical limits. The good thing is, it does not have to be perfect, it just needs to be good enough so you can equalize and get nice, addictive bass with no annoying resonances and nice, powerful tactile feel.

Bass in small rooms is a solved problem.

 

[thewas]

As to how low the speaker should maintain a "constant directivity" characteristic, the impression I get from Griesinger and Geddes is that above 700 Hz is where constant directivity matters the most from a psychoacoustics standpoint. Imo constant directivity down to the Shroeder frequency (150-300 Hz ballpark) would be excellent, and even lower would be even better.

For best performance, it is necessary to control directivity across the whole frequency range, including low bass. The most difficult part to get right is the important 100-500hz range.

I agree and it is possibly one of the regions I enjoy the sound of wide baffle designs.

 

[MattHooper]

I know this is a very old post I'm responding to but...

Also, in general I have tended to prefer wide-pattern speakers in highly damped rooms, and narrow-pattern speakers in relatively reverberant rooms.

After lots of experimenting in my room, I seem to have gravitated to a similar preference.

Though admittedly I haven't used a super narrow dispersion speaker in my room. But since I've had plenty of very wide (omnis) to relatively wide (coax designs and others) I do tend to decrease some of the reflectivity in my room.

With the following caveat:

I agree that wide dispersion speakers throw a bigger soundstage, but imo there are trade-offs involved. The same psychoacoustic mechanism which perceives a wider soundstage when significant early sidewall reflections are present also degrades image precision. And in my experience clarity and soundstage depth can also be degraded by early reflections. Toole's findings indicate that the benefits of wide-pattern speakers outweigh the downsides for most listeners.

Here are some arguments against early reflections, which may have implications for the wide-pattern vs narrow-pattern speaker debate. These statements may also be thought of as arguments for treatment of the early reflection zones:

"The earlier and the greater in level the first room reflections are, the worse they are. This aspect of sound perception is controversial. Some believe that all reflections are good because they increase the listener's feeling of space – they increase the spaciousness of the sound. While it is certainly true that all reflections add to spaciousness, the very early ones (< 10 ms.) do so at the sake of imaging and coloration... The first reflections in small rooms must be thought of as a serious problem that causes coloration and image blurring. These reflections must be considered in the [louspeaker] design and should be also be considered in the room as well." - Earl Geddes

I've done a mind-numbing amount of playing around with reflectivity in my room (as I've mentioned I have thick curtains I can place in any position along any wall, and some diffusion too). Of course it's mostly playing with high frequency reflection attenuation or enhancement, but that's good enough to get the results I like. I can go from a super damped sounding room to quite reflective.

What I have found: If I really dampen down side wall reflections (and I can do that for backwall as well), to no surprise the original recorded reverbs or acoustics tend to be more prominent. The "looking in between the speakers in to a recorded space."

But in terms of "losing image specificity" by introducing more sidewall reflections, I actually find there can be some benefit to image specificity. So, with really damped sidewalls, if I'm listening to an acoustic guitar and drum set playing (and other instruments) I can be very aware of the exact little acoustic pool of reverb they are sitting in. But in a way there is so much sonic information, like I am 'seeing' the reverb space around every instrument it almost seems to get a bit jumbled together. Very hard to put it to words, but it's almost like seeing through all the instruments to the instrument behind and it's reverb. The sound is more detailed about all that info, but a bit less solid and dense.

When I start introducing some more sidewall reflection, it's like the sonic images become both more present and dense and a bit more separated and focused. The imaging actually seems more clean and delineated. So it actually "helps" imaging in that respect.

BUT...if I keep going and introduce more reflections it starts down the path of now becoming more diffuse. The leading edge of each "image" - e.g. a trumpet bleating, a guitar strumming, is a bit more vivid and is still fairly focused, but it's like the "body" of the sound starts to dissolve in to this elevated "lightened" hashy acoustic space, like washing out the background. And so it feels less contrasty and precise in terms of imaging.

Again...it's not always easy to put in to words the subjective results of these things. But that's what I hear.

 

[Bjorn]

If you compare a speaker with constant directivity (cd) to 700-800 Hz area vs one with cd and similar beamwidth down to the Schroeder frequency in several small rooms, you'll see that the latter will generally have a much more even frequency response below 700 Hz. In some rooms the speaker with cd to 700-800 Hz will have a frequency response of a roller coaster below the point where it looses directivity.

Obviously large frequency deviations matter to the tonality, and time domain behaviour will also be very different.

Specular energy after 10 ms is important. How much depends on the angle it's arriving from and how the level is relative to the rest. If the level is high compared to earlier energy and it comes from a certain angle, even reflections arriving as late as 35-40 ms can very audible with certain frequencies. IMO it doesn't make much sense to say that up to 10 ms is good enough and that's contrary to all studies that went into development of certain studio designs. While it's true that the first 10 ms generally matters more then what comes later, one could say the same for reflections arriving within 5-6 ms. And as mentioned; the audibility highly depends how the level compares, the angle it's arriving from, and music material also place an important role in the audibility.

RTx graphs or reverberation time are not valid for small rooms. There's no diffuse sound field in small rooms; meaning that the sound intensity in the same no matter the position in the room, and secondly; that the sound intensity is the same in every direction. A small room will never meet these criteria’s. The small acoustical space is dominated by focused specular reflections.

 

[Duke]

If you compare a speaker with constant directivity (cd) to 700-800 Hz area vs one with cd and similar beamwidth down to the Schroeder frequency in several small rooms, you'll see that the latter will generally have a much more even frequency response below 700 Hz. In some rooms the speaker with cd to 700-800 Hz will have a frequency response of a roller coaster below the point where it looses directivity.

I agree with you. The most recent audio show I attended, I was not in charge of our room and was able to leave for a while every now and then and listen to other rooms. The three rooms with the best sound in that 100-800 Hz ballpark ALL used loudspeakers which have good pattern control in that region. One was a big horn system (Klipsch Jubilee) and the other two were dipoles. The big Klipsch really sounded fantastic in that region, combining pitch definition with impact, and was easily among the best I've ever heard in that region (imo it did have other issues).

Specular energy after 10 ms is important. How much depends on the angle it's arriving from and how the level is relative to the rest. If the level is high compared to earlier energy and it comes from a certain angle, even reflections arriving as late as 35-40 ms can very audible with certain frequencies. IMO it doesn't make much sense to say that up to 10 ms is good enough and that's contrary to all studies that went into development of certain studio designs. While it's true that the first 10 ms generally matters more then what comes later, one could say the same for reflections arriving within 5-6 ms. And as mentioned; the audibility highly depends how the level compares, the angle it's arriving from, and music material also place an important role in the audibility.

My understanding is that the 10 milliseconds figure comes from this line of thinking: The ear gets most of the information it needs for intelligibility from the 700-7000 Hz region (according to Griesinger), and the gammatone filtering characteristic of the ear calls for an essentially reflection-free interval of 10 milliseconds for good clarity down to 700 Hz. I totally agree that there is further improvement from pushing the onset of reflections further back in time than that, but 10 milliseconds is achievable in most rooms, whereas 35-40 milliseconds is either impossible or expensive to achieve in most rooms.

RTx graphs or reverberation time are not valid for small rooms. There's no diffuse sound field in small rooms; meaning that the sound intensity in the same no matter the position in the room, and secondly; that the sound intensity is the same in every direction. A small room will never meet these criteria’s. The small acoustical space is dominated by focused specular reflections.

Agreed. I sometimes carelessly say "reverberant field" when I should be saying "reflection field" or "reflections" in the context of small rooms. The good news is that at least some of the reflections in a small room can be deliberately "aimed", assuming suitably directional loudspeakers.

 

[Bjorn]

Klipsch Jubilee was actually released many years ago. They sold some to customers as a 2-way design before they basically made it a cinema speaker as 3-way. You could still buy the 2-way version but needed to know what to ask for. The 2-way design with low crossover was Paul's dream speaker. They have made some changes to it now and added veneer.

I used the K-402 horn (top horn of Jubilee) as a reference when we designed our horn. Also tested it with the Celestion AXi-2050 driver, which Klipsch uses a modified version of now.
Klipsch K-402 on the right side below. It's a well designed horn.

 

[dasdoing]

I agree that wide dispersion speakers throw a bigger soundstage, but imo there are trade-offs involved. The same psychoacoustic mechanism which perceives a wider soundstage when significant early sidewall reflections are present also degrades image precision. And in my experience clarity and soundstage depth can also be degraded by early reflections. Toole's findings indicate that the benefits of wide-pattern speakers outweigh the downsides for most listeners.

Here are some arguments against early reflections, which may have implications for the wide-pattern vs narrow-pattern speaker debate. These statements may also be thought of as arguments for treatment of the early reflection zones:

"The earlier and the greater in level the first room reflections are, the worse they are. This aspect of sound perception is controversial. Some believe that all reflections are good because they increase the listener's feeling of space – they increase the spaciousness of the sound. While it is certainly true that all reflections add to spaciousness, the very early ones (< 10 ms.) do so at the sake of imaging and coloration... The first reflections in small rooms must be thought of as a serious problem that causes coloration and image blurring. These reflections must be considered in the [louspeaker] design and should be also be considered in the room as well." - Earl Geddes

"The earlier a reflection arrives the more it contributes to masking the direct sound." - David Griesinger

"When presence is lacking the earliest reflections are the most responsible." - David Griesinger

why not just make the triangle wider instead of relying on a "chinese copy" coming for the sidewalls?

 

[Duke]

why not just make the triangle wider

If the speakers are too far apart you can get a "hole in the middle" effect, so ime there's often a juggling of tradeoffs. And sometimes the room is not very wide to begin with.

 

[dasdoing]

If the speakers are too far apart you can get a "hole in the middle" effect

I heard about that but could never reproduce it.
also since the mirrored speaker and the real one become one phantom speaker (precedence effect), there should be the same hole there

 

[dasdoing]

here is what happens,
you have a bad speaker at the reflection point.
the result is a not so good phantom speaker somewhere between the two.
you could just eliminate the reflection and put your speaker there where the phantom is.

 

[Duke]

here is what happens,
you have a bad speaker at the reflection point.
the result is a not so good phantom speaker somewhere between the two.
you could just eliminate the reflection and put your speaker there where the phantom is.

View attachment 301203

That first same-side-wall reflection is not something I have studied a great deal, as the approach I take is to simply minimize it through pattern control and aggressive toe-in. So consider the following to just be speculation.

I think there is some widening of the apparent source width but I'm sure how much. The wall reflection is weaker than the direct sound AND it arrives after a significant time delay, both of which would tend to place any phantom image closer to the speaker. The spectral content of the reflection may also play a role; I would expect that the greater the spectral discrepancy relative to the direct sound, the greater the tendency for the reflection to be perceived as a separate sound source... whether that's desirable or not is a matter of opinion.

 

[Descartes]

Yes, the more speaker you have the less room reflections are desirable. In the EBU recommendation there is also a lower reverberation time suggested for multi channel listening.

Some also say stereo can't be good, but I have heard very convincing stereo setups. An almost no very good stereo to multichannel upscale which comes close to the very good stereo setup. The sense of enveloping is only good mit auro 3D or similar setups with higher placed speakers or with setups with omnidirectional and very well places back channel speaker. With no higher places speaker you have to play with the room acoustic like in stereo to get the feeling of enveloping sound. It is harder to build this room acoustic with more speakers. Or do you know some more tricks like placing additional speakers at +/- 60°.

One other important aspect is the positioning in the room. If the speakers are not places symmetrical in the room or the first reflections provide a uneven frequency response and high power (placement close to the wall); in this cases it is better to have less reflections aka a speaker with narrower directivity even in a small room.

In a 9.4.6 multichannel speakers in a medium size room 18 x 20 x10 feet it is best to have narrow directivity!

 

[test1223]

In a 9.4.6 multichannel speakers in a medium size room 18 x 20 x10 feet it is best to have narrow directivity!

Did you test it in a real world set up? Envelopment is hard to create even with that many speakers. The recording technique is also essential. Which 3D audio track captured envelopment well for such a set up?

 

[dasdoing]

That first same-side-wall reflection is not something I have studied a great deal, as the approach I take is to simply minimize it through pattern control and aggressive toe-in. So consider the following to just be speculation.

I think there is some widening of the apparent source width but I'm sure how much. The wall reflection is weaker than the direct sound AND it arrives after a significant time delay, both of which would tend to place any phantom image closer to the speaker. The spectral content of the reflection may also play a role; I would expect that the greater the spectral discrepancy relative to the direct sound, the greater the tendency for the reflection to be perceived as a separate sound source... whether that's desirable or not is a matter of opinion.

there might be actually more to it, as delayed copies extract ambiance: https://www.stereophile.com/content/extraction-ivsi-generation

 

[Bjorn]

why not just make the triangle wider instead of relying on a "chinese copy" coming for the sidewalls?

That works well if you have the combination of needed width and a speaker with constant directivity that's maintaied also high in frequency. You can get a huge stage in front of you.

 

[tmuikku]

Now, I'd like to raise a question, not sure if its appropriate for this particular thread but here it is as its related to the topic

Assume you've got perfect horizontal directivity, what ever that is, but imaging and spaciousness are 3D stuff at best aren't they? What about height and depth? If image is attached to the speakers (height and or depth wise) can we do something about it with directivity and positioning? What is the situation with your speaker setup, nice and wide image due to optimized lateral reflections, but not very tall? or is it full "front wall painting" or even a 3d show?

Hi all!

this thread came back to alive conveniently right when I was doing some listening experiments

I've found out perception of stereo image shifts considerably at some particular listening distance. Perception seems to shift from 2D and slightly far and hazy sound to more enveloping and clear 3D kind of presentation when listening at close enough distance, with small enough listening triangle.

This seems to be what Griesinger has been studying: basically when direct / room sound ratio is high enough brain locks in, separates important direct sound to its own neural stream while background sound gets its own. Now its possible to hear envelopment, get engaged, direct sound has clarity and so on, brain considers direct sound important and pays attention. Listening too far away, and its just one blob of sound, direct and room sound are combined into single neural stream, basically brain thinks its just noise, not important as it cannot focus on it.

Here is link to a paper http://www.davidgriesinger.com/Acoustics_Today/AES_preprint_2012_2.pdf but about all his lectures and papers and presentations seem to revolve around this phenomenon.

Anyway, my point is listening distance seems to make such a dramatic difference in sound that it should always be mentioned discussing about hifi stereo. Basically it feels like local room is largely not audible when listening close enough, and it doesn't seem to be much about some particular early reflections or their time delays, but just about D/R at the listening spot. Although time and attenuation and direction of early reflections likely have their own effect on perception I'm not sure any of it matters if one is listening too far away, I mean the "image" could be made bigger or smaller but there would be no envelopment for example, or engagement if taking Griesinger studies literally.

Now, lets use some logic on this. For example if question is are lateral early reflections a good thing? And the answer seem to depend on what's your listening distance! If one listens far away, where its already a big hazy blob of sound, you could make it even bigger by having more of the same. But, if one likes to listen at the close proximity, hear more accurately what is on the recording, go and listen close enough distance, which turns the hazy blob reflections into envelopment. In this case I think it would be good to suppress early reflections front of the listening spot in order to reduce "room noise" and to extend the critical distance bit further out into room, hopefully all the way to a practical listening distance. Polar opposite advice and correct one depends on preferred listening distance! A great source for confusion if listening distance is not taken as context.

I speculate suppressing strong early reflections front of listening spot helps to balance out the room sound so that the later reflections arriving from all directions are now relatively higher in level. This to me seems like could sound better as envelopment. I mean, at the critical distance ratio of direct sound and room sound is some constant and by manipulating the earliest reflections what effectively happens is that weight of the "room sound" ought to move from strong early frontal reflections to later and come from all around. Intuitively this ought to make nicer envelopment, but I'm just speculating as I'm not a pro on this.

This should be something everyone can listen to with their setups; Put mono noise or spoken words for both speakers for maximally strong phantom center. Make listening triangle quite small perhaps under 2m / 6ft. Now, move back and forth on the center normal and listen carefully clarity and size of the phantom center. There ought to be quite clear transition between hazy (too far) blob of sound to quite pinpoint and small clear phantom center ( close enough). Between is transition between the two. Learn what this audible critical distance is in your room and which sound you like. Now listen with music, do you still hear it? In my room and speakers its one step transition, like stepping inside sound. All room treatment and loudspeaker DI and stuff like that can be now optimized for your preferred sound. If you like the close up sound, treatment is likely bit different than if you like the far field sound.

Any thoughs? Everyone, be sure to find out what is the critical distance with your setup and which side you are listening on to be able to relate any advice to your setup, to your preference and situation. And to actually learn to hear what your room sound sounds like Have fun listening!

 

[tmuikku]

How to get perfect sound?
And the question which speaker room combination is perfect and how should the ultimate goal look like? A "standard" speaker with narrow directivity in a studio like dry room? All horns oben back in a big room with diffusing walls? Line arrays (horizontal wide and vertical narrow diretivity)?

Hi, having heard the transition between direct and far sound and records that can sound good on both, or just on the far listening, i'd say good speaker is such that has smooth DI. Smooth DI would help to have balanced sound if listening beyond the critical distance, which is most of any room I think and what most people seem to prefer. But it should work for the close listening as well, as it possibly affects perceived sound at least to some extent, shouldn't hurt.

I think level of DI doesn't seem too important other than it most likely affects the critical distance. On the other hand practical listening distance usually needs to be something practical, perhaps 2-3m, in living room context so its likely DI greater than few dB at some bandwidth is required to make it happen. At least, directivity and room acoustics should be manipulated to reduce strong early reflections in order to reduce early portion of the room sound, to extend the listening distance and affect quality of envelopment.

For me best sound seems to be when listening right around the critical distance, at the transition. Sitting there I can lean forward to zoom into the sound, great clarity and envelopment, and lean backward to get more distance which makes it interactive and fun. Very even DI and low diffraction speaker the frequency spectrum seems stable so short listening distance, or moving back and forth doesn't change frequency balance much at all. Moving some only changes the spatial feel which because can be adjusted per recording, per interest Some records sound too weird on the close proximity without much local room influence but I can just lean back and it smoothens out.

Having said that someone might like always to listen within the critical distance, some seem to like listening on the far field. I speculate many haven't ever heard sound closer than the audible critical distance or haven't paid attention how much the sound differs either side. Judging from pictures from hifi shows it looks like most of the rooms are setup for the far listening. There might be single seat thats on the close enough proximity, while most of folks are on the far side... which is fine as long as you know which of the two sounds you like.

If one likes the close sound, higher DI system would suit, if one likes the far sound lower DI system would make more sense I think. Either case smoother and flatter DI would likely sound better than a lumpy one, or a beaming one.

 

[Duke]

there might be actually more to it, as delayed copies extract ambiance: https://www.stereophile.com/content/extraction-ivsi-generation

My understanding is that (assuming a conventional stereo system) the in-room reflections function as carriers for the ambience cues on the recording, and that they do this best when they are spectrally correct, arrive neither too early nor too late, are neither too strong nor too weak, arrive from many different directions, and decay neither too fast nor too slow. In my opinion that first same-side-wall reflection arrives too early in most rooms. I prefer for the strong onset of lateral reflections to happen after a longer time delay. This can be accomplished by using sufficently directional speakers and toeing them in aggressively, such that the first strong lateral reflection for the left-hand speaker is the long across-the-room bounce off the right-hand wall, and vice versa.

 

[digitalfrost]

arrive neither too early nor too late

 

[Duke]

I've found out perception of stereo image shifts considerably at some particular listening distance. Perception seems to shift from 2D and slightly far and hazy sound to more enveloping and clear 3D kind of presentation when listening at close enough distance, with small enough listening triangle.

This seems to be what Griesinger has been studying: basically when direct / room sound ratio is high enough brain locks in, separates important direct sound to its own neural stream while background sound gets its own. Now its possible to hear envelopment, get engaged, direct sound has clarity and so on, brain considers direct sound important and pays attention. Listening too far away, and its just one blob of sound, direct and room sound are combined into single neural stream, basically brain thinks its just noise, not important as it cannot focus on it. [emphasis Duke's]

Yessss!

The direct sound must be sufficiently loud, and my understanding is that the time interval between the direct sound and the strong onset of reflections also matters. A reflection-free time interval is needed in order for the ear/brain system to separate the direct sound from the reflection stream.

Moving your listening chair closer not only increases the relative loudness of the direct stream, it also geometrically increases the relatively reflection-free time interval. Not by a huge amount, but still imo arguably enough to help. And this relatively reflection-free time interval contributes to BOTH clarity/proximity/presence AND envelopment/immersion.

If you haven't seen it yet, this lecture is really good, and the processed samples section starting around 12:40 is especially educational in demonstrating the detrimental effect of a strong first reflection on clarity (my understanding is that it's actually a double reflection, with both reflections arriving simultaneously at the right ear):

Obviously the time intervals will be much shorter in home audio. Imo taking steps to maximize the time interval between the direct sound and the strong onset of reflections contributes to simultaneously getting both clarity/proximity/presence and envelopment/immersion, BUT the trade-off of foregoing a strong early same-side-wall reflection is that we lose the resultant broadening of the apparent source width.