Do we know if adding directivity to the bass frequencies adds to the sound quality?

[617]

Aaargh....the instant I see a study with a listening distance of 1m,.....i quit reading.
Anybody else feel this way?

1m can't even get into the acoustic far field, unless the speaker is a pretty small bookshelf.

That's a good point actually. 1M for the FR measurement would capture the modal chaos but I think you'd want further distance for both the listening tests and the decay measurement.

It was a small bookshelf speaker. Pretty sure it was a Genelec of some kind. It's an interesting study.

I'd be willing to accept the idea that decay is hastened even if steady state bass response is still the same.

My only question is if near-field bass also produces similar decay improvements. Any idea?

 

[sigbergaudio]

They had both 1M and 3M

 

[617]

They had both 1M and 3M

If only we knew someone who had both expertise designing enhanced LF directivity speakers and had access to high quality measurement equipment, we could settle this once and for all.

 

[sigbergaudio]

If only we knew someone who had both expertise designing enhanced LF directivity speakers and had access to high quality measurement equipment, we could settle this once and for all.

What is the question exactly?

 

[617]

What is the question exactly?

Well, it would be nice to confirm the very surprising but intuitively correct findings of that paper - that enhanced LF directivity attenuates decay of LF tones but does not excite room modes differently.

If this is so, this is an extremely good argument for cardioid bass. It would seem it is better than room treatment at LF.

Dip into your marketing budget and spend an afternoon testing it!

I thought the cardioid bass was an exercise in over engineering but it looks like it works.

 

[Bjorn]

I do not know much more than the concepts that uniform directivity is one feature of good sound quality, I also understand getting that uniform directivity down as low as possible is also another feature of good sound quality. Its obvious why we do not have commercial designs that have uniform directivity below say 800hz or 700hz likley due to the mostrosity of bass bins.

Have any science based research or even if its experienced based subjective support to the idea if directivity to as low as possible for the mid bass to 300hz or even lower if its possible produce a significantly better sound as opposed to a standard bass cabinet like the M2?

Having a uniform directivity down to the Schroeder frequency or slightly below because it's a transition zone makes a lot of sense. This means the reflected energy will be more like the direct signal. So you have less coloration and a more even frequency response. But for subfrequencies there's isn't any benefit in small acoustical spaces because the room modes will dominate and directivity control is thus lost.

Here's a midbass horn with directivity control quite low in frequency. The measurement space was too small to see exactly how low it was constant, but like earlier explained it's not a point to really go lower.

 

[Bjorn]

There have studies of monopoles, dipoles and cardioid in small spaces. And the result have been no real benefit other than a certain placement can favour one design. But they all trigger room modes equally much with various placements. The exception would be if for example a dipole doesn't extend as low and thus doesn't trigger the lowest room modes.

I have had both dipole and monopole in the same room BTW. With optimal placement of both, there haven't been any benefit with the dipole who have directivity control low anechoic.

 

[sigbergaudio]

There have studies of monopoles, dipoles and cardioid in small spaces. And the result have been no real benefit other than a certain placement can favour one design. But they all trigger room modes equally much with various placements. The exception would be if for example a dipole doesn't extend as low and thus doesn't trigger the lowest room modes.

I have had both dipole and monopole in the same room BTW. With optimal placement of both, there haven't been any benefit with the dipole who have directivity control low anechoic.

I guess the finding in the paper supported this, but also found the sound to decay faster (so reflections attentuates faster), which makes sense, and should be a good thing?

 

[Bjorn]

I've no experience with cardioid main speakers, but do have some with prosound subs used from 100Hz down, outdoors.
Sound quality takes a small hit whenever cardioid is deployed imo. Not huge, but definitely audible. The stronger the cardioid nulling lobes, the more audible the hit.

Which is no surprise considering how ineffcient a cardioid is at low frequencies. Distortion goes up.

If someone believes in directivity control for sub frequencies in a small acoustical room, they should get several huge sub horns and place them next to each other.

 

[617]

Aren't you guys like neighbors?

 

[sigbergaudio]

Aren't you guys like neighbors?

We do live in the same country, I guess that counts as being neighbours in the grand scheme of things.

Are you suggesting I walk over to his house and discuss instead of discussing on ASR? I only know roughly where he lives, but according to Google maps it would take around 5 days to walk, so I think ASR is good.

 

[sigbergaudio]

Well, it would be nice to confirm the very surprising but intuitively correct findings of that paper - that enhanced LF directivity attenuates decay of LF tones but does not excite room modes differently.

If this is so, this is an extremely good argument for cardioid bass. It would seem it is better than room treatment at LF.

Dip into your marketing budget and spend an afternoon testing it!

I thought the cardioid bass was an exercise in over engineering but it looks like it works.

Not sure it's such a surprising finding, as you say it makes intuitive sense. I will add comparing in-room decay between Manta and SBS.1 to my growing list of things I probably won't have time to do anytime soon. No particular reason to distrust the findings in the study.

 

[Bjorn]

I respectfully disagree … A properly designed cardioid should reduce or altogether remove the need for room treatment.

Maybe not.

Plus the directivity is so wide that it will lead to early arriving specular energy. So you have issues in both the frequency and in the time domain behaviour.

Room treatment isn't something we can get away with for an excellent result in a small room. But it's certaintly possible to reduce the need. And the best way to do that is by having speakers with a very narrow directivity. Cardioid speakers are horizontally in the area of 120° to 160° in midrange and treble (they vary and are generally not super constant), and they get wider below 200-300 Hz. At 200 Hz they are normally as wide as a wide baffle speaker with no cardioid. And vertically cardioid satelite speakers will become very wide already below 800-700 Hz, while a tall cardioid can maintain a vertical directivity of around 120° to 150 Hz area.

Both horizontally and vertically that's not really a particular narrow dispersion that avoids room reflections that much. To achieve something truly narrow and have less room intereaction, you need a different speaker design.

 

[gnarly]

If someone believes in directivity control for sub frequencies in a small acoustical room, they should get several huge sub horns and place them next to each other.
View attachment 337742

Yep, it works. Here's my bloc, 22 ft perimeter.. so maybe a 50hz horn

 

[Flaesh]

the instant I see a study with a listening distance of 1m,.....i quit reading.

On the contrary, I sometimes read about desktop audio systems. While listening to my system from a distance of ~5 meters.

 

[Rick Sykora]

Not sure if it was intended or not, but the more key question is whether your speaker has constant directivity in the entire midrange bandwidth. Many will get down to 1 kHz, but not so many get down to 200-300 Hz. This is more advantageous to sound quality and requires more work to achieve.

 

[Bjorn]

This is where the spinorama score is nonsense. It gives high score to speakers that only has constant directivity in the higher frequencies. Unfortunately this is leading many to be believe they are buying a high quality speaker, when they are in fact buying something mediocre at best.

 

[Andrej]

I had a pair of speakers with controlled directivity down to 1kHz, crossing over to an 8" seas excel in a large box tuned to about 35-40Hz, with DSP and high order x-over slopes. Once I placed the same 8"driver in a large waveguide, good down to about 175Hz, the perceived sound quality improved dramatically, in a a living room with no acoustical treatments. Equalized to same "target curve". There are other benefits from waveguides other than directivity control which I expect also contributed.

 

[Scgorg]

So no measurement comparing monopoles (sealed) dipoles (panels and bass reflex) and cardioid below schroeder?
This is an interesting question. Intuitively it seems like radiation pattern wouldn't make much difference in the modal frequencies; the waves are still vastly larger than the space.

The advantages of cardioid alignment in outdoor and large space PA systems don't apply to domestic spaces.

Ferekidis and Kempe investigate and compare the low-frequency mode coupling in small rooms of monopoles, dipoles, and cardioids in in this paper: https://www.aes.org/e-lib/browse.cfm?elib=12663
The figures mostly speak for themselves, but the cardioid manages to couple as well as the dipole and monopole regardless of room position (e.g. where the dipole couples poorly and the monopole couples, well, it behaves similarly to the monopole and vice versa). They also note the benefit of being able to rotate the cardioid speaker for controlling the mode excitation (e.g. by pointing the cardioid null in the direction of an intrusive mode). This can also be used to strongly reduce front-wall SBIR, particularly if the speaker is pulled out from the wall far enough that the first dip occurs where a conventional speaker is omnidirectional (or close to it).

One of my speakers, the Gradient revolution, has a dipole bass section that can rotate independently of the top part of the speaker, this way you can direct the dipole nulls in such a way that a mode is minimally (or maximally) excited.

Overall I agree with Geddes that the room is the main determining factor for low-frequency reproduction (and that the natural solution is multi-sub), but this does not mean that the loudspeaker doesn't matter (as Ferekidis and Kempe show). The room modes will still be the same, regardless of speaker, but how they are excited depends on the source(s). None may sound "right", but some may be closer to "right", and some may give the listener a greater flexibility in adjusting the speaker to the room.

 

[617]

This is where the spinorama score is nonsense. It gives high score to speakers that only has constant directivity in the higher frequencies. Unfortunately this is leading many to be believe they are buying a high quality speaker, when they are in fact buying something mediocre at best.

I agree with your implication that the preference score has limited use. It is worth remembering that only small number of commercial speakers offer any intentional directivity control below the tweeter, much less the woofer.