Open Baffle speakers

[Adi777]

I used to have a Martin Logan, it is easier to make the speaker "disappear". I believe OB could do that if you have room to play around. You could hear the box resonate on conventional loudspeaker if you own one. Of course, there are box speaker out here that has lower box resonance but at high price.

Perhaps I will be able to arrange an audition of the Open Baffle loudspeakers from Thivan Labs.

 

[fpitas]

I'm a firm believer that everybody should listen to the type of speaker they prefer; but if you're hearing a box resonate, that just means it's a crappy speaker.

 

[roog]

Yes, this is very interesting to me. How such a huge OB can sound with professional acoustics and perfectly placed in the room.

I suppose a well designed and executed infinite baffle speaker should provide the answer.

 

[kemmler3D]

Can you write something more about this?

Box speakers (as far as I know) win on directivity control (OB speakers have basically none). The directivity control means box speakers have the capability of producing a "sharp" stereo image by virtue of having more direct and early-reflected sound reach the listener than late-reflected. OB speakers are inherently heavy on late reflections, which tends to create a "big" stereo image, and more even tonality, but not one where the instruments seem to have exact positions between the speakers.

Box speakers also win on SPL (mainly in low frequencies), all else held equal. Pound for pound, I think that means they would also tend to win on THD, but I don't think a lot of people build OBs with weak drivers, so I haven't seen that that is a big factor either way.

More knowledgeable people may find things to correct here...

 

[fpitas]

Box speakers (as far as I know) win on directivity control (OB speakers have basically none). The directivity control means box speakers have the capability of producing a "sharp" stereo image by virtue of having more direct and early-reflected sound reach the listener than late-reflected. OB speakers are inherently heavy on late reflections, which tends to create a "big" stereo image, and more even tonality, but not one where the instruments seem to have exact positions between the speakers.

Box speakers also win on SPL (mainly in low frequencies), all else held equal. Pound for pound, I think that means they would also tend to win on THD, but I don't think a lot of people build OBs with weak drivers, so I haven't seen that that is a big factor either way.

More knowledgeable people may find things to correct here...

Not a correction, but a comment. The large cone excursion of bass drivers for an OB means more Doppler distortion. I suppose that means one should cross over relatively lower to minimize that effect.

 

[olegtern]

In the correct implementation, you cannot blindly tell which speaker design you are listening to. All the comments that OB sound somehow special based on not very correct implementation, they should not have a special sound, they should have proper sound.

Open baffles have pros and cons, then the question of implementation, as with all speakers.

Paired with a good closed subwoofer — a great match for OB.

 

[olegtern]

Box speakers (as far as I know) win on directivity control (OB speakers have basically none).

This is not true about OB. A dipole is the only radiator that is directional down to the lowest frequency, and this allows to control the directivity of the speakers in a very wide range. Linkwitz website is a huge source of information on this topic: https://www.linkwitzlab.com/Constant_directivity_louds.htm

 

[kongwee]

In the correct implementation, you cannot blindly tell which speaker design you are listening to. All the comments that OB sound somehow special based on not very correct implementation, they should not have a special sound, they should have proper sound.

In real life, you can tell. You don't have the room and speaker to match properly. You have preference like tonality, details, spacious......etc base on your expenditure. Like under $1000, you can sacrifice this and have that.

 

[kemmler3D]

This is not true about OB. A dipole is the only radiator that is directional down to the lowest frequency, and this allows to control the directivity of the speakers in a very wide range. Linkwitz website is a huge source of information on this topic: https://www.linkwitzlab.com/Constant_directivity_louds.htm

Fair, maybe it is better to say that OB speakers can't really have controlled narrow dispersion. I guess "full width in two directions" counts as controlled in a sense.

 

[olegtern]

In real life, you can tell. You don't have the room and speaker to match properly. You have preference like tonality, details, spacious......etc base on your expenditure. Like under $1000, you can sacrifice this and have that.

Once again my point is, if you recognize an "enclosure design sound" it's only the sight that something is wrong.

Or maybe the owner of the system prefers the sound to have such a recognizable character, it is not forbidden. Or that he only had $1,000 and sacrificed something. For me it's the same.

 

[olegtern]

Fair, maybe it is better to say that OB speakers can't really have controlled narrow dispersion. I guess "full width in two directions" counts as controlled in a sense.

They may have a controlled narrow dispersion, but it will be in the shape of figure 8. It's even more consistent than typical speakers, which change directivity from narrow at midrange and treble to circular at low midrange and low frequencies. I do not claim that this is better, it's just the properties. (And like any speaker, a poorly designed one can have an awful directivity) And need to take into account the back radiation, but it can provide benefits, not only problems (Linkwitz wrote about it).

 

[kongwee]

Once again my point is, if you recognize an "enclosure design sound" it's only the sight that something is wrong.

It is not wrong to able to listen to the box sound, a lot of times it is intentional. Not everyone into detail, transparency. You can have $100k speaker with premium chassis, part, driver and sound boxy too.

 

[olegtern]

It is not wrong to able to listen to the box sound, a lot of times it is intentional. Not everyone into detail, transparency. You can have $100k speaker with premium chassis, part, driver and sound boxy too.

Can you name such a 100k speaker? All I listen to don't have such problems. And yes, boxy sound = wrong sound, can't understand what you arguing.

 

[-Matt-]

Due to the fact that open baffle speakers radiate in figure-8 pattern, filling room with a sound, our brain can ignore room acoustics/reflections much easier, just as it does with natural acoustic sources.

Hmm, interesting, however, the next part seems to be a non-sequitur...

Plus, again due to figure-8 open baffles has less problems with bass - room modes are less excited - less boomy sound... and no enclosure resonanses really helps too.
So, it is not a mystery, but pure physics/acoustics.

Why would a speaker with a figure of 8 radiation pattern excite fewer room modes than one where the sound is predominantly radiated forward (possibly with narrow dispersion)?

 

[olegtern]

Why would a speaker with a figure of 8 radiation pattern excite fewer room modes, than one where the sound is predominantly radiated forward (possibly with narrow dispersion)?

Modes — it's a bass region, where closed speakers radiate 360°.

 

[-Matt-]

Modes — it's a bass region, where closed speakers radiate 360°.

So you are saying that at low frequencies (below 80 Hz?) a standard box type speaker becomes effectively omnidirectional (this part we agree)... but an open baffle speaker keeps its figure of 8 radiation pattern? I'd be interested to see klippel data that shows this. Do you know of any such measurements on open baffle speakers?

Edit: Here is the sort of data I'm talking about for a box type speaker (from the Genelec 8361A review):

The fully red part on the left is showing the omnidirectional behavior. It would be great to see how an open baffle design differs in this region.

 

[olegtern]

So you are saying that at low frequencies (below 80 Hz?) a standard box type speaker becomes effectively omnidirectional (this part we agree)... but an open baffle speaker keeps its figure of 8 radiation pattern? I'd be interested to see klippel data that shows this. Do you know of any such measurements on open baffle speakers?

Box speaker became omni when baffle dimensions become smaller than the wavelength, that's why the baffle-step effect exists. For modern typical narrow speakers this usually occurs in the hundreds of Hz.

And the dipole below the baffle step takes on a shape of 8, which may helps not only (or not so much) in the modal mode, but at low-mid frequencies, if properly positioned in the room.

I never saw Klippel dipole measurements. Don't even know if this method is correct for dipoles, may be only a real anechoic measurements are needed, I never dive in.

There are many dipole measurements and modeling on DIYaudio etc. Something like this:

 

[olegtern]

Edit: Here is the sort of data I'm talking about for a box type speaker (from the Genelec 8361A review):

Genelecs are smart box speakers They control directivity lower than typical same-size speakers because of design.

A good thread with models of closed box, cardioid and OB speakers:

 

[-Matt-]

Thanks,

I had just found this other open baffle thread and was about to post this simulated open baffle directivity plot:

So in theory, low frequencies can be beamed almost symmetrically forward and behind the speaker (with reduced sideways radiation).

I'd still like to see real measured klippel data for an open baffle design to see how close they get to this theoretical ideal.

Edit: In the first few posts open baffle designs were championed for their "room filling" sound (which to me implies omnidirectional behavior, which would tend to more strongly excite room modes). It seems more accurate to state the possible advantages of the open baffle design as controlled directivity that reduces sideways radiation, particularly at low frequencies.

 

[olegtern]

So in theory, low frequencies can be beamed almost symmetrically forward and behind the speaker (with reduced sideways radiation).

I'd still like to see real measured klippel data for an open baffle design to see how close they get to this theoretical ideal.

Edit: In the first few posts open baffle designs were championed for their "room filling" sound (which to me implies omnidirectional behavior, which would tend to more strongly excite room modes). It seems more accurate to state the possible advantages of the open baffle design as controlled directivity that reduces sideways radiation, particularly at low frequencies.

In open space - yes. In small rooms (all our rooms are small compared to low frequency wavelengths) it is much more complicated.

Once again I will doubt that Klippel is a proper way to measure OB at low frequencies because some space needed to sum front and rear sound, thus nearfield measurements can be confusing. But I posted DIY free-field measurements, I think they are ok to see whats going on.

I can agree with your last thesis. Good way to think about it in three different regions.

At higher frequencies, OB can add feeling of deeper space because of rear radiation and Haas effect, if you have enough distance to the wall and it can be a good thing. Or make unwanted reflections if the wall is close and it's bad. Side radiation can play a game too, but not very much.

In low-mids reducing of side radiation may be a good thing if you place speakers right, I illustrated it. Rear radiation not very problematic, but can create SBIR if speakers are close to the wall.

In bass (modal) region you can think of OB as more woofers in the room (one woofer acts like two with opposite polarity). This in many cases gives a more distributed modal picture and can produce more flat bass. But maybe not. It's just as dependent on placement in the room as it is with any other speaker.

And because OB often generates less bass compared to box speakers, with less modal problems, bass can sound very dry and fast. No bass — no problem