Introduction of Vera Audio Coherence 12 - a high quality speaker many can afford

[Sokel]

But is it the distance between the planar tweeter and the bass driver you see in the picture of Bjorn's speakers we are talking about? I may have missed something.
I thought that was it.

You mention 500 Hz. That doesn't seem to be an impossibly long distance then between then in that case.

If I start from a calculation example that Kimmosto brings up in the thread I referenced but pop in 500 Hz instead:
With sound speed = 344 m/s and XO frequency = 500 Hz, c-c = 1.2 * 344000 / 500= 826 mm.

So 826 mm distance between drivers in that case, given the 4 order crossover.
With the addition that I don't know where to put the c in c-c distance with an oblong planar tweeter.

In any case, Bjorn can describe the design later.

I mention 500Hz (at minimum) because of the planar driver's specs if I have guess it right.
On the other hand Bjorn says that he wanted an uninterrupted range for the sensitive area (which traditionally are the voices) and by that it can't be 500Hz either.
I admit I'm intrigued,it's rare to see such a distance between a planar driver (even if the one I look has a 250Hz-20kHz range by specs,so usuable at an octave higher) and a big-ish woofer given their response.

 

[digitalfrost]

Want to introduce the Vera Audio Coherence 12 speaker to the ASR community.

Looks interesting, but the black is a bit too much for me for such a large speaker. Will other colors be available?

 

[Matt_Holland]

I mention 500Hz (at minimum) because of the planar driver's specs if I have guess it right.
On the other hand Bjorn says that he wanted an uninterrupted range for the sensitive area (which traditionally are the voices) and by that it can't be 500Hz either.
I admit I'm intrigued,it's rare to see such a distance between a planar driver (even if the one I look has a 250Hz-20kHz range by specs,so usuable at an octave higher) and a big-ish woofer given their response.

The sensitive area is usually thought of as 2-4KHz (where mids cross with tweeters commonly). However this I believe is based on the frequency range our hearing is most efficient.

 

[Sokel]

The sensitive area is usually thought of as 2-4KHz (where mids cross with tweeters commonly). However this I believe is based on the frequency range our hearing is most efficient.

Of course you're right.I was thinking about it from what Linkwitz said,that it's the voices that have to be uninterrupted.
But it makes more sense from your point of view for this speaker.

 

[Matt_Holland]

Of course you're right.I was thinking about it from what Linkwitz said,that it's the voices that have to be uninterrupted.
But it makes more sense from your point of view for this speaker.

Historically hifi magazines always talked about the “sensitive area” around the crossover region at 2/4KHz. I think this is more likely because many speakers failed to create a smooth crossover transition off-axis leading to inconsistent sound quality from room to room, or just in general. The perceived fix to this would to move the crossover point away from this “sensitive” frequency range believing that our hearing is more critical of errors in that range. In reality it’s due to it being harder to achieve off-axis consistency between drivers crossing over at higher frequencies.

 

[Bjorn]

2 way design and bass reflex

The speaker is a 2-design and active as mentioned before with the choice of either built-in plate amplifiers or external electronics.

The top driver is a planar transducer that covers the tweeter and most of the midrange. Bottom driver is a 12” woofer.

During the development, a large amount of drivers were tested. These two drivers were picked because of the best sound alone and not due to price. I can tell you that the most expensive drivers are not always the best, neither in regards to measurements or how they sound.

The planar driver has super low distortion combined with high sensitivity and good power handling. This driver did something we didn’t achieve we neither smaller broadband drivers or coaxial drivers. More about this later.

And the 12” woofer is the best we tested and offers very low distortion, high sensitivity and high capacity.

It’s a bass reflex design. It would not be possible to reach the high SPL in the lows with a sealed enclosure. While bass reflex has gotten a negative rumor among some audiophiles this has very much to do with either too small enclosure or/and too short/small ports/vent. But that’s not the case here, and bass is both powerful and tight. Besides considerably higher SPL than a sealed box, we also achieve lower excursion and distortion. This is one of the benefits of a larger enclosure.

 

[Bjorn]

No fabric/magnetic grill at the moment

We’re not using any fabric to cover drivers at the moment and it’s something I would prefer to avoid unless the demand is big. The is simply because it has some negative effects that’s really impossible to avoid.

As one who has worked a good number of years with acoustics, I can tell you that no fabric is is really sound transparent. They all effect the sound it different ways. Commonly, they will reflect some in higher frequencies. Or those who attenuate more evenly can steal several dBs in sensitivity.

So while I understand the need to protect the drivers from children, it’s something we haven’t focused on because we are a very much high-end brand that wants to bring the highest quality.

 

[Bjorn]

Finish

The initial plan was to offer the speaker in either 100% piano black finish or piano black with a wooden top. However, it may be possible with custom painting in other colors.

Below is a picture with an oak wooden top.

 

[Bjorn]

Directivity

Let’s talk some about directivity, which is a huge topic in itself. The goal was a uniform horizontal and vertical dispersion over a wide area. A general weakness with many speakers today is that they only have a constant directivity in the higher frequencies. For example above 1 KHz and below this the directivity control is lost and we then have what was called a collapsing polar in acoustical circles. This leads to a difference in the reflective energy, and IMO such speakers don’t sound tonality correct without acoustics treatment.

With Coherence 12 we wanted therefore a speaker that could maintain the directivity much lower in frequency. The horizontal dispersion is 180°, meaning 90° to each side. According to Harman/Toole wide dispersion like 180° is a benefit. But I think this depends very much on the room and how one listens. I believe both wide and narrow horizontal dispersion has its place and what’s better will depend.

Originally, we wanted to maintain the wide dispersion in high in frequency as possible. Doing that with a wide band driver is challenging though, because such drivers are larger. Something we experimented quite a bit with was using an acoustical lens to keep wide directivity high in frequency. This wasn’t completely successful as it lead to other issues.

By using a coxial driver it’s easier to maintain directivity in the higher frequency. We tested a good number of coaxial drivers and did AB tests besides obviously measuring. The problem with most coxial drivers are frequency deviation as the two drivers effect it each other. They neither sounded or measured as well as other options. Below is a crude indoor measurement of a coaxial driver used in a prototype. No gating is used.

After testing many drivers we had initially landed on a wide band driver. This driver could cover a large frequency area, maintained the 180° dispersion quite high in frequency, and sounded like a good piston tweeter in the highs. However, we made a decision to try out several other types of drivers, and among these were several planar/ribbon transducers. Two of these sounded incredible good, and one slightly better than the other. Despite that the planar driver narrowed horizontal earlier in frequency, it had a clarity, detail and insight into the music material the piston driver couldn’t match. So it was an easy choice.

The directivity of the planar driver changed the dispersion of the speaker. The speaker narrowed now earlier in frequency horizontally. The narrowing from 180° starts around 5 KHz. One can discuss if this is negative compared to maintaining a wide dispersion in the highs. I think there are points for both sides.

Vertically by changing from the piston driver to the planar we went to a wide dispersion high in frequency till a very narrow vertical directivity in parts of the frequency. This is something I believe is very beneficial as vertical reflections from ceiling and floor are only detrimental.

But the narrowing vertically means that you basically have to sit to get a good treble and higher mid response. If you stand up, the higher frequencies will be partially lost because it’s outside the listening window. This gets better further away from the speaker.

So the horizontal directivity is constant from about 200 Hz area till 5 KHz and narrows above. Vertically, we’re going to need to do 100% anechoic measurements to be certain. But the trait is that the dispersion narrows some above 400-500 Hz area, remains much the same till 1.5 KHz and narrows again above this frequency. It’s quite beamy vertically in the highest frequencies.

 

[Matt_Holland]

I’m really enjoying your posts and very interested in the design story behind the speaker, but wish you could post it all in one go. The drip feeding is infuriating!

No one is commenting about it because we don’t know the full story. Just tell us everything and then we can get on with discussing/promoting the design. Please

 

[Bjorn]

What’s important in directivity?

Let’s look a bit at the directivity. The directivity of the Coherence 12 is somewhat unusual. We have seen speakers with a uniform horizontal directivity above about 1 KHz has scored high on ASR and spinorama tests. In my opinion, it’s more important to remain the directivity down to the Schroeder frequency vs remaining it very high in frequency. Especially when the directivity is initially wide (180°). The room contributes less to the highest frequencies anyway and we are general less sensitive to as well. The most important frequency range for speech and also manyt instruments has tradionally been between 500 Hz and 5-6 KHz. And that’s covered with a constant horizontal dispersion with the Coherence 12 and it also goes lower.

Another important matter is how the speaker interacts vertically. In a Danish study, they found the “floor bounce” the most important factor and the ceiling reflection the second most audible. The first floor bounce is right in the fundamental area, lower midrange and upper bass. If the level is low here, the speaker will sound lean and the frequency area above will dominate the tonality with sounding brighter. This is actually how most speakers measure when placed in a room, unless one is lucky and get peaks in the same range. This again leads to listening fatigue kicking in much earlier, especially with poor recordings.

The Coherence 12 completes avoids the first floor bounce and also greatly minimized both reflections from ceiling and floor above Schroeder. Combined with a horizontal dispersion that is kept constant to approximately 200 Hz, it will end up measuring more even when placed in the rooms compared to most other speakers. Also those speakers that score very high on a spinorama.

So as a mentioned in an early post: What good does it do if a speaker measures well anechoic but doesn’t measure that well when placed in an actual living room? This is also why we don’t put much emphasize on spinorama. We could have designed a speaker that would score higher, but that wouldn’t measure that well in an actual room.

 

[WTW]

Is this a serial novel about a loudspeaker?

 

[Bjorn]

Diffraction

Cabinet diffraction is often overlooked in speaker designs. It’s common to see very expensive speakers with no or little focus to minimize it. Diffraction happens when sound travels the surface of the cabinet and meet edges. Any edge will cause a comb filtering and a peak/cancellation in the response. It’s well documented.

In acoustics, the most detrimental reflections are those that arrive the earliest after the direct signal. Cabinet diffraction happens even earlier and is therefore something that’s important to avoid.

The cabinet of the Coherence 12 is super elliptical. Acoustically this is very close to a sphere, which is the best type of cabinet to avoid diffraction. The result, and as we will see later a response that is extremely free of ripples in the response. This leads to a sound that is more open and subjectivily more “airy” or “free” and the sound is also smoother.

 

[Bjorn]

Some pictures of the prototype.
Rear with plate amplifier:

When chosen with external electronics, a 4-way speakon connector is used.

The cable can either be speakon to speakon or speakon to banana plugs. Cables as shown below with follow with the speaker.

 

[Bjorn]

Cabinet

When you have a large cabinet like here, bracing is crucial to avoid audible resonances. The cabinet has been very well braced. Cabinet material is thick MDF.

Dampening material has also been emphasized a lot. Many materials and different thicknesses have been tested. We’re not simply using common cotton stuffing here.

The base is made out of plywood with aluminum underneath for strengthening. And custom Sorbothane rubber feet are tailored to the weight of the speaker.

 

[Matt_Holland]

Is this a serial novel about a loudspeaker?

I made that point above. We want to binge it all in one go!

 

[Matt_Holland]

@Bjorn this is terrific. I like the design ethos a lot.

Did you test different heights for the woofer? In theory you could have it higher until the floor bounce cancellation frequency is just outside the woofer’s pass band?

 

[Bjorn]

@Bjorn this is terrific. I like the design ethos a lot.

Did you test different heights for the woofer? In theory you could have it higher until the floor bounce cancellation frequency is just outside the woofer’s pass band?

Yes. Firsly, an earlier prototype had the woofer much higher. Something that would have given better spinorama data.

And experiments were done with woofer at different heights close to the floor.

 

[Koeitje]

Yes. Firsly, an earlier prototype had the woofer much higher. Something that would have given better spinorama data.
View attachment 403404


And experiments were done with woofer at different heights close to the floor.

Why did you choose a lower placed woofer then and up to what frequency does the woofer play?

 

[Matt_Holland]

Why did you choose a lower placed woofer then and up to what frequency does the woofer play?

He explained it in one of the previous posts. The low woofer removes the cancellation due to floor bounce. This is typically around 300-600Hz depending on woofer height and listening distance. The aim is to have the higher frequency drivers operating above the frequency at which they would otherwise create a floor bounce cancellation.