Visible gap between the coaxial assembly and enclosure on my Genelec 8351B — does this look normal?

[WhiteBear]

It's a cosmetic trim.

Thank you. I understand why it may be seen as a cosmetic trim.

My reason for seeing it differently is that this area is part of the visible transition around the front coaxial assembly / waveguide area. Genelec’s own MDC/DCW description talks about smooth transitions and diffraction-free joints in this region.

So my concern is not just that a trim line exists. It is whether this level of visible gap and unevenness is what should normally be expected around this part of the speaker.

 

[WhiteBear]

The product class is "utilitarian professional tool." These speakers are not dressed up for audiophile living rooms in wood or chrome or whatever. Looks are barely even an afterthought.

I agree that Genelec monitors are professional tools first, not luxury furniture.

That is also why I am not concerned about ordinary cosmetic marks in places that are not visible during normal use. My concern is specifically about the front coaxial assembly area, because it is always visible at close listening distance and is one of the most visually central parts of the speaker.

For me, the issue is not decorative luxury. It is finish consistency and what should reasonably be expected from a reference monitor in this product class.

 

[WhiteBear]

Tangential but relevant:
The waveguides in my 3 KEF Blade 2 Metas are consistently spaced 2 card thicknesses from the surrounding enclosure.
The waveguides in my 2 KEF LS60s are all flush with the surrounding enclosure.
The waveguides in my 2 KEF KC92 subs are consistently spaced 1 card thickness from the surrounding enclosure.
FWIW.

Thank you, that is useful context.

I have also noticed that some KEF coaxial products appear to have more clearly defined spacing by design, depending on the model. So I understand that a visible gap can be intentional in some designs.

My question here is more specific to Genelec 8351B / The Ones: whether this degree of visible and uneven gap around the front coaxial assembly is typical for this design, or closer to the outer edge of normal visual tolerance.

P.S. Your posts have been quite helpful to me when choosing speakers and learning about this field.

 

[WhiteBear]

Looks like normal tolerance or even deliberate "shadow gap".
Is this even a concern if there's some distance between you and the speaker?

In my normal use, the listening distance is roughly 70–90 cm, and the gap is clearly visible to me at that distance.

Compared with other Genelec coaxial units I have owned or seen, my current pair looks noticeably more pronounced. That is why I posted this.

I had understood Genelec’s descriptions of smooth and continuous transitions around the coaxial / waveguide area as implying a very tightly finished visual transition. So when I saw this level of visible gap, especially on both monitors, I found it difficult to simply treat it as an ordinary cosmetic detail.

This is from the listing on Genelec's site:

View attachment 535369

Looks to me like there's a small gap between the baffle and the driver, enough that you might be able to stick a business card in edge-wise. Definitely normal and not something to be concerned about at all.

I have to be honest: this official image is exactly why I find my unit difficult to accept.

To my eyes, the unit in this image looks clean, tight, and consistent around the coaxial assembly. I do not see a gap comparable to the section on my unit where the edge of a standard paper business card can enter and get caught.

This is the kind of finish I expected from Genelec’s public product images and from a monitor in this product class.

So if this image is being used as a comparison, I actually think it supports my point rather than the opposite. The visible gap on my unit does not look representative of the finish shown in Genelec’s own images.

This is where my main question becomes more specific: if my pair is representative of the typical finish for The Ones, then I can accept that my expectation may have been wrong. But if my pair is closer to the outer edge of Genelec’s acceptable visual tolerance, then I think it is fair to ask whether that is a reasonable tolerance boundary for a flagship reference monitor.

 

[Subwaffler]

My concern is not simply that a seam or shadow line exists. It is that the gap on my unit is wide enough in some sections for the edge of a standard paper business card to enter and get caught.

Your best bet then is probably to not go sticking business cards into the gap, then they won't get caught.

Seriously, though - it's fine. Stop worrying.

 

[audio_tony]

Your best bet then is probably to not go sticking business cards into the gap, then they won't get caught.

Seriously, though - it's fine. Stop worrying.

First world problems.....

 

[solderdude]

I contacted Genelec, and they told me this condition is within their acceptable limits and is not considered a fault.

 

[anlin]

Thank you. I understand why it may be seen as a cosmetic trim.

My reason for seeing it differently is that this area is part of the visible transition around the front coaxial assembly / waveguide area. Genelec’s own MDC/DCW description talks about smooth transitions and diffraction-free joints in this region.

So my concern is not just that a trim line exists. It is whether this level of visible gap and unevenness is what should normally be expected around this part of the speaker.

A 0.4 mm gap is for all intents and purposes diffraction free, it's about 2% of the wavelength at 20kHz. No meaningful diffraction will occur due to it.

The enclosure is cast aluminium and powder coated, both of which mean there will be some small amount of variance from one enclosure to the next. The driver is mounted (and sealed) from the rear and the black outer ring is part of the suspension of the midrange driver so you can't (and don't need to) have a press fit joint there.

Genelec already answered your last concern: it's normal and expected.

 

[RexrothPigeon]

if Genelec has said it's fine, and you aren't bothered by the aesthetics, and you don't think it negatively affects the sound, and how you feel about it is contingent on how others feel about it or what others have anecdotally experienced as reported in a thread on a niche forum, then I think it's ok and you might as well just decide to feel ok about it

OR you could be upset, for sure, your choice

 

[NTK]

From what information I was able to find, I think what happens to OP's Genelec is probably "within the design intents". To have 2 concentric parts fit together and have a visually even small gap between them, you'll need very tight assembly tolerance and an assembly that is designed with that in mind. Here we are probably looking at a nominal gap width of a fraction of 1 mm, and to have a gap that is visually even all around, you'll need both parts to be almost perfectly circular and concentric to within a very small fraction of 1 mm.

Here is a picture of an example of the kind of issues design engineers typically have to deal with.


Now, to the actual design of the part and assembly ... Here is the cross section of a Genelec coax driver. Looks like the mid-range driver cone is composed of a foam membrane bonded to a (smaller) thin rigid cone at the back. The foam membrane is bonded to the outer driver frame at its outer edge and the foam membrane. The foam membrane is allowed to flex at its outer edge (between where the thin rigid cone ends and where the foam is bonded to the outer frame of the driver) and functions as the "surround".
Notice that the location of the outer edge of the mid-range cone (the foam part bonded to the frame) is located by the bonding process and is probably not very tightly controlled.
(Picture source: https://audioxpress.com/article/r-d-stories-genelec-8351-acoustically-coaxial-sam-system, annotations by me)

The way the coax driver is located to the speaker enclosure is actually designed for good concentric alignment, with o-rings to "decouple" the driver from the enclosure. However, because the outside edge of the surround is only located by the bonding to the driver frame, the concentricity between it and the circular opening of the frame isn't tightly controlled, and therefore, IMHO, the Genelec design does not aim to ensure, and is not adequate for ensuring, that the gap between the driver and the enclosure opening is visually even all around. Since the wavelength of 20 kHz sound wave is 17 mm at 20 °C, a concentricity mismatch of a small fraction of 1 mm will not matter.
Acoustically, I believe how well the driver edge is flush against the enclosure is far more critical (and therefore the mentioning by Genelec of the "diffraction-free" joint between the MF cone and the "DCW™" – Genelec's name for its "directivity control waveguide").
(Picture source: https://www.fast-and-wide.com/image...s/genelec 8260a - public white paper - v1.pdf)

 

[Norcal]

I don’t understand the point of posting to a forum asking a question and then not accepting the overwhelmingly consistent (and expert) advice.

 

[WhiteBear]

From what information I was able to find, I think what happens to OP's Genelec is probably "within the design intents". To have 2 concentric parts fit together and have a visually even small gap between them, you'll need very tight assembly tolerance and an assembly that is designed with that in mind. Here we are probably looking at a nominal gap width of a fraction of 1 mm, and to have a gap that is visually even all around, you'll need both parts to be almost perfectly circular and concentric to within a very small fraction of 1 mm.

Here is a picture of an example of the kind of issues design engineers typically have to deal with.
View attachment 535457

Now, to the actual design of the part and assembly ... Here is the cross section of a Genelec coax driver. Looks like the mid-range driver cone is composed of a foam membrane bonded to a (smaller) thin rigid cone at the back. The foam membrane is bonded to the outer driver frame at its outer edge and the foam membrane. The foam membrane is allowed to flex at its outer edge (between where the thin rigid cone ends and where the foam is bonded to the outer frame of the driver) and functions as the "surround".
Notice that the location of the outer edge of the mid-range cone (the foam part bonded to the frame) is located by the bonding process and is probably not very tightly controlled.
(Picture source: https://audioxpress.com/article/r-d-stories-genelec-8351-acoustically-coaxial-sam-system, annotations by me)
View attachment 535459

The way the coax driver is located to the speaker enclosure is actually designed for good concentric alignment, with o-rings to "decouple" the driver from the enclosure. However, because the outside edge of the surround is only located by the bonding to the driver frame, the concentricity between it and the circular opening of the frame isn't tightly controlled, and therefore, IMHO, the Genelec design does not aim to ensure, and is not adequate for ensuring, that the gap between the driver and the enclosure opening is visually even all around. Since the wavelength of 20 kHz sound wave is 17 mm at 20 °C, a concentricity mismatch of a small fraction of 1 mm will not matter.
Acoustically, I believe how well the driver edge is flush against the enclosure is far more critical (and therefore the mentioning by Genelec of the "diffraction-free" joint between the MF cone and the "DCW™" – Genelec's name for its "directivity control waveguide").
(Picture source: https://www.fast-and-wide.com/images/stories/White_papers/genelec 8260a - public white paper - v1.pdf)
View attachment 535460

Thank you very much for the detailed technical explanation. I really appreciate the time you took to look into the structure and provide diagrams and reasoning.

Your explanation about the surround, bonding process, rear mounting, sealing/O-rings, and the difficulty of maintaining a visually even circular gap makes sense to me. It also helps me better understand why this may be within the design intent rather than a defect.

I originally posted because I could not find many public examples that looked similar to mine, and I wanted to understand whether my pair was unusual or within the normal range for The Ones series.

I still personally wish the visible finish were tighter on my pair, especially because it is visible at close listening distance. But your explanation was very helpful in understanding the mechanical and acoustic side of the issue.

Thank you again. This is exactly the kind of technical context I was hoping to learn from this thread.

 

[Andreas007]

I can understand the optical distraction, especially if all stock photos show "perfect" examples (are they really perfect or was PS involved?).
Anyway, you could compare it with a car, for example: Stock photos always show a car with lowest and most even gaps. If you buy one you must be very, very, very lucky to get such a car. So, just be satisfied with what you have (excellent speakers), or go the hard way and exchange for something else hoping for the best.

 

[WhiteBear]

After reading the replies, I have taken some time to think more clearly about what my concern actually is.

I understand the technical explanations given here. I understand that this may be normal manufacturing tolerance, that the driver is mounted and sealed from the rear, and that the acoustic impact is likely very small or negligible.

So my question is not only whether this is a functional fault. Of course, that was my first concern, and Genelec has answered that they do not consider it a fault.

My remaining concern is about the tolerance boundary for a flagship reference monitor.

If my pair is representative of the typical finish for The Ones, then I can accept that my expectation may have been wrong.

But if my pair is closer to the outer edge of Genelec’s acceptable visual tolerance, then I think it is fair to ask whether that is a reasonable tolerance boundary for a product at this level.

For me, this would be easier to accept in either of two ways:

1. if many other 8351B / 8361 / The Ones owners show a similar level of visible gap, or
2. if Genelec provides non-confidential measurement data or a test summary showing that this level of gap has no measurable acoustic or performance difference compared with a smaller-gap unit.
   

Genelec told me that my monitors are within their accepted limits and that no measurable acoustic issue was found. I understand that position. However, no measurement graph, tolerance value, or non-confidential test summary was shared with me.

I also understand the point that a 0.4 mm gap is very small compared with the wavelength at 20 kHz. My point is not to claim a proven audible defect from this gap.

My point is that customers who buy a monitor at this level are often paying not only for audibility, but also for engineering precision, consistency, and trust in the product as a reference tool.

If this level of visible gap is within tolerance, then I think the useful question for current and future buyers is:

Is this a reasonable tolerance boundary for a flagship reference monitor?

 

[kemmler3D]

However, no measurement graph, tolerance value, or non-confidential test summary was shared with me.

I also understand the point that a 0.4 mm gap is very small compared with the wavelength at 20 kHz.

Not to dispute the validity of your concern, but if the latter is true, then how would diffraction show up in a graph?

 

[NTK]

I found this picture in Genelec's website (link: https://www.genelec.com/mastering/8341a-w371a-stereo-system). I don't think yours looks significantly worse. Regrettably I don't think Genelec gives cosmetic perfection of their products a very high priority, given the market it targets.

 

[RexrothPigeon]

Is this a reasonable tolerance boundary for a flagship reference monitor?

Yes

(but why not just be honest: You don't like it, and you're looking for support for your belief that you shouldn't have to accept it. You frame it a few different ways, but this is what's really happening here.)

 

[WhiteBear]

Yes

(but why not just be honest: You don't like it, and you're looking for support for your belief that you shouldn't have to accept it. You frame it a few different ways, but this is what's really happening here.)

That is a fair criticism. I did have difficulty accepting it, and I wanted to understand whether that reaction was reasonable or whether my expectation was simply wrong.

 

[WhiteBear]

I found this picture in Genelec's website (link: https://www.genelec.com/mastering/8341a-w371a-stereo-system). I don't think yours looks significantly worse. Regrettably I don't think Genelec gives cosmetic perfection of their products a very high priority, given the market it targets.

Thank you very much.

I really appreciate that you took the time not only to provide detailed technical explanations and annotated images earlier, but also to find this additional Genelec image.

Your comments have been very helpful in understanding this issue more objectively. I also think they may be useful for other users who have similar concerns or questions in the future.

 

[tmtomh]

Thank you very much.

I really appreciate that you took the time not only to provide detailed technical explanations and annotated images earlier, but also to find this additional Genelec image.

Your comments have been very helpful in understanding this issue more objectively. I also think they may be useful for other users who have similar concerns or questions in the future.

I have a pair of 8351s as my main stereo listening speakers (and am quite happy with them). I just took a piece of 110lb card stock, which I believe is more or less equivalent to a typical business card, and I could easily insert it the same way you did yours.

I gently inserted the corner of the card stock in the lower-left of my R speaker - the speaker detailed in the first image below - because that looked like the largest area of visible gap - I think one can pretty clearly see where the largest gap is, in the lower-left quadrant of the circle, around 7-8 o'clock. I honestly never even noticed this or thought to look at it until just now when I saw your post, and in real life in my listening room I had to almost put my nose into the middle of the driver to get close enough to clearly see any gap, whether wider or narrower.

I didn't try inserting the card stock anywhere else, because when I inserted it in the first location I realized that the surround is a fairly soft, very flexible foam-like material, and so it will very easily give at its edges, making it easy to insert the card stock anywhere. The second image below is the top 2/3 of the coaxial driver of my L speaker.

In any event, after reading the entire thread, I understand that your concern is the aesthetics of it, and in particular what those aesthetics say about engineering precision and build-quality standards for a premium product. I understand what you are saying, but with respect I think I will have to agree to disagree with you on two counts:

1. I don't share your view that this degree of acceptable tolerance of this part of the speaker is an indicator of substandard quality, or insufficient quality for the price. And I would also hypothesize that with the enclosure being aluminum and the surround being a very different material (and the screws and driver enclosure underneath being yet other materials), that small tolerance is not only considered acceptable, but probably also useful in different spaces and seasons where variations in temperature and humidity could cause the gap to vary by fractions of a millimeter.
2. Looking at my own speakers, and some of Genelec's own images, and the photos other members have posted, on the whole I simply have a different perception than you do - that is, I do not see the gaps around your surrounds as consistently or notably different than the norm.

I'm not trying to tell you how you should feel or what you perceive. I'm just communicating my own perceptions in the context of a discussion. I sincerely hope this thread is of some value to you in making you feel better about this issue, as it would be a shame to have one's music-listening enjoyment of these great (and yes, expensive) speakers diminished by this kind of thing.