Ascilab C6B Speaker Review

[YouDontHaveEnoughBass]

That’s not a factor for the tuning frequency for the port/pr

 

[a4eaudio]

That’s not a factor for the tuning frequency for the port/pr

The driver is irrelevant to the port length/width (or PR weights) to tune to a box to a specific frequency.

BUT if the drivers have different TS parameters they will model/perform differently in different enclosures. Thus, a different driver will almost always result in a different target enclosure volume and target tuning frequency.

 

[markk]

Problem is not only the maximum SPL in bass, but also harmonic distortion and intermodulation distortion. The woofer in C6B, while having great midrange performance (when isolated), have weak mechanical compliance. Therefore the distortion in bass frequency and go to roof below 100Hz. Don't be fooled by great midrange distortion on the frequency sweep test. This test is done by plays a continuous, sliding tone from low to high frequencies to speaker and measure the distortion at one frequency at a moment only. So it is a indicator about distortion performance but not a represent of what happens in real speaker. When playing real music with both bass and midrange frequency signals at the same time, the weak compliance will make intermodulated distortion high too and affect the midrange performance.

Of course, this speaker is near the top in it's price range if you accept their design choice of narrower directivity, since better woofers cost much more. But it is fine (good) only in grand scheme of speaker, even when limiting to a two-way speaker category.

While I don't disagree with the first paragraph, I would say that max SPL and distortion are two sides of the same coin. Max spl at low frequencies is a function of displacement. To put it another way, I can reduce any of your objectionable IM and HD by lowering the drive level, since nonlinear distortion is level depenedent, right. I mean, distortion isn't a problem at, say, a listening level of 75 dB. So again, max spl is limited by HD and IM products. The same problem expressed in a different way.

But I don't see how you seem puzzled by the "narrow directivity" design choice and come to the conclusion you did. Really, this has more of a middle of the road directivity curve in terms of slope. Not as wide dispersion as a small WG setup, but much more dispersion than, say, a prosound two way with a 12 woofer and giant horn.

And if you look at the importance of the parameter weights in Olive's papers, listener preference is only weakly predicted by the actual slope of the DI curve, as opposed to the low frequency extension and smoothness of the on axis and power response curves as shown by the importance of the NBD and LFX parameters. The actual slope of the DI curve isn't in the predictive model.

Meaning there is no clear winner in terms of what's the "perfect slope" for the DI curve. I prefer a slightly wider dispersion shape to the DI curve. But, so what? My preference isn't better from the model data. You may prefer a different slope to the DI curve as well. But you can't generalize that your preference is better for anyone else. At least, not from the available study data.

So again, outside of the LFX problem with this unit, it can't really be faulted. All you have to do is as Shoba mentioned (and I had mentioned in an earlier post) to "fix" this unit, if you think it needs a fix, is to fix the low frequency limit with a pair of low frequency drivers. Easy enough to do with two bass modules, dsp, two additional channels of amplification. You get the additional benefit of being able to add some active LF room correction. Since, well, your room may not fit the "average" room that is used in Olive's studies to generate in room curves... There are limits to applying these study results, as good as they are. (And, well, they are probably the most objective data we have!)

 

[dfuller]

While I don't disagree with the first paragraph, I would say that max SPL and distortion are two sides of the same coin. Max spl at low frequencies is a function of displacement. To put it another way, I can reduce any of your objectionable IM and HD by lowering the drive level, since nonlinear distortion is level depenedent, right. I mean, distortion isn't a problem at, say, a listening level of 75 dB. So again, max spl is limited by HD and IM products. The same problem expressed in a different way.

Correct. With that said, we can see that the distortion rises from a relatively high frequency with this woofer, crossing 1% at around 120hz (albeit mostly D2) at 86dB/1m anechoic. Erin's Klippel LSI measurements show its actual distortion-limited xmax (TD=10%) to be only about +/-2.8mm, and the limiting factor is the mechanical compliance. This is a driver that, in spite of its low Fs, really wants to be a midrange crossing at about 200hz or so.

TLDR, the important bits from Erin's review of the SB17CAC35:

• One-way linear excursion measured approximately 2.8mm for this test sample. This is very low for a midwoofer and indicates this particular drive unit is best served as a midrange. I’d be leery of pushing this below 80Hz (as a starting point).
• Midrange distortion (>200Hz) is really something to behold. -50dB from the fundamental (about 0.30% THD) at 100dB. Very, very clean midrange. Of course, the downside to this is the lower frequency distortion which increases drastically below 100Hz as you apply more voltage to the speaker.
• Max SPL measures nicely at 100.9dB when running the “typical” bandpass region of 80Hz to 1600Hz. The compression is the limiting factor here. Curiously, when opened up from 40Hz to 3.2kHz the max SPL is still the same, however, the distortion significantly increases. Very interesting to see this. And additional proof that this drive unit should not be crossed low as to avoid distortion below 200Hz.

Curiously, the SB16PFCR25 in the F6B is more suited to use as a midwoofer in spite of its considerably lower performance motor (lacks shorting rings) and lower calculated xmax of +/- 4.5mm, and this bears out in measurements of the F6B vs the C6B.

ETA: I'd bet the C8C is using the same driver as its midranges; they cross around 150hz with an LR4 slope. The distortion performance is impressively good in its operating range there.

 

[YouDontHaveEnoughBass]

This is making me more confident in my hunch that the F6B/S is actually the best of the bunch; it's sealed enclosure + internal high pass means it never reaches the xmax and it shows in distortion where it outperforms all except the silly priced purifi variants

Yes it needs a sub but IMO they all do and the little sealed beaut has a natural roll off that integrates perfectly without need for an AVR or such managing a high pass

 

[Michael Kohler]

The C6B is, in my opinion, an interesting loudspeaker to look at from two different perspectives.
On its own, it is an excellent example of what can be achieved with a well-engineered passive two-way loudspeaker. The engineering, driver integration, crossover design and measurements are already there, packaged into a relatively small enclosure. There is no need to reinvent something that has already been done properly.
But I think the C6B becomes even more interesting when you stop thinking of it simply as a complete full-range loudspeaker.
The first approach is to use it exactly as it is: a conventional two-way loudspeaker. This gives you a relatively compact, simple and very capable system.
The second approach, and the one I find particularly interesting, is to add two subwoofers underneath the main loudspeakers and allow the C6B to concentrate more on the midrange and treble.
This is not necessarily about trying to get more bass. The real advantage is to remove some of the low-frequency workload from the mid-woofer. Once the subwoofers take over the lower frequencies, the main driver no longer has to simultaneously operate as a woofer and a midrange driver over such a wide bandwidth.
That gives you a much more flexible system.
The important part is that the crossover between the C6B and the subwoofers does not have to be treated as an arbitrary fixed point. Depending on the room, listening distance, subwoofer capability and personal preference, you can experiment with the crossover frequency and level and find the combination that works best in the particular system.
You can also adjust the subwoofer output independently, rather than trying to make the main loudspeaker do everything. In other words, the C6B can remain the carefully engineered, measured part of the system, while the subwoofers give you another degree of freedom in dealing with the room and the lowest octaves.
And this leads to the second important point: multiple subwoofers.
Rather than relying on a single subwoofer and trying to place it at the "perfect" position, I would use the general approach advocated by Dr. Geddes regarding multiple-subwoofer systems. The idea is not simply to produce more bass, but to use multiple low-frequency sources to excite the room differently and reduce the severity of the inevitable room-related peaks and nulls.
This is, for me, one of the biggest advantages of the concept.
The lowest frequencies are where the room becomes a major part of the loudspeaker system. Below the transition region, what we measure at the listening position is influenced heavily by room modes, boundaries and the interaction between the loudspeakers and the room. A conventional stereo pair trying to reproduce the entire bass range can therefore leave us fighting the room rather than simply listening to the loudspeaker.
With two properly positioned and integrated subwoofers, we have another tool for dealing with this problem.
So, for me, the most interesting way of looking at the C6B is not necessarily as "a small two-way loudspeaker that needs subwoofers." I see it almost the opposite way:
It is an exceptionally well-engineered compact two-way loudspeaker that can form the upper part of a much more sophisticated modular system.
You get the benefits of the existing engineering and measurements in a small package, while the low-frequency section can be separated from it and optimized independently.
That gives you a system with considerably more flexibility than a conventional full-range loudspeaker. You can experiment with the subwoofer crossover, level and placement, while the C6B continues to do what it was designed to do.
For me, that combination — a high-quality compact two-way plus two properly integrated subwoofers — is potentially the sweet spot between simplicity, performance and flexibility.
It also follows a principle that I think is often overlooked in high-end audio: there is no particular virtue in forcing one loudspeaker driver or enclosure to reproduce everything from the lowest bass to the highest treble if the system can be divided into more manageable tasks.
Let the C6B do the part where its engineering is strongest, and let the subwoofers deal with the part of the spectrum where the room becomes the dominant problem.
That, in my opinion, is a very compelling way to build a system around the C6B

Hello Shoba, thanks for your contribution. I think you hit the nail on the head, as we would say in Germany.
A 2 plus 2 system consisting of 2 high-quality bookshelf speakers, combined with 2 subwoofers, brings first-class sound results that large floor-standing speakers usually don’t achieve.
I would choose the bookshelf speakers in an active version, though. They sound even better than passive ones and aren’t more expensive. And I would go for the two subwoofers as sealed subwoofers; they’re better than the ones with bass reflex ports or passive membranes. And then you’d need a preamp with bass management, something like a miniDSP Flex would work well.
Such a combination will definitely sound better in most rooms than 2 big floor-standing speakers. A setup like this really sounds as good as hi-fi can sound nowadays.

 

[Dougey_Jones]

Seems like a perfect speaker if you plan on crossing it over around 80hz. I really want a pair for my near-field desktop setup, kinda pricey for this use case though.

 

[Azrael]

Just in case the SB Acoustic SB17CAC35-4 has been used: what does it actually sound like when the compliance of the suspension is the limiting factor for a clean Xmax and that limit is exceeded? With the driver in question, that would only be 2.8 mm.

I’m not the first person in this thread to point this out, but I can’t quite remember who was the first. *edit*: It was @dfuller.

Perhaps I was a bit too quick to blame the passive membranes for one or two issues, even though there isn’t much to suggest that their Vd is sufficiently large.

@amirm: Quite apart from that: could you please also show the impedance response for passive speakers? Such diagrams are already quite informative.

 

[MZKM]

Reserved.

 

[dfuller]

Just in case the SB Acoustic SB17CAC35-4 has been used: what does it actually sound like when the compliance of the suspension is the limiting factor for a clean Xmax and that limit is exceeded? With the driver in question, that would only be 2.8 mm.

This would be a question for someone like Lars @ Purifi. I bet there are some white papers on their site about it - let me take a look.

 

[ShadowFiend]

While I don't disagree with the first paragraph, I would say that max SPL and distortion are two sides of the same coin. Max spl at low frequencies is a function of displacement. To put it another way, I can reduce any of your objectionable IM and HD by lowering the drive level, since nonlinear distortion is level depenedent, right. I mean, distortion isn't a problem at, say, a listening level of 75 dB. So again, max spl is limited by HD and IM products. The same problem expressed in a different way.


So again, outside of the LFX problem with this unit, it can't really be faulted. All you have to do is as Shoba mentioned (and I had mentioned in an earlier post) to "fix" this unit, if you think it needs a fix, is to fix the low frequency limit with a pair of low frequency drivers. Easy enough to do with two bass modules, dsp, two additional channels of amplification. You get the additional benefit of being able to add some active LF room correction. Since, well, your room may not fit the "average" room that is used in Olive's studies to generate in room curves... There are limits to applying these study results, as good as they are. (And, well, they are probably the most objective data we have!)

No, maxSPL and distortion is related only. Max SPL is the maximum sound the driver can produce before getting damaged. It is the product of force factor (Bl) of motor, the withstanding of suspension system, the voice coil. The driver with big voice coil, strong motor, big cone area, strong suspension is normally the one with high max SPL but it does not guarantee low distortion, especially in lower SPL in midrange if the motor and surround is not optimized for low distortion.

I do not agree that the LFX problem can easily be fixed. Theoretically, it can be solved in the way you and Shoba mentions, but that is in theory. In practice, incorporated subwoofers to speakers is not an easy process technically. Simple low-passing subwoofer and high-passing main speaker is likely a disaster without measurement. And measuring requires knowledge, patience and time and I do not expect a majority of customers have that. Some automated bass management software can help but they cost money also.

IMHO, the product should be evaluated based on what it offers direct out of the box, without any addons or special knowledge. And C6B is a good product, even great for the money, but fall shorts in an important area.

But I don't see how you seem puzzled by the "narrow directivity" design choice and come to the conclusion you did. Really, this has more of a middle of the road directivity curve in terms of slope. Not as wide dispersion as a small WG setup, but much more dispersion than, say, a prosound two way with a 12 woofer and giant horn.

And if you look at the importance of the parameter weights in Olive's papers, listener preference is only weakly predicted by the actual slope of the DI curve, as opposed to the low frequency extension and smoothness of the on axis and power response curves as shown by the importance of the NBD and LFX parameters. The actual slope of the DI curve isn't in the predictive model.

Meaning there is no clear winner in terms of what's the "perfect slope" for the DI curve. I prefer a slightly wider dispersion shape to the DI curve. But, so what? My preference isn't better from the model data. You may prefer a different slope to the DI curve as well. But you can't generalize that your preference is better for anyone else. At least, not from the available study data.

I do not puzzled by the "narrow directivity" design choice. What I want is put a notice that while the measured performance of C6B is great in midrange/treble area, it is not guarantee that every person will like it if wider directivity is what he/she prefers

 

[amirm]

@amirm: Quite apart from that: could you please also show the impedance response for passive speakers? Such diagrams are already quite informative.

Oh, no, I measured it but forgot to post it. I am in China with no access to my NAS so have to add it in when I get back. Sorry about that.

 

[amirm]

I do not puzzled by the "narrow directivity" design choice.

Directivity is not "narrow" but narrower than average.

 

[RickS]

…@amirm: Quite apart from that: could you please also show the impedance response for passive speakers? Such diagrams are already quite informative.

As a placeholder, here is one from AsciLab’s thread (phase will apparently have to wait for Amir’s)…

 

[markk]

No, maxSPL and distortion is related only. Max SPL is the maximum sound the driver can produce before getting damaged. It is the product of force factor (Bl) of motor, the withstanding of suspension system, the voice coil. The driver with big voice coil, strong motor, big cone area, strong suspension is normally the one with high max SPL but it does not guarantee low distortion, especially in lower SPL in midrange if the motor and surround is not optimized for low distortion.

I do not agree that the LFX problem can easily be fixed. Theoretically, it can be solved in the way you and Shoba mentions, but that is in theory. In practice, incorporated subwoofers to speakers is not an easy process technically. Simple low-passing subwoofer and high-passing main speaker is likely a disaster without measurement. And measuring requires knowledge, patience and time and I do not expect a majority of customers have that. Some automated bass management software can help but they cost money also.

IMHO, the product should be evaluated based on what it offers direct out of the box, without any addons or special knowledge. And C6B is a good product, even great for the money, but fall shorts in an important area.



I do not puzzled by the "narrow directivity" design choice. What I want is put a notice that while the measured performance of C6B is great in midrange/treble area, it is not guarantee that every person will like it if wider directivity is what he/she prefers

Without getting too far into arguing, nonlinear distortion in a loudspeaker driver is mostly a function of displacement in the form of displacement related nonlinearities in Bl, K, and L which are all a function of x. The only other notable nonlinearity is the inductance variation with current, L(i). (Now this isn't strictly all, but good enough for modeling).

I will concede that in the higher end of any drivers frequency range distortion is less related to displacement and other factors come into play. Higher quality drivers may have less distortion than lesser drivers d/tdesign choices so the relation between max spl, displacement and distortion are not as related as would be the case in the lower end of a unit's operating range.

As DFuller noted above, the driver (if it is that SB) does very well on measured Klippel nonlinearities higher up in frequency as the strain of displacement subsides.

I would argue though, as a practical matter, in a 5-7" drive unit, like this one, max SPL is indeed limited by displacement and a very good surrogate for distortion.

I mean, what do we see, poor distortion numbers under 100 hz as distortion rises and displacement rises. As would be the case for virtually any two way unit with a 5-7" LF driver, fed a full range signal down to 30 hz, whether helped out by any variation of a mass loaded reflex box of your choice. I'm not at all picking on this loudspeaker. It's just not possible for any two way with this Sd to generate undistorted bass at signficant SPL's d/t displacement related distortion. You could upgrade to a Purifi mid woofer, get a lower midrange distortion pattern of probably dubious audibility, but the reality is that the Purifi woofer would only likely give you an additional 3 dB of headroom (my guess, might be a little more, but doubt much more) before you get similar displacement limited distortion numbers.

You are correct that that it would not be easy to add two LF units and DSP correct them. I would not recommend this if you don't have measurement gear and haven't spent some time thinking about and designing crossover units. Definitely not a beginner project. But a lot of us have been designing, measuring and modeling for quite some time so it would not be a particularly insurmountable challenge.

 

[boomboom]

People keep mentioning subwoofers for this but amir noted that his bass heavy tracks sound superb except some extreme cases, how relevant is the measured distortion in real life?

 

[Darkatomz]

IMO, the C6B was the first passive bookshelf speaker that I would say had a moderate, maybe 'adequate' amount of bass (yes, distortion was noticable at high SPL), but if you want any kind of clean reproduction below 100Hz (which is what bass is...), you will always need a dedicated sub.

 

[markk]

People keep mentioning subwoofers for this but amir noted that his bass heavy tracks sound superb except some extreme cases, how relevant is the measured distortion in real life?

I don't mean for my comments to imply that these are somehow deficient in bass. My beef is more that all two way units with a 5-7 woofer really can't play at realistic volumes. But "realistic volumes" are in the eye of the beholder. In a moderate room, moderate levels, I'm sure they are excellent. And for the price, really quite outstanding.

Plus, if you decide you don't like them, I suspect they will have very good resale value. They're a known quantity. It did occur to me to just buy three of these and mate them with low frequency units for a front three setup. But I've already bought the drivers to go down the diy path, so, oh well...

 

[ShadowFiend]

@markk
While I agree with you that at lower frequency and high volume, SPL is more related to displacement but that it is not an only factor. A great example is SW34SWPL and SB34NRXL from SB Acoustics, both are 12" driver, near the same Sd, same manufacturer, same 3" voice coil but if you see the measurement of distortion of them by member IamJF in diyaudio, the SB34NRXL has better distortions at both 85dB and 95dB SPL in the area of 40 Hz up. On range of 40-80Hz and no high pass filter, at 85dB SPL, SB34NRXL has THD of 0.8% while SB34NRXL has 3-4%. At 95dB SPL, SB34NRXL has THD of 3% while SB34SWPL has 8% THD. SB34SWPL has longer mechanical stroke and very stiff surround so it can produce more max SPL but THD is much better on SB34NRXL. The optimized cone, surround and motor has also big impact.

Back to 5-7" driver, I also agree that max SPL is also limited due to compression, but there are a audible different within this limited range. I know it because I also design speaker for myself, and have direct experience with several 6-7" drivers including SB17CAC and Purifi PTT6.5X. While great as a midrange driver, bass quality of SB17CAC is not up to task compared to better driver like PTT6.5X, 18W/8531, 18WU/8741, WF182BD09, even sound less impressive than 18W/8434.

You and I, as many ASR members, have enough experience and knowledge to incorporate subs to bookself speaker, but average customers of this product don't. They will only see a glowing review in the webpage, consider it as a perfect purchase, buy it then use it out of the box without subwoofers. That is why I think normal buyer should not rely on the IMHO "with-subwoofer" score when purchasing speaker, and rate this C6B as "Fine (happy panther)", not "Great (golfing panther)" personally.[/USER]

 

[Zagato]

I have been following this thread with interest, but for all the advanced technology employed I'm sure that most people, listening to music in their own home, would not be able to distinguish this speaker from the excellent Revel M106 released 13 years ago and about which Amirm concluded his review by saying "The Revel M106 is one of the most perfect bookshelf speakers I have heard."

Revel M106 Bookshelf Speaker Review

This is a review and detailed measurements of the Revel M106 bookshelf speaker. It was kindly purchased and drop shipped to me. It is not a new sample but came to me with full packaging and protective wrapper. The M106 costs US $1,000 each or $2,000 for a pair. It is only sold through dealer...

www.audiosciencereview.com

I know this speaker is no longer made but my main point is that we already reached perfection 13 years ago.