Fosi Audio Box X5 Phono Preamp Review

[krabapple]

"Component of the formula"? It's just two components, THD and noise. Generally, they are not measured separately. And THD is (largely) irrelevant for phono stages. And, as has been known for years, phono stage measurements of a MM stage without a cartridge connected are also basically irrelevant. This is particularly true when you're measuring bargain bin products and cannot trust that the designer did not use a completely inappropriate opamp. In the words of someone else here who has measured this sort of thing extensively, the selection of the input opamp used in this device was "incompetent." In real life, it will never perform as measured. That it is anywhere close to the top of the "rankings" is either due to this incompetence (at best), or purposeful deception.

LOL, OK!

In the end, there are not enough measurements (generally) to fully characterize the phono products measured, plus they are not performed in a way that matches real life, so the measurements just aren't that useful except for sorting out the real junk that has obvious problems other than SINAD. You're never going to use the measurements conducted here to actually tease out a top performing unit, because 1) they are not nearly thorough enough, and 2) are not conducted under real-world usage conditions. I am not the only one who wishes those charts would go away, because they look an awful lot like "rankings" and probably result in uninformed or underinformed people buying things that don't deserve to be near the top of any "ranking". And who can blame them? The impression given is that it's a good product, when it's merely adequate, at best.

LOL, OK!

That said, the Cambridge uses an NE5532 input op-amp. I had to waste a bunch of time on a YouTube video to figure that one out, so you're welcome. That's a proper choice, probably did not allow it to "cheat" like this Fosi on the SINAD measurements, and in real life and actual use connected to a real phono cartridge there is every reason to believe it would outperform the Fosi by a good margin. That it was designed by competent British engineers with (presumably) lots of experience with phono stages also suggests it will be better. At the current $200, which to buy is a no-brainer, if you're obsessed with having "top of chart" performance. Or just get a Schiit Mani 2. The Schiit is a far safer choice that costs a few bucks more.

Personally, I would never pay money for this Fosi since it has no rumble filter. That also goes for any other phono stage. Why pay money for something that is probably no better than and offers no more features than (excepting MC compatibility) what Denon/Marantz has put in all of their receivers basically for free for years? I guess if you don't have a receiver to connect it to... Still, I often wonder how many people buy something like this thinking they're getting an improvement when, well, they're not. Denon/Marantz just keeps using that same phono stage with its active RIAA over and over. And it's pretty good. So is the Fosi, but for $35 more you can get something that actually has useful features. There's just no good reason to buy this thing when a Mani 2 exists. Heck, I don't care. Even take a flyer on an $80 Aiyima T3 Pro. It can't be much worse.

My use case is digital transfer of vinyl, I can apply a rumble filter in software later.

 

[Heinrich]

... also suggests it will be better. At the current $200, which to buy is a no-brainer, if you're obsessed with having "top of chart" performance. Or just get a Schiit Mani 2. The Schiit is a far safer choice that costs a few bucks more.

Personally, I would never pay money for this Fosi since it has no rumble filter. ...

Phono is a topic that still ventilates a lot of misunderstandings. SINAD from a certain threshold on may not pay off due to the inherent limitations of the media. The obsession with illusionary data is due to its readily availability compared to a similarily competent power amp. As can be seen in the list of pickup measurements, distortion at a mere 5kHz would easily exceed 10% (ten), while only the very best get below 3%, the expensive ones. Would you expect that hefty malus from choosing a humble elliptical over a Shibata stylus? There you are, while the Shibata as such won't guarantee excellence either.

In short, pick your poison by taste. Phono is a matter of subjective choice alone. Or would you argue that 3% of HD is better than 10%? At such figures counting doesn't mean anything no more. All schema in discriminating by data is blown up, too bad anyway. And that's for brand new records at the outer grooves.

On rumble, do you know that the pickup can show more or less of that rumble - yeah the pickup has a damping on its own. It works, measurement shows. There is a counter force needed, don't choose a too light tonearm. Etc pp, so many variables--again.

Considering all that, does it pay to select for the best, or for some competent compromise? A few bucks more, you say. Pay, pay, but for what improvement? Better take vinyl for what it is. A rational decision making will see the flexible X5 as an option. It was said before: yes, used with MM is loses some dB of SINAD, because it is optimized for MC. But even with MM it is in the good middle field. It will not make itself known by noise, granted. Rumble doesn't ever overload the device, and can be filtered down the chain. Every other is plain excellent, and for absolutely sure orders of magnitude above any need.

 

[mike70]

Phono is a topic that still ventilates a lot of misunderstandings. SINAD from a certain threshold on may not pay off due to the inherent limitations of the media. The obsession with illusionary data is due to its readily availability compared to a similarily competent power amp. As can be seen in the list of pickup measurements, distortion at a mere 5kHz would easily exceed 10% (ten), while only the very best get below 3%, the expensive ones. Would you expect that hefty malus from choosing a humble elliptical over a Shibata stylus? There you are, while the Shibata as such won't guarantee excellence either.

In short, pick your poison by taste. Phono is a matter of subjective choice alone. Or would you argue that 3% of HD is better than 10%? At such figures counting doesn't mean anything no more. All schema in discriminating by data is blown up, too bad anyway. And that's for brand new records at the outer grooves.

On rumble, do you know that the pickup can show more or less of that rumble - yeah the pickup has a damping on its own. It works, measurement shows. There is a counter force needed, don't choose a too light tonearm. Etc pp, so many variables--again.

Considering all that, does it pay to select for the best, or for some competent compromise? A few bucks more, you say. Pay, pay, but for what improvement? Better take vinyl for what it is. A rational decision making will see the flexible X5 as an option. It was said before: yes, used with MM is loses some dB of SINAD, because it is optimized for MC. But even with MM it is in the good middle field. It will not make itself known by noise, granted. Rumble doesn't ever overload the device, and can be filtered down the chain. Every other is plain excellent, and for absolutely sure orders of magnitude above any need.

... and do you think an amp or dac with 95dB SINAD will be audibly better than other with 80dB?

SINAD shows better engineering, but after certain threshold, is better to check for features, construction, price.

I use vinyl since decades and with a decent TT I don't listen to any rumble or surface noise from my listening position. I don't know if many people talking about analog have real experience with a decent analog system or they talk based on grandpa experiences. Or, maybe I'm just a lucky guy.

 

[Heinrich]

... and do you think an amp or dac with 95dB SINAD will be audibly better than other with 80dB?

SINAD shows better engineering, but after certain threshold, is better to check for features, construction, price.

I use vinyl since decades and with a decent TT I don't listen to any rumble or surface noise from my listening position. I don't know if many people talking about analog have real experience with a decent analog system or they talk based on grandpa experiences. Or, maybe I'm just a lucky guy.

Vinyl playback is structurally non-transparent. The medium has its limitations, and there is no way to circumvent these. The errors are gross. So much so, that the listener's evaluation is aesthetical, not hierachical. There's no better by numbers, because we do not observe a threshold of audibility anymore. The errors in vinyl are above that threshold anyway, by orders of magnitude!

To assume that like 80dB of SINAD pushes all errors below the threshold of audibility is a comparatively lame stance. With vinyl we are forced to evaluate the severity of clearly audible error in regard to subjective assessment. I do not know if such has ever been done in the analog realm. AT least it is individual.

Courtesy of a member we, for instance, are invited to compare the objectively vast difference in high frequency distortion for different stylus shapes. A silly cheap conical stylus versus an elaborated costly sharper shape. Many thanks to the contributor!!

Dropbox

www.dropbox.com

Dropbox

www.dropbox.com

I, personally, don't find a huge difference - all this crackling and sibilance distracts me anyway. That's why I said: "Chose your poison by taste."

 

[krabapple]

Recent replies here have me thinking of Donald Rumsfeld's famous word assemblage: ...there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns—the ones we don't know we don't know.

Also have me thinking: vinyl people are strange

 

[ryanmh1]

A few bucks more, you say. Pay, pay, but for what improvement? Better take vinyl for what it is. A rational decision making will see the flexible X5 as an option. It was said before: yes, used with MM is loses some dB of SINAD, because it is optimized for MC. But even with MM it is in the good middle field. It will not make itself known by noise, granted. Rumble doesn't ever overload the device, and can be filtered down the chain. Every other is plain excellent, and for absolutely sure orders of magnitude above any need.

I don't think we disagree, generally. My point was to respond to someone who felt this was a great value and was (probably) not able to fully apprehend the technical reasons that much of the perceived "value" is a smokescreen. This "designed to the (poorly designed) test" product gives a false sense of security that it has been competently designed, when exactly the opposite is true, in certain respects. And I do not believe for a minute this was "optimized for MC"--at least not intentionally. No one "optimizes" a $100 box to work with cartridges that start around $400, and go up precipitously from there. My "great value" Eroica LX is now a ridiculous $900. But, to my point, look at the next comment below yours: "SINAD shows better engineering, but after certain threshold, is better to check for features, construction, price." Ironically, the first half of this is not necessarily true with phono preamps as @pma has amply demonstrated to all who care to listen...

We'll agree to disagree regarding the need for rumble filters. Suffice to say that with all the ported speakers out there, I think you need one. Ported box designs have virtually no damping for the cone below the port tuning frequency. It will just flap away wildly, which is just dumb to allow to occur.

 

[ryanmh1]

That said, the Cambridge uses an NE5532 input op-amp. I had to waste a bunch of time on a YouTube video to figure that one out, so you're welcome. That's a proper choice, probably did not allow it to "cheat" like this Fosi on the SINAD measurements, and in real life and actual use connected to a real phono cartridge there is every reason to believe it would outperform the Fosi by a good margin. That it was designed by competent British engineers with (presumably) lots of experience with phono stages also suggests it will be better. At the current $200, which to buy is a no-brainer, if you're obsessed with having "top of chart" performance. Or just get a Schiit Mani 2. The Schiit is a far safer choice that costs a few bucks more.

I have to correct this. I finally found close-ups of the PCBs in the Cambridge units. Right at the input there are four discreet transistors Q1 to Q4 in the Solo. In the Duo, each of the moving coil and moving magnet circuit paths have stacks of what appear to be parallel discreet transistors. Why there are more than in the Solo, and why the circuits appear different, I don't know. Without a schematic (and since these are pictures of tiny surface mount devices) it's just not possible to tell exactly what is going on, but this all tends to suggest Cambridge is still using a heavily paralleled (to reduce noise) discrete transistor input. I can't imagine why you would need all those discreet transistors in a front end if that wasn't what you were up to. Another clue is that they also used discreet inputs on the previous 651A phono (which was thru hole), but put it in a little metal box conveniently labeled "Discrete Phono Input". They also appear to have some or another implementation of a split RIAA compensation which is partially active and partially passive, since they pull off an extremely good 90mV overload all the way to 10kHz, which then drops back a bit at 20kHz, but still more than adequate. Then there's a properly implemented rumble filter which is "always on", and perfectly fine since it's flat down to about 25Hz, after which it drops like a rock.

That's how you build a phono stage! Wow. It was bugging me that Cambridge was getting the performance they were out of some 5532, and they're not. They've done much, much more. And all for $200 or $350, respectively? I'm noting that only to compare it to this Fosi, which can't even hold a candle to that sort of engineering and value. We already know the numbers Fosi stacks up are a fiction. But Cambridge appears to have actually done it, and in one of the more difficult ways possible by actually engineering it--and without any obvious measured mistakes--instead of just implementing something or another of off some datasheet somewhere.

If you're going to spend over a hundred bucks on a phono stage, why not just spend the extra money to get something truly great? I would actually take pride of ownership in that unit (which I soon will since I've now talked myself into buying one). I was starting to despair thinking there wasn't an semi-affordable phono stage out there that wasn't full of mistakes. As it turns out, there is. Cambridge, and it was pretty much staring me in the face the whole time. That's what you expect when something has shockingly low noise figures. But as the Fosi proves, it ain't always when you get with some of this stuff.

 

[mike70]

Vinyl playback is structurally non-transparent. The medium has its limitations, and there is no way to circumvent these. The errors are gross. So much so, that the listener's evaluation is aesthetical, not hierachical. There's no better by numbers, because we do not observe a threshold of audibility anymore. The errors in vinyl are above that threshold anyway, by orders of magnitude!

To assume that like 80dB of SINAD pushes all errors below the threshold of audibility is a comparatively lame stance. With vinyl we are forced to evaluate the severity of clearly audible error in regard to subjective assessment. I do not know if such has ever been done in the analog realm. AT least it is individual.

Courtesy of a member we, for instance, are invited to compare the objectively vast difference in high frequency distortion for different stylus shapes. A silly cheap conical stylus versus an elaborated costly sharper shape. Many thanks to the contributor!!

Dropbox

www.dropbox.com

Dropbox

www.dropbox.com

I, personally, don't find a huge difference - all this crackling and sibilance distracts me anyway. That's why I said: "Chose your poison by taste."

OMG, the sibilances in the CB file are unbearable ... the ML file is miles ahead better.
At least for my ears

 

[Heinrich]

That's how you build a phono stage! Wow. It was bugging me that Cambridge was getting the performance they were out of some 5532, and they're not. They've done much, much more. And all for $200 or $350, respectively?

Thanks! You illustrate quite convincingly the relevance of my previous criticism.
Namely in celebrating miniscule objective improvements by vast complications which don't match the need, while intentionally not knowing the need**, but all for relatively low cost as it is just and only a riskfree preamp board. Ignoring the degradation down the chain to the speakers - consider to design a power amp, for instance, that meets the specs of the glorified preamp in regard to HD and overdrive recovery and more. Won't? Well, what is the preamp worth then? And just again we missed the 10% (ten) Harmonic Distortion of even the most expensive cartridges with a quite humble signal in the grooves--new, not worn out grooves.**

I would actually take pride of ownership ...

That's more about social engineering than electrical engineering, me thinks.

OMG, the sibilances in the CB file are unbearable ... the ML file is miles ahead better.
At least for my ears

I leave it to you to evaluate the relevance of the frictaives' sibilance and additional crunshing noises with and for your ears and mind. Thing is, when I'm listening to vinyl, which I do occasionally, these distractions are just there with whatever stylus shape. I cannot un-hear them. Then the amount of the percentages doesn't matter no more--it is just a fail. It distorts the experience regardless. In order to not disrupt the flow I have to train myself to igore it actively. As an ol' vinyl guy I can and do. Hop over it, no mountain too high ... ;-)

We'll agree to disagree regarding the need for rumble filters. Suffice to say that with all the ported speakers ...

That's all too true for one. But, ported speakers rarely are designed to match the content of modern, digital recordings. A tuning at 40Hz for the better, 30Hz for the very best, 50Hz and above for all the rest, the un-loading below tuning is a general problem. From a system engineer's perspective the problem is attached to the ported speaker, not to the vinyl record. Hope you get my argument.

Only for completeness, the rumble won't exceed the preamps capabilities, it will not be overloaded by it**. But the cartridge maybe. If rumble leads to excessive wobble that problem has to be solved with the cantilever design, or by damping the arm, or by simply adding a stabilizing brush as Shure did.

**Could show measurements, but who would take note?

 

[Mnyb]

The so called rumble filter is also there because tone arm resonances are real , you can simply not trust a vinyl system in the bass it should be bandwidth limited .
It's not just because the warps the whole player & arm etc are a jello at some frequencies ?

I think it's optimistic to try to listen organ music with 16Hz fundamentals on vinyl you sure get something from your player but how much really originated in the groves ?

 

[Heinrich]

Spectrum (peak hold) taken from an old LP, Pink Floyd's Animals, the Dogs piece. No strings attached, plain out of the Fosi X5. The 30Hz component is an artifact from the individual record--guess where it originates in, I've no clue, not seen in any other--the arm resonance at 13Hz isn't that prominent, right? And I proved it to be the fundamental of that mechanical system.

What's more interesting is the very sharp cut at 50Hz, see? And this record was deemed to be very HiFi back in the day, showing some challengeing heft. The picture repeats with classics, even disco**. The medium is not 'limited'. It is just bad in its own right. So, please think it over, what are you all talking about? DO the measurements, derive reasonable conclusions.

Some may be trapped still in the old ages of not knowing, but buying instead, big money trying to polish the BS.

I for myself won't abandon, or even digitize my collection. I keep my deck in working condition, but that was it. On the Fosi X5 I discussed its merits and a single, easily ignorable letdown above in some posts. With MM it will show like 6dB more noise than an MM optimized design, but STILL will be a top middle class performer with no other caveats. At a price well below those middle class contenders.

** real low bass by today's standards would need too much space on the record reducing playing time severely. Read the literature.

 

[mike70]

I leave it to you to evaluate the relevance of the frictaives' sibilance and additional crunshing noises with and for your ears and mind. Thing is, when I'm listening to vinyl, which I do occasionally, these distractions are just there with whatever stylus shape. I cannot un-hear them. Then the amount of the percentages doesn't matter no more--it is just a fail. It distorts the experience regardless. In order to not disrupt the flow I have to train myself to igore it actively. As an ol' vinyl guy I can and do. Hop over it, no mountain too high ... ;-)

i understand, but that "noises" you mention ... are inherent to the record status. Without the proper care and cleaning it can be noisy as you wish.
When you have records in good shape, that noises aren't audible from the listening position ... and the distortions from conical styluses are far more evident compared to a fine line stylus.

I understand also, you're tired of that (or bothers you too much) and with all the others "no no", you don't like the format, and it's ok.
For people that likes the format (maybe we're crazy, yes) that facets doesn't "count" and the difference between a conical and a fine line are evident ... adding that lifespan is something like 4x-5x more and the pressure on the groove is far less, i think is a no brainer.

 

[Heinrich]

i understand, but that "noises" you mention ... are inherent to the record status.

I don't think so. The noises I mean are intermodulation products generated by tracking errors generated by high volume high frequency fricatives. It's not the record status, as I play 'wet' using rubbing alcohol.

I understand also, you're tired of that (or bothers you too much) and with all the others "no no", you don't like the format, and it's ok.

I said, that what you use for vinyl playback is a matter of taste, not numbers. Vinyl is inherently too bad to be ranked objectively. I never said the format was unusable--to the contrary. I use it. I bought the Fosi X5 for a purpose: getting rid of my bulky A/B amp, and still having need for a phono pre, go figure!

... the difference between a conical and a fine line are evident.

Yep, they are evident if you focus on that failing that even the finest styluses show. It is not more or less, it is the plain fact that it is a fail. In some kind it is digital: working or not and nothing in between. The fail is so evident--again with ALL stylus shapes, that it doesn't matter by hwo much it fails. It just stands out in the playback and has to be mitigated not by ever more costly stylii, but by a state of mind, actively ignoring the fail (like with klicks n' pops) as to keep the flow.

That's the "magic" of vinyl. Active engagement, not the handling, but the state of mind.

Examples:

A mere mono 2.5kHz at 33cm/s - see the asymmetries, and how the odd, hilariously distorted shape never repeats with exactness:

The (effing competent, modern) stylus in overdrive, 2.5kHz, 45cm/s, short before skipping the groove

Nearly the same picture at 5kHz, 11cm/s, a littele bit worse

How is that to like?

But we get into the usual hamster wheel. "If you measure the vinyl, you don't like it. Hence your argument is invalid." The twists with the 'noises' above was just a preparation. As I said, better not measure, believers!

 

[mike70]

i know the measurements are bad, and the distortion is higher, blah blah ... but i think we're talking about mars and venus.
Everytime i try to tell you that vinyl in a decent system sounds good you start with the graphs and measurements everybody knows.

You don't need to convince me about vinyl inferior facts. I know it so well.
What i'm telling you, is with a decent analog system, records / fine line stlylus in decent shape, i don´t listen to any audible distortion, even i can compare to digital side to side with headphones and i can't perceive a "high distortion".
That's all.

With digital, i can perceive some tiny details in high frequencies more pronounced or sometimes a tiny better decaiment in cymbals, as an example, but less "distortion" ... no.
And i close my comments with this, if you can understand rightly what i wrote, i'm glad ... in other way, ok, go on.

 

[Heinrich]

You don't need to convince me about vinyl inferior facts. I know it so well.

They are catastrophic, actually 8)

What i'm telling you, is with a decent analog system, records / fine line stlylus in decent shape, ...

That's my caveat: all these criteria are useless. What is 'decent' by the way. Is it such that ...

... i don´t listen to any audible distortion, even i can compare to digital side to side with headphones and i can't perceive a "high distortion".

So, for the sake of *not* argueing, it is your subjective perception. My point: stop praying by the book of measurement. It's orders of magnitude too bad anyway. Relax and listen, it's better just because it's so bad! (And stop buying expensive gear.)

Add.:
In order to claim honesty, here's another on "need highpass, hence Fosi's is not-so-good". But that's it--no need to expose myself more in terms of 'scientific'.

A quite audiophile record from the past, namely Eno/Byrne, watch the boom-boom using 43Hz and its 1st overtone, and not the least the plateau in the bass - very modern, very much demanding back then! Once with my Denon DP37-F using electro/mech damping of the tonearm, and once without; difference about 6dB, putting every SME 12" to shame ... Oh yes, it comes at the expense of elevated lower content, but that's just a little physics and math.

 

[ryanmh1]

I'm not sure what you're trying to prove with that other than the need for a rumble filter. And if the medium is so bad the equipment doesn't really matter except for how cheap it is, then the Art Precision Phono is still better. That's only $60 (so almost less than half the Fosi) has good overload, and a nice rumble filter. I bought one just now for grins. Plus, it has some buttons on it, a knob, blinky lights, a rumble filter, and some loading options. If you don't like the look, for $5 someone sells a new case you can print out for it. (Plus, I would just about guaranty (if someone worries about it) that the noise figures won't drop like a rock when a cart is hooked up because odds are it's just a 5532 or njm2068. Will report back in the proper thread.)

 

[Heinrich]

I'm not sure what you're trying to prove with that ...

I’m not sure who misunderstood whom.

... other than the need for a rumble filter.

A rumble filter, as discusse dpreviously, is nothing but blatant nonsense. So where’s the real issue?
The problem lies either with the cartridge or with the speakers, and it should be addressed there in a targeted and appropriate way. Look: a rumble filter does not help the speakers if they are being driven digitally (!) below their tuning frequency (unloading). Most would need 50 or higher as a cut-off, while the rumble type cuts off at 20. And the filter does nothing to help the cartridge stay in the groove. It’s just smoke and mirrors, as usual.

And if the medium is so bad the equipment doesn't really matter except for how cheap it is, then the Art Precision Phono is still better.

Equal, roughly. As you put it: "drops like a rock", now with MC.

That's only $60 (so almost less than half the Fosi) has good overload, and a nice rumble filter.

My Fosi took 95 all included (Europe). The artsy Art is about 99.

Will report back in the proper thread.

Thanks.

 

[DVinylfan]

Pink Floyd's Animals

Eno/Byrne

These are two of my favourite, most listened to and longest-owned records.
I'd use them for appraising a new piece of equipment in my system because I know the recordings so well, I think they sound great compared to most of my other records, and never tire of hearing them. Thanks for sharing the measurements.
The role of the phono preamp is a very interesting topic. I was seduced by the argument that the quality of the phono preamp is especially important, since it amplifies the signal by an order of magnitude greater (from millivolts to volts) than a pre- or power amp.
The logic of this still seems to hold, but the more I read here about well performing and measuring budget phono preamps the more I suspect I overspent on mine.

 

[ryanmh1]

A rumble filter, as discusse dpreviously, is nothing but blatant nonsense. So where’s the real issue?
The problem lies either with the cartridge or with the speakers, and it should be addressed there in a targeted and appropriate way. Look: a rumble filter does not help the speakers if they are being driven digitally (!) below their tuning frequency (unloading). Most would need 50 or higher as a cut-off, while the rumble type cuts off at 20. And

I'm not going to argue until you can make some sense. Instead, I'll lecture. You post a chart of a 42Hz fundamental with what appears to be a significant 12Hz rumble component. Depending on the slope of the filter, even a modest filter with a corner of about 20Hz could be expected to smash that down a lot. So, I quickly modeled up a small ported bookshelf speaker with a Focal midwoofer I had some specs for (around 3mm Xmax), and loaded it into a small box ported to 40Hz. Power handling is okay and the cone motion is fairly controlled until around 33Hz. Below that, it quickly turns ugly. At 12Hz, it can take almost nothing. At 20Hz, it can take about double the power (which is still is not much). 12Hz could destroy the woofer. Now, apply a second order filter with fc=25Hz. What was out-of-control, woofer destroying cone motion at 12Hz and 10W into the speaker becomes probably a non-event. That is still a bit too much for this tiny speaker, and some might argue a 30Hz corner might be better. But guess what? Some cheapo products like a Schitt designed for cheapo speakers like this offer just that--actually, an even higher selectable corner frequency, should you want it.

I think the Precision Phono is probably around a 20Hz second order. Even that would increase my little hypothetical speaker's power handling at a 12Hz rumble frequency from about .75W to 7W. Cone excusion is cut by about 70%. Since the rumble is a fixed component not really tied to the music, in acoustic terms, that's double the volume for the rest of the system (with a filter you say is too low and does not work). But, a 20Hz rumble filter works just fine. Why? There is nothing to suppress from 20Hz to around 35Hz. If you have this problem in the Fosi? Well, you're just screwed if you try to play loud. You can't turn up the music without blowing the woofers.

So, stop telling people rumble filters are "blatant nonsense". In my example, I just saved my speakers and kept on crankin' it and rocking by pushing a button you say I didn't need and would not work unless it was at 50Hz. While a third order filter at 20Hz would be ideal, or a second order at 30Hz, a second order filter (12db/oct) around 20Hz probably does get the job done even on small bookshelf speakers.

 

[EJ3]

I'm not going to argue until you can make some sense. Instead, I'll lecture. You post a chart of a 42Hz fundamental with what appears to be a significant 12Hz rumble component. Depending on the slope of the filter, even a modest filter with a corner of about 20Hz could be expected to smash that down a lot. So, I quickly modeled up a small ported bookshelf speaker with a Focal midwoofer I had some specs for (around 3mm Xmax), and loaded it into a small box ported to 40Hz. Power handling is okay and the cone motion is fairly controlled until around 33Hz. Below that, it quickly turns ugly. At 12Hz, it can take almost nothing. At 20Hz, it can take about double the power (which is still is not much). 12Hz could destroy the woofer. Now, apply a second order filter with fc=25Hz. What was out-of-control, woofer destroying cone motion at 12Hz and 10W into the speaker becomes probably a non-event. That is still a bit too much for this tiny speaker, and some might argue a 30Hz corner might be better. But guess what? Some cheapo products like a Schitt designed for cheapo speakers like this offer just that--actually, an even higher selectable corner frequency, should you want it.

I think the Precision Phono is probably around a 20Hz second order. Even that would increase my little hypothetical speaker's power handling at a 12Hz rumble frequency from about .75W to 7W. Cone excusion is cut by about 70%. Since the rumble is a fixed component not really tied to the music, in acoustic terms, that's double the volume for the rest of the system (with a filter you say is too low and does not work). But, a 20Hz rumble filter works just fine. Why? There is nothing to suppress from 20Hz to around 35Hz. If you have this problem in the Fosi? Well, you're just screwed if you try to play loud. You can't turn up the music without blowing the woofers.

So, stop telling people rumble filters are "blatant nonsense". In my example, I just saved my speakers and kept on crankin' it and rocking by pushing a button you say I didn't need and would not work unless it was at 50Hz. While a third order filter at 20Hz would be ideal, or a second order at 30Hz, a second order filter (12db/oct) around 20Hz probably does get the done even on small bookshelf speakers.

I would never play a record (since the mid 1970's) without this analog RUMBLE FILTER:
It's -1/2 dB at 20 Hz, -1 dB at 17.5 Hz, -2 dB at 15 Hz, -3 dB at 14 Hz, - 5 dB at 12 Hz and -10 dB at 10 Hz.