I am not quite understanding the benefit of cardioid (or dipoles) at low frequency rooms. I thought what we can not distinguish direct sound and room reflections at low frequencies and room modes play an essential part below the Schroeder frequency.
The main disadvantage any speaker which radiates out of phase backwards is that there needs to be a significant distance to the back wall. That is why I am not so interested in ripol designs
The main disadvantage any speaker which radiates out of phase backwards is that there needs to be a significant distance to the back wall. That is why I am not so interested in ripol designs
For mids, yes. But for subs, only the cancellation path-length matters even if somewhat close to a wall.
I once made an open baffle sub that had pretty good sound. But the shortest half-distance was maybe 3-4 feet and the longest maybe 6 feet or so, much bigger than those puny H-baffles. And the 15-inch driver resonance was just north of 20 Hz. The baffle was hidden under a table.
B.
Humm, it seems that MFB technology is surpassed by more efficient control systems.....
Sensor Control – Coda Audio
Sensor Control – Coda Audio
Sensor based feed back has the problem of time delay. Devialet developed a "feed forward" approach for specific loudspeakers based on measurements (including laser interferometry), SAM but I have not seen anything like that for subwoofers. It should have a much lower time delay than a feed back approach.
I don't see why not, it 'cured' everything wrong with this room/system, both of which................ hmm, it's been wiped clean, bummer: Home - Audiophile Nirvana
Found the speaker, which required significant digital XOs, DSP, but it was the room where DSP really showed its stuff: Compostela - Vintage Speaker Revival
GM
"MFB" is the usual generic term for ALL the ways of sensing speaker output and using negative feedback to correct it. The Coda Audio link falsely says the term applies to the very vintage and rather cheaply made Philips MFB speakers.... which were pretty great as minimal speakers in those days.
There are a dozen ways to sense the output of a speaker. Using an integrated accelerometer module glued to the cone dust cap being favoured today (and likely the "secret" method in the Coda Audio woofer).
But anybody wanting to know more about MFB benefits might have a peek at that write-up. Advocates of MFB especially cherish the plot showing how impulse response is improved compared to rumble-on tuned boxes.
Of course there is a "time delay" as Monteverdi says. But it occurs at the speed of light while the audio operates at the speed of sound. Pre-distorting a signal to correct speaker or room errors has some value, but unless you have a corrective feedback loop, you ain't got no feedback.
B.
Last edited:
In general everything is very confusing, especially the bold part.
I thought it was a GT error, so I saw the original in English.
And no, the word is distortion! That is, you say that the LF signal must be distorted before it leaves from the speaker (with MFB or whatever) to recover after some way what is lost but with the benefits of feedback ...... ?? ? I think it would have made more sense to use the word correction, that is, to adjust the intensity of the signal, or correct it in phase, in time, in whatever, but "distorting"? What would be the strictly technical sense of doing that? And how do I recognize that I cannot approach knowledge in the least to Einstein's theory of relativity, (which has even been questioned in some aspects in the modern era) as to discuss the speed of light here, (? ) neither about the speed of sound (I understand that whales have special sensors developed by mother nature especially for underwater sounds, but I do not want to divert the subject or make it even more confusing, at least for me ...), then , sorry, I see that I am not up to the necessary knowledge (as you also mentioned and warned) to discuss in this thread, perhaps in some other thread more accessible to the initiated) Anyway, I have seen a thread where you recognize your limitations on the subject yourself, but it is a few years ago, although we can all learn, because for that we are here, apart from the fun, it gives the feeling that it is something vertiginous your learning) so I prefer not to do something personal. I will not name it.
In another order of things, you have changed the epigraph of your posts, the current one causes me rejection, I prefer the previous one, I remember that I prayed something like you were on the theme "MFB" since 1957, when I was 7 years old . Now they are just "aspirations", go .... You, how old are you currently? Only for curiosity.
Last edited:
Do you understand why you are confusing ?
In bold what you say,here, what coda audio says :
Sensor Control – Coda Audio
HISTORIA
Aunque los modernos subwoofers de audio profesional están cargados casi todos de puerto o bocina, la idea del control de retroalimentación en los altavoces no es nueva. La primera patente fue solicitada en 1933 por Smythe y, a principios de los años 70, Philips desarrolló un sistema de altavoces llamado Motional Feedback (MFB), que era un sistema de retroalimentación para altavoces de alta fidelidad basado en un sensor de aceleración piezoeléctrica. Por diferentes razones, esta tecnología no tuvo éxito en el mercado de alta fidelidad. Hoy en día, algunas empresas de alta fidelidad utilizan la tecnología MFB en sus productos (Linn, SilberSand, etc.). Debido a limitaciones técnicas, especialmente a alta potencia, la tecnología MFB no era adecuada y nunca se ha utilizado en ProAudio.
La principal diferencia entre MFB y la tecnología controlada por el sensor de audio CODA es que mientras el MFB mide la aceleración utilizando un sensor piezoeléctrico, CODA Audio utiliza un sensor electrodinámico pendiente de patente, que mide la velocidad de la bobina móvil y ofrece las siguientes ventajas:
El acelerómetro piezoeléctrico es menos preciso, especialmente en excursiones altas, produciendo grandes cantidades de distorsión.
Los altavoces producen campos de CA magnéticos variables dependiendo de la posición de la bobina de voz, que es muy fuerte en controladores de audio profesional de alta potencia y alta excursión. Las fuentes de ruido externas perturban la funcionalidad del sensor piezoeléctrico. El sensor electrodinámico CODA Audio mide la velocidad de la bobina móvil con una tolerancia de 0.1% a 60 mm de recorrido. Está protegido contra fuentes de ruido externas y es preciso incluso a niveles extremadamente alto
So, you can clarify ?, many terms mixed here!
The sensor you call "accelerometer" is an electric piezo (do you remember the first phonographic capsules based on that principle? An electric piezo material generates electricity (P: E: a quartz crystal) when its structure is modified (it is compressed and / or dilates), that is not an "electrodynamic accelerometer" (Coda say´s), whose principle is the same as that of the speakers, you can attach a small sensor of that type to the cone, or even work with something much more sophisticated like using a double VC, something easy to build these days, isn't it? One coil moves the cone by the electromagnetic induction coming from the amplifier, and the other coil tests that movement and sends a signal to the amplifier to correct the detected anomalies.
Wow ! perfect !
And who knows what the anomalies will be without knowing in which environment (room) this artifact will work ???
Ohh, as I said, blah, blah, blah, none of this has proved useful to be mass produced by any major manufacturer.
Phillips left the MFB, that's what you say, so why was it? Explain to me, I want to know.
What Coda Audio says is motivated by commercial impulses and can't be trusted.
Mostly (but not all) MFB relates to the motion of the cone. It seeks to make the cone motion correspond more precisely to the music signal*. There are lots of ways of sensing cone motion. Philips' 1975 10-cent piezo crystal is one lousy way.
The only difference - electronically speaking - between acceleration and velocity is one capacitor, as anyone who knows Calculus 101 can tell you.
Because today's cone woofer drivers are a piece of stupid inadequate engineering, it follows that even the best corrective feedback loop will be challenged accordingly. Therefore, it has been difficult to sell systems to the general public that either have enough feedback to be helpful or which run without self-destructing long enough for the manufacturer to make it to Fiji and retire rich.
But, as a DIYaudio project.... absolutely ideal. "A hint to the wise, is sufficient"
B.
* it is left an exercise for those readers who think they know a whole lot about speakers to intuit whether making the motion of the familiar cone woofer closer to the signal helps or hinders the lower bass FR. You know who you are.
Last edited:
I think that the difficult thing is to transmit knowledge in an entertaining and understandable way without going into details that atomize the main topic to be discussed. At least in a forum of general interest, no university thesis or doctorate is being rendered here.
First, his proposal was to venture into the theory of spacetime to understand which is the best bass, (Question and objective of the OP) - now we must also enter Calculus 101 ...
There can be hundreds of imaginable ways to sense the movement of the cone, but possible to be practical and effective .... I have enough fingers left over with one hand.
Hello,
I need a little help please.
I use the SBA SB17NAC35-4 speaker for 100Hz - 2KHz. (3 ways design) in 6,5 liters internal volume.
I like their sound, the transients are perfect.
I want something with a little more details, microdetails do not satisfy me.
So, I want to replace it with another speaker; I'm thinking of the SATORI MW16PNW-4.
Do you think it is suitable for a 6.5 liter closed box?
Thanks in advance.
I need a little help please.
I use the SBA SB17NAC35-4 speaker for 100Hz - 2KHz. (3 ways design) in 6,5 liters internal volume.
I like their sound, the transients are perfect.
I want something with a little more details, microdetails do not satisfy me.
So, I want to replace it with another speaker; I'm thinking of the SATORI MW16PNW-4.
Do you think it is suitable for a 6.5 liter closed box?
Thanks in advance.
I never heared the direct servo subs, they are rare on this side of the ocean. So i can't judge those.
But of the subs i know, a ripole or a sealed box with an QTC lower than 0.7 and a low enough FS are the ones i think are the best systems for good sound. Both give (the illusion) the bass like it was intented, while ported or horns (any kind) and TL's distort the bass a bit. Mostly in a good way, but still...
But of the subs i know, a ripole or a sealed box with an QTC lower than 0.7 and a low enough FS are the ones i think are the best systems for good sound. Both give (the illusion) the bass like it was intented, while ported or horns (any kind) and TL's distort the bass a bit. Mostly in a good way, but still...
I had a servo controlled subwoofer.
It has very tight, percussive sound, with small distortions.
Comparable to Force-Canceling design.
Greets!
Please elaborate as it makes no sense to me as presented: "I want something with a little more details, microdetails do not satisfy me."
It models in Hornresp with a 0.96 Qtc, though can stuff it pretty good and get it down to a ~ 0.7 Qtc. Anyway best to start your own thread.
GM
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.