Esgigt,
It has occurred to me that MFB is most typically used as a cost/size compromise to replace a decent sub-woofer, well restored Philips MFB's certainly being the exception to the rule
.Art
What's your point? Besides showing off your ill informed opinion about MFB, you show none.Esgigt,
It has occurred to me that MFB is most typically used as a cost/size compromise to replace a decent sub-woofer, well restored Philips MFB's certainly being the exception to the rule
Art
Don't blame me for manufactures who screw-up the MFB principle..
And what's wrong with a successful attempt reproducing low bass out of a small enclosure?
If you've never heard good MFB implementations, don't condemn them, but listen to them first.
Every amplifier generates negative voltage, otherwise it would be a rectifier.
What should be meant is negative impedance.
Obtained by velocity feedback.
Which makes the system having a very high damping and a nearly 6 dB/o slope around the resonance, which is very simple to equalize.
But the system response remains resonant, still governed by a standard second-order high-pass equation, just highly damped, the voice coil having no special properties of acceleration and deceleration.
(Rythmik certainly products nice drivers).
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Thanks for guidance about mounting. I'm certain others have found mounting an ACH01 to be pitfall-full and leading to false signals.
Holding an accelerometer soundly is not an original design goal for a general purpose driver. I'll prolly try famous acoustic BluTac.
Another reason to simply use a series resistor to sense back-EMF. Like ACE-Bass, eh. Or better, a bridge.
Ben
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Toole recently had an interesting article explaining why EQ does not fix rooms (contrary to the expectations of a lot readers here). At best, it papers over the auditory envelope.
I think Toole's critique applies to your results. Yes, you can tweak a non-MF driver to sound on pulses like a "fast" MF speaker. But then you have a weird FR for the driver on music. In a sense, MF is an automatic EQ but always pushing the speaker towards linearity.
It is contrary to my intuition to believe that EQ would change those horrible bass reflex box tone bursts into something clean like the way IPAL MF does it, even if you could make the sound superficially similar.
Ben
Ben,
EQ does tend to have an inverse effect on phase, but to actually change the impulse response the way IPAL MF does requires temporal as well as EQ changes, in other words FIR filters. The FIR filters get the response "in shape", the MF keeps the response in shape at various (and extreme) drive levels. If one does not push the system to extremes, the MF portion of the circuit is not doing much of the "heavy lifting".
Art
Hi bentoronto,
Post #186: "Toole recently had an interesting article explaining why EQ does not fix rooms (contrary to the expectations of a lot readers here). At best, it papers over the auditory envelope."
Could you, please, post a link to, or, pertinent excerpts from this paper?
Regards,
Post #186: "Toole recently had an interesting article explaining why EQ does not fix rooms (contrary to the expectations of a lot readers here). At best, it papers over the auditory envelope."
Could you, please, post a link to, or, pertinent excerpts from this paper?
Regards,
Well, I did say the Sonys were perhaps not an ideal implementation of MF and in fact I did say they suck so I guess that did occur to me.
As I have outlined about a dozen times, there are real problems to address (good design, properly sizing a system, treating the room) which will provide benefits orders of magnitude greater than the benefits provided by MF, these should be addressed first. What good is MF if your max flat ported box sounds like a boom machine (bad design), your 5 inch woofer is incapable of realistic output (properly sizing the system) and the room makes everything sound like you are in a sewer pipe (room treatments)? MF can't fix any of that.
Neither eq nor MF will fix room problems. How could it? The room affects the sound AFTER the sound leaves the speaker. Since I've mentioned at least 3 or 4 times now that the room should be properly treated before even considering MF, any reader that thinks eq will fix room problems would have to be pretty dim. Eq can give you a flat response at one point in space but it can't "fix" a room.
You completely miss the point. Bolsterst was suggesting that if you want to compare MF vs non MF, both systems should have the same frequency response. I've told you dozens of times, what we hear is mostly frequency response. And if the MF and non MF system both have the same frequency response it will be difficult to tell them apart until you push the systems will into the danger zone of non linear behavior.
Again, the accuracy of tone bursts is hardly important. How much time do you spend listening to tone bursts in a day?
Never mind superficial. If the MF and non MF systems are eq'ed to the same response they will sound quite similar, regardless of tone burst shape. The benefits of MF won't be readily apparent until you push the systems hard, at which point your system is undersized and should be upgraded.
Thanks for your interest. Please excuse my laziness in not previously finding the link. Toole is my hero, an engineer (really, he's a physicist) who understands perception and good research methods. But I gather you're interested in his provocative room EQ thoughts.
Took a while, but I think this is it although title may seen odd (or others can help find it too):
AES E-LIBRARY
The Measurement and Calibration of Sound Reproducing Systems
it is a free pdf download.
AES E-Library The Measurement and Calibration of Sound Reproducing Systems
Another recent and related piece:
History of Multi-Sub & Sound Field Management (SFM) for Small Room Acoustics | Audioholics
and
http://aplaudio.com/downloads/Reading_Dr_Toole.pdf
Sadly, no acoustics forum at DIY. But good if you wanted to start a thread in subs for critiquing Toole's ideas.
Ben
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You shouldn't apply MF in a vented box (I stated that multiple times. I know reading is difficult) and neither do I use a 5" or advocate them...
who gave you that stupid idea? It wasn't me...
I was just throwing out real world examples. The Sony MF speaker is a ported box, so are any number of other commercial ready made MF (and non MF) speaker models. The Rhythmic sub can be built ported (as per their website) and so can the IPAL. The Sony uses a 5 inch woofer, as do many other models of MF speakers.
ALL of this has been covered in this discussion, I know reading, comprehension and retention are difficult but don't worry, I don't forget and I'll remind you. I can provide direct quotes and links to previous topic points if you like.
Regardless, MF is limited only to making the cone act in a slightly more linear fashion, this is really the least of your worries in a properly designed system in a properly treated room, as I've mentioned several times.
ALL of this has been covered in this discussion, I know reading, comprehension and retention are difficult but don't worry, I don't forget and I'll remind you. I can provide direct quotes and links to previous topic points if you like.
Regardless, MF is limited only to making the cone act in a slightly more linear fashion, this is really the least of your worries in a properly designed system in a properly treated room, as I've mentioned several times.
Hi wagigt,
Meyer Sound has been working on feedback for ported PA systems since the late 70ties. Perhaps the most ambitious MFB system to date is the Meyer’s PSAC (Pressure Sensing Active Control) from 2000. It's a feedback system with multiple loops of which the calculation process is done by an analog computer to minimize the delay. PSAC was used in the Meyer X10, a large ported 2-way studio reference monitor that is highly regarded.
Klaus Gruber of A.C.T. built ported subwoofers (mainly) for the German 'hifi' and 'HT' market.
Cheers,
Djim
The primary purpose for using MFB with vented enclosures is not to reduce distortion like in the Phillips system. Rather, it is to electronically manipulate the T/S parameters to affect an improved, extended response in a smaller enclosure. Based on my investigation of one of Sony’s MFB subwoofers, I don’t think they were even doing this…just including it for marketing purposes I think. I think I'll see if I can dig up my measurements and post them tonight...should bring some levity to this thread.
I meant to mention the similarities between AceBass and Rythmik systems. If you look at the patents it becomes clear that the Rythmik circuit makes use of the same current feedback arrangement AceBass uses to manipulate effective mass and compliance. The one weakness in the AceBass system was the manipulation of damping by positive current feedback is adversely affected by voice coil temperature. For damping manipulation, Rythmik replaces the positive current feedback approach with negative velocity feedback from a second voice coil which is not affected by VC temperature.Brilliant +1.forr rightly mentioned
Also one of the better written patents in terms of education rather than obfuscation.
Attachments
Hi bentoronto,
Thanks for posting the Dr. Toole links in Post #19.
This would be an interesting subject to chase after, and used to keep me awake at night in the late 1970s. Now there is almost too much literature on the "internets" to keep up with.
Here is another Toole quote from History of Multi-Sub & Sound Field Management (SFM) for Small Room Acoustics | Audioholics
: "...Room resonances at low frequencies behave as minimum-phase systems and properly matched parametric EQ can repair both the amplitude and time domain problems. Off-the-shelf automated "room EQ" or "room correction" programs may or may not be able to do this properly. Many do not..."
So, the right type of EQ applied correctly can be helpful.
I remembered another article by Dr. Toole that discusses "Damping Factor", and-in a roundabout way-may be pertinent to this MFB discussion:
http://www.roger-russell.com/wire/damptoole.htm
Regards,
Thanks for posting the Dr. Toole links in Post #19.
This would be an interesting subject to chase after, and used to keep me awake at night in the late 1970s. Now there is almost too much literature on the "internets" to keep up with.
Here is another Toole quote from History of Multi-Sub & Sound Field Management (SFM) for Small Room Acoustics | Audioholics
: "...Room resonances at low frequencies behave as minimum-phase systems and properly matched parametric EQ can repair both the amplitude and time domain problems. Off-the-shelf automated "room EQ" or "room correction" programs may or may not be able to do this properly. Many do not..."
So, the right type of EQ applied correctly can be helpful.
I remembered another article by Dr. Toole that discusses "Damping Factor", and-in a roundabout way-may be pertinent to this MFB discussion:
http://www.roger-russell.com/wire/damptoole.htm
Regards,
Room resonances present as standing waves and occur in pretty specific locations; as we know, walking around the room will give a variety of different frequency response patterns. In the corners and near walls it gets boomy and out in the center of the room it's often near full cancellation.
There's no way eq can fix that. (MF can't fix that either.) If you correct the response at one point in space the response will get worse at other spots.
It's easy enough to fix the response for a single listening position, or even a broad area like a couch (assuming the couch is placed wisely). But there's absolutely no way you can fix the whole room with eq.
Room treatments and/or multiple subs with constructive/destructive interference averaging action will do a much better job than eq.