- Jan 22, 2008
I clearly stated LF or bass. Midrange has many other problem but excursion and Bl variation is not one.I stated no visible movement with a specific 15" Midrange (for front horn loading) driver when driving the speaker with a signal containing bass, which would cause very large displacement with classic 15" Bass Driver like EVM15B or JBL 2226.
Perhaps because you are deliberately opinionated.So you are just being deliberately obstuse.
Read again. I clearluy stated "optimization conducted by passive means". Current drive is an active process (unless you want to put a 1kohm resistor in series).Clearly you are mistaken, IF for the added mechanical damping electric damping is reduced.
At the cost of increased power draw.No, but current drive means Re is no longer material. Current drive cancels Are variations contribution in the driver's acoustic output.
Such created damping is purely electrical; as such it does not compensate the effects of Bl loss, which are quite well taken into account by providing a low source impedance.A conductive voice coil former with the correct resistance provides electromechanical self damping of the driver, so driving it with an AC current source doesn't cause LF peaks and poor transient response, due to the absence of electrical damping from the driving amplifier.
Yes, and Lenz says that there is energy dissipated. If damping is superior, energy demand increases.Basic laws of physics? Lentz among others?
When the voice-coil temperature increases, thus its DCR, current drive will result in faster thermal avalanche than voltage drive. I'm very familiar with the destructive limits of loudspeakers.Once the voice coil leaves the air gap output drops off so rapidly, we do not add appreciable LF output anyway. But cooling of the voice coil is comprised, potentially creating a thermal avalance condition that delaminates the voice coil glue.
I would say it's almost irrelevant. The audience wants high spl and they want it for many hours in a row.Interesting, what was the HD under those conditions? And compression?
Then come PHL loudspeakers.At Xdam the BL is likely 10-20dB down on standard Xmax BL.
I designed an analogue protection system that worked well enough to ensure the speakers would work consistently from the beginning to the end of a festival night, and from day one to day x. Later, this system has been ported in digital platforms by Linea reserach (now Martin Audio) and Powersoft.A servo loop could be used to make this usable in practice, again, Sub use only. The protection circuitry against thermal or mechanical avalanche conditions would be interesting. I'd not volunteer to do that without a serious DSP maybe not even with.
Because a long VC results in large waste of power. We want both efficiency and spl.At the same time, why not specify a longer voice coil, drop midband efficiency (ultimate LF Output is down to Xmax and cone area anyway) and you have a Sub that has better inherent linearity with exactly the same 32Hz (or whatever frequency you pick) output?
I'm familiar with Servo Drive, only good for shaking trousers. Also familiar with M-Force. Quite better.Or, why not use an industrial rotary motor or a a set of linear motors a do a modern version of Danleys "ServoDrive". You can easily get a 1sqm carbon fiber honeycomb panel and get way past +/-1" linear excursion.
Interesting. I've played quite a lot with the PCM4222 evaluation board, even tried different input stages. With the digital low cut filter turned off and DC coupled it was the best performing AD converter in null tests. In listening tests I always found it to sound a little blunted / liveless dynamically and somewhat hazy on top.I have been using various Burr-Brown / TI "Advanced Segment DAC" parts, under software control and with some use of non-documented features and slightly non-standard analogue stages.
Other than that the CS43131/198 is really good as DAC. Especially if used dual mono and possibly using multiple DAC's per channel.
ADC I have been using TI parts, the PCM4222 is nice. The TLV320ADCX140 range is good for lower end gear.
I have been unimpressed generally with ESS.
Something I'd like to try is to build an ADC/DAC using the industrial 20-Bit / 1 MspS ADC/DAC Chips from Linear, these tend to be 50 Bux plus a piece, but we could get a 768kHz sample rate 20 Bit ADC/DAC without digital filter.
Add an FPGA and trade sample rate and bit depth with simple filters, so averaging two samples give us 384k/21 Bit, while averaging four gives 192k/22Bit.
With likely 300 USD+ in chip's alone this would be not a cheap device.
Something like this I might call:
And try to make it look appx like this:
View attachment 111394
It's my impression that that is what AA filters in converters and plugins today mostly are designed for. I use discrete DACs that allow for using your own filters (within the limits of its processing power, of course), and then one I use (not my design) because it sounds by far the least colored, cuts gently and a lot lower than what is almost always used today. For AD I use a Lavry Gold, which has more latency than the competition, and my guess is that this is down to a reconstruction filter with a bigger window. With the usual filters it should have very little latency, since from the way THD behaves at different amplitudes it seems not to be using delta sigma modulation.That sounds like a case of designing the filters to look good on paper (specs) while cutting some corners.
(Intersonics) ServoDrive was remarkable for what it was, especially when it was (1980s). I'm pretty sure those cones moved.I'm familiar with Servo Drive, only good for shaking trousers. Also familiar with M-Force. Quite better.
Perhaps because you are deliberately opinionated.
Read again. I clearluy stated "optimization conducted by passive means". Current drive is an active process (unless you want to put a 1kohm resistor in series).
At the cost of increased power draw.
Such created damping is purely electrical; as such it does not compensate the effects of Bl loss, which are quite well taken into account by providing a low source impedance.
It's a xfmr which primary is the voice-coil and the secondary a shorted turn. It's a common trick used to compensate the increase of impedance due to the inductive element (Le)
Yes, and Lenz says that there is energy dissipated. If damping is superior, energy demand increases.
When the voice-coil temperature increases, thus its DCR, current drive will result in faster thermal avalanche than voltage drive.
I would say it's almost irrelevant. The audience wants high spl and they want it for many hours in a row.
Then come PHL loudspeakers.
I designed an analogue protection system that worked well enough to ensure the speakers would work consistently from the beginning to the end of a festival night, and from day one to day x.
Because a long VC results in large waste of power. We want both efficiency and spl.
I'm familiar with Servo Drive, only good for shaking trousers. Also familiar with M-Force. Quite better.
Interesting. I've played quite a lot with the PCM4222 evaluation board, even tried different input stages. With the digital low cut filter turned off and DC coupled it was the best performing AD converter in null tests. In listening tests I always found it to sound a little blunted / liveless dynamically and somewhat hazy on top.
Watch Mr. Carlson's video on youtube about capacitor replacements, and then go to Mouser and don't spend more than $5 on any cap. You'll be fine.WTF have all the posts in common with the question at the very beginning of the thread?
The question was:
Can someone help provide some idiot guidance on which are the better quality film type caps for audio use?
I personally don't believe that "better" is the correct wording. Quality film type caps should have:
1. tight capacitance tolerance (5% or smaller),
2. at least 2x voltage rating in relationship to the DC operating voltage,
3. small ESR (in the requency band of interest),
4. small DF,
5. at least 3x AC current rating in relationship to the RMS opreating current,
6. small tempco (if you want to create military products)
Check the cap you have chosen within your circuit (prefer meter reading vs. golden ear disbelief)
It depends what you expect. If the capacitor is used to determine the LF frequency response of a whole unit by defining a dominant pole, its correct. If it is used in an intermediary stage (like the coupling caps between PI and output tubes), it's less important as the -3dB LF sould be significantly lower than the desired overall response.1. tight capacitance tolerance (5% or smaller),
Again it depends very much of the circuit. Is leakage an important factor? Is the voltage coefficient important (it relates to distortion).2. at least 2x voltage rating in relationship to the DC operating voltage,
ESR is in most cases indifferent, particularly in film caps. Contrary to electrolytic, the ESR is stable and not modulated by signal, so does not introduce distortion. Low ESR is a requirement for electrolytic caps used in smps.3. small ESR (in the requency band of interest),
Dissipation results in increasing damping of tuned circuits. It may or may not create issues in filters, but is inconsequential for caps used in coupling position.4. small DF,
Yes.5. at least 3x AC current rating in relationship to the RMS opreating current,
Or simply a stable oscillator.6. small tempco (if you want to create military products)
What the Hell is the problem with understanding this?! Thor is, certainly on a single read, right in everything he says. I've had a current driven MFB loudspeaker on my list of projects I plan to do for years now. And if someone would pay me I'd start work on it right now. But I think you've got to shape the input signal for the impedance curve. And the other thing I would do differently is have the microphone inside the cabinet because I would want to keep the transfer function of the bass low pass faithful and uncontaminated by the mid output and in room noise. Of course you have the radiation resistance problem but that's trivial. There may also be some unwanted feedback issues but that's practical engineering. (I may well be disabused of both those positions but I'll find out in due course. )Tell me how a cone that doesn't move can produce loud bass, except if loaded with a particularly efficient horn.
You're right, that's why I deleted my offtopic post.WTF have all the posts in common with the question at the very beginning of the thread?
I've had a current driven MFB loudspeaker on my list of projects I plan to do for years now.
And the other thing I would do differently is have the microphone inside the cabinet because I would want to keep the transfer function of the bass low pass faithful and uncontaminated by the mid output and in room noise.
Of course you have the radiation resistance problem but that's trivial. There may also be some unwanted feedback issues but that's practical engineering. (I may well be disabused of both those positions but I'll find out in due course. )
The shorted, or semi-shorted, VC is a truly lovely idea but I don't think you can bring down Qm all the way for quite a few reasons, but you probably can take it part-way. You are going to lose a helluva lot of practical power handling if you take it all the way, and need more amplifier power. You lose the impedance hump, which probably has a mean of 30 ohms (and might have a peak of 100) which has now been brought down to 6 ohms, or even 4, so your amp is now in a totally different ballpark, in a region close to the peak spectral content of music.
I don't doubt for a second that it works, is probably excellent, and might even be practical domestically with over-specced drivers and now that we have free power with Class D
I also like it because it backs up my long held position against the bollocks over low-loss rubber surrounds being better. The last thing you want is a high Qm; not only does it vary by itself but the higher it is, the more changes in Qe show up in Qt.
These drivers badly need damping and having them generate back EMF to be gobbled up by the amplifier might even be thought one of the worst ways to do it.
So I'm doubtful of its commercial future, but there's nothing wrong with it in principle
Before I start my reply I wanted to ask you whether Ansar are still in business? Their website appears to date from 2019 and is not that functional. In about 1992, which I see must have been very soon after they started, I needed some parts quickly (we didn't have standard next-day delivery back then) so drove up to Cricklewood Electronics where I spotted these capacitors. I can't remember what it was I was buying, but since I had been getting samples of all sorts exotic capacitors to audition from people like Leclanché (sadly now defunct, for capcitors at least) decided to grab a handful of them. They came out very well. It's astonishing how well one can remember impressions, even from 30 years ago, but my only complaint was they were just missing a tiny bit of sparkle. Otherwise they were right at the top. Ironically, with my more mature priorities today, which don't strive for tinsely detail as much easy detail with some body to it, they would have come out on top. In fact, some of them ended up in the tweeter section of a lovely system I used at home for non-critical, non-stressful, listening for about 20 years. Only that sort of longevity tells you that something was absolutely right, and you come away with a real love for systems like that.I did two prototypes, one a Subwoofer with 6 X 10" Drivers, sealed and one a vented box where the the MFB was similar to the Meyer solution.
What happens in a room at low frequencies is a minefield and there are numerous aspects to it which I can't (or won't) cover here. I have read reams and reams on this topic and I'm very unimpressed with what's out there in general, with some of it being just plain wrong. In fact, one of the fundamentals - universally agreed on, AFAICS, and which I had previously taken as obvious - has a glaring mathematical error in it. The problems weren't solved by the Eureka project (the one done in the '80s by KEF and B&O into room effects ), though it possibly could be if one recalibrated the data. That data could validate what I believe the situation to be, but it would be a mountain of work and in some ways is only doing in real life what I would do in software. (Analytical software, not in-action DSP). From what I have seen in things like people's use of Directivity Index and from loudspeaker designs that I know about, I don't think anyone has got this quite right, though I know that Andrew Jones has been looking at this for a very long time, from first realising that the bass he had been expecting when measuring behind a speaker wasn't there! A few people have got aspects of it, and I know that for certain, but I'm not sure anyone has the full picture. (Well, nor have I because I haven't yet written the software and I don't know what might come up as I do so.) Maybe Andrew does, but he usually gives away everything he knows (if you have ears to listen) and I don't think I've heard him speak excitedly on the topic. But I may have missed it if I hadn't got to understanding it fully when it was mentioned.Well, think this through some more. The Mic based systems I used helped a LOT with room effects.
Yup. And I'm making it worse by putting it in a high SPL space with a rising response as you go down in frequency. Fortunately it flattens off below resonance but this is still the aspect that worries me the most. I know it can work because there are some Low Frequency measurement systems that do it this way (and it's a lovely solution to ever diminishing signal level) but assuming they run at 2.83V, that's not the same as party level in a large domestic monitor.The biggest issue is to get a sufficiently linear sensor. This is surprisingly non-trivial.
Yeah, yeah. I'm actually a little closer to your position than I was, not least because I remembered that I had done a fully equalised bass section (at least on one of the bass units) and at the time I viewed this as generally good for the amp as it brought down the total impedance hump. And, in spite of it being less than half of two drivers in parallel, it never caused a problem to any amp.Really? What is the impedance hump? It is the electrical representation of a mechanical resonance. If we do not short-circuit the voice coil and feed such a speaker from a current source we get a huge LF response hump and a very resonant system.
How is that mitigated using a low output impedance Amplifier? By injecting a current that opposes this resonance. These blind currents are out of phase with the voltage but are very real. Except in this case the dissipated power is "destructive", that is, it "destroys" some of the
Let us for a moment ignore the shorted turn damping and apply some strictly mechanical damping solution, be it the grease-pots of the original 1930's eckmiller coaxial, the Goodmans ARU or the Dynaudio "Variovent".
What is the result of the correct tuning of this element? The impedance "hump" flattens to the desired system Q. Does that make the speakers blow up?
Damping must be supplied somewhere. Doing so requires energy to be absorbed.
How this is done varies, but ultimately the same energy is required to be input into the system to get a given acoustic output and for an equally damped system it will be equal. Preservation of energy et al.
As remarked, we had drivers with such voice coil formers existed in the 80's and worked very well in practical terms. And no, they did not overheat or blow up amplifiers. So this is not a problem.
Don't forget, the voice coil is wound around a solid mild steel (or similar) core and surrounded by a large ring of solid mild steel etc. That are already two shorted turns and are one of the reasons for the poor electrical efficiency of moving coil (or moving magnet) speakers, something that could be corrected for example using more efficient motor systems (electrostatic which we now get as MEMS, piezoelectric etc.).
Well, yes and no. You want, in my view a Qm that is equal to Qt with linear damping of the spring/mass resonant system.
Typically spiders and surrounds the produce low Qm are not very linear. This does have some potential practical benefits, in some specific situations.
Yup. Then again, in a lot of ways having an internal combustion engine drive a car is a way worse solution than electrical drive, for a wide range of reasons (reliability, longevity, efficiency).
Yet they dominated the whole sector for over 100 Years, for reasons outside of the scope of the direct technical solution.
If the principle is implemented correctly, it will allow relatively commodity grade systems to be materially improved. That applies to the kind of lower end audio systems all over the range, be it portable sound system, monitors or home audio.
No doubt high end systems could also be improved, but less so, or similar performance could be attained for lower budgets.
Thor, you mentioned the Dyneaudio Variovent. I used those "on spec" once and never was able to do sufficient testing to arrive at a final opinion about their usefulness. Do you know why they didn't remain popular?
My experience was that I preferred the sound of the Variovent-designed cabinet when I sealed it entirely.
Before I start my reply I wanted to ask you whether Ansar are still in business? Their website appears to date from 2019 and is not that functional. In about 1992, which I see must have been very soon after they started, I needed some parts quickly (we didn't have standard next-day delivery back then) so drove up to Cricklewood Electronics where I spotted these capacitors.
What happens in a room at low frequencies is a minefield and there are numerous aspects to it which I can't (or won't) cover here.
From what I have seen in things like people's use of Directivity Index and from loudspeaker designs that I know about, I don't think anyone has got this quite right
but I'm not sure anyone has the full picture.
The subwoofer use case is a good deal simpler than that of a bass unit in a loudspeaker system.
It's not just the wavelengths but also the integration with something that has different directivity.
I don't mind saying here that the usual solutions to the baffle step are categorically wrong, but anyway I'm going WAY further than that.
I probably would put a microphone on the outside with a sub because of the room pressurisation and tricky things like absorbtion coefficients of walls which are nearly impossible to estimate. Those get solved automatically.
Although I have an elegant solution for a short coil in a long gap, I don't want my linearity or the limited dynamic range of a domestic loudspeaker used up by someone opening a door, and at the moment I think that output of the other speaker (though some of it will come through anyway) is probably something I don't want in my feedback loop. But I could change my mind as I haven't done this yet and there are plenty of unknowns.
Anyway, those are my reasons for wanting the mic inside rather than outside the speaker.
One of the things tipping the scales is that I prefer the idea that my speaker will try to keep the cone stationary with a gust of air rather than flapping around.
This could be beneficial when it comes to doing outdoor measurements
Meyer seem to me to be selling a flaw as a virtue here.
I don't see how you can know your system is delivering the target response you wanted with a mic on the outside, especially with another speaker in the room.
I probably need something with a nice high resonant frequency but I've thought of a few potential solutions like putting it in a tube, behind fine mesh to act as a resistor, a MEMS mic, accelerometers... But you probably know what the scale of the problem is, having put something near to the cone's surface already.
is the amp just as well off delivering the current it would otherwise have had to? Or is there an optimum? It would be nice to be kind to the amp.
There are a few things in this area (which I have left below) that I never disputed, but I still don't think dissipating it near the coil is a great idea and I would rather use the surround as that helps with the mechanical impedance mismatch between the cone and the surround. I don't think spiders usually dissipate much, else we wouldn't have QMs of 5 or 7, but they too can have an impedance mismatch messing up what would otherwise be a perfectly pistonic region in any driver, so the more the better.