Such a situation is not physically possible without going to every higher and higher slopes, which can't really be done passievely. The number of possible lobes at the crossover is directly related to the order of the filter (for a fixed driver spacing) so once you pick the order the number of lobes is fixed. And remember that all of this only applies to the vertical polars in my case (NOT the horizontal ones), which I have always said are far less important.
I only ever said that I "typically" use electrical third order filters, but they are seldom symmetrical. "Ideal" is obvious isn't it? Flat listening axis response with as wide a lobe free polar pattern as possible. If the drivers are acoustically in-phase or not at the crossover I really don't know (but I doubt it), I don't look at phase per see. The vertical lobes are generally NOT symmetrical. If this is "pretty much the LR relationship" then its purely coincidental.
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Lynn
I don't think that I'd agree that below cutoff the horn "unloads" the driver - certainly not in the snse of a ported enclosure below cutoff for example. The driver is still "loaded", but it can't radiate sound hence it is ineffective and as such any signals in that frequency region are wasted excursion. That's the reason for the HP filter. But, 6 dB is remarkably effective at excursion control even if it is not so effective at SPL limitations (excursion is linear not log in nature). I have often used 6 dB filters for compression drivers as this is really all that's needed in any home setting. Even in pro the problems are usually high frequency energy above the passband from clipping, which have incredible electrical energy and burn out the voice coil. Its possible to crash a diaphragm in a compression driver, but its a fairly rare cause of failure.
Sometimes I regret my playing with the great elephants as I have certainly no commerce interest to promote, but beeing that as it is, I will give some clarifying statemants around my design purposes.
First, regarding my 6 db/oct crossover for the MJAO, I tend to agree with Lynn. You can't press the MJAO above much more than 100-105 db in the lower midrange or it will go wild. But my last solution find was in fact associated with the midrange no crossover fall. I definitely heard noices that I couldn't really associate but to this effect. So I introduced a 6 dB crossover also for the HP of the midrange and this set the solution. It was measured to go with the tweeter.
As you all know OB tend to put out a, with the help of room reflections, relatively homogeneous soundfield. I usually listen to classical music and jazz. That's what I use to estimate my speaker constructions.
Most listening is on axis or at a very small departure.
Regarding Bratislav's question,
The MJOA came in as a selfcontaind project before a planned EP clone construction. During this period I was challanged to timealign the MJAO (still has to be done) and there was also presented the Vifa tweak: http://www.tweakaudio.com/EVS-2/Modding_the_Emerald_Physics_spe.html . All in all i don't really think about these speakers as competing design. They do things different, but well, that's all.
With the regard to the explicit mentioning of Emerald Physics. They never tried the Vifas, I think that's probably why their speakers look the way they do now.
Ok guys, that was another overstatement. But my find was actually that, when properly EQed the Alphas are very solid performers up to 1 kHz and over there is not much energy actually transmitted. So the Vifas can absolutely take care of the rest.
/Erling
First, regarding my 6 db/oct crossover for the MJAO, I tend to agree with Lynn. You can't press the MJAO above much more than 100-105 db in the lower midrange or it will go wild. But my last solution find was in fact associated with the midrange no crossover fall. I definitely heard noices that I couldn't really associate but to this effect. So I introduced a 6 dB crossover also for the HP of the midrange and this set the solution. It was measured to go with the tweeter.
As you all know OB tend to put out a, with the help of room reflections, relatively homogeneous soundfield. I usually listen to classical music and jazz. That's what I use to estimate my speaker constructions.
Most listening is on axis or at a very small departure.
Regarding Bratislav's question,
The MJOA came in as a selfcontaind project before a planned EP clone construction. During this period I was challanged to timealign the MJAO (still has to be done) and there was also presented the Vifa tweak: http://www.tweakaudio.com/EVS-2/Modding_the_Emerald_Physics_spe.html . All in all i don't really think about these speakers as competing design. They do things different, but well, that's all.
With the regard to the explicit mentioning of Emerald Physics. They never tried the Vifas, I think that's probably why their speakers look the way they do now.
Ok guys, that was another overstatement. But my find was actually that, when properly EQed the Alphas are very solid performers up to 1 kHz and over there is not much energy actually transmitted. So the Vifas can absolutely take care of the rest.
/Erling
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Just on a practical note: I've used the Le Cléac'h 3rd order filter for several years and it works well for me. Never tried it with a passive x-over, but that should be easy, too.
I know you've spoken of this quite a bit thru the threads. I would be very interested to know more. The conventional view seems to be that the diaphragm is not well controlled below the horn cut-off, so it risks damage and distortion. But is it really any less well controlled? How could this be measured?
Of course large excursion that results in no usable sound is not going to be a good thing, controlled or not.
Please allow me to re-introduce my handy tool in that context :
http://members.aon.at/kinotechnik/diyaudio/dipol/doppler_intermodulation_distortion.xls
If you have your horn simu already done - by Hornresp of David J. McBean for example - its a quick and powerful way to calculate XO slope needed in order to not exceed excursion limits.
All explanations on the "how to" are given in a few words on the second sheet.
The "IM barrier" is what you have to check and to make up your mind what your minimum XO requirements in a specific case may be.
Michael
This is completely the point. The load on a diaphragm for any transducer is fairly small so changes in it are not that big a factor. The problem is that any excursion below cutoff is simply a waste, and total excursion is a factor. But -6 db is an extremely effective lowering of excursion since excursion is linear. But the idea that cutoff has to be well below the crossover is a waste of space in my mind. This requirement makes the horn much larger with a much slower flare - more pressure in the horn and more distortion (although thats not a significant factor). My waveguides have the "horn cutoff" - such as it is - at just about the crossover point. So the acoustical response drops like a stone below the crossover with only a single pole electrical HP filter. The combined acoustical response does not have an electrical analogy in this situation since the HP function of a waveguide is not a simple HP filter.
Measure the excursion not realy possible, but measure the distortion that can generate it's more easy.
Not with the acoustic response but with the electrical impedance measure.
See the pre-impulses of distortions.
Just referring to the width of the band where each driver contributes significantly to the response. LR2 being much wider than LR4 for example. Thanks for the idea, I have a project right now that this filter may help deal with some issues.
My only worry here is that phase and distortion may get "squirrely" ( to use a technical term) near the cutoff. Thus the recommendation to cross an octave above the cut off. It should not be too hard to see this in measurements, right? I'm sure you and a few other folks here have examples.
This is the sort of thing I'm looking for. Would be interested to see the cut-off behavior of different horns. I need to do some measuring myself.
Hey Brandon,
I just tried it and both 3rd and 5th order, down 6dB at Fc, worked pretty well to overcome the AC offset and center up the lobe. Proper polarity is obvious -- slight ripple in the XO region one way and a deep null the other way. Thanks, John!
Hej Erling,
Vifas are good dome tweeters, but that's about it. No 1" dome is going to cope too well with sub 1kHz crossover point (Vifa recommends 3500Hz, 2nd order). Even vastly more capable Millenium is rather pushed at 1400Hz.
E-P used a pro compression driver in waveguide, which conservatively will have at least 10dB more headroom than any dome tweeter (perhaps even more). But my understanding it was 15" Eminences that simply couldn't be pushed as high - that is main reason the new CS-2 looks like it does today.
That is why I was surprised to see you seemingly take a step back. I have no doubt your CS-2 incarnation sounds good, I'm just surprised you don't find it inferior.
Bratislav
As I have said waveguide theory doesn't really define a "cutoff", but if I use Horn theory it would be about 800 Hz for my devices. I have data on them, but what is it you are looking for? I don't do distortion measurements for the obvious reason (that they are meaningless, in case it wasn't obvious).
I think horns/waveguides are basically minimum phase as they go through the cutoff frequency and start rolling off 3rd order or so. So the "phase distortion" is nothing you wouldn't expect from the acoustical magnitude response.
I certainly don't think that is true. The functions that define the transfer characteristics are complex ones requiring an infinite number of terms (a power series in ka), like Bessel functions, and don't have a constant slope equivalent. And they're anything but minimum phase, in fact they are dispersive near cutoff (the physicists dispersive where the wave speed varies with frequency). How can this possibly be minimum phase? As I have said before, the whole concept of minimum phase is an electrical circuits one and is ill-applied to acoustics.
Well, that's certainly nothing we need to theorize about, it's easily measured. Brandon has some recent horn/waveguide measurements with SoundEasy and it measures real phase. Maybe he'll have time to figure out if they are (almost) minimum phase or not.
Soongsc used Sound Easy to measure the frequency vs phase on a Jordan driver he had under test. He could alter the phase from trailing to leading the frequency response above 8 KHz, without affecting the frequency response in any gross way. Certainly not as grossly as he affected the phase response.
However, this was out beyond the smooth pistonic band pass, within which the two remained essentially unchanged. Perhaps it is this pre break up portion of the drivers full FR that can be called minimum phase. Certainly the portion that changed does not meet any form of minimum phase I know about.
Bud
Just another one of these MANTRAS, I have proven you to be wrong so many times in the past.
“Min phase” in this context – in simple practical terms – means that you can correct (equalise) for flat frequency response – and subsequent perfect impulse response (and thus CSD as well) at any point upstreams you like.
The point here is that “min phase” behaviour is to be achieved to an as wide as possible room angle – meaning that the correction applied to meet a postulated FR respectively IR goal is valid over the entire room angle where acoustic min phase condition can be preserved.
Above directly leads to the concept of TAC distortion (TAC = time of arrival consistency) I and thend have spoken about recently - though in the context of discussing diffraction alignment issues.
Low TAC distortion is key if we seek perfectness in audio.
Good directivity control – what your focus has been in wave guide theory Earl - is just a byproduct of this holistic concept.
XO phase alignment issues as discussed at the moment I suggest to be seen in the same frame.
Michael
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Hej Bratislav,
You speak Swedish ?
Regarding the Vifa tweeter. With comparison with the MJAO I wouldn't really put a definitive judgement about which is the best. They do things a bit differently and both do sound very good.
But trying a lower crossover I was surprised to se how the Vifa could cope with it. There seems to be some confusion about this Vifa unit at present. So the way I used to arrive at the present crossover at 937 Hz , LR 48 db/oct, was by extensive listening to certain CDs which I am quite familiar of the recording venues. It's covered in this thread: http://www.audiocircle.com/index.php?topic=53821.120 and it should also be very clear that this is only a test baffle.
As usual the proof is in the pudding. You test this, and I don't think your should have ingoing prejudice, but it is not the first best solution, it might the second best.
My current thoughts is that your contryman D OB G actually might have hit the right solution by taking up the 18sound 6ND430 to explicit duty in the midrange and also keeping crossover down on the low side for tweeters.
I didn't think this way was a very viable one, but testing this Vifa, I realised it had very good potential. What this is really pointing to is that you can success doing things differently and still have good results.
Regards,
/Erling
You speak Swedish ?
Regarding the Vifa tweeter. With comparison with the MJAO I wouldn't really put a definitive judgement about which is the best. They do things a bit differently and both do sound very good.
But trying a lower crossover I was surprised to se how the Vifa could cope with it. There seems to be some confusion about this Vifa unit at present. So the way I used to arrive at the present crossover at 937 Hz , LR 48 db/oct, was by extensive listening to certain CDs which I am quite familiar of the recording venues. It's covered in this thread: http://www.audiocircle.com/index.php?topic=53821.120 and it should also be very clear that this is only a test baffle.
As usual the proof is in the pudding. You test this, and I don't think your should have ingoing prejudice, but it is not the first best solution, it might the second best.
My current thoughts is that your contryman D OB G actually might have hit the right solution by taking up the 18sound 6ND430 to explicit duty in the midrange and also keeping crossover down on the low side for tweeters.
I didn't think this way was a very viable one, but testing this Vifa, I realised it had very good potential. What this is really pointing to is that you can success doing things differently and still have good results.
Regards,
/Erling
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