The accuracy would depend on how long the device was. The plane wave model is not too bad for shorter devices of not too great a flare, if one is only interested in the impedance. For directivity, the plane wave assumption is hopelessly inaccurate.
Again, it depends on the specifics. A well radiused "waveguide" will not have any significant mouth reflections. My own devices are proof of that. There are no impedance irregularities exhibited in them as witnessed by the compression drivers impedance curve. Any device will have mouth reflections if the termination is abrupt.
Hi guys,
I have a set of Ariels and ME2's, that I am using in a 9.1 Dolby Atmos home cinema setup together with six 18" subwoofers. I am now thinking about finally adding the 4 overhead speakers to complete the Atmos setup and as I don't have lots of hight in the room, I wouldn't be able to place additional ME2's on the ceiling.
So, I want to ask you guys, what are my best options? I would need something that is at max around 12cm (or 5") in depth. Can the ME2's be modified in depth while keeping the same internal volume by increasing hight and width? Anything else in terms of other projects that you can think of "close enough" or even using the same drivers?
Thanks much in advance!
I have a set of Ariels and ME2's, that I am using in a 9.1 Dolby Atmos home cinema setup together with six 18" subwoofers. I am now thinking about finally adding the 4 overhead speakers to complete the Atmos setup and as I don't have lots of hight in the room, I wouldn't be able to place additional ME2's on the ceiling.
So, I want to ask you guys, what are my best options? I would need something that is at max around 12cm (or 5") in depth. Can the ME2's be modified in depth while keeping the same internal volume by increasing hight and width? Anything else in terms of other projects that you can think of "close enough" or even using the same drivers?
Thanks much in advance!
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Hmm, using the Vifa's in a tiny closed-box enclosure is a possibility. What surprised me is you have some spare drivers, since they went out of production about 10 years ago. I think I might have bought the very last ones that Madisound had.
The forum members probably have good suggestions for other drivers that have very smooth response, extended bandwidth to 5 kHz, and no peaks above that. Most small drivers get really rough between 5 and 10 kHz, and require an aggressive crossover to suppress the roughness and peaking.
Nice to meet you, too! I was zipping around with Peter of SoundSmith, Alex of RAAL (and his new ribbon headphones), and Thom Mackris, my neighbor and principal of Galibier turntables (and now amplifiers). Also got to meet Thorsten Loesch at the iFi booth ... I need to continue that conversation on-line, both of us have lots more to chat about digital conversion.
The really wild 5-way Chinese all-horn system, to my surprise, actually sounded pretty decent. Didn’t expect that; super-expensive systems usually sound awful, and this one was pretty good. Not at all bad for an introduction to the US market.
Also got to meet Bill of Great Plains Audio for the first time in person, a real pleasure. Nice guy, and I really admire keeping the great Altec legacy going, with Alnico versions of the 416, 515, and 604 Duplex, which was in audition at Room 1110 in the Tower.
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I hope Bill of GPA experiments with beryllium diaphragms ... I told him to get in contact with the folks at Materion, who can probably provide a sample 288 diaphragm if he provides an aluminum version as a template. How beryllium works with the traditional tangential surrounds ought to be interesting, since Be has much better self-damping than aluminum and should be resistant to fatigue cracking (the problem with the original 288's back in the early Seventies).
I also mentioned to Bill that the same folks in Asia and Europe who like drivers with Alnico magnets will also probably like field-coil magnets, and they should be easier to make than hard-to-source and hard-to-machine Alnico. Unlike the field-coil magnets of the 1930's which operated at hundreds of volts (since they were used as filter chokes in radios), modern ones can be wound for 5 or 12 volts, readily available from any computer power supply at very moderate cost. Just a different number of turns, that's all.
Why audiophile firms charge astronomical prices for drivers with field-coil magnets is a mystery to me. All drivers before WWII used field-coil magnets, and it was hardly exotic technology, dating back to the original Rice & Kellogg patent. Yes, they require a power source, but computer power supplies are dirt-cheap. Granted, drivers with Alnico and field-coil magnets appeal only to the hard-core audio nutcases out there, but the $300,000 Chinese system used both field-coil magnets (on all 5 compression drivers!) as well as US-made Materion beryllium diaphragms. (To best of my knowledge, Materion is the only source in the world for beryllium foil suitable for loudspeaker diaphragms.)
I also mentioned to Bill that the same folks in Asia and Europe who like drivers with Alnico magnets will also probably like field-coil magnets, and they should be easier to make than hard-to-source and hard-to-machine Alnico. Unlike the field-coil magnets of the 1930's which operated at hundreds of volts (since they were used as filter chokes in radios), modern ones can be wound for 5 or 12 volts, readily available from any computer power supply at very moderate cost. Just a different number of turns, that's all.
Why audiophile firms charge astronomical prices for drivers with field-coil magnets is a mystery to me. All drivers before WWII used field-coil magnets, and it was hardly exotic technology, dating back to the original Rice & Kellogg patent. Yes, they require a power source, but computer power supplies are dirt-cheap. Granted, drivers with Alnico and field-coil magnets appeal only to the hard-core audio nutcases out there, but the $300,000 Chinese system used both field-coil magnets (on all 5 compression drivers!) as well as US-made Materion beryllium diaphragms. (To best of my knowledge, Materion is the only source in the world for beryllium foil suitable for loudspeaker diaphragms.)
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Hi Joe! I don't know if what we discussed a long time ago is related, but I was puzzled why different bass drivers (say, 15" professional monitor drivers) sound different in a passband where they are in the piston response region (100 to 500 Hz, for example). Aside from gross distortion (which should be a non-issue in a pro driver well below 90 dB playback levels), I couldn't think of a likely mechanism that would set them apart in the inherently flat part of the spectrum, aside from various differences in the magnetic system.
Fro example, I was expecting two drivers, such as the Altec/GPA 416 and the JBL 2235, to sound pretty much the same (if not identical) in the 100 to 500 Hz region at domestic listening levels. At domestic levels, they are far from the overload region, and THD and IM distortion should be well audible thresholds. These are movie-theater drivers, after all, just in different historical eras.
But they actually sound quite different (well, at least that's what I heard, and repeatably so). Why?
Well, the magnetic systems are different. The modern 2235 has an overhung voice coil, while the Altec and GPA have an underhung voice coil. The 2235 voice coil is partially in a region where the flux lines are not straight, while the voice coil of the 416 or 515 is in a region where the line are straight (inside the gap). Once the 416 or 515 VC leaves the gap, of course, they become quite nonlinear, but are well-behaved below that. The onset of magnetic distortion is much more abrupt with an underhung VC, which is an indirect pointer against using them in a vented box without an external low-level highpass filter that creates a B5 or B6 response curve.
Fro example, I was expecting two drivers, such as the Altec/GPA 416 and the JBL 2235, to sound pretty much the same (if not identical) in the 100 to 500 Hz region at domestic listening levels. At domestic levels, they are far from the overload region, and THD and IM distortion should be well audible thresholds. These are movie-theater drivers, after all, just in different historical eras.
But they actually sound quite different (well, at least that's what I heard, and repeatably so). Why?
Well, the magnetic systems are different. The modern 2235 has an overhung voice coil, while the Altec and GPA have an underhung voice coil. The 2235 voice coil is partially in a region where the flux lines are not straight, while the voice coil of the 416 or 515 is in a region where the line are straight (inside the gap). Once the 416 or 515 VC leaves the gap, of course, they become quite nonlinear, but are well-behaved below that. The onset of magnetic distortion is much more abrupt with an underhung VC, which is an indirect pointer against using them in a vented box without an external low-level highpass filter that creates a B5 or B6 response curve.
I gave you my explanation before as to why your expectation wasn't met:
the Altec woofer has much lower mechanical damping(*) than the JBL (specifically, Fs/Qms = 3.5 vs 8.0).
IOW, the Altec woofer exhibits less inertia than the JBL and responds more readily to the microdynamics of the driving voltage.
This is irrelevant in the context of loud PA applications, but makes a lot of difference w.r.t. how the two woofers sound in a home hi-fi system when playing softly (or when reproducing the subtle low-level information in a high-crest factor dynamic recording).
Now, there may of course be more to it. But based on my experience with a number of woofers and systems, I think mechanical damping definitely plays a prominent role in explaining this difference.
Marco
(*) mechanical damping can be measured at resonance as the ratio of acoustical resistance to moving mass (Rms/Mms), which can be shown to be directly proportional to the ratio of resonance frequency to mechanical "Q" (Fs/Qms).
Surely the change in frequency response is more likely due to the change in voice coil impedance affecting the load on the passive crossover, rather than crossover components themselves heating up a lot and altering their values ?
I guess it depends on the size of the driver/voice coil relative to the heat producing crossover components, but it seems likely that the voice coil is going to get a lot hotter than large ceramic resistors or inductors when it is physically smaller yet dissipating a much higher proportion of the power, especially at bass frequencies where there shouldn't be much dissipation in a crossover except for coil resistance.
The impedance of the driver critically affects the response of a high order filter that is relying on that load for damping, even relatively small changes in driver impedance of half an ohm or less can have a large effect on the response curve depending on filter topology.
This is particularly a problem in a typical 2 way where the bass is doing the work of heating up the voice coil of the midbass driver but the midrange to treble crossover at higher frequencies where we are more sensitive is what is suffering as a result when the Q of the filter gets thrown out by the extra resistance resulting in peaking of the response.
It's quite instructive to measure the response of a crossover at the driver when adding additional resistance in series with the driver to see just how far the response can go out with a small amount of added resistance...
It's also one reason I like to use a zobel network on a midbass / midrange driver even if I could get the same transfer function with less components by adapting the filter to the drivers natural impedance rise - the zobel network helps to swamp any impedance changes near the crossover frequency resulting from voice coil heat, keeping a more stable impedance for the low pass filter section. (Another reason is it helps to swamp effects of inductance modulation with cone displacement on the crossover, which can cause a form of intermodulation distortion between bass and higher frequencies where the crossover is sensitive to impedance variations)
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That makes good sense on the surface.
But i keep finding the more i make my speakers perform well in a reflection free environment, the better they sound when forced into the domain of reflections.
I am reminded of an event somewhat inverse to this but, on reflection, not so much. I had the opportunity to listen to a recording I knew well (Pasha Siku by Sukay, a Peruvian pan flute ensemble) played through a good pair of speakers out in a field, with a wall behind and grass beneath. Even though the recording was presumably mixed and mastered in a conventional environment the tonality sounded completely normal. The lack of room tone, though, was a distinct bonus but just as important to me was I heard imaging on the bass drum that I didn't know was possible—it had a very specific apparent point of origin.