Such dome mid drivers do very little excursion therefore any mechanical effect related to suspension should not show any effect!
This sounds very heavy! The magnet structure should not have changed that much - how was sensitivity of these drivers?
Xmax - when demanding >110dBSpl at 450Hz ... you need some membrane movement ...
Do you ever attended a PMC demo session? These people are crazy 🤓
I have not posted on this forum for some years, but hopefully I can add something useful to this thread in response to the two most recent posts, and by suggesting something that is largely missing from considerations so far...
The balsa ring in the ATC dome is required to prevent bell modes that would otherwise cause the coil to rub on the pole pieces with such a narrow gap. This is just one key to the ATC dome's high performance. (I am not sure a "long coil" ATC dome ever existed, although possibly they supplied a variant to Yamaha for use in their electric pianos???). However, the need for the balsa ring begs mention of the engineering required to ensure a driver works continuously at its rated power output...
The lack of such abilities of many other drivers is why "sales orientated" specifications like "peak music power output" came into existence - that is, a fudge to make specifications look good. ATC were unique at the time of their original design in manufacturing drivers that could meet their specified continuous power dissipation without falling apart. Such is requisite in many professional monitoring applications, but rarely so in typical domestic listening environments.
If anyone has dissected a Bliesma driver, then it would be good to know how they are constructed and therefore of any such limits they might exhibit. In the datasheets I have been able to locate, the power handling of the Bliesma 75mm domes is specified as "N/A", which is an unfortunate oversight on their part. Whilst continuous high power operation might not be required, there remains a genuine advantage from being able to reproduce high peak SPLs with low distortion too due to the nature of music (at least the type generated acoustically by hitting things).
As to domes in general, the 75mm diameter is an engineering compromise that accommodates (most of) the commonly-accepted "vocal range" as best as possible. Displacement limits low-frequency crossovers to about 350Hz in most applications, and a fundamental diaphragm resonance at about 4.5kHz limits the high frequency end. ATC used to show a 100mm dome that I do not think ever made it into production (???), but this had a useful bandwidth of about 250Hz to 2.5kHz and therefore provided a greater compromise in vocal reproduction.
Methods to improve performance then appear to be limited. A longer gap might appear a good idea, but even a double suspension is close to its usable limits with higher displacements; Multiple domes are easy to integrate together at lower frequencies, but require leaving just one operating in the higher part of the operating bandwidth to avoid directional issues. And coned drivers... they just introduce additional issues that the domes avoid.
Nearly always, however, (as mentioned in this thread already) the biggest compromise that sets performance is the low frequency performance of the tweeter employed. Interesting here is that the bigger ATC models used to employ 34mm tweeters, whereas those in their smaller models used superior but lower power-limited 25mm drivers. The best compromise remains the target in any loudspeaker, and the 75mm midrange dome might very well be just that where realistically high SPLs are required.
The balsa ring in the ATC dome is required to prevent bell modes that would otherwise cause the coil to rub on the pole pieces with such a narrow gap. This is just one key to the ATC dome's high performance. (I am not sure a "long coil" ATC dome ever existed, although possibly they supplied a variant to Yamaha for use in their electric pianos???). However, the need for the balsa ring begs mention of the engineering required to ensure a driver works continuously at its rated power output...
The lack of such abilities of many other drivers is why "sales orientated" specifications like "peak music power output" came into existence - that is, a fudge to make specifications look good. ATC were unique at the time of their original design in manufacturing drivers that could meet their specified continuous power dissipation without falling apart. Such is requisite in many professional monitoring applications, but rarely so in typical domestic listening environments.
If anyone has dissected a Bliesma driver, then it would be good to know how they are constructed and therefore of any such limits they might exhibit. In the datasheets I have been able to locate, the power handling of the Bliesma 75mm domes is specified as "N/A", which is an unfortunate oversight on their part. Whilst continuous high power operation might not be required, there remains a genuine advantage from being able to reproduce high peak SPLs with low distortion too due to the nature of music (at least the type generated acoustically by hitting things).
As to domes in general, the 75mm diameter is an engineering compromise that accommodates (most of) the commonly-accepted "vocal range" as best as possible. Displacement limits low-frequency crossovers to about 350Hz in most applications, and a fundamental diaphragm resonance at about 4.5kHz limits the high frequency end. ATC used to show a 100mm dome that I do not think ever made it into production (???), but this had a useful bandwidth of about 250Hz to 2.5kHz and therefore provided a greater compromise in vocal reproduction.
Methods to improve performance then appear to be limited. A longer gap might appear a good idea, but even a double suspension is close to its usable limits with higher displacements; Multiple domes are easy to integrate together at lower frequencies, but require leaving just one operating in the higher part of the operating bandwidth to avoid directional issues. And coned drivers... they just introduce additional issues that the domes avoid.
Nearly always, however, (as mentioned in this thread already) the biggest compromise that sets performance is the low frequency performance of the tweeter employed. Interesting here is that the bigger ATC models used to employ 34mm tweeters, whereas those in their smaller models used superior but lower power-limited 25mm drivers. The best compromise remains the target in any loudspeaker, and the 75mm midrange dome might very well be just that where realistically high SPLs are required.
"And coned drivers... they just introduce additional issues that the domes avoid."
I'm interested in your perspective on this. Can you please elaborate?
I'm interested in your perspective on this. Can you please elaborate?
Coned drivers have problems terminating energy at their diaphragm edges that are simply not apparent in a dome driver, because a dome is clamped rigidly (one hopes) to the voice coil former. Whilst considerable effort has gone into reducing these resonant artefacts, eliminating them altogether seems to be a good idea. And if a 75mm diameter driver can achieve sufficient specification, a dome would seem to be the better option.
The import issues would only be there if customs charges you an import fee.
The big thing ordering from Audio-hi.fi is to make sure they double box the drivers to survive any rough handling by DHL, who is the carrier they use.
The T34Bs I purchased from AHF were in the factory box without any extra packaging, so they arrived with one of the back chambers detached. Not a big deal in theory but it wasn't as simple of a fix, since the design of the tweeter and the lack of adhesive availability in the US complicated the repair. AHF wasn't very responsive and Bliesma didn't handle shipping mishaps, so I ended up repaired it myself. In retrospect I should have just paid return shipping and put it back in AHF's hands, but I didn't want to risk further shipping damage and waiting even longer.
Anyways, you probably won't have the issues I had as long as you make sure they use extra packaging to protect the drivers if (when) they get knocked around hard enough.
Its possible for Qtc to end up that low from the correct rear volume and dampening material usage.
Sometimes DATS doesn't detect Qtc correctly and reads the impedance peak wrong if it isn't that symmetrical. This almost always throws off TSP measurements with higher frequency peaks, mostly mids and tweeters that have larger diameter VCs with slight double hump peaks. The presence of another smaller peak can caused by insufficient VC former venting (airflow restriction) coupled with the air cavity under the VC winding. Its very common with larger VC dome drivers, especially if they employ ferrofluid.
Based on my experiences, importing from Canada to the US can be more expensive than importing from European countries (depending on their export fees if any apply). I didn't pay any extra fees importing from Audio-hi.fi. The other issue is availability, which can be the case with Be drivers and the current situation with the raw material itself.
Some information for you, if you order you can phone him directly and ask double packaging:
Romanov Andrey - +358 40 751-6776
https://finstor.fi/
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Regarding the cone edge resonance problems that most dome drivers inherently avoid - larger VC diameters often have greater tendency to produce radial resonance modes. This is due to the more flexible edges of unsupported, open ends on larger VC formers.
Some companies like ATC stiffen the VC former edge with a ring of lighter material (ie Balsa wood). Most larger VCs are stiffened with an additional layer of fiberglass, nomex or by a rolled edge on the former itself, as some compression drivers employ.
I use to add a thin viton o-ring when reconing midbass drivers with longer VC formers. This isn't so really a problem with very short and stiff VCs. Very long, unsupported VCs made from thinner kapton with short windings can suffer from severe radial modes. These VC radial modes can produce high amplitude sharp peaks, some worse than the breakup of Alu/Mg cone drivers.
Most of the time these peaks are way out of the useful Fc upper limit, but if unchecked, they can cause the outer VC windings to contact the upper pole plate at higher SPLs. This can be problematic on very large VC diameter midbass / midrange drivers. It shows up as a high Q, sharp peak up past the primary cone breakup.
You can test a drivers tendency to produce radial VC modes by sweeping it with a 4V sinewave, listening from the side of the driver basket windows for HF peaks between 5 to 10k. The peak will sound louder from the side than from the front. If you do hear this happening, take necessary measures to filter out the peak with a notch if the driver will be played very loud for longer periods of time ie PA use.
Some companies like ATC stiffen the VC former edge with a ring of lighter material (ie Balsa wood). Most larger VCs are stiffened with an additional layer of fiberglass, nomex or by a rolled edge on the former itself, as some compression drivers employ.
I use to add a thin viton o-ring when reconing midbass drivers with longer VC formers. This isn't so really a problem with very short and stiff VCs. Very long, unsupported VCs made from thinner kapton with short windings can suffer from severe radial modes. These VC radial modes can produce high amplitude sharp peaks, some worse than the breakup of Alu/Mg cone drivers.
Most of the time these peaks are way out of the useful Fc upper limit, but if unchecked, they can cause the outer VC windings to contact the upper pole plate at higher SPLs. This can be problematic on very large VC diameter midbass / midrange drivers. It shows up as a high Q, sharp peak up past the primary cone breakup.
You can test a drivers tendency to produce radial VC modes by sweeping it with a 4V sinewave, listening from the side of the driver basket windows for HF peaks between 5 to 10k. The peak will sound louder from the side than from the front. If you do hear this happening, take necessary measures to filter out the peak with a notch if the driver will be played very loud for longer periods of time ie PA use.
I never detected such issues with the Bliesma drivers but I also didn't search for it. I did some pretty cruel tests and even managed to destroy one mechanically (to low frequency at very high level - it went into Xdamage. This will not happen with a propper crossover). High frequency resonance was always stable and it never sounded extra distorted.
Resonance frequency of the A and B version is very high, I would think the dome stiffens the coil former? The former is also very short, looks sturdy. With the weaker membranes resonance is way lower ... everything is for sure less stiff.
Resonance frequency of the A and B version is very high, I would think the dome stiffens the coil former? The former is also very short, looks sturdy. With the weaker membranes resonance is way lower ... everything is for sure less stiff.
I think there is some confusion here between resonances that are linear (and ever-present), and those that are distinctly non-linear due to a driver not functioning as desired at high power outputs. My apologies for the confusion, but a coil former flexing and leading to rubbing of the motor pole pieces is generally the result of the latter. If it is not, it really is not a good choice!
Even with an 8R coil impedance (the ATC's are normally 16R), the power dissipated by the driver with a 4V sweep is a mere 4*4/8=2W. Testing at the ATC's specified power input requires an amplitude of in excess of 30V, and I certainly warn against putting your ear close to the driver in such a case! It is the avoidance of such mechanical faults that requires the former stiffening. Any such defects cannot be linearly "filtered out": It is instead a sign that a driver needs replacing or repairing.
As I hinted earlier, and for anyone interested in appreciating the engineering limits of a driver design, I thoroughly recommend leaving any driver operating at its recommended power input - most will only last in the order of minutes, some an hour at a push; I would suggest the ATC is one of the few (if not the only one) that will likely endure until you turn off the test, and work normally thereafter too.
This does not bode well. Some real figures for the Bliesma maximum power input would be a welcome addition...
ATC SM75-150 has a nominal power rating of 75W. I'm pretty sure they will take that with ease forever. But so will the Bliesmas.
Maximum Input Power of 150W and max Programme Power 300W but I could not find any definitions for them. (frequency range, filters, time etc.)
Maximum Input Power of 150W and max Programme Power 300W but I could not find any definitions for them. (frequency range, filters, time etc.)
Where was the Bliesma quoted at a "maximum power input" of 150W? It is not quoted on any of the datasheets I managed to obtain. Is there any independent verification of this figure from the sort of test I described above?
No - that's the Rating of the ATC SM75-150! The Bliesmas still have no official rating.
I put a sweep with 27V at the driver (120W for a few seconds) - that was no problem at all thermal but the frequency was to low...
A 2nd driver survived and with a proper crossover there would not have been a problem of course. But as I wanted to know the limits ... now I know 🤓
I put a sweep with 27V at the driver (120W for a few seconds) - that was no problem at all thermal but the frequency was to low...
A 2nd driver survived and with a proper crossover there would not have been a problem of course. But as I wanted to know the limits ... now I know 🤓
Thank you for your clarification. I would suggest a figure of 150W for the Bliesmas is overly optimistic let's say. Achieving a genuine rating of 1W per mm coil diameter remains an engineering achievement that many manufacturers do not meet. I really hope someone from Bliesma can prove my pessimism misplaced, as that would flag a genuine technological advance.
I would also say 150W steady RMS is to much. Even the ATC is only rated for 75W! But as it could take 120W without any sign of compression I would think it can also take the 75W long term.
I tested some 1" with 20kHz sine signals (Bliesma and ScanSpeak) and they don't survive 25W in that condition! At 15W the ScanSpeak 664000 get's a membrane temperature of 80°C! I estimated coil temperature from power compression to 165°C.
Bliesma doesn't cool as good, was stable at 10W but is more sensitive from the beginning, max SPL is about the same. Both had about 2dB of calculated power compression at that state.
Let's see if I find time to do the same tests with the M74.
I tested some 1" with 20kHz sine signals (Bliesma and ScanSpeak) and they don't survive 25W in that condition! At 15W the ScanSpeak 664000 get's a membrane temperature of 80°C! I estimated coil temperature from power compression to 165°C.
Bliesma doesn't cool as good, was stable at 10W but is more sensitive from the beginning, max SPL is about the same. Both had about 2dB of calculated power compression at that state.
Let's see if I find time to do the same tests with the M74.
I know for sure the ATC will survive for more than 24 hours at its rated maximum power input. I believe this is largely attributable to its voice coil manufacture, and the heat sinking capability of its relatively large motor system. I think actual coil temperatures, that as you mention, can be well in excess of 100C, would surprise many people. It should certainly give cause to think again about thermal compression and crossover level matching.
It is remarkable to me that the ATC dome appears to employ no exotic materials (barring the high temperature adhesives and kapton former), yet remains such a milestone in audio engineering so many years after its development. My contribution to this thread was intended to highlight that we do not always compare "apples with apples" on this forum.
Without doubt, the ATC mid will take almost double its continuous power rating with a typical crest factor music signal. I've worked with a few of the SCM 3 ways that used the big dome and there is no question they can take alot while giving most of it back well into rock concert SPLs. Thats what they're good at, but they don't have the lowest THD levels. For sure the engineering is without compromise. The motor on the mid is bigger than some pro audio woofers.
The radial VC resonance mode test works very well. Its an eye opener how many drivers suffer from this issue, but most of the time you can notch it out since its usually not that severe in amplitude coming from the front side of the driver. Sometimes the dustcap will carry it out forward, especially the domed type dustcaps.
The radial VC resonance mode test works very well. Its an eye opener how many drivers suffer from this issue, but most of the time you can notch it out since its usually not that severe in amplitude coming from the front side of the driver. Sometimes the dustcap will carry it out forward, especially the domed type dustcaps.