Can someone link independent TS measurements for the 8NDL51? I'm going back and forth between the 8NDL51 and 8MBX51 for my HI down size.
Thanks!
Thanks!
FWIW:
"Spec sheet, FS = 66Hz, Zmax at FS = ~50 Ohms.
Out of box, FS = 80Hz, Zmax at FS = ~58 Ohms.
Breakin routine, 10 minutes at 30Hz, 20V RMS, Excursion ~6mm
Allowed to cool 20 minutes. (Motor structure was warm to the touch.)
Broken in, FS = 68Hz, Zmax at FS = ~50 Ohms.
Measurement method, true voltage source impedance check, ARTA Steps 1/48'th octave. Drive voltage 2.83VRMS."
"Spec sheet, FS = 66Hz, Zmax at FS = ~50 Ohms.
Out of box, FS = 80Hz, Zmax at FS = ~58 Ohms.
Breakin routine, 10 minutes at 30Hz, 20V RMS, Excursion ~6mm
Allowed to cool 20 minutes. (Motor structure was warm to the touch.)
Broken in, FS = 68Hz, Zmax at FS = ~50 Ohms.
Measurement method, true voltage source impedance check, ARTA Steps 1/48'th octave. Drive voltage 2.83VRMS."
Yes. They changed the surround to a stiffer one without telling or changing the datasheet. The new driver measures very different - nicer in the resonant area but double the THD in the normal area. Also Qms went down significant and in my listening test the driver showed less detail in the music. Even the distributor didn't know and asked in the factory what's going on.
When I remember right it's just H2 from the membrane resonance (half the frequency of the resonance) - it will go away with a passive crossover or a series notch (Purifi paper).
I wanted to build my cinema speaker with the Beyma and it took 7 samples of 8" until I found a new one which I was happy with.
@IamJF That's extremely frustrating. Consistency is everything. If you can't count on driver specs being accurate, the driver isn't useful IMO.
To evaluate a driver's purpose and usefulness, I always purchase at least 3 drivers to determine if it has sufficiently consistent properties when used in non-matched pairs.
To evaluate a driver's purpose and usefulness, I always purchase at least 3 drivers to determine if it has sufficiently consistent properties when used in non-matched pairs.
I respect Scott a lot for his work but these measurements ...
That's rubbish. A condenser microphone doubles H2 (which is dominant) every 6dB of SPL.
A studio microphone is specified at 0,5%, measurement microphones sometimes with 1% THD. But 5% ... That's 2,5% at 159dBSpl, 1,25% at 153dBSpl, 0,5% at about 145dBSpl. When he had 150dBSpl during the measurement ... the mic THD will likely have some influence.
Here some measurements from measurement microphones at 1kHz:
A GRAS 40BD has about 2,5% THD at 160dBSpl and would have 5% THD at 166dBSpl - costs about 2k and is really no special mic. One of the B&K 1/4" has even less sensitivity and would probably get in the 2% THD area at 165dBSpl.
I know the ScanSpeak 8" drivers and NO WAY the B&C tops them at "normal" levels. Maybe Purifi is a little better.
This is the metal membrane 8" 22W/8857T00:
8Vrms is 9dB louder as 2,83Vrms. Sensitivity is specified 86dBSpl/2,83V, so at 8Vrms we land at the 95dBSpl curve (@400Hz). THD is below 0,2% in a wide range. Even at the limit what they are able to deliver (about 25V) they stay below 1% THD - these are exceptional drivers!
I'm sorry to say but either these measurements are not reliable or the driver is in terms of THD just average. But I would not trust these measurements.
More losses due to increased damping in the suspension.
It's a trend in audio, even more so in hifi.
That's why I don't like ring radiator comp. drivers and dome tweeters with thick surrounds.
They measure well, but fail to properly reproduce the input signal (slightly exaggerated for clarity).
It's also one reason why Stanislav Malikov (BlieSMa) uses thin surrounds.
I used a few of them for an industry project, had 1-2 in spare and did my measurements and a prototype. Then ordered 3 new ones - and these had the changed rubber surround. No way to get the old ones. The complete project ... back to the start.
But at least I detected the PA-driver low SPL strange behavior of some drivers and know a lot about 8" drivers now 🤓
Btw, the old 8P300 had a Qms of 15-20! The new one less than half ... and nobody cared or noticed.
I contacted a German studio monitor manufacturer who is using this driver a lot and the answer was "we don't care, we correct with DSP" ... 🤔😳
Measurements of any kind remain (in my view) a tool to indicate performance; nothing more and nothing less.
A complex world lies hidden beneath the measurable values.
It therefore doesn't surprise me that Beyma was not immediately able to provide an explanation for your findings.
Purifi drivers are top notch, in terms of measurable performance. I mainly see the 'limitations'.
These drivers have been developed with modern (marketing-induced) dogmas in mind, ultimately inexorably limited by Hofmann's iron fist.
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D(efinitive)S(olution)P(rovider).
Funny how supposed audio professionals believe they can correct (solve?) something in the electro-mechanical-acoustic domain by using digital tools.
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It may be a bit of a bold statement and it's not intended to cast doubt on Purifi's innovative R&D.
Bruno is the most brilliant audio engineer I know and I don't doubt Lars Risbo's qualities either.
Ultimately, every designer has a specific philosophy, considering the intended application and performance level.
While Japanese engineers tackled the breakup of a large aluminum dome in a well-thought-out mechanical way 30 years ago,
Purifi opts for (rather complex) solutions in the crossover (perhaps they could have solved this easily with DSP 😎).
Note: this does not eliminate the (material) signature of the cone, but only reduces the excesses inherent to the material (breakup peaks).
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@Ro808 Purifi drivers are very expensive and not that sensitive.
One should be able to expect a minimum standard of tolerance and performance, even if some of us don't care or can't perceive it. That's no excuse. For those of us who don't use DSP, it shouldn't be expected we tolerate sloppy production practices.
One should be able to expect a minimum standard of tolerance and performance, even if some of us don't care or can't perceive it. That's no excuse. For those of us who don't use DSP, it shouldn't be expected we tolerate sloppy production practices.
"Extremely clean SPL and distortion response and no more sign of any resonances. It is a challenge to find a matching tweeter with such low distortion."
Now there will undoubtedly be people - especially on a particular forum - who genuinely believe that at such low distortion levels, there is little or no audible 'coloration' of the reproduced signal.
Those folks who 'pursue absolute transparency' and therefore rely solely on measurement data.
Massive ignorance is hard to eradicate and this is illustrated by the state of the world.
I was pleased to notice that Yevgeniy Kozhushko (HiFiCompass) at least understands what determines the subjective experience:
"So, we got to a very interesting point. You can do measurements and discuss them for a very long time, but no one really knows how they are related to our subjective feelings in general. Undoubtedly, there is some kind of correlation - a flat frequency response indicates the absence of obvious humps and dips, which lead to an ear drilling or the bleaching of the music instruments and distortion of the timbre. Low non-linear distortions can increase the resolution of the system, reduce the amount of "mud", especially at high volume levels. The radiation pattern may give us a hint about spatial characteristics of the being shaped virtual sound picture. In fact, that’s all. Not very much at all.
There are many more nuances that can not be measured, but leave a noticeable imprint on the sound signature of the speaker. Many people claim that the main factor affecting the sound signature of a speaker is a quality of its magnetic system and the membrane material is secondary. My point of view on this question is the following: the magnetic system is undoubtedly very important, a lot depends on it, especially the overload capacity of the speaker, but the membrane material properties are the main factors determining the speaker's “breed”, character or sound signature. Namely it is the combination of its unique characteristics - the Young modulus, density and internal damping and, possibly, something else that determines the unique sound signature that we hear as its own “voice”. Believe me, each material sounds differently."
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That each material got it's own properties that can affect sound is true, but that you can't measure it is not i think.
But you need to look more closely to the distortion profile, especially IMD, and to the resonances, that varies with cone material, and is not only limited to the one big peak, but also a lot of smaller arround them. But i firmly believe you can measure more than you can hear, you just have to have the right tools and knowlodge to know how. I learned a lot by studying Kippel measurements and try to linkt hem to what i hear (of certain speakers i know well).
But there is also a lot of snake oil mysticsim arround this, where subjective data is presented as objective for commercial or ego reasons. Or people who hear something but don't know how to measure it, so they invent somthing to explain...
But you need to look more closely to the distortion profile, especially IMD, and to the resonances, that varies with cone material, and is not only limited to the one big peak, but also a lot of smaller arround them. But i firmly believe you can measure more than you can hear, you just have to have the right tools and knowlodge to know how. I learned a lot by studying Kippel measurements and try to linkt hem to what i hear (of certain speakers i know well).
But there is also a lot of snake oil mysticsim arround this, where subjective data is presented as objective for commercial or ego reasons. Or people who hear something but don't know how to measure it, so they invent somthing to explain...
When you have "digital" in your name then you can do everything in the digital domain ..... 😉
Regards
Charles