Yeah, that's why there was a question mark after "smoother" 🙂 The SPL-curve in the datasheet is difficult to draw conclusions from, but the impedance-curve usually does tell the truth. Smoother impedance is typically a good indicator. But it is also possible they added more smoothing to the new drivers datasheet.I thought the same at first (not having the 5530 at hand), but is it really smoother? Because I don't think there's a reason why to pay for just lighter.
I also think that the 4550 and 4554/4555 would be pretty much the same, wouldn't they? The cost is also similar,
Anyway, this is the BMS 4554 + Gen2 (could it be even smoother?):
I have a confession to make - I fell in love with this. It sounds so right and natural....
(4554/EXT)
I'm interested in a version for the 5530ND if you can make one. Do you need some measurements?
The electrical impedances published in datasheets are the last thing I would make any conclusions on, as those are often unbelievably worse than in a good horn. Sometimes I wonder how can they even achieve such bad curves...
Sure, you can try to measure the dimensions. Seldom it then really fits on the first try, but that can be iterated, at least we can try.
Sure, you can try to measure the dimensions. Seldom it then really fits on the first try, but that can be iterated, at least we can try.
One problem I am running into when looking at the option of a large round "midrange horn" is where to put a supertweeter to fill in the upper range. To time align it you'd have to mount it right behind the horn; same for a decent driver spacing. I was looking at synergy horns previously and thought maybe you could make a quasi-synergy horn with a midrange CD and a supertweeter, but I doubt that the performance of that would be very good and would probably exhibit a lot of the same problems as a coaxial CD.
Yeah, you are right. For compression drivers I agree. In this specific case the two drivers seems to be measured on the same horn though, which had me drawing conclusion from the ripples below 3 kHz.
- Still something to be improved. This is probably the last iteration of the 4554 kit, now I need to finish the how-to...
Regarding the 5530ND, here are some frequency response curves measured on a flat DI 340mm waveguide:
Neither of these have a perfectly smooth throat, but the red one is with a somewhat smoother one. The orange is measured with a 25mm cylindrical exit from the driver's phase plug, and therefore less smooth. Smoothing 1/12th octave. I'd show with less smoothing, but didn't save these measurements (rest assured that nothing big is hiding in the smoothing). The only strange thing is the small dip at roughly 2.6kHz. It seems to be inherent to the driver somehow, as it has been present in every waveguide I have measured it on. Overall it really is a superbly smooth driver though.
Neither of these have a perfectly smooth throat, but the red one is with a somewhat smoother one. The orange is measured with a 25mm cylindrical exit from the driver's phase plug, and therefore less smooth. Smoothing 1/12th octave. I'd show with less smoothing, but didn't save these measurements (rest assured that nothing big is hiding in the smoothing). The only strange thing is the small dip at roughly 2.6kHz. It seems to be inherent to the driver somehow, as it has been present in every waveguide I have measured it on. Overall it really is a superbly smooth driver though.
The 4591 is a single diaphragm mid-range river, rolls off ~18dB per octave at 6kHz.
Like the 1.4" and 1.5" coax, the BMS 4592 HF drops off steeply below 7kHz, requiring the mid high crossover point to be very close to 6kHz.
The B&C 464 HF plays an octave lower, and it's roll off is ~12dB per octave, much more latitude in crossover placement is possible.
The extra bandwidth of the B&C DCX 464 HF allows the mid to be limited to a decade (400-4kHz) of operation, reducing intermodulation distortion that accompanies high diaphragm excursions required when running so low.
Limiting the BMS midrange to a decade of operation would put it in the 600-6kHz range.
Let's say the typical Sd for a 1" exit 1.75" voice coil driver is 16cm2 and the the best one can do 600Hz in the living room. That would suggest an Sd of 64cm2 for 300Hz. Maybe a 3.5" dome would be the closest to that and a 4" dome larger. I've read somewhere the BMS mids have an Sd of 55cm2 or so (and probably high excursion), maybe the Faital HF1440 is similar to that, at any rate it's probably the best performer in this test https://audiohorn.net/test/compression-driver/1.4inch/ The HF on the old JBL 2450SL with a large 4" dome doesn't seem bad either, another measurement: https://www.audioheritage.org/vbulletin/showthread.php?31657-Truextent-diaphragms-measurements
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This is the 5530 on an ATH waveguide, 5.5 ms window, no smoothing.
The B&C mid is probably larger since the specs says 4.0" voice coil diameter, compared to 3.5" of the BMS. Could expect that much more SPL at LF based on that.
To me the crossover frequency appear to be pretty locked in on both ultimately, in general I'd rather have a crossover at 6KHz than 4KHz .
The waveguide is a big asymmetric one for a new Dutch & Dutch speaker I'm working on. The 5530 is great in some ways, but it will most likely not be used in this speaker.
Interesting that the high frequency peak shown in BMS' datasheet is also so clearly present in your measurements. Even in my unsmoothed measurements I only see a ~2dB peak. Mabat's measurements of his BMS driver shows something similar. I wonder where the discrepancy comes from?
Send me a PM, I have a pair that I could lend you for measurements. I am in Prague at least once a week (Barrandov and Písnice), I can drop them off basically anywhere around.
This is the 4550 on another waveguide. The angles are 0, 15, 30, 45, 60, 75, and 90 degrees. As you can see, the peak just below 20 kHz is most pronounced on-axis, and it's gone when you move beyond 30 degrees. Therefore, I presume you didn't measure your 5530 precisely on-axis.
Is there any rule of thumb regarding which horn section (diameter) influences which frequency dispersion?
E.g. we see that the 1.4" throats start beaming at ~10kHz. This is roughly the relation dia=wavelength for beginning of beaming. Does this also indicate that the section of the horn around e.g. 36cm diameter is more or less responsible for the 1kHz region?
E.g. we see that the 1.4" throats start beaming at ~10kHz. This is roughly the relation dia=wavelength for beginning of beaming. Does this also indicate that the section of the horn around e.g. 36cm diameter is more or less responsible for the 1kHz region?
Constant-directivity horns commonly behave like this - it's mainly a directivity issue. You can see it clearly in a simulation, for a 1" throat this starts around 15 kHz. It's also a sign that the actual wavefront is clean, as it behaves exactly accoring to the model.
Gen2 horns are (intentionally) not CD and this region is then a lot smoother, directivity wise. Balancing act, I guess.
If you have a flat-DI waveguide, you should find the same when looked closely, IMO.
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Yes, in the simulations you do see that sudden increase in directivity in around 15k for a 1" throat, but I think the peak in response around 19k that the BMS drivers have, is designed to be there. It's a controlled resonance to help extend the CD's response to 20 kHz.
For reference, below is a 1" Beyma 171 on the same waveguide as the 4550. Quite different behavior in the top octave.
For reference, below is a 1" Beyma 171 on the same waveguide as the 4550. Quite different behavior in the top octave.
The difference in directivity can be only due to a different wavefront "shape". BMS is simply closer to the prediction for an idealized wavefront. It can also have an intentional resonance in that region, that doesn't go against each other. In an ideal case, the on-axis SPL increase happens even without any resonance though, and corresponds to the large increase of directivity. You can see this behaviour in a simulation for a constant-acceleration source, without normalization.
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