As for the HF1440, I can only speculate about the intended function (perhaps to increase the volume of air behind the diaphragm for a lower resonant frequency?), but there is a multitude of thin "escape slots" from the rear of the diaphragm to the damped chamber inside the driver body. Almost paper thin felt-like layers are used as spacers. When I first saw it, it took me a while to even understand what's going on. So the closed volume inside the driver (under the front cover) is coupled to the air behind the diaphragm by these slots.
Does anyone have an idea for what it really is?
Does anyone have an idea for what it really is?
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You would not be able to see that relief on the bottom unless you cut one in half, get engineering drawings, or check for excessive clearances at the bottom of the gap, with a non magnetic 'feeler gage'.
Looking at the other 2, there is no visible large clearances from removing the diaphragm either, yet the problem is fairly obvious.
You can see in the impedance of the driver that there is a secondary resonance in the suspect area, the third impedance peak would not be there if the driver did'nt have a internal issue. Persisting on a PWT means it is a internal issue caused by bad engineering.
it is also a fairly common problem plaguing many a compression driver.
Compliance mismatch between diaphragm /phase plug would disappear if put in a vacuum chamber and measured ususally.
Sure it is equalization in some way.
When EQing the hole in the response away by raising it with digital EQ, you will usually amplify the resonance that should not be there in the first place.
Honestly not touched a HF1440 due to it's obvious issues.
As for smaller exit compression drivers, you ever tried the D2415K?
21mm exit, dual diaphragm JBL.
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If an added series resistance helps, it must be doing exactly the same thing as a digital EQ would, i.e. actually eliminating the resonance by feeding an "inverted" signal.
No, it's difficult to source JBL drivers here, just to try them. But I would love to.
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With low output impedance amplifier the driver impedance shows how the driver itself affects circuit current with constant voltage from amplifier, impedance is just relationship of voltage and current, and when voltage is constant peak in impedance means current is low. Current on the other hand makes the force in the motor and we get some acoustic frequency response from it. Adding simple series resistor reduces current of the circuit for the whole bandwidth, but now the bandwidth that had impedance peak got relatively less reduction in current, while bandwidth that had low impedance got relatively more current reduction. This means acoustic output reduces most where driver impedance plot shows low impedance, and comparatively less, where there are peaks.
Why there is peaks in the impedance plot then? Those are from back EMF, when the voice coil moves a lot (with relatively little force) it generates more back-EMF = reduced total current = impedance peak. I don't know what resonance this is, either somewhere in the cavity, or the main resonance, although main resonance is probably the lowest impedance peak isn't it, where spring and mass balance each other? In this case, it is kind of weird that acoustic output is low even though the voice coil moves a lot, perhaps there is hint what it is and where it happens, perhaps compression is gone there, as if the diaphragm worked in free air or something?
edit. just speculating, perhaps it's resonance between back chamber and front if they are connected and the system "unloads" there or something. If you can run the driver without back chamber you'd see if anything happened to that impedance peak. I do not know why it is there, perhaps this kind of resonance / coupling (or what ever it is) between front and back enables more power handling or something, and the trade-off resonance somewhere, which is tuned there about at 2kHz if that is region where people could have EQ dip anyway. This way it seems more like a feature and not a bug. Still, one should not EQ boost it too much, makes lot of excursion and likely distortion. Perhaps in home use one could just EQ it without penalty.
Why there is peaks in the impedance plot then? Those are from back EMF, when the voice coil moves a lot (with relatively little force) it generates more back-EMF = reduced total current = impedance peak. I don't know what resonance this is, either somewhere in the cavity, or the main resonance, although main resonance is probably the lowest impedance peak isn't it, where spring and mass balance each other? In this case, it is kind of weird that acoustic output is low even though the voice coil moves a lot, perhaps there is hint what it is and where it happens, perhaps compression is gone there, as if the diaphragm worked in free air or something?
edit. just speculating, perhaps it's resonance between back chamber and front if they are connected and the system "unloads" there or something. If you can run the driver without back chamber you'd see if anything happened to that impedance peak. I do not know why it is there, perhaps this kind of resonance / coupling (or what ever it is) between front and back enables more power handling or something, and the trade-off resonance somewhere, which is tuned there about at 2kHz if that is region where people could have EQ dip anyway. This way it seems more like a feature and not a bug. Still, one should not EQ boost it too much, makes lot of excursion and likely distortion. Perhaps in home use one could just EQ it without penalty.
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More likely this though
1440 datasheet doesn't show the dip. I remembered it was there as well, like in hf10ak, and if they were at same frequency while very different size and type drivers I thought it could have been designed feature. Well, what ever it is, probably not very useful for home audio because 99% of other driver don't have this dip in frequency response around 2kHz which makes them easier to use. Anyway, interesting stuff, please continue Here example how to manipulate the dip with passive parts, for hf10ak though: https://www.diyaudio.com/community/threads/ath4-waveguide-inspired-multi-way.384410/post-7488788
Absolutely a interesting topic indeed🙂Anyway, interesting stuff, please continue
Section 5.1.3.2 in the first attachment, elaborates on the specific issue, of parasitic resonances as they were termed in 1978, what i call a cavity resonance wether technically correct or not.
https://patents.google.com/patent/US5117462A/en
As both the magnet and voice coil are commonly located on the side of the diaphragm facing the pole piece, the magnetic pathway includes both the phasing plug and the surrounding pole piece. In order for the voice coil to be free to vibrate, however, it must be disposed within an annular air gap, which will be referred to herein as the coil space. Ideally, the coil space should be made as small as possible since air in the magnetic pathway adds reluctance to the magnetic circuit which lessens the field strength at the voice coil. Nevertheless there is a considerable volume of air in the coil space surrounding the voice coil as well as in the spaces along the inner edge of the surround and outer edge of the diaphragm, which are continuous with the coil space. This region, including the coil space and the space along the surround and outer edge of the diaphragm, is thus an uncoupled region since it is so far from the inlets of the phasing plug air passages that variations of air pressure in that region are coupled little or not at all to the phasing plug and thence to the throat. These pressure variations thus result in energy losses that lead to heating of the loudspeaker but do not result in the generation of useful sound output. The uncoupled region also causes cavity resonance effects that distort the overall sound output of the speaker due to anomalies in its frequency response. Such resonances, known as parasitic resonances, present a significant design problem for the speaker designer (“The Influence of Parasitic Resonances on Compression Driver Loudspeaker Performance” by Kinoshita, et al. presented at the 61st Convention of the Audio Engineering Society in 1978 and available as preprint no. 1422 (M-2).). It would be useful to couple the pressure variations in the uncoupled region around the voice coil to the throat of the horn, in addition to the pressure variations produced by the diaphragm, to improve the efficiency and sound quality of the loudspeaker. Use of the additional pressure variations could be expected to reduce heating in the region around the voice coil as a result of repeated compression and rarefaction of the same air in that region, to produce an increase in the efficiency of the loudspeaker, and to reduce parasitic resonances.
Yes a coil can be a useful trick, the "sine cap" solution works well for some applications
Just need to make sure the power dissipation of the resistor/s is sufficient.
Else the amp will most likely be having a bad day.
And i am still a fan of passive XO's to some degree.
When you have spent considerable time, on dealing with large, high voltage power transformers, that heats up and resonates at 80-100 db due to harmonics caused by diode rectifiers.
Or trouble shooting, total devastation of communication networks due to bad filter caps in electronics. One might develop some personal prefernces, when it comes to switch mode power supplies and PWM outputs🙃
yes it is not really a attractive feature in any driver. Quality dsp solutions might make it easier to live with for some.
In the case of the HF10Ak, there is no doubt about it really. But it is also a more trditional style driver and diaphragm.More likely this though
Legis did some experiments with the HF1440, some change in that area can be seen from damping differences. Distortion plots look different to what goes on with the HF10AK. All of Faitals own horns have a more loading beamy nature to them, many of the drivers seem designed to work with that sort of horn.
https://www.diyaudio.com/community/threads/shadow-of-the-colossus-build-thread.357825/post-6355321
I can advise Oberton ND45. Better than: HF10AK, RCF ND350, BMS 4552, 18s ND1075, Celestion cdx1430, B&C DE250
Hi again,
here's a quick follow up of my recent post #14982 in which i showed my first measurements of the EXAR550 with a HF1460. I reprinted the horn in a much higher quality. Today I had the opportunity to remeasure it outside. I measured the full 360° in 10° increments with 0,3V input and 8ms gating. I also printed a new rear cover for the HF1460 with a larger enclosure volume than the original which cleared up a resonance around 1400 Hz.
0-60° 1/24th smoothing (I think the little dip at 2,7kHz stems from my enclosure. I'll experiment with some damping material next.)
ViCAD overview with EQ applied.
polar map normalized to 10°
I have my pair of EXAR 550s mounted on my two 18" beyma 18QLEX1600Fe 100l sealed subwoofers right now with 48db/oct crossover at 360 hz and it sounds amazing. With a little bit more tweaking and maybe a better suited 15" woofer it is pretty much the top of what one could reach in terms of on and off axis linearity. I can't imagine there will be anything significantly better than what i have right now.
Thanks again Marcel for your dedication in your ath project. Keep up that great work!
here's a quick follow up of my recent post #14982 in which i showed my first measurements of the EXAR550 with a HF1460. I reprinted the horn in a much higher quality. Today I had the opportunity to remeasure it outside. I measured the full 360° in 10° increments with 0,3V input and 8ms gating. I also printed a new rear cover for the HF1460 with a larger enclosure volume than the original which cleared up a resonance around 1400 Hz.
0-60° 1/24th smoothing (I think the little dip at 2,7kHz stems from my enclosure. I'll experiment with some damping material next.)
ViCAD overview with EQ applied.
polar map normalized to 10°
I have my pair of EXAR 550s mounted on my two 18" beyma 18QLEX1600Fe 100l sealed subwoofers right now with 48db/oct crossover at 360 hz and it sounds amazing. With a little bit more tweaking and maybe a better suited 15" woofer it is pretty much the top of what one could reach in terms of on and off axis linearity. I can't imagine there will be anything significantly better than what i have right now.
Thanks again Marcel for your dedication in your ath project. Keep up that great work!
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It's terrifyingly big. Is the driver really that "irregular" above ~6 kHz?
Now I can only recommend putting a piece of a sparse open-cell foam into the extension part of the waveguide.
Overall, I think it's a very good result and I can imagine it sounds in a satisfactory way.
If you're able to go to 400 Hz, it's just brilliant.
Now I can only recommend putting a piece of a sparse open-cell foam into the extension part of the waveguide.
Overall, I think it's a very good result and I can imagine it sounds in a satisfactory way.
If you're able to go to 400 Hz, it's just brilliant.
I personally like the size. It's large, yes and doesn't have much WAF left to it but it's something extraordinary and not your average home speaker, which i like.
I pretty much ignored the waviness above 6kHz as its only +-0,5 dB for the most part but your right, it shouldn't be there. It's also apparent with shorter or longer gating.
I wouldn't nessessarily say it's the driver. Maybe the Horn is ringing a bit, maybe my turning measurement stand is rattling or it's a reflection stemming from the seam between base an petals, which i have yet to fill with putty.
I do have some open cell foam here. I can easily try to cut a cylinder with the right diameter, plug it in the throat extention and see what happens. Thanks for the tip.
I pretty much ignored the waviness above 6kHz as its only +-0,5 dB for the most part but your right, it shouldn't be there. It's also apparent with shorter or longer gating.
I wouldn't nessessarily say it's the driver. Maybe the Horn is ringing a bit, maybe my turning measurement stand is rattling or it's a reflection stemming from the seam between base an petals, which i have yet to fill with putty.
I do have some open cell foam here. I can easily try to cut a cylinder with the right diameter, plug it in the throat extention and see what happens. Thanks for the tip.
Are the wiggles >6k also there without the enclosure? Could be multiples of the first resonance.
The print looks amazing! What center-to-center distance do you use between the Beyma and the horn? I'm planning to build an Ath 520G2 with an SB Acoustics SB34NRXL75-8 in a sealed 40L enclosure and am curious if using a 1.2*λ crossover (600hz) as the ctc distance might cause any issues.
Thank you!
Or use an open-back driver, including printing the cover with a grille to protect the diaphragm.
Those Tymphany compression drivers that you like, they have gaps in the diaphragm too. It almost looks like they're trying to vent it, like a subwoofer.
That is wild.
In my office I have a HTPC that's hooked up to my speakers for "serious" listening, but 95% of the time, I just listen to podcasts on my phone. (I work from home.)