PS EDIT, I mean basket and not 'spider' in this post. The basket is resonating... Sorry for the mix-up.
I just received a pair of SB Audience Bianco 15" open baffle drivers. They are cheap, but have promising data. The first thing to do when taking out the driver is tapping on the cone... Sure enough I can hear this driver goes deep. The 15" pro driver it replaces has a much higher pitch to the tapping sound. BUT...there is aspider basket resonance ringing like a bell in the background. Checking with a FFT app using my phone I see a peak around 170Hz...
So up with the Pico Scope and sound pressure meter and measure. I get driver Fs at 34Hz, driver out of the box, never played a note, so that is reasonable I think. Electrically I see nothing peaking around 170Hz.
Tapping on the cone and using the sound pressure meter's mic I get this FFT after several taps (Scope on 'peak hold').
So I feel this driver is actually well made. It is cheap and the basket is pressed steel. You get what you pay for. I think the focus has been on motor and cone, while the money is being saved on the basket. Which is actually good because the basket is what a diy'er can most easily do something about. I have decent enough tools to make plywood stringers to re-enforce the basketspiders. I even have carbon and kevlar fibers and epoxy. But I think it will be plywood attached with Sikaflex. The inside of the basket spider will receive a thick coat of Sikaflex. I think this should dampen out the spider resonance and also strengthen the basket to be a bit better.
Any thoughts on this process?
Thanks for constructive comments.
I just received a pair of SB Audience Bianco 15" open baffle drivers. They are cheap, but have promising data. The first thing to do when taking out the driver is tapping on the cone... Sure enough I can hear this driver goes deep. The 15" pro driver it replaces has a much higher pitch to the tapping sound. BUT...there is a
So up with the Pico Scope and sound pressure meter and measure. I get driver Fs at 34Hz, driver out of the box, never played a note, so that is reasonable I think. Electrically I see nothing peaking around 170Hz.
Tapping on the cone and using the sound pressure meter's mic I get this FFT after several taps (Scope on 'peak hold').
So I feel this driver is actually well made. It is cheap and the basket is pressed steel. You get what you pay for. I think the focus has been on motor and cone, while the money is being saved on the basket. Which is actually good because the basket is what a diy'er can most easily do something about. I have decent enough tools to make plywood stringers to re-enforce the basket
Any thoughts on this process?
Thanks for constructive comments.
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I see alot of pro drivers with this issue. The stiff spider is part of the many little potential problems, including VC leads, basket and surround all contributing.
If you are measuring the resonance with the woofer in free air, the edge of the basket will ring like a bell in most cases and that may be what you're seeing as well. I dont like steel basket drivers for several reasons, but one of my favorite mid drivers is the Eminence Beta 8A which of course has a steel basket, although its made with a relatively thick gauge for its size and that makes a big difference. There are also a few cast basket drivers that are pretty flimsy. The cast frame Deltalite and Kappalite drivers have relatively skimoy baskets and out of the box they show resonances in the 100 - 500 Hz area as well.
There's are of course many things you can do to dampen a steel basket, but once you mount the driver on a baffle, that already dampens that alot, to the point the other little potential resonance sources are then of much greater impact. I would at least mount the driver and re-test before you solely point the finger at the spider being the main culprit. That also includes driver break-in, which from my experiences can take over 100 hrs in some cases.
If you are measuring the resonance with the woofer in free air, the edge of the basket will ring like a bell in most cases and that may be what you're seeing as well. I dont like steel basket drivers for several reasons, but one of my favorite mid drivers is the Eminence Beta 8A which of course has a steel basket, although its made with a relatively thick gauge for its size and that makes a big difference. There are also a few cast basket drivers that are pretty flimsy. The cast frame Deltalite and Kappalite drivers have relatively skimoy baskets and out of the box they show resonances in the 100 - 500 Hz area as well.
There's are of course many things you can do to dampen a steel basket, but once you mount the driver on a baffle, that already dampens that alot, to the point the other little potential resonance sources are then of much greater impact. I would at least mount the driver and re-test before you solely point the finger at the spider being the main culprit. That also includes driver break-in, which from my experiences can take over 100 hrs in some cases.
Ok thnx I will try mounting the driver and check.
Does it do any harm in dampening and strengthening the spider/basket? I am pretty sure I will do it even if just for experimental sake.
Does it do any harm in dampening and strengthening the spider/basket? I am pretty sure I will do it even if just for experimental sake.
Looks like a pretty narrow spike. Are you sure it will be audible?
I'm really curious what you mean by plywood stringers. Could you please elaborate?
I'm really curious what you mean by plywood stringers. Could you please elaborate?
Ooops. I meant BASKET, not spider! The basket is what is resonating at 170Hz...
I doubt I will hear it when the full range of music is playing, I am not that audio precise. But it really is audible when just tapping the cone, so what if? I see no reason not to eliminate it. If I can't hear it directly, it may mess up smear something or whatever and I may end up trying all kinds of things just because of it.
I mean plywood pieces cut to fit on the back of each basket 'leg'. Not really stringers, more like spars I guess. Anyways just something that will stiffen and strengthen the basket.
I doubt I will hear it when the full range of music is playing, I am not that audio precise. But it really is audible when just tapping the cone, so what if? I see no reason not to eliminate it. If I can't hear it directly, it may mess up smear something or whatever and I may end up trying all kinds of things just because of it.
I mean plywood pieces cut to fit on the back of each basket 'leg'. Not really stringers, more like spars I guess. Anyways just something that will stiffen and strengthen the basket.
Theres actually a dip at 160Hz-170Hz out the front on the SPL measurement rather then the peak suggested by your tapping resonance test. But if it is the basket ringing maybe measurements out the back of the OB would be different?
Back to basics then. Its not clear from your post where your resonance is actually coming from. If you dont clarify the source its going to be hard to mod.
Can you retest resonance by tapping the basket directly on the mid-strut and then the circular surround between the struts to confirm the source.
Then mod with quick attenuation eg blutac on the mid-points of the basket and remeasure.
Then you will know where and how to mod.
Using wood stringers to stiffen may have unintended problems eg driving resonace higher into the midband where it may be audible or taking the structural curve and integrity out of the basket
Blutac mass attenuation can be augmented if needed by sticking stones on the blutac and taping over. Otherwise make little sand bags. Dry sand in the sun, pour into plastic to make mini sand bags and tape them on obsessively so if the plastic deteriorated in ten years no sand spills.
It will sound much better with the 160Hz peak fixed. Its guaranteed to sound better when you're not worried about some hidden issue 🙂
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That's interesting but makes sense. The resonance it taking energy and there is an acoustic dip.
I will try and isolate the resonance better using your tips...
Good point about potential pit falls when trying to stiffen the basket. More isn't always more...
I will try and isolate the resonance better using your tips...
Good point about potential pit falls when trying to stiffen the basket. More isn't always more...
What about using 1 cm thick cork strips glued using neoprene glue, later sourround it with a black cloth tape for a better look?
So I have some results. I really struggle with time for everything and just went ahead and strengthened the basket. Not really knowing what I'll achieve, but the stock basket is simply thin sheet metal, too thin. I have other stamped woofers and none are this thin. So what can go wrong...?
The plywood is fastened with epoxy I have mixed graphite powder into, making a super strong bond. Also painted black.
Here again is me tapping the cone while scoping the electrical output of the mic with my PicoScope:
The signal starts off with the large swing at fs, a little over 30Hz, but dies off quickly and turns into lower amplitude signal at about 170Hz. This is the high pitch 'ringin' I am complaining about. Granted, this is the driver laying on the table on it's magnet. Mounted this is likely no issue... but I cannot leave well enough alone.
Here is the strengthened basket while tapping. I included the electrical output of the voice coil into the other scope channel:
(different day, different channels. I should have kept the red trace on the mic, for easier comparisons)
So, the high frequency ringing is still evident at the beginning but now that is the component dying off quickly and the remaining oscillation is at driver's fs, about 38Hz now. So I think this mod increases the frequency of driver fs resonance. I guess the 170Hz resonance is no longer sapping energy from the woofer's own fs resonance and allowing it to freely resonate. I did this test over and over since the electrical signal was both so smooth, but also lasted for so long, not expected.
(Edit ...I mixed the mic and electrical scope traces. The red trace is electrical, the green is via the mic on the second pic with the modded basket.)
So did I make the woofer too resonant? I wonder b/c looking at the FFT of me tapping the cone I got this (again done many times to confirm):
There is that huge peak at resonance now. +8dB! Luckily it does not sound like this...
Here I send a train of 10x 40Hz sines (now the red trace is the electrical input from the signal generator):
And 200Hz:
For the above I included a piezo electric vibration sensor the driver was laying on. I do not think it has a very flat response, but it still gives interesting outputs. Also note I am using a signal generator directly, no amp, so the driving impedance is 50ohms.
Edit2:
The mic output is very similar for the stoc vs strengthened, but there is some difference after the sine train, looks better for the modded version at 40Hz while no real difference at 200Hz...
Looking at the stock basket measurement at 200Hz there seems to be a lower frequency noise component on the blue trace. This must be the mains 50Hz. I guess this day I had the setup so that this came in and me not noticing before now. The piezo pickup is very high impedance and noise is always an issue with them.
end edit...
That's all I have to show. Unfortunately I just didn't have time for proper and more measurements this time.
Regarding the big hump on the FFT when tapping the cone... I really cannot hear any boomy bass. Just solid and clear. I will take measurements some day when time permits.
I think they sound very good, I am no audiophile when it comes to perfection, and since the speakers are still under development I am not picky either way. I don't know how stock versions of this driver sounds, I bet they are fine too just as they come.
The plywood is fastened with epoxy I have mixed graphite powder into, making a super strong bond. Also painted black.
Here again is me tapping the cone while scoping the electrical output of the mic with my PicoScope:
The signal starts off with the large swing at fs, a little over 30Hz, but dies off quickly and turns into lower amplitude signal at about 170Hz. This is the high pitch 'ringin' I am complaining about. Granted, this is the driver laying on the table on it's magnet. Mounted this is likely no issue... but I cannot leave well enough alone.
Here is the strengthened basket while tapping. I included the electrical output of the voice coil into the other scope channel:
(different day, different channels. I should have kept the red trace on the mic, for easier comparisons)
So, the high frequency ringing is still evident at the beginning but now that is the component dying off quickly and the remaining oscillation is at driver's fs, about 38Hz now. So I think this mod increases the frequency of driver fs resonance. I guess the 170Hz resonance is no longer sapping energy from the woofer's own fs resonance and allowing it to freely resonate. I did this test over and over since the electrical signal was both so smooth, but also lasted for so long, not expected.
(Edit ...I mixed the mic and electrical scope traces. The red trace is electrical, the green is via the mic on the second pic with the modded basket.)
So did I make the woofer too resonant? I wonder b/c looking at the FFT of me tapping the cone I got this (again done many times to confirm):
There is that huge peak at resonance now. +8dB! Luckily it does not sound like this...
Here I send a train of 10x 40Hz sines (now the red trace is the electrical input from the signal generator):
And 200Hz:
For the above I included a piezo electric vibration sensor the driver was laying on. I do not think it has a very flat response, but it still gives interesting outputs. Also note I am using a signal generator directly, no amp, so the driving impedance is 50ohms.
Edit2:
The mic output is very similar for the stoc vs strengthened, but there is some difference after the sine train, looks better for the modded version at 40Hz while no real difference at 200Hz...
Looking at the stock basket measurement at 200Hz there seems to be a lower frequency noise component on the blue trace. This must be the mains 50Hz. I guess this day I had the setup so that this came in and me not noticing before now. The piezo pickup is very high impedance and noise is always an issue with them.
end edit...
That's all I have to show. Unfortunately I just didn't have time for proper and more measurements this time.
Regarding the big hump on the FFT when tapping the cone... I really cannot hear any boomy bass. Just solid and clear. I will take measurements some day when time permits.
I think they sound very good, I am no audiophile when it comes to perfection, and since the speakers are still under development I am not picky either way. I don't know how stock versions of this driver sounds, I bet they are fine too just as they come.
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Thinking about it I think all this work with the basket strengthening is just the same as mounting the driver in a baffle. LOL all the work and to what?
Some of these issues are precisely why I stopped using pro audio drivers. On paper they have some attractive aspects, especially high sensitivity, and in some ways they seemed perfect for my needs. But some of the stamped frame drivers are just not made all that well. Most all have cone resonance issues due to the lightweight materials required for high sensitivity. And on top of that, many include noisy turbulent cooling techniques for the voice coil. They are up to the task of "loud for cheap", but not audiophile grade stuff. Only when you spend much more to get some seriously well built pro drivers do some of these issues abate, but never seem to completely go away.
The Bianco is not PA, it is designed and intended for open baffle audio (HiFi) speakers. With a Qts of about 0.7 they should work great in a closed box too.
Regarding PA, Well mostly the cheap PA driver perhaps. I have som every nice vintage 15" drivers like EV15B and Peavey Black Widows I've cannibalized out of swap-meet PA speakers I got for nothing (they were not the expensive drivers of the day either, but certainly better than cheap stamped drivers). Also the vintage JBLs are quite nice. New drivers are great too if you don't go cheap. Granted to get high efficiency you must sacrifice low end extension, but 40-ish Hz and great speed and articulation in the bass is perfectly ok for me.
Regarding PA, Well mostly the cheap PA driver perhaps. I have som every nice vintage 15" drivers like EV15B and Peavey Black Widows I've cannibalized out of swap-meet PA speakers I got for nothing (they were not the expensive drivers of the day either, but certainly better than cheap stamped drivers). Also the vintage JBLs are quite nice. New drivers are great too if you don't go cheap. Granted to get high efficiency you must sacrifice low end extension, but 40-ish Hz and great speed and articulation in the bass is perfectly ok for me.
Sure. I have the 12" OB Bianco driver. The first version. I am familiar with the line. I have several other pro audio drivers of various brands, some with stamped frames, some with cast frames. Most are not great, with one or two exceptions.