Hi Everyone,
Edit: Issue resolved. My amplifier was nowhere near sufficient enough to drive my subwoofers adequately. After strapping a Crown XLS2500 across the drivers, things are great. Cheers!
I built a dual 15" Ripole subwoofer using Dayton RSS390HF-4's. Everything works great as expected until transient bass notes hit, then it sounds similar to the suspension/coil bottoming out. The issue is that I hear this when there's only 3-4mm of excursion. My ignorance on the physics of this exact topic leaves me just with some bad feelings, as if the suspension is just not okay in this application, but I'm having a hard time identifying which parameters I should be looking at. I've measured the THD to see if there's anything obvious going on, like resonances from the slots, or significant dominance of even vs odd harmonics....etc. Nothing pops out. The THD plots are clean at 95dB 1m, generally less than 1% in the sub range.
Here's a recording of the sound.
Recording of "blatt, blatt, blatt" sound
I'm wondering if there's a slight imbalance of pressure on the cone from the cavity geometry, since the backwall of each cavity is curved (to reduce the Q of the 1/4 wave resonances), which may put an uneven load on the cone, which might be able to "rock" the cone to one side during its stroke, and maybe the coil is actually rubbing on the magnet / pole piece during these louder, transient signals? I'm somewhat convicted in this belief at the moment since the driver in free-air excurts significantly more before I start to hear the suspension doing suspension-y things.
This is the impedance sweep of the ripole.
And this is the THD measurement @ 1m of the Ripole, DSP already applied (dipole correction boost, cavity resonances reduced, 20Hz and 105Hz steep crossovers, room correction
)
And here's the THD measurement of the full integrated system measured at 2.5m, listening position:
I did a quick experiment. I "sealed" the front cavity on carpet by rotating the enclosure 90deg, leaving only the dual rear cavities open, the output changes to that of a monopole, and is expectedly more efficient. It gives the sound you would expect of a large driver in an undersized enclosure. But the strange suspension sound diminishes quite a bit, if not completely. However, since I don't have a way to directly measure the "sound" of the suspension / coil noise, I suspect I'm just experiencing a higher "signal to noise" ratio, given the expected efficiency boost of no longer being a dipole flapper.
Anyways, I am curious if others are having this issue. I am looking for help identifying root cause / physics of the issue. I would also love to be able to better select a subwoofer driver for this application. I followed all the info I knew at the time of purchase for this application, aiming for a final Qts of 0.7 in enclosure, choosing a driver with low distortion motor desgin, high excursion, and designing the enclosure cavity sizes scaled up from my previous build, where I used 4x Peerless SLS 10" subs, chambered. (they sounded good)
Edit: Issue resolved. My amplifier was nowhere near sufficient enough to drive my subwoofers adequately. After strapping a Crown XLS2500 across the drivers, things are great. Cheers!
I built a dual 15" Ripole subwoofer using Dayton RSS390HF-4's. Everything works great as expected until transient bass notes hit, then it sounds similar to the suspension/coil bottoming out. The issue is that I hear this when there's only 3-4mm of excursion. My ignorance on the physics of this exact topic leaves me just with some bad feelings, as if the suspension is just not okay in this application, but I'm having a hard time identifying which parameters I should be looking at. I've measured the THD to see if there's anything obvious going on, like resonances from the slots, or significant dominance of even vs odd harmonics....etc. Nothing pops out. The THD plots are clean at 95dB 1m, generally less than 1% in the sub range.
Here's a recording of the sound.
Recording of "blatt, blatt, blatt" sound
I'm wondering if there's a slight imbalance of pressure on the cone from the cavity geometry, since the backwall of each cavity is curved (to reduce the Q of the 1/4 wave resonances), which may put an uneven load on the cone, which might be able to "rock" the cone to one side during its stroke, and maybe the coil is actually rubbing on the magnet / pole piece during these louder, transient signals? I'm somewhat convicted in this belief at the moment since the driver in free-air excurts significantly more before I start to hear the suspension doing suspension-y things.
This is the impedance sweep of the ripole.
And this is the THD measurement @ 1m of the Ripole, DSP already applied (dipole correction boost, cavity resonances reduced, 20Hz and 105Hz steep crossovers, room correction
)
And here's the THD measurement of the full integrated system measured at 2.5m, listening position:
I did a quick experiment. I "sealed" the front cavity on carpet by rotating the enclosure 90deg, leaving only the dual rear cavities open, the output changes to that of a monopole, and is expectedly more efficient. It gives the sound you would expect of a large driver in an undersized enclosure. But the strange suspension sound diminishes quite a bit, if not completely. However, since I don't have a way to directly measure the "sound" of the suspension / coil noise, I suspect I'm just experiencing a higher "signal to noise" ratio, given the expected efficiency boost of no longer being a dipole flapper.
Anyways, I am curious if others are having this issue. I am looking for help identifying root cause / physics of the issue. I would also love to be able to better select a subwoofer driver for this application. I followed all the info I knew at the time of purchase for this application, aiming for a final Qts of 0.7 in enclosure, choosing a driver with low distortion motor desgin, high excursion, and designing the enclosure cavity sizes scaled up from my previous build, where I used 4x Peerless SLS 10" subs, chambered. (they sounded good)
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How confident are you about the amount of excursion before this happens? If you haven't done it already, you can make a device to help estimate the excursion more accurately - see https://www.linkwitzlab.com/faq.htm#Q29
I'm confident that excursion is not the reason for the noise sound i'm hearing. I've done a few more tests. I used a sine generator and cranked the lineOUT level until I heard the noise/distortion/artifact/rocking mode... I discovered that at very low frequencies, I could crank the level as high as it would go, and the driver was moving near its limits, and still not generating the noise/distortion.... Then I increased the frequency by 1Hz for each subsequent test, adjusting the output level until I could hear the noise, then incrementally backing off the level 0.1dB at a time, until the noise was no longer audible. This is the result.
At 16 and 17Hz, my amplifier just wasn't powerful enough to drive the loudspeaker any further. at these two frequencies I didn't hear any noise/distortion, but at 18Hz ,I could detect it finally, so I presume I was fairly close to the detectability threshold, only shy of amplifier power by a few dB. Anyways, you can clearly see centered at 27Hz, there's a noticeable phenomenon, where the ripole/sub is driven to noise somehow with lower power. The excursion decreased as you would expect proportional to the ratio of frequency (f2/f1)^2.
I also noted the SPL at 1m for the audibility threshold of the noise for each of these frequency points. Remember to keep in mind, this is not related at all the frequency response. This is simply the amount of output SPL the Ripole can generate at each frequency (1Hz per test), before some noise/distortion/rocking mode is audible. And, the above graph is the necessary LineOUT level used to drive the system to these levels.
I'm beginning to suspect there's a standing wave / turbulence issue here, where at some frequencies (notably near 27 hz) air is finding a difficult time entering and exiting from the ripole cavities. (I'm imagining a trumpet without a horn flare, and only some discrete notes can efficiently exit the tube due to the impedance mismatch between the "tube" and the infinite impedance of the room).
All thoughts on this are welcome. I'm really scratching my head. How can I determine if this is a box design issue (geometry / volume / slot area...etc) vs a driver issue (ideally without having to construct yet another enclosure).???
At 16 and 17Hz, my amplifier just wasn't powerful enough to drive the loudspeaker any further. at these two frequencies I didn't hear any noise/distortion, but at 18Hz ,I could detect it finally, so I presume I was fairly close to the detectability threshold, only shy of amplifier power by a few dB. Anyways, you can clearly see centered at 27Hz, there's a noticeable phenomenon, where the ripole/sub is driven to noise somehow with lower power. The excursion decreased as you would expect proportional to the ratio of frequency (f2/f1)^2.
I also noted the SPL at 1m for the audibility threshold of the noise for each of these frequency points. Remember to keep in mind, this is not related at all the frequency response. This is simply the amount of output SPL the Ripole can generate at each frequency (1Hz per test), before some noise/distortion/rocking mode is audible. And, the above graph is the necessary LineOUT level used to drive the system to these levels.
I'm beginning to suspect there's a standing wave / turbulence issue here, where at some frequencies (notably near 27 hz) air is finding a difficult time entering and exiting from the ripole cavities. (I'm imagining a trumpet without a horn flare, and only some discrete notes can efficiently exit the tube due to the impedance mismatch between the "tube" and the infinite impedance of the room).
All thoughts on this are welcome. I'm really scratching my head. How can I determine if this is a box design issue (geometry / volume / slot area...etc) vs a driver issue (ideally without having to construct yet another enclosure).???
You need to put a lowcut/subsonic filter there. The range where the driver doesn't provide any useful spl needs to be cut out to prevent it from doing excessive excurstion. Also, EQing it below its FB is quite destructive, no matter what REW or other tools say.
Hi ICG,
I have an LR4 HPF at 20Hz, the driver resonance is at 16.7 Hz, per measurement. I've tried moving that HPF around to multiple frequencies, even as high as 45 hz. There continues to be some wonky sound every now and again based on level and frequency of excitation (things I "KNOW" are related so far). The EQ is only using IIR parametric direct form II filters, and I think there's like 5 or 6 filters in place. A couple filters to boost the low end (well within the capabilities of this driver as demonstrated in free-air operation, no noise/distortion after filtering), and a few filters to notch resonances and a couple to overall gradually shape to the room response curve.
Could you be a bit more specific about what phenomenon or mechanisms would be harmed or excited by Eq that you were thinking about?
I have an LR4 HPF at 20Hz, the driver resonance is at 16.7 Hz, per measurement. I've tried moving that HPF around to multiple frequencies, even as high as 45 hz. There continues to be some wonky sound every now and again based on level and frequency of excitation (things I "KNOW" are related so far). The EQ is only using IIR parametric direct form II filters, and I think there's like 5 or 6 filters in place. A couple filters to boost the low end (well within the capabilities of this driver as demonstrated in free-air operation, no noise/distortion after filtering), and a few filters to notch resonances and a couple to overall gradually shape to the room response curve.
Could you be a bit more specific about what phenomenon or mechanisms would be harmed or excited by Eq that you were thinking about?
Below 38Hz will not be possible unless you take a really serious hit in maxspl.
Clack clack clack is physical damage. over excursion
its a bunch of boost, plus a speaker design with not much cone control.
if the rear magnet is bump back plate for clearance , and your still getting clack.
your pushing it. wayyyy past xmax
pretty good speaker if its hitting and hasnt straight locked yet.
some dont last that long. ones that do last they clack here and there eventually it always clacks.
it kinks the cone. others few clacks and its gone.
pretty tough speaker
its a bunch of boost, plus a speaker design with not much cone control.
if the rear magnet is bump back plate for clearance , and your still getting clack.
your pushing it. wayyyy past xmax
pretty good speaker if its hitting and hasnt straight locked yet.
some dont last that long. ones that do last they clack here and there eventually it always clacks.
it kinks the cone. others few clacks and its gone.
pretty tough speaker
Thanks WhiteDragon. It's not hitting, but it's the only sound noise I can think of to compare it to. The cone is barely moving when I get the distortion/ noise. MAYBE, 3mm, possibly 4mm, Absolutely nowhere near 14mm.
But yeah, I agree, it I were getting actual clacks, she'd be done.
I shared a little bit above, that I tested in 1Hz increments to find how loud I could operate the ripole until I started to faintly hear the distortion/noise/rocking emerge. At 16-18Hz, I couldn't generate the noise with my setup. It was moving about 12mm pk, and not a hint of the noise present. But at 27Hz, for example, the cones were able to create that noise with considerably less stroke. Any ideas?
But yeah, I agree, it I were getting actual clacks, she'd be done.
I shared a little bit above, that I tested in 1Hz increments to find how loud I could operate the ripole until I started to faintly hear the distortion/noise/rocking emerge. At 16-18Hz, I couldn't generate the noise with my setup. It was moving about 12mm pk, and not a hint of the noise present. But at 27Hz, for example, the cones were able to create that noise with considerably less stroke. Any ideas?
usually random is kink cone or dust cap or spider working loose.
if its rolling or cone rocking there can be coil scrape. sounds kinda like clack.
but is more of a noise decay to it.
heard class d amps get angry too, same thing sounds like clack but is more electrical noise.
flyback or false triggers to " advanced protection circuits"
pulling juice, the magic of switch mode or scratchy sounding amp limiting
if its rolling or cone rocking there can be coil scrape. sounds kinda like clack.
but is more of a noise decay to it.
heard class d amps get angry too, same thing sounds like clack but is more electrical noise.
flyback or false triggers to " advanced protection circuits"
pulling juice, the magic of switch mode or scratchy sounding amp limiting
The box design should not be an issue, but if the baffles are not perfectly flat, the warped frame could result in coil drag.
Air leaks around the driver can also make noise. Tinsle lead obstructions are also a possibility.
I had a new driver that sounded (and felt) like it was "bottoming out" well before Xmax, it "fixed" itself when driven hard, there was probably a piece of glue in the gap that was dislodged.
I did not hear your recording (don't have a Google account), but any of those issues could be responsible for a "Blat Blat Blat" sound.
Your driver's Xmax is 14mm, you should be able to see them move 28mm peak to peak (over 1 inch) without hearing extraneous noise, other than vent noise. The SPL you have shown in the above distortion charts could be achieved at a fraction of that excursion, so wouldn't show any problem
The suspension shouldn't make noise until well past Xmax.
Push the drivers evenly by hand to at least that excursion in either direction, feel for resistance, listen for any scraping noises.
Most modern high excursion drivers suspensions set Xlim before the coil former can contact the back plate.
Also, I should point out that I'm currently listening to just the left 4-way tower (the ripole is connected) and I just measured 95dB SPL at my ears, nearly 3 meters away. Listening to "Make us Stronger" track which is heavy electronic beat for most of it. It's at least 90 % great at this level, but occasionally I can hear some "blat blat" underneath the music, which goes away with decreased volume level. When I eventually add the right side tower I would expect another 3dB, which is plenty loud for most of what I'd listen to. I do fear that movie soundtracks will cause distraction with heavy bass/explosions.
Anyways, I just wanted to give some perspective, that this sound it's absolutely rotten, its just when I turn it up apparently past this point, or with bass containing PSD near that 27 Hz region, it gets "blat"y.
When I threshold for the noise with sine waves, it doesn't sound like blat blat blat, it sounds more akin to coil scrape (actually kind of sounds like a synthesizer with beat frequencies). If it's helpful for diagnosis, the enclosure barely vibrates....indicating a rather good force cancellation. I don't have too many comparison points for this, but with each driver capable of 150N of force at 30Hz, I'm impressed that the enclosure doesn't "move" much. It's close to zero vibration, but certainly not zero.
Or Qts, Qms
if a driver has " more control at resonance"
some woofer impedance curve peaks might shoot up to 30 or 40 ohms.
But if it has more control or high control. impedance peak shoots wayyyy up there 50 to 70 ohms indicates more control.
once thats over slam down to 4 or 3 ohms
So looking at impedance curve depending on " alignment"
if the double hump impedance has huge first hump , has control there.
or likewise some alignments the second hump has more control there.
not really, unload zone
so what frequency a class d starts crying when pulling big juice.
somewhat clued in by impedance curve. low current, slam high current, low current slam, high current.
ride the impedance roller coaster, tube amps hate it more...switch modes really hate it.
physical or electrical crackle one of the 2
if a driver has " more control at resonance"
some woofer impedance curve peaks might shoot up to 30 or 40 ohms.
But if it has more control or high control. impedance peak shoots wayyyy up there 50 to 70 ohms indicates more control.
once thats over slam down to 4 or 3 ohms
So looking at impedance curve depending on " alignment"
if the double hump impedance has huge first hump , has control there.
or likewise some alignments the second hump has more control there.
not really, unload zone
so what frequency a class d starts crying when pulling big juice.
somewhat clued in by impedance curve. low current, slam high current, low current slam, high current.
ride the impedance roller coaster, tube amps hate it more...switch modes really hate it.
physical or electrical crackle one of the 2
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Hi there 🙂
The problem about low end boosts is, they increase the excursion a lot. Especially if the boost is very high and the worst is if it's below the fb. Even above fb the EQ can cause severe excursion, lowering the max spl vastly. EQing a sub below its capabilities will lead to a much lower frequency range but also reduce the loudness it's capable of. A driver resonance of below 20Hz is extremely low and sounds like you've tried to push your sub way below its capabilities. Unless you've got a 15"+ sub, it probably can't provide the spl your (massive?) EQ would require.
Thanks for the insight. I tend to agree, however I've designed this system with that in mind already. I'm using dual 15's which have a free-air resonance at 19Hz, from the factory. When you slot load them in a ripole enclosure, the qts increases and the Fs reduces by something close to 15-20%. My measured Fs of this system (which does not depend on eq, only the physics of the driver and enclosure air loading) is 16.7Hz.
From there, I apply some equalization as shown in one of the above posts. max boost I think is about 13.5dB at 25Hz, which does indeed result in some boost also being applied below, something like 10dB at 16 hz IIRC. Anyways, yes EQ definitely has a known effect on reducing headroom, but like I've mentioned the issue is not excursion related. I hear the noise issue even when the driver is barely moving. And in contrast, at 17Hz for example, running a sine wave with enough level to get nearly 12mm excursion (1-way), the noise doesn't show up. The noise appears to only show up with extreme level or particular frequencies.
My goal is to figure out the actual responsible mechanism of the mechanical noise. So far, I can confirm it is not strictly excursion related. That is to say, large excursions at some frequencies do not result in the noise appearing. By contrast, low excursion at the "right" frequency ranges does indeed excite something responsible for the audible noise phenomenon.
I appreciate your responses.
If you can press the drivers past 14mm one way with no scrape feel, and you don't see excursion of more than 28mm peak to peak, it's probable you are hearing some gain stage issue, digital clipping from the +13.5dB 25Hz PEQ boost.
Or possibly amp clipping- some amps don't sound bad when clipped, others make it sound like a broken speaker.
Compare the same excursion with a 25Hz sine wave with and without the PEQ.
Should get +3dB from doubling cone area, and another +3 dB from doubling power, total of around +6dB.
That's the issue, it's not able to reproduce that frequency at that level. For anything below 20Hz and a boost of 10dB you'd need to more than quadruple the membrane surface. So at 16Hz you'd need dual 24" to be on the same level. Or, in other words, what you want isn't possible - no matter if you see it or not!
Hi Brandon,
Did you try to rule out the filters and DSP SW completely ? the tests above where with the filters in and moved around somewhat?
It sounds more like a control issue - but whether it's simply the woofers or on the input side is another matter ;-)
Unfortunately, however nice the DSP filter setups might look - I've seen and experienced a lot of hiccups in this across systems.
White dragon has a point also on that - for ClassD (?) it could be powersupply pumping is provoked, it is at the lowest impedance - but frankly it is also not overly low - depends on the power output you are pushing. You shift the Q and thus the impedance by closing off one side - so that will have an impact on that.
Best advice is to try and pull the system back to basics, step by step fully ruling out the parts in the chain.
Did you try to rule out the filters and DSP SW completely ? the tests above where with the filters in and moved around somewhat?
It sounds more like a control issue - but whether it's simply the woofers or on the input side is another matter ;-)
Unfortunately, however nice the DSP filter setups might look - I've seen and experienced a lot of hiccups in this across systems.
White dragon has a point also on that - for ClassD (?) it could be powersupply pumping is provoked, it is at the lowest impedance - but frankly it is also not overly low - depends on the power output you are pushing. You shift the Q and thus the impedance by closing off one side - so that will have an impact on that.
Best advice is to try and pull the system back to basics, step by step fully ruling out the parts in the chain.