Acoustic response includes both magnitude and phase. So like Boden said, step response is a function of acoustic response.
So if sealed and ported have the same acoustic response, then they have the same step response.
It's also worth noting that phase trace of the bottom end roll-off is almost entirely due the mag trace roll-off.
Iow, magnitude roll-off is minimum phase.
So the order of the acoustic magnitude roll-off establishes the phase trace, and is what we hear I think.
If and only if, sealed subs are operated within their excursion limit at the very lowest frequency at desired max SPL,
then yes sealed certainly has a two-order advantage over ported.
But I think it only takes a little number crunching with the piston calculator, to see how quickly that condition of operation gets violated.
https://www.baudline.com/erik/bass/xmaxer.html
Of course, the way to meet the condition of operation is to keep SPL low enough to stay within excursion at the lowest freq...
...which is almost invariably dang low compared to the rest of the system's SPL capability.
Guess I need to ask what do you call the last low octave?
Why would you assume that?
I call the last low octave to be 20-40Hz. So 20hz is key freq.
@20hz, I can only get to 107dB 1m with a single sealed 18" driver with 19mm xmax. (18n862)
But I guess I could put the six of those 18"s i have, stacked together sealed somehow, to reach 122dB.....
Naw, scrap that idea...ports work better.😀
Hi,
Energy of content in typical music recordings drops very fast below about 60-80 Hz. This saves the day, and normally for listening music loud there is no need to design a system for full SPL level @20 Hz, which is hardly attainable with most ported systems either.
Regards
Put them in a corner and you already get 6dB for free.
Unless your room is really big, but there is also plenty of room gain at that point.
So in a multi-sub system that will also add up nicely until we'll reach the pesky room mode region.
Wouldn't recommend going for 122dB btw, if you wanna listen and enjoy music for the rest of your life
He does have a large room, and also uses his speakers outdoors at times, so sealed is pretty much a no-go for him.
122 dB capability does not mean that any sane individual would drive them to their limit indoors for any amount of time. Giving yourself 30 dB of headroom, that gives 92 dB. Similarly, I don't know of anyone that drives their car at 8500 rpm all day long.
Hi Bazukaz,
latest ported subs I built recently have a f-3 @25Hz. I don't see much of a need for 20Hz either, but I do for 30Hz.
For me, adding a 2nd order shelf filter to extend the bass response of a sealed box woofer means that the response is flat down to the point of rolloff.
Here is an example using the SB34NRX75-6 woofer, a 12" driver I am quite familiar with. With a 6 dB shelf filter at 32 Hz, we go from an F3 of 40 Hz to an F3 of 27 Hz. The Group Delay is better in the EQ'd system as well... lower GD from 40 Hz on up. Only below 40 Hz is the GD higher with the EQ system, and this would be true of any sealed box system that had an F3=27 Hz without EQ.
In actual practice, the 2nd order shelf filter would be developed using measured near field data, not a simplified simulation. But the final filter would not be too far different from this.
j.
Thanks diyuser,
yes, my purpose of high SPL capability is not to listen to average SPL at crazy high levels, but to have complete linearity for headroom.
It adds a whole lot to sound quality ime/imo, to have unclipped, uncompressed linearity for +18dB headroom over average SPL levels.
It all depends. 122 dB is not that loud at 20 Hz. But even if listening less loudly a system with headroom is always fun to listen to. And a lower corner frequency does indeed improve group delay further up. And don't forget to dimension all your coupling caps for a very low cutoff frequency (< 1Hz) in order to further reduce group-delay. Only one intentionally chosen pole (or pole pair) should be higher up in frequency in order to form a decided target response together with the woofer.
And yes, a chain that is going really low does indeed add to the fun. It doesn't usually have to go very low AND loud but there is always a chance for it of getting "caught on the left foot". I have a sampler by Barbara Hendricks wehre there is some subsonioc noise on one track that can cause frightening movements of the woofers.
Regards
Charles
Bad news, Mark: that BMS driver has an effective diameter of 394mm, or about 15.5 inches, which will only get you just over 104 dB at 1m in a sealed box.
It is quite interesting that a box tuning with a higher Q can have less group delay further up although this may sound counter-intuitive at first.
Regards
Charles
Haha...that's good news! I was just grabbing max SPL using the piston excursion calculator i linked above. Never bothered with max sealed measurements.
Calculator specifies:
- basic piston formula:
- SPL = 112 + 10 * log(4 * pi^3 * Ro / c * (num * Vd)^2 * f^4)
- Vd = (.83 * diam)^2 * pi / 4 * Xmax
Yay, but LOL too...
....Because we all know max SPL is going to get derated big time once thermal compression begins to set in...
Hi Jim, I just ran a quick sim in hornresp of that woofer, 50L box, and a low shelf that appears to match what you used.
(always hard to translate shelving filters exactly between programs/processors, but I'm confident it's close)
The woofer has a power rating of 200 watts. Using that power rating, here is the displacement (excursion) HR predicts.
Woofer has 11mm xmax. I think it could be dang easy to exceed xmax without some form of hpf in place.
Or add a voltage limiter. Or just keep the volume down ALL the time.
BTW, i tried an experiment using frequency dependent voltage limiting instead of a hpf, hoping to mitigate the group delay a hpf would add.
It worked as far as limiting voltage and excursion...but guess what...
group delay / phase was the same when limiting was hit, just as if a hpf was in place. No free lunches in audio, huh?
Hi Mark
I guess that this does still sound better than a voice-coil hitting the backplate ! 😉
Regards
Charles
So I did some ditortion measurements on microphones - hope this hepls to choose the right tool for speaker measurements:
https://www.diyaudio.com/community/...ement-microphones-actual-measurements.411218/
https://www.diyaudio.com/community/...ement-microphones-actual-measurements.411218/
Hi Charles, you made me laugh
Because I know that sound all too well.....😀
Hey, the best song I've ever found for umm...exploring the voltage it takes for my subs to make that sonic event occur, LoL,
has been Joe Walsh's Ordinary Average Guy
It a good track because the kicks occur right at the beginning, and I can ease voltage up in increments where the backplate strike is soft when finally hits.
I like knowing where the edge is, for setting peak limiters.
I wouldn't blatantly dismiss the validity of ported enclosures even as a person who favors sealed box bass. I do confess there are some decent ported designs out there and some of them can rival some sealed designs in quite a few ways.
This is basically implying that certain ported alignments sound better than others, but it depends on how well the driver is optimized for a specific type of enclosure. Its not just Qts, Fs and Vas which determine a specific enclosure application. While these are important as starting quidelines, there are other smaller design traits which make a woofer suitable for a specific enclosure types and even specific tunings thereof. Some driver features and specs don't necessarily single it out for just one specific enclosure tuning, but usually indicate more of an optimal range of tuning which should be aimed for to get the best from the driver.
For most ported alignments, I find drivers with a Qts in the range of .36 - .42 to be best suited for ported boxes. This allows for a tuning which has about the same box volume Vb as the driver's Vas and puts the tuning frequency Fc the same as the driver's resonant frequency Fs. In simpler terms this is defined as a QB3 alignment. While this type of tuning in theory has some drawbacks compared to other alignments (ie SBB), it allows the driver to behave like it would in free air, duplicating its TS parameters as they were measured in that environment.
That brings me to the next important criteria which makes a QB3 alignment the best of both worlds, combining the strengths of sealed and ported boxes. Drivers with the lowest possible Fs allow the lowest box tuning Fb, which gives you a low cutoff frequency while not affecting the critical midbass, as the port isn't practically contributing output in that range. This gives you sealed box upper bass with the low end extension of ported box. Your ears are far more sensitive to group delay and phase shift in the upper bass (60 hz +) than further down in the lowest octave where the port is mainly doing its job.
The drawbacks of the above type of ported alignment is that it requires a large enclosure, but the benefits can be significant as long as you take care to avoid port resonances and midrange spill. The port length also is less for the given alignment tuning, so it minimizes the chance of significant port resonances associated with longer ports.
The last important traits of a decent ported box woofer is decent Xmax, a large, linear behaving spider and surround, plus low Le (if you intend to cross the driver further up in the midrange). Higher woofer LP cutoffs require a well dampened cone and suspension with minimal radial breakup, caused by radial cone resonances reflecting back from the surround (the typical FR kink around 500 hz to 1k found in most LF drivers).
If you follow these guidelines closely, you'll end up with a ported system which can meet or in some cases even outdo the resolution, output and low end extension of a sealed design.
This is basically implying that certain ported alignments sound better than others, but it depends on how well the driver is optimized for a specific type of enclosure. Its not just Qts, Fs and Vas which determine a specific enclosure application. While these are important as starting quidelines, there are other smaller design traits which make a woofer suitable for a specific enclosure types and even specific tunings thereof. Some driver features and specs don't necessarily single it out for just one specific enclosure tuning, but usually indicate more of an optimal range of tuning which should be aimed for to get the best from the driver.
For most ported alignments, I find drivers with a Qts in the range of .36 - .42 to be best suited for ported boxes. This allows for a tuning which has about the same box volume Vb as the driver's Vas and puts the tuning frequency Fc the same as the driver's resonant frequency Fs. In simpler terms this is defined as a QB3 alignment. While this type of tuning in theory has some drawbacks compared to other alignments (ie SBB), it allows the driver to behave like it would in free air, duplicating its TS parameters as they were measured in that environment.
That brings me to the next important criteria which makes a QB3 alignment the best of both worlds, combining the strengths of sealed and ported boxes. Drivers with the lowest possible Fs allow the lowest box tuning Fb, which gives you a low cutoff frequency while not affecting the critical midbass, as the port isn't practically contributing output in that range. This gives you sealed box upper bass with the low end extension of ported box. Your ears are far more sensitive to group delay and phase shift in the upper bass (60 hz +) than further down in the lowest octave where the port is mainly doing its job.
The drawbacks of the above type of ported alignment is that it requires a large enclosure, but the benefits can be significant as long as you take care to avoid port resonances and midrange spill. The port length also is less for the given alignment tuning, so it minimizes the chance of significant port resonances associated with longer ports.
The last important traits of a decent ported box woofer is decent Xmax, a large, linear behaving spider and surround, plus low Le (if you intend to cross the driver further up in the midrange). Higher woofer LP cutoffs require a well dampened cone and suspension with minimal radial breakup, caused by radial cone resonances reflecting back from the surround (the typical FR kink around 500 hz to 1k found in most LF drivers).
If you follow these guidelines closely, you'll end up with a ported system which can meet or in some cases even outdo the resolution, output and low end extension of a sealed design.
H hifijim,
thank you very much for the explanation and simulation.
Like Charles, I agree that:
Kindest regards,
M
thank you very much for the explanation and simulation.
Like Charles, I agree that:
namely because the "accepted wisdom" I read claimed the opposite.
Kindest regards,
M
Hi Mark - Yes, the VituixCad sim has an almost identical excursion plot at 200 W.
If I thought I would ever come close to pushing 200 W through this driver, I would use 2 or more of them. My personal rule of thumb for SPL / excursion limits is I design for hitting Xmax at 40 Hz, and that defines the SPL limit for a sealed box woofer, whether it uses a bass EQ or not. For this driver, that would be about 85 W and 107 dB.
The kind of operator who would drive a woofer to Pmax, either accidently on purpose, or purposely by accident, is not a good candidate to operate a sealed box woofer system with LT bass EQ.
Right, okay clear.
Nothing wrong with personal situations, but it's a bit confusing to read it as general advice 🙂