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Post by ThomasW on Apr 8, 2012 7:14:24 GMT -7
In most standard subwoofer alignments the output is limited by the thermal capacity of the driver's motor system. IOW how much power the voice coil can handle before it melts. IB subs are a different animal, the output of the sub is limited by how much excursion the driver/drivers have. The following 4 posts illustrate why we 'derate' Pmax for IB sub use and the effect doing that has on output and frequency... First is the Dayton RSS390HF-15" with it's mfgr's 500 watt Pmax rating Xmax limit is hit at 35Hz, 112dB Attachments:
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Post by ThomasW on Apr 8, 2012 7:16:15 GMT -7
Now if we derate the Dayton RSS390HF-15" Pmax to 100watts, Xmax limit is hit at a more reasonable ~17Hz, but the output drops to ~99dB. Attachments:
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Post by ThomasW on Apr 8, 2012 7:26:06 GMT -7
Next is the Fi IB3 18" using the mfgr's 560 watt Pmax rating. Xmax limit is hit at 20Hz with 112dB output Attachments:
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Post by ThomasW on Apr 8, 2012 7:31:08 GMT -7
If we derate the IB3 18's Pmax to 350watts the excursion limit is hit at approx 13Hz with 100dB output Attachments:
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Post by ThomasW on Apr 8, 2012 7:47:11 GMT -7
What's the moral of this story? If you want it to play loud and low, use multiple drivers .....  |
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Post by FOH on Apr 8, 2012 8:31:08 GMT -7
Thomas,
Perfect timing, good explanation......
Thanks
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Post by chrisbee on Apr 8, 2012 9:55:49 GMT -7
I'm not so sure. No direct connection is suggested between lowering the power and using multiple drivers.  Not to mention mutual proximity gain! Yeah!!  I'd like a nice graph of two or four drivers to prove his argument.  So far Thomas has only turned down the volume. Now we need him to turn it right back up again! ;D A.Pedant.  |
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Post by severianb on Apr 8, 2012 10:05:03 GMT -7
Great explanation with pictures. There truly is no replacement for displacement.
I hope I never run into XMAX at 20hz with my 4 IB3s. The windows might crack.
I don't know exactly how low War of the Worlds goes, but I was able to play it reference level without any weird noises from the drivers, just severe tactile sensations.
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Post by FOH on Apr 9, 2012 11:04:37 GMT -7
WoTW, the lightning scenes, the LFE plunges down, deep deep down into the 4-5hz range with relatively high signal level. Attachments:
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Post by Pete Mazz on Apr 16, 2012 3:37:27 GMT -7
I always get a kick out of folks "bragging" about their sub being 500 watts. Like it has anything to do with freq response or sound quality.
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Post by satch17 on Apr 28, 2012 10:08:24 GMT -7
hmm, 4 drivers with 13hz pass should be 106db, yes i want to see that drywall powder maker graph too so if heat and dc signals are a worry for boxed subs, and there are amps with little lights that come on for this warning. wouldnt it be nice if we had a little touch sensor hovering 30mm above the driver surface (or whatever the xmax for whatever speaker) maybe on the very edge of 1 sub that illumiated an LED to warn you? and if you could real-time record the event you could cross reference and isolate the signal to a graph. |
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Post by bigjon on Apr 28, 2012 17:49:01 GMT -7
I always get a kick out of folks "bragging" about their sub being 500 watts. Like it has anything to do with freq response or sound quality. These are the same people that say they have a fast car because the speedometer goes up to 160mph. |
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Post by drdyna on May 7, 2012 4:28:28 GMT -7
I always get a kick out of folks "bragging" about their sub being 500 watts. Like it has anything to do with freq response or sound quality. Yeah, just like all the guys on youtube that like to make videos of clipping amplifiers driving a speaker way over xlim to the point where you can hear the driver bouncing back and forth off of it's mechanical limit. I actually started a movement to stop cruelty to loudspeakers (it's a joke, but not really) just for funsies. www.youtube.com/watch?v=-v6_jiqaDpkYou can search for the song "Bass, I love you" it's amazing how many people choose this song as some sort of "theme" for which to destroy their speakers to. |
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Post by chrisbee on May 7, 2012 5:40:36 GMT -7
They are only trying to outdo me with my 8 x 15" IB. I recorded mine from inside the IB enclosure. There were only half a dozen videos of that track back then. Now there are 30 pages of videos listed. The infrasonic "mines" are just silly. They are completely inaudible except on crap subwoofers with loads of distortion. They also set a severe limit on how loud the piece can be played due to excursion limits. The composer claims to be able to hear these very low notes on his home sub. Point proven, I think. |
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Post by drdyna on May 7, 2012 5:48:33 GMT -7
They are only trying to outdo me with my 8 x 15" IB. I recorded mine from inside the IB enclosure. There were only half a dozen videos of that track back then. Now there are 30 pages of videos listed. The infrasonic "mines" are just silly. They are completely inaudible except on crap subwoofers with loads of distortion. They also set a severe limit on how load the piece can be played due to excursion limits. The composer claims to be able to hear these very low notes on his home sub. Point proven, I think. Yeah, if I turn it up louder than I did in that video I can hear the walls react a little to the "mines" but it's really just a "puff" of pressure, doesn't really feel like a note. Reminds me a bit of the infrasonic depth charges from U-571. |
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genesplitter
New Member
Linkwitz Pluto pvc pipe speakers + 18-inch IB manifold
Posts: 21
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Post by genesplitter on May 21, 2012 14:36:57 GMT -7
If you double the number of drivers but keep the same amp, so that the amp provides half as much power to twice as many drivers, does the SPL increase 3dB?
If you double the number of drivers and double the number of amps, so that each driver gets the same power as before, does the SPL go up by 6dB?
Lastly, does the woofer cone need to move 4 times more to play a note at half the frequency? ie If 20Hz = 1 mm woofer excursion then 10Hz = 4 mm excursion and 5 Hz = 16 mm.
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Post by ThomasW on May 21, 2012 17:34:30 GMT -7
Download a copy of WinISD or Unibox.
Model the drivers and amplifier power, your questions will be answered
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Post by atledreier on Sept 6, 2012 0:29:31 GMT -7
The infrasonic "mines" are just silly. They are completely inaudible except on crap subwoofers with loads of distortion. They also set a severe limit on how loud the piece can be played due to excursion limits. I love that song for it's massage value. Those low, low vibrations aren't really puffs, they are notes of at least a few cycles (I can count 5 or 6). They are below my subwoofers' tuning, but only just. (I don't have an IB yet), and the amount of air moved is phenomenal. But yes, it's cool when they are inaudible, like you say. No puffing or mechanical noise in my subs, just a nice massage. |
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Post by blitzer on Oct 24, 2016 13:34:11 GMT -7
I have had my 4 x 18" FI sub in place for 3.5 years now. Here is the build thread: ibsubwoofers.proboards.com/thread/1979/chicago-christmas-build Nobody has been able to answer this question and I have not seen an answer for it anywhere. It just does not have the mid bass oomph as other super high quality subs with less drivers and smaller drivers. I am a bass SNOB and I can't stand even a tiny bit of boom in my bass. So - explanations that start with - other sub woofers just boom away and just sound louder and with IB subs they are quieter because of no boom are not expected as I have had a large IB sub for years now. I a fully taking this into account. I have Magnepan speakers and can't stand boxy sound either... I understand that drivers where the volume of air behind and in front of it is greater than 10 x VAS are limited by excursion and not by heat.... I understand that you can't pump as many watts into and IB sub compared to non-IB all things equal... OK, so... so what? Assuming an IB sub is following the wave front and rising and falling based on the current going through it... Assuming a SEALED sub is doing the same thing....assuming that this test would be within the limits of both the subs. I am thinking that if you took a super slow motion video of them side by side - they would both be moving in unison - when one is up the other would be up - responding to the current....therefore essentially making the same sound pressure differences in the room... So..... as you turn it up - eventually one of the subs hit it's excursion limits. So, let's only turn it up to just before that happens. I would still think both the sealed sub and the IB sub would be giving out similar sound pressure.... BUT this appears not to be the case. The sealed sub is much louder. I just can't figure out the mechanical reason why my IB sub with twice as much xmax as a sealed sub does not play as loud and does not seem to pressurize the room in the same way. Again, I understand that the sealed sub has the air pressure to help control the cone. Basically, assuming the an IB sub as a larger xmax - what is the mechanical reason why an IB sub needs more drivers than a sealed sub with smaller xmax? Please don't just say - because a sealed sub can handle more watts because of the back pressure and because of thermal reasons. That does not give me a mechanical reason why that is the case. Am I being clear? I have just been considering going back to non-IB because of this. I have borrowed a JL audio f113 that has a single 13.5" driver that is boom free, but gives me a ton more mid bass. The only think I can think of is that the sealed sub's cone may start moving up a curve that would lead it to a much greater xmax...but the air pressure or the voice coil restricts it so it does not complete it's journey to match the voltage going through the voice coil the same way it would in an IB sub. This would mean that the sound is essentially clipped, so to speak, because the driver does not go as far out as it should. Basically, a plot of a sinewave of a sealed driver would cause the sinewave peaks to be flatten out, but have a much faster rise time between and THAT would account for the increase in loudness?  ? This has been bugging me for years!!! Please help. |
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Post by ThomasW on Oct 24, 2016 20:38:39 GMT -7
Hi,
It would be interesting to see plots of your IB compared to the JL audio f113.
In many instances something like the lack of really low bass creates the psychological impression that there's more higher frequency bass output.
That said, if you want more 'slam' build a couple sealed midbass modules (MBM) and set them to do their thing. Doing that will also take the load off your Maggie woofers and as a result they should sound even better.
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