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(8) Sealed Incriminator Audio Judge 21" build


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SME,

 

I don't know how to say this other than I think you should build a few L/T-modded full bandwidth sealed subwoofer systems. It's not an exercise in philosophy.

 

No.  It is an exercise in engineering, which is the application of physics theory and empirical data together to solve a problem.  What I'm talking about is physics, not philosophy.

 

To better illustrate what I've been talking about, I've prepared a couple of pictures taken from WinISD simulations.  Each simulation involves a pair of HST-18 drivers inside a box of about 8 cuft box, using the published T/S parameters.  Note that this is about the same box size per driver that was used in the system Ricci tested.

 

What I've done is to show what happens if you modify certain driver parameters.  The first plots are simulated impedance.  The second plots are simulated SPL at 1 meter for a constant voltage sweep with voltage chosen such that the amp would be supplying 3000W per driver into the minimum impedance, which for the HST-18 is 3.9 ohm.  For the pair of drivers, that would be 6000W total.  FWIW, this voltage is about 108V.

 

For starters, the real HST-18 is depicted in yellow.  There are two ways to modify the in-box resonance without changing the box size.  First off, the suspension compliance or Vas can be changed.  The blue curve shows what happens when we double Vas, which causes the driver resonance Fs, to drop to about 11 Hz.  Unfortunately, we see that doubling Vas doesn't actually do much in this box.  The reason is that the box is rather small, and as I've argued repeatedly on this thread already, the *small* box response doesn't change much when Vas changes.  As such, we want to consider changes to Mms instead.  The green curve shows what happens if we half the Mms (Fs=22 Hz).  The red curve shows what happens if we double Mms (Fs=11 Hz).  Lastly, we can look at what happens if we could hypothetically double BL.  The HST-18 with double BL is depicted in gray.

 

Let's start with the impedance curves:

 

post-1549-0-84732400-1456599919_thumb.png

 

We can easily identify the resonance frequency for each system by the frequency where the peak lies.  As expected, increasing Mms decreases the resonance frequency while decreasing Mms increases the resonance frequency.  Increasing the suspension compliance drops the resonance frequency too, but not very much because for this box size, the box air spring dominates the system compliance.  Finally, doubling the BL has no effect on the Fs as should be expected.

 

Another thing we can use the impedance curves for is to estimate efficiency, but to do so, we must also look at the response curves, which I will show below.  Taking the sensitivity at a particular frequency and dividing it by the impedance gives you the efficiency of system at that frequency.  This gives you an idea of how much power the driver must dissipate as heat.  Note that this is not exactly the same as how much power the amp must supply because, depending on the impedance phase (not shown here), a substantial amount of power that is not consumed by the driver gets dissipated in the amp instead.  (This discussion deserves a separate post.)

 

Okay, here are the response plots I promised:

 

post-1549-0-05581800-1456599923_thumb.png

 

Remember what I said about how Mms doesn't matter for low frequencies?  Here it is.  The green, yellow, and red curves all converge to the same response at 5 Hz and below.  The increase in response due to lower resonance via increased Mms (yellow vs. green and red vs. yellow and green) is most pronounced at around 20 Hz or so, but it's actually very small!  The red system with four times the Mms as the green system and Fs of 11 Hz versus 22 Hz is only about 2 dB more sensitive at 20 Hz.  By the time you get to 10 Hz the difference is only 1 dB.  Now look at what happens to high frequencies.  The green system with 0.5 X Mms absolutely smokes the yellow and red systems.

 

If we look now at the blue curve, we see that the doubling of suspension compliance actually gives it some advantage for low frequencies, but no more than about 1 dB.  This is because the air spring is the major contributor here.  Furthermore, another doubling of suspension compliance (assuming this is even feasible for the design) will yield an even smaller gain because of diminishing returns.  This is a small box, and it's the box size that matters the most, by far.

 

Now look at the gray curve, where we've doubled BL.  Its resonance frequency is precisely the same as for the yellow curve (the unmodified HST-18), but its response looks totally different.  Its high frequency peak response is more like the green system.  Indeed in the high frequency limit, doubling BL gives you the same improvement as halving Mms, which is apparent in this example by the green and gray curves converging as you go higher in frequency.  Where things get real interesting is when we look at the low frequencies.  In the middle frequencies near the resonances, the gray system actually looks pretty lame when compared against the others, but look at what happens below 10 Hz.  The gray system takes a substantial lead over all the others.  Remember what I said about the efficiency in the lowest frequencies?  I said that Mms doesn't matter at all.  I also said that Vas matters only if the box is medium or large because the box air spring dominates.  Lastly, I said that the only way to get more efficiency in a small box was more motor strength.  Now we can clearly see that doubling BL gives us a 6 dB advantage in the lowest frequencies.  This is despite the compromised performance in the middle of the range.

 

Now imagine taking these curves shifting them vertically so that they all peak at the same SPL.  Can you see just how wrong your predictions of ULF performance would be?  You'd see Bossobass Dave arguing about how the blue system needs 5.5 dB more LT to equal the performance of the red system, but ironically, the blue system actually beats the red one below 25 Hz.  What about the gray system with lots of extra BL?  You might conclude it is way inferior to the red one because it needs something like 11 dB more LT, but in reality, it handily beats the red one at 10 Hz and below.

 

I hope this demonstration clears up the confusion here, but I know some people will find it very hard to think about things differently than they have been for many years.

 

Edit: One more point deserves mention.  All sealed and I.B. alignments roll-off at 12 dB/octave.  However, the width of the transition region between where the roll-off first begins and where it reaches a full 12 dB/octave depends greatly on the Qtc.  For Qtc well below 0.707, the roll-off begins very early and the transition region is very wide.  With such systems, you often don't see 12 dB/octave behavior until well below 10 Hz.  With Qtc at 0.707, the region is very narrow and the response transitions from flat to 12 dB/octave quite rapidly.  With Qtc above 0.707, you get the hump where response actually rises before the resonance and then descends below the resonance more steeply than 12 dB/octave until it settles back down to 12 dB/octave.

 

Edit2: Typo correction: Increasing Mms decreases the resonance frequency.  Thanks Luke for pointing this out.

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I don't care about F3.  Outside the context of the sensitivity vs. frequency (measured response) and impedance vs. frequency (to derive efficiency and amp demand), F3 is totally meaningless.  Furtherm

Heard about that one too Luke.       +1 That about covers it.   They flogged the hell out of those subs at the GTG. They were impressive while running too.  A lot of guys at the GTG have broke

So I take it a couple of HS24s went poof at a GTG? Who cares. Happens. I suppose Dave and Nick might be defensive because of a recent discussion advocating humongous amounts of power? Oh well, use it

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No.  It is an exercise in engineering, which is the application of physics theory and empirical data together to solve a problem.  What I'm talking about is physics, not philosophy.

 

To better illustrate what I've been talking about, I've prepared a couple of pictures taken from WinISD simulations.  Each simulation involves a pair of HST-18 drivers inside a box of about 8 cuft box, using the published T/S parameters.  Note that this is about the same box size per driver that was used in the system Ricci tested.

 

What I've done is to show what happens if you modify certain driver parameters.  The first plots are simulated impedance.  The second plots are simulated SPL at 1 meter for a constant voltage sweep with voltage chosen such that the amp would be supplying 3000W per driver into the minimum impedance, which for the HST-18 is 3.9 ohm.  For the pair of drivers, that would be 6000W total.  FWIW, this voltage is about 108V.

 

For starters, the real HST-18 is depicted in yellow.  There are two ways to modify the in-box resonance without changing the box size.  First off, the suspension compliance or Vas can be changed.  The blue curve shows what happens when we double Vas, which causes the driver resonance Fs, to drop to about 11 Hz.  Unfortunately, we see that doubling Vas doesn't actually do much in this box.  The reason is that the box is rather small, and as I've argued repeatedly on this thread already, the *small* box response doesn't change much when Vas changes.  As such, we want to consider changes to Mms instead.  The green curve shows what happens if we half the Mms (Fs=22 Hz).  The red curve shows what happens if we double Mms (Fs=11 Hz).  Lastly, we can look at what happens if we could hypothetically double BL.  The HST-18 with double BL is depicted in gray.

 

Let's start with the impedance curves:

 

attachicon.gifZ.png

 

We can easily identify the resonance frequency for each system by the frequency where the peak lies.  As expected, increasing Mms decreases the resonance frequency while decreasing Mms increases the resonance frequency.  Increasing the suspension compliance drops the resonance frequency too, but not very much because for this box size, the box air spring dominates the system compliance.  Finally, doubling the BL has no effect on the Fs as should be expected.

 

Another thing we can use the impedance curves for is to estimate efficiency, but to do so, we must also look at the response curves, which I will show below.  Taking the sensitivity at a particular frequency and dividing it by the impedance gives you the efficiency of system at that frequency.  This gives you an idea of how much power the driver must dissipate as heat.  Note that this is not exactly the same as how much power the amp must supply because, depending on the impedance phase (not shown here), a substantial amount of power that is not consumed by the driver gets dissipated in the amp instead.  (This discussion deserves a separate post.)

 

Okay, here are the response plots I promised:

 

attachicon.gifSPL.png

 

Remember what I said about how Mms doesn't matter for low frequencies?  Here it is.  The green, yellow, and red curves all converge to the same response at 5 Hz and below.  The increase in response due to lower resonance via increased Mms (yellow vs. green and red vs. yellow and green) is most pronounced at around 20 Hz or so, but it's actually very small!  The red system with four times the Mms as the green system and Fs of 11 Hz versus 22 Hz is only about 2 dB more sensitive at 20 Hz.  By the time you get to 10 Hz the difference is only 1 dB.  Now look at what happens to high frequencies.  The green system with 0.5 X Mms absolutely smokes the yellow and red systems.

 

If we look now at the blue curve, we see that the doubling of suspension compliance actually gives it some advantage for low frequencies, but no more than about 1 dB.  This is because the air spring is the major contributor here.  Furthermore, another doubling of suspension compliance (assuming this is even feasible for the design) will yield an even smaller gain because of diminishing returns.  This is a small box, and it's the box size that matters the most, by far.

 

Now look at the gray curve, where we've doubled BL.  Its resonance frequency is precisely the same as for the yellow curve (the unmodified HST-18), but its response looks totally different.  Its high frequency peak response is more like the green system.  Indeed in the high frequency limit, doubling BL gives you the same improvement as halving Mms, which is apparent in this example by the green and gray curves converging as you go higher in frequency.  Where things get real interesting is when we look at the low frequencies.  In the middle frequencies near the resonances, the gray system actually looks pretty lame when compared against the others, but look at what happens below 10 Hz.  The gray system takes a substantial lead over all the others.  Remember what I said about the efficiency in the lowest frequencies?  I said that Mms doesn't matter at all.  I also said that Vas matters only if the box is medium or large because the box air spring dominates.  Lastly, I said that the only way to get more efficiency in a small box was more motor strength.  Now we can clearly see that doubling BL gives us a 6 dB advantage in the lowest frequencies.  This is despite the compromised performance in the middle of the range.

 

Now imagine taking these curves shifting them vertically so that they all peak at the same SPL.  Can you see just how wrong your predictions of ULF performance would be?  You'd see Bossobass Dave arguing about how the blue system needs 5.5 dB more LT to equal the performance of the red system, but ironically, the blue system actually beats the red one below 25 Hz.  What about the gray system with lots of extra BL?  You might conclude it is way inferior to the red one because it needs something like 11 dB more LT, but in reality, it handily beats the red one at 10 Hz and below.

 

I hope this demonstration clears up the confusion here, but I know some people will find it very hard to think about things differently than they have been for many years.

 

Edit: One more point deserves mention.  All sealed and I.B. alignments roll-off at 12 dB/octave.  However, the width of the transition region between where the roll-off first begins and where it reaches a full 12 dB/octave depends greatly on the Qtc.  For Qtc well below 0.707, the roll-off begins very early and the transition region is very wide.  With such systems, you often don't see 12 dB/octave behavior until well below 10 Hz.  With Qtc at 0.707, the region is very narrow and the response transitions from flat to 12 dB/octave quite rapidly.  With Qtc above 0.707, you get the hump where response actually rises before the resonance and then descends below the resonance more steeply than 12 dB/octave until it settles back down to 12 dB/octave.

 

Edit2: Typo correction: Increasing Mms decreases the resonance frequency.  Thanks Luke for pointing this out.

 

Almost everything you said in bold is wrong. Higher motor foce lowers Qe/Qt and hinders LFE in a specific sealed enclosure. Yes higher motor force lowers the Qtc alignment but it also raises the F3 of the sealed system accordingly. 

 

You are missing massive elements in your WinISD edits and screen shots. Mms DOES matter as it depicts the LFE of a sealed system. Does it sacrifice sensitivity up top? Yes. But extra mass increases sensitivity down low (below 45 Hz). 

 

Also Vas needs to be looked at along side Qe/Qt as both of the latter determine box volume. You can't look at one thing without looking at the other. 

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Just to clarify when working with Thiele/Small equations it helps to choose a set of variables to define and then derive the others from those variables.  When I input these imaginary drivers into WinISD, I defined the following variables:

 

BL, Re, Rms, Vas, Mms, Le, and Sd.

 

I let WinISD automatically calculate the other values such as Fs, Qes, Qms, and Qtc.  In all my simulations I kept the box volume and power input constant.  Note that it's perfectly valid to choose another set of variables to define provided that: (1) the variables defined are sufficient to describe the model of the driver and system completely without being redundant; and (2) the ones we want to vary in our studies are part of that set.  Apart from (2), I chose to define those specific variables because they are more physical in origin.  For example, a bigger magnet may give more BL.  A longer coil more BL and Re.  A heavier cone more Mms.  A more compliant suspension more Vas, and so on.  Likewise, you never change Fs, Qes, Qms, or Qtc without having changed one of these other more physical variables.

 

Almost everything you said in bold is wrong. Higher motor foce lowers Qe/Qt and hinders LFE in a specific sealed enclosure. Yes higher motor force lowers the Qtc alignment but it also raises the F3 of the sealed system accordingly. 

 

You are missing massive elements in your WinISD edits and screen shots. Mms DOES matter as it depicts the LFE of a sealed system. Does it sacrifice sensitivity up top? Yes. But extra mass increases sensitivity down low (below 45 Hz). 

 

Also Vas needs to be looked at along side Qe/Qt as both of the latter determine box volume. You can't look at one thing without looking at the other. 

 

In terms efficiency in the *lowest* frequencies, Mms doesn't matter at all, and BL^2/Re matters a hell of a lot.  My simulations clearly demonstrate this (red, yellow, and green curves).  In terms of middle frequencies, more Mms will give you a a bit of a boost but it's essentially due to the consequential increase in Qms/Qes/Qts.  That's it.  I'm sorry that this disagrees with your intuition.

 

I believe there are other reasons to add Mms to a design.  Mostly it's a matter of signal shaping.  My red curve (double HST-18 with double Mms) shows a ~4 cuft per driver sealed box with an F3 of 20 Hz.  For those that like their subs to have the flattest frequency response possible without electronic signal processing, that's a real plus.  It's probably good for sales.  OTOH, a lower Q alignment might provide a better match to room gain because of the wider transition region where the roll-off is shallower than 12 dB/octave.  Furthermore, if the intent is to use signal shaping to boost the bottom end, then there's no longer a need to use added mass to shape the signal.

 

Yes, high motor force (as shown in the gray curve) reduces sensitivity a lot in the middle frequencies.  In the gray curve, you can see diminished sensitivity compared to baseline (yellow curve) across the 10-100 Hz range.  But below 10 Hz the gray curve beats the others.  Above 100 Hz it beats all but the green curve, too.  Another thing to note here is the gray impedance curve.  The impedance is much higher for the gray curve, so while its sensitivity is low from 10-100 Hz, its efficiency actually remains high throughout that range.  This is reduces the amount of power dissipated in the voice coil and is likely a net benefit if you are using LT because you usually have plenty of spare headroom (in terms of voltage) in the middle frequencies.

 

And yes, Vas needs to be looked at.  That's what the blue curve is for.  Did you read my post?

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Yep, that's me... short-sighted and presumptuous. :unsure:

 

Beside the fact that the RF driver is a universe of different from the IA driver, A quote from Josh in the thread you linked:

 

There's a bunch of ways to skin the cat. Lets be honest here 8 of the HT15's or 18's like we heard at Brandons place are overkill already, unless you are well past any sane playback level. I've been interested in pushing the limits of what you can get from a certain amount of volume with cost be damned for a long time.

 

Notice that Josh's stated reasons for the use of the RF drivers includes a cost be damned budget and that it's just something he's been interested in exploring for a long time. That's after the disclaimer that a system with multiple far less expensive drivers is acknowledged to be effective to the point of overkill proportions, answered in a calm, matter-of-fact way.

 

That's a far cry from your stated reasons of keeping things simple, cost effective and reliable when pushed to system limits, followed by accusatory ranting nonsense.

 

Not much is being made of the durability thing, which you posted as one of 2 reasons for selecting IA over SI when James asked the simple Q.

 

 

 

 

You said "a variety of reasons", but only mentioned 2 reasons, durability and budget constraints. Anyone following your thread might, just maybe, be compelled to mention that the HS24 is more cost effective in $/liter displacement and to question why you think the IA driver is more durable than the HS24.

 

Once those 2 differences are dispelled, there's no way to un-dispel them by yelling and flailing your arms while accusing me of nefarious deeds.

 

In the final analysis, you'll eventually learn that everything I posted is correct. The HS24 is 50% more cost effective for a sealed, full bandwidth subwoofer system, driver-for-driver, is easier to power to single digits in-room and is more durable in the long term because of that fact. You'll also learn that no driver will exhibit lower Fs from 36 Hz to 26 Hz after 100 hours of use. The rest of the ranting you post is unfortunate and unnecessary, but not relevant to those facts.

 

 

Cost was not a factor with the HS24. 

 

As I already stated, "keeping things simple" was a reference to the box construction and bracing. 

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A few quick FEM simulations. 18" driver in 4 ft^3 sealed with 1000 watts. Driver 1 has a motor force (BL^2/Re) of 150. Driver 2 has a motor force of over 300. Same mass, same soft parts, etc. Solid red line is the 1W/1M response and the dotted red line above it is with 1000 watts applied. Higher motor force does not always result in more low end. Small sealed boxes you can easily over-motor it and neuter low end extension. Driver 1 = 32 Hz F3 and higher motor force Driver 2 = 49 Hz F3. 

 

Driver 1 T/S's:

18inchDriver1_150BL.jpg

 

Driver 1 Enclosure simulation:

18inchDriver1_150BL_4ftSealed32HzF3.jpg

 

Driver 2 T/S's:

18inchDriver2_320BL.jpg

 

Driver 2 Enclosure simulation:

18inchDriver2_320BL_4ftSealed50HzF3.jpg

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Are you at least enjoying this new system after all?

 

That's all that really matters. 25hz and down... you shouldn't be missing the Ghorns at all.

 

 

I'd move that number up higher but I know you still love the Othorns and your mega mains. I would too!

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Are you at least enjoying this new system after all?

 

That's all that really matters. 25hz and down... you shouldn't be missing the Ghorns at all.

 

 

I'd move that number up higher but I know you still love the Othorns and your mega mains. I would too!

 

So far for 25hz and up for both music and movies the Othorns are still my favorite.  Even for concert blu-rays, or any other music, I prefer the horns even over my mains. 

 

This hobby would be a lot cheaper if simple reference playback was enough.  Reference plus the subs 20db+ hot is just too fun. 

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Nice dodge. ;)

 

25hz and down, dear boy. How is it?

 

lol, that was actually unintentional!

 

25hz and down is nice, but amp limited for my listening tastes.  The subs flat to 3-4hz at reference plus another 6db does nothing for me. 

 

Getting back to post #1, we all knew 11kw wouldn't last long!

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Right. You will probably find that you are still limited in this range even with the amp upgrades. Though I hope I'm wrong!

 

To be completely honest, <10hz is on the chopping block but I still have a lot of testing/experimenting to do. 

 

Seeing it on SpecLab lab is nice and all, but if I don't notice it when I know it's coming and that's all I'm listening for or trying to feel the couch rumble for and I still don't I'm not sure what the point is. 

 

Like I said though, jury is still out on it. 

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It's these g'damned concrete floors, man.

 

A set of Crowson's might be your next angle.

 

Yeah I've thought about that as well.

 

I just had a funny thought...directly above my HT (in the kitchen) I get PLENTY of <10hz rumble.   I should just move the TV upstairs and watch movies from there!  :lol:  :lol: :lol:  

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Lol! I meant your speakers. ;)

 

But you're also terrible at telling jokes. :P

 

Obviously nobody should jump to conclusions at this point. Will have to wait longer til you can get MOAR POWAH in the room for the subs. That and break in those drivers some more.

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That's what sucks about bass. A few years ago the only place in our rental unit with good bass was the guest bathroom, and it was the furthest away from the little baby 12" sub I thought was great at the time. My how time changes perspectives.

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That's what sucks about bass. A few years ago the only place in our rental unit with good bass was the guest bathroom, and it was the furthest away from the little baby 12" sub I thought was great at the time. My how time changes perspectives.

 

Time to start a whole new fad!

 

We put our ULF subs on the opposite side of the house.

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A few quick FEM simulations. 18" driver in 4 ft^3 sealed with 1000 watts. Driver 1 has a motor force (BL^2/Re) of 150. Driver 2 has a motor force of over 300. Same mass, same soft parts, etc. Solid red line is the 1W/1M response and the dotted red line above it is with 1000 watts applied. Higher motor force does not always result in more low end. Small sealed boxes you can easily over-motor it and neuter low end extension. Driver 1 = 32 Hz F3 and higher motor force Driver 2 = 49 Hz F3. 

 

--- see original post for images ---

 

I've summarized the output values for each driver below:

 

f   #1 lo #2 lo #1 hi #2 hi

10  65    67    96    96

20  77    76    107.5 105

30  83    80    114   111

40  86    83    117   114

60  87    85    119   117

80  87    86    119   118.5

120 86    87    119   120.5

 

Indeed, the driver with the smaller motor has up to 3 dB more higher sensitivity from 20-100 Hz or so.  Below 20 Hz, however, is a different story, but unfortunately, there is a problem with the high power simulation for driver #2.  If you look closely at around 17 Hz or so, there is a knee where the roll-off slope changes abruptly.  My guess is that your simulated driver is running out of Xmax at that frequency for the power level you chose.  Now, if you are designing a system using that tool, it would be good to know when Xmax limits your output, but in this case we're talking only about sensitivity and efficiency.  For a fair comparison, that feature shouldn't be there.

 

Note that driver #2 wins by 2 dB in the low power sweeps but merely ties #1 in the high power sweeps.  The low power sweeps reflect what would happen if we weren't overpowering the driver.  If the volts per driver were lower in that same box, you would see driver #2 overtake #1 somewhere probably very near 17 Hz, and below 10 Hz, driver #2 would increase the lead up to 3 dB, which can be shown mathematically by virtue of the fact that you doubled (BL^2)/Re while leaving the other physical parameters unchanged.

 

Now I totally get that a lot of people would prefer a flatter passband and a lower F3.  For a system designer looking to get the most output from the amp in the 20-30 Hz range, a driver with less BL or more mass (for higher Q) may be preferred.  But this thread is focused on a build involving 8 X 21" sealed woofers with the express intent of going for broke in the ULF department.  By ULF, we mean < 20 Hz right?  How about < 10 Hz?  Will Luke have enough headroom for his > 20 Hz tastes with 8 X 21" drivers?  I assume so, and if he doesn't, his horns will fill that gap, right?  This is all about < 20 Hz performance, and for that, high BL^2/Re and Cms as low as reasonably possible seems to be the way to go.  I think Luke made a solid choice here.

 

And let me just remind everyone also (Ricci has mentioned it multiple times), driver #2 with more BL has higher efficiency.  Go back to my plots and compare the gray curve to the yellow curve at 10 Hz.  (Note that my gray curve has 4X (BL)^2/Re of the yellow curve, versus a 2X change in electrodynamic's simulations.)  The sensitivities are equal at 10 Hz, but the impedance of the high BL driver is 9 ohm, twice as much as the 4.5 ohm for the lower BL driver.   For the 108V RMS required to nominally output 3000W per driver, the high BL driver is dissipating only 1333W, whereas the low BL driver is dissipating 2666W.  In this sense, the higher BL driver may "win" even where its sensitivity is somewhat less than the lower BL driver.

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A lot of good points are being made here by everyone, and there are pros and cons no matter what driver I chose for this build.

 

I need to add though, I could have been more upfront for why I went the direction I did, but I was trying to avoid drama and comparing driver A to driver B type of stuff.  Holy buckets it couldn't have backfired worse...

 

You know what they say about hindsight. 

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I was thinking about your stiff suspensions and long break-in time and thinking about how most people that buy these things are buying one of them and going all-out with it.  You have several subs and nowhere near enough amp to exercise them properly.

 

Maybe, when you aren't busy testing or playing a ref+++, you driver only two or four woofers at a time.  This way you can work them harder and break them in quicker.  There are pros and cons to the different configurations you can choose.  With four woofers, your load impedance changes either up or down.  With two woofers, you can hopefully get them all broken in quicker.

 

I'm interested to see how much break-in helps you.  I expect any benefits to be in the ULF, of course.  Look at my graph showing reduced suspension stiffness.  I'm not sure you'll see that much change, but if you do see a change, it'll be mostly at the bottom.

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