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Old 06-23-2012, 10:38 PM - Thread Starter
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It has been a little quiet around here since the re-design, so I figured that we might light it up a bit.

Let's talk about efficiency vs. depth.

Traditional thinking is that high sensitivity drives have no low end and low end drivers dominate bottom end sensitivity.

By forfeiting the top end, the triple X drives win the low end right?

NOPE!

I'll go ahead and nuke a hole in this theory and say that it is upside down...low sensitivity drives don't have any high end.

For example, here is the re-xxx in 8 cubic ft against another set of drivers in the same sealed enclosure, 8 cubic feet. I'm not saying which, but if you poke around a bit you can find them.

The re-xxx has no sensitivity advantage anywhere.

From 60hz up, they just suck 10X the power for a given spl.

As for maximum spl, the re plops out around 42mm +/-, so dual 18's with +/- 20 will be pretty much the same but at much less power.

HONK!

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Old 06-23-2012, 11:16 PM
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Just a matter of total displacement, right? When I model quad JBL 2226's sealed, with the right amount of power I can get them to equal the extension and output of a single RLp18 sealed. The JBL's dominate high up though with the same amount of power.

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Old 06-24-2012, 11:27 AM
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LTD, I think what you are trying to quantify is how to maximize displacement for a given power at LF with direct radiators. IB is probably your best bet for this, as far as enclosure types are concerned.

It would be interesting to see distortion curves for both of these examples. What 18s? DataBass willing to do a shootout????

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Old 06-24-2012, 03:16 PM
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Efficiency vs. depth ignores the crux of the matter, which is Vd.

I think you could have both at the same time if you kept the light cone and long voice coil and were willing to pay for the magnets required to maintain the same flux density as a short coil motor over longer excursion.

You could keep the VC mass from lower efficiency by decreasing its diameter.

Noah
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Old 06-24-2012, 08:11 PM - Thread Starter
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i'm not talking about total displacement this time. i'm talking about sensitivity--how much sound you get output from a given electrical input.

what i was actually shooting at is the claim that low "nominal" sensitivity drivers have some sort of sensitivity advantage on the bottom end.

i don't see this as being the case.

what i see is cubic foot for cubic foot, low nominal sensitivity drivers just lack the top end.

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Old 06-24-2012, 08:52 PM
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I just modelled the B&C 21 (Fs = 37hz) vs the Mach V 21 (Fs = 19hz )

Below 80hz, the mach V seems to show about 3db more output across the board, but above 80hz, the B&C takes the edge (inductance is a big factor in this too)
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Old 06-24-2012, 09:19 PM
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Voltage sensitivity is one thing. Actual efficiency is another. Most people only care about voltage input but it doesn't tell the whole story. One of the best features in HR is that it can generate a constant power result for comparison. Too bad it can't model complex inductance which can snuff out quite a bit of deep bass sensitivity. Don't forget that wherever the impedance maxima is will jack up the efficiency in that range tremendously so comparing systems with radically different impedances is complex.

Sry on my DROID here.
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Old 06-24-2012, 11:42 PM
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Quote:
Originally Posted by LTD02 View Post

i'm not talking about total displacement this time. i'm talking about sensitivity--how much sound you get output from a given electrical input.

Understood; my point was that due to practicality/cost efficiency tends to vary in reverse proportion to Vd.
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what i see is cubic foot for cubic foot, low nominal sensitivity drivers just lack the top end.

Agreed.

Noah
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Old 06-25-2012, 03:51 PM
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What about if you want to be flat to 10hz or 5 hz? That top sub will need some wicked EQ to get there and the XXX could probably do it with room gain alone(in my room anyways). If you are comparing 30hz and up then yeah, no contest.

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Old 06-25-2012, 04:34 PM - Thread Starter
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"What about if you want to be flat to 10hz or 5 hz? That top sub will need some wicked EQ to get there and the XXX could probably do it with room gain alone(in my room anyways). If you are comparing 30hz and up then yeah, no contest."

that is the conventional wisdom mk, and my post is that conventional wisdom isn't quite right.

both are equally sensitive on the low end based on cabinet volume. the frequency response below 20hz is identical.

however, the flyweight driver is MUCH more sensitive on the top end.

so, instead of thinking about eq'ing "up" the lowend of the high sensitivity drivers, we should think about eq'ing "down" the highend of the high sensitivity drivers.

the benefit? ~8x less power compression in the upper bass with the high sensitivity drivers.

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Old 06-25-2012, 04:40 PM - Thread Starter
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"I think you could have both at the same time if you kept the light cone and long voice coil and were willing to pay for the magnets required to maintain the same flux density as a short coil motor over longer excursion."

give it a try. for a given enclosure volume, adding woofers (a proxy for more magnets and more cone area) doesn't increase low end sensitivity. if i understand what you are saying noah.

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Old 06-25-2012, 05:01 PM
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Quote:
Originally Posted by LTD02 View Post

however, the flyweight driver is MUCH more sensitive on the top end.
so, instead of thinking about eq'ing "up" the lowend of the high sensitivity drivers, we should think about eq'ing "down" the highend of the high sensitivity drivers.
the benefit? ~8x less power compression in the upper bass with the high sensitivity drivers.
One might argue that you aren't gaining any "headroom" by cutting out the top end but you sure will save yourself from compression up top. That's good! Also, if the 'bring down the top end' is done digitally, someone else could argue that you would lose digital resolution up in that region.

I'm not though...lol, I'm pretty much going to be doing (or trying) this with quad 2226's ...soon, yes...soon. I know, I know. tongue.gif

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Old 06-25-2012, 05:14 PM
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Well, I have recently tried both routes. I had relative high sensitivity with my 8 18's and brought up the low end(which you can do with enough displacement) and I am testing out 12 13 inch drivers which are built for a lower end which needs no boost down low but more drivers to equal the upper end. I am putting together a thread soon. Once I get the time to take pics and get my computer working right that takes the graphs I will start the thread. Getting lots of power today is cheap.

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Old 06-25-2012, 07:25 PM
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Quote:
Originally Posted by LTD02 View Post

"What about if you want to be flat to 10hz or 5 hz? That top sub will need some wicked EQ to get there and the XXX could probably do it with room gain alone(in my room anyways). If you are comparing 30hz and up then yeah, no contest."

that is the conventional wisdom mk, and my post is that conventional wisdom isn't quite right.

both are equally sensitive on the low end based on cabinet volume. the frequency response below 20hz is identical.

however, the flyweight driver is MUCH more sensitive on the top end.

so, instead of thinking about eq'ing "up" the lowend of the high sensitivity drivers, we should think about eq'ing "down" the highend of the high sensitivity drivers.

the benefit? ~8x less power compression in the upper bass with the high sensitivity drivers.

Hi LTD,

I've made posts pointing to this minor, but key shift in perspective over the last 6-8 years. Some get it, some don't, and many more misunderstand or mis-apply it in both directions.

Related to Ricci's post, you can go too far either way, as the impedance curve and Fb of the system do play a factor in the sound and change in sound with increasing level. In the simplest of examples, a BagEnd 18" is a bit too far, and a 70dB @ 1W woofer with 16Hz Fb in a small box is a bit too far the other direction for practical use up to ~80Hz. Either will "work", but with compromises which could be easily improved.

There is no correct use, just a balance of compromises.

Remember that the sealed box air spring and driver compliance combine as one, so for a given cone size, the softer driver will be a little more sensitive at LF until the box is very small. Once cone size and compliance are similar, LF sensitivity is dominated by box size, especially if Q is not excessively high or low. As Ricci pointed out, significant LF inductance can also shave sensitivity down low and skew the models, so as always, parameters and models correlated to real measurements rule.

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Old 06-25-2012, 07:54 PM
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Quote:
Originally Posted by LTD02 View Post

"I think you could have both at the same time if you kept the light cone and long voice coil and were willing to pay for the magnets required to maintain the same flux density as a short coil motor over longer excursion."
give it a try. for a given enclosure volume, adding woofers (a proxy for more magnets and more cone area) doesn't increase low end sensitivity. if i understand what you are saying noah.

I wasn't saying more magnets would increase sensitivity, but that they could eliminate the loss in sensitivity normally incurred by the long VC needed for high Vd.

Noah
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Old 06-25-2012, 09:17 PM
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Noah is making some good points here as well. There is never a free lunch and to some extent going all out for efficiency usually involves some tradeoffs in stroke, ruggedness and or thermal handling (somewhat offset by efficiency but once the excursion quits responding in a linear fashion to power input more heat is generated.) Drivers with powerful motors, good efficiency, inductance combating measures and long stroke generally start to cost quite a bit more to make. Mark rightly points out it is all about balance and design goals.

Noah,
Smaller diameter but long coils can cause issues with cone flex and rocking at high excursions.
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Old 06-25-2012, 11:41 PM - Thread Starter
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"a BagEnd 18" is a bit too far, and a 70dB @ 1W woofer with 16Hz Fb in a small box is a bit too far the other direction for practical use..."

lol mark. that's hilarious. i think that i understand where you are coming from in saying that bagend goes a little too far. the f3 of the hypothetical driver that i show is around 45hz or so, but other than cost, what's the downside of the bagend approach?

this is essentially what scott is doing with his system. while his pile of jbl 2226's might not be the most cost effective path to the goal, it is one that works.

josh, noah, good points. however, i kind of disagree with some of the points. a driver with 1/2 the xmax is much easier, cheaper, and will perform better than the super high xmax drives. can't eminence crank out 18" drives with 10mm xmax for less than a quarter of what an re xxx goes for? all put in the same enclosure volume, the 4x drivers will have much greater high frequency sensitivity to boot while maintaining the same sensitivity down under.

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Old 06-26-2012, 12:07 AM
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My method is definitely not the most practical or effective... however, I will be cheating because I will have a summation of bass content <120hz across twelve JBL 2226's clustered together which will also be boosted by PVG/room gain.

I hoping for some sort of small room/cluster effect and if things go as planned we will have some nice documentation on such. smile.gif

Hey, John. I would like to see Eminence produce an 18" version of the Dayton DVC15. Seems like something they could do. Imagine that, a nice sub $200 18"er. smile.gif

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Old 06-26-2012, 12:43 AM - Thread Starter
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scott, you were savvy enough to pick up a pile of those drivers for a song, so my comment was a general one, not directed at you.

"Hey, John. I would like to see Eminence produce an 18" version of the Dayton DVC15. Seems like something they could do. Imagine that, a nice sub $200 18"er."

i have been noodling it. the question is what does one mean by an 18" version of the dvc15. the money question seems to be whether to go for overall sensitivity or overall low q.

i.e., in a 4 cubic footer sealed, do you want a q of 0.80 which produces more spl or a q of 0.60 which produces less spl, but more "control"?

given that we are talking about low excursion designs, eminence can likely manufacture them. i suspect the price would be much lower than $200...

a quad of 18's per side would bring some bliss to most folks home systems. a grand piano is large for a reason. :-)

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Old 06-26-2012, 01:38 AM
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Oh I know. I just wanted to clarify that I have not gone completely delusional and state that the way I am doing it is the 'best' way to go. It's sure expensive... tongue.gif
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i have been noodling it. the question is what does one mean by an 18" version of the dvc15. the money question seems to be whether to go for overall sensitivity or overall low q.
i.e., in a 4 cubic footer sealed, do you want a q of 0.80 which produces more spl or a q of 0.60 which produces less spl, but more "control"?
given that we are talking about low excursion designs, eminence can likely manufacture them. i suspect the price would be much lower than $200...
a quad of 18's per side would bring some bliss to most folks home systems. a grand piano is large for a reason. :-)

That's the great thing about the DVC15, it's versatile. A real-world DVC18 would probably sit somewhere between those two. An overall Qts between .4-.5 and a nice, soft suspension. Fs ~20hz. Work with ~15mm Xmax. Prolly have to upgrade the VC to 2.5" to carry the extra mass of a heavier cone...maybe. A simple upgrade and overall beefing up while keeping costs down. Realistically an Eminence built version like this could cost under $200, I would think. I bet it could be pretty popular too if were just as versatile. Nice 3-5cuft sealed cabs, large vented and possibly IB use. Yyyyeaahhh. cool.gif

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Old 06-26-2012, 07:43 AM
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John,

Why stop at only 4 18's? How about 16 $50 closeout 12" car drivers like the infinities? Why does anyone buy one good driver?

What is wrong with the BagEnd approach? There is really high distortion and no low bass headroom. Compression out the wazoo. You need like 8.

Do you need 150dB of upper bass headroom in a house or is 135dB probably adequate for most listening? Where do people usually run short on headroom first?

Its not efficiency versus Q. It is efficiency versus displacement. This is what Noah is pointing out. Think of it like a see saw. Efficiency is on one end and displacement is on the other.Increase one and the other goes down. There is a nice middle ground where you get a good balance of both. This is what Mark is saying.

I've never subscribed to the high efficiency drivers are less sensitive in the deep bass myth to begin with. Why do you think I spent so much effort on the 21's in small sealed enclosures? I thought for awhile I might end up going with those over the current setup.


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Old 06-26-2012, 09:21 AM
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John,
Why stop at only 4 18's? How about 16 $50 closeout 12" car drivers like the infinities?
Hmm, link?

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Old 06-26-2012, 09:29 AM
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That's why I like what ive got going right now, the best of both worlds biggrin.gif RE 18's for the low end, and the quad 2225h's for 40hz and up smile.gif Man it sounds awesome...but still have some work to do!

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Old 06-26-2012, 09:37 AM
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Quote:
Originally Posted by Scott Simonian View Post

My method is definitely not the most practical or effective... however, I will be cheating because I will have a summation of bass content <120hz across twelve JBL 2226's clustered together which will also be boosted by PVG/room gain.
I hoping for some sort of small room/cluster effect and if things go as planned we will have some nice documentation on such. smile.gif
Hey, John. I would like to see Eminence produce an 18" version of the Dayton DVC15. Seems like something they could do. Imagine that, a nice sub $200 18"er. smile.gif

When will this monstrosity be chronicled? This is the LCR only? What are you gonna use for subs? Small explosive devices underground?

JSS
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Old 06-26-2012, 09:47 AM
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Lol!

I'm ordering my midhorns next week so I hope sooner than later....like I keep saying. I know. I'm awful. redface.gif Held back by budget but I get a holiday bonus soon (woot!!) and ...if someone would buy my XA2's then I'd be all set. biggrin.gif

LCR's. Dual dual-opposed sealed 18's (RLp18's) for subs behind LCR's.

scottmains2.png

Props to John (LTD02) for the mockup pic.

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Old 06-26-2012, 09:55 AM
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Originally Posted by LTD02 View Post

"a BagEnd 18" is a bit too far, and a 70dB @ 1W woofer with 16Hz Fb in a small box is a bit too far the other direction for practical use..."

lol mark. that's hilarious. i think that i understand where you are coming from in saying that bagend goes a little too far. the f3 of the hypothetical driver that i show is around 45hz or so, but other than cost, what's the downside of the bagend approach?

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John,

What is wrong with the BagEnd approach? There is really high distortion and no low bass headroom. Compression out the wazoo. You need like 8.

Do you need 150dB of upper bass headroom in a house or is 135dB probably adequate for most listening? Where do people usually run short on headroom first?

The Bag End example is a little extreme, as there are two parts contributing. One is the drivers used, and the other is the Fb & alignment of the design type. By definition of the ELF design, the target is to put the Fb centered on the upper operating corner. This is IMO very wasteful and unnecessary as we now readily have EQ available to achieve whatever frequency response we have. Ricci was on the money directing you to look at the real impedance and SPL vs. current^2/Re, which should make it more clear why an Fb at the high frequency corner is so wasteful.

Ricci's comment about 150dB vs. 135dB and high distortion from the BagEnd designs is also key. The shape of the frequency response does have an effect on the distortion, similar to how a horn amplifies distortion harmonics of frequencies well into the roll off. Finally there is the behavior at high drive level and in compression, where the Fb and Q play into how the response shape changes as it is driven harder. While not always dramatically visible in sweeps, it is clearly there, and if you consider the real world use of complex signals, it makes sense that this effect can be more audible than some might think in looking at the compression through increasing frequency sweeps.

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Old 06-26-2012, 10:05 AM
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Lol!
I'm ordering my midhorns next week so I hope sooner than later....like I keep saying. I know. I'm awful. redface.gif Held back by budget but I get a holiday bonus soon (woot!!) and ...if someone would buy my XA2's then I'd be all set. biggrin.gif
LCR's. Dual dual-opposed sealed 18's (RLp18's) for subs behind LCR's.
scottmains2.png
Props to John (LTD02) for the mockup pic.

OMG. What in the world are you going to use for surrounds? X-over point from 15s to midhorn? Listening distance adequate? Those are non-trivial C-C distances there....

The real question is: Can you SURVIVE a screening with this system?

But seriously. With such high efficiency, nearly any hiss/distortion in the electrics may come across as in your face, not buried in the noise floor as with lower sensitivity devices. Wow. This will be some thread.

JSS
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Old 06-26-2012, 10:19 AM
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Originally Posted by Looneybomber View Post

Hmm, link?

http://www.amazon.com/Infinity-Reference-1260w-1200-watt-High-Performance/dp/B0028AVGEO/ref=pd_cp_e_0/190-3323293-3244033

Ok so not exactly $50 but still a ridiculous price and not a bad driver really...$928 to have 16 shipped to your door. Add 1 EP4000 $300. Add 1 DCX2496 $300...Add $200 to get REW or an Omnimic system going. Add $270 for the enclosures and miscellaneous, PL, wires,connectors,etc. Build 4 dual opposed sealed systems of 4 12's each.

Total = <$2000 and a big perma grin on movie night. cool.gif
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Old 06-26-2012, 10:43 AM
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Originally Posted by maxmercy View Post

OMG. What in the world are you going to use for surrounds? X-over point from 15s to midhorn? Listening distance adequate? Those are non-trivial C-C distances there....
The real question is: Can you SURVIVE a screening with this system?
But seriously. With such high efficiency, nearly any hiss/distortion in the electrics may come across as in your face, not buried in the noise floor as with lower sensitivity devices. Wow. This will be some thread.
JSS

Yyeahh. The only thing I'm really worried about is the potential hiss or self noise. At the ~100hz the system will be in excess of 100dB sensitive and ~110dB sensitive through the entire midrange up to the low treble. Hard to tell from the picture but the C-C distance is acutally quite tight. I'm not concerned with that. Listenning distance will be about 10ft. This isn't dissimilar from any uber JBL cinema system MKtheater has installed and his room and seating situation was identical to mine. I'm not too worried. Crossover stuff is all up in the air cuz ...who knows what will work best when the rubber meets the road. However, I am shooting for ~300hz for bass to mid and between 1-2khz for the top. Each channel will have it's own DCX. Will sum LFE output to mains for extra bass. biggrin.gif

Will unfortunately be power limited and held back for a while with what little I can get from the wall. frown.gif Uber high sensitivity ftw!

My Dual 18" LLT subs 120dB down to 10hz

 

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Old 06-26-2012, 11:06 AM
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Originally Posted by Ricci View Post

Noah,
Smaller diameter but long coils can cause issues with cone flex and rocking at high excursions.

I agree on the cone flex, but isn't rocking stability determined by the spider and surround?

Either way, continuing with the same flight of fancy, rather than a smaller diameter VC with the same number of layers, it could be the same diameter but less layers, which will keep the mass of copper from increasing and also help flux density by reducing the radial magnetic gap.
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Originally Posted by LTD02 View Post

...other than cost, what's the downside of the bagend approach?

As you yourself pointed out, low freq efficiency depends directly on box size, and the Bag Ends use small boxes.
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Originally Posted by LTD02 View Post

josh, noah, good points. however, i kind of disagree with some of the points. a driver with 1/2 the xmax is much easier, cheaper, and will perform better than the super high xmax drives. can't eminence crank out 18" drives with 10mm xmax for less than a quarter of what an re xxx goes for? all put in the same enclosure volume, the 4x drivers will have much greater high frequency sensitivity to boot while maintaining the same sensitivity down under.

Not sure what you're disagreeing with, as no one said otherwise.

Yes, you can buy more smaller drivers, but they tend to have less xmax so I think you'd be hard pressed to equal the Vd of a real sub driver.

Noah
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