DevilDriver

A single Dual 2 ohm speaker can be wired to a 1 ohm or 4 ohm load. A single Dual 1 ohm speaker can be wired to a 0.5 ohm or 2 ohm load. If you're using multiple speakers, then the possibilities grow from there.

I had a bacon, mushroom, and cheddar cheese omellette with some hashbrowns. Delicious. Edit: I am in zee chat. Feel free to join.

Or you could use AeroPorts, and either swap out PVC lengths for daily/SPL... or plug up one port for daily (to lower tuning). I did this one summer when I competed, had 4 4" Aeroports, external, and had my SPL length PVC and daily length PVC. nG True, not sure why I was only thinking slot port. Utilize several aeroports for high SPL, and plug them for daily usage. Great point Noah.

Scott, I see you reading. Please feel free to add if you have pertinent information or corrections, as you are clearly the more knowledgeable of the two of us.

Well, this idea would take some extra work, but you could try and work out a sort of variable Fb port. Build an enclosure with a very large slot port. When you want to switch to a daily tuning, add a layer of mdf inside the port (lining both sides of the port wall). It's not the greatest solution, but it is an option if you're really hard up for big numbers out of a single sub, while keeping some daily capabilities.

It's where the cool kids hang out. pssst shoot me a im, i cant seem to find you on mi buddy list I'm at work; meet me in chat?

It's where the cool kids hang out.

EBS FTW, assuming it's predominant usage will be home theatre. If it's for an even mix of stereo and theatre, or mostly stereo, then something like 4-5 cubes tuned to 20-25Hz might be satisfactory.

It's that type of thinking that creates improvements. Start imagining it, then start creating it, then start selling it. Use your ideas before someone else does.

Yup, those are the ones if Lukas has the pictures right. They won't be available individually though; you'll have to buy a full Exodus kit. Might be worth it though: the Exodus kits I have used have always been stellar. Yup, those are the new Exodus drivers. My amplifier wants to make sweet love to them. I am guessing (this is total speculation, by the way) that CSS (www.creativesound.ca) might have a similar offering in the not-too-distant future. I know Bob at CSS wants to offer kits based off of drivers that are entirely his; he won't be offering anything Exodus, so that rules out this driver; he won't be offering the Extremis (for obvious reasons); that really only leaves one alternative, and I think that's Bob sourcing his own long throw 6.5" drivers, though I think they'll be more intended for low midbass performance, based on a couple of conversations. Anyways, I think if we badger Kevin enough he might be willing to offer the EX-6.5 separately in the future. Maybe send an email every single day? Haha. I remember reading some information about the new tweeter he's working on that sounds interesting as well.

Lower Q, smaller enclosure?

Think of other companies they build for and take a wild guess.

Yup, those are the ones if Lukas has the pictures right. They won't be available individually though; you'll have to buy a full Exodus kit. Might be worth it though: the Exodus kits I have used have always been stellar.

Whoever that reviewer is, they stink. Errr.....nice job!

New Pirates = teh worst I wish I could force myself to be irresponsible with my money.

Wait till the Poly's are available from Ascendant Audio again and use it as an excuse to go active. FTW.

Taking Back Sunday - What's It Feel Like to Be a Ghost

I will be adding the Differential Drive (aka Dual Gap) technology when I get a chance. Though it does allow for some flexiblity in terms of keeping BL linear, it shows more benefits in power handling by increasing surface area and air flow over the coil substantially. The W7 is a very simple method: it's a standard overhung design with some machining done in the pole piece. If the right amount is done in the right places, you can achieve surprisingly linear BL, but it becomes increasingly more challenging to achieve this at very high levels of excursion. Of course, I'm of the opinion that a speaker that takes 1kW with 30mm of Xmax is more than enough for my ears.

Conclusion As you can see, every gap treatment has its own inherit advantages and disadvantages. Each treatment has a particular application where it will prove to be more beneficial than the other options. So when should you use what? Well, here are my opinions. Tweeters: None of the above. I’ll stick to an underhung design, thank you very much. Midrange: Of the three, it would probably be Split-Gap that I would use. The low inductance helps give your speaker a wider bandwidth while still achieving good stroke. Split Coil can be utilized with good success, though you’ll need to put some copper in the motor to gain wide bandwidth. Midbass: For a similar reason as above, the winners would be Split Coil or Split-Gap. Inductance is not as much of an issue for a speaker designed solely for midbass, so Split Coil might be my choice for the improved power handling the larger coil offers. Subwoofer: This would probably be LMT or Split Coil for me. Both of them offer ridiculous stroke capabilities. Both have higher moving mass (which is great for increasing low frequency performance, manifested in a lower Fs). Inductance is of very little concern, as the inductive corner frequency usually falls above the bandwidth in which a subwoofer would be used. Full Range: Split-Gap is the clear winner here. It’s capable of achieving good excursion for low frequency performance while keeping inductance low for high frequency performance. If you can overcome the cone breakup that is inherent in any full range design, you’ve probably got a winner. Split Coil isn’t an awful option here either, but it’s probably not your best choice. Hopefully this helped answer some questions you might have about the linear BL gap treatments AND remove some of the bias you might have read in previous discussions. If you have questions or find an inaccuracy in anything above, please be so kind as to comment. I would love to hear other opinions or concerns. Cheers, Neil

Manufacturing Costs Pretend you’re a manufacturer. You look forward to applying an intelligent new technology to your product. But what if this technology prices your product out of contention? At that point, selling your product proves to be more challenging. The lower you can keep your manufacturing costs, the more profit you can make, or alternatively, the lower you can price your product, making large volume sales more easily achieved. As I have already mentioned, Split-Gap has higher costs for the top plate, especially with longer stroke. However, it also has a smaller voice coil. Split Coil has more voice coil length to it. LMT has a lot more voice coil length to it, and to achieve a given B, requires a wider and deeper magnet structure (because the gap is wider than normal to accommodate the windings). Split-Gap also has royalty/licensing fees you must pay if using that gap treatment. Which is the least expensive to manufacture? Well, LMT is clearly the most expensive. In first place, it’s kind of a tie between Split-Gap and Split Coil. In many applications, production cost for Split-Gap will be lower, even with licensing fees considered. In very high excursion applications, you’ll probably find Split Coil to be less expensive.

Manufacturing Tolerances When you’re building large-scale products where you are shipping pallets of speakers out, you want to make sure that nearly every speaker will measure the same and fall within the customer’s accepted tolerances. When you start fiddling with the motor, it becomes even more critical that these tolerances are met. Split-Gap is probably the best here. It is very, very easy to machine the gap within very tight tolerances. Split Coil and LMT, on the other hand, prove to be a little more challenging. Controlling the positioning of the windings is not as easily achieved. Little changes in the number and location of windings can cause big issues with asymmetry of the BL curve, especially in LMT. If you take a look at the Eclipse SW8200 that was measured by npdang at DIYMA, you can see this very clearly. Overall, Split-Gap likely has the easiest achieved tolerance, followed by Split Coil, with LMT third best.

Scalability Some companies want to utilize a specific gap treatment for all their speakers. Use of those listed so far is most predominantly found in low frequency speakers, ie. subwoofers. The reason for this is obvious: to produce high SPL at low frequencies, you need a lot of linear excursion to achieve high displacement. At higher frequencies, less stroke is needed. So how easily can these gap treatments be utilized in other speaker designs? Be sure you have looked at the pictures above and fully understand the concept. Part of the “scalability” of each gap treatment is the size of the motor for each. Though Split-Gap needs a taller top plate, the voice coil is very small and the motor is not very deep. LMT is similar in many respects to a standard overhung design, so large excursion requires a long voice coil, which means a very deep motor to accommodate. Split Coil follows the same concept. LMT also needs a wider motor than either of the two other gap treatments. So in terms of the sheer size of the motor required, Split-Gap will usually be the smallest. The other concern is how easily the gap treatment is applied to the speaker. Imagine a tweeter with a 2mm tall voice coil. How easy will it be to vary the density of the coil in the gap? It won’t be very easy at all, and thus LMT proves to have little value here. Split Coil will work a little better, but the motor will be a bit deeper. Split-Gap will usually work the best here. However, it should be noted that the gap is so tight, the voice coil is so small, and the top plate is so short, that the advantages of any of these gap treatments are less visible for high frequency performance with small tweeters. Overall, all three gap treatments are best suited for low frequency performance where high stroke is key. However, if you want to apply these treatments to smaller speakers for higher frequency performance, Split-Gap is probably your best bet.

Power Handling Everything you just read above is transferable to the concept of power handling. A larger voice coil will usually handle more current, all other things considered constant. We know LMT has the largest coil, Split Coil has the second largest, and Split-Gap has the smallest coil. This is an easily understood concept: LMT is capable of handling the most power while Split-Gap has the lowest power handling capabilities.

Inductance and Inductance Variation This is a key factor in many speaker designs. Inductance (Le as a thiele/small parameter) is a key limiter in the bandwidth of a speaker. If a speaker begins to roll-off at a given frequency, it can usually be attributed to inductance. If you can keep inductance low, you will have a wider bandwidth in which the speaker will play accurately. NOTE: Le is a tricky parameter to compare. First, it varies with a number of factors, including frequency and power. When comparing various speakers using their published Le specification, be sure to divide the value of Le by the value of Re (the DC resistance of the voice coil). A speaker is a reactant load and an increase in Re will result in an increase in Le, though the corner frequency at which roll-off begins remains the same. In short, a speaker with a DC resistance of 4.0 ohms and an inductance of 2.0mH is actually better than a speaker with a DC resistance of 2.0 ohms and an inductance of 1.5mH. So what is the key factor in the inductance equation? It’s almost exclusively the length of the voice coil. A longer voice coil will have higher inductance. A smaller voice coil will have lower inductance. Though inductance can be decreased through use of shorting rings or copper sleeves, the voice coil length is the primary variable when considering inductance. Based on what we know so far, Split-Gap usually has the smallest coil, followed by Split Coil, followed by LMT. Let’s also consider the usability of shorting rings. The notch in the top plate of a Split-Gap design is very easy to fill with copper and help lower inductance. If you want to add copper to the gap in a Split Coil or LMT motor, you need to widen the gap, which drops your B, which drops your efficiency. In terms of inductance, Split-Gap is the clear winner, followed by Split Coil, with LMT taking the last position.

BL Linearity All three gap treatments very clearly help to linearize BL over a speaker’s stroke; there is no arguing that. But are all the gap treatments equally linear over long distances? Which gap treatment is easy to achieve ridiculous levels of linear BL? The answer here is very simple. If you’re familiar with underhung vs. overhung arguments, you’re likely aware that, while underhung designs are capable of more linear BL, they are very hard to achieve linear BL over a very large stroke at an affordable price. Remember how I mentioned that tall top plates can get pricey with inconsistent magnetic field strength? These disadvantages come directly into play with an underhung speaker, and sadly, making taller and taller top plates is the only way to achieve more stroke with an underhung design. This same argument is very applicable when comparing the three gap treatments we’re looking at. Split-Gap uses a coil that is smaller in height than the height of the gap and suffers from the same effects outlined above for underhung speakers. If you want really huge stroke from a Split-Gap speaker, be prepared to fork over some cash for your top plate. Oh, and make sure that you have a good magnet structure to keep that top plate as saturated as possible. Another consideration: by machining a notch in the top plate, Split-Gap sacrifices some BL at rest. This can be controlled by working with the depth of the notch in your top plate, but is clearly visible in many Klippel and Dumax results for Split-Gap speakers, where there is a plateau of sorts at rest and then BL product rises once the coil begins to move in the forward and rearward directions. LMT and Split Coil, on the other hand, fall more within the realm of overhung speakers. If you want to add more stroke, add more coil height. As the coil gets taller and taller, the backplate needs to be moved further and further back on the speaker. Here, the use of double or triple stack magnet structures proves much more affordable than machining a very tall top plate. It’s easy to get the stroke and gain the clearance with Split Coil and LMT. Now it’s worth noting that because LMT allows the manufacturer to customize the layers of windings at various points in the coil, the voice coil can theoretically be designed for an absolutely obscene amount of stroke AND LMT will allow the speaker engineer to carefully guarantee ruler flat BL until the entire coil has left the gap. Split Coil, on the other hand, will see BL begin to drop slowly as it reaches its outer excursion limits. Still, it is very capable of huge excursion without a very tall top plate. All things considered, the LMT is probably the best for huge stroke with perfectly flat BL. Split Coil is next, with Split-Gap usually bringing up the rear.