DevilDriver

Efficiency/Flux Efficiency Looking at the title of this section, you may be thinking “Did he just say the same thing twice?” Actually, I haven’t at all, and this is one of the keys to differentiating between the technologies. When one of the original comparisons of gap treatments first came out, there was some very clever wording used. The poster often referred to flux efficiency and efficiency in similar posts, giving many the impression that they were virtually one and the same. The fact is that they are not necessarily the same at all. Let’s break that concept down for a moment. The term flux efficiency refers to how efficiently the flux in the motor is used. I know, weird. This concept is very simple: a given length of voice coil in the gap (L) is capable of integrating with a given magnetic field density or strength (B ). If L is too short, the flux capability of B will not be full utilized. This would be an example of low flux efficiency. Efficiency of a speaker, on the other hand, is very different. A highly efficient speaker does not necessarily need the best flux efficiency. For example, a speaker with low B and small L while having high Mms (moving mass), will still be inefficient, even though it is possible that flux efficiency is very high. Hopefully that’s clear as mud. So which gap treatment is the best? Well, let’s look at flux efficiency first. In case you were unaware, all of the B does not lie in the gap: there is some B in what’s called the “fringe field”, or more easily understood as the outer limits of the gap. If you wanted to achieve very high flux efficiency, you would ideally have a coil that is able to use all of the B in the gap AND all of the B outside of the gap. Of course, that’s near impossible to do. But which gap treatment does it the best? That’s likely Split-Gap. Split Coil does a great job of utilizing B in the fringe field, but sacrifices some of the B integration in the middle of the gap. LMT requires a larger gap than typical due to the variable layers of windings (to avoid scraping coil in the gap during its travel). So Split-Gap should be the most efficient design, correct? Nope. Remember that notch that Split-Gap has? Guess what: it actually sacrifices some B, similar to how the wider gap required for LMT sacrifices some B. The further you move the top plate from the coil, the less B is utilized. So when you machine a notch in the gap, you are giving up B. This will actually drop your speaker’s efficiency, even though you have likely increased flux efficiency. Split Coil, though it is less flux efficient, does not sacrifice any B from the top plate at all. Likewise, LMT does not do so either. Split-Gap is likely the least efficient design from this standpoint. These issues can be overcome by adding more to the magnet structure, though this is pointless once you have saturated the top plate. You could make a taller top plate if you’d like, but this grows increasingly expensive and it is harder to achieve a consistent magnetic field through a tall top plate. Split Coil drops efficiency because it intentionally sacrifices the most dense flux (in the middle of the gap) for the least dense flux (in the fringe field). LMT sacrifices efficiency because the gap needs to be wider to accommodate the thicker layers of windings at various points in the coil. The last part of the speaker efficiency equation is the moving mass of the speaker. Forget about the other soft parts for a moment and think only of the voice coil’s role here. Split-Gap uses the smallest voice coil, so it’s moving mass is the lowest. Split coil generally uses a smaller voice coil than LMT (though this depends on the number of windings on the LMT coil) and thus has the second lowest moving mass. LMT usually has the highest moving mass. However, minor differences in the moving mass pale in comparison to large changes in the BL of a speaker. In conclusion, Split-Gap is the most flux efficient design. However, Split Coil will likely result in the most efficient speaker, followed by LMT, and, lastly, Split-Gap.

Split Coil From what I can find via research, the concept of a split coil is roughly 3 decades old. Though there has been seemingly little interest in this gap treatment for many years, it is also increasing in popularity, due in part to a desire to achieve higher excursion levels while keeping BL linear, and in part to Scott Atwell’s utilization of the technology on a few very popular designs of late. If you haven’t already heard, Scott Atwell was the very talented engineer at Resonant Engineering (and the Destijl buildhouse), who has since moved on to Fi Car Audio (and its associated buildhouse). Of the three gap treatments listed here, Split Coil is the only one that is not covered via a patent, pending or otherwise. The concept, as you can see below, is pretty much the opposite of the Split-Gap concept. Here we have no modifications to the top plate, nor do we have varying layers of windings on the voice coil. Instead, we have some of the voice coil located in the upper region of the gap with some of the voice coil located in the lower region of the gap, with a noticeable split between the two sections. As the speaker begins to move, an equal number of windings enter the gap as the number that exit. Pretty easy to grasp, I think. Perhaps the two best examples of speakers that utilize Split Coil would be the Resonant Engineering XXX (with an obscene 54mm of Xmax) and the Ascendant Audio Poly 6.5” (with an equally impressive 11mm of linear one-way excursion). I would expect to see more split coil designs in the not-too-distant future. With the preliminary (and important) background information out of the way, let’s move on to the areas that I have identified as “relevant” to speaker design.

LMT (Linear Motor Technology) This gap treatment is growing in popularity. This treatment is a clever one designed and patented by Thilo Stompler of TC Sounds. If the name rings a bell, it’s because TC Sounds does OEM work for several companies. This technology is a few years old now and likely to be featured in future OEM and direct sales products from TC Sounds in the future. See the image below: You’ll notice that the top plate is not machined in any way. TC Sounds manipulates BL through the speaker’s stroke by utilizing a variable density coil. In layman’s terms (and in case the image does not make this clear), the voice coil has varying layers of windings at different sections along the former. By adding more coil at the upper and lower limits, BL is higher than on a typical speaker when the coil approaches the outer limits of the gap. This gap treatment is featured on products from SoundSplinter (Rl-s), Eclipse (SW8200), and some direct offerings from TC Sounds (most notably, the LMS-5400).

Split-Gap This is a fairly (in)famous gap technology that many of you will already be aware of. Originally patented as XBL^2 by Daniel Wiggins and David Hyre (formally of Adire Audio/Extremis Audio, now of Acoustic Development Technologies), this is now being referred to (and trademarked) as Split-Gap, which is a much more accurate and understandable term. The term indicates exactly what you see pictured below: As you can see, there is a notch of sorts that is machined into the top plate. If we forget about the notch for a moment, the speaker appears to be underhung (meaning the coil height is shorter than the gap height), though it is very close to being evenhung (meaning both the coil and the gap are of the same height). However, that little notch in the top plate makes the speaker behave in a different method than both underhung and evenhung. As the speaker moves, an equal amount of windings enter one region of the gap as the number of windings that exit the other gap. This gap treatment can be found in a large number of past and present speakers, including many products from Adire Audio, Creative Sound Solutions, Blueprint, Ascendant Audio, and many others. It is worth noting that of those 4 companies I listed, two no longer exist and one switched from using split-gap a few years ago. However, in no way does that represent the abilities of the technology.

Prelude In case the title is insufficient in describing the concept here, I’ll briefly explain it. There are currently three well-known methods of achieving linear BL product. If you’re not sure why this is important, please read the Understanding Power Compression thread. This treatise of sorts will be a method of comparing the three primary technologies (hereto referred to as “gap treatments”). I cannot stress this enough: There is no “best” gap treatment. If you have a particular design in mind, there may be one particular gap treatment that will work best for that design, but in no way does that mean it is always the best option. As such, I will be outlining the differences from one gap treatment to another by comparing their value in various aspects rather than comparing the gap treatments as whole pieces. At the end, I will try to summarize what situation(s) each gap treatment is most likely to provide positive results in. Let’s start with a history of each, shall we? Note: I attempted to provide a quick and crude visualization of what each gap treatment looks like. Please forgive me if the drawings aren’t perfect.

Disclaimer The first thing I must make abundantly clear is that, though I feel all information listed below is highly accurate, it is possible I am wrong in certain areas. Let’s face it: I’m human. Though the concepts are well understood, much of what I discuss is my interpretation and opinion on a given set of circumstances. I come into this with absolutely zero bias and I feel that gives this more validity than other comparisons of a similar nature that you may have read. Above all, please read in the interest of gaining another viewpoint. Table of Contents 1.0 - Prelude 2.0 - Split-Gap 3.0 - LMT (Linear Motor Technology) 4.0 - Split Coil 5.0 - Efficiency/Flux Efficiency 6.0 - BL Linearity 7.0 - Inductance 8.0 - Power Handling 9.0 - Scalability 10.0 - Manufacturing Tolerances 11.0 - Manufacturing Costs 12.0 - Conclusion

When I have some cash, I'm going to jump on this or a similar deal here, I think.

Wootage fo bifday

I loved the old XXX. I heard one of the new XXX's and I had my doubts, but it was fantastic. That said, the price is very, very high (especially if you're buying in Canada). For the cost vs. performance ratio, the Q's are probably a better option, especially if you're going ported. The XXX has a big strength in it's linear excursion, but in a ported enclosure, you'll never even approach the limits, unless you have so much power on tap that you'll be putting the coil in trouble thermally. With the new XXX here in Canada, you will be looking at $1000-$1500 dollars for a 15"; even after shipping and duties, the Q's will be much more affordable.

Looking good so far Scott.

LEAP 5 is up for those who know where to look

It should be good to go in about an hour. I have to run out, but I'll post a link when I get back.

What's your intent for this? I would guess that it's SPL, but it's severely undermotored if that's the case....

Hmmm, if everyone wants LEAP, maybe I'll upload it on my server and share it with everyone.

"Yuli said" is great evidence dude. I remember when you used to make sense.... If I recall correctly, Yuli also said you get port noise if you go with too large of a port, which has never, ever happened to me, nor anyone I've ever met. But this isn't about Yuli at all. It's about pulling crap out of your ass and calling it fact. This is all theoretical for you because you know absolutely nothing about the Sundown Audio products.

I know Scott didn't mention that he was considering this before, but maybe they'll be able to rework the suspension to allow a little more Xmax; that seems to be the limiting factor, but I think it's tough to get a good, long throw suspension on a 6.5" driver, especially without going to a really custom frame. Still, the first iteration was so good that you can't not be excited for the next.

More material in the mids, so you'd get more use out of it there.

A nice slow day at work feels good on a Friday.

I blow a damned gasket every time I see someone post on Canadian Car Audio about the Sundown products. Those Alberta and BC guys are just ridiculous and illogical. On the topic of the two amps that are being compared, there really is no comparison to be made. I do like Kicker and some of their reps are fantastic guys (Tracy Focht comes to mind), but let's break things down a bit. SAZ-1500D is less expensive. SAZ-1500D has a longer warranty. SAZ-1500D can handle much lower loads (ZX1500.1 "can" go below 2 ohms but only in very ideal situations, whereas SAZ-1500D can get under 1 ohm pretty easily) SAZ-1500D can easily be repaired and replaced. SAZ-1500D has better, more easily accessed support. It seems like an easy choice to me.

Coke cookies, maybe? Any 3000d's there Jacob?

I'm sorry, I'm a little lost with some of the acronyms flying around I feel a little ADD^^ (I had to go there) http://en.wikipedia.org/wiki/SPARS_Code

Perhaps this should be prefaced by saying these are all opinions. For whatever reason, this always ends up being very hotly debated topic. I would say in general, you will here this most often: Vinyl DVD-A or SACD CD Cassette 8 Track I can't put reel to reel in there because I've never heard it (and don't know anyone who has) and digitally stored media is too all encompassing (what is the audio codec? what is the bitrate? is it transcoded? etc.) My personal preference, however, will always be vinyl or FLAC. Vinyl can be great if you're playing a well mastered recording for the first time. After 10-15 times, the experience might not be quite as enjoyable. With FLAC, I am guaranteed a "lossless" recording every single time. FLAC is easy to transport and widely available on oink.me.uk. The argument always seems to arise in the concept of converting from one format to another. Jim made a great point when he said reel to reel, empirically speaking that is. However, many companies are using all digital recording (which is becoming increasingly popular) and this eliminates any losses from analog to digital conversion. As far as raw capabilities are concerned, DVD-A has to be near the top based simply on storage capabilities. Of course, we can always make an argument for audibility: can you really hear the difference between a v0 mp3 and vinyl? A lot of people have difficulty proving that they can. To me, regardless of the medium, it comes down to who mastered that particular release. I know on a few occasions I have preferred a vinyl LP to the CD version or vice versa, only to find out that any differences could easily be attributed to the difference in mastering techniques.

Pretty much. Is there a difference? No doubt. Is it audible? Extremely unlikely. Will it cause damage? Virtually impossible. Another way to think of this: if you have two speakers in a ported enclosure, the one closer to the port moves less (servo effect). Naturally, the one moving less will have a less exercised suspension. Does it matter? Nope...

Exactly. Like virtually everything, it's a negative if it detracts from the intended design and a positive if it adds to the intended design.

It depends on the application. In a lot of standard high power subs, you'll find a pole vent to help dissipate heat. However, a pole vent can be a bad thing. In terms of cooling, the idea is to move as much air past the coil as possible. A pole vent usually means that the vent is one of the exit points for the air that cools the coil. If we plug this pole vent and change some motor internals (like adding venting to the pole piece), you may find that there are other ways to route the air and cool the coil more efficiently. This is something that is done on the BTL from Fi Car Audio.