DevilDriver

I love Iron Laws. Why? Well, they are so succinctly and aptly named: they are infact, iron. Good luck breaking them! If you've been a browsing member of the online audio community for a while, you have no doubt heard about Hoffman's Iron Law. What's it all about? Well, it is quite simple. Forgive me if I am misquoting here, but I think JimJ put it best when he said: "You can have low end extension, high efficiency, or small enclosure size. Pick two." Please note that while many people use this statement related to enclosures, it applies to the speaker you're using as well So what does that mean? And why is that the case? Well, as you may have heard me say once before, speaker design and engineering is a game of compromises. The best speaker (if there truly is such a thing) is the one that has the lowest impacting compromises. Let's say you you drive a little Dodge Sprint or another vehicle with a relatively small cabin and little-to-no room for an enclosure. Of course, you're a bass head and you want to hear those lower notes banged out with some authority. To top it off, you're a cheap bugger and want a lot of sound without buying an expensive amplifier. You build your miracle enclosure, install everything, power it up, and surprise! Those low notes just aren't there. You tried to have your cake and eat it too, which just doesn't work in the real world. Naturally, you think there must be something wrong with the sub or amplifier. Now you have switched every product imaginable in and out. The good news is that an amplifier rated much higher than the RMS of your sub has given you that low end beat you're looking for. The bad news is that you just cooked a voice coil. And this is Hoffman's Iron Law at it's finest. If you want a low end monster, you had better step up the power or build a behemoth enclosure. If you want to keep your amplifier costs to a minimum, you had better build a huge enclosure or accept a very high rolloff with very little low end. If you want a small enclosure, be prepared to buy a big amp or give up that low end you love. What is the specific relation between these by-products? Simply put, the efficiency of any speaker system is directly proportional to the enclosure volume and the cube of the f3 (the frequency at which SPL is down 3dB). If you halve the efficiency of your speaker system, you may also halve the volume of the enclosure. However, if you decrease the f3 of your speaker system by a factor of two while retaining the same efficiency, you would have to increase the enclosure volume by a factor of 8 (2^3=8). Let's say you have an enclosure with an efficiency of 90dB/w/m that is 2 cubic feet in size. Suppose the f3 of this system is 30hz. However, you've decided you want a heavy bottom end and wish to drop the f3 to 15hz. Without decreasing efficiency, this change would require an enclosure measuring 16 cubic feet in size! That is quite a change, and hardly affordable in a vehicle. With a lot of preamble, I think that adequately explains how things work on the enclosure side. But as I mentioned earlier, this applies to a normal speaker prior to installation as well. I'll cover this when I get a chance, but to provide a starting point: where n0 = reference efficiency (% based) Fs = the resonant frequency of the driver (measured in Hz) Vas = Volume of air which, when acted upon by a piston of area Sd, has the same compliance as the driver's suspension (measured in m^3) Qes = electrical "Q" of the driver at Fs (unitless) n0 = (9.614 * 10^-7 * Fs^3 * Vas)/Qes * 100

Nice video showing a speaker built from start to finish.

To expand on an article that I wrote quite a while ago... Defining Xmax is extremely challenging. If we are intending to define Xmax as the point at which distortion is audible (which seems to be the belief of many), then we are opening a very large can of worms. For one, we would need to get a better grasp of what distortion is acceptable, what distortion is most offensive, and how different types of distortion is perceived. While there has been great work contributed to this science of audibility (most notably by Drs. Geddes and Lee), it is still a field where more is discovered all the time. From a purely theoretical standpoint, I look forward to many developments in the understanding of distortion. From a simplicity standpoint, it is best to stick with the 70% BL and 30% Cms targets. At the very least, a push for a true industry standard with confirmed measurements (ie. CEA compliance for subwoofer) would be a great step in the right direction.

Excursion is a large contributor to high output in any driver on the market. Typically, larger excursion (seen visually as how far the cone moves in and out) means more sonic output. However, with excursion come challenges. As the driver moves outward, the voice coil begins to move out of the gap. This causes a drop in the magnetic force (or BL) and results in a few negative effects, including a large theile/small parameter shift, lower efficiency (magnetic flux decreases), less control over the voice coil (transient response increases, making the driver sound sloppy), and introduces distortion into the output. Knowing these effects, there was a need to design a parameter to describe the limit of excursion while still remaining

To very briefly expand on a thought: BL Compression is the least resolved issue. Cms compression has been something understood very well for quite some time; things like wide roll surrounds and various spider designs have made Cms compression a relatively solvable issue. BL compression is still a big problem. There are treatments out there that intend to resolve this issue (split coil, XBL^2, and LMT), but each has their own inherent issues. One thing often forget by those who are big fans of certain designs is that there is no free lunch in engineering. To name a couple, XBL^2 sacrifices BL and efficiency, split coil suffers from significant flux modulation and inductance issues, and LMT suffers from high Mms, high inductance, flux modulation, and generally poor transient response. Speaker engineering is often about making the most appropriate compromise, rather than trying to avoid compromise at all; you'll find the second route very challenging.

Power compression is a topic that is rarely discussed, but always important. When you hear someone call various theile/small parameters a

NP: 3 Inches of Blood - Fear on the Bridge

Interior work is one of those marvellous things where practice makes perfect, and practice is expensively wasted. Good Luck, Neil

A large part of the power handling is based on the ratio of surface area to mass. Using flatwound voice coils increases surface area while keeping mass the same, and thus, power handling would increase. The % of increase this causes is debateable, but I'm sure that Shawn could fill you in without a problem regarding his specific designs. Cheers, Neil

Prototypes means I will have to open my wallet again. Neil

www.SundownAudio.com Cheers, Neil

Now there is a nice candidate for IB in my basement. Cheers, Neil

If TC's BL and Cms curves are as flat as they say they are then, power compression aside, those parameters will hold true in a real world application. Of course, if power compression is bad enough and doubles Re, then Qts/Qes will be bumped up nicely Cheers, Neil

Well, not necessarily. A 6.5" may be able to excurt further than a 6x9 when looking at similar surrounds, but most widely manufactured 6x9's will be quite suitable. Cone shape has very little to do with distortion; it is still predominantly about the suspension and motor. Cheers, Neil

And obviously there is no need to thank, publically acknowledge, or pay those who provide said engineering. Granted, that only applied in a specific situation. Cheers, Neil

It seems obvious to me that eD's forte is marketing and not engineering. Cheers, Neil

Wow, that Qts/Qes is so low it's retarded; if Fs were a little higher, that would be a stunning candidate for a horn; still would be pretty stellar. I don't see it working very well IB or in sealed alignments of Qtc 0.8 or lower, which in my opinion negates a lot of the advantages of going with shallow mount sub, but it should do very well in small ported enclosures; of course, this brings the obvious challenge of trying to get a low Fb in a small enclosure. The other odd thing I have noticed is that those who don't have the room or aren't willing to make the room often aren't willing to pay the price either, so if this will be a fairly expensive venture, I'm not sure that it would work out as a high volume seller. We'll have to wait and see how well it's received. Cheers, Neil

Finally got some time to send the money. Cheers, Neil

If only you had it this weekend; I will be in Winnipeg Friday, Saturday, and Sunday. Cheers, Neil

edit: n/m, not even worth it.

rear fire, make the box tall and shaped like this IIII\ with the subs in the \ part. you will need to fiddle with the height a bit, but you will gain a somewhat horn loaded design and a VERY efficient listening area.

sorry if i missed this on a previous thread, but what are your design goals? do you want a wider bandwidth? what do you want for your fh and fl? do you want high output? do you want a 4th order, 6th order, or 8th order bp? how much room can you give up? Qts/Qes is so low that a 6th or even 8th order bp would likely work best.

most TL's used for bass will be fairly simple, because there is less need for a choke or any stuffing in them.

i wanted a low end beast, so i extended the length of the line and increased the mouth to 5". it is fun though.