Reading TS Parameters

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I'm thinking about taking the plunge and building my own subwoofer. I've done a tremendous amount of research thus far, so I have a reasonably good understanding of what I need to do and how best to go about it. One area I'm not terribly comfortable with though is deciphering all the information contained within the TS parameters.

My intention is to create a ported sub approximately 14-15" in each dimension (H, W, D), using a 10" driver and a 200 watt amp. I know how to interpret a few of the TS parameters -- like Fs -- so I understand some of the specifications, but several of the ones related to appropriate cabinet size and type (bass reflex vs acoustic suspension) I'm not entirely certain of.

Can someone tell me which of the TS parameters I should concentrate on to build a ported sub about the size I need? Also, what ranges or tolerances (plus and minus, in other words) those parameters should be within in order to be considered good for my application? Just some general guidelines is all I really need. Once I have a direction I'll take it from there.
 
There is no way to answer your question well. You can look for a speaker that will fit a type of design but you seem to have already chosen the box type and volume

Actually, room layout and limited placement options have decided for me. :p


Check these out:
Thiele-Small Explained?
Thiele-Small

I will indeed. Thanks for the links.


If you have a driver in mind there are a few people here that will help you with a design that will blow you away!

I don't have a driver in mind just yet. I wanted to understand how to read the parameters before I got my heart set on something, only to find it wasn't suitable. Once I have a better idea of how to decipher those numbers then I'll probably do that; ask what others think of my choice.
 
It's difficult to "read" them. What you need to do is get a box program- there are lots that are free, or very good ones you can pay for. Run some designs using the parameters for various drivers and see what you get. IMO, deciding on a specific box and looking for a driver is an exercise in frustration. Compile a list of drivers that look interesting, then run box designs for them. With luck, something will stand out as a winner. (run both sealed and ported designs)
 
deciphering all the information contained within the TS parameters
If you are to comprehend the issue in depth, you will need a background in Physics: namely simple harmonic oscillation, damped harmonic oscillation, and driven, or forced, harmonic oscillation. Once you have the math equations for these down pat, it will be smooth sailing from then on. When it comes to tuning sealed boxes, the basic math is easy to do with pencil and paper - no need to resort to simulation software unless more sophisticated parameters are being investigated.
 
If you are to comprehend the issue in depth, you will need a background in Physics: namely simple harmonic oscillation, damped harmonic oscillation, and driven, or forced, harmonic oscillation. Once you have the math equations for these down pat, it will be smooth sailing from then on. When it comes to tuning sealed boxes, the basic math is easy to do with pencil and paper - no need to resort to simulation software unless more sophisticated parameters are being investigated.

Surely it can't be that hard. How are others doing it then? If you can't make heads or tails of the TS parameters without intimate knowledge of physics it seems logical to assume very few people would be able to make DIY speakers. At some point knowing what to look for in a driver -- spec's wise -- has to factor into the plans, so in that regard everyone (or virtually everyone, anyway) who makes a speaker would have to possess some ability to understand the parameters.
 
Dayton Audio T1003K 10" Titanic Mk III Subwoofer Kit

Hi,

just start looking at good subs near what you want. Typical parameters
will start jumping out at you. For what you want sealed is the way to go.

So you want a 10" driver and a 14"x14"x14" box. No problem.

Cost ... what basically happens as you pay more the driver becomes less
efficient, requiring a bigger amplifier, but as its less efficient it goes lower,
and generally the driver excursion capability increases - this determines
maximum volume as long as you have enough driving power.

Your other option is a low Qts 10" driver with a PR in that box volume.

Parameters are quite different to sealed.

e.g. Peerless XLS10 10" Subwoofer (830452) and Passive Radiator (830481)

rgds, sreten.
 
Surely it can't be that hard.
"Hard" is in the eye of the beholder. The way I see it, fiddling with simulation software without knowing what's going on is the same thing as reducing Arithmetic to operating a calculator. It's a free country, and there's nothing wrong with aspiring to be a carpenter. Why, a carpenter may marry a virgin visited by angels, and who knows what may happen next.
 
Some information off the top of my head.

Fs, is, as you already know, the driver's pistonic resonance.
Qts is (in my mind) a measure of how well the driver "rings" at resonance, when connected to an amplifier. A low Qts means it doesn't ring much around resonance, so the lower frequencies will "sag" in the frequency response chart. Some form of aid from the cabinet will be needed for acceptable bass response. Really low Qts drivers (<0.3) will need a horn, as a simple port won't provide enough gain.
Now, Qts is derived from Qms (driver's mechanical damping, we can't change this easily) and Qes (electrical damping). Qes represents how well an amplifier of zero output impedance (so the driver is damped as best it can be by an amplifier) damps the speaker. Qes is usually the dominant one when Qts is being derived.
The upshot of this is that a resistor of a couple of ohms can (by decoupling the amplifier and speaker a little) increase Qes, thus increasing Qts, making a low Qts driver usable in cabinets that would prefer higher Qts (such as sealed box or even open baffle), or a really low Qts driver usable in a bass reflex design (which are much easier to construct than a large horn).
For a given cabinet type, a higher Qts will need a larger cabinet than a lower Qts. The tradeoff here is that the higher Qts one will go lower (most other things being equal).

So, given a couple of subwoofers,
Dayton Audio RSS265HO-4 10" Reference HO Subwoofer 4 Ohm
Peerless 830668 10" Paper Cone SLS Subwoofer

I could tell you that both would work in a ported box tuned in the low 30s, the Peerless would probably require a larger box, but it will also work in a sealed cabinet (which tend to be smaller than ported ones), as the higher Qts allows this. As a subwoofer driver, I'd take the Dayton, as it has much greater power handling, which would allow some thermal abuse (or use of very small cabinets and serious amounts of eq).

I'm not sure (being a first-year A level student) how correct all this is in the world of Physics, but it's stood tests on winISD and the like.

Chris
 
so the lower frequencies will "sag" in the frequency response chart. Some form of aid from the cabinet will be needed for acceptable bass response
Three things: one, a "sagging" response may be corrected by other means as well, eg boundary reinforcement or EQ. Two, a higher Q may be (and usually is) the result of a weaker magnet, which in turn may give rise to a host of other issues down the line. Three, a series resistor is a really dumb thing to use. It wastes valuable efficiency and turns it into heat, as though there wasn't enough of that going around in a stereo system! Taking into account the inevitably highish output resistance of a tube amp, for example, is one thing; adding superfluous resistance where none existed before is entirely another.
 
bbggg,
1 - agreed, though I'd avoid low frequency eq as much as possible.
2 - A weaker magnet directly means higher Qes (as back EMF is lower), what are these other issues you speak of?
3 - Speakers are inherantly low efficiency. A series resistor may dissipate some heat, agreed (nothing compared to the voice coil itself though), but getting a decent bass response on, say, an open baffle will require either lots of eq, or a usably high Qts (most would agree ~1 is a good place to start) to negate the need for the hideous power requirements equalisation will need.

Chris
 
Bass EQ is not "hideous". Any which way one chooses to equalize a woofer, its maximum SPL limits remain the same. As for the rest of your comments about Qs, I strongly suggest what I wrote before, about studying harmonic oscillations. Of especial import in this case is the range of solutions of the differential equation for subcritically damped oscillations. It will sort out Ps and Qs for good! :)
 
The power requirements for any serious eq tend to be high, and require sturdy drivers and amps to make the most of such a design. In terms of Vd, you're quite right, max SPL is a constant. As soon as power handling kicks in (ie, really small -therefore inefficient- cabinet), you've got a new set of problems ahead.

I shall have a read when I'm back at college (1st September), as I'm currently on my break - my brain is a marshmallow. ;)
For the time being, the information in my original post is what I've been able to pick up. The rules of thumb seem to apply, but the exact reasons (which I'm sure you know a lot more about :) ) remain a little mysterious to me.
 
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