Following the lead
After watching 123Toid's / Toid's DIY video:
I thought to myself, what else could I possibly be dismissing on single driver performance?
Well, just for fun I stopped by PE's Home Subwoofer page and did as I always do, Sort from Cheapest. First thing that pops up is the Goldwood GW-406D, a 6-1/2" poly sub that is currently on sale for $12.13 USD. That's pretty darn cheap. And looking at the rest of the specs, you'd probably dismiss them without a thought - 16 Ohm, 85dB @2.83V, 60/90W, 2mm excursion - not the most promising. As I've said before, you need to read into the specs rather than just gloss over things. Let's break it down.
16 Ohm and 85dB@2.83V. These NEED to be taken together. What you are looking at is 85dB @ 1/2 W. 2.83^2=8.0089/16=0.500556W. In order to get it up to 1W, you'll need to be pushing 4V, which would put it up at 88dB +-.
Ok, so you need more power, a minus right there.
But wait! there's MORE!
Is there a way to wire them up to get 8 Ohms or something else? Well, 4 in parallel would be 4 ohms and 8 in a series / parallel combo would get 8 ohms. 4 Ohm ~91dB @ 1 W and 8 Ohm ~88dB.
4 drivers - 1.87 cu.ft. box, 3" port @ 4-3/4" long, Fb & Fp 38Hz, F3 30 Hz, 240/360W
8 drivers - 3.74 cu.ft. box, 3" port @ 1-1/4" or 4" port @ 3-1/4", Fb & Fp 38 Hz, F3 30 Hz. 480/720W
Of course, this is in the same style as the video, Isobaric / Compound configuration.
Ok, what does all this mean? This is something I learned a long time ago from a guy in the PA business - doing sound for State Fairs and Country music acts - he'd take 4-10" or 4-12" over 1-15" any day as they'd hit harder (faster) and generally deeper. The more voice coils you can combine the better. So what that translates to is that each speaker (or combined speaker) has to move less to make the same amount of air be moved. Here's the hypothetical math: let's say that at a certain power a driver moves 1mm and displaces X amount of air. Now you place another driver on the same face right next to the first. you now have 2x's the cone surface, so each driver only needs to move 1/2mm to displace the same X amount of air. If you put 4 on the same face, then that's 4x's the cone surface and each only has to move 1/4mm to displace that exact same amount of air. Not necessarily intuitive, but when you think about it, extremely simple to understand.
What would I do? Well, at that price, they're almost worth trying either a pair of 4 drivers or a single 8 driver. 4 = $48.52, 8 = $97.04.
Fun exercise in thought, and that's just with the first driver that comes up. I haven't even looked at anything else yet.
*PS - I did a quick check of just putting 2 in a box like the video, and you get a 0.94 cu.ft. box, 2" port 4-5/8" long, same Fb, Fp, F3, and 120/180W @ 8 ohm. Total $24.26 That's intriguing too! Hmmmm...
**PPS - Fb = Fbox, Fp = Fport, F3 = -3dB point.
I just realized that these are Dual Voice Coil drivers - 8 ohm each, and that the specs given on PE were for them wired in series. Under the Manuals and Resources, Goldwood gives you the specs for the driver wired in parallel, 4 ohm. It really doesn't change anything, and my analysis of the SPL is pretty much the same based on the rounded off numbers from PE. So there you go.
For $48 is would be worth building a box a measuring it surely!?
Thanks. I have kept ISO in my mind for a very long time, but it sometimes slips to "the back of the closet", only to be found a year or two later. 🙂
Actually, the other TV speaker drivers I had bought that I was going to try a Line Array style build, I think I might just redesign into a similar style of ISO/Compound, but with the drivers in line instead of opposed, just for looks sake. It'll be a much smaller box, since I don't really have the room for a Line Array at the moment. It'll show two main drivers and 4 tweeters with some Dollar Store Amps and power supplies, for cheap fun.
BTW, did you see my question on the ISO100 video?
It was on the video. I asked it either last night or this morning, about the BOSS driver.
If the specs are real and the build quality is good, for an extra $16, you'd bump the power up to 1600W/3200W total for just about 0.33CF more and about the same response, but 1.5mm less Xmax. I know how you feel about BOSS, so it's just a "theoretical" move.
Oh yes. I responded to that this morning. I personally don't trust anything Boss, so it would be hard for me. I actually have a video coming out this weekend or Monday about Watts and how they mean very little. I'm sure you already know what I will be talking about, but I would need to know real specs on the Boss before I could recommend them. And even then, I probably never could, lol.