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.
Been toying with the idea of a VERY inexpensive sub-woofer, eyeing on the price / performance /specific use ratios. Looking for something to go under the desk, so small/thin would work. Price should be a large factor, so sort low-high. Response should be down in the mid 30's to high 20's.
So off to the Sub-Woofer and woofer pages of PE again. Sub-Woofer pages start off at $16 US minimum and only go up. The first is one I already spoke of above. Has possibilities, but price adds up quickly. Next ones on the page are on back order and then the prices just keep climbing.
Woofer page. Sort again and #2 on the list a 6.5" at just under $7 US. A couple of quick checks in my software show that a box of ~2 Cu.Ft. tuned to 33 Hz shows acceptable response. Throwing it into WinISD as Iso gives a fairly nice response from about 85-29 Hz. And if you tighten that up to 80-30 Hz, there's only about a 1.3 dB differential over the band. To throw it out there even more, you've got 150 Hz @ +1 dB, 60 Hz @ +3.9 dB, 33 Hz @ +4.2 dB, and 27 Hz @ -3 dB. That's using only 1 pair in the box for a total of around $14 US. And I think that would work well with my feet and legs basically enclosed by the desk foot well and the sub against the wall.
Now to design a preamp sub/sat filter for a 2.1 with some of the stuff I've got. Hope they have them down the road! 😀
**Nick, I'm still designing the standers for the ESOs. Once I get through all this other life stuff I can start on them.
Here's a little bit of what I'm thinking for these:
Now this would be custom fit to be slim in the footwell of my desk, with the slot port at the bottom. Like I said above, not that terribly loud as compared to others, but more than sufficient in this particular situation. Paired with the desktop ones I have on slate for when I get my office sorted and finished, should be a fair match. And for $14 USD, worth a go.
I love this! My only concern would be the port. That is a very small port for those woofers. Typically you want between 1/3-1/2 the size of the woofer. So maybe a 3" port? Not sure what the length would be ont hat. Have you check out port velocity at whatever wattage you are thinking?
Area calculates out to just over a 2-1/8" round port. The Port velocity is at the 120 W max it might hit, which puts it at 14 m/s. Sitting at 60 W rms, it's down at 10 m/s.The excursion is what is bothering me. It should be moving a lot more. Granted, they only have an XMAX of 3.5 mm, but as low as they show, and at the 120 W setting? I can zip the WDR and the WPR if you need to see them, to see if I messed up somewhere.