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Digger8 Sub - diggity dig it all the way to 20Hz

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  • fastbike1
    replied
    Re: Digger8 Sub - diggity dig it all the way to 20Hz

    Can you give some more details of your box model? I'm using the factory specs and Jeff Bagby's WBCD and I can't come close to your F3/F10 values, either vented or PR.
    My PR model uses the Dayton 10" PR.

    In 24 liters net tuned to 27Hz (seems about optimum flat), I get F3/F10 27/23. Good looking response curve and within xmax limits. Given this response, I can see why you didn't hear anything at 20 Hz. By my model, 20 Hz is 22 dB down.

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  • Kevin G.
    replied
    Re: Digger8 Sub - diggity dig it all the way to 20Hz

    VERY Cool...I have been hoping to build something in a more vertical alignment, for my theater room. I have plans for putting my mains behind some columns, how would two of these do in a larger room?

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  • Sidi
    replied
    Re: Digger8 Sub - diggity dig it all the way to 20Hz

    That's a nifty box mate. I have one of the 15" cast frame PRs from PE I got at the tent sale for $15.... I may make an adaptation of your build for the bedroom :D

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  • prighello
    replied
    Re: Digger8 Sub - diggity dig it all the way to 20Hz

    Nice, I've been looking for something like this.

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  • jsr
    started a topic Digger8 Sub - diggity dig it all the way to 20Hz

    Digger8 Sub - diggity dig it all the way to 20Hz

    The original post and details are below, but due to improvements that were made by individuals, I thought I'd update the post with some of the info.

    I'll start with the original design goals. I wanted 3 goals: LF extension down to low 20s, very small size, minimal price. Unfortunately, like the business motto "low cost, high quality, fast schedule...pick 2 of the 3", no commercial or DIY offering could meet all 3 goals. There's commercial subs that will hit low 20s with somewhat decent pricing, but they're HUGE (in my standards...anything more than 2cf is big for me, but most that would do low 20s was 3cf+), and ones that are very small and dig low, but cost several thousand due to the need for fancy drivers that include built-in feedback, amps with circuitry to read the feedback and dynamic EQing based on the feedback. So I dug around for a low cost driver that would work well in a small enclosure while reaching low 20s. I found a few, but the Harmon cousins JBL GTO804 and Infinity REF860 were the most affordable while providing the requisite performance. Plus, I had the Infinity before and knew it could perform. Next was the PR...one that is affordable but decent enough to meet design requirements. The Dayton PRs are the most affordable PRs I could find. Everything else was IMO, either too pricey for the design goal up to outrageously priced for something that's essentially a weight suspended by suspension members. I later mentioned a higher cost, but better performing alternative that some have chosen to use in their Digger8s. I then needed an amp that was affordable to maintain the minimal cost goal. Originally, I chose the Yung amps due to their low price (considerably lower than any other competitor) and initial information that they did not have a HPF built-in. Unfortunately, that information was wrong and it turned out the Yung HPF is set higher than their competition which limited the LF extension. There are threads on other forums that go into quite a bit of detail on which resistors to change to lower the HPF corner frequency. However, many have used the Bash 300 amp instead since it has a lower HPF Fc that does not interfere with the design of the Digger8 but aids in keeping over-excursion in check. Some recent sales on the Bash 300 also made it an affordable (not quite as cheap, but much closer) alternative to the Yungs.

    As mentioned, the original Digger8 with the original un-molested design goals are below and it is the lowest cost option. You get a mid-20Hz, compact well performing sub for ~$175 in parts cost (not including cab). But it wouldn't hit 20Hz without the Yung being modified for the HPF Fc. And it was excursion limited so you wouldn't use the full power of the amp. Still besting any commercial offering (and to my knowledge DIY as well) in meeting all 3 goals.
    For about 63% more cost (~$110 with current parts cost), you can upgrade the Digger8 to be better in almost every way, from one that surprises you with what it can do to one that amazes you to what it can do. The sub is the same...choose the JBL GTO804 or the Infinity REF860. Most have chosen the Infinity due to the slightly higher Xmax. I chose the JBL as I think the basket was prettier (yeah, I don't see it now of course) and I wanted to try it. There is minimal performance difference between the 2, so pick the one you like or the one that's cheaper when you're browsing Amazon. The PR is now an Acoustic Elegance PR12-970. Cost for the PR goes up from $35 for the Dayton to $60 for the AE. The AE comes in a weight that requires no added mass. It is slightly larger in OD (about 1/4in) than the Dayton, so account for in the cab cutout. But it has CONSIDERABLY more Xmax and will not bottom out. It is also quite a bit beefier, which doesn't matter for the original Digger8, but will if a more compact one is made. Just keep in mind though that AE is not fast in delivery. Your 3 weeks quoted leadtime will easily run into 3 months, some have waited 6-9 months in past orders. The amp, as mentioned, is a Bash 300. It has the HPF already correctly set for the Digger8 to perform its best. It has a slight 1dB boost at around 22Hz which doesn't really do much to performance.
    So the Digger8i ("i" for improved?) now reaches down to 20Hz F3, is not excursion limited (both drivers have plenty of Xmech), can handle more power and still retains the very small 9x14in footprint and gross 1cf volume.

    Digger8 V2?...this was an idea to make the Digger8 even more compact. With the use of the Bash 300 and it's capability to adjust boost and HFC Fc, the V2 takes a similar route that many use to get more extension out of their subs, EQ boost. I typically never designed using any EQ because the cost of amps with EQ capability was typically more than I wanted to spend on the sub as a whole. And modeling subs, there's not many subs (even very highly regarded ones) that can hit 20Hz without EQ help...But the Bash is a decent priced alternative to those higher dollar ones. Looking at my Digger8, it appears the cab can be shortened 3in, making the external dimensions 9x14x17 without the active and passive drivers physically interfering with one another. I was shooting for 4in lower height, but I don't think it's possible. However, I still have the Dayton PR which has a smaller basket, so I don't know the clearance with an AE PR. I may order the AE in the future and confirm all fitment, but my wife continues to yell at me at volumes where the Dayton is not bottoming out, so there's not much motivation. If someone with a Digger8i would like to cut some wood and try the 9x14x17 size, it will help confirm fitment for a possible Digger8 V2. One thing to note though that my personal Digger8 has the PR mounted lower than my recommendations, so that affords me a bit more space to shorten the cab.
    If the cab size is possible, then the Bash 300 resistor settings would be R26 = 15 kohms and R25 = 220 kohms.
    On the AE PR12-970, add ~250g of weight (if you can't get there, 100-150g is fine, you just give up a few tenths of extension).
    F3 is the same as original Digger8. A word of caution...the resistors on the Bash are not easy to get to since the board they're on is glued in place. If you can remove the board, they're easy.
    Keep in mind though that the only difference in size is height. The footprint is unchanged so unless you have special fitment considerations, the normal Digger8 will likely fit anywhere the V2 would. But I just like being able to make a 0.85cf gross volume sub hit 20Hz with authority.

    Original Digger8 Info:
    I snuck away from the screaming baby for a couple of hours this past weekend to finish a project that I've had going on for some time (my wife was very happy with me). My house is small so I need compact equipment everywhere. Most commercial and DIY subs are too large for my house, especially ones that can dig into the low 20s or below. And small subs, be it commercial or DIY, couldn't dig low enough for what I wanted (although DIY typically dug a bit deeper). So not finding a commercial or DIY offering that satisfied my size and low end extension needs, I decided to see what I could make.

    I call it the Digger8. It's only a single 8" sub, but digs all the way down to 20Hz F3. And my son loves excavators, aka diggers, so it's a tribute to him also as he helped me with this project (as much as a 3.5yr old can help).
    Active Driver = JBL GTO804
    PR = Dayton SD315-PR 12"
    Mass = 575g additional to the 200g PR mass

    Modeled response shows the following. No EQ to boost or cut anything, just a 2nd order LR2 filter (which is what the plate amp uses) set at 100Hz for the model. Frequency Response pics in Post #23.
    F3 = 20.17 Hz
    F6 = 18.56 Hz
    F10 = 17.08 Hz

    I ran some sine sweeps down to 15Hz. Although I can't really hear much at 20Hz (I think my hearing drops off quickly around mid-high 20s), testing it upstairs starting shaking my floor. I moved testing downstairs as my wife was getting mad at me for "breaking our house" as she calls it. It has strong audible output down to my hearing limit. And below my hearing limit, seems to have good output to "feel" the bass (something I like when watching movies). Both drivers are moving quite a lot at 15Hz.
    Small size overall of 1cf gross (about 0.85cf net) with a 9" x 14" footprint and 20" high. The Dayton PR runs out of steam at higher power. If I find it inadequate, I'll replace it with a PR with more excursion (have one in mind already). Active driver is a JBL GTO804 8" sub (really like the aesthetics of this driver, especially the unique basket which unfortunately is hidden). Has a healthy 11.5mm of one way excursion. Amp is a Yung SD300 class D which is more than needed for this project, but for $15 difference between the 200W and 300W, I chose more power. Enclosure has a brace connecting the left, right, top and bottom for bracing. The PR doesn't have to be mounted as low as I did (see the pics). I must've mis-measured something during the planning stages as I was afraid the PR would contact the JBL, but it can be about 1.5" higher.

    Here's some pics of the bare MDF sub. Right now it's serving as the living room sub (where two 12" commercial subs used to reside...they're still there, but right now just collecting dust off to the side). I plan to move it upstairs where space is smaller than my living room (and use the 2 commercial subs I have for my living room). Hopefully it doesn't actually "break our house" as my wife is predicting, though it can feel like it upstairs.
    Attached Files
    Last edited by jsr; 03-19-2014, 02:43 PM. Reason: Updated design info
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