No announcement yet.

More Fun with the Peerless STW350F.. and passives...

  • Filter
  • Time
  • Show
Clear All
new posts

  • More Fun with the Peerless STW350F.. and passives...

    After enjoying the heck out of my Peerless STW350F subwoofer, I needed to change up a few things. Originally, I settled on about 3.5 cuFt net in a vented box tuned in the high teens; I debated much over what configuration to go with in this thread:

    .. and I eventually covered the build in this thread...

    But a little while back, all of the gear was moved to a different room with a different layout. Unfortunately, that layout wasn't conducive to good bass with where the subwoofer needed to go. And the box was kind of big and little bit of an eyesore (to some, I'm told..) for where it was placed in the room. There were a few nulls from the space and placement that led me to be dissatisfied with the in room performance. The subwoofer certainly didn't underperform, I just needed to move the subwoofer and there weren't very many good places to put it. My options were limited, and the box limited that even more. I eventually snuck it to the back corner of the room, which yielded much better results, but still had some issues. One issue in particular was that now it was closer to seating area, so I could hear more of the mechanical noise produced by the behemoth motor with extensive venting.

    Eventually, my better half decided that the room needed some bookshelves, and those bookshelves were going right where the sub was. So a new design was in order. Luckily, I've had some experience integrating subwoofers in to cabinetry, so after putting some bookshelf designs on paper, I had some rough starting dimension for a new enclosure. The dimensions for the base cabinet that would become the subwoofer are a little flexible, but for uniformity's sake, I tried not to vary more than a couple of inches. And instead of making maple-flavored sawdust first in the form of new bookshelves, I decided to make formaldehyde-flavored MDF dust first to make sure the new design would be satisfactory.

    I decided to go with a trio of CSS Audio APR12 passive radiators. I purchased a few of them a while back when they had some B-stock units (should have bought more, darn it!) so I had them on hand. It was between the APR12's and Earthquake SLAPS M12's; the SLAPS M12 has more Xmax but doesn't support as much weight, white the CSS units handle MUCH more weight and appear to be more reputable (I struggled to find and official answer for the SLAPS M12 unit as one spec was kind of listed in the owner's manual, and another cautionary spec listed in some other documentation from the MFG via some interweb meanderings). It requires three or four APR 12's to do what two or three SLAPS units can do, so APR12's are definitely the more costly route.

    From one of the threads above...:

    "#E in Red - Quartet of CSS APR12 PR in 4 cu.ft

    Tuning: 17.9 hz
    F3: 16 hz
    Power In: 750 watts
    Vents: --
    Filters: [email protected] Q1 Gain1
    PR Wt: 1100 grams per PR

    Strengths and weaknesses: Lowest tuning I could find with PR's. Adds significant cost for FOUR PR's. A pair or triplets of PR's could tune lower, but would limit SPL and amplifier input. Already limited amplifier input due to excursion limits of PR. NO PORT NOISE!!! A slightly sagging response which could be fixed with a HP filter @ 14 hz, Q of 1, but it would cost you 100 watts and some SPL (But not much as the sag would be gone). Best PR alignment I could find. Rolloff mimics a vented enclosure instead of the additional 6db/octave typical of other PR setups (like the two below).​"

    Click image for larger version

Name:	image.png
Views:	202
Size:	110.6 KB
ID:	1494747​

    I found that I could achieve approximately the same tuning with three passives instead of four by limiting power in to 750 watts without the PEQ, and only loading 800 grams or so on each passive. It gives a slightly drooping anechoic response (1-1.5 db from 35 to 18 hz). Since I haven't swapped out my crown XLS 1500 for the XLS 2000, or added a second XLS1500, I figured I would power both of the subs off of one amp, feeding them 525 watts each. That should keep PR excursion in check. The subwoofer itself doesn't care about over excursion. It laughed at the full power attack of the XLS1500 down to 10 hz where the amp choked.

    Oh, did I say BOTH subwoofers?? Yup, you heard that right. We had TWINS!! I stashed away a second STW350F before they became endangered, and then NLA. So happy day for me

    The next challenge was figuring out how to fit three passive 12" radiators and one giant 15" subwoofer in to a small box. I was aiming for as small as 2.4 cu ft (ideal sealed box was right around 2.2 cu ft), but unlike most subwoofer builds where you are almost compromising the extra box volume for a higher WAF, I actually had to add more volume to make it all work. In order to keep the passives and drive from interfering, I needed around a 20" wide baffle. In order to fit two passives height wise, I needed a 26" tall box. And to physically put the passives on the side of the box, I needed a minimum of a 13" deep box. So after some maths, a 26x20x13 box yields right around 3 cu ft gross. Subtract driver volume and I'm closer to 2.6 or 2.7 cu ft. That will work.

    WinISD shows around an 18 hz f3 with tuning around 16 hz. That happens to be almost identical to the vented enclosure I was using, except a slightly sharper rollofff due to the passives being 5th order instead of 4th order. So, off to make some sawdust!


  • #2
    So, to start off the day, I couldn't find my 1/4" spiral fluted up cut bit, so off to the local hardware store to get a new one. I lucked out and they had one left on the shelf. Back to the shop... Into the second cut and... DOH!

    Click image for larger version

Name:	IMG_3991 small.jpg
Views:	140
Size:	317.7 KB
ID:	1494757​

    Ok, Home Depot here I come! Two more 1/4" bits (that wasn't the first time I've broken a bit...) and we can get going. The pattern is simple: dado all edges and centers on the baffle and back, dado two edges and center on the sides, dado only the center on the top and bottom. Route three holes for passives and one for the subwoofer, then use the drop from the subwoofer cutout to route and brace for the back of the sub. Cut a couple of window braces and gakk up the windows in them cuz it's one of those days, drill out some elongated holes in the circle brace to compensate for any misalignment, and use some scrap pieces for the center spine bracing. Do everything twice, cuz we're building two subs, remember? Done.

    Click image for larger version

Name:	IMG_3993.jpg
Views:	122
Size:	254.3 KB
ID:	1494758​

    Looks like it lays out just fine, so lets start some assembly.

    Click image for larger version

Name:	IMG_3995.jpg
Views:	124
Size:	222.5 KB
ID:	1494759​

    Click image for larger version

Name:	IMG_3996.jpg
Views:	130
Size:	208.3 KB
ID:	1494760​

    Lets drop a baffle on and we have ourselves a box!

    Click image for larger version

Name:	IMG_3998.jpg
Views:	126
Size:	210.8 KB
ID:	1494761​


    • #3
      A few from the side. Minimal bracing so we'll see how it runs...


      Now for some clamps. Lots and lots of clamps... I pulled half of them off already...

      Test fit the sub and... uh oh.. some idiot used the wrong measurement to set the brace for the rear of the sub. The sub sits an inch proud of the baffle. Geez... Guess I better pull that out. I'll leave the main brace, though. In the future, I may build a new cradle with dowels to extend to the back panel. We'll see how much the back panel flexes ​​first. I'm using T nuts and 10-32 socket head screws to secure the driver to the baffle. Wood screws are NOT sufficient. Learned that the last time around...

      Click image for larger version

Name:	IMG_4002.jpg
Views:	144
Size:	244.2 KB
ID:	1494764​

      Fits. And now from the side...

      Click image for larger version

Name:	IMG_4003.jpg
Views:	127
Size:	151.0 KB
ID:	1494765​

      I predrilled all of the holes for the passives and t nuts. Took the boxes home, pulled out the box of APR12's I had sitting on the shelf, and let my kids help me bolt things down. They about died when I puled the sub out of the first box and they saw how massive the thing is. I even let them try to move it. They pretty scrappy kids, but flyweights, and still young. But they were nothing but smiles, giggles, and excitement to see it get put together. I used Neutrik connectors that JUST barely fit in the corner and had to run some new wire to the second sub.

      Sub one, sitting in the corner. Dual passives facing the wall. After placing the second sub, I had to temporarily rotate it 90 degrees in the corner so the dual passives face out. Boxes are ugly ducklings as they are still naked. They will get a nice coat of lacquer, then some solid maple applied panels and probably decorative wire mesh instead of traditional speaker cloth. They should match the soon to be bookshelves.

      Click image for larger version

Name:	IMG_4004.jpg
Views:	123
Size:	352.0 KB
ID:	1494766​


      • #4
        After getting both boxes loaded with drivers and running a few wires, I wired up my XLS1500. I decided to keep it in bridged mode and present a nominal 8 0hm load to the amp. I was running it with the gain at about 230, so i figured I still had a fair amount of gain to play with. Well, I'm still running it at 230... These things sound CLEAN. And man do they rumble. My initial impression is that it outdoes the vented box in just about every way. I haven't run it full tilt yet, but I already feel concussed after watching a marvel flick with the fam this evening.

        After some initial break-in for the new sub (remember, one has been in service for a few years, the other was still new in box...) I pulled out the DATS to measure impedance peaks. I measure each box individually with about 20 feet of wire between the DATS and the box. I then compared it to my WinISD model. I had a few sets of specs for the driver and couldn't remember which ones were the most recent; my subscription lapsed for Parallels and they are holding my Windows partition hostage with all of my more recent speaker data. So I went ahead and re-measured my existing woofer last week when I was in the planning stages to compare it to what I thought was the most recent Peeless data. Here's what I found...

        WinISD model
        Click image for larger version

Name:	IMG_4006.jpg
Views:	167
Size:	423.2 KB
ID:	1494770 ​

        Measured IN BOX Data

        Click image for larger version

Name:	IMG_4007.jpg
Views:	122
Size:	335.4 KB
ID:	1494771​

        If I'm not speaking out of turn.... Wow. i mean... WOW> Hows that for accuracy!! Seriously, I'm blown away. BOTH boxes measured to within .3hz on the bottom peak, and 1 hz on the upper peak. It looks like I may have over-written the second file. Cuz... why not.. Doh.

        A few notes about the APR12..
        I'm pleasantly surprised by them. I think they are WELL worth the money. I picked them up at as B Stock due to some rusty washers, but I'd pay full price them. And I may yet be ordering another pair to raise the bar and get my full 1000 watts per sub. Like I said in an earlier post, the CSS passive radiators and Earthquake SLAPS M12's were the only two passives I could find that could handle the loud, deep, tuning that I was looking for with this driver. And I tried A TON of passives. The APR12's are super easy to work with, well built, and tuning is a cinch. QC appears to be very tight as well, considering how closely the two different boxes measured to each other. I couldn't believe how much weight you can hang on these - and they ship with ALL of the weights that you could need, so I didn't need to run around looking for washers of the right dimensions to cobble together some weight system. So A+ to CSS Audio. This things rock!

        A few notes about the STW350F..
        I'll so more about it later, but I am still enamored with this driver. It's gorgeous, built like a tank, and takes every bit of abuse I throw at it. And it wipes the floor with any other sub I've owned in everyday. SQ is superb. And adding the second one was, well, maybe overkilll. Yes, I said it. Seriously, I think I have shellshock. But adding the second one was necessary to fix the room issues I have. And boy did it fix it. Prodigous amounts of clean, impactful, powerful bass. I may be turning down the crown amp. Due perhaps to my eagerness, or maybe my haste, or maybe just old fashioned laziness, I didn't set up a separate amp for the second sub and just wired them in series with the amp bridged. At 8 ohms, it puts out 1050 watts, so each sub is only seeing up to 525 watts, vs the 1550 the single sub may or may not have seen a time or two... At these power levels, the three APR's should be plenty happy and not run in to any excursion issues. It would also allow for a touch of DSP, which has been the plan all along. But for now, this thing ROCKS!

        Also, comparing the in-box DATS sweeps of the old driver and new driver show me that they are also incredibly consistent. It also shows me that the old driver is quite robust (I already knew this, but this is just one more evidence); after a couple of years of daily use and weekend abuse, it hasn't varied much from the original TS specs - certainly not enough to change the box tuning.

        For now, I'm going to go enjoy these behemoths.