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The Half-sheet Heroes - Quick and dirty HT monitors

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  • The Half-sheet Heroes - Quick and dirty HT monitors

    Initial idea: Take some spare parts and bargain bin drivers to make an econowave style monitor for HT use... But paired down to a more off-the-cuff / seat-o-the-pants approach to keep the build easy and fun. This laid back approach will follow through most of the project.

    Tweeter: $8.50 MCM 1.35" titanium compression driver (53-1225). It included a horn, but was extremely thin and chintzy. I think the factory response graph shows for it. I had some p-audio PH-2510 horns which are nearly identical as those from the latest klipsch heresy (iv) mid, except no woofer cutout. Fortunately there was still a mold line for the cutout so easy enough to shave down with a flap wheel on an angle grinder.

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    Midbass: $19 MCM 12" 8ohm pro style woofer (55-2952).

    Crossover: I was able to get it down to 4 components. The tweeter just gets a 1.5uf cap to reign in the horn peak, and an 8ohm parallel resistor to drop the level down. I used the factory graph with the factory horn.. I know this is a fools errand, but I ran with it and it seemed to pay off. The woofer already had a nice natural rolloff due to the paper cone and the high sloping impedance. So it just got a baffle step circuit and nothing else (3.5mh, 8ohm)
    I took some PE buyout terminal cups that had xo boards attached; desoldered the original components and mounted the new in place. Fortunately I have some tiny drill bits so I could make new holes for different placement.

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    Cabinets: I'm cheap and lazy so just used some ACX plywood finished with water based poly; sprayed with my hvlp setup. But this is where the namesake comes in: A single half-sheet (4x4ft) of plywood was used to make both enclosures. Which would be easy for anyone to get home no matter what car you try to cram it in. In fact the way the cuts go one could even get away with purchasing two 2x4ft sheets (one for each) which you could probably manage get those home on a bicycle.

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    Enclosures ended up a little over 1 cu. ft. Acoustic suspension (sealed). Lined with some denim insulation batting. I decided to recess the horn and woofer a bit to not make them look like total garage built speakers. I free-hand routed the horn recess and used a simple self built circle jig for the woofer.
    Last edited by DrewsBrews; 09-04-2020, 11:17 PM.

  • #2
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    Bear in mind I did use the factory response graphs. I imagine the different horn cleans it up a bit and maybe boosts the bottom octave a bit too. Sealed box leads to an estimated 80hz f3 which integrates well to my 8" Dayton powered sub.

    I had them in place for a while with the TV. I then decided to switch them out for a week with my smaller music-oriented bookshelves to do a comparison, but the wife requested I put these big suckers back so she can hear her shows better! I guess that says something to the detail and dynamics!


    • #3
      They look nice.


      • #4
        They actually look great for a quick n dirty.
        Though, with the size and look, they would never be allowed int eh house around here...garage, yep.
        Good work


        • #5
          Thanks guys!
          The size is about as small as you can get for a 12" 2-way @ 13.25"w 18"h and 11.75"d. The econowave designs seem to start with a standard size pa cabinet.

          As far as look... yes I've had family over and see the "staring down the gun barrel" look on their face after they sit down on the couch. As can be seen on one pic, I made some grills that mute the visual impact down to black rectangles, much less intrusive. Though ive never left them on for long.. Mostly made them in case friends show up with their littluns. I have always admired the contemporary look of bare plywood.. Though, that may be more of a style for a dedicated listening space. Since they get thumbs up from the wife they may be there for a while. I have entertained the idea of veneering the sides and painting the front/back face black for a more classic look... Or possibly just a nice dark gel stain over the polyurethane instead?


          • #6
            Cool project.
            As far as the finish goes, they really do look pretty nice. You used decent plywood, I can only seem to find good stuff hit or miss.

            I remember a speaker design I saw as a youth in the red radio shack speaker building book. It had wood sides which were slightly larger than the top/front/back/bottom. They fancied up the sides and did a grill cloth wrap on the top/front/bottom, or at least part of the bottom. Your plywood is good enough to look nice with a little fine sanding and a finish put on it I think. Maybe something like that would work.

            Whatever you end up doing with it, it's impressive to have a 12" 2-way built with one 4x4 piece of 3/4. The fact that you can use 2x4 handi-panels opens it up to almost anyone on earth!

            I'm imagining they're leaning towards movie duty, but are they music-inclined as well?

            Zarbo Audio Projects Youtube Channel: * 320-641 Amp Review Youtube: *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
            *Part 2 *Gluing multiple curved laminations of HDF


            • #7
              Your radioshack speaker description reminds me of some of the klipsch tangents. (T10, T20.... up to T50 I think) Which do look pretty snazy! That is definitely an option to easily adapt... Just paint the whole speaker black and finish some extra side pieces to glue/screw on from the inside. That could help stiffen up the sides also since internal bracing was minimal. I could probably still use the grills I made too. hmm...

              Yes, an often overlooked part of the hobby is the logistics in getting big sheets of panel goods home undamaged. While I was designing this project I started to realize this could be a very accessible build, all around. The first cuts are just 11.75" wide rips down the 48" length. 2 per enclosure, hense single 4x4' or two 2x4' sheets. Then each is segmented into 3 panels. Same 3 lengths for all so could be cut in stacks. Cuts could be done with a circular saw with a decent blade and straight edge guide. Holes just require a jigsaw if not recessing the driver flanges. A drill to start the jigsaw cuts and for the screw holes. Router not absolutely required but nice to quickly clean up the edges with a flush trim bit. The crossover is about as easy as it gets... mentally split it to the 2 components per driver and it's pretty easy for anyone to understand. Low part count keeps cost down to about $10 per crossover. The only glitch being the horn. I picked them up for $3 each +shipping on clearance, which is no longer available. They are still out there for $30 each on average. but that is hardly the bargain bin price this project calls for. The Goldwood GM-600PB has similar dimensions and would give an even more retro look. But, it is much deeper so to maintain similar alignment might need to be mounted on an additional block of 3/4" ply and the woofer back mounted.. or something like that.

              It is surprisingly good for music. Very engaging and live. Takes about 10min to get used to your ears being force fed after switching out standard efficiency direct radiator speakers. Those horns reach out and touch ya, though the midbass play a big part too since crossed around 2k. Very revealing, you can plainly hear all the throat adjustments and lip smacking of the singer in recordings with a sensitive mic. Good for any vocals male or female as long as the recording is good, gives the effect of the mic cable plugged straight into the speakers. Almost larger than life. Those tweeters have some nice attack. Sometimes drums, symbols, and guitar plucks are so crisp they give me shivers (the good kind). I found myself playing Nils Lofgren live recording of "Keith Dont Go" over and over... louder and louder. They image, but it feels more artificial as if you are getting whatever the equipment at the recording studio was set to. Overall a very precise sound as if the speaker IS the amp the instrument is plugged into.. which can be addicting, but not necessarily quite as natural "just sitting in the room with the musicians as everyone plays" experience as more refined speakers. I cant fault it since that is what I was shooting for. I'm sure there are better, but ignorance is bliss for me at the moment.

              As they break in more the 100hz hole seems to be getting shallower. I recently did a freq sweep (sub off) and can hear it somewhat where there seemed to be about none before. Normally this would bug me, but I don't notice it so much anymore when listening. It seems to do well with good upright bass recordings except for the lowest notes (the sub picks up those). Maybe I don't notice a missed note with all the other instruments mixed in, or possibly the sub starts supplementing enough to get the job done.

              One other note Id like to point out is the TV in the photo is about as small as flatscreens get. A 40" I think. So that probably makes the speakers look even bigger since alot of folks have bigger screens to mentally compare to anymore.
              Last edited by DrewsBrews; 09-08-2020, 01:51 AM.


              • #8

                Are going to do anything about that big peak up near the upper end of the speaker's bandwidth?
                Brian Steele


                • #9
                  Due to the changes I've made that would stray from the graphs used.. I should pick up a mic and do some testing before continuing any further down the rabbit hole. I realize posting up real test graphs would probably get more interest here anyway since you can't hear what Im hearing to get a taste.

                  I can't hear above ~15.7k and my wife even lower so it isn't something we notice if it even really is there.


                  • #10
                    How would this work in a larger, ported enclosure ?
                    I know the initial design was to stay small. But, would a larger, ported enclosure push the Fs lower without any crossover mods needed ?

                    I'd love to build something like this, but I'd want it to play lower.


                    • #11
                      Absolutely! I have been kicking around the idea of trying a double-height version with rear port. Dimensions remaining the same except ~37" tall so would just use a full sheet of ply/mdf for the pair instead of half sheet. F3 calculates around high 40s- low 50s, but the rear port should help out in-room depending on placement.

                      Also I looked into the 4ohm woofers they offer of the same design. Crossover values change obviously due to impedance change but could get a slight boost in sensitivity if the amp can handle 4ohm.

                      However I already have another project on the bench so that needs to be done before more sawdust is made.
                      Last edited by DrewsBrews; 09-10-2020, 03:08 PM.


                      • #12
                        Do you have any simulation graphs of the larger cabinet ?

                        I was thinking about even using a different, rather inexpensive 12" driver - maybe something like the Dayton PA-310.


                        • #13
                          The graph would show little change. just a little bit of extension off to the left.

                          The pa-310 driver would require completely different (more complex) crossover.

                          The drivers are the foundation of a speaker design. You can change other things if it suits the drivers but the majority of the time the other way around doesn't work out unless the replacement has a very similar response, or you make appropriate adjustments...Which often ends up being a total redesign.

                          Good speaker design is so much more than just putting a couple drivers together in a box. There is alot of time put into finding which drivers work well together. I shelved countless potential combinations because they just required a much more complex (expensive) crossover than the end result was worth. The only way you find that out is by getting the graphs in the tools and putting in the work. Eventually you get a feel for it and can make guesstimations just by looking at the graphs.. Something you get better at with experience. The only reason I went forward with this project was they seemed to fit together so elegantly with the bare minimum electrical component count. Certainly not a perfect design, most would say 2khz crossover point for a 12" is too high for hifi. I was indeed taking a bit of a gamble with some things so I wasn't willing to spend alot of time on the build. But I am impressed enough that they will probably stay as the everyday tv/movie speakers.
                          Last edited by DrewsBrews; 09-10-2020, 10:06 PM.


                          • #14
                            Understood. Thanks

                            I'm still trying to find something more "full range" that is a simple, inexpensive build like this tho.


                            • #15
                              Originally posted by Serenitynow View Post
                              I'm still trying to find something more "full range" that is a simple, inexpensive build like this tho.
                              I think that is something alot of us are looking for. It's taken me a few years of searching to come up with this design.

                              I did run these without subwoofer for a several months due to living in a multi-level apartment style condo and trying to be courteous the the neighbors. I knew I was missing out on some, but there were moments when I couldn't believe the low notes it was hitting. Room gain can help out quite a bit. Another 30+hz of extension from the larger ported cabinet would be pretty dang satisfying to me.

                              Figuring everything up in my head.. total part and material cost for this project, excluding any shipping/tax, came in around the same as a pair of pa-310s. Another option: The c-note kit is probably one of the best bang for the buck options out there for inexpensive diy.
                              Last edited by DrewsBrews; 09-11-2020, 01:36 PM.