Returning to Hapy Sounds - Part 1

In the midst of the Summer 2019, I added the ability to listen to music to Hapy, the 1972 TDI-powered microbus (See Making Hapy Sounds Part 2, for example). Today, I start my revisit with the front speakers. In this part of the front speaker improvement, I create very very small speaker boxes for a pair of 5-1/4" speakers with materials readily available at the hardware store; remove the speakers from the door cards and mount them into those speaker boxes; and last, get it all into the bus. Unlike most of my posts, the overwhelming majority of the measurements are in inches rather than mm. This is because here in the US, all of the published material about speakers is in inches. So, any information I put here can be more easily cross-referenced.

Why?

Diablo Royale pod

I guess it makes sense to start with answering the question "why are you making a change". There are a couple of reasons. First, the door cards that I made out of pressed cardboard are starting to fail. Unlike the original cards, the material I used was not designed for this purpose. So, over time, as some moisture appeared (this is the Pacific NorthWest, after all), the cards started to bend, and pull away from the doors. With the 5-1/2" speakers mounted in the lower part of the card, the card condition deteriorated more quickly as the speaker added a swing-weight whenever the door was opened or closed. So, when the door was closed, the bottom of the card (and the speaker) were not mated to the door, allowing the speaker to kind of hang in space a little bit.

I decided to replace the pressed cardboard cards with a laser-cut PVC set from WerksBerg. These precision-cut PVC cards are great, and many options are available, but a pre-cut hole for speakers is not one of them. I decided that I didn't really want to cut the PVC. This leads to our second reason: while the sound was okay, it wasn't awesome and maybe it could be better while driving. The only real upside to the speakers being in the doors was the added sound we got in the music festival camping lot when we opened the passenger door. When driving around, there was music, but it lacked some clarity. Of course, the road, engine and wind noise contributed, but that's another whole story... and solution path for another day. I think speakers just hanging in space (back not enclosed) negatively impacted the quality of the sound, and the cards were not going to last much longer.

Options

schedule 40 4" cap

So, if the speakers are not going to be in the door, what other options are there? There are a few. Some folks cut holes in the toe kick. This brings the advantage of having speakers facing you, but they are still down by your feet. Some bus owners replace the little fresh air vents with little speakers. This option moves the sound closer to your ears, which is great, but you lose those vents, and the only speakers that fit in there are super small (like 2" tweeters).

If you have a parcel shelf under the dash, you can set/mount speakers in boxes placed on the shelf. The shelf narrows on the outer edges, so speakers most likely fit best near the center of the bus, near the central air pipe. I don't have those shelves, but even near the center they do not look terribly deep. When I first bought Hapy, a prior owner (PO) had mounted small boxed speakers to the big metal air vent boxes. They didn't work, and the PO had taken the stereo with him so I pitched those speakers. Of these options, I do prefer rear-facing / under-the-dash locations over the door cards. The trick will be figuring out how to mount them, and exactly where they will provide sound best.

5-1/4" Thinking

test fitting 5-1/4 speaker

So, we start with figuring out a way to mount / hang speakers under the dash such that they won't get damaged yet they fling sound towards us. The 5-1/4" round speakers I have are kinda large for the space. Sure, 6-1/2" round speakers are bigger, and more common, so finding a speaker box or pod that fits the 6.5 is definitely easier. Still, I have the 5-1/4's and the smaller footprint will play to my advantage now, since the new location will be inside the cab, potentially near our knees.

Ever seeking cheap, yet effective, solutions, I constructed one. But, of course, not without checking out off-the-shelf options:

• There is a guy (Diablo Royale) on eBay who makes plastic speaker pods in Texas. I bought a pair of his mounting pods for Oliver so I could mount the front speakers down by our feet, against the outer walls (See MGB Interior Panels - Part 1 or better yet MGB Gets Sound - Part 1). Diablo Royale had pods that fit 5-1/4" speakers, but they were still open-backed, $50US per pair and at least 6 inches across at the top by 4 inches deep. The base was at least 7 inches across. Looking at the under-dash, that would have been pretty ugly. Without a flush backwall, which would be nearly impossible with the contours up there, the sound would not throw as well. To make them fully enclosed / flush, I would have to construct a rear side.
• There are MDF speaker boxes, wrapped in trunk carpet. These are also larger, but at least they have a back. The smallest ones I saw for the 5-1/4" round speaker were 8 inches square (or larger as rectangles) and 5 inches deep. If I had a parcel shelf, they might fit, but really only in the center since those parcel shelves get shallow as these near the door A-pillar.

better view of a
metal bracket attempt

Those are basically your off-the-shelf options. For the space we are targeting, they are not terribly good. So, we get out of the (speaker) box, and see what we can come up with. Our requirements are few: the speaker requires a 4-1/2" hole to sit into -and- it needs just under 2 inches (1-13/16 inches) from the mounting surface to the rear of the "box" for the cone and magnet.

It turns out that a 4" schedule 40 PVC pipe cap is a great starting point for a speaker pod. The one I found is 2 inches deep from lip to rear wall, but I saw deeper ones on the 'net. The inner diameter is 4-1/2 inches. I know; you're asking "but you said 4 inch cap". Yes, that's right. The schedule 40 4" cap refers to the industry standard 4" pipe, which is an approximation of the inner diameter of the pipe. Since the cap goes around the outside of that pipe, there is additional diameter to account for the thickness of a schedule 40 PVC pipe (here's a link for more dimensions). Neat, eh? Oh, and these are about 1/2 the price of the Diablo Royale pods at less than $15US each, made-in-USA, they are available at your local hardware store -and- they have a back wall.

5-1/4" Speaker to Cap

Once in hand, we need to figure out how to mount the speaker to it, and then how to mount the unit into the bus. I started with the second question first by moving the speakers around while playing the stereo. I concluded that the farther to the outside I could put the speaker, the better the overall sound. I resolved with placement directly below the dash vents. To mount, I bore a pair of holes through the cap, and mounted the cap/pod to the metal vent cover. Since the vent cover could be removed and replaced, I could use bolt/nut /washer fasteners instead of self-tapping or sheet metal screws. I think the nut-bolt combination creates a better, more reliable attachment.

plastic mounting tabs

For mounting the speaker to the cap/pod, I started with the smallest angle brackets I could find at the local Ace hardware store (3/4") when I got the caps. I also tried 1/2" brackets but they were no better. I probably could have super-glued something plastic, but that seemed flimsy. After a lot of drilling, cutting measuring and more cutting, I abandoned the 3/4" angles. I tried 1/2" angles, but they did not line up right with the speaker cover holes. I bought a set of angles online that had a channel, but even the smallest set like these were too large. I even tried constructing mounts with some scrap wood (1/2" wide and thick by 3/4" tall), but they were too bulky.

 

So, how did I resolve it? In true ghetto style, of course. While cleaning up my garage, I found a lid for one of those larger rectangular plastic storage tubs. The lip bent around 90* and extended about 3/4". With tin snips, I cut a series of pieces out, each about 1/2" wide and at least 1/2" into the top of the lid. This produced 8 little plastic "L" shapes to construct mounts out of. I marked and drilled holes, and then cut away the excess material with the snips. They are barely visible now, and once I wrap the pods with trunk carpet of some other fabric, they will mostly disappear.

 

5-1/4" Pod Wiring

With the physical mounting solved, I turned to wire routing. Ideally, I would have included a wiring cup. I omitted it because the flat bottom of the cap/pod will be pressed against the bus for mounting. Then, I thought about putting a cup on the side. I figured between the curvature and the shallow space within, it simply wouldn't work. So, instead, I drilled a small hole in the side of the cap/pod, and sent the pair of speaker wires through it. Leaving some slack in the wires within the cap/pod, I applied a blob of caulk into the hole to seal it back up.

Polyfill?

polyfill'd

My last step was adding some polyfill into the cap/pod. Simply, polyfill interrupts the sound wave moving on the back-side of the speaker when sound is produced by the cone. This interruption improves the projected sound out of the front of the speaker, and tricks the speaker into acting like it is in a larger enclosure: so, more bass. Using polyfill (or not) is kind of a religion with audio folks. I figure speaker enclosure manufacturers wouldn't use it if it didn't do something beneficial, and the 6x9 boxes I got for Hapy's rear speakers were polyfill'd. This cap/pod thing is super small for this speaker, so if it was going to do anything for a small speaker, this is the kind of scenario where it might. Still, the probability that I would really notice is virtually 0 (especially in the while-driving din), but I did it anyway. Ultimately, this cap/pod is about creating a safe means of mounting the speaker, with a hope that the sound is improved through it's proximity to the listener. The sound could not be measurably worse by moving it a foot closer in an enclosed cap/pod -versus- hanging in a loose, flapping door card down by your feet. Quite the opposite, I think it is much better. At least, it is set up to be.

isolation foam

When I get around to making the interior nicer with carpet and other fabrics, I will cover the cap/pods with whatever material I am otherwise using along that front wall so they visually disappear. Or, I'll simply cover them with trunk carpet. Before final assembly, I put some closed cell foam between the speaker cap/pod and the vent cover I mounted it to. This should help isolate the sound / vibrations a little bit. You can see the foam in the picture on the right as well as the markings I made to get the speaker aligned for drilling the mounting holes. Last, I simply plugged the wires into the speakers, set the speaker into the cap/pod, set the grill atop and attached it to the brackets. I took the assembly out to the bus and simply re-attached the vent covers with the speakers attached. The wires dangling from the cup/pods were tied into the existing front speaker wires that used to be in the doors, and then tucked away. I may apply a wire wrap to disguise them a little better, but I think they look good enough for now.

Testing

wired up and fired up

Because of my lack of a warm workspace where the bus fits, and a young puppy who can't be out in the cold for more than 15 minutes at a time, I still have not completed the install of the replacement seats. So, testing consisted of playing the stereo without moving the bus. Still, I think moving the 5-1/4" speakers made a difference. Considering that our legs no longer interrupt the sound waves, the speakers are about a foot closer to our ears, and the speakers are contained, there should be some benefit. Ultimately, I probably didn't need to move the 5-1/4's for sound improvement. It is absolutely possible that the open space behind the speaker in the door cavity actually helps the lower frequency sound form better. But, I didn't want to cut the new cards and this was kinda fun, and this was something I could mostly do in a warm garage, with a puppy underfoot.

That's it for today. thanks, as always, for following along-