MasterBath Build: What happens when Flint repurposes blown JBL speakers

[Flint]

Several months ago I had proudly found a use for an old pair of JBL full-range speakers which had nice plastic enclosures and excellent wall mount brackets I always wanted to take advantage of. I've been carrying these things around with me from home to home since I shut down my recording studio where these served as a simple reference to low end speakers like boomboxes and clock radios. They had a decent sound for their size and where weather resistant, and they were small, like a 3-1/2" cone small.

I had mounted them in my master bathroom where I have an Echo Dot which gets lots of use playing music, news/weather, and the audio from my phone or tablet via Bluetooth. I used a small Dayton Audio Class-D amp I had laying around to drive them. Overall it worked well and I got used to the true stereo imaging and higher, clearly SPLs than I had experienced earlier.

Well, one day the left speaker was making a strange noise when no sound should have been playing at all. It was like rubbing or rustling fabric and by the time I moved over to investigate the reason for this odd sound it snapped into a straight up very loud whistling which then suddenly stopped - I knew what that meant. When a small speaker bursts into a loud noise then suddenly goes completely silent it can only mean one thing - it was blown. Also, the amp was too hot to touch - so I quickly unplugged it.

With a blown speaker and my desire to at least maintain the stereo sound in my bathroom, I started considering options to mount new speakers where the now useless ones were previously installed. I had run wire to those locations and I liked how it sounded in the room. However, I wasn't excited about any of the mounting options I could think of or find and really wanted to replace the blown speaker with an identical model. After searching more weeks for either another set of these speakers OR a replacement driver with no luck, it dawned on me I could just use the old enclosures and mount a new, probably better, small full-range drive in and than hang them just as they were before but with a better speaker and, intuitively, better sound.

I disassembled the blown speaker and found I could repurpose the enclosure and input cup, but the front baffle would have to be replaced to accommodate any speaker which wasn't exactly the same diameter as the original. So I measured the box and calculated the internal volume. With that data, I researched every raw driver supplier I could find and modeled every small full-range driver which seemed like it would work until I narrowed it down to two that seemed like good choices. One was a small 3.5" Peerless driver and the other was a slightly smaller 3" Tang Bang speaker - both of which were readily available from Parts Express.

After reading the reviews, looking at other people's projects with these drivers, and modelling peak output and even dispersion patterns, I decided to go with the Tang Bang 3" driver.

I also needed an amplifier to replace the now blown Dayton Audio amp. I assumed I'd just pick up another similar amp from Parts Express when I discovered a sale on a new 2.1 stand along Class-D amp with a crossover and subwoofer output. The literature bragged that it could generate 50 watts into 4 ohms for each of the stereo outputs and 100 watts into 4 ohms for the subwoofer output. It also had more than one input including Bluetooth, and was small enough to fit the location where I placed the previous amp. Also, at the time, with the sale it was the same price as the current version of the amp I had blown, so I went that route. Order placed, but only for the amplifier. I wanted to second guess my speaker selection some more now that I might add a subwoofer.

Suddenly new vistas opened up and I decided those tiny little full-range speakers needed a subwoofer. So, more research, talking myself down from insane options (like an infinite baffle sub - imagine that), and so on. Ultimately I landed on a very decent 10" subwoofer driver from Dayton Audio, the High Fidelity version of their Reference Series products.

When I modeled the performance and realizing I needed it to operate into the 125 - 175Hz range (yes, making it a bass bin, of sorts), this driver would work nice in a basic sealed box which could easily fit almost invisibly into the leg space in my wide countertop which I believe was intended as a vanity with a chair in that spot.

So, we are off to the races - a plan, drivers on their way, and the intent to do this as properly as I could.

 

[PaulyT]

my desire to at least maintain the stereo sound in my bathroom

Sometimes perhaps this little obsession can go too far?

 

[Flint]

Between coats and sanding sessions on my Line Array speakers' subwoofer boxes, I did small projects for the new bathroom speakers.

Here's the original JBL speaker after I pulled off the grill:



First up was removing the electronics from the input cups on the JBL speakers, a simple de-soldering job. Then I decided I would make the plastic boxes less likely to ring and vibrate by deadening them somehow. After much thought, I chose to use Plastidip spray on rubber coating on both the outside and the inside of the enclosure. Since the boxes were a slightly faded white to start with, I used a can of white on the outside and about half a can of gray on the inside and coated the plastic after taping off the areas I needed to remain clean for mounting or the baffle:







Once the rubber coating was fully dry, I could note the added weight and even how dead the sides were when I tapped on them. This was a smooth move. My only concern is that it will peel off or scratch off too easily when handling them. Hopefully I can assemble the speakers and mount them without the rubber coming off.

 

[Flint]

The next step was to make new front baffles to mount the small drivers in. Since the old plastic baffles were easily removed with four screws making a method to mount a new baffle in their place, I just carefully measured the original front plates and replicated the mounting shape with MDF using my table saw. It was far easier than I anticipated. The new MDF baffles fit snuggly into the boxes and will be held in place with ample glue/caulk and four bolts.

Here's the basic baffles after shaping.


Since they are small, I hung them on wire from coat hangers to coat with ample amounts of Shellac which will seal the wood so I can paint with a color later. My instinct is to go with white, but I may decide to add some color to my bathroom.


Here's the driver resting in the baffle.

 

[Huey]

Great Dane would be so proud! lol To each their own, I guess. Enjoy the new bathroom rig!

 

[Flint]

Finished sealing the MDF with shellac and sanding several time. Now I am putting about three light coats of spray on gloss white enamel on to get a smooth finish. I may stick with the white, or I may choose a nice color for my bathroom on the top coat. Not sure.

Any opinions? Should I go with white finish on the front baffles, or color? Note that the speaker is black framed with an off-white banana fiber cone and a silver metal on the phase plug in the middle. I was going to use silver bolts to mount the baffles, so expect four silver metal bolt heads to be showing at the corners. I was thinking a light sky blue or sea blue gloss finish.

 

[Wardsweb]

A true audio enthusiast. DIY takes the hobby in a new direction and new heights. Most of all, having fun. If you're into audio and not having fun, you need to find a new hobby.

 

[Flint]

Well, with your lack of suggestions I decided to go with a light blue with a tinge of green which happens to match the clock I have on the wall in my bathroom. After painting, drying, and cleaning up the baffles, I assembled the speakers:

I had some sheets of thin closed cell foam laying around from a different project, so I cut rings for gaskets.


Here's the assembly process. I also put a very thin bead of pliable silicon caulk along the inside edge of the baffle/box edge.


Here they are completed.


And installed:



I measured them using my test gear and I'll post the frequency response chart later. I was very pleasantly surprised by the sound and the measurements. For the money, I highly recommend these drivers for any application like this where high SPLs are not necessary, or when adding a subwoofer.

 

[Deleted member 133]

That room could use some acoustic treatments!

 

[Flint]

That room could use some acoustic treatments!

Can you imagine that?!?!

Talk about a mold trap! How would one do that? I guess a styrene plastic diffuser would work, but all the decent absorbers I know would hold humidity.

 

[Deleted member 133]

Faux-velour shower curtain? For sound absorption.

300 wood handled sponge loofah back scrubbers hung very tightly together? For sound diffusion.

A clothesline full of Euro-cut Speedos? For...

 

[Flint]

I finally got around to testing the amplifier I had been using, thinking the speaker shorting out may have blown the amplifier. It appeared to power on just fine with no indications there were any issues. I put a multimeter set to AC Voltage across the outputs and measured negligible voltage from the jacks. I switched the multimeter to read DC Voltage and discovered the channel the blown speaker was attached to was feeding a solid 24V DC out the banana jacks. Well, that'll do it. Since the JBL speakers were well made and healthy prior to this, I fear the amp failed and caused the speaker voicecoil to fail and short out.

Then I remembered the history of this amplifier. It is the Dayton Audio DTA-100a Class-T amp I picked up years ago. When I originally received it I could not get it to work at all and it would not come out of protection mode. So, I arranged a warranty replacement, but they wanted to test the amp before sending me a replacement. I sent the amp back and the tech at Parts Express interacted with my via many emails repeatedly telling me the amp was functioning perfectly. He even stated that he played a set of speakers in the repair facility for an entire day using the amp and had no issues. So, replacement cancelled they sent the amp back to me where it sat on a shelf for over a year as I had already started using a higher quality amp where I had intended to use this one.

Fast forward to a few months ago and I had totally forgotten about the issues I had with the amp initially and when I hooked it up everything seemed to work perfectly. However, for about a week before it obviously failed I was noticing the sound being more distorted than I remembered and kept telling myself I should look into it. Since the speakers has a protection circuit to reduce overvoltage failures, it is entirely possible the amp was putting out the 24VDC the entire time as long as it also feed an AC audio signal on the same channel. The blown speaker may have been absorbing the 24V, mostly as light, but still putting many volts into the voicecoil as DC until it finally overheated.

I was thinking about contacting Parts Express to explain the situation, but I doubt they will do anything about it.

 

[mcad64]

It looks like it was a magical build out from blown speakers!!!! Wait...that sounds like a song!!!

PS: I like the blue colour!!

 

[Deleted member 133]

I'm more than a bit of a packrat and tend to keep a ton of old audio, computer, etc. gear and parts. I don't always, but when I pull something from service and put it into storage, I try to "tag" it and indicate any known issues at the time. And in some cases the final line on the tag reads "Use For Parts Only."

Your amp's service issues remind me of what I'm going through with a NAD amp. One channel had been cutting out from time-to-time and I put it in storage. Ten years later I wanted to use it again - but when I saw its tag I knew it was not worth the risk - in case it developed more than just a wonky channel. So I had a full service done on it, brought it home, hooked it up and ... the moment I turned on the power and the protection relays closed there was a loud pop/bang sound and it went dead. The amp went back to the shop and is apparently badly fried. They are having problems getting parts. Which reminds me that it's been several weeks and I should call. I've also been too scared to hook another amp up to the speakers to check if they were damaged or not.

Jeff

 

[Wardsweb]

I've also been too scared to hook another amp up to the speakers to check if they were damaged or not.
Jeff

Take an ohm meter and see if it reads several ohms, is short or open. You can also push in on the cone. Hands on either side of the dust cape, push evenly and slowly. The cone should move in and out smoothly. If it feels scratchy, the voice coil has over heated and is rubbing against the magnet structure.

 

[Deleted member 133]

Take an ohm meter and see if it reads several ohms, is short or open. You can also push in on the cone. Hands on either side of the dust cape, push evenly and slowly. The cone should move in and out smoothly. If it feels scratchy, the voice coil has over heated and is rubbing against the magnet structure.

I ran a speaker cable to another amp in my racks and confirmed that the speakers are ok.

Whew!

Jeff

 

[Flint]

I gotta say, after living with these speakers for a few days and listening to the radio, music, and even taking a few phone calls with them as speakerphone speakers, they sound amazingly natural and clean. They don't have any real bass output, but they are very natural sounding down to at least 150Hz. When I get the subwoofer built and installed (likely to be within a week, or so), the system will be very nice sounding.

I recommend these full-range drivers to anyone looking to make a small rig - especially if you are going to add some sort of bass speaker to fill out the bottom end. Like a two way speaker with a 4 inch woofer and a crossover at 200Hz to 500Hz.

 

[Flint]

It is subwoofer building time!

Today I picked-up a sheet of 3/4 inch MDF and cut all the panels and braces for the subwoofer going into my bathroom. It is going to be a sealed enclosure, so the accuracy of the sizes isn't as critical. What does matter is that there are no air leaks at all.

Here's the sides, top, and bottom with the braces dry-fitted together before gluing:


The front woofer baffle is double thick so once the glue holding two sheets together dried, I routed out the woofer hold with a recess to counter sink the woofer and a smaller hole which will become the input cup:


I glued up the sides and braces tonight, so tomorrow I can finish assembling before rounding over the edges with a router and starting the finish.

 

[bmwuk]

Subwoofer for the bathroom? Hope it doesn't sound crappy...

 

[Flint]

Subwoofer for the bathroom? Hope it doesn't sound crappy...

God that was bad... I hope you are proud of yourself, cuz I'm not.