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Author Topic: Victorian Boombox Mk. II brainstorming  (Read 3199 times)
J. Wilhelm
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« Reply #25 on: April 12, 2019, 09:32:09 am »

Disaster.

I just made a $22 mistake.

I happily went to the hardware shop to buy the Burgundy colour spray to finish the sconce bases, and tonight I proceeded to give the bases a new coat of paint. It was all perfect when I noticed something funny happening on the surface of the drying paint.

It started cracking. As the paint dried it started cracking and peeling like if I had sprayed a layer of paint remover. I tried to remove the paint with a rag before it dried, but to no avail, the surface was already the consistency of hard rubber, smeared cracked and half peeled across black and red layers of paint. Obviously the paint was already too thick as well, but the solvent of the new paint was the culprit.

When layering paint, boys and girls, always make sure that the solvent in all the layers is the same. If the top coat has a much stronger solvent (Rustoleum) it will soften, crack and peel the underlying surfaces (Krylon, and god knows what solvent was used for the factory finish).

Now the sconce bases are a mess. The finish is completely destroyed. I don't feel like buying paint stripper and stripping or sanding all the paint. I might as well throw away the sconces and buy a new pair. I could substitute the sconce bases for wood plates, but the point of the prototype is to demonstrate the most quick and efficient way of building this over and over again. I'm not making a one-off.

I'm so angry at myself for overlooking that important detail.

I probably won't have time to work on this project this next week. I have to do my tax report this weekend and in the middle of next week I will be shutting down the shop where I work and move to another one of our shops. Luckily I didn't lose my job, but this is the third time in as many years that I have to close a shop and move.
« Last Edit: April 12, 2019, 09:42:54 am by J. Wilhelm » Logged

J. Wilhelm
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« Reply #26 on: April 15, 2019, 03:24:52 am »

Ch ch ch changes.... Ch ch chanaanges.... To quote the late David Bowie.

After my tantrum (no, not really), and after doing my tax work, I got a little time on Friday and Saturday, and I found a new pair of sconces. I moved away from the type that I found before. Being a little more clear headed, after the taxes, I realized that insisting on the first pair of sconces I showed was creating problems for me, and I wasn't following my own advice on simplifying the build.

To begin with, I should not be painting the sconces at all. I didn't in the first generation Boombox. Also the Mk I box had issues regarding the strength of the sconces. When walking in public during meetings or SXSW, the neck of the sconces would bend if I hit something or someone hard enough. The shorter the arm of the sconce, the better.

So I got these short sconces, round base, and no necks. They're very round, and made from thicker metal plate. Finished in flat black they already have gold pinstriping. Not as sexy as the black and gold pipes from before, but I eliminate any structural issues, and I promise not to paint them.

And noting that the PVC enclosures are substantially heavier than the satellite speakers of the Mk I, it makes more sense.

Changed to this lamp base instead



The horns now look a bit more natural, and I'm trying to decide whether to give them a wooden plate or base of some kind to make them removable and they can stand on their own like the computer sound system they comprise.

The shades still need to be attached somehow, but the PVC enclosure is rigidly held by a threaded lamp pipe, and I'm figuring out whether to just wire the cables directly, or add an RCA phono jack to the back of the speaker, right inside the lamp threaded pipe. Easier said than done, but it's worth it. I just worry about being able to get the "stand alone" RCA jacks in the future.

The lamp shades and speakers. Note the threaded lamp rod through the back of the lamp holder.









I think I'm liking a little bit of white with the red and black. At the risk of adding too many colours I wonder if that would be workable...
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« Reply #27 on: April 15, 2019, 09:15:31 pm »

Then later this Saturday I came back after work and found a little time to paint a new set of wooden plates. I couldn't get the same shape as before, so I chose the simplest shape I could find. Being able to find parts over and over is very important, and I'd you can't find them, you should be able to make them on your own. So a plain rectangular shape is better.

The new plates are simpler and darker with a semi satin finish done by over-spraying the piece, just to erase the wood grain.



I think that the darker Burgundy colour is a much better match. I can't believe how much difference a simple shade of colour has on the final look. I think it's also better to erase the gloss or shine of the paint. Matte finish looks good because the colour is already very dark.

So I just present below the plates on the subwoofer cabinet and place the satellite speakers on the sides. The Boombox will have a very compact "vertical" look because the lamps have no necks. All is good, I think, because it will give the piece an odd geometry more akin to another era.

I also purchased a brassy handle that I though felt very comfortable in the hand. It is rather long, so it can only fit transversely over the subwoofer cabinet.

This presentation gives you an idea of what the final piece will look like









It may look like I may be close to getting to the end, but looks are deceiving. None of the Bluetooth wiring has been done. The lamp shades are attached to nothing as of yet, and there is no bezel for the satellite speakers. Additionally I'd like to explore making the bases detachable and with feet or a base to allow them to angle a bit upwards as satellite speakers.

And let's not mention the top console that has the on/off button and the headphones jack. In that sense this Boombox is remarkably similar to the Mk. I build., but there is no room at the top for the little console. I may just place it in the back or maybe over the small red plate in front below the subwoofer port... I don't know yet...
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« Reply #28 on: April 16, 2019, 01:46:51 am »

Those lampshade/sconces are really going to have the satellite speakers in them, right?
That's been my assumption, they are speaker cones ala phonograph.

I like the idea of the steel handle on top, but it looks modern industrial.  Is there a cabinet handle in the black/bronze style at the hardware store that might match the sconces more (in my imagination of a recent visit to Lowes there is).


For the bit of what PVC between the lamp shade and sconce, consider painting it black.  I think that would blend it in as part of the sconce before the cone starts.

Assuming I'm right and those are going to be speakers, I'd fasten them to the side (really good glue?), but consider setting them high (perhaps on level with the main body's cone).  That might yield and attractive, unusual silhouette. 

On looking at the side view, I feel the black box body is at a crossroads.  You could stop there and have this neo-victorian post-fancy-artstyle device, or add more victorian to it.  Much like the routered edges of the plaques, the box itself needs edge or corner dressing.  I've seen Michaels  carry these corner plates (like you'd find on an antique suitecase or jewelry box).  That or some fancy filligree line work around the edges (perhaps in the red or white).

That's just some thoughts that came to my mind.  What I'd do next if it was my project.  I look forward to seeing what you come up with.

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« Reply #29 on: April 16, 2019, 09:35:43 am »

Those lampshade/sconces are really going to have the satellite speakers in them, right?
That's been my assumption, they are speaker cones ala phonograph.

I like the idea of the steel handle on top, but it looks modern industrial.  Is there a cabinet handle in the black/bronze style at the hardware store that might match the sconces more (in my imagination of a recent visit to Lowes there is).


For the bit of what PVC between the lamp shade and sconce, consider painting it black.  I think that would blend it in as part of the sconce before the cone starts.

Assuming I'm right and those are going to be speakers, I'd fasten them to the side (really good glue?), but consider setting them high (perhaps on level with the main body's cone).  That might yield and attractive, unusual silhouette.  

On looking at the side view, I feel the black box body is at a crossroads.  You could stop there and have this neo-victorian post-fancy-artstyle device, or add more victorian to it.  Much like the routered edges of the plaques, the box itself needs edge or corner dressing.  I've seen Michaels  carry these corner plates (like you'd find on an antique suitecase or jewelry box).  That or some fancy filligree line work around the edges (perhaps in the red or white).

That's just some thoughts that came to my mind.  What I'd do next if it was my project.  I look forward to seeing what you come up with.



Yes See my last post in the previous page of this thread. The lamp shades house an airtight PVC pipe enclosure which serves as speaker cabinet, and will hold a small 2-inch mid-range driver (see pictures in the last page above your first post). The shades themselves are just cosmetic, though. They are acoustically transparent because they're made of cloth.

The sconces will be bolted to the centre of the sides of the  subwoofer, but tilted upward by about 45 degrees, as I did with the first Victorian Boombox (look down the list of threads in Tactile. There is a thread dedicated to the original Victorian Boombox - it's not too far down the list because I updated it not too long ago.).

There is special hardware that comes with the sconce kit. A flat plate is strongly attached with screws to the centre of each side of the subwoofer (wood screws) . Machine screws the protrude from the metal plate in the opposite direction which go through two holes in the metal sconce base, and you have knurled brass knobs to fasten the sconce base, to let you detach  and re attach the sconces at will.

The reason for this arrangement is to avoid damage during shipping. The second reason possibly could be for the sconces to function as normal satellite speakers do, that is, placed far away from each other. However having detachable satellite horns, requires that I add or attach a wooden plate to the sconce base, so the sconce doesn't tilt forward under its own weight; the PVC speaker enclosures are very heavy, and the little speaker is all the way to the front (see pictures in the previous page).

The handle will be a bit hard to get from regular big box hardware shops. The one you see in the picture is antique brass finish over aluminium from Home Depot (I don't know if that shows well in the picture - I took the picture in the morning and the natural light was very blue, so you may see it as white steel, it's actually dark golden). The one I used in the first Victorian Boombox was actual black wrought iron, hand made and all bumpy, rust and all, but I found it  by serendipity at Hobby Lobby about 8 years ago and they don't carry anything that big any longer (see that other Victorian Boombox thread for pics) .

The handle must be big and comfortable to allow you to carry the Boombox which is relatively heavy once assembled (this one is much smaller, but the original weighed 32 lbs), but most cabinet handles are small and uncomfortable, they don't fit a whole human hand.

The other constraint is that once I move out of the US, I will need to either mail order the handles or find a replacement made in Mexico (I need to make the same unit over and over again - this is a model for sale, not a one-off like the original). Actually it will be much easier to get a wrought iron handle in Mexico and I'm  betting I will find some small shop to make them for me. But for the moment though, I have to use a handle as large as I can find at Home Depot and either in a gold tone or black (Home Depot is widely present in Mexico as well) .

I'm ambivalent on the corners of the subwoofer as you say. But something is telling me to leave the black edges alone. I feel that there will be something akin to rivets on the wood, even if it's only one rivet per corner. . I still have to bolt the wood plates and decorated the routed edges. I need to see what it looks like before committing to another embellishment. When I started the project, I was thinking of those laser cut panels you wrote about instead of the plates, but I decided to wait on that and get the basic stuff done. I think I'd like the box edge proper be more industrial.

The white PVC needs to be painted black, as you wrote, though for some reason I like the red black combination with white highlights... I don't know why exactly . It's definitely a Non Victorian color scheme. I'd say more natural in 1960's "Mod" Britain. But I have a clue in the back of my mind:

When I was a little kid I used to build speakers out of tin cans and then I'd spray them red black and white. And when I was in high school and later in my first year of college, I used to build analogue surround sound processors out of Radio Shack parts (Dolby 3 channel type /1970s Quadraphonic 4 channel type - really simple to build). And I was smart enough to research contemporary progress on something called  "Binaural Sound" which is the basis of many 3D surround sound schemes used in the audio and video game industry today (though the math, Laplace transforms, eluded me at the time, a couple of years would pass before I was mathematically savvy to understand the theory).

But back in my first year, I knew everything about Op-Amps and I'd buy small breadboard and LM 1458 chip. Radio Shack used to sell these really neat black remote-control shaped boxes with space for a 9V battery and breadboard. The little box was meant to connect to a second amplifier in your house, taking input from the front amplifier, and the surround output to drive the rear speakers of your home sound system. And guess what colour scheme I used to paint the enclosures? Black and red with a white pinstripe. I'd print a British Underground logo which read "Underground Sound" and I'd sell the boxes to my college mates.  Grin so you see, this is a long standing tradition of mine...

The actual idea is to use gold pinstripe on the routed edges of the wood plates, matching the handle and pinstripe on the sconce bases. I haven't really thought about a 4 colour scheme. Officially it's Black, Oxblood and Gold.
« Last Edit: April 16, 2019, 08:28:59 pm by J. Wilhelm » Logged
J. Wilhelm
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« Reply #30 on: April 16, 2019, 08:40:02 pm »

Aaargh! Last night I just noted a defect on the brassy handle I got from Home Depot. The gloss finish is cracking and peeling! Actually, it can be scrathed off with just the fingernail!! That is horribly poor quality for cabinet handles. Normally cabinet handles made from brushed metal are finished with a ceramic based lacquer or powder coating that is tougher than nails. You can take a torch to the handle and the paint will not melt or burn (I know because I tried aging some brushed nickel cabinet handles years ago). You should only be able to remove the finish by sanding. So I'm very bummed to see that happening to this handle. I can't pass on this low quality to the consumer, though I really like th handle.  I'm going to have to search again...

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« Reply #31 on: April 21, 2019, 07:43:04 pm »

Very cool J. Wilhelm! Shocked
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« Reply #32 on: April 22, 2019, 01:39:54 am »

Very cool J. Wilhelm! Shocked

Thank you! It's something that I revived out of a need for a new shop. But I've been very busy this last week, changing work office and yesterday I was too late and too tired to do anything with it. I'm having a hard time adjusting to the new schedule at work.

I will try to do something this week. Although the new schedule will bring more money and precludes the need for a second income, I still want to open a new shop. My plans for this go beyond my school loans.

I guess I will try developing new products for the summer as well - assuming I have any time for it! And honestly the new work schedule is the gentlest least intrusive way to earn more money! Getting a second job would imply working 7 days a week, so I wouldn't even know when to build anything!
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« Reply #33 on: April 26, 2019, 08:58:07 am »

Gilding the Lilly...

I'm sorry I haven't got much progress to show folks. I've been extremely busy with work for the last week, just trying to adjust to a new schedule and new route, and not sleeping and not eating much, apparently.

I'm slowly settling in, and I have a lot less free time to build things, so this is going to be a challenge. I'm nowhere close to the point where  could quit my job to work full time on this - but if I strike it just right, I hope I could be at some point. It's been a long time since I was a dedicated maker.

Last weekend, I the gilded plates with a very expensive enamel which to me looks just like Testors enamel  Undecided  But admittedly after drying for 3 days, the finish does look like old gold leaf. What made the paint look horrible on the Pickelhaube's spike is what makes it look nice this time around.






This below is a mock up of what I think it would look like. I haven't angled the side speakers upward yet, but I'm debating whether to do that or leave them in horizontal position. In theory they could even be made movable, but keeping the horns tight would then be an issue. I will explore that idea soon.








This boombox is proving to be very much the same as the Mk I in many respects, including design faults, and one of those is the need for a pre-amplifier. The sound coming out of the box seems low for the power rating of the amplifier, and I know what the problem is. I went through the same issue with the Altec Lansing PC speaker system in the first Boombox.

The issue is the input of the speaker system's amplifier: it expects to be plugged to a *power amplifier*, usually a 3-5 W chip on the motherboard of a computer. But, normally hi-fi audio devices are tuned to line-level input which means (correct me if I'm wrong) a 1mV signal. In this case the input of the computer system must match the output of some little amplifier chip, something like an LM 386, Realtek ALC662, or some such.

The last time I solved the problem by building a tiny 10X voltage amplifier which I powered with a 9V transformer and connected in between the output of the iPod dock, and the amplifier's input's. I'm going to have to do the same this time, but connecting to the output of the Bluetooth receiver. The sound quality should be good, it's just the inconvenience of having to build an extra amplifier and an additional power supply for it. The amplifier's voltage multiplication should be very low to insure that no distortion is introduced into the signal - the lower the power amplification, the cleaner the signal will be. I just want to increase the peak to peak voltage of the input by a little bit. The sound should be very clean and frequency response fairly flat way past 20kHz at 10X amplification with good operational amplifier chips.

I have a good mind to perhaps use something like a compact external sound card instead, connected via USB, and thus have the ability to use the whole boombox as an external sound card as well. We'll see. I just need more time to work on this box than I seem to have!
« Last Edit: April 26, 2019, 09:08:01 am by J. Wilhelm » Logged
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« Reply #34 on: April 26, 2019, 01:40:45 pm »

What did you use as a Clear coat on the handle to ensure the gold paint/leaf  doesn't wear off with handling? 
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« Reply #35 on: April 26, 2019, 06:17:23 pm »

That is looking brilliant! I think the idea of making it an external souncard sounds good - maybe make that an optional extra to the main system?

Yours,
Miranda.
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J. Wilhelm
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« Reply #36 on: April 27, 2019, 11:12:31 pm »

What did you use as a Clear coat on the handle to ensure the gold paint/leaf  doesn't wear off with handling? 

Actually, I'm going to return that piece as defective. I just used it for the photo with a coat of polyurethane. I think the issue was a bad batch in the factory. I'll be looking for substitutes, but for the moment I'm sticking with that model. The wrought iron ones I used to find don't exist anymore.
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« Reply #37 on: April 27, 2019, 11:16:45 pm »

That is looking brilliant! I think the idea of making it an external souncard sounds good - maybe make that an optional extra to the main system?

Yours,
Miranda.

Thank you! I never used a sound card in the Mk. I because it had the iPod Dock already and that functioned as an audio/video hub of sorts. I think the pre-amplifier is mandatory, so it can't be an "extra," but it would be a nice feature on what is otherwise an inexpensive speaker system. I'm a very Old School audiophile, who mourns the loss of sound quality as soon as we made everything portable, so I need lots of inputs outputs and control knobs to be happy. There's a number of solutions available out there.
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« Reply #38 on: April 28, 2019, 02:11:10 pm »

Actually, I'm going to return that piece as defective. I just used it for the photo with a coat of polyurethane. I think the issue was a bad batch in the factory. I'll be looking for substitutes, but for the moment I'm sticking with that model. The wrought iron ones I used to find don't exist anymore.

Here's a place to check out.  It has some vintage looking pulls:
https://www.vandykes.com/cabinet-pulls/c/508/

Also, here: https://www.houseofantiquehardware.com/decorative-knobs-and-pulls
 
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« Reply #39 on: June 09, 2019, 09:47:35 pm »

Some minor progress and wading through some issues.

I had planned to use Latex construction glue from the beginning to install the wood plates, based on my positive experience with the MkI box, and it does work great, with enough adhesive power to lift the entire Boombox by the handle. The issue is that the moisture in the latex glue warped the wood plate, which was carved from a part of the tree where the rings are very curved. The result is that the plate lifted from the edges by a millimetre or so, and the latex having cured, it had frozen the plate into a slight curved shape, like a potato crisp.

It's too much of an effort to try to remove the very strong glue and start from the beginnin with a new plate for one millimetre of warp. I'll chalk it up to the standard hiccups you suffer when prototyping. This unit will not be sold anyway. I need it as a reference. So I just drilled six holes and I found these great wood screws called "pocket hole screws" which turned out to be ideal for installing the wood plates on the subwoofer unit.


The screws are finished in bronze and look a bit like rivets, so I think they add a nice touch. And they seem to be holding well with the compressed paper construction  Roll Eyes And in the future, however, I will also use epoxy glue in the screw hole, to make sure that the screw doesn't strip the thread in this material. The strength of the box is very important because it determines how much force you can apply when supporting the speakers as well.


I also hit a snag with the lamp installation hardware. The screws holding the sconce base are metric M4. 07, and getting brass knurled knobs in the USA in that size will be hard. The idea is to have detachable speakers, so the user needs to be able to use hand - tightened nuts to secure the sconce. The company who made the lamp did provide two tiny 5 or 6 mm spherical nuts, but if the user loses those tiny pellets I could not replace them... Otherwise, the sconces are fairly secure and feel very solidly attached to the box.


I will try to figure a way out of this issue. Maybe use different lamp installation hardware, but that will add cost. I also ended up using chassis-mount RCA phono jacks embedded with epoxy directly into threaded Rods which replaced the in-socket  on/off switch. This seems to be the most practical way to connect the speakers to the box, because you can use any number of phono plug to RCA jack cable adapters commercially available. But unfortunately with Radio Shack being a faint memory and Fry's Electronics being ungodly far away and horribly under supplied like the worst Tesco or Walmart you've ever seen, it means that I have to order those jacks online...

I'm still trying to figure out how to attach the lamp shades. They're basically made from cloth covered wire. I found these aluminium wire clips that I could attach to the PVC speaker body, but the clips are horrendously soft and painted with something that flakes off if you even look at it the wrong way. But I like the notion of these lamp shades being detachable, to replace or avoid breakage...


The speaker installation went without a hitch. The units were screwed into the PVC, but I used spacers to leave a gap between the driver and the PVC. The idea was to use the latex glue to seal that gap, in lieu of the typical rubber foam gasket. I need to figure out how to paint the speaker enclosures. The way I made these was to assemble all the parts first, because it's be too difficult to protect the paint when drilling holes. I may paint it with a rubberized paint. There is a black or gray rubber spray you can purchase.


The quality of the sound is surprisingly good for such an inexpensive system. The bass is very deep. The problem for my audiophile ears, is that the tweeters are too small and not very efficient around 1kHz (voice range). I get nice treble and fantastic ground shaking bass, but for some songs it will obscure human voice a bit. Since I have to add a preamplifier, I'm thinking I could even add a pair of mid-range speakers. The problem is where to place them!

All of these are serious issues that raise the cost of the Boombox. I need to make sure that I'll have a good supply. Oh well.  I'll just keep working on it!  Cheesy

Cheers,
J. Wilhelm


« Last Edit: June 09, 2019, 11:45:21 pm by J. Wilhelm » Logged
Kensington Locke
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« Reply #40 on: June 10, 2019, 02:58:16 pm »

I like the look with the screws.  adds a bit more texture.
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« Reply #41 on: June 10, 2019, 06:48:04 pm »

That is looking so smart! The colours really are perfect. I hope those design issues don't cause too much trouble - I'm sure you will come up with wonderfully creative solutions for all them.

Yours,
Miranda.
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« Reply #42 on: June 11, 2019, 08:01:56 pm »

That is looking so smart! The colours really are perfect. I hope those design issues don't cause too much trouble - I'm sure you will come up with wonderfully creative solutions for all them.

Yours,
Miranda.

I like the look with the screws.  adds a bit more texture.

Thank you! I do like the way it's going. I remain hopeful on resolving the issues. The box already sounds good enough to sell, but I think it could be a bit better. The aesthetics are also good enough, but just need something else. I think the hardware issues are easy to fix, but I have very little free time  to do it.

I don't normally go for artifices, but I think in this case adding texture by way of rivets might be a good idea. Also not off the table is using black textured felt. It could be applied under the sconces and the top, taking advantage of the 1mm gap between the wood plate and the Formica.

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« Reply #43 on: June 12, 2019, 03:14:13 am »

Love the design process - gives a better understanding of the how's and why's of the development of new products!
And the boombox itself isn't half bad!
Well done, sir!
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« Reply #44 on: June 19, 2019, 11:22:40 am »

Love the design process - gives a better understanding of the how's and why's of the development of new products!
And the boombox itself isn't half bad!
Well done, sir!

Thank you. Oh and what a process it has become. I've not had much time to do anything on this project on account that I was working toward obtaining my dual citizenship and between work and looking for a new job, surprise rent increases, school loan payments, etc., well I just don't have the time. Having lost the first battle (but not the war) toward dual citizenship last week, I consoled myself this weekend by working on the boombox.

The last time I had mentioned something along the lines of the frequency response of the system being deficient in the mid range.

Looking for professional reviews online I had my worst fears confirmed and it turns out that the system, as designed by the maker does have a mid-range 400 Hz to 900 Hz deficiency. The reviewer came to the conclusion that it was not a shortcoming on the speaker units themselves, but rather a sound profile built into the amplifier itself. A bit like a Karaoke machine, this system has a massive bass and treble boost that leaves the vocals nearly invisible.

My aim was to see if I could see patterns in the frequency response which I could target and fix somehow. In the website I visited, a reference microphone was calibrated for laboratory conditions and a computer was used to accurately measure the frequency response of the speakers at various angles. The idea is to use a single variable pitch "whistle" to test the performance from 20Hz to 20 kHz in the human hearing range. Then the writer used a computer-programmable black-box doohickey called a "DSP" in between the sound source and the amplifier to correct for deficiencies before they sound is generated by the speaker cones. The idea is to make the frequency response for the system as flat as possible.

My approach was much simpler. I decided to test it myself with far cheaper equipment than that used by the review website. I used a white noise generator on my smartphone and connected the output directly into the amplifier. I also downloaded an excellent real-time frequency analyzer for Android. I did not calibrate anything, I did not use a reference mic. This is the cheapo built in mic in my phone. This is MASH style "butcher surgery" I will be performing on the system. I just want it to sound better.

Time averaged snapshot of frequency response using white noise
Unmodified system as shown in the last photos. Mic at dead center at 1 m of distance

On the floor (carpet)


On a wooden table


The curve looks very spiky because this is a real time snapshot of the sound profile coming from the white noise generator. The sound source is not a steady tone or "whistle." In real time the spikes you see are moving up and down and you can "smooth the spikes" by taking a time average over longer and longer times depending on how smooth you want to see the curve - and in fact this curve already is timed averaged by some unspecified number of milliseconds - but on the smartphone the curves are still bobbing and bubbling up and down as I took the snapshot.

You see the problem right away. There is a massive 10 dB bass boost at 100 Hz and a greater 15 dB boost at 6 kHz. For those of you old enough to know what I'm talking about, this profile looks like the way you would set a cheapo 1980s car equalizer preamplifier you bought at Pep Boys (an aftermarket auto parts chain in the USA) for your Ford Escort. This is not good.

I will not repeat the language and expletives used by the professional audio reviewer when looking at this system. He was very thorough and funny, but looking thorough his reviews of even very expensive top of the line professional audio systems... let's just say the reviewer on the website is NOT the kind of person you would invite to a wedding party, on account that he would critique and find all sorts of faults with the bride, groom, family, guests and even the dog. He would end up kicked out of the reception and the newlyweds would be planning a divorce the day after.

So what to do?

For starters, I wanted to see if I could "fill the gap." I had a pair of cheap amplified speakers for my computer, So I connected the speakers and set them up in the following manner (see photo below). The tiny PAM8403 amplifier chip in the speakers is of the same type used today in smartphones. It belongs to the "Type D" family of amps, meaning that it uses a square wave pulse which is then smoothed to drive the speakers - sometimes erroneously called "digital amplifiers." These "digital" amps are extremely efficient thermodynamically converting up to 90% of the battery power to sound. That also means lower heat dissipation, so they can be smaller. But at 10% total harmonic distortion for a meager 3 W, even my vintage 1985-era 45 W Garrard home stereo produces *far cleaner* sound at maximum volume. So I knew beforehand I probably didn't want to incorporate this chip into any modification.

System with commercial pre-amp speakers 3W total with Type D power amp (PAM8403)


PAM8403 driven speakers response all by themselves


Combined Boombox + PAM8403 driven speakers, maximum output


Same as above, but lowering larger amp's output while holding the PAM amp at max


The frequency response of the PAM8403 driven speakers is fairly flat all by themselves. Very nice, but as you can see, there is zero bass on this system. All fine since I only want to fill a gap between ~ 400Hz and 1 kHz roughly. When I turned on both amplifier systems, I noticed that at maximum volume the little PAM amplifier could not keep up with the bigger one so you still get a "saddle" frequency profile. I did manage to get a flatter response by adjusting both systems' volume down individually though.

But this is not good. The volume is very much reduced this way. The tiny amp is no match for the larger amp. So then I decided to just think outside the box. The way that I did when I was a kid putting speakers in tin cans and just experimenting.

Why not rip the drivers out of the PAM- driven speakers and connect them in series with the larger amp twitters? There is no crossover in this system other than the one built onto the amps board. Doubling the impedance rating from 4 Ohms to 8 Ohms is not going to hurt the amplifier. Often amplifiers are rated to operate between 4 and 8 Ohms and the load in the amp will be reduced anyway. The combined impedance of both types of speakers may give me a greater bandwidth and the composite speakers will also feature a greater acoustical area to push the air in the mid range.

I figured those twitters were too small to be full-range speakers anyway. They make great twitters, but they are to small to push longer wavelengths. regardless of how you tuine them, lower frequencies require larger diameter drivers simply because lower frequency waves carry a lower acoustic energy density, so you need a bigger area anyway.

So I set up to break those PAM driven speakers apart.

Breaking apart the amplified speakers


The PAM8403 amplifier (3W)


I needed a plan. I needed to see how to install the speakers. I could have left them in their original enclosures and attached the whole enclosurtes. But that doesn't look steampunk. And I wanted to tweak the acoustic profile of the speakers to see if I could patch a specific hole in the profile around 350 Hz which persisted, no matter what I did.

I realised these PAM speakers were -oddly enough- REAL ported speakers. Unlike the more expensive sub-woofer satellites, these speakers were designed around a Helmholtz resonator (Port Bass Reflex type). Some more expensive systems will be designed as acoustic suspension speakers and others as Bass Reflex - regardless of the performance. So why not design my own Helmholtz resonator and tweak it myself?


Hemholtz Resonator speaker enclosures built from PVC caps and tubes. Original setup tuned to 600 Hz.


Speaker test setup with composite satellite speakers


So I set to make make two Helmholtz resonators from PVC caps and noticed right away that the 2-inch diameter caps matched that of the speakers exactly. Holy Serendipity! What a stroke of luck. So it's all about gluing it together and designing the length of the neck (pipe) of the Helmholtz resonator. Thanfully that worked well for a 1 cm diameter pipe with a ~6 cm length - targeted to 600 Hz at first, trying to see if I could see anything in the frequency response. The unmodified system had just 2 large spikes. Maybe I could add a third spike.

Frequency response of system with 8 Ohm composite satellite speakers. Enclosures tuned to 600 Hz.
You can see the resulting spike in the center near 600 Hz.


Alright.so I have managed to add a spike at 600 Hz, and thus steal some energy from the bass and treble. But the 600 Hz spike is too sharp. I thought that perhaps if I tuned the Helmholtz resonator further away from mid-range that the bandwidth of the speaker would widen. So I cut more pipe and tuned it to 200 Hz

Frequency response with Helmholtz resonator tuned to ~200 Hz, dead center


Frequency response with Helmholtz resonator tuned to ~200 Hz, 45 degree angle from center


So this is where I am folks. The placement of the satellite speaker is crucial. You can get a better mid-range response with the Helmholtz resonator enclosures facing you, on top of the other speakers, and I figure the best location will be mounted on some arms being held on top of the "horns." The mid range speakers could also be tilted upwards at an angle, but noting that they must be in the same plane as the twitters in the horns; otherwise at certain frequencies you can get "echos" because the human brain is fast enough to detect sound wave arrival times as a result of evolution which gave us the ability to detect sound 360 degrees around us (Binaural Sound- I'll save that for another time).

The frequency response is very much flatter at a 45 degree angle from the center of the boombox, and dead center you still have this "saddle" profile, but the bass and treble boost is much lower than before (this being a logarithmic scale and all, a total peak to peak of less than 10 dB is much better than 20 dB!!).

Oh well. I'll keep working on it!

Cheers!

J. Wilhelm

~~~
« Last Edit: June 19, 2019, 11:37:43 am by J. Wilhelm » Logged
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« Reply #45 on: June 19, 2019, 01:40:42 pm »

That is a great color...on some of the panels it looks a bit more pinkish though. Brighther than on the....horns (whats the word for the cones there?)
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« Reply #46 on: June 19, 2019, 06:41:11 pm »

Thank you, that is Burgundy according to Rustoleum, but it looks either darker or lighter to human eyes depending on lighting. I was put off by the Fire Engine Red at the beginning. I was aiming for Oxblood. The best way I can describe the horns (lamps shades) is multi-faceted like a red rose. They match better in person.
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« Reply #47 on: June 20, 2019, 02:07:14 pm »

As a paint-person I can tell you: Its the surface-color that makes it brighter, as well as the layer-thickness. Might look like a white door on a grey car, if you know what I mean.
A darker part, right next to a pinker part. If they dont sit next to each other, no one will ever notice I guess.
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« Reply #48 on: June 20, 2019, 11:43:21 pm »

As a paint-person I can tell you: Its the surface-color that makes it brighter, as well as the layer-thickness. Might look like a white door on a grey car, if you know what I mean.
A darker part, right next to a pinker part. If they dont sit next to each other, no one will ever notice I guess.

Some colors are more forgiving than others. Human perception is important. It's been shown people have different sensitivities to different colors. And digital cameras will not post process the information detected in the same way. The human brain compensates automatically.

At first I thought I couldn't match the lamp shades, but the fabric on the lamp shades /horns is like silk in person. Very metallic. You don't get the full effect on camera, because you only have one exposure at one angle. But having stereoscopic sight, depending on the angle of the light source, one eye sees one shade of color and the other a different shade. The color becomes three dimensional.

I took a class on Radiative Heat Transfer in grad school, which encompasses all the physics of reflection absorption and scattering of light. And I learned how mathematically complicated light behavior can be when interacting with surfaces. Molecules will reflect and absorb different colors in different directions with different intensity. You can basically control which color is reflected in which direction and how scattered it will be giving very different results depending on the materials used at the surface. Some of that is exploited in iridescent auto paints.

A very dramatic example of how scattering affects perception is when you sandblast metals. If you sandblast a mirror finished piece of silver, it will turn a very light pastel shade of brown /pink. When polished the angle of the light will reflect recognizable colors from the light sources, like blue from the sky, green from the trees, etc.

I figure the metallic shades are like the Joker in a deck of cards, giving you different tones and shades revolving around a main color. Some of that reflection given by the lamp shades will match the flat burgundy over the wooden panels.
« Last Edit: June 21, 2019, 12:27:28 am by J. Wilhelm » Logged
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« Reply #49 on: July 01, 2019, 04:43:54 am »

So, 8 days ago I went out to find an appropriate way to hold the two new speakers onto the box. I found these "metal banister brackets" which I had seen days before and seemed like a good way to hold the speakers. The thing is, the PVC resonator tubes are very strong and made from a standard copper-tube pipe size, and these gave the idea I could use copper-plated "split-ring" pipe hangers. Pretty hefty stuff, all tied with 3/8 inch machine bolts and nuts. Grossly overbuilt and heavy, but isn't that what Steampunk is all about? It looks like the black banister brackets are made from some tin alloy. Very soft but very heavy.











These speakers can swivel and be fixed in place by tightening a single bolt, thanks to some clever furniture hardware. The split ring clamps hold on tightly to the resonator pipe, and the idea is that the user will adjust the angle of the speakers, which will presumably be covered by a smaller set of horns / lamp-shades / whatever, which I still don't have in my hands. I could use the same size of lamp shades, but I feel that would obscure the two lower horns. So now I'm looking for a new pair of horns.

The idea to place the horns in the back came from my roomate who suggested I needed the extra space for a second pair of horns. Otherwise, I can just drill a new pair of holes and mount the black brackets on the opposite end (front) of the box, and that would put the smaller speaker drivers on the same plane as the lower speakers. The bolts holding the swiveling brackets do not screw directly into the MDF (the board's too soft), but rather into steel "T-Nuts" with a circular flange which screw into the MDF from outside (I deemed insert type nuts to be too weak given the constitution of the MDF).

There are advantages to both positions. At the moment, since there is no crossover separating the mid-range speakers from the tweeter speakers, there is a chance for sound wave cancellation and/or comb filtering when I place the speakers in the rear position as shown (same frequencies emanating from both speaker sets are out of phase). And I didn't even mention the virtual "echoes" due to human binaural hearing being able to pick the difference in phase at certain frequencies... Oh well, it's a Pandora's Box of problems. On the other hand, when placing the speakers close to the rear and pointing upward, the sound will bounce off the sides of the subwoofer and spread the sound in all directions, minimising sound cancellation, not to mention throw the vocal range sounds upwards and outwards directly toward the listeners, which does audibly "open up" the stereo separation.

I have yet to perform audio tests on this configuration as shown to see what the frequency response is and to look for any obvious problems such as sound cancellation and comb filtering. The easy thing to do in either case is to open a second pair of holes in the front and cover them with the bolts when not in use, so the user has a choice of speaker position - rear or front. A second pair lampshades (of any size), however will only fit in the rearward configuration. In the front configuration I would need to cleverly come up with a different way to dress up the white plastic.
« Last Edit: July 01, 2019, 06:28:59 am by J. Wilhelm » Logged
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