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Discussion Starter #1
Hi AVSers,

Recently, I have designed a compact wireless Bluetooth speaker that I intend to build in the forthcoming future. Personally, I love the aesthetic appeal of vintage radios and classic guitar amplifiers, hence, my inspiration for this concept in particular. I have already sourced all of the parts from vendors that are necessary to complete this project, but before starting the build I wanted to receive feedback with regards to a few speaker design decisions that I am considering.

1.At the moment, I plan to use two full-range Dayton Audio ND91-4 3 ½ inch Aluminum cone drivers for this build. I picked the ND91-4 because the performance specifications for this little driver are quite amazing. Based on the specifications and comments provided on the parts express webpage they yield a decently broad frequency range and offer good bass response (for their size).Does anyone have any other small speaker driver recommendations (3 – 4 ½ inches) for me to consider? Price is not a major concern.

2.I plan to build the enclosure (8 ½ x 5 ½ x 4 inch) using ½ inch thick carbonized bamboo. Although carbonized bamboo is a grass and not a wood, I have read that it has good acoustic properties and is relatively inexpensive. Has anyone ever built any bamboo speaker enclosures? If so do you recommend the use of this material for acoustic applications? Perhaps I should use MDF wood (homogeneous properties) for the best result, but MDF is ugly and it might be a massive pain to apply veneer to cover it. Any other material recommendations (walnut, maple, etc)?

3.In my current design, I have implemented a 3 ½ inch passive radiator to dissipate air-flow at lower frequencies. However, I am tempted to use a porthole to conserve space (I am also not sure if two ND91-4 drivers could even displace enough air to even move a 3 ½ inch passive radiator). Does anyone recommend using a porthole over a passive radiator? Vice-versa?

4.To drive the speakers I am thinking about using a TDA 7492 Class D digital audio amplifier board. It has multiple 50W channels and comes equipped with a horizontal heat sink to dissipate heat (a must, I don’t want to start any fires). I think that this is a pretty good option, but can anyone suggest anything better?

5.Is the design cool, or does it suck? I don’t want to build anything that doesn’t look cool.

I have attached images of the speaker design (3D-rendering) and components that I have discussed. If anyone has any other suggestions to improve this build or if you are interested in updates, please let me know. Thanks for your time! I am sorry for the long winded question(s).
 

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Personally, I love the aesthetic appeal of vintage radios and classic guitar amplifiers, hence, my inspiration for this concept in particular.
I've thought about doing a similar project, but have too many projects ahead of it right now.

If you really want a classic guitar amp look, use baltic birch plywood, cover it with tolex, and do the corners with metal corner protectors. Mojotone has everything you need to make it look like an amp. I've bought plenty from them for my amp building needs.

Carbonized bamboo could also look good. Be very careful of the dust, and holy moly do the splinters from this stuff hurt—tiny needle torture.
 

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Yeah, bamboo is tough to work with. Very brittle, easy to split. Drill holes before inserting fasteners.

Looks like a cool project. I like your design, very sleek and simple.

I've also thought about turning an old antique radio into a BT speaker and keep looking for the right deal on an old radio box. I think you'll be OK with amp cooling as long as you have ventilation in the box. You'll probably want a 12V power supply, find a very good one (the brick type) as that is what might really get hot if it is underpowered. 12V is good because its easy to find 12V to 5V converters that likely would be what powers your BT receiver board, but you can also find 19V to 5V converters on Ebay as well. Think about adding a 5V USB charge port to the back of the unit, so you can charge a phone or even hook up something like a Chromecast Audio through the aux port. (or you might even consider also integrating a Chromecast Audio).

I see the 'charge' indicator. You didn't say if or how you plan to integrate a battery, that might be the tricky part. I just always planned on having mine plugged in. I'm curious what you plan there.

I've messed with some cheap BT audio receiver boards. There are several low cost ones out there to choose from, unfortunately a lot of them have a really annoying loud beep when you connect. You might be best off considering using a more expensive enclosed unit with RCA outputs, that is what I will be doing. Also, if you just buy a cheap board you sometimes have to mess around to get rid of PS/Ground hum.

Post your progress, I'd like to see how it goes. Good luck.
 

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3.In my current design, I have implemented a 3 ½ inch passive radiator to dissipate air-flow at lower frequencies. However, I am tempted to use a porthole to conserve space (I am also not sure if two ND91-4 drivers could even displace enough air to even move a 3 ½ inch passive radiator). Does anyone recommend using a porthole over a passive radiator? Vice-versa?
I love the design! It looks great. Just a real quick question about your passive radiator. My understanding is you want to use one 3 1/2 PR for 2 3 1/2 full range speakers. Is that correct? If so, you typically need at least match the size of the speakers if not exceed it. In this instance you would want to use two 3 1/2 PRs at least.

Please note that I have not modeled this in win isd. Having said all this, assuming the speakers and PR can tune well together, I love PRs. And in any project they work well with, I use them. Good Luck with your project.
 

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I quickly modeled those speakers and a 6 1/2 PR would be really good if you added about 30g to it. With a ported setup, it would tune almost identical, but you may have some issues with port noise, depending on how many watts you actually use from that amp. The problem with those speakers and a port is that if you go with anything bigger then a 1" port, your port will have to be really long. That limits how much power you can drive the speakers due to chuffing (aka port noise). Assuming you use a 12v 4a, you would get about 48 watts total and 24 to each speaker. Modeling it you will probably have port noise. If you use any more than that, it is highly likely you will experience port noise. All said, it would be probably be better to use a 6 1/2 PR.

Here are a few pictures that show what I am talking about.




*You could do two - 1" ports but each to them would have to be around 12" long. Which would be hard to do in that enclosure, but not impossible.
 

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Discussion Starter #6
@Greyskies

Great recommendation! I was thinking about doing something very similar to that. I have googled a number of beautiful amplifier design concepts in the past and they are amazing to look at(check out this Versoul). I think that I can source every part for a similar build from a number of part supplier vendors, but building the chassis might be a headache (perfect fit and panel mount layout). I am also thinking about using leather corner protectors instead of metal corner protectors. They are cheaper and they look very hipster (I like hipster).
 

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@DanPackMan

I am not completely sure at the moment, but I think that I can find internal charge circuit designs on the web; I might just scrap one of my old computer chargers and buy a lithium ion battery just to experiment with this concept. Have you ever used nimh batteries by any chance? I might be capable of sourcing some for a good price, but I hear that they catch fire. In the past I have developed a PVC speaker that had to be plugged in at all times and it was very annoying (until purchased a 9V battery holder for the device, which was a lot better than looking for a wall to plug into). If your speaker device does not require a significant degree of power I would recommend buying one. I have attached images of the PVC speaker build btw. And thanks! I am glad that you think that the design is cool.
 

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@Al Toid

You are very correct. I was thinking the same thing, but since the inner diameter of the speaker is only about 3 inches (can’t get any speaker excursion on the ½ inch think mounting), it might not be necessary to size up at all. But that is a great observation; I will need to look into that. And thanks for modeling the acoustic performance for the design! That’s awesome! I am not very savvy using these types of design programs. But how did you model the enclosure for this specification (length, width and depth dimensions) to obtain this data? Because my current enclosure’s build (8.5 x 5.5 x 4 inches) cannot physically accommodate a 6 ½ inch passive radiator. And yea, porthole positioning and size can be a major pain. From what I read, PRs are a lot easier to implement.
 

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But how did you model the enclosure for this specification (length, width and depth dimensions) to obtain this data? Because my current enclosure’s build (8.5 x 5.5 x 4 inches) cannot physically accommodate a 6 ½ inch passive radiator. And yea, porthole positioning and size can be a major pain. From what I read, PRs are a lot easier to implement.
Your Welcome. I'll always model something for someone, I enjoy doing it. I basically figured out what your internal volume was and used that to model. The easiest way for me to do that was to take your external dimensions ((8.5 x 5.5 x 4 inches) and the size of your material (1/2) and insert it into this site. It'll easily give you the internal volume in cubic feet. I then used that number, as well as the speaker and PR measurements in order to give you an idea of what it would sound like. I didn't check to see if you could fit the passive radiator in your current sized box, but rather the volume of your enclosure. And for the volume, it is pretty perfect for it.



As far as your concern with the speaker not hitting xmax, that may be true, but remember the PR still needs to have 1.5 to 2 times the amount of displacement as your main speakers. A 3 1/2" PR with two 3.5" speakers will not be able to achieve that.

*After I modeled it, I was seriously considering of ordering some parts and building something with these. :D They model really nicely. I still love the idea and think they are great with the right sized PR. If you can resize the box a little while keep the internal volume similar, you could have something really nice here.
 

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I might just scrap one of my old computer chargers and buy a lithium ion battery just to experiment with this concept. Have you ever used nimh batteries by any chance? I might be capable of sourcing some for a good price, but I hear that they catch fire.
Lithium Ion batteries can be a fire hazard as well. Either way, the key is a proper charge circuit with a cutoff sensor and not over charge. I've not made a charger yet. There are charger board modules out there, not sure I'd know what to use. I've looked at this before;

http://electronics-diy.com/electronic_schematic.php?id=813

They also make all kinds of battery and chargers for RC hobbyists, but that stuff seems expensive. Another choice is take a battery and charger from a power tool, like the 12V Craftsmen Nextec, those are kind of cheap used.
 

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@Al Toid

Thanks Al Toid for the link! I will certainly use this in the forthcoming future! And yea, I think that you are right about adding a 6.5 inch PR. Initially, I was not sure if these drivers would even displace enough air to even move a PR. But, I have Youtube’d a number of videos of DIYers demonstrating the capabilities of the ND-91, and I am very impressed with their low-end excursion. These guys are little monsters, and I would certainly encourage their use!
 

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@DanPackMan

This is sick! $34 for a 6000mAh 12V battery is not a bad deal at all. Thanks for the suggestion. I will probably exploit a very similar option.
 

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That battery is the pretty much the exact one I used in my last build. I took an old Dewalt Drill case and made an AM/FM, bluetooth 2.1 speaker build. The battery is amazing. I ended up getting over 14 hours of continuous play out of my unit.

Here is the build. At 2:45 I show the battery inside the case I used:

 

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Great recommendation! I was thinking about doing something very similar to that. I have googled a number of beautiful amplifier design concepts in the past and they are amazing to look at(check out this Versoul). I think that I can source every part for a similar build from a number of part supplier vendors, but building the chassis might be a headache (perfect fit and panel mount layout). I am also thinking about using leather corner protectors instead of metal corner protectors. They are cheaper and they look very hipster (I like hipster).
That Versoul is beautiful. You'd be surprised how forgiving building the chassis and cabinet is. Here's my Bass-O-Matic.
 

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@ Al Toid

Dude I love this build! And HIVI makes amazing speakers that kick a$$ for a very low price. I have used them in a few of my own builds. Also, 14 hours of playback is terrific. I checked out a few more of your YouTube videos and I subscribed! Thanks for documenting and sharing your knowledge. Keep up the great work. I have a few questions though. Are you satisfied with that MP3 module? Is the Bluetooth reception pretty good? And is that module Bluetooth 3.0 or 4.0?
 

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@GreySkies

Nice build! Are the seams hidden underneath the metal corner protectors? Also, is the chassis a classic amp chassis or a topless project box?
 

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Nice build! Are the seams hidden underneath the metal corner protectors? Also, is the chassis a classic amp chassis or a topless project box?
Thanks! The biggest seams are along the bottom, at one end and hidden with corners front and back. I'd take a picture of the bottom seam, but it's hard to see, even in person. If you were to take the corners off a commercially made amp, you'd be surprised how sloppy they can be—corners hide a lot.

The chassis itself was a Peavey Basic 50 (see below for an example) that I was originally just going to re-Tolex, as it was pretty bad, and had been stapled in place. However, when I took the old Tolex off, the cabinet had a good bit of mold, so I built a new cabinet and separated the amp into a head. I painted the chassis, and redid the lettering. And now, all the knobs go to 11.

And while it looks great and sounds good, I didn't want to pass it off as something it's not, so I left the original Peavey stuff on the back of the chassis.
 

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Dude I love this build! And HIVI makes amazing speakers that kick a$$ for a very low price. I have used them in a few of my own builds. Also, 14 hours of playback is terrific. I checked out a few more of your YouTube videos and I subscribed! Thanks for documenting and sharing your knowledge. Keep up the great work. I have a few questions though. Are you satisfied with that MP3 module? Is the Bluetooth reception pretty good? And is that module Bluetooth 3.0 or 4.0?
It is Bluetotth 3.0, but I am happy with it. I would say, the sure bluetooth board is still the best I've used, but I wanted the AM/FM tuner. But so far, I am really happy with it's performance. It sounds great! Thanks for the great words of encouragement.
 
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