First build - speaker inside old radio

[Aaerio]

Hello all,

I launch myself into an interesting challenge and as it’s my first speaker building, I want to share with the community my designing process and my interrogations to get some advices and see if my conception is good or if I'm going the wrong way.


Thank you for reading and for your answers. (Sorry in advance for the long post and for my english I write from France) and if you have questions or remarks at any point please don't hesitate!

----

My project is to turn an old and broken radio from the 50's into a modern loudspeaker.

In a nutshell, an old looking radio station with a good sound and modern features (like Bluetooth) control by the existing buttons and pots from the radio. There is also a turn table on the original radio, if I can make it work it will be nice to be able to use it with the speaker.

The goal is to create a speaker that I could put in my living room and listen music with, l doesn’t want it to rumble the walls but a bit of dB will be welcome. I also want it to sound good, I'm not in quest of perfection as I have a short budget (150€ maximum for the drivers and all the electronic components) and some constraint inherent in the nature of my project.

----

Step 1:

I disassembled the radio, disoldered and removed all the old components and the driver.
Once the radio empty, I was able see the room available inside and take the measurements I needed.​

----

Step 2:

With my measurements, I use SketchUp to model the radio. It gives me a good idea about the space available and the constraints I need to take into account for designing the enclosure that I will put inside the radio.

//in turquoise blue the enclosure, in yellow the turntable, in grey a metal block where I will put the electronic, in transparent blue a glass panel with radio station print on it.

If I'm taking the less weird looking enclosure shape I can make and as I'm thinking about building it with 0,55'' (1,4cm) plywood, I ended up with a maximum gross volume of 5.4 liters and a front panel of 14,8cm (5.8”) of height and 25.2cm (9,8”) of width to accommodate my driver(s).

At this point a lot of questions already pops up in my mind:

• Do that kind of L-shape enclosure will have a negative effect on the sound produce by the speaker? If yes, should I modify the shape to have rectangular block but loosing space available on the front panel to mount my drivers and a bit of volume?
  
• A glass panel with the radio station print on it will be in front of the front panel of the enclosure (and the drivers mounts on it) for about half the height available. I'm sure it will affect the sound of the drivers behind it at some point but as I don't really have other choice except using really small drivers above it. should I really worry? Is it that bad?

I didn't stop my work on these questions, of course I will modify my design according to your recommendations and advices.
​

----

Step 3:

From the beginning of project I think about building a 2 ways crossovers because it looked easier and cheaper to build than 3 ways and I will have a larger frequency coverage with 2 drivers than with one full range.

I will also try to implement a bass reflex enclosure as I'm seduce by the possible bass extension.

So, with my 3D model and some experimentations on it, I know now that I may have room to put 2 small woofers (around 3,5") and 2 very small tweeters on the front panel. But after looking at some driver’s spec sheets and trying some configurations in windISD, I saw that I was very limited by the volume of my enclosure.

I have now 3 solutions:

1. use a sealed enclosure may work but “ciao” bass extension
2. Use 1 woofer and 1 tweeter and go mono
3. Use 1 woofer and 2 tweeters and make a kind of 2.1 sound system

I need some advices at this point to make my choice.

I also struggling with the power of the drivers and the amp.
For the mono hypothesis: I made some crossover simulation with passive crossover designer putting a Dayton Audio TD20-F and a Dayton Audio TCP115-4 (which match with my enclosure volume) in series because they are both 4 ohms drivers and came out with good results. And I was thinking about using a 100W mono amp. What do you think? Is it too powerful for the use I will have?
​

----

Okay, I think I will stop here for now
There is already a lot of questions in my post and if you came through this loOong reading, thanks you.

Again, I'm here to learn and I know it's an humble building compare to other project in this forum but I really want to make it right.

Thank you for reading and for your answers.

Have a good day!

 

[Sonce]

What a gorgeous looking radio! Do keep all knobs, preferably with some real usage (volume control, input switch, etc).
L-shape enclosure is not a problem. Also, do not worry much about the partial obstruction of the midbass, just make sure the tweeter has a clear "view". Internal volume is good for two Dayton Audio TCP115-4 (bass-reflex box), wired in series (8-ohms total impedance), but check if there is enough space for the tweeter. Each woofer has 40W power handling, so you can use a 100 W amplifier (for both woofers), but that is an overkill. Mono with bass-reflex box is just fine.

 

[rayma]

Each woofer has 40W power handling, so you can use a 100 W amplifier (
for both woofers), but that is an overkill. Mono with bass-reflex box is just fine.

Seconded, go for mono. Even 10W or 20W should be plenty. The turntable may not be usable, though.

 

[Aaerio]

Thank you both for you answers.

What a gorgeous looking radio! Do keep all knobs, preferably with some real usage (volume control, input switch, etc).

Indeed, looks very nice, I'm very happy about it
I'll do my best to bind every control to the button and knobs.
the original functions of the knobs were (from left to right) :

• high/low balance (must keep)
• on/off + volume (must keep)
• rotate the antenna to adjust the signal quality (need to find another feature)
• radio station selection, I really like to see the indicator moving while turning the knob, I may add a radio receiver to the project to keep this knob with the original function

I was also thinking about using the buttons to switch between the inputs (just like you suggest). there is 4 buttons so :

• Bluetooth
• jack or rca
• turntable
• radio

On paper it looks simple but as I have no experience in electronic it's going to be different in real life.

Tell me if I wrong, I may need something a board like this to manage the inputs and bypass the rotating button with my buttons. I going to clean and unsolder all the wires from the switch component to see how it works because at the moment it looks a bit … messy.

Any advice to connect the old knobs and buttons to the new devices?

Even 10W or 20W should be plenty. The turntable may not be usable, though.

If I understand well, you are suggesting that 100W divided on 2 drivers in series is too much power? should I go for less powerful drivers or just the amp? I ask because I can't find woofer that go below 100Hz if I decrease the power.

For the turntable, I think you're worry about the vibrations, there is an ingenious system to prevent this. I don’t know if it's enough but the all turntable is mount on spring so I hope it will be Okay.

Have a good day !

 

[horst303]

My suggestion is that you use a full range driver, then you save a lot of time and money worrying about a crossover, or which tweeter you should get, I would use two 3" drivers in parallel, my personal preference is Tymphany (Peerless), but there are many very good manufacturers out there.

 

[Kay Pirinha]

What about coaxial car speakers? They usually fit to volumes of about the same size.
Perhaps you might want to replace the baffle by one that you made yourself with appropriate cutouts.
Btw, in my youth I've scrapped so many old and beautiful radios. I'm regretting that wholeheartedly. Hence, seeing any old and beautiful radio becoming salvaged almost makes tears running down my cheeks .
Best regards!