First project: Inventory optimization

[letiennam]

Hello,
After having been a rather silent reader or only built speakers, now I would like to try my hand at a small project. As this is the first speaker I have built myself and share the progress with you guys, I would be very happy to receive feedback.
The starting point is the warehouse on the top floor of my house where the almost finished speaker cabinet is kept. Back about 10 years ago, the speaker was bought by my cousin from Japan - he is an automotive engineer, a powertrain designer and a permanent resident in Japan. He often bought components for me because Vietnam used to have few official distributors at that time.
The original speaker cabinet is handmade in Japan from mahogany, for the sides, top and bottom. Its external dimensions are Width 200x Height 343x Depth 263 mm. However, with the 25mm thick edges, its internal volume is only about 8.5l. The front panel is removable and originally made of brass with dimensions Width 149 x Height 299 x Depth 10mm. Because of the small volume, I have had difficulty for many years in choosing 5in mid woofers, they usually require a larger volume to be able to produce bass. However, the speaker cabinets are finished quite nicely so I have always kept them waiting for the opportunity to come to me. Recently, I found the SB15CAC30-4 seemed like a suitable choice with a volume of 8.5l so I bought one to test and continue this project. They will be for my 7 year old son for Christmas. He needs speakers for learning English, studying online via Zoom and listening to music. Therefore, in addition to being a gift, of course it will be my task.
The idea I came up with was to provide the SB15cac with a passive radiator in a speaker cabinet of about 8,5-9,5l. Since the front panel is removable, I can change the volume a bit. The passive radiator I'm looking at is SB15SFCR-00. The PR I have on hand is the Wavecor PR182BD01.
The tweeter I'm planning to pair with the SB15CAC is the Seas 27TBCD/GB-DXT. I have many other tweeters but I read about Mr. Jon Marsh's "PSD Modula" that this tweeter is suitable for 83-85dB applications so I think it's suitable for the SB15CAC

Thanks to Jon Marsh for agreeing to help me with the PR optimization, but I'll still try to implement it myself while he handles more urgent projects. And once again I really appreciate your comments to complete this little project.

Below are pictures of the speaker cabinet as they came out of the warehouse. They have a lot of scratches, they are the result of a few house moves. The first thing I need to do is sand off all the old paint and re-sand the wood to remove as much of the scratches as possible.

[letiennam]

The sanding work was quite boring for the last weekend.The old scratches were fading. I didn't take many pictures during the process.
This is the end of Saturday last week when it was finally sanded with 600 grit sandpaper

This was Sunday evening when I sanded with 800 grit sandpaper.They have a certain shine to reflect the light

[JonMarsh]

It appears that you have very nice wood structure in the original cabinet, and with a little planning and care (if the right materials are available for you!) the results should be very nice.

Curiously, I have 4 SB15CAC-8 on hand, and I also have the SB15SFCR passive radiators. The only "gotcha" for the latter is that their mounting space for additional weighs (when required) are too small to use the SB PR weights; one would have to find fender washers of a convenient size and mass.

Note, the PR182BD01 is a very old product, discontinued at this time, and not in stock at most sellers of Wavecor PRs- you have some though, so as a homework exercise I'll leave calculations for it and the SB15CAC-4 to you for now.

I did run calculations for the SB15CAC-4 + SB15SFCR in a 15L enclosure, and 8.5 L.

For the 8.5L alignment, it's advisable to add some mass to the PR, due to the small enclosure volume. The default moving mass of the PR is 62 grams, and I would recommend increasing it to about 97 grams with additional weights.



This produces a nice quasi QB3 alignment with a gradual roll off and a reasonably low FB considering the drivers.





If was doing this from scratch, I'd probably use a 15L net enclosure design, which would work well without any added PR mass.

[JonMarsh]

Now, I'm not going to hi-jack this thread with this idea, just mention it in passing, but given the number of SB15CAC-8's I have, and SB15SFCR PR's, and Seas DXT tweeters, it seems like falling out of a tree natural to consider a NatalieP like crossover topology MTM, in about 28L, like the good old days with PE Dayton Enclosures. I might even have two of those around somewhere, but I think I need to do a clean sheet on the enclosure design.

The only thing I'm lacking at the moment is spare time...

[letiennam]

Sorry for the late reply. Thank you Jon. Much appreciated.
Well the slow work continues. This past weekend I spent some time trying out a new oil finish that I came across while chatting with a friend. In addition to audio, he also enjoys playing and collecting guitars, and the talk about finishing speaker cabinet mentioned Danish oil and tung oil. I chose tung oil because they are readily available and because it is said to have a hard, plastic-like finish when dried and is often used in lacquered products. It also protects the wood from changes in humidity, which is a concern in the typical spring weather in the North East of Vietnam, where humidity levels rise to 90% causing the water vapor in the air to condense and form on the surface of objects.
This is my first time applying tung oil. Because mahogany is a relatively hard wood, it will take more time for the tung oil to penetrate into the wood. I dissolved refined tung oil with pine oil, the first layer is quite thick.

They seep down and turn the wood red - a characteristic of mahogany when it is soaked in oil.
When the tung oil mixture is exposed to sunlight, it produces heat and some air bubbles. Here they are after 48 hours of applying oil, the oil has completely dried. The next job is to sand and continue to apply the next layers and wait for them to dry,....

[letiennam]

One task performed while waiting for the oil to dry is to create the shape of the front panel. As talked with Mr. Jon from his Modula PSD project, I edited to make them suitable for SB15cac and Seas DTX.

One trick I did to speed up the process was to buy bamboo from the chopping board product in the supermarket. The cutting board is 32mm thick and I will combine it with a 15mm sheet of baltic plywood to get an overall thickness of 47mm. Then 7mm will be inside the 2 side edges and 40mm is the outer front panel that needs to be CNCed according to my idea above.

[JonMarsh]

That's one of my favorite procurement "tricks" from years ago, though these days some varieties of bamboo have been easier to source, and also some of the front panels are much larger!

😂

[letiennam]

My "trick" didn't work as expected, the compressed bamboo layer in the middle cracked during the CNC work - or maybe they had already cracked. They looked very unsightly so I decided to leave them aside.



In parallel with the "bamboo cutting board trick", I asked another brother who is a carpenter to find 2 pieces of hardwood for the front panel. After hearing what I needed, he sent 2 pieces of ironwood. According to him, these 2 pieces of wood have been treated and have a long waiting time - about 5-6 years, they will not have any cracks or shrinkage anymore. The work continues

Because the thickness of the 2 pieces of wood I was given was larger than the original bamboo wood - they were up to 55mm thick, so the drawing needed to be revised.


The work of "sharpening" rough wooden panels is taking place again. After a high speed with many fibers, the speed was adjusted to a lower speed to get a more beautiful semi-finished product.



This is the result right after removing the dust from the machine and placing it on the front for testing


Luckily, they were a tight fit, waiting for screws and measurements.

[Reet]

Excellent CNC work on those baffles, and great colour match of the wood as well! The design is reminiscent of B&W woofer cabs, and I may borrow some design elements here for my own future projects.

[theSven]

The baffle is gorgeous indeed! I have never heard of ironwood before though, which is rather funny since it is a town in Michigan and I had to learn about many trees in my youth. Somehow that term never came up. None the less I'm looking forward to seeing this speaker finished and you can share the listening experience.

[Steve Manning]

Very nice ...... I hear ironwood is very hard on tools.

[letiennam]

Excellent CNC work on those baffles, and great colour match of the wood as well! The design is reminiscent of B&W woofer cabs, and I may borrow some design elements here for my own future projects.

thank you. the idea of this speaker appearance comes from Kii three btx and Perlisten S4B. i am very interested in the control and dispersion of sound waves the tweeter produces. with this front panel, i hope it helps the Seas dxt perform well in dispersion of sound waves. i am happy to share the 3d design file if you are interested.

[letiennam]

Very nice ...... I hear ironwood is very hard on tools.

I paid for a new drill bit, which I will use every time I do wood CNC service at my local supplier. However I was told that ironwood still seem softer than bamboo. When CNC on bamboo wood, the CNC supplier broke a drill bit.

[letiennam]

The baffle is gorgeous indeed! I have never heard of ironwood before though, which is rather funny since it is a town in Michigan and I had to learn about many trees in my youth. Somehow that term never came up. None the less I'm looking forward to seeing this speaker finished and you can share the listening experience.

Ironwood seems to be a general term for wood families famous for their hardness and having a specific gravity greater than that of water. The 2 wooden panels I was given are white ironwood, they come from South Africa. Our native ironwood is green ironwood, which is harder and more durable than white ironwood. However, native green ironwood has been banned from exploitation in my country. I also really hope to finish these speakers soon, although my work at this time takes more time, I also have to overtime more.

[Reet]

It looks like Mahogany to me, very nice.

[technodanvan]

This really is quite beautiful, I'm looking forward to seeing it with a finish on it!