custom small speaker box from solid log - to vent or not to vent

Thread Starter

pmeysemb

Joined Jan 8, 2018
7
Hi folks.
Since this was a bit of work to do, I'm looking for some advice.

I am basically hollowing out a fairly large aspen log (with a CNC) and re-using some old 4 inch speakers I saved from an old 5.1 system. I'm doing this project to teach my son that building things is an okay alternative to buying them.

I seem to recall that the old plastic enclosures that I had to destroy to get the speakers out had some very small ports molded into them. I'm wondering if it would help if I put a similar port into the face of my log speakers. Obviously, drilling into the faces of the log is a commitment!

I am going to power this with a small, new simple receiver like a Pyle 2X15 or maybe even a 2X30 (or50!). (something like the PCAU22)

Do you think this is necessary? Any thoughts?
Thanks.
 

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Thread Starter

pmeysemb

Joined Jan 8, 2018
7
That would be no. I imagine I'm (or my son) will use this more as a "boom box" style or bedroom system. I plan on attaching the small receiver right to it so it will be nice and portable.
 

Alec_t

Joined Sep 17, 2013
11,737
Have you researched loudspeaker enclosure design? There are numerous designs (some ported, some not) and calculators, available on the web. The ideal volume takes the natural resonance of the driver (loudspeaker) into account.
 

MrChips

Joined Oct 2, 2009
22,069
Hollowing out a large aspen log sounds like an ambitious effort to me. You did not state the size and volume of the enclosure.

Edit: I did not see the photo before. Very impressive setup you have there.

Loudspeaker and enclosure basics
Every loudspeaker has a natural free-space resonance frequency at the low end of the frequency spectrum. Hence the sound level peaks at this low frequency resulting in a booming effect. When the speaker is enclosed in an air-tight enclosure the resonance frequency rises.

The theory behind ported enclosures known as bass reflex speakers is to divert the pressure wave from the back of the speaker towards the front through the port and out of phase with the front wave. The aim of this is to suppress the resonant frequency and hence produce a flatter frequency response. To get the port to work correctly at the right frequency the port must be tuned by adjusting the area of the opening and the length of the duct.

This works well with large loudspeakers and large enclosures.

Having said this, I believe that it would take a lot of effort to achieve this easily with a hollowed out log and such a small loudspeaker (4-inch). My suggestion would be to omit the port and line the interior walls of the enclosure with sound absorbent material such as wall insulation.
 

Thread Starter

pmeysemb

Joined Jan 8, 2018
7
Hollowing out a large aspen log sounds like an ambitious effort to me. You did not state the size and volume of the enclosure.

Having said this, I believe that it would take a lot of effort to achieve this easily with a hollowed out log and such a small loudspeaker (4-inch). My suggestion would be to omit the port and line the interior walls of the enclosure with sound absorbent material such as wall insulation.
Thanks MrChips. Yes, the hollowing out part was ambitious, but what better things do I have to do with my time when it's -20 outside. :) I used the CNC to do the opening and the "front" side of the log and used the plunge router to clear enough space in the "back" side of the log for the driver clearance. The original plastic enclosures had small ports but it looks like they were more decorative rather than effective. I suppose they did this for looks and for the fact that they can easily mold plastic.

I'll go with no ports and see if I'm satisfied. I suppose I can always tear it apart and carve some ports later, too. I found another set of bigger speakers from an old car audio install that might require real ports. I just may try them with that project. Thanks for the advice.
 

Travm

Joined Aug 16, 2016
324
Wooden clamps on the CNC. I like it. Do let us know how your speaker turns out. I think i'd also love it if you took about 5 steps back and posted a picture of your shop!
 

Thread Starter

pmeysemb

Joined Jan 8, 2018
7
An update: I finished the initial speaker log with no ports and it sounds pretty good (for a set of 4" speakers) Then, after looking a while, I found an old set of 5.25's from an old car audio install so I decided to do another one. For the bigger one, I decided to use ports (as good as I could do them). I figure the ports are about 7" long by 3/4" (as I used a forstner bit to cut them). I can't get a log this size under the CNC router anyway. So, anyway, the ports are working great in the larger speaker set. I can feel lots of air moving through them at higher volumes. I'm not exactly sure they improve sound quality, but my son was impressed by the amount of air moving through them! I made a space for the small Pyle amp on the back. I'm still thinking about a handle for one or both of these.
Here's the small one:
20180117_075645.jpg
..and a few of the the larger one:
20180117_075700.jpg

20180117_075719.jpg

20180117_075739.jpg
 

Thread Starter

pmeysemb

Joined Jan 8, 2018
7
A few hours for each one. Since I can't get the "back" pieces under the CNC, I had to hog them out by hand with a long reach bit. That was the hardest part. I'd guess I spent about 3-4 hours total on each log.

Now, I'm thinking about whole set, including a subwoofer. :)
 

MrChips

Joined Oct 2, 2009
22,069
Better you than me. I built my own pair of speakers the conventional way, 3-way system with tweeter, mid-range and 15" woofers. Each speaker enclosure is 36" tall.
 

Thread Starter

pmeysemb

Joined Jan 8, 2018
7
Why do you have two speakers? For stereo? You would need to wear the speaker box around your neck to hear the stereo effect.
Well, I was going to cut them in half, but that kind of defeats the portability aspect. :(

For the small one, my initial thought was like an old boom box. I think they'll both make good conversation starters at parties. :)
 

Thread Starter

pmeysemb

Joined Jan 8, 2018
7
Why do you have two speakers? For stereo? You would need to wear the speaker box around your neck to hear the stereo effect.
Also, I suppose for the same reason these do? They're getting over $400 for these little gems. https://store.thodio.com/products/thodio-ibox-mini-high-density-tiger-stripe-bamboo
https://store.thodio.com/products/thodio-ibox-mini-high-density-tiger-stripe-bamboo
I suppose mine would be the "poor person" version, then. (like all the rest of my stuff) :)
 

Audioguru

Joined Dec 20, 2007
11,249
They have two stereo speakers close together so they can sell at double the price and make double the rip-off. Bose makes a portable little Bluetooth stereo speaker and it sells for $200.00. It sounds great for its tiny size. My son bought me a cheap Chinese copy but its bass is poor.

All raw half-decent speakers have a detailed datasheet listing all the important spec's and a recommended enclosure design.
 
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