PVC pipe speaker?

Hi,

I am planning on making a jbl speaker alternative using the "Dayton Audio TCP115-4" and the SB Acoustics "SB12PFCR-00 Passive Radiator" in a 1.6 liter box with a tweeter i have yet to choose and i have a few questions about my plan:

  • Could i acoustically use a pvc pipe as an enclosure for this
  • Can someone please check my calculations if they get the same results in winisd? I would much appreciate it!
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thanks for reading and hopefully replying!
Nanno Haasjes
 
I’ve built lots of speaker systems from PVC, I don’t think the material is worse than any wood product. I’ve made t-line prototypes, used it for ports, midrange enclosures, and STEM projects. The STEM speakers were cool, one was vented one was sealed. It was cool, I wish I took video. Oh well.

Back on topic, I don’t know how you will implement a passive radiator. A woofer at one end and the PR at the other? A ‘C’ shaped pipe? A large pipe with a wood flat front? I’ve seen PVC used all kinds of ways. Damping a tube may be difficult, bracing as well. If you think you need to brace it brace the outside. 1.6l it shouldn’t be a problem.

Also, look at the many PVC connectors and shapes of joins, joints, and couplers, there are a lot pf possibilities there.
 
Back on topic, I don’t know how you will implement a passive radiator. A woofer at one end and the PR at the other?
Yes that's what i was looking for. Kinda took inspiration from the jbl flip and charge

.
Damping a tube may be difficult, bracing as well. If you think you need to brace it brace the outside. 1.6l it shouldn’t be a problem
By damping do you mean stuffing the thing up with some non sound reflecting stuff? If so does this need to be at just the wall? And hey im kinda new to speaker building, what is bracing😁?
 
Yes that's what i was looking for. Kinda took inspiration from the jbl flip and charge

.

By damping do you mean stuffing the thing up with some non sound reflecting stuff? If so does this need to be at just the wall? And hey im kinda new to speaker building, what is bracing😁?
Bracing is used to make the walls of a box more rigid. You shouldn’t have the problem of stiffening a small 1.6L PVC tube. It should be pretty good as it is.

Damping is stuffing, sound absorbing stuff — everything from tar paper, roofing felt, carpet underlayment, upholstery materials, foam, pillow stuffing, quilt ticking, wool blankets, fiberglass, and rockwool. The issue is getting the right density to limit the resonances, harmonics, and midrange ‘echos’. The next issue is keeping it in place, a bit of glue, or caulk might be better on PVC, to keep the damping in place. The first thing I would try is a cylindrical section of fiberglass maybe 50-75mm thick placed about 1/3 of the way down the tube from the woofer.

Warning, opinion here: In my experience foam and polyester stuffing do very little to damp any resonances. I’m a big fan of wool, if you can find it, and fiberglass, if you can stand the itching.

My default damping material is golden retriever hair. 😉
 
In my experience foam and polyester stuffing do very little to damp any resonances. I’m a big fan of wool, if you can find it
by wool you mean wool that's shaved from an sheep and hasn't been processed in any other way than washing the dirt and sheep poop out of it. Or do you mean processed to string stuff. anyways i can get both.

how much does wool affect the air volume? is this something like 10% slower air or is this more like 5%? or like 20%?
 
do you know how strong this effect is and if this is still true with a passive radiator at one end and the driver at the other end?
??? Its 'strength is a function of its air mass 'plug' + TL resonant length, ergo its stuffing density is damping it down to 'x' Qtp. Adding a PR is a substitute for a vent of the same piston area and its length based on its acoustic mass and assuming we're just adding a vent to the existing tube to lower its tuning, then yes. FWIW, long before we had software me n' others were designing TLs using vent formulas.
 
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do you know how strong this effect is and if this is still true with a passive radiator at one end and the driver at the other end?
The damping affects the higher modes more than the wanted bass frequencies, so there may be room for you to choose the right amount. Keep in mind that you don't want these modes in your passband unless they've been chosen by you to stay.
 
by wool you mean wool that's shaved from an sheep and hasn't been processed in any other way than washing the dirt and sheep poop out of it. Or do you mean processed to string stuff. anyways i can get both.

how much does wool affect the air volume? is this something like 10% slower air or is this more like 5%? or like 20%?
Yes, long fiber wool is the best in my opinion. It seems everyone has their favorite though. You’ll have to wash it with detergent thoroughly to get out not only the poop and dirt but the oils as well. Wool will increase the volume slightly; since wool is a natural fiber it varies a lot and I don’t know of any solid figures on how much it affects air volume.

You hit on a big misconception about damping, it doesn’t slow down the sound. I remember an article in Speaker Builder where various types of stuffing were applied to a simple transmission line speaker, a straight pipe like yours. One of the tests was an impulse test to measure the speed of sound through the pipe. All of the stuffing measured the same as an open pipe except for the size of the impulse. The speed of sound doesn’t change. What happens is the sound gets filtered, most notably the higher frequencies and overtones. The higher frequencies get caught by the fibers as vibrations and get turned into heat. I prefer to do the stuffing by ear because the shape of a t-line can filter out upper frequencies too.

In your case I would build the speakers without any stuffing. Then listen to them. If the voices have too much sibilance or seem edgy or barky then try some damping. Increase stuffing as you need it and stop when it sounds like someone with a mouth full of bread. Then take some out and you’re done. I find I end up over stuffing and then have to take some out. You want to reduce the harmonic that is at the length of the pipe, which for your pipe should be a relatively high frequency. Which is good because that’s where wool is most effective.

For quick and dirty, you can put in a pretty dense softball sized (15cm ball) amount in there about 1/2-1/3 of the way down behind the woofer and you should be very close to what you need.