What do you guys/gals think of PVC for FR enclosure?

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
FR driver and PVC tubing

Trying not to hijack thread here. But it's relevant. FR driver and pvc tubing.
I'm planning on trying to produce a BIB using pvc tubing with divider in the middle and ff125wk driver.
I realise the dimensions won't be narrow and deep like a regular BIB and the mouth up top won't expand either but if volume is right acc to the calculator could it still work okay?
I'm using pvc as I have no woodwork skills apart from being able to rout circles.
 
Zarathu, thx a mil for posting. A couple questions I have out of curiousity, since I'm experimenting out of my realm....

1) Would there be any value to mixing square enclosures amongst the tubes so one gets a mix of even and odd harmonics?

If the purpose is to reduce harmonic back flow through the speakers why would you want to increase it? And why would you want to increase the one which doesn’t bring clarity to the music?

2) Why does the fiberglass heat up from the sound waves in your opinion? And at what SPL levels?

Dickerson’s research is a long long article. I have no idea, why fiberglass is more effective. Im sure there is something in the physical properties of fiberglass material, but I’m not a physical chemist, so I have no idea.

In my line arrays, I have to really push them, and since each speaker only produces 1/17(5.8%) of the total sound of the array per channel in the mid range, the SPL is negligible. Suppose they are producing 75 db. This means that each speaker is only producing 4.5 db, which is lower than a whisper.

The warmth I feel is after a few hours of use as the total sound collects.

I suggest you purchase the book.

Most people just use very heavy boxes; you probably should too.
 
Be sure to look into some claims made here a little deeper. On audibility of harmonic distortion personally I'd avoid third order even if it has been said to enhance perception of detail in some cases. One should realize that the detail which is perceived isn't real. Not something I'd want in any form or way. It probably won't work out that well on all types of music either.

Boominess often is a frequency response problem. Arraying more and more drivers will change overall frequency response. Room modes can play a role too. Don't guess, measure!

If anything, most people would prefer 2nd order harmonics over 3rd. They tend to sound more musical. At least that's what I've been able to find in most studies on this subject. I'm not saying you should want any of them in any large quantities though.

Fiberglass certainly is an affordable sound absorber that works over a wide frequency range. Perfect for use in sealed enclosures, not as much for ported ones as you shouldn't want those fibres flying freely.

To see the effectiveness of any damping material in your enclosures compare the impedance curve of the speaker within the enclosure to a free air curve.
 
Be sure to look into some claims made here a little deeper. On audibility of harmonic distortion personally I'd avoid third order even if it has been said to enhance perception of detail in some cases. One should realize that the detail which is perceived isn't real. Not something I'd want in any form or way. It probably won't work out that well on all types of music either....

I intend to and I see Vance Dickason's book is now up to the 7th Edition.

But before I can do that, it's onward with the construction. Today, I'm headed into work to make PVC dust. I have to shave off 20 PVC encaps flat to mount the P7's. I also am going to try to paint 4 of the mounts gloss black using Krylon Fusion spray paint. Then a few coats of Krylon Fusion Clear. Maybe I'll paint 1 tube as well, just for a pic I'll post later today.

I received the last 4 P7's from Madisound yesterday, but forgot to order the binding posts! I'll have to rush ship them...

The remaining 20 magnets should be here tomorrow...

This Wednesday, I should have a first listen to 12 P7's per side.
 
Be sure to look into some claims made here a little deeper. On audibility of harmonic distortion personally I'd avoid third order even if it has been said to enhance perception of detail in some cases.

In a line array there isn’t any distortion, so we are not talking about harmonic distortion in the back wave of sound. Even if I run my speakers at 120 db, each mid range speaker is only asked to put out 6 db of that, and so there is no harmonic distortion in the back wave at all. Additionally, the amount of harmonics that come through is small after being absorbed by the fiberglass.

So we are only talking about the small amount of harmonics 180 degree out of phase which comes back through the speaker cone and muddies the sound. You won’t actually hear it due to the Haas effect since it will be only a couple of millisec after the original sound, but it will be perceived as a muddying effect.

And even order harmonics bring a bigness to the sound, whereas 3rd order brings clarity and timbre. If you use tubes as your cabinet, then you won’t have any even order harmonics coming back through the wave since the physics of sound in a closed tube simply doesn’t allow even order harmonics to be produced. So the back wave consists entirely of the original sound 180 degree out of phase and odd order harmonics. But remember since the line array is not producing distorted harmonics, its only the natural harmonics of the music itself.

You have to understand the physics of what is happening here and not get confused with thinking we are talking about harmonic distortion or not understanding the physics of sound.
 
Well I perfectly understand the physics of both line arrays and harmonics, yet I do not agree that 3th order harmonics bring clarity. Any deviation from the intended direct sound would still be distortion. If it seems to bring clarity it would still be a deviation from what should have been heard. I know what you're getting at, I just wouldn't want that.

Sorry to say but I disagree whole hearty with your claim here.

This also has nothing to do with the Haas effect. All kind of harmonics propagating back trough the cone would definitely be a form of distortion. No way around that.
 
And even order harmonics bring a bigness to the sound, whereas 3rd order brings clarity and timbre. If you use tubes as your cabinet, then you won’t have any even order harmonics coming back through the wave since the physics of sound in a closed tube simply doesn’t allow even order harmonics to be produced. So the back wave consists entirely of the original sound 180 degree out of phase and odd order harmonics.
Are you talking about the harmonics produced by the speaker/cabinet or the effect of harmonics on timbre? The harmonics of interest already exist in the signal, it is not desireable to add or subtract (distort) them
 
I'm liking the sheen of this paint. This is just the first coat of gloss black on 3 of the backsides of the tubes and 4 mounts. More to come...

Tacky in 15 minutes. 30 minutes dry enough to handle.
 

Attachments

  • P1070252.jpg
    P1070252.jpg
    479.1 KB · Views: 123
Last edited:
Sorry to say but I disagree whole hearty with your claim here.

No offense, but you don’t understand what I’m talking about, claim or not.

So we’ll just have to let it go since I’m not going to go into explaining the physics of even and odd order harmonics in music(as well as their effects on perceived sound) and the physics of sound propagation in closed cylinders.
 
...I’m not going to go into explaining the physics of even and odd order harmonics in music(as well as their effects on perceived sound) and the physics of sound propagation in closed cylinders.

That's what this is all about people! I'm transitioning from a rectangle to a tube enclosure for this array. Zarathu has given some good insight, although I've not read the suggested book yet.

I aimed for a smallish tube, close to sphere, because of the diffraction results posted by Dave earlier in this thread
So observe the "cube" response and since this is the same as rectangle, one sees my "boomy" statement realized from this enclosure.

olsen-baffleshape-fr.gif
 
Last edited:
Supply some literature that supports these claims.

I've read a whole lot of them and the general agreement does not fit your description at all.

Start with showing how second order wave coming back trough a cone can cause boominess... That's a pretty big one right there. It would need to include measurements to show us what happens. I'm not going to assume you're right. Even all AES graphs I've come across claim the opposite of your story here.

Don't let it go, educate us!

Edit: Every even and odd harmonic I aim to hear has already been recorded and is in the songs I play. I have no desire to add any more to that.
I've done the best I could to limit what my speakers and room add here, second order would be the most forgiving as it's easier masked. Yet I'd try to keep all added harmonics to a minimum. This starts with using speaker drivers with shorting rings.
 
Last edited:
That's what this is all about people! I'm transitioning from a rectangle to a tube enclosure for this array. Zarathu has given some good insight, although I've not read the suggested book yet.

I aimed for a smallish tube, close to sphere, because of the diffraction results posted by Dave earlier in this thread
So observe the "cube" response and since this is the same as rectangle, one sees my "boomy" statement realized from this enclosure.
olsen-baffleshape-fr.gif

You do realize that a driver in the middle of a cylinder corresponds pretty good to the 3rd picture, right? The radius of your endcap will determine the success of it's anti diffraction shape (that's what these pictures show).

The sphere has to have a pretty big radius to be effective over a wide enough frequency area (Think B&W 800 series)

attachment.php
 

Attachments

  • BW802.jpg
    BW802.jpg
    99.5 KB · Views: 199
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.