[BoomieMCT]

So I started a project today. It is sort of the result of the following facts;

1. I've been looking into open baffle and transmission lines a lot recently.
2. I have extra parts (things I bought because they were interesting / on sale) lying around.
3. My dad needs "ambient" speakers for his living room.

I was kind of inspired by the Linkwitz Plutos. The woofers are Audax HP170M0 that I bought because they were cheap and I wanted to test them for open baffle use. The tweeters are Tang Band W1-1070SEs I bought because they looked cool and I wanted to test them. I'm currently using a first order Butterworth x-over crossed over at 900 Hz (although the tweet takes a dive before that - not sure why). The Pluto uses a 4LR crossed at 1000Hz - this is the best I could do with the parts available on hand.

I have tested the woofer enclosure as a stuffed transmission line, sealed and with a port. I think I like the TL setup the best. It wasn't the lowest reaching, but it sounded the most laid-back and natural. I haven't built a stand yet which is why it is standing on two boxes. I have included a plot of FR with the mic in the bottom of the port (no stuffing on that plot though).

 

[BoomieMCT]

Here is a closer shot of the construction of the top. Right now the tweeter is just sticking in that hole. I will build a nice face for it to attach to. The back of it is not closed. I'm not sure if I should build a sealed back for it. The tube should be pretty well stuffed to absorb high freqency.

 

[BoomieMCT]

Not bad looking for speakers I thought of and started yesterday. This is the tops. The stands are still drying.

 

[Anthony]

Lookin' good. I'm glad my "shim" tip paid off (I told him to use sandpaper taped to the PVC to shave the tweeter baffle to exactly the right contour).

When's the crossover going to be done? Or are you still breaking in the woofers?

 

[BoomieMCT]

Lookin' good. I'm glad my "shim" tip paid off (I told him to use sandpaper taped to the PVC to shave the tweeter baffle to exactly the right contour).

When's the crossover going to be done? Or are you still breaking in the woofers?

You mean this crossover? I'm still playing around but I'm probably going with a simple first order Butterworth. It will eventually be *in* the tube instead of on the ground.

 

[BoomieMCT]

Done. Breaking in now. The omni-sound is excellent - the soundstage is almost as big as my OBs. I haven't done a FR yet but this does upright bass fine, so I'm guessing an F3 of 65ish. *Much* easier to get bass out of these then open baffle.

 

[wig]

Looks like a good project.Can't wait to see the end results.I think I mite build me some.I'll let do all the work first.lol:bigsmile:

 

[BoomieMCT]

Looks like a good project.Can't wait to see the end results.I think I mite build me some.I'll let do all the work first.lol:bigsmile:

It's not much of an investment to play with.

(2) Audax HP170M0 6-1/2" Paper Cone Woofer ($26)
(2) Tang Band W1-1070SE 1" Full Range Driver ($22)
(2) 47uF capacitors ($2)
(2) 0.7mH inductors ($8)
(2) Binding posts (I love these ones but they are overkill, $12)
(2) 40 inch long 6" Schedule 40 PVC pipes ($30 for one 10' piece)
I used two cans of Rustoleum stone textured paint which was another splurge, ($16)
About $5 worth of Acoustafill.
The wire and what MDF is needed most DIYers will have lying around.

So, my pair is $121. I'm sure one can use other componants - my selection was mainly governed by what I had lying around. Also, these are easy to build ported or sealed if one prefers.

A friend of mine said these remind him of the GR-Research AV-0's. I'll take that as a compliment. Had I planned these out I might have used the Dayton 7" reference woofer and a higher order x-over. As it is, I'm pretty happy with these.

 

[wig]

Thats cheap boomie.I need rear surround's badly.this seems to be just what I need.

 

[BoomieMCT]

Thats cheap boomie.I need rear surround's badly.this seems to be just what I need.

Cool. You can cut $25 off the price by using non-textured paint and Radio Shack binding posts. If it helps here is a pic of all the wood parts needed. A circle jig for your router is basically required.

One set of circles fits over the top on the outside of the tube and allows the woofer to fit. Mine is held in with two screws in the back and the tweeter's faceplate on the front. The woofer is screwed into the edge of the PVC pipe (doesn't touch the MDF at all!).

Another set of circles goes in the bottom on the inside of the tube. In my case (since I went TL) these are only about a half inch wide all around. I drilled four 3/8" holes in these (half on the MDF half on the PVC) to put the leg dowels into. You could make this a ported or sealed design by easily modifying this piece. This is held in by four screws around the edge.

The tweeter fits into a 1 1/2" hole I drilled with a hole saw bit. I made the tweeter faceplate / shims from 1/4" MDF. I used Anthony's tip to get the back curve right by gluing sandpaper to some extra 6" tube and using that to sand the back of the faceplate. The tweeter and its faceplate is held in by four #4 x 1/2" brass screws.

The baseplate is just a square of MDF. The legs are four oak 3/8" dowels. I think I cut them 4" long. I use four rubber stickies for feet - you can easily put spikes or whatever on if you like.

The only tip is that I drilled a 3/8" hole through the side of the PVC tube about 6" up from the bottom. I ran a dowel through there and sanded the edges flush. This is to keep the stuffing from falling out of the tube. This is best done before painting!

 

[BoomieMCT]

About the crossover

There was another thing I wanted to mention. Since these are designed to be placed away from walls I was concious about baffle step diffraction. Since the woofer basically has no baffle other then its own cone, the F3 of the baffle step would be at about 900 Hz (see attached graph). Instead of using a BSC in the crossover (which I was trying to keep simple) I relied on the fact that the crossover is at 900 Hz and that the woofer has a natural 7dB advantage in sensitivity over the tweeter. That gave me a starting point from which I played with the x-over values a bit.

 

[wig]

Hey boomie,If I use the 7'' speakers I'll need to move up to 8''pvc.the wood ring on the top mite need to be moved inside the pvc.will they mest with my sound?

 

[BoomieMCT]

Hey boomie,If I use the 7'' speakers I'll need to move up to 8''pvc.the wood ring on the top mite need to be moved inside the pvc.will they mest with my sound?

8" PVC is not carried by the Lowes and Home Despots here. It can be obtained through special order but it would get quite expensive then (almost $100). The cutout hole for the 7" drivers are 5 3/4" inch so they should still fit (6" pipe is a 6" inner diameter, not outer). I never really know what will actually fit until I have the pieces in my hands and play with them for a while (which is why I had leftover parts in the first place).

Since I posted my desire to use them I have thought of one drawback; I know the TL enclosure works well with drivers with an Fs of 65 Hz. The Dayton 7" reference series has a much lower Fs (in the 30's I think) so it might not tune the same. It should work fine in the same enclosure with a port though.

Other thoughts include replacing the Tangband tweeter with a Hi-Vi B3N (rated highly on ZaphAudio). The larger driver would be harder to mount into the side of the tube though. . . .

 

[BoomieMCT]

I was asked to make some better pictures / descriptions of this project. The first picture is a detail shot of the tweeter assembly. I chamfered this out as best as I could, it really smooths out the response around 1.5kHz. I'd like to seal the back but haven't figured out what to use to do that. The second picture is the inside of the top of the tube. Here you can see the tweeter opening into the main compartment. The fluff at the bottom is Acoustastuff. The last picture is a detail shot of the bottom of the tube. There are dowels on the inside of the tube that keeps the Acoustastuff from falling all the way out. Other then that I put just enough lip on the inside of the tube to fit the legs.

The last picture is a quick FR.

 

[Guest]

Boomie, did you use the same 6" PVC to test TL, sealed and ported? I did a little research on TL out at http://www.t-linespeakers.org but it got my head spinnin a bit. If you used the same pipe for each, what did you change for each enclosure type?

 

[BoomieMCT]

Boomie, did you use the same 6" PVC to test TL, sealed and ported? I did a little research on TL out at http://www.t-linespeakers.org but it got my head spinnin a bit. If you used the same pipe for each, what did you change for each enclosure type?

Yup. The only thing I changed was what got screwed into the bottom of the pipe. You may be able to tell from the pics above the bottoms are just 6" diameter MDF circles that are screwed in through the side of the PVC. I made three bottoms - an open one for TL (shown), one with a port and a sealed one. Actually the sealed one became the ported one so I guess I only made two.

 

[BoomieMCT]

I couldn't figure out a way to seal the back so I made a notch filter to tame the spike I kept getting at 1kHz. L = 0.10 mH, R = 6.5 ohms, C = 33 mF. I've been listening for an hour and may claim sucess.