Tubifex writeup finished!!!!

[Paul Carmody]

I did this project last fall. I was actually very proud and pleased with the results. I just never got around to actually doing a formal writeup.

http://sites.google.com/site/undefinition/diy/tubifex

The project doesn't have a real paint job yet. I made them for my friend, and he said he'd decide how he wanted to finish them. Still waiting for a verdict....

addendum: I did this writeup in tiny fragments in-between tending to "baby matters" around the house, so there may be errors. Let me know so I polish it up.

[jkim]

Speakers look awesome, Paul. Really nice with measurements of the finished system, too. One thing I can say is about the following,

"The acoustic slopes are pretty steep (6th order LR or so). It's not how I would have originally chosen for things to turn out; but the inductance on the woofer gets REALLY intense by about 2500 Hz, so there's no real way to get the woofer's acoustic slope any shallower without negating the notch filter--and you still have a massive impedance spike to deal with."

The slope may look like 6th order around the xover frequency. But it's only because the RS125 has a cliff from 2.8 kHz to 3.5 kHz in its raw response. The crossover topology you used cannot produce a Linkwitz-Riley 6th order acoustic filter when used with the RS125. If you look at your filter slope beyond what is shown---yes, the crossover's phase characteristic is affected by a driver's rolloff way beyond the crossover frequency---, you will see that the overall rolloff is 4th order (perhaps a bit lower than 4th order). Moreover, the tweeter is wired in normal polarity. And the drivers' acoustic centers are pretty much aligned. So, technically this is a 4th order LR design, even with steepness around 3 kHz and a notch at 12 kHz on the midwoofers' rolloff.

Jay

[LouC]

I like these. Simple & high tech looking. Might be right at home with chrome & glass modern decor. Looks like they could be painted or use the self stick vinyl veneer.

If they sound right, they are right. I have no doubt your ears are well educated.
So how do they do with all those contemporary, over compressed, badly engineered recordings?

I loved your comments about 93 db being "loud" (IMO it really is). Gotta wonder why people talk about needing 110 db capability in their homes.

[frost_51]

Sexy speakers Paul.

Is PVC a suitable substrate for any type of veneer?

[rone]

Tubifex are worms that live in sewage - used to have aquariums - FYI
Interesting speakers, though.

[Paul K.]

People who listen at 110 dB SPL have to have lost most of their hearing long ago. 90 dB, at 1 meter, is louder than I like usually.
Paul

I like these. Simple & high tech looking. Might be right at home with chrome & glass modern decor. Looks like they could be painted or use the self stick vinyl veneer.

If they sound right, they are right. I have no doubt your ears are well educated.
So how do they do with all those contemporary, over compressed, badly engineered recordings?

I loved your comments about 93 db being "loud" (IMO it really is). Gotta wonder why people talk about needing 110 db capability in their homes.

[J.Lee]

Thank You for finishing these.... thought I'd missed them.

[Paul Carmody]

The slope may look like 6th order around the xover frequency. But it's only because the RS125 has a cliff from 2.8 kHz to 3.5 kHz in its raw response. The crossover topology you used cannot produce a Linkwitz-Riley 6th order acoustic filter when used with the RS125. If you look at your filter slope beyond what is shown---yes, the crossover's phase characteristic is affected by a driver's rolloff way beyond the crossover frequency---, you will see that the overall rolloff is 4th order (perhaps a bit lower than 4th order). Moreover, the tweeter is wired in normal polarity. And the drivers' acoustic centers are pretty much aligned. So, technically this is a 4th order LR design, even with steepness around 3 kHz and a notch at 12 kHz on the midwoofers' rolloff.

Thanks for checking it out Jay. I think you're right about the slope. I'll have to look at a graph with a larger scale to be sure.

So how do they do with all those contemporary, over compressed, badly engineered recordings?

Excellent question. You know, the more designs I do, the less I am wanting to make my speakers "analytical sounding," and instead I relax certain frequencies a little bit to make the speaker more enjoyable in the long run (and also allowing more music to be played through them, even if the recording/mastering isn't perfect).

Is PVC a suitable substrate for any type of veneer?

I have no idea. The only reason I think it wouldn't would be if PVC tended to shrink or expand with changes in temperature or humidity. But I don't know if PVC does that.

Tubifex are worms that live in sewage

I know, isn't it great! My wife thought of the name; she's a biology teacher. I figure sewer pipes/sewer worms... why not?

[DaytonPioneerRules]

I like these. Simple & high tech looking. Might be right at home with chrome & glass modern decor. Looks like they could be painted or use the self stick vinyl veneer.

If they sound right, they are right. I have no doubt your ears are well educated.
So how do they do with all those contemporary, over compressed, badly engineered recordings?

I loved your comments about 93 db being "loud" (IMO it really is). Gotta wonder why people talk about needing 110 db capability in their homes.

it would depend on what frequency hit the 110 db. if a 1khz signal hit 110db youd start running. but if a 15hz signal hit 110 db you wouldnt hear it in the slightest. there are graphs of human frequency responce you can look up. the human ear is most sensitive at 1k - 2k hz. infact the frequency range an "average" person will even perceive as sound is usually 18-18k hz

[Sibelius40]

Wow - cool lookin' build. I may do these as a Christmas present for my brother who has a somewhat modern decor to his house. Thanks for publishing this...

[spasticteapot]

You'll pardon my asking, but do you have any xover-less in-box measurements? Especially for the tweeter? I tried modelling something like this in the EDGE and, well....it wasn't pretty.

[robert]

Since Pontifex is "high ranking priest," "Tubifex" could be "high ranking tube" Too bad we won't get to hear them!!!

Cheers / Robert

[jamikkim]

I think I like these better than "Totally Tubular" in terms of looks, although I would try and go with a different colour

Is there any reason why the tweeter tube in both designs isn't even smaller in diameter?

[john trials]

Is there any reason why the tweeter tube in both designs isn't even smaller in diameter?

I'd like to know this, too (although the tweeter tube houses the crossover, so making the tweeter tube smaller diameter could be a problem).

1) Could the tubes be mounted directly to each other (maybe with the tweeter off of the vertical centerline a bit), totally avoiding the 1" spacers?

I thought there was an advantage to having the drivers as close to each other as possible in an MTM configuration, and offsetting the tweeter was better when the speakers are not toed-in (although with these, there should be little high frequency diffraction, correct?).

2) Would eliminating the spacers and offsetting the tweeter require crossover tweaking?

Keep in mind: I'm not criticizing the design...just trying to learn more about speakers. I have some 6" PVC tubing, so this design is tempting me!

[Paul Carmody]

I used 4" PVC for the middle tube because 3" PVC made things look disproportionate; also the 3" doesn't have much "contact area."

1) Could the tubes be mounted directly to each other (maybe with the tweeter off of the vertical centerline a bit), totally avoiding the 1" spacers?

Sure, you could take out the spacers. I'm not sure if that would help or harm the rigidity of the speaker. I did them because that's how Mike V. did his Tubulars.

I thought there was an advantage to having the drivers as close to each other as possible in an MTM configuration, and offsetting the tweeter was better when the speakers are not toed-in (although with these, there should be little high frequency diffraction, correct?).

Well, when drivers are closer together, you can sometimes reduce comb filtering. I suppose in the Tubifex the driver spacing is a bit less than optimal, but from a normal listening distance of 2 meters or more, the vertical listening window is pretty big and comb filtering shouldn't be a problem.

Offsetting tweeters is actually more advantageous for those who toe in their speakers. Think about it: when a tweeter is centered, and the speaker is pointed straight at you, then you will get twice the diffraction at certain frequencies. If you offset the tweeter, it is no longer equidistant from the sides of the baffle, therefore you won't get quite as pronounced "diffraction peaks"

2) Would eliminating the spacers and offsetting the tweeter require crossover tweaking?

Nope. You can always move drivers closer together. It's spreading them apart that's dangerous (see "comb filtering above")

[dian1511]

Really slick. They look like they would fit into or with more modern decor...or under the wings of a starfighter. Intergalactic worms?

Darren

[john trials]

I used 4" PVC for the middle tube because 3" PVC made things look disproportionate; also the 3" doesn't have much "contact area."


Sure, you could take out the spacers. I'm not sure if that would help or harm the rigidity of the speaker. I did them because that's how Mike V. did his Tubulars.


Well, when drivers are closer together, you can sometimes reduce comb filtering. I suppose in the Tubifex the driver spacing is a bit less than optimal, but from a normal listening distance of 2 meters or more, the vertical listening window is pretty big and comb filtering shouldn't be a problem.

Offsetting tweeters is actually more advantageous for those who toe in their speakers. Think about it: when a tweeter is centered, and the speaker is pointed straight at you, then you will get twice the diffraction at certain frequencies. If you offset the tweeter, it is no longer equidistant from the sides of the baffle, therefore you won't get quite as pronounced "diffraction peaks"


Nope. You can always move drivers closer together. It's spreading them apart that's dangerous (see "comb filtering above")

Paul, thanks for the quick response, and great explanation.