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Re: Two PI: A Little Bright OR Light in the Bass? [message #76206 is a reply to message #76131] Sat, 06 April 2013 00:07 Go to previous messageGo to next message
my0x is currently offline  my0x
Messages: 23
Registered: October 2012
Location: Huntington, NY
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Nice build...I like the rabbeted joinery with te Finnish ply & cork!

m@
Re: Two PI: A Little Bright OR Light in the Bass? [message #76229 is a reply to message #76206] Sun, 07 April 2013 20:00 Go to previous messageGo to next message
themilford is currently offline  themilford
Messages: 66
Registered: May 2009
Viscount
Thanks! I'm really happy with the way they look too.

So, today I got around to restuffing these with proper fiberglass insulation. I got equivalent to R11 sans the paper backing.

I ended up covering the bottom, one side and the front. I made cutouts for the drivers and used some spray tack to make sure the stuff stayed on the walls... The rear wall already had a sheet of felt glued to it. For giggles I also put one more slice of fiberglass on the top wall as well... so two short walls, a long wall and the front with cutouts...

And woah! Pretty deep bass on par with my Audio Notes. I realized now that I sized these cabinets just ever so slightly smaller than the plans specified... so I bet some of the issue is coming from there... I built these a while ago, I'm not sure what I was thinking at the time why I made those changes... I should have kept my notes... but I remember doing some figuring with the various box calculators online. Who knows... All I know is the next pair I do will probably be towers... or something in between.

BTW: I like the sound of these with the smaller gauge, .60mH coils over the 14ga .50mh I had in there... it's for sure a smallish difference but it seems to tame that vintage upper midrange (low treble?) a tad and possibly bring out a little more of a bump around 100hz... not sure why, but I can hear that.
Re: Two PI: A Little Bright OR Light in the Bass? [message #76231 is a reply to message #76229] Sun, 07 April 2013 20:39 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 17605
Registered: January 2001
Illuminati (33rd Degree)

Ouch, yeah, I hate to say this 'cause they look so good. But the box as designed is pretty much as small as you want to go with those drivers. With the port too short and the box too small, the alignment shifts even further, de-emphasizing the bass and over-emphasizing the lower midrange...

Re: Two PI: A Little Bright OR Light in the Bass? [message #76245 is a reply to message #76231] Tue, 09 April 2013 08:05 Go to previous messageGo to next message
themilford is currently offline  themilford
Messages: 66
Registered: May 2009
Viscount
I just measured my box out and I ended up building mine at approximately .02 ft3 smaller... I think this was an accident. As you can see I made them slightly narrower but I made them deeper to make up the volume... I think I must have fudged it a little when I started assembling them.

Either way, fixing the port length and swapping the stuffing made a HUGE difference.

Quick question... I'd like to make a larger box for my next pair but don't wanna go a big as the tower... would their be a benefit to say going with a 2 to 3 ft3 box? I assume for port length I would just calculate for a 40hz port?

Re: Two PI: A Little Bright OR Light in the Bass? [message #80479 is a reply to message #76092] Sun, 14 September 2014 12:55 Go to previous messageGo to next message
themilford is currently offline  themilford
Messages: 66
Registered: May 2009
Viscount
Hey Wayne,

I asked this a while back and didn't receive and answer:

"Quick question... I'd like to make a larger box for my next pair but don't wanna go a big as the tower... would their be a benefit to say going with a 2 to 3 ft3 box? I assume for port length I would just calculate for a 40hz port?"

I'm building a pair of these for a friends and the towers are too big for his space... but he'd like the benefit of floor standers and maybe slightly stronger bass... is there a size/volume in between the regular 2PI and the 2PI tower that will work?

Thanks!
Re: Two PI: A Little Bright OR Light in the Bass? [message #80482 is a reply to message #80479] Sun, 14 September 2014 19:30 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 17605
Registered: January 2001
Illuminati (33rd Degree)

The problem with stretching the standard model to form a tower is that standing waves develop inside. Our tower was mathematically modeled to make sure neither the midwoofer nor the port are in a pressure node at lower midrange frequencies, which prevents response ripple. This was verified with measurements, of course. So there's your problem - You probably shouldn't modify the designs unless you can validate them with measurements.

Re: Two PI: A Little Bright OR Light in the Bass? [message #80913 is a reply to message #76092] Tue, 09 December 2014 12:11 Go to previous messageGo to next message
themilford is currently offline  themilford
Messages: 66
Registered: May 2009
Viscount
Ok, making my next pair for a friend.

I'm using 3/4" Finland Birch this time so I'm slightly increasing the size accordingly. will be locating the port on the front this time as well...

One question, I don't have tube stock for the port so figured I can sandwich a 2.25" square of stock to the front baffle making up the 1.875" length of the port and drill a 2" hole through that. This should add some mass and bracing to the front. But I notice that the plans call for the port I.D. to be 1.91" and my bit is exactly 2". how would I adjust the length of the port to make up for this?

Also, is it ok to center the port on the bottom?

And finally, has anybody put in the time to measure out a slightly smaller TwoPi Tower? I would love to simply double the volume of the regular TwoPi but I don't have the software or knowledge to work this out. Having a TwoPi with a tad more bass that that doesn't need a stand but isn't as huge as the TwoPi Tower would be fantastic for me and my WAF.

Cheers,
DJ
Re: Two PI: A Little Bright OR Light in the Bass? [message #80914 is a reply to message #80913] Tue, 09 December 2014 15:27 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 17605
Registered: January 2001
Illuminati (33rd Degree)

Your comments are right in line with my impressions too. The two π model has a lot in common with Audio Note speakers. The bookshelf version is a little smaller , so has a slightly higher f3 and the tower version is larger, so has lower f3. But both models have the same tonal character as Audio Notes.

I also agree with you on the coil. I don't even offer a larger guage option because I prefer the 18gu coil.

The first speakers I ever built were one π and two π models. Those have been staples of mine for decades. Even after I moved towards uniform directivity designs, I've always retained the one π and two π models. They're simple designs that sound very good.

Re: Two PI: A Little Bright OR Light in the Bass? [message #80917 is a reply to message #80914] Wed, 10 December 2014 08:16 Go to previous messageGo to next message
themilford is currently offline  themilford
Messages: 66
Registered: May 2009
Viscount
Hey wayne, thanks for your insight... however I think you may be replying to an earlier post.

Sorry for the zombie thread.

Just trying to ascertain whether I need to make an adjustment to the port on the new pair of Two Pis I'm building. Any of you guys use adding wood/baffle thickness to build up the port depth?


Re: Two PI: A Little Bright OR Light in the Bass? [message #80921 is a reply to message #80917] Wed, 10 December 2014 10:21 Go to previous messageGo to previous message
Wayne Parham is currently offline  Wayne Parham
Messages: 17605
Registered: January 2001
Illuminati (33rd Degree)

You're right. I was replying to the first post in the thread, not the most current one.

I'll respond to your more recent comments this time.

I like using blocks of wood built-up to make a port. Your 2" drill bit is fine. The small difference between that and the 1.91" I.D. of the tube in the kit is inconsequential. There's more difference in other areas - a loudspeaker is a pretty wide-tolerace device with lots of electro-mechanico-acoustic shift in its paramaters.

As for re-positioning the port, the bookshelf model is small enough that standing waves line up in the upper midrange where the damping material does a pretty good job attenuating them. So I'd be reasonably comfortable with minor mods, and would expect little change. But we can't know without measurements, of course.

However, the tower model is a different story. The larger the box is made, the lower in frequency the standing waves modes line up. Large boxes tend to have standing wave nodes in the lower midrange, and these lower frequencies start passing through the damping material. It becomes less effective at lower frequencies. So we have to be more careful with placement of driver, port and damping material.

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