AudioRoundTable.com - RDF feed
https://audioroundtable.com/forum/index.php
Two PI: A Little Bright OR Light in the Bass?
https://audioroundtable.com/forum/index.phpindex.php?t=rview&goto=76092&th=18413#msg_76092
I've been living with a pair of 2PIs on and off, in and out of my system for the past few years now.
While the tonal balance is a tad on the "middy" or "vintage" side which I like, I think overall they are lacking in bass... or maybe it's just a that they are a tad bright?
I've only ever really compared them to my Audio Note Js and I'm running them with a pair or Bottlehead Paramours... the Js are flatter sounding... not a ton more bass... but they have it where is counts for most rock records... and although some folks think they are a tad on the bright side as well, when they listen at my house... the PIs are surely brighter still. It is particularly egregious when playing music with prominent jangly or distorted guitars and bashy cymbals. Basically around 2-3k...
I've got 14 gauge wire throughout, 0.51mH 14 AWG Perfect Layer Inductors, Solen 10uf caps and a 20ohm wirewound across the tweeter like the older design called for. lightly stuffed with polyfil.
I read one tweak might be to swap the film caps for oil-filled motor run caps... But I really feels it's more a lack of bass.
Any thoughts?]]>themilford2013-03-30T19:04:56-00:00Re: Two PI: A Little Bright OR Light in the Bass?
https://audioroundtable.com/forum/index.phpindex.php?t=rview&goto=76097&th=18413#msg_76097
That's true, the one π and two π speakers have rather high f3 points. They don't dig really deep, and are intended to be used as surrounds, or if mains, to be supplemented with subs. The two π tower had deep full bass though, so if subs are out of the question, you might consider building tower enclosures.
]]>Wayne Parham2013-03-30T21:50:04-00:00Re: Two PI: A Little Bright OR Light in the Bass?
https://audioroundtable.com/forum/index.phpindex.php?t=rview&goto=76105&th=18413#msg_76105
I dunno though... I just wonder if I did something wrong. Because I made a pair some years ago (w/ the CTS tweeter so no cap) but don't remember them being so bass shy.
Did I make the port to short or something? Do I need more stuffing? Should I have used R13 instead of Polyfil? Should I have used different coils or caps? is the resistor the wrong value? Do they just need more break in time?
I haven't really put many hours in on them over the years. Just a few sessions here or there...
]]>themilford2013-03-31T15:14:06-00:00Re: Two PI: A Little Bright OR Light in the Bass?
https://audioroundtable.com/forum/index.phpindex.php?t=rview&goto=76106&th=18413#msg_76106
You could always check your cabinet to see if the port is too short, I suppose. The plans call for 1-7/8" length. R13 insulation should line the rear, bottom and side nearest the port. So check everything, if you think you might have sone something wrong. You might even want to have the woofer checked, if you think they used to sound differently.
To my rears, they sound very powerful and not "bass shy" but they do lack the deepest bass. Like most of my designs, you really need to augment them with subs for the bottom octave (20-40Hz).
]]>Wayne Parham2013-03-31T16:19:39-00:00Re: Two PI: A Little Bright OR Light in the Bass?
https://audioroundtable.com/forum/index.phpindex.php?t=rview&goto=76109&th=18413#msg_76109
How the heck did I manage to make the port a 1/4" too short!
Hmmm... how much of a difference would that make in the bass?
Also, what's an elegant solution to elongating it without tearing the things apart?
]]>themilford2013-03-31T17:52:22-00:00Re: Two PI: A Little Bright OR Light in the Bass?
https://audioroundtable.com/forum/index.phpindex.php?t=rview&goto=76110&th=18413#msg_76110
I mean the polyfil just sorta gets stuffed in there and the R13 lines the walls... I don't really like working with R13 in the house... but if you feel it's essential I'll grab some this week and try it out.
Also, as a tangent... any thoughts on playing with the crossover a little in terms of fine-tuning? I have parts on hand to try a "solen split" 1st order... I feel like most of the bright energy is focused in this x-over region.
In any case, I'll try the port first... then the stuffing... and report back.]]>themilford2013-03-31T18:09:47-00:00Re: Two PI: A Little Bright OR Light in the Bass?
https://audioroundtable.com/forum/index.phpindex.php?t=rview&goto=76112&th=18413#msg_76112
I just glued & taped little port extensions in there... seems to help a little bit with the very lowest bit of bass.
Wondering if a little more stuffing might help tame the high upper mids a tad and fill out the upper bass a tad more...
I'll report back in a few more...]]>themilford2013-03-31T19:19:40-00:00Re: Two PI: A Little Bright OR Light in the Bass?
https://audioroundtable.com/forum/index.phpindex.php?t=rview&goto=76114&th=18413#msg_76114
Yeah, having the port too short will make the speaker lack bass in the 60Hz region and overexaggerate midbass and lower midrange in the 80Hz to 120Hz region. Then not having the right damping material will make matters worse, tending to make the speaker be hollow sounding. The insulation attenuates internal standing waves, and in this speaker, those occur in the upper midrange. So I'd say the two accidental modifications probably tended to make the speaker sound kind of "thrummy", having an unnatural over-emphasis of the midrange.
]]>Wayne Parham2013-03-31T20:22:07-00:00Re: Two PI: A Little Bright OR Light in the Bass?
https://audioroundtable.com/forum/index.phpindex.php?t=rview&goto=76126&th=18413#msg_76126
Some pics for yous guys:
Cork-lined front baffle, Finland birch plywood, rear panel is particleboard. Finished with about a bazillion coats of tung oil and paste-wax-buffed to a shine.
FWIW: I love the utilitarian, mid-century modern look of birch plywood. I'll take it over fancy-schmantzy veneers any day.
So the tweaking continues...
So, I swapped the .51mH, 14ga coil for a .60mh, 20ga coil I had on hand. It's getting closer to what I remember the older pair of these I made years ago sounded like? Why is that? What is happening here?
Also, added more polyfil just before this swap and that seemed to help a little too... but minimally so...
What is the resistor on the tweeter doing btw? I have a 20ohm there... is that the correct value?]]>themilford2013-04-01T15:23:48-00:00Re: Two PI: A Little Bright OR Light in the Bass?
https://audioroundtable.com/forum/index.phpindex.php?t=rview&goto=76131&th=18413#msg_76131
I love the looks of that cabinet. The cork front is a nice touch, as is the rabbet edge. Good work!
Looks like a nice little Bottlehead system too.
The 20Ω resistor across the tweeer is there just to shunt the Zmax peak around 680Hz. It prevents excessive energy way down low. You can't really tell it's there, it's just a snubber, an impedance control device. Again, it just protects the tweeter from getting excessive energy down low.
Now for the cabinet. I see that you installed the port on the back. This change, paired with the change of stuffing material is probably what has caused the differences. Could be that the polyfill has settled over time, and has become less effective at absorbing midrange standing waves.
I suggest installing fiberglass insulation before evaluating any other changes, like the larger coil. Your 0.6mH coil is not so much bigger that I would expect to to make a huge difference, but still, let's get back to a baseline. You can't really do that since the port is in a different position, but I don't think that will be a problem if you use R11/R13 lining the walls. Might want to cut a hole in the insulation where the port is though, or perhaps line the front instead of the back. But definitely go with fiberglass insulation, and then see where you're at.
I've tried other damping materials over the years and find most to be lacking, some really bad. What I often find in other padding materials is they are less effective at attenuating midrange. Sometimes not only that but they can also modify cavity resonance and detune the box. I'm not sure if the problems with other materials are that the fibers are too heavy and/or rigid to vibrate and absorb energy or if it's more of a bulk/mass thing where the sheets just acts like a solid block. Could be a little bit of both. But whatever the case, I find good old fiberglass insulation works best.
Fiberglass insulation may be a little irritating to your skin when you install it, but once it's there it doesn't enter the air. The sound of the loudspeaker may vibrate the fibers, but they don't break free. And glass is a quite benign, really. It does not cause cancer, and is probably one of the safest fiberous materials to use. It's not like asbestos, but probably gets associated with that in some people's minds because it looks similar. So I think it is probably the best, safest and most effective material to use for this purpose. I find no downside to using the stuff.
Beyond that, I often tell people not to make cabinet mods without testing. The reason is you don't want a port to be in a pressure node of a standing wave. All cabinets have internal standing waves, and that's why we use insulation inside, to attenuate the standing waves.
Large cabinets are particularly sensitive to cabinet mods because internal standing waves are at low enough frequency the insulation is only partially effective. So the positions of the midwoofer and the port are really important. However, the smaller one π and two π cabinets are small enough that the standing waves are in the upper midrange where insulation usually does a very good job. So they tend to be a little less sensitive to cabinet mods, provided the insulation is effective.
That's why I suggest using fiberglass insulation - It could be that you've put the port in a pressure node that causes a midrange peak, and the polyfill you are using is unable to attenuate it. But once you use fiberglass insulation, I think the port position will matter less. Should get you back to where you want to be and sounding good.
]]>Wayne Parham2013-04-01T18:38:27-00:00Re: Two PI: A Little Bright OR Light in the Bass?
https://audioroundtable.com/forum/index.phpindex.php?t=rview&goto=76206&th=18413#msg_76206
m@]]>my0x2013-04-06T05:07:42-00:00Re: Two PI: A Little Bright OR Light in the Bass?
https://audioroundtable.com/forum/index.phpindex.php?t=rview&goto=76229&th=18413#msg_76229
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. ]]>themilford2013-04-08T01:00:12-00:00Re: Two PI: A Little Bright OR Light in the Bass?
https://audioroundtable.com/forum/index.phpindex.php?t=rview&goto=76231&th=18413#msg_76231
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...
]]>Wayne Parham2013-04-08T01:39:56-00:00Re: Two PI: A Little Bright OR Light in the Bass?
https://audioroundtable.com/forum/index.phpindex.php?t=rview&goto=76245&th=18413#msg_76245
3 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?
]]>themilford2013-04-09T13:05:56-00:00Re: Two PI: A Little Bright OR Light in the Bass?
https://audioroundtable.com/forum/index.phpindex.php?t=rview&goto=80479&th=18413#msg_80479
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!]]>themilford2014-09-14T17:55:16-00:00Re: Two PI: A Little Bright OR Light in the Bass?
https://audioroundtable.com/forum/index.phpindex.php?t=rview&goto=80482&th=18413#msg_80482
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.
]]>Wayne Parham2014-09-15T00:30:50-00:00Re: Two PI: A Little Bright OR Light in the Bass?
https://audioroundtable.com/forum/index.phpindex.php?t=rview&goto=80913&th=18413#msg_80913
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]]>themilford2014-12-09T18:11:23-00:00Re: Two PI: A Little Bright OR Light in the Bass?
https://audioroundtable.com/forum/index.phpindex.php?t=rview&goto=80914&th=18413#msg_80914
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.
]]>Wayne Parham2014-12-09T21:27:51-00:00Re: Two PI: A Little Bright OR Light in the Bass?
https://audioroundtable.com/forum/index.phpindex.php?t=rview&goto=80917&th=18413#msg_80917
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?
]]>themilford2014-12-10T14:16:42-00:00Re: Two PI: A Little Bright OR Light in the Bass?
https://audioroundtable.com/forum/index.phpindex.php?t=rview&goto=80921&th=18413#msg_80921
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.
]]>Wayne Parham2014-12-10T16:21:42-00:00Re: Two PI: A Little Bright OR Light in the Bass?
https://audioroundtable.com/forum/index.phpindex.php?t=rview&goto=80923&th=18413#msg_80923
would something like this be useful for calculating such a problem?
http://vikash.info/audio/standing_wave_calc/]]>themilford2014-12-10T17:34:40-00:00Re: Two PI: A Little Bright OR Light in the Bass?
https://audioroundtable.com/forum/index.phpindex.php?t=rview&goto=80924&th=18413#msg_80924
Of course this can be shifted a little... but I haven't the first idea how to model anything. I'm a little mathematically disinclined.
I've played around with the link from above but I don't even know what I'm looking at or how it relates to what I might be building.
]]>themilford2014-12-10T17:51:18-00:00Re: Two PI: A Little Bright OR Light in the Bass?
https://audioroundtable.com/forum/index.phpindex.php?t=rview&goto=80925&th=18413#msg_80925
That kind of tool is useful, but only marginally. It calculates the modes, but it doesn't model the cabinet and tell you the effect of sound source placement on response. This is what the Martin King spreadsheets do, and they're much more useful because of that.