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Old 9th March 2006, 03:19 AM   #121
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Quote:
Originally posted by Godzilla
Hi GM... I think your 1197 speaker is a rather pretty ugly duckling.

Closing your eyes or turning out the lights may have one thinking they are involved with a great beauty.

Noticing the cute phase plugs on the 1197's i wondered if you've heard the Pioneer B20's with phase plugs? I love my B20's and had them cranking late last night before running off to krav maga training.

They sound just fine stock to me but i wondered about any improvements in midrange clarity phase plugs may offer.

I may just cut those dustcaps out one day. Any thoughts?

Godzilla
Greets!

Different strokes..... Yes, these 'disappear', and while definitely not the Last Word in resolution, they still sounded far better than I figured they would. Folks with a small room and/or budget could do a lot worse for more money. I'd like to see a well done one from Dave's dwg. perched on a Tony G.? massive 'T' stand, all in Ash/White Oak.

Yes, I tested numerous tweaks on the B20 including phase plugs, though not nearly as nicely done as Dave's. Small tapered ones mostly affect the HF so it took a big one to make enough difference in the mids to suit me (huge 500W shop bulb with a crinkly alum. foil cover). The best tweak I tried that transformed it into a real HIFI contender also would increase its cost at least 5x, so no longer an 'el cheapo' nor easy tweak.

It blew up when an amp failed so didn't get to do some other things; so for now, damping the frame/motor, selective damping and stiffening of the diaphragm, doing the $0.98 tweak, and replacing the DC with a large phase plug that pleases your aural sensibilities works for me.

GM
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Old 9th March 2006, 11:39 PM   #122
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Greets!

My sim peaks around 55 Hz also, though only ~3 dB, so is beneficial rather than distracting. The ~16 dB/octave roll-off will help with room matching too. My way is loosely based on conical horn expansion theory, so I imagine you can figure it out.

Anyway, plug these into the ML-TQWT WS and tell me what you think:

L = 113.38"
SO = 2.036"^2
SL = 265.464"^2
xO = 0.6825 (77.38")
density = 0.2 lbs/ft^3
rp = 3.25"
lp = 1.5"

GM
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Old 10th March 2006, 12:37 AM   #123
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Quote:
Originally posted by pjanda1
I know folks have said bracing is unneccessary. However, it seems to me that it couldn't hurt, especially for larger versions. How about vertical panels between the divider and the front and back? I'd swiss cheese them of course. Could there be any harm?

In the original, the quarter wave tuning is an octave below the Fs right? That would put the second mode right at the drivers Fs. Does making it shorter than ideal (for example, a Hemp BIB 70" tall mean the driver isn't as damped at resonance as it should be? I know that the driver gets too high if it is taller, but what if one extended the enclosure above where the divider attaches to the baffle?
Greets!

A pipe's dominant modes are axial, so tapering automatically makes it stiffer, but it increases its bell modes, so ~the last third of its length needs to be increasingly stiffer. This is also the BW where any obstruction affects its LF output, ergo any additional stiffening needs to be via thicker panels and/or external bracing.

Folding it further stiffens it, so unless the unsupported panel area near/at the mouth gets > ~1 ft square, then 19mm BB ply or similar stiffness is probably sufficient, but if you look at TC's BIB sketch you'll see he added an internal stiffener inside the mouth, so apparently he felt the need for it with the hardwood he used, technically making it a MLTL.........

AFAIK.

Correct, since a tapered pipe has both odd and even modes, the driver's peak is reinforced by the pipe's peaking. Due to the pipe's odd order nulls being closely spaced on either side of it though supresses it somewhat.

If the mouth is extended as a straight pipe, then it will act as a large vent, lowering Fp and changing its modal distribution. This can be a good tweak if done right, so will need to be simmed using the 'sections' WS.

GM
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Old 10th March 2006, 08:48 AM   #124
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Thanks as always Greg. I'll try those dimensions out in a minute in the ML TQWT sheet. Your own based on conical expansion theory -I think I see what you're driving at. I'm not as up on horns as I should be, but it's time I was, and this looks to be a good opportunity to remedy this apalling lapse!

One thing that's occured to me guys since I've looked at the dims and the scaned picture Andrew emailed: Terry's original box was effectively just the original enclosure, for the FF125K (Fs allegedly 78Hz, if you can believe the Fostex measurements), with the dimensions slightly modified to account for his using 1" wood. That's not a criticism BTW -just an observation that might be pertinent as regards box turning. I would've thought, especially given Greg's comments in an earlier post, that that original box was tuned way too low for the intended FF driver, and Terry's use of the RS 1354, with it's lower Fs would in this respect be the happier match.

Best
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Old 10th March 2006, 12:23 PM   #125
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Just plugged the B200 into the dimensions you suggested Greg. Result -that's the best response I've ever seen from this enclosure. Bar none. I am rapidly coming to the conclusion that this needs to be built.

Regards
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Old 10th March 2006, 07:59 PM   #126
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Keep it going guys. This has piqued my interest to the
point where I bought some wood.


I just was to going to try one one for the sound effect
of this build using some edge glued 5/8 x 72 in x 12 panels.


This slims down the dimensions and I'd be using something
smaller than an 8". I'd like to lay out in standard 6"
wide stock.


Is this doable? What suggestions for the driver in
sub-hemp or B20 size? Might it be something I have
like the RS 1197?
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Old 10th March 2006, 11:02 PM   #127
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Quote:
Originally posted by Scottmoose
Just plugged the B200 into the dimensions you suggested Greg. Result -that's the best response I've ever seen from this enclosure. Bar none. I am rapidly coming to the conclusion that this needs to be built.

Regards
Scott
Greets!

I posted it quite awhile ago when the B200 first appeared on the forums, but AFAIK, no one built it. I guess since it's not 'T/S flat' enough. FWIW, the cab part of this FR plot is typical of reflex/pipe speakers before T/S and I find it interesting that many folks, especially those of us who grew up with them, find them more 'musical' than current fare, typically referring to them as 'toe tapping'............

T/S specs are nice to have when trying to squeeze the last ounce of performance out of a given bulk or to hit a target alignment, but if size isn't a big deal then these simple designs are hard to beat IMO. Several years ago I did a straight MLTL for the late, lamented RS 40-1354 which has the same general FR plot and really opened some folks eyes at one of the Atlanta DIY Meets with its solid +/- 3dB from ~40 - 12.5 kHz measured response (no BFC or super tweeter since I built them for a hearing impaired friend) filling a fairly large hotel conference room full of people.

GM
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Old 10th March 2006, 11:18 PM   #128
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Greets!

For the BIB pipe you ideally need a driver with a 45-50 Hz Fs, and assuming the 12" width is accurate and the standard 6" is actually 5.5" x 0.75", then the driver ideally needs to be ~5", so the 40-1354 is the only FR driver that comes to mind.

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Old 11th March 2006, 10:07 AM   #129
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I thought that vent size looked familiar. I reckon I'm going to build this -not perfectly 'flat', but nor are rooms for that matter. Nice to use some of the pre T/S proceedures that might be lost otherwise too.

By the way, Greg: how on Earth could the original box (Terry's dimensions effectively) work with the FF125K Fostex used, with a 72Hz Fs? I can't figure that one at all, it's tuned so far below Fs. I ran a couple of inconclusive sims: their cut-off point's are about right according to MathCad, (which astounded me), but the rest seems a little weird. Any thoughts?

Regards
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Old 11th March 2006, 01:54 PM   #130
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Greets!

Not really, I haven't seen any of the Japanese design books or read their various design philosophies, or whether TC even copied the design exactly or not.

That said, historically, the Japanese audiophile apparently covets all things W.E./Altec/RCA/JBL and vinyl/RTR tape sources, so with a low Qts driver their preference has been for an impedance matching amp which effectively doubles Qes and/or has up to 20 ohms of adjustable damping, further increasing the effective Qes, dramatically increasing cab Vb and lowering Fb (Fp) requirements. Now we have a ~critically damped driver in a corner loaded ~IB alignment that has a low amplitude ~one note bass note to fill in down where the source material is at least -24 dB and the amp is rolling off to add a little artificial 'weight' or 'fullness' to the recording.

Works for me since I noticed early on that the bigger the cab I built and the lower I tuned it, the more natural/'live'/'fast' the music sounded and why the only IB I built (~300 ft^3 false wall cavity with four Altec 515Bs) ultimately wound up with long ducted vents.

With today's wide BW, long linear throw sub drivers, digital XO/EQ, and cheap super low output impedance mega power though, it's definitely not the way to go design wise if you want to hear all the music/special effects on some digital recordings.

GM
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