vifa p22wp-01 transmission line

[prickears]

Just toying with the idea of a transmission line setup using the vifa p22wp-01
in a three-way set up, but just not sure exactly where to start.

SPECS; 4 ohm nom
RE. 3.0
fs 30 Hz
qms 2.2
qes .31
qts .272
sd 235 cm2
vas 77
90 db sens
bl 10.2


I'm led to believe the specs make it a fairly good candidate for a tl, although i'm not sure what makes it so.......... I have used them in BR with good results, however i feel that these drivers have more to give than i can extract from them in a bass reflex design. I would love to make this project fly but i'm not sure how to work out taper ratios, driver placement and other associated hoo haa for a given driver. If i could get them going without destroying an entire rain forrest, that would be a big bonus . If you have trudged down this road b4 what advice could you give (Other than, GIVE UP!!!!)!

[GM]

Well, MJK's website is required reading for all things TL and you can accurately model the results in his software. There's also a yahoo! groups forum to help you along the way if need be.

I don't agree that its published specs make it a prime candidate for TL loading if you want max flat bass extension unless driven with a high output impedance due to its low Qts. For this you want a large BLH. For the theoretically highest SQ in a box alignment, then a max flat impedance TL is it, but we're talking about a small, heavily stuffed TL with a ~108.5 Hz Fp, so not even good for mid-bass.

http://www.quarter-wave.com/

http://tech.groups.yahoo.com/group/quarter-wave/

GM

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Thanx GM,
Your feedback has been very useful, this driver then is more bass reflex suitable then? They are currently being used in a BR setup, 23 litres with a port 80x50x190 mm rectangular and flared. Bass is strong and clean except for an audible dip around 80 hz (Tested with my tone disc). I don't have measuring equipment but the dip must be at least 4 db. The boxes are made from 25 mm mdf, the drivers are resessed flush, with a half inch radius round off internal around the driver. I have tried internal damping, figuring it could be caused by standing waves, but to no avail. I suspected a TL could be the answer but am obviously off coarse again. I am certain its not a room response problem, as it happens in every room. Where did I go wrong? What would you suggest for a flat response with this driver? I tried a bigger box (30L) but they went VERY shy. Thanx again, Mick.

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This is my latest project, and its a dismal failure. Such a failure in fact that I shall totally (almost) clean sheat it Hence the reason for looking at a transmission line enclosure.

The midrange to top end is as sweat as anything i've heard, to be honest, open almost to a fault, tons of head room, astounding detail, yet never hisses an ess, listening to Dianna krall, Donald Fagen, and the like, (except on overly bright recordings, ie, some modern pop and the like). Imaging in this range is dead bang pinpoint. Sound stage is nice and wide, and sounds like vocals are coming from dead centre and five feet back. It is therefore this part that I really need to keep intact.

But then the bass is just plain crap, as sweat as the rest of it is , the bass is a polar opposite to be frank.

I guess the side firing bass is a good concept, if you hold bass directly responsible for the global financial crisis........... WOW what a flop!

In a vain attempt to save face (and bass), I plugged the bass port completely, (the bass port is actually external) and added another bass driver in parallel, (I did this because the box was 30 ltrs and winisd tells me a sealed box for 1 bass driver is 13 ltrs), and halved the value of the 1st order slope on the xo. That helped a little but is far from a cure. Clean sheet me thinks.

The best bass i've had from them so far is the 23 ltr box I mentioned in an earlier post, Except for that annoying dip at around 80 hz that I could not seem to cure, which gave them a 'lack of bass attack' sound, although the rest of it (bass) sounded tight, clean, and powerful with good extension.
Could the box LxWxH ratios have caused this? Seems like a likely suspect as far as I can tell.

Figure the 23 ltr box, rear vented, but all drivers on the front baffle might be the go. That is in keeping with the KISS principle.

As you can see from the photos, I have experience, but i'm far from an expert. Any Thoughts, always welcome.

Mick.

[tsmith1315]

At a glance, it looks like the port frequency in the 23L enclosure is very low, like ~25Hz. Am I correct?

[prickears]

Thanx for your reply,
I get around 45-Hz, am i calculating wrong?

[tsmith1315]

Maybe I misconstrued your port dimensions. 80mm x 50mm rectangle opening x 190mm long?

I'll recalculate, maybe it's too late in the evening for math...

[prickears]

I calculate that 5x8 = 40 or the same as a 7.15 cm tube (diam). A quick glance in Weems book chart seems to suggest around 45 hz for that length. Do rectangles and tubes behave differently? or did I just plain get it wrong? If so, what is the right method?

Thanx again, Mick.

[tsmith1315]

My mistake. It's indeed too late for math, it took me 20 minutes to notice I was insistent on considering the radius as a diameter and halving it again while converting to inches... duh.

As long as the rectangle is not too skinny, the equivalent diameter is fine.

For future reference, here's the formula:

Lv=((1.463*10^7*Rv^2)/(Fb^2*Vb))-1.463*Rv

Lv = vent length in inches
Rv = vent radius in inches
Vb = box volume in cubic inches

at 45 Hz, that's about 8.6 in, 21.8cm... Close enough for estimates.

Sorry for the confusion!

[prickears]

Geez Tim, ya had me worried for a while.......but I really do have to learn this algebra thingy sometime real soon, (been just relieing on online calcs and the like).

Still not getting this tranmission line thing though, I've gotta confess. My 'Great sound stereo speaker manual' by David Weems, suggests that a low Q driver is generally a good
TL choice, GM certainly disagrees. Does this depend on the type of TL in question?
Alternatively is Weems book considered 'old hat' now?

One thing is certain, it is still a hotly contested theory from where I stand!


Thanx again for your input.