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Old 9th January 2008, 05:47 PM   #971
GM is offline GM  United States
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Greets!

With today's digital TD capability it may be doable, but this is moving up into our acute hearing BW, so perceived SQ may be poor. Only one way to know for sure. Anyway, I tried several different alignments for just such a TH yesterday and while I could get a nice flat response I could only do so with an optimized expo flare, so was pretty big for a 6.5" driver and its low Xmax limited it to ~105 dB, so didn't bother to save it. In theory you'll have to make it with smooth bends, proper radiused corners though, not the 'stepped' designs you can get away with in (sub) bass-horns.

Fh = Fs*Qes/2 says the Focal won't go high enough and the PHL way too high, though adding series resistance to lower its 'Fh' can in theory be used to smooth it out, but haven't simmed either one yet, so not sure this is even relevant in a TH. Note too that with expo flare you'll need a Fl*0.707 to load all the way to 80 Hz = ~56.56 Hz flare frequency.

Hmm, should be around 8 dB/W/m/2 pi space gain on average in it ~flat passband.

GM
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Old 9th January 2008, 10:06 PM   #972
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All the reports are that TH’s SQ is very good, but yes proper radiused corner(s) would be needed, removing the simplicity benefit, but keeping other benefits – would just one such bend be needed?

An expo flare that’s pretty big for a 6.5" driver would I imagine still be a lot smaller than a typical 80 Hz midbass? lower distortion is my aim rather than high SPL, but 90 dB stock + 8 dB 2 pi space gain = a healthy 98 dB.

I’m rusty on horn formula & terms, but iirc Driver mass rolloff guideline at the upper end of the range (Fmh) is Fs*2/ Qes; and above that rolloff is at 6 dB/ octave?
That’s 615 Hz for the PHL and 250 Hz for the Focal, so in theory I calc the Focal would be 1.7 dB down at 320 Hz. Iirc though dropoff is often less than theory predicts, and what rolloff remains might be managed in the crossover.

A 57 Hz flare would be big, maybe better to go for 90/ 100 Hz with a 64/ 71 Hz flare.

Would a midbass TH generally likely have benefits over a conventional midbass horn??

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Old 9th January 2008, 10:51 PM   #973
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G'day Otto88

There's some info on a 60-240Hz Tapped Horn I built on my webpage. It had a very broad flat pass band, probably the widest bandwidth I've seen so far in a Tapped Horn. The driver is an 18 Sound 10W400, with a 70Hz Fs. It went silly loud with very little power and cone excursion.


The PHL you mention is probably worth a look, the Focal has too low an Fs for a 80Hz Tapped Horn. To get the two octave bandwidth you desire, your driver choice will have to be spot on. Try modeling some drivers with a 100-140Hz Fs.

Cheers

William Cowan
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Old 10th January 2008, 12:20 AM   #974
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Hi William

If the 10W400 with an Fs of 70 Hz works well in a 60 Hz TH – suggests to the PHL 3451 with an Fs of 80 Hz could work well in a TH of about 90 Hz - what other parameters made the 10W400 excellent for a 60 -240 Hz TH?

The lack of proper radiused corners did not compromise the upper range’s SQ?

Thanks
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Old 10th January 2008, 01:07 AM   #975
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Mmm, the Qes of the PHL is much lower than the 10W400

But the Qes of the Focal 6W4311 is within 10% of the 10W400's (0.40 v 0.44), and while the driver is much smaller (so lower sensitivity, but 90 + 8 dB is still pretty handy sensitivity), the Xmax is also within 10% of the 10W400.

Would somone have time to sim the 6W4311 (specs above)?

I have a pair of 6W4311's, but fwiw they're on sale at e-speakers:
http://estore.websitepros.com/173675...scounted+Items

Thank you
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Old 10th January 2008, 02:37 AM   #976
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Greets!

OK, but they're all subs, right? Our hearing acuity isn't very good down low or we wouldn't be able to tolerate a typical in-room response.

Right, they don't have a long path-length, so one bend is plenty.

How big an 80 Hz mouth is will depend on the throat size, flare factor and boundary loading. Since a 0.7 hypex is common it will be longer than an expo, but with a smaller mouth so it will be somewhat smaller in bulk for the same gain BW. A tapped horn OTOH has 1/2 WL loading using two drivers in effect, so will be considerably smaller.

If sims are to be believed, a TH has considerably more distortion than an optimized FLH, but if Earl Geddes is right, then it's irrelevant beyond HOMs due to reflections, so maybe it's better to have a rough bend to damp them down before reaching the mouth.

$#!^ You're right of course. I normally proofread my posts before sending, but was in a hurry and copied the wrong field on my spreadsheet, sorry.

To me, the only advantage to the tapped horn is it's smaller for a given gain BW.

GM
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Old 10th January 2008, 04:24 AM   #977
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William,

An Fs of 50 Hz with a mouth of 80 is 1.6:1, which I thought was towards the upper end of the “rules of thumb”. Is that (first subject to a sim) right?

GM,

A conventional 80 Hz straight midbass would be about 1m/ 40” deep, is a big WAF problem for me - pretty well kills it.
But as the TH’s line length is vertical (and height is not an issue), and eg William’s 60 Hz TH with a 10” driver - depth is only ~0.4 m/ 17” deep, this arrangement makes it doable.
It could be initially done without a bend, and one added later . .

I haven’t done horn modelling, as Volvotreter’s spreadsheet showed me that they were all too big for me. Throat size would be the 6.5” driver with a moderate compression ratio of say 1.7(?), and flare you recommend 0.707.
To integrate in the XO with drivers above at say 240 Hz, the mouth would need to be at the top of the horn, so boundary loading would be only 1/ 2 space(?).

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Old 10th January 2008, 04:42 AM   #978
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Quote:
Originally posted by otto88
Mmm, the Qes of the PHL is much lower than the 10W400
Greets!

Well, look at the formula I screwed up, it all depends on the ratio of Fs:Qes as to which has the widest BW potential.

Anyway, I simmed the PHL using ML's math for both a 56.56 - 615.38 Hz and 56.56 - 320 Hz with/without series R compensation and while it smoothed the 320 Hz TH, all it did was lower the 615.38 Hz TH's efficiency.

Bottom line, the wider BW alignment was the better damped, just as efficient and considerably smaller than the 320 Hz alignment, so not a good plan IMO to 'short change' a TH's HF BW.

The Focal OTOH had to be tuned to Fs to get it to 80 Hz, though at a lower efficiency with more 'ripple' and it didn't matter whether I used a 250 or 320 Hz Fh. Not surprisingly, it's smaller.

GM
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Old 10th January 2008, 04:44 AM   #979
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Old 10th January 2008, 05:28 AM   #980
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Greets part deux!

You can fold a FLH too.

?? How do you build a tapped horn without a fold to couple the front and back of the driver to it?

Yes, best to assume 1/2 space for this BW unless measurements prove otherwise.

GM
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