Collaborative Tapped horn project

Post #3193

Hi just_a_guy,

Finally on break from the home remodelling (until morning). Looks like your new measurement supports the information you got from your first measurements in Post #3130. It's even smoother in the low end, maybe the stuffing in the mouth attenuated the response a little too much.

As littlemike pointed out before (Post #3164) extending the driver to mouth distance reduces the dip in front of the first major peak, actually it influences both dips around the first peak. It would be relatively easy to experiment with a mouth (port) extension, e.g.: in the attached SPL graph I added 12" to your existing horn. Obviously, this is only an example, and as you pointed out in Post #3166 sooner or later it will create other problems.

Anyway, it looks like you're quite close. Thanks for the information.

Regards,
 

Attachments

  • first peak and dips.jpg
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Yeah, it's overstuffed at the time of the measurement, just wanted to get a feel for what extra stuffing would do and overstuffed gave the smoothest measurement.

Anyway, it would appear that you are an information junkie just like me, looking for the details. So you might appreciate the following.

You may remember that aceinc made a TH-SPUD clone outfitted with css trio 8's. Unless you followed him to hometheatreshack.com http://www.hometheatershack.com/forums/diy-subwoofers/16807-tapped-horn-build-th-spud-2.html you didn't catch the end of the story. I've been waiting for several weeks for him to mention it here as I'm not an active member there but it looks like he gave up on it without asking our opinion.

He shows 3 measurements, his old subs in room, the TH clone at the mouth and the TH clone in room (facing up). IMO he could have gotten some pretty good measurements out of it if he just measured it outside and stuffed the throat and mouth carefully. IMO he might have misinterpreted his own measurements and it's room modes (not TH harmonics) making the measurement look bad below 60 hz, and experimenting with stuffing the throat and mouth (the only accessible areas left) would have helped tremendously above 60 on the 2 big peaks.

I've attached my interpretation of his measurements, the TH impedance peaks should be right on or very close to the vertical red lines I've drawn and room modes are circled in red. (Compare his first and 3rd graph and I'm sure you will see they are room modes.)

An externally hosted image should be here but it was not working when we last tested it.


I spent hours studying the 3 measurements (the only 3 diy examples we had - Cowan's, littlemike's and aceinc's - and out of those only littlemike even attempted to try stuffing) while designing my own, so thanks to them.
 
Post #3203_aceinc_CSS-Trio Dual

Post #3203_aceinc_CSS-Trio Dual

Hi just_a_guy,

I've been following aceinc's thread about his Trio-Dual, and found it very informative (and rmk's thread at audioholics and avsforum on the TD TH-SPUD). You are right, I plead guilty to being "an information junkie". As you point out his measurements show some room influence. If I remember correctly he didn't use any stuffing/lining in his enclosure.

All very interesting.

Regards,
 
Don Snyder said:
Every thing else being equal!

Ah, that's the rub. If we want to compare a single taper tapped horn to a double taper
tapped horn, it would seem that we must keep all the lengths constant, S2 constant, and
the total volume constant. Why total volume? Because of Hoffman's Iron Law ...

Hoffman's Iron Law states that the efficiency of a woofer system is directly proportional
to its cabinet volume and the cube of its cutoff frequency (the lowest frequency it can
usefully reproduce). The obvious implication is that to reduce the cutoff frequency by a
factor of two, e.g. from 40 Hz to 20 Hz, while still retaining the same system efficiency,
you need to increase the enclosure volume by 2^3 = 8 times!

Will this be apples-to-apples, allowing S5 (the horn mouth) to vary? If you agree that it
will, I am willing to develop the geometry and see if the double taper has an advantage.

~Don

All absolutely correct, which is where part of the improvement for a 2-rate taper TH comes from -- if you keep the total cabinet volume constant, a smaller cross-section halfway along means a larger cross-section at the mouth, which increases efficiency.

Ian
 
In room response is pretty bad, GM was right about the dip at 80 hz being worse in room. This measurement was taken with the sub corner loaded and mic in my listening position. Mouth moderately stuffed.

An externally hosted image should be here but it was not working when we last tested it.


I've got the tools to flatten the response as it sits, or I could move it out of the corner and get somewhat flatter response (placement is everything) but lose the acoustic benefit of the corner load.

First listening impressions - I think it's going to be fine when eq'ed properly but getting wide bandwidth from this thing in room might be tricky.

BTW, the peak at about 54 hz and the pimple on the peak at about 115 hz are room modes and as GM pointed out the exaggerated suck out at about 85 hz is room related.
 
Freddy actually built one of these things , .. wow !!

How does it compare vs. your K-15s etc ..

My own reverse TH with a 6x9 TB subwoofer isn't bad at all (and would've been perfect for my car if I'd thought to make it 6" shorter :( ), so I currently have the drivers on sale on the trading post so I can experiment with some of the 4 ohm 6.5" TB sub drivers.



Observed vs Theoretical impedance:
http://www.diyaudio.com/forums/showthread.php?postid=1666254#post1666254

Theoretical response. In practice, I got down to the mid 30Hz with authority.
 
nineleaves started a thread over at speakerplans and I had a piece of plywood
http://www.speakerplans.com/FORUM/topic24838.html

"built" is a loose word with this many gaps

warped and poorly cut flooring plywood mess -- T-slot just jammed in
http://img148.imageshack.us/img148/4782/ithslotone.jpg

input Z for various mouth opening size - Martin 1844
http://img217.imageshack.us/img217/2672/inth151844inputz.gif

general effect of polyfill at the start of the line
http://img216.imageshack.us/img216/5019/ith1844polyeffect1.gif

input Z with 295070
http://img99.imageshack.us/img99/7278/ith295070z1.gif

response in middle of my kitchen with 1844 vs Dayton 295070 - - hornresp looks real close
http://img135.imageshack.us/img135/1199/ithna1844vs295070fr.gif

response in corner with rectangular vent vs T-slot vent
http://img148.imageshack.us/img148/4674/74cfithcorner2slots1.gif

sketch
http://img148.imageshack.us/img148/5483/ithroughsketch.gif

Karlson 15 with Audio Nirvana 10 vs inverted tapped horn wiht 295070
http://img135.imageshack.us/img135/8307/k15nirvanavsith295070.gif
 
Is there an advantage to having more than one taper in a Tapped Horn? Of course there is!
As iand said earlier, making the middle smaller will allow the mouth to be larger.

Attached is the input screens for two horns that have the same lengths, same S2, and the
same total volume.
 

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those look FAB -- also Walt's comment :^) -- - I don't go anywhere - can't drive due to inner ear prob - and am nearly destroyed from reflux choking at nite for many years - - if could figure out how to reduce the "gerd "then might come back to life for a little while to piddle with speakers