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Old 30th December 2011, 07:41 PM   #1231
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Originally Posted by weltersys
Those of us that have actually measured single TH against multiples have found the low corner does not change as it does for FLH in multiples.

Going from one to four cabinets with the same voltage drive gives a 12 dB increase in level, and the increased frontal area provides greater directivity, which can add even more level on axis.

Those level increases make it easy to think the low corner has gone lower, but so far I have not seen any actual measurements showing that to be the case.

Art Welter

Quote:
Originally Posted by GM View Post
OK, just so I'm clear since I still haven't built/measured a TH; you're saying that this simmed ~6 Hz downward shift of a single Vs 2S-2P and the ~12 Hz Vs 4S-4P [eg = 2.83 V, 2 pi] is all due to increased on -axis directivity? Or is HR being overly optimistic?

TIA,
GM
My observation is that HR is overly optimistic in predicting a downward shift of the low corner in TH response.
On axis directivity increases more in multiples at upper frequencies than lower, so even if Hornresp took directivity into account, the result should be more upper frequency (around 100 Hz) on axis SPL increase rather than more LF.
My actual tests with one TH compared to two show the response goes lower only by a minute amount, and that amount hardly changes when the second cabinet is unpowered and shorted.

Tom Danley or Ivan Beaver have posted charts of the TH-115 with one, two and four, the low corner hardly changes at all.

Typical TH behave more like a BR (which hardly go lower in LF corner in multiples) than FLH, which do go lower in low corner and level in multiples.

Art

Last edited by weltersys; 30th December 2011 at 07:46 PM.
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Old 30th December 2011, 10:34 PM   #1232
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Quote:
Originally Posted by tb46 View Post
Hi Y'all,

You have been busy, just some observations:

1. Post #1217: There was an update to the Furysub drawing: see Post #535 for the updated drawing LIVE SOUND Specific Tapped Horn thread..., there is a lot of subsequent discussion; see #563 for my attempt at an AkAbak simulation; there never was any resolution as to the lack of agreement between screamer's measurement, and the Hornresp SPL derived from the drawing.
Thanks for the links. Makes it easier to steer in the right direction.


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Originally Posted by tb46 View Post
2. I don't believe that a tapped horn - optimized for the low end capabilty of the driver - ends up with the driver's Fs below the speaker's passband. On the contrary, the Fs should be in the passband if you are looking for low end extension. The 3015LF just happens to call for a big box (see stadium horn), and it works just fine as long as the box is big enough. The SS15 is optimized for a reduced low end and high output, but not for the driver's low end capability (that's where you get to the stadium horn, or larger).
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Originally Posted by tb46 View Post
4. As an alternative for Crescendo: how about going the route that justin went with bjorno's T-TQWT? Maybe as a dual, a very easy build, and not as big as a tapped horn. Doesn't look like that would be hard to try.

Happy New Year Y'all. :-)
This is actually making me think a bit (in a good way)
I think the fact that 2 stadiumhorns may be 4-5dB louder than this dual from 30Hz-up is where I'm playing tug-of-war. My thinking is getting the most energy out of the drivers I have from a reasonable size - stadiumhorn being on the fence of reasonable. Maybe you can help me think this through: In the end, the 6 stadiumhorns would provide more energy. For bigger shows, this is a definite plus. I typically have a Sprinter van (tall & long) for transport, so size, while being a concern isn't the biggest concern. Maybe if the dual T-TQWT was 3-4dB or so more sensitive it would be enough to justify using 2 drivers in 1 enclosure (instead of using those 2 drivers in 2 stadiumhorns and gaining almost twice the energy). Sorry if I'm being difficult.

Hope you all have a safe and amazing New Year!!
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Old 31st December 2011, 01:03 AM   #1233
Djim is offline Djim  Netherlands
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Hi Oliver,

Sorry, but it looks like I owe you one. I see now my text in post #1226 was in contradiction. Anyhow, the context is not changed over the last year and I really think that the Fs should fall below 1/3WL and above 1/4WL of a tapped horn, optimised for PA. Somehow that turns in the best balance between low end, high sensitivity, box dimensions and max SPL. The second reason is to suppress cone losses, more specifically those within the cone.

If the Fs of a driver falls just above 1/3WL, the higher resonances in the cone (4 diagonal nodals) often meet
the full wavelength resonance of the TH system. If they do, it can result in cone damage at max settings. Less obvious but also something to consider, it can change the suspension over time. That's why I don't like foam type surrounds for PA subs as all resonances have to be dealt with by the spider. That these points of the driver and a system fall together is nothing new. 'Old' drivers with untreated cones and low mass suffered a lot from them during the golden age of FLH's. People often identify it with over excursion but that is actually a wrong assumption.

Over excursion always leaves certain marks and will be very audible by the user. Sudden death or sudden drop in SPL, besides hammering or scrapping sounds of the VC former against one of the plates, are caused by over excursion. The effects from resonances within the cone before it gets damaged are often not heard by the end user. By the time they become audible, it is often already too late and the cones are already damaged, if not destroyed.

Nodals, circle and diagonal in form, only happen when the suspension is no longer able to absorb the energy from these cone resonances. For TH’s there is an extra point of attention since the cone hasn’t a 'compressed air spring’ from a closed back, like in traditional FLH’s. In other words in TH’s the suspension has to deal completely with resonances and losses by the cone (Dynamic Compression). This is where the differences in concepts and differences in quality between drivers become obvious.

I have attached an overview of most important cone resonances that can be used to optimise TH’s for PA. Hopefully I didn’t make too many mistakes this time, but if I did, let me know.

Click the image to open in full size.

The pluses and minuses represent the direction of cone parts in relation to the first half of the waveform of the resonance.

Last edited by Djim; 31st December 2011 at 01:19 AM.
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Old 31st December 2011, 01:40 AM   #1234
Djim is offline Djim  Netherlands
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Maybe this picture makes it more visual.


Click the image to open in full size.
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Old 31st December 2011, 02:04 AM   #1235
tb46 is offline tb46  United States
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Hi Djim,

Thanks for the additional information in Posts #1233 and 1234. I'm sure that breakup modes keep loudspeaker designers awake at night, and this clearly reinforces your point about driver quality.

Regards,
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Old 31st December 2011, 02:05 AM   #1236
tb46 is offline tb46  United States
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Hi Crescendo,

There are always more questions, aren't there?

For maximum output with low end extension to 30Hz, and without regard to the size it's the stadium horn.

Using Don Snyder's data: the stadium horn is 48"H x 25.44"W x 36"D, that's 720.4 L_external. In Hornresp - with the segments set to Par - the volume is given as 606.824 L_net. When you take a look at the Hornresp simulation, you will see that this horn can be tweaked a little to smoothen out the response, and to reduce the size a little bit, but it's pretty close as it is. Unlike the SS15 this one does not look like jbell spend a lot of extra time refining it, but it still came out fine.

The stadium horn will reach 11.6mm displacement @ 260W into 8 Ohm (Eg=45.61V) @ 41Hz. The T-TQWT Dual will reach 11.4mm displacement @ 600W into 4 Ohm (Eg=48.99V) @ 42Hz. I'm attaching Hornresp Spl response screens at these levels and at 1W. Depending on which frequency you pick the T-TQWT Dual is quite a bit louder (at a bit more than twice the input power) at that excursion level.

I have not drawn the T-TQWT (for the external volume), but it seems simple enough. In Hornresp the net volume is 453.176 L_net. That's a good 150 L smaller than the stadium horn (or 921.9 L_net for 6ea.). So you're trading of volume for a second driver and roughly twice the required power, but you're gaining 3 to 4 dB more output and a flatter response (in the simulation).

And then there is the question, what does it sound like, and how does it project? Would one be better for outdoors, and the other better for indoors? And so on....

Regards,
Attached Images
File Type: jpg 3015LF_Dual_T_TQWT_v_Stadium_horn_1W_SPL.jpg (78.3 KB, 255 views)
File Type: jpg 3015LF_Dual_T_TQWT_v_Stadium_horn_11mm_SPL.jpg (81.0 KB, 250 views)
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Last edited by tb46; 31st December 2011 at 02:09 AM.
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Old 31st December 2011, 03:06 AM   #1237
GM is offline GM  United States
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Quote:
Originally Posted by weltersys View Post
On axis directivity increases more in multiples at upper frequencies than lower, so even if Hornresp took directivity into account, the result should be more upper frequency (around 100 Hz) on axis SPL increase rather than more LF.

Typical TH behave more like a BR (which hardly go lower in LF corner in multiples) than FLH, which do go lower in low corner and level in multiples.
Just as theory predicts.

Seems reasonable based on what I know and the TP, TH sims I've typically done in HR show barely a 1 Hz offset from [1] to [8] speakers, but then it turned around and made FLH like predictions with a TH layout that's a bit different than any I've seen posted by others, so it makes me wonder if HR is wrong.

GM
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Old 31st December 2011, 03:54 AM   #1238
Djim is offline Djim  Netherlands
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Maybe I should make it more practical... Use 3015lf's in a DJK Push-Pull setting (vertical aligned) in any type of design and you should hear the difference clearly in that they will keep their low end and transients (less compressed) much longer as you step up in power, compared to two single units.
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Old 1st January 2012, 05:33 PM   #1239
tb46 is offline tb46  United States
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Hi djim,

I agree, that's why I often look at tapped horns with two drivers used in some form of push-pull arrangement, e.g.: Post #1229. I also like the djk's PPSL design.

Regards,
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Old 1st January 2012, 06:01 PM   #1240
tb46 is offline tb46  United States
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Hi GM and weltersys,

I remembered and took another look at the chart of "Normalized Acoustic Radiation Resistance - piston in an infinite baffle". That should be available in a lot of places. My "library" is still in storage-as I don't seem to be able to get the remodeling finished after the last move-so I found it by googleing "acoustic radiation resistance v." the second entry is the Handbook of Acoustics, Malcolm J. Crocker, P.1390.

I vaguely remember that-a long time ago-I did a series of measurements after reading a comment in the Audiocyclopedia, that doubling of the number of drivers more strongly affects the very low end of a speakers response, than the middle range. Which I took to mean e.g.: @ 50Hz v. @ 500Hz; and, I found this to hold true. In other words: there is a greater increase in SPL if you are on the 6dB slope of the curve (ka<2) than if you are in the horizontal section (ka>2).

From this I conclude, that David McBean's Hornresp is probably correct. I'll leave it up to the experts to crunch the numbers in any particular case as I'm math-challenged, but I'll attach a quick spreadsheet screen print (any corrections are highly welcome):

Regards,
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File Type: jpg Acoustic Radiation Resistancejpg.jpg (75.8 KB, 210 views)
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