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Old 10th January 2012, 03:34 PM   #1331
tb46 is offline tb46  United States
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Hi,

Looking at Djim's higher resolution picture of the DSL-TH115 SPL measurements a little closer: it seems to me that at 20Hz the difference between the lines is more than 6dB, the same holds true for 30 and 40 Hz, at 50 Hz the red line is already showing compression problems, the brown to blue difference is about 6dB. Anyway, I don't have the data sets to look at, I don't have more than a rudimentary idea of the measurement setup, and - as much as I like to ponder about audio and loudspeakers - I certainly would not base any conclusions as to the validity of a simulation software on this graph.

Measuring at 10m/100W is not a valid way to get data to compare to the results of a small signal TS/no losses/no compression simulation in software. It's a great way to evaluate the behaviour of PA loudspeakers and systems, and to compare different loudspeakers or systems to each other; provided the measurement system response is very well known.

Thanks to everybody's observant input David found the problem in his software, and his proposed model should get closer to the "measured results" and to general expectations.

I just hope we will not loose accuracy in the simulation of individual speakers driven internally by multiple drivers.

Either way though, Hornresp is a great tool that makes a lot of analysis possible to laymen like me. Without it (or Akabak) I would be reduced to the "good old days" of calculate/cut/try/measure when it comes to horns and all the variations on tapped enclosures, and who's got the time?

Regards,
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Old 10th January 2012, 07:23 PM   #1332
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Quote:
Originally Posted by David McBean View Post
Hi Everyone,

Many thanks for all your recent inputs. While there are some understandable differences in the sets of data that have been provided, on balance the measured results would appear to be closer to the predictions made by the proposed new Hornresp multiple speakers model, rather than the existing model.

To summarise the differences between the two models:

Two speakers connected in parallel compared to single speaker - same voltage:
Existing model:
+6dB at low frequencies and +3dB at high frequencies (see Old_2P.png).
Proposed model:
+6dB at low frequencies and +6dB at high frequencies (see New_2P.png).

Two speakers in connected in series compared to single speaker - same voltage:
Existing model:
+0dB at low frequencies and -3dB at high frequencies (see Old_2S.png).
Proposed model:
+0dB at low frequencies and +0dB at high frequencies (see New_2S.png).

Kind regards,

David
David,
This has been a fascinating exchange.

The coherent addition of 6 dB is proven with two small two way horn speakers measured at 2 meters as shown in post 1264.
The 0 dB gain of doubling series cabinets is proven by the measurements of one and two dual Lab 12 cabinets in series in post 1322, the net gain of two is about .75 dB over the measured range.

Important points:

A)Because of path length difference, large flat front arrays measured close relative to the array frontal width will cause upper frequency incoherence which will result in less additional gain (or even attenuation) in multiples.

B)A large array becomes an additional boundary as the lower wavelength approaches the array width, increasing forward directivity, which imparts gain relative to the frontal area in addition to the 6 dB coherent addition.


An example of boundary gain can be seen in post 1244, a shorted non-powered cabinet along side a powered cabinet increases response by about 1 dB from 30 Hz to 120 Hz.
Going from one to two ported cabinets of half that frontal area (WSdualLab12) results in a .66 dB LF gain.
Looking at Djm’s rendering of Wayne’s FLH pair in post 1322, the pair increase by 2 dB in the LF, both the FLH and TH sets of cabinets are almost the same exact frontal area.
In #1324, Djim renders the 1-4 difference in the TH-115 as 2.5 dB.
This small LF difference spread from four different cabinet types measured by three individuals indicates that frontal area increasing boundary size increasing forward directivity is behind the LF increase over 6 dB, not horn related phenomenon.

Even though I’d prefer the change from the old model, the proposed model will actually be less representative of one meter multiple large cabinet measurements, though it will be a bit closer to 10 meter measurements.

Unfortunately, neither model will exactly correspond to real world multiple cabinet results because of the increased boundary size and HF cancellation.

I’d suggest mentioning points A & B if you do decide to implement the change.

After reviewing all this data, I do agree with you that TH don’t require a different set of rules from FLH or BR.
Multiples of different bass cabinet designs will exhibit different response variations from a single, and Hornresp won’t be predictive of those differences.

Hornresp will still be a great simulation program, and better for the change.

Art Welter
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Old 10th January 2012, 07:42 PM   #1333
Mark Kravchenko --- www.kravchenko-audio.com
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Acoustically small areas are being considered in the low end due to the small surface area of the cabinets in relation to the wavelength of sound. That may account for the less than ideal loading of multiple cabinets as frequency decreases.
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Old 10th January 2012, 08:47 PM   #1334
epa is offline epa  Netherlands
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Quote:
Originally Posted by David McBean View Post
Hi Everyone,

Many thanks for all your recent inputs. While there are some understandable differences in the sets of data that have been provided, on balance the measured results would appear to be closer to the predictions made by the proposed new Hornresp multiple speakers model, rather than the existing model.

To summarise the differences between the two models:

Two speakers connected in parallel compared to single speaker - same voltage:

Existing model:
+6dB at low frequencies and +3dB at high frequencies (see Old_2P.png).
Proposed model:
+6dB at low frequencies and +6dB at high frequencies (see New_2P.png).

Two speakers in connected in series compared to single speaker - same voltage:

Existing model:
+0dB at low frequencies and -3dB at high frequencies (see Old_2S.png).
Proposed model:
+0dB at low frequencies and +0dB at high frequencies (see New_2S.png).

The results generated by the proposed new model are consistent with AkAbak predictions and the standard SPL summing rules for coherent / correlated signals. The new model does not however, allow for bass extension due to mutual coupling of multiple horn mouths - it seems from measurements that this is not really an issue anyway, in that the real-world coupling between adjacent speakers is not as tight as perhaps first thought.

Please note that these are the only two model options under consideration - I not want to deviate from the standard models in an attempt to better fit measured data. Also, I don’t want to include both options in Hornresp - it could be confusing for some users, and make comparison of results more difficult.

If anyone believes that it makes more sense to retain the old model rather than change to the proposed new model, could they please let me know as soon as possible, either by way of this thread or by private e-mail to the address given on the Hornresp web page. Thanks.

Kind regards,

David
wil this also affect 0,5 ,1 ,2,4 pi settings ,in the graph?
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Old 11th January 2012, 05:58 AM   #1335
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Quote:
Originally Posted by tb46 View Post
I just hope we will not loose accuracy in the simulation of individual speakers driven internally by multiple drivers.
Hi Oliver,

You can rest easy - the multiple drivers model remains the same :-).

Kind regards,

David
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Old 11th January 2012, 06:08 AM   #1336
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Quote:
Originally Posted by epa View Post
wil this also affect 0,5 ,1 ,2,4 pi settings ,in the graph?
Hi epa,

No, it won't. Changing the Ang setting will have the same effect as it does now.

Kind regards,

David
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Old 11th January 2012, 06:30 AM   #1337
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Default Multiple Speakers

Hi Everyone,

Thanks for your comments on the relative merits of the old and new models. Taking into account all the feedback received to date, the following alternative new model has been developed which allows for bass extension due to mutual coupling of multiple horn mouths (other than for tapped horns and bass-reflex systems), and also still remains consistent with the standard SPL summing rules for coherent / correlated signals.

Screenprint New1_2P.png shows two front-loaded horn speakers connected in parallel, compared to a single speaker with the same drive voltage. The -3dB point for the two speakers in parallel is 69Hz, as shown. The -3dB point for the single speaker is 77Hz.

Screenprint New1_4P.png shows four front-loaded horn speakers connected in parallel, compared to a single speaker with the same drive voltage. The -3dB point for the four speakers in parallel is 63Hz, as shown. The -3dB point for the single speaker is 77Hz.

Screenprint New1_2S.png shows two front-loaded horn speakers connected in series, compared to a single speaker with the same drive voltage. The -3dB point for the two speakers in series is 69Hz, as shown (interestingly - the same as for the two parallel speakers). The -3dB point for the single speaker is 77Hz.

Screenprint New1_4S.png shows four front-loaded horn speakers connected in series, compared to a single speaker with the same drive voltage. The -3dB point for the four speakers in series is 63Hz, as shown (interestingly - the same as for the four parallel speakers). The -3dB point for the single speaker is 77Hz.

The alternative new model seems to "tick most (if not all) of the boxes" as I currently understand them. Can anyone see any problems in adopting the alternative new model in preference to either the existing model or the original new model?

Based on earlier feedback, multiple tapped horns and bass-reflex systems in the alternative new model currently do not have the bass extended, but this can be readily changed if required to make them perform the same as for other systems - with the bass extended.

Could Art in particular, please comment on whether or not tapped horns and / or bass-reflex speakers should be treated any differently to other speaker types in the alternative new model - the available data now seems to be a bit inconclusive in this regard.

As you may have gathered, I have not been getting much sleep lately... :-).

Kind regards,

David
Attached Images
File Type: png New1_2P.png (26.3 KB, 209 views)
File Type: png New1_4P.png (26.4 KB, 207 views)
File Type: png New1_2S.png (25.7 KB, 206 views)
File Type: png New1_4S.png (26.2 KB, 204 views)
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Old 11th January 2012, 02:01 PM   #1338
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Good stuff here. I have only briefly skimmed through.

Has anyone read the AES paper by Don Keele Maximum Efficiency of Direct Radiator Loudspeakers? Obviously we are comparing various other alignments here not just DR's but there seems to be a lot of common overlap. Some things that I feel may have impact...Theoretical maximum efficiency is much more easily met at higher frequencies first. Secondly the size of the radiator/s involved relative to the frequency has impact on the maximum efficiency possible. Thirdly the size, shape or area of the radiator/s involved can also have impact on how far away from them is considered to be "direct" or nearfield sound. This would be the "bubble" that Tom D. sometimes mentions. A larger radiation area gives a larger further extending bubble. This probably also has some effect on the rate of drop off with distance according to the inverse square law. These are just some hunches that I have. I have observed some strange things measuring subs.

FLH's have the largest radiator area usually.
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Old 11th January 2012, 11:03 PM   #1339
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Quote:
Originally Posted by David McBean View Post
Hi Everyone,

Thanks for your comments on the relative merits of the old and new models. Taking into account all the feedback received to date, the following alternative new model has been developed which allows for bass extension due to mutual coupling of multiple horn mouths (other than for tapped horns and bass-reflex systems), and also still remains consistent with the standard SPL summing rules for coherent / correlated signals.

The alternative new model seems to "tick most (if not all) of the boxes" as I currently understand them. Can anyone see any problems in adopting the alternative new model in preference to either the existing model or the original new model?

Based on earlier feedback, multiple tapped horns and bass-reflex systems in the alternative new model currently do not have the bass extended, but this can be readily changed if required to make them perform the same as for other systems - with the bass extended.

Could Art in particular, please comment on whether or not tapped horns and / or bass-reflex speakers should be treated any differently to other speaker types in the alternative new model - the available data now seems to be a bit inconclusive in this regard.

As you may have gathered, I have not been getting much sleep lately... :-).

Kind regards,

David
Get some sleep, things will be more clear then!

From the observations gleaned in the recent past posts, (Djim’s handiwork has been particularly helpful) and over the years of listening and measuring, it appears to me there is very little difference in the LF response gain between multiple cabinets whether BR, TH, or FLH.

From a model perspective, I see no evidence supporting an almost 1/3 octave lowering of the low corner of four FLH compared to one, though evidence supports a minor LF corner (F3) lowering in multiple FLH.

The important boxes not ticked are the reduction of upper frequencies in multiple cabinets, and the LF increase due to the larger boundary created by multiple cabinets.
I doubt those two issues could be addressed in Hornresp without major code addition, though the boundary issue might be addressed with a “cabinet frontal area” addition.
Presently, this important consideration is not included, but can be simulated by “stretching” the last horn segment, though that still does not agree with measured results.
As a mental construct, (or a Hornresp input) consider two sealed cabinets, each the same volume, but one having a frontal area of 10 x10 meters , the other 1/2 meter x 1/2 meter square.
The 10 x10 meter cabinet could be considered a 180 x180 degree horn, or a sealed box, but regardless of what it is called, the two identical volume sealed boxes will both have a drastically different measured response in free space and half space.

sebDIY posted charts in 1311, the Punisher and the TH-115 both suffer from the “unplugged cabinet syndrome”.

Doober originally posted the Punisher plots, he wrote 17 December 2009 at 5:38pm:
“Shortly after posting the plots I realized what was causing the dips. For the plot of one box I had an unpowered box sat on top. For the plot of 3 boxes I had a stack of four, one unpowered. It would seem that the unpowered box is sucking a bit of the energy from the powered one at those points. The fact that the dips are smaller on the 3 cabs plot backs this up.”

An example of the above problem and boundary gain can be seen in post 1244, a shorted non-powered cabinet along side a powered cabinet increases response by about 1 dB from 30 Hz to 120 Hz over the single free standing cabinet, picture included again.

From all the data it is apparent FLH do increase slightly over +6 for doubling in the LF, and the low corner goes down by only a 1 or 2 Hz.
Going from 2 to four, another slight increase over +12 is observed, but none of the examples shown seem to be over +15, a 3 dB increase over what would be expected.

TH also exhibit the slight increase in LF over +6 or +12, but no LF corner decrease.


In light of the obvious difference an unpowered cabinet makes in reducing level at some frequencies and adding level at others, I’d suggest the deviation of +6 or +12 gain at upper bass horn frequencies may be due to diffraction into adjacent cabinet’s mouth area causing the reflected output to be out of phase, progressively attenuating upper frequencies, which results in a flatter response in multiples when combined with boundary effect increases at low frequencies.

Whatever is behind the upper attenuation in multiple bass horns, and whether any model can be made to account for them, they are apparent in measurement.

Your new proposal lowers the low corner from 77 Hz to 69 for 2 cabinets, an 8 Hz difference, then down to 63 Hz for 4 horns, almost a 1/3 octave decrease in low corner.
None of the measurements indicate a LF corner change near as drastic as that, the model seems to be about 4 times measured results for the 12Pi, Chorn, Punisher, Labhorns etc.

As can be seen clearly in my “dummy cabinet” picture, a baffle doubling frontal area adds 1 dB.
When the ground plane mirror reflection is considered, doubling frontal area quadruples area.

This would make for a different LF extension in full space compared to half space, probably not part of the Hornrep model.

The large boundary increases directivity so forward gain is increased, while level to the sides and behind is reduced, which can be measured with any cabinet type of large array.
“Barn doors” were often added to theater horns for this reason.

I have included a revision of my own findings- my written Chorn charts previously posted had some clerical errors and a stupid amplifier mistake which became apparent after comparing them to later Smaart charts.

Art Welter
Attached Images
File Type: jpg SimMeasured.jpg (87.2 KB, 155 views)
File Type: png Dummy.png (73.8 KB, 23 views)
File Type: png Chorn Rev.png (19.0 KB, 23 views)
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Old 11th January 2012, 11:09 PM   #1340
djk is offline djk
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"Has anyone read the AES paper by Don Keele Maximum Efficiency of Direct Radiator Loudspeakers? "

I have, that's why I don't try and build full sized 30hz bass horns.
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