Single sheet TH challenge

I also like the djk's PPSL design.

I was very intrigued by his PPSL as well, so I modeled and planned a cutsheet. But, after further reading, the 6dB EQ increase required for this design seems to go beyond the 3015LF's thermal capabilities (unless I'm totally missing something). Maybe it's just a great design for other drivers and not particularly the ones I was attempting to utilize.
 
Hi GM and weltersys,
-Snip-
From this I conclude, that David McBean's Hornresp is probably correct.
Hornresp predicts the low corner drops in frequency in multiples in the sims for both TH tested in the charts below.
As you can see, the low corner changes no more for two TH than with a “dummy” (undriven) cabinet along side the driven cabinet.

On the basis of actual measurements I conclude that David McBean's Hornresp is incorrect in predicting that the low corner of TH lowers in multiples.

In post #380 Jim (jbell) writes:
“Yes the ss15 is leaving a bit of 40hz behind in single cabinets. I always tell anyone building, run pairs or quads. It's flat to 40 in quads, and pretty respectable in pairs. “

The idea that TH low corner goes lower in multiples is not supported by any actual measured response as far as I have seen.

I just went through this entre thread and could not find any actual measured response curves for a single SS15 compared to two or four, other than simulations have you seen a comparison anywhere showing a drop in TH response in multiples?

Art Welter
 

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Hi Djim,
Do you have any examples/images to show to get a better idea? Have you heard this type of TH design before? If so, impressions? Are there any simmed or measured responses floating around that you know of?
Thanks!
Hi Crescendo,

The principle behind Push-Pull is not too difficult and explained in several threads. It all comes down to suppression of non-linearity's from drivers. This non-linear phenomenon is a collective name for several factors that are in play. I my view there is one specific factor that becomes even more important in relation too Tapped Horns. The absence of an 'air-spring' like other loadings have, puts extra stress on the drivers cone and its suspension in a TH system. In case the cone resonances fall together with the system resonances of the TH I believe you will see higher dynamic compression figures. To my ears it can actually ruin the PP effect. Especially in the last power up stage, when the forces in the cone become bigger as the PP can deal with.

The suppression of non-linear behaviour by a Push-Pull setting is nothing new. Some major sound system manufacturers have been using the PP for this reason. The difference between their version of the PP and DJK’s PP(SL) is the arrangement of the drivers. Traditional PP arrangements use both drivers on the same driver panel. One of the drivers is flipped over and re-poled in order to put them in phase. The difference with DJK’s version is that he puts them in a 'bottom-on-top' arrangement, vertically aligned or whatever the correct word is in English.

In the traditional way the PP-effect is only max in the lowest part of the bandpass of a sub while in DJK’s version, the PP-effect is extended over pretty much the entire bandwidth of the sub. You can maximise the PP effect by arranging the drivers as close as possible. Like DJK mentioned, the effect will be the greatest for drivers that suffer most from these non-linear behaviour and often that are the lower budget drivers.

High budget LF PA drivers have been carefully researched to guarantee the lowest losses possible by the cone. For instance; pressed cone rings, dual spider techniques, flux-rings, carbon cones, fibre enforced cones, vertical pressed slots in surrounds and even old fashion liquid treated cones (like modern mixtures with water repellents) are all examples of suppressing losses by the cone, especially at the highest excursion for PA drivers.

Now more practical... Does PP work? Yes it does! Is it predictable? Well, till some degree. HornResp, Akabak and other modelling software can't model the effects of non-linear behaviour and other losses. I believe you can predict the points where PP will be effective by calculating the resonances in the cone.

If you want solid proof about the effects of Push-Pull for yourself, just build one of the many examples with a PPSL arrangement for your 3015lf's. Build two separate basreflex subs, each of half the volume of the PPSL and same tuning. Hook them up and let your ears decide if it worth for you and your drivers.
 
Hi Djim,

I've read a lot about PPSL designs (djk has posted his and some others on this and other forums) - but, I am having trouble picturing a properly designed, vertically aligned, bottom-on-top, PP TH (possible??). I've seen a few "PP TH", but the drivers were mounted in such a way that it seemed they would cause cancellations (one driver further up the horn than the other). I was thinking the drivers would have to be equidistant to S1 (is that the proper way to describe that thought?). So, I don't think I have yet seen a proper PPTH on this forum.

If you want solid proof about the effects of Push-Pull for yourself, just build one of the many examples with a PPSL arrangement for your 3015lf's. Build two separate basreflex subs, each of half the volume of the PPSL and same tuning. Hook them up and let your ears decide if it worth for you and your drivers.

I was very close to building one - but, with the information I have been given, it wouldn't be a smart idea to design a PPSL for my 3015LFs.

djk's style PPSL requires Q=2 filter (+6dB) at the cut-off freq.
2 x 3015LF = 900W AES/1800W Max
900W +6dB = 3600W. That's twice the max power handling capabilities of the 3015LFs.

Please correct me if this is wrong.
 
djk's style PPSL requires Q=2 filter (+6dB) at the cut-off freq. 2 x 3015LF = 900W AES/1800W Max 900W +6dB = 3600W. That's twice the max power handling capabilities of the 3015LFs. Please correct me if this is wrong.
True, since you want to play D&B and Dub music that can have constant waveforms below 40Hz.

That's why I suggest you could design your TH in such way that the -3dB point falls together with its excursion dip. That way your make-up eq doesn't cost much extra excursion and can you get a flat response from the otherwise 'normal' -3B point. The downside is that below the -3dB point your roll off becomes more steep.

Oh.. how so?
The centre point of the sound source is in the cone. S2 becomes interesting as one magnet makes up the extra cone volume of the other.

Anyway, I'm late as usual so I'm closing down for today....
 
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Here is an example of push-pull drive in a hornsub:
Lots of measurements and other technical data on that page, including documents specifically about its push-pull drive, like these:
Look at the construction photos in the links below to see the layout. You'll notice the drivers are very close together. This helps ensure good summing, for cancellation of harmonics through the band. They're actually closer than necessary for cancellation through the passband, which is a good thing to ensure harmonic reduction is most effective.
What you may not notice in the photos is the symmetry of the acoustic load. Attention should be paid to chamber sizes, to make sure they are the same. One does not want to introduce an asymmetrical acoustical load, since asymmetries and nonlinearities are what we are trying to mitigate.
 
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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.

Hi Oliver,

This can be readily demonstrated in Hornresp. The light traces in the attached screenprint show the normalised acoustical impedance of the air load on one side of a circular vibrating piston of area A set in an infinite baffle. The dark traces show the normalised acoustical impedance of a vibrating piston of area 2 x A.

In this example, you can see that the difference between the black and gray resistance traces is considerably greater at 100Hz than at 1000Hz.

Kind regards,

David
 

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On the basis of actual measurements I conclude that David McBean's Hornresp is incorrect in predicting that the low corner of TH lowers in multiples.

Hi Art,

The attached Hornresp screenprint compares a single William Cowan 60Hz tapped horn (gray trace) against two William Cowan 60Hz tapped horns connected in parallel, with SPL levels suitable normalised. As far as I can see, it predicts pretty much the same general differences as your actual measured comparison - certainly close enough for all practical purposes.

From a theoretical perspective, there is no reason why the low frequency response characteristics of multiple tapped horns should be any different to those of multiple front-loaded horns having similar mouth areas. The laws of physics remain the same for the two horn types.

Kind regards,

David
 

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On the basis of actual measurements I conclude that David McBean's Hornresp is incorrect in predicting that the low corner of TH lowers in multiples.
WHAT?:grumpy:
Certainly you are not claiming this because of your Keystone TH? Your TH and lots of other designs are not built in a manner that closely matches the Hornresp model, your TH for example terminates not at the end of the path but along the last ~40cm of the path. You also have provided measurements that there is a positive gain when you build an additional structure onto the front of the cabinet giving it additional frontal area so to say that there is no gain from arraying subs to increase frontal area seems to fly in the face of this.

Did you party too hard over the holiday???:confused:
 
The two graphs imply...

  1. that a pair of the Cowan 60 Hz horn have improved response over a single below 70Hz
  2. that a pair of Keystone TH also have improved response over a single Keystone TH, below approx 100Hz
The shape of the graph does not change much when comparing a single with a pair of TH.

However, the graphs do 'shift to the left' or experience a downward frequency shift which appears to represent additional extension by a few Hz.

Regards, Ben
 
"Please correct me if this is wrong. "

The 6dB boost is a requirement of the 6th order design using a low Qts woofer, it is not needed per se for a PPSL design.

The PPSL principle may be applied using sealed, vented, dipole or horn configurations; the driver parameters selected according to the type of loading you wish to employ.

Danley uses semi co-planar PP mounted drivers in several of his TH designs. The spacing of the driver center-to-center determine to how high of a frequency the distortion cancellation can occur. For normal driver mounting we say optimum coupling occurs if the sources are no more than 1/4W spaced. For the reduction in 2nd harmonic distortion it then needs to be no more than 1/8W. For 12s mounted with c-t-c of 13" that would be around 130hz, for 15s mounted with c-t-c of 16" that would be around 106hz.

"D&B and Dub music that can have constant waveforms below 40Hz. "

Does it really? Most spectrum analysis I have seen shows a healthy amount of 2nd harmonic present too, reducing both power and excursion requirements. For shows that have a lot of D&B and Dub music, I generally put up three double 15 PPSL per each double 12 horn mid. With my 30hz PPSL I am more concerned with running out of x-max in the 50hz region (region of maximum level in most dance music) than I am of running out of power on those occasional 30hz notes.
 
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True, since you want to play D&B and Dub music that can have constant waveforms below 40Hz.

That's why I suggest you could design your TH in such way that the -3dB point falls together with its excursion dip. That way your make-up eq doesn't cost much extra excursion and can you get a flat response from the otherwise 'normal' -3B point.

Oh yes! That's what the next design will be. This go around, I would just like to use what I have on hand for the several upcoming shows. After the 1st 1/4 of the year, I should be able to begin building cabs with the above mentioned qualities. I just need that below 40Hz energy - if I didn't, I would have a 6-pack of SS15s by now :)

The downside is that below the -3dB point your roll off becomes more steep.

Yeah, that's why I want a fairly low (freq) -3dB point. We'll get there!

The centre point of the sound source is in the cone. S2 becomes interesting as one magnet makes up the extra cone volume of the other.

So, like positioning them differently..? or adding more cabs..or..??
 
For shows that have a lot of D&B and Dub music, I generally put up three double 15 PPSL per each double 12 horn mid. With my 30hz PPSL I am more concerned with running out of x-max in the 50hz region (region of maximum level in most dance music) than I am of running out of power on those occasional 30hz notes.
You say this like you have a different high SPL rig? Care to share?
 
Originally Posted by weltersys
On the basis of actual measurements I conclude that David McBean's Hornresp is incorrect in predicting that the low corner of TH lowers in multiples.
Hi Art,

The attached Hornresp screenprint compares a single William Cowan 60Hz tapped horn (gray trace) against two William Cowan 60Hz tapped horns connected in parallel, with SPL levels suitable normalised. As far as I can see, it predicts pretty much the same general differences as your actual measured comparison - certainly close enough for all practical purposes.

From a theoretical perspective, there is no reason why the low frequency response characteristics of multiple tapped horns should be any different to those of multiple front-loaded horns having similar mouth areas. The laws of physics remain the same for the two horn types.

Kind regards,

David

David,

The fact that in most respects Hornresp sims are very close to reality is proof that your theory is, for the most part, sound. Your program is incredibly useful.
I have seen (and experienced)plenty of real measurements showing the low corner of FLH lowering in multiples, this feature is lacking in TH as far as what I have measured, and thus far I have seen no other actual measurements supporting it.

From what I can see of the two William Cowan 60Hz tapped horns connected in parallel, the LF response has increased by about 2 dB compared to the upper response.

The Hornresp sim for the SH15 shows the low corner dropping almost 10 Hz using four cabinets, a much larger spread.

Looking at the LF response of one and two of a 2x10” tapped horn with a similar rolloff as the William Cowan horn, I see no difference, in other words, the 2 dB (or so) increase Hornresp predicts does not occur.

Do you have any real-world measurements that reflect the theoretical dropping of the LF corner in TH that Hornresp predicts?

Cheers,
Art
 

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