Single sheet TH challenge

[CRESCENDO]

Originally Posted by tb46

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.

[Djim]

Crescendo, you can also use DJK's Push-Pull principle in a TH. PP is not limited to basreflex. The only trick is to design it in such way that both drivers are placed in a vertical arrangement crossed by the centre of both drivers, to get the max effect of PP.

[CRESCENDO]

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!

[weltersys]

Originally Posted by tb46

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

[jbell]

maybe we can impose on flipc to do some measurements.... he has a dozen.

[Djim]

Originally Posted by CRESCENDO

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.

[Djim]

The PPTH in a Tham style folding is the most easy way to get DJK's PP driver arrangement. You have to make up for the differences in sound source points but it's an easy layout.

[CRESCENDO]

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.

Originally Posted by Djim

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.

[CRESCENDO]

Originally Posted by Djim

The PPTH in a Tham style folding is the most easy way to get DJK's PP driver arrangement.

Oh, that looks pretty cool. Thanks for sharing! My brain thanks you

Originally Posted by Djim

You have to make up for the differences in sound source points but it's an easy layout.

Oh.. how so?

[Djim]

Originally Posted by CRESCENDO

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.

Originally Posted by CRESCENDO

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....