TH-18 Flat to 35hz! (Xoc1's design) - Page 85 - diyAudio
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Old 7th September 2012, 09:17 PM   #841
Djim is offline Djim  Netherlands
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Hi Oliver,

The DSL’s all seem to use relative high compression ratios and capable drivers. I think the trade-off for less capable drivers is less compression at cost of low end or high compression at cost of compression losses (lower excursion than predicted).

Click the image to open in full size.
(highest pressure zone just outside the throat to prevent turbulences at the throat)

I think Art was right, the "V" throat seems to be intended to increase the horn-path and correction of the pressure zone. Later DLS designs don’t have anything that looks like cone correction at all. They can afford since they use capable drivers and several developing stages; model-build-measure-remodel-improve-rebuild-measure...

I like Epa’s view of post#835 about cone correction at S4. Perhaps something like; the percentage of the horn-path taken by the driver, divided by the factor compression-expansion difference between S2 and S4.

(Martin, hope you have a speedy and comfortable recovery!)

Last edited by Djim; 7th September 2012 at 09:20 PM.
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Old 7th September 2012, 09:32 PM   #842
tb46 is offline tb46  United States
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Hi Djim and epa,

Thanks for your explanations. That's about what I was thinking, I still don't quite get why one cannot get there from here with a throat chamber/S2 opening. Oh well. The throat your picture shows looks like it might be great for a symmetrical TH. Djim your throat picture has it all: MDF - BB - OSB..... :-).

Regar
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Old 8th September 2012, 01:02 AM   #843
Djim is offline Djim  Netherlands
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Sorry Oliver,

Was in a hurry...

Click the image to open in full size.
(highest pressure zone just outside the throat to prevent turbulences at the throat)
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Old 8th September 2012, 03:23 AM   #844
tb46 is offline tb46  United States
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Hi Djim,

Thanks again. It 's like I thought, the cone becomes part of the sidewall of the horn path, but there is also a very small compression chamber. I'll attach what I was thinking of (something like Klipsch's "rubber throat"). The whole thing becomes completely untractable without Hornresp/AkAbak.

Regards,
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File Type: pdf De_Throat_1.pdf (5.7 KB, 108 views)
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Old 8th September 2012, 04:58 AM   #845
Djim is offline Djim  Netherlands
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Hi Oliver,

Both volume and throat area determine the compression ratio. Just be careful you are not trading one for the other : - ) But I get what you mean now, thanks for clearing up. My reason to choose for a small as possible chamber and a large opening is to keep the speed at the throat-edge as low as possible and trying to keep as much upper band but I agree that larger chambers can have their advantages when it comes to low frequency (and shorter horn-path means less folding).

You were right, my drawing was meant for Sym-TH's. For more traditional folds and easy build I was thinking.....

Figure 1. needs a 'broom' or 'stump' on the end to prevent turbulences.

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Old 8th September 2012, 02:41 PM   #846
tb46 is offline tb46  United States
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Hi Djim,

Maybe we could look at your figures in Post 845 as having S1=S2 in the middle of the cone with an small "stub" or damping chamber attached to the right towards what used to be S1 with this "damping volume" performing a similar function as the 1/4 wave and Helmholtz resonators we pondered about in the Collaborative thread?

That brings up the thought, what happens with two drivers?

Regards,
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Old 8th September 2012, 07:55 PM   #847
Djim is offline Djim  Netherlands
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Hi Oliver,

Interesting, any specific post of the Collaborative thread I need to look at?
I simulate it pretty conventional, actually. To make it work the S2 area need to be smaller as S3 area and S1 area, otherwise the pressure zone shifts.

Click the image to open in full size.


About the 'two drivers', that's what I used in my dual-tham or PPTH Tham, as you might remember :-). To be honest I really don't get why dual 15" driver TH's aren't more popular for PA. It beats the crap out of any 18" design when it comes to input/output in relation to system volume. The dual tham we designed were about 440 litres, played 40Hz with authority, low cut at 30hz and beats the Cyclops on all levels.
Nevertheless, you can discuss the advantage of PP-settings with quality drivers for PA. If you point the driver magnets to each other in the same S4/S5 area you can gain a couple of dB's at the 1/4WL between them. If you do it right you can make that happen around full wave or 5/4 of the horn, there were compression happens.
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Old 9th September 2012, 12:09 AM   #848
tb46 is offline tb46  United States
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Hi Djim,

Looking back at the Collaborative thread my thinking was mainly directed at the upper frequency peaks and at response extension; don't know how applicable that really is to these PA THs. I asked a question in Post #1004 and followed up in 1012/1013.

I found some additional references in Post #1499:

"...Post #1139/1146/1175: MaVo shows pictures of the interior of the DTS20; Post #1140 explanation by cowanaudio.

In Post #1147: Marcello provided a link to the tapped horn patents.

In Post #1174/1183: jnb shows the effect of a resonator in an AkAbak simulation, with and without damping (e.g.: polyfill stuffing in a PVC tube).

In Post #1187: Cordraconis presented his AkAbak for Dummies script with explanations for the individual elements...."

Do you have a link to your "dual-tham"? edit: Just found it in the Single Sheet thread Post #1247.

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Old 9th September 2012, 04:25 AM   #849
Djim is offline Djim  Netherlands
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Hi Oliver,

Although I am not an Akabak user it was an interesting read, only a pity they didn't put up pics with their findings for 'comic' readers like me ;
What I do know is that simulations can become tricky above the 1 WL resonance of a 1/4WL folded bass-system. Tiny differences between the ideal world of prediction and the world of clumsy wooden dimensions can begin to mesh up things. Also the use of a point source rather than a true area source and the absence of real world losses can be a handicap. In other words creating small band absorbers above 1 WL is difficult for 'one shot one trail' predictions.

As you already considered, how important are spikes and dips above the sub range? Although high level PA subs are usually not used above 120Hz, there is still a crossover-area that needs to be considered so your remarks are legitimate for me.

The dual-Tham project dates from 2010 and I showed you in May 2011 in post#63 of the PPSL thread :-)

Last edited by Djim; 9th September 2012 at 04:30 AM.
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Old 9th September 2012, 06:33 AM   #850
epa is offline epa  Netherlands
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hi jim
intresting discusion.
actually next week im gona design a dual setup with the 15 nlw 9401,
and i was considdering the your design.
only "problem" is how to deal with the different s4 area's..
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