TH-18 Flat to 35hz! (Xoc1's design) - Page 52 - diyAudio
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Old 3rd March 2012, 08:50 PM   #511
Xoc1 is offline Xoc1  United Kingdom
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Quote:
Originally Posted by Djim View Post
We didn’t have any problems powering the 18LW2400 up till 1800 Watts (complex noise burst following AES/IEC guidelines and power measured by current/voltage method to prevent calculation errors from thermal rising of the Re). It was beyond the 1800 Watts when excursion became unstable and yes at 1800 Watts it shows quiet some excursion, still far below Xlim. All four cabs (including mouth and ‘broom’ bracing as suggested in my earlier post) are build/owned by a hardstyle DJ, who punish them with a Labgruppen FP9000 (2 cabs per channel, cut at 36Hz -110Hz / 48dB/oct) and no driver has returned since… To be honest I don't think this driver will do any better in the Keystone.

The B&C drivers 18SW115 are tested by somebody else but I have no reason to doubt his findings.
Quote:
Originally Posted by Djim View Post
The Xoc1-TH18 loaded with a 18Sound 18LW2400 does allow 1800 Watts (1.5 x AES power) without any excursion problem with the low cut at 33Hz. If you want to use this driver in the Xoc1-TH18 with the full 2400 Watts, I would use a low cut above 37Hz (measure the impedance to pinpoint the exact frequency) .

The Cox1-TH18 loaded with the B&C 18SW115 (4Ohm!) does give low end extension by a couple of Hertz but more importantly it is a couple of dB’s louder in sensitivity, below 38Hz, compared to the (half price) 18Sound 18LW2400.
Hi Djim
Very pleased to hear about positive results.
This is very useful information for other prospective builders and users.
Its obvious that you have taken care with your measurements. Have you been holding out on us, this is the first I have heard about these builds!
Have you any more details you would like to share?

Quote:
Originally Posted by Djim View Post
Hi Art,

The Keystone mouth is much less of a mystery as you might think. It is actually not that difficult to simulate in HornResp if you do it right. I do agree that above its full wavelength it become less accurate. This counts for most models from HornResp because HornResp 'sees' no forms (like the extra volume of corners) but only 'sees' the general layout and its volume in an ideal way.

The problem with the HornResp model you are using, is that is based on wrong inputs. The centre for the Keystone mouth is wrong positioned which makes the total length of the hornpath way too long! The extra volume between the driver and the mouth is not represented at all in the model you are using. If you look carefully to my model you will see it is much more accurate and the resonance points are located very accurately. But it needs better CAD modelling to be more precise. If you are interested I can share in detail, in your Keystone thread if you want.

As you already know, I also agree that symmetric circular narrowing of the mouth will not improve excursion stability nor does it improve LF extension. It does not in our models and it does not in reality. The form for this narrowing is the key for successful improvement and yes it is possible.
I think that it would definitely be worth looking into the Keystone TH design more closely. Whatever Art has done it it definitely working.
Art built many variations of his cabinet to find the sweet spot. The TH18 is CAD and Sim only. I first posted this design 10 months ago and we are still looking for a way to improve on it.

I still think that the throat is the key to getting the last bit of control out of the TH18 design. Squeezing down the throat area is definitely possible. Josh Ricci has shown that higher compression in the throat is practical. Also reducing the throat opens up the possibility of increasing the path length.
David McBean recently posted on the Hornresp thread that VTC should include the cone volume, but how many of us are even bothering to do that!
I think that the offset nature of the TH throat is more complicated than the Hornresp model.
Imagine a sim where S2 is reduced to almost zero. The reported compression ratio would be massive, but in reality there would still be a conciderable cross sectional area at the S2 point, due to the baffle cut out and the actual shape of the speaker cone.......
Regards
Martin (Xoc1)
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Old 4th March 2012, 12:05 AM   #512
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Quote:
Originally Posted by Xoc1 View Post
David McBean recently posted on the Hornresp thread that VTC should include the cone volume, but how many of us are even bothering to do that!
I think that the offset nature of the TH throat is more complicated than the Hornresp model.
Imagine a sim where S2 is reduced to almost zero. The reported compression ratio would be massive, but in reality there would still be a conciderable cross sectional area at the S2 point, due to the baffle cut out and the actual shape of the speaker cone.......
Regards
Martin (Xoc1)
Martin,
Since Hornresp uses a flat piston as the model, if S2 is reduced, the compression ratio would be massive unless VTC is representative of the cone area.

Modeling with S1 and S3 of the same area and S2 reduced with VTC including the cone volume does give slightly different response curves from the way you modeled the TH18, though they may still not reflect the actual response or the "cone control" that may result.

Art
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Old 4th March 2012, 12:20 AM   #513
tb46 is offline tb46  United States
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Hi Martin,

You are basically talking about introducing a choke point at the S2 location, but when you do that in Hornresp the tapers of both, the S1 to S2 and the S2 to S3 sections get changed. One way you may get close is to add all the length from S2 to S3 into L34, and setting the new S3 to the old S2. Then set L23 real short e.g.: 1cm. That way you can choke S2 without affecting the taper from the old S2 (now S3) to S4. You can still adjust S1 and L12 to suit. The other point where you can squeeze the output of the throat chamber is through the area and length of the coupling element Ap1/Lpt. The throat chamber will still be the cone volume plus any spacer volume (it does not seem to be very critical in Hornresp). It is important to remember, that Hornresp does not model frictional-or other-losses.

Regards,
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Old 4th March 2012, 01:48 AM   #514
Djim is offline Djim  Netherlands
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Hi Martin,

The actual build I was talking about are not our creations and the owner/builder is a client so we had limited time to do serious testing. He was tired carrying our heavy dual 18inch basreflex designs (Monacor loaded) any longer and prepared to give up some low end extension in favour of higher SPL’s. Yesterday I heard from my colleague he changed the compressors in his crossover so I am wondering how long it will take before we see any of his drivers back in our workshop .

You can design a negative of the cone volume that you can attach to the panel it is facing for correcting the cone volume in order to correct S2. However, it does not correct the impedance differences between the left side and the right side of the driver nor does it correct the location of the high pressure zone to the centre of the driver, as we discussed. For that, I do believe the best solution so far, I already showed in post#172 of the "18TBX100 vs 2lab12" thread (see same picture below) is the best way to go from. This is a rough example and I am still working on the shapes. However I still prefer to have the lowest narrowing/throat compression possible since it only creates more losses and often makes the usable bandpass smaller besides the doubts mentioned earlier.


Click the image to open in full size.


I am also still working on the text of Art’s Keystone but my limited CAD skills make it even more time consuming besides my horrible writing speed
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Old 4th March 2012, 04:16 AM   #515
Djim is offline Djim  Netherlands
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LINK to Keystone thread
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Old 4th March 2012, 09:35 PM   #516
Xoc1 is offline Xoc1  United Kingdom
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Thanks for all the replies Lots to take in and concider!
We all know that Hornresp has limitations when it comes to tapped horn design.
It is relatively easy to take the Hornresp model and export it into Akabak to add extra sections.
Perhaps a more simplistic approach would be to ignore the Vtc and Atc settings but compensate for the physical volumes of the speaker cone and baffle board by the shape of the throat section.
As I have said before the compression ratio reported at S2 by Hornresp seems wrong to me. At this point in a offset TH horn if we imagine the piston of the speaker moving in and out, 50% of the air that is displaced /compressed in the throat does not even get to the S2 point in the horn.
Also to use a ramp that tapers from S1 to S2, as in the Othorn for instance, seems wrong to me. It might give better efficiency higher in the passband in a hornresp model, but why does the taper not continue right across the face of the speaker - as it does in some classic FLH designs. Is it because it performs better, or is it because it is easier to sim?????
This might take some time to resolve. Not much spare time at the moment.
A good start might be to get some data together on the actual physical shapes of some of our favourite speaker cones,
Regards Martin (Xoc1)
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Old 5th March 2012, 09:22 PM   #517
Xoc1 is offline Xoc1  United Kingdom
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Question Driver Dimension Request

I have sketched out the throat area of the TH18 and the PDF shows the cross sectional area at S2 - Hornresp calculated S2 area being 460 cm sq and actual area being approximately 729 cm sq!
I say approximately as I do not have any 18" drivers at hand to measure.
I have added some dimensions:-
Suspension outer (or inner diameter of the basket) A
Cone Diameter B
Dust Cap Diameter C
Suspension Ht from mounting face D
Cap Ht from mounting face E
Cone Depth from mounting face F
If anyone has some suitable drivers to hand, that could measure these dimensions to get a more accurate model it would be appreciated.
Regards
Martin (Xoc1)
Attached Files
File Type: pdf Throat Vol TH18 Br.PDF (70.5 KB, 145 views)
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Old 6th March 2012, 01:15 AM   #518
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Quote:
Originally Posted by Xoc1 View Post
I have sketched out the throat area of the TH18 and the PDF shows the cross sectional area at S2 - Hornresp calculated S2 area being 460 cm sq and actual area being approximately 729 cm sq!
I say approximately as I do not have any 18" drivers at hand to measure.
I have added some dimensions:-
Suspension outer (or inner diameter of the basket) A
Cone Diameter B
Dust Cap Diameter C
Suspension Ht from mounting face D
Cap Ht from mounting face E
Cone Depth from mounting face F
If anyone has some suitable drivers to hand, that could measure these dimensions to get a more accurate model it would be appreciated.
Regards
Martin (Xoc1)
Just for the heck of it it measured the 18SW115. Taking into consideration the the volume of air in the 18mm (circular) baffle cutout and the Air Volume (Vtc) in front of the driver is approximately 4920cc. I know the discussion lately has brought up that none of us have really taken Vtc into consideration
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Old 6th March 2012, 04:07 AM   #519
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Played with my Akabak script a little more tonight. If anyone want to play with it I added some drivers. Just remove the block on the T/S line for the driver you want to run. Added the VTC from measuring one of my B&C 18SW115 drivers. I'm still learning things in Akabak so don't be to hard on me if you find mistake let me know




COPY BELOW THIS LINE

|Rev5 - Model based on how geitmans built the spud script and now accounting for Vtc

|TH-18 Flat to 35hz! (Xoc1's design) on DiyAudio.com Collaborative effort

|I have not taken into account the bracing as it makes my head spin adding so many sections of script (I am working on it though)

|TundraLTD Enjoy!!


|================================================= ================================================== ================================================== ============

|Network node numbers for this tapped horn system:

| 0-Voltage-1
| |
| -Chamber-5-Driver-------------------------------------------------------------------------------------------------------------
| | |
|8-Duct-9-Duct-10-Duct-11-Duct-12-Duct-13-Duct-14-Duct-15-Duct-16-Duct-17-Duct-18-Duct-19-Duct-20-Duct-21-Duct-22-Duct-23-Duct-24-Duct-25-Duct-26-Duct-27-Radiator

|================================================= ================================================== ================================================== ============

Def_Const | Data for Vtc Chamber
{
Vtc = 4923.00e-6; |Throat chamber volume (cubic m)
Atc = 1210.00e-4; |Throat chamber cross-sectional area (sq m)

Sd = 1210.00e-4; |Diaphragm area (sq m)

Ltc = Vtc / Atc;
}

Def_Driver 'Driver'

|READ THIS
|Simply remove the block for the driver you wish to Sim
| <-block (in front of Sd) REMEMBER to only have one drive unblocked at a time

|18Sound 18LW2400-8
| Sd=1225.00cm2 Bl=25.77Tm Cms=1.07E-04m/N Rms=5.90Ns/m fs=35.0003Hz Le=1.35mH Re=5.00ohm ExpoLe=1

|B&C 18SW115-8
| Sd=1210.00cm2 Bl=28.31Tm Cms=1.21E-04m/N Rms=10.10Ns/m fs=30.9998Hz Le=1.70mH Re=5.10ohm ExpoLe=1

|B&C 18TBW100-8
| Sd=1210.00cm2 Bl=30.07Tm Cms=8.38E-05m/N Rms=6.78Ns/m fs=35.0003Hz Le=2.45mH Re=6.50ohm ExpoLe=1

|Precision Devices PD1850-8
| Sd=1150.00cm2 Bl=31.41Tm Cms=1.32E-04m/N Rms=6.65Ns/m fs=29.9999Hz Le=1.00mH Re=5.40ohm ExpoLe=1

|BMS 18N850v2-8
| Sd=1213.00cm2 Bl=25.11Tm Cms=1.18E-04m/N Rms=6.10Ns/m fs=29.7001Hz Le=0.89mH Re=5.00ohm ExpoLe=1

|Void Acoustics V18-1000-8
| Sd=1230.00cm2 Bl=34.96Tm Cms=9.35E-05m/N Rms=6.46Ns/m fs=34.5311Hz Le=2.20mH Re=5.50ohm ExpoLe=1

|18Sound 18NLW9600-8
| Sd=1134.00cm2 Bl=30.55Tm Cms=8.13E-05m/N Rms=6.62Ns/m fs=33.9997Hz Le=2.11mH Re=4.70ohm ExpoLe=1


System 'System 1'

Filter 'HighPass' |Highpass filter - 12dB Butterworth (change 'fo=***' and refresh for changes)
fo=31Hz vo=1
{b2=1;
a2=1; a1=1.414214; a0=1; }

Filter 'LowPass' |Lowpass filter - 48dB Butterworth (change 'fo=***' and refresh for changes)
fo=100Hz vo=1
{b0=1;
a8=1; a7=5.125831; a6=13.137071; a5=21.846151; a4=25.688356; a3=21.846151; a2=13.137071; a1=5.125831; a0=1; }

Driver Def='Driver'
Node=1=0=25=5

Duct 'Throat chamber' Node=5=9 SD={Atc} Len={Ltc} visc=1
Duct 'D1' Node=8=9 HD=53.5cm WD=5cm Len=21.92cm visc=50
Duct 'D2' Node=9=10 HD=53.5cm WD=8.6cm Len=19.23cm visc=50
Duct 'D3' Node=10=11 HD=53.5cm WD=11.8cm Len=6.75cm visc=50
Duct 'D4' Node=11=12 HD=53.5cm WD=10.4cm Len=24.92cm visc=1
Duct 'D5' Node=12=13 HD=53.5cm WD=12.1cm Len=10.6cm visc=1
Duct 'D6' Node=13=14 HD=53.5cm WD=12.9cm Len=11.5cm visc=1
Duct 'D7' Node=14=15 HD=53.5cm WD=13.8cm Len=15.17cm visc=1
Duct 'D8' Node=15=16 HD=53.5cm WD=14.9cm Len=9.35cm visc=1
Duct 'D9' Node=16=17 HD=53.5cm WD=15.5cm Len=9.54cm visc=1
Duct 'D10' Node=17=18 HD=53.5cm WD=16.2cm Len=8.6cm visc=1
Duct 'D11' Node=18=19 HD=53.5cm WD=16.8cm Len=11.72cm visc=1
Duct 'D12' Node=19=20 HD=53.5cm WD=17.6cm Len=15.21cm visc=1
Duct 'D13' Node=20=21 HD=53.5cm WD=18.7cm Len=16.42cm visc=1
Duct 'D14' Node=21=22 HD=53.5cm WD=19.9cm Len=49.74cm visc=1
Duct 'D15' Node=22=23 HD=53.5cm WD=23.4cm Len=10.26cm visc=1
Duct 'D16' Node=23=24 HD=53.5cm WD=26.9cm Len=11.11cm visc=1
Duct 'D17' Node=24=25 HD=53.5cm WD=29.6cm Len=28.49cm visc=20
Duct 'D18' Node=25=26 HD=53.5cm WD=40.9cm Len=28.49cm visc=1
Duct 'D19' Node=26=27 HD=53.5cm WD=50.8cm Len=19.93cm visc=1
Radiator 'R1' Def='D19' Node=27
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Old 6th March 2012, 02:10 PM   #520
tb46 is offline tb46  United States
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Hi TundraLTD,

Nice AkAbak work again. Thanks.

Regards,
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