TH-18 Flat to 35hz! (Xoc1's design) - Page 51 - diyAudio
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Old 2nd March 2012, 03:23 AM   #501
Djim is offline Djim  Netherlands
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Hi TundraLD,

All models assume that drivers are linear all the way up to Xmax and don’t suffer from power compression, changing characteristics, changing resistance and so on. Our models only show ideal behaviour from an ideal sinus signal that do not represent the complexity from signals like music. Therefore in our real world the predicted SPL and excursion will not be reached with the calculated power. If you power them enough so they will reach their Xmax, the excursion below the excursion dip can become unstable/uncontrolled. Therefore in most cases TH’s for PA could be best cut at or just below their excursion dip if you want to use them to. You also can improve excursion stability below the excursion dip by applying a slot opening in the throat of a TH. The ideal form of such slot is still being discussed.


For Art:

The model you are using in your post# 498 for your Keystone shows different resonance points at different locations from your measurements. Also is the SPL response very different. I think your model is not a good representation because it doesn’t represent the right volumes at the right spots.

Your measurement:

Click the image to open in full size.


Differences in my model with your model (compare the response and resonance points ):

Click the image to open in full size.

Last edited by Djim; 2nd March 2012 at 03:32 AM.
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Old 2nd March 2012, 04:50 PM   #502
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Quote:
Originally Posted by Djim View Post
Therefore in most cases TH’s for PA could be best cut at or just below their excursion dip if you want to use them to. You also can improve excursion stability below the excursion dip by applying a slot opening in the throat of a TH. The ideal form of such slot is still being discussed.
For Art:

The model you are using in your post# 498 for your Keystone shows different resonance points at different locations from your measurements. Also is the SPL response very different. I think your model is not a good representation because it doesn’t represent the right volumes at the right spots.
Djim,

The Keystone exit shape can not be modeled with Hornresp, the simulation used simply represents the physical path length, shape and cabinet volume.

In the actual Keystone cabinet, to get the LF the sim predicts caused upper frequency response problems.
The Keystone exit took dozens of prototypes to derive the best compromise between top and bottom response.
I opted to loose a few Hz at the bottom for a smoother and more extended top, if one were crossing at 80 Hz (or lower) rather than 100 Hz, a different exit could be used providing more LF.

In fact, the Keystone exit as built can be reduced and get "flat to 30 awsomeness", a "step down mode" plate can be bolted on for the few gigs that require a bit lower response.
The chart below shows some of the various response curves possible with the simple addition of a small external piece of plywood.

Of interest, I tried applying a slot opening in the throat of the Keystone, it did not improve either excursion control, or frequency response.

PASC has noted in his comparison:
"Measured the TH18 Xoc1 and it stops at 117dBs using similar power as input for this driver in the Keystone (past 2300Wrms 8ohms loaded, without clipping the Machine AB+H 9400 amp).
Changed the drained battery for one with full 9V and goes to 126.2 peak holder from 38 ~ 97Hz band, also with very good hi-fi sound, and a bit better defined says my friend who also plays bass guitar.
The cone control IMO, wasn’t as good as in the Keystone, which sound I preferred, maybe because I’ve owned a DJ PA in past, where lows are more present than at live music that my friend is more used to."


Having not compared the two designs using the same speaker, I can only defer to PASC, but having hit the BC18SW115-4 loaded Keystone with as much power as I have available, it still sounds clean when other speakers sound like they are coughing their guts out .

Art
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File Type: png Keystone StepDown.png (103.0 KB, 717 views)
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Old 2nd March 2012, 06:16 PM   #503
Djim is offline Djim  Netherlands
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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.

About PASC’s comments, his story is a little unclear to me. He measures the Xoc1-TH18 with a 18Sound 18LW2400, that has a AES power rating of 1200W.
Quote PASC: "Bellow 38Hz cone control is absent with 18LW2400 at Pe limit."
Therefore it is no surprise his driver will become unstable after more than 2Kw continue sine wave, don’t you think? (Ps how many driver are stable at twice their AES power rating?!)

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.



Last edited by Djim; 2nd March 2012 at 06:38 PM.
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Old 2nd March 2012, 07:55 PM   #504
PASC is offline PASC  Brazil
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Hi Djim!

Where have I stated continue sine wave?
I'm not crazy yet. Maybe a little bit, but...

By me sine waves are only used to make sweep tests to see what the response (around 1W), to take T/S parameters, and to brake in a driver, but this at 1/4 Pe limit = AES amount (that numbers made or made up, with low cut of 40Hz-more than 3dBs bellow using pink noise... to rise SPL = sensibility numbers for the incautious who cannot interpret it, be impressed).

Cleared that, I would say that time that the 18LW2400 barely can take 1200W, with pink noise or music, also obvious with the low cuts stated (38Hz till 96Hz LR 24); increase power and the cone travels insanely; don't try low cut at 30Hz with that kind of power from real amps capable to sustain and surpass 2300WRMS continuous, 8 ohms p/c, not that today's ms ****;

After 18LW2400 we tried 18TBX100, which allowed more power, with better control, but final SPL would be around same program (pink noise and music).

Than put the 18NLW9600 in and cone control was OK with same band, with around a dB peak more than the 18TBX100. If you had the money for 18 Sound 18NLW9600 and or a B&C 18SW115, 4 ohms would be my choice. If not, play 3 dBs less at power amp and you will have near same.

Keystone, I tried only with the 18NLW9600, which with mouth restriction allowed 2300WRMS easily, peaking above 128dBs, with good cone control.

Also tried other low cuts from 25Hz above till 200Hz, cone control remains and sound was always Hi-fi, nearly flat.
Sorry for no good picture but was the only one taken when band was 25 till 200Hz

http://img1.uploadhouse.com/fileuplo...f781d5df5b.jpg

So think it can be used for DJ and live music.
Would not use a sub past 100Hz.
Made THs for 6”, 12”, 15” and 18” drivers, and always cone control was the problem in box; that's why a restriction at throat or at mouth will give results; think only a few drivers from the candidates will actually do well innit, playing all the bass guitar notes at same level and defined as they are played live; why? because I will hear music thru the loudspeaker.

So a friend, bass guitar player, will help me to make good choices.
Regards,
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Old 2nd March 2012, 09:01 PM   #505
Djim is offline Djim  Netherlands
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Hi Pasc,

Lol…. But my quote comes from your post (click the link in my earlier post) “Bellow 38Hz cone control is absent with 18LW2400 at Pe limit”

But thanks for clearing up so quickly. It does make me curious about your method of measuring Power. We didn’t have any problems powering the 24LW2400 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, sill 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.

Last edited by Djim; 2nd March 2012 at 09:06 PM.
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Old 2nd March 2012, 11:00 PM   #506
PASC is offline PASC  Brazil
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Hi!
First time I see this 24LW2400 being mentioned.
This must move some air; but also the cone must weight a lot to not bend and sensibility should be lower. Own you the T/S.
Is it a new driver from 18 Sound as it not appears at their site yet? Will contact local dealer.
Regards,
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Old 2nd March 2012, 11:06 PM   #507
PASC is offline PASC  Brazil
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Hi!
As think I known what happens when abuse the driver above its thermal and mechanical limits as well as how it affect it's longevity (and how I will make glad factory which sells and the reconing service will be within it = what comes first).
One year of normal use within limits is enough to loosing to much the spyder of the driver tells a big loudspeaker factory owner; this will change the T/S parameters a bit and so the predicted response...
So why have I to surpass these limits when I know what will happen, only to have between a dB or two more and at what cost?
Hardstyle DJ isn't a problem when he is well instructed and red lights of control desk are avoided; if lowcuts are proper like mentioned, beside amps like this famous one, which helps to mantain things working, avoiding clips and when power is peak power. If not a compressor will help.

As I know little from this well named and expensive amp, and specs downloaded from factory site, and this one isn't tested by abeltronics, can you give me more details on it.
Like what I read on PDF:
Peak total output both channels driven - 9000W
Maximum output power P/C both working 4500W-2ohms, 3000W-4ohms, 1600W-8 ohms, 800W-16 ohms
Bridged...
I cannot read continues power.
But read "all the power all the time".
To also clear, is it continues (senoidal thru) measured WRMS, till senoidal signal remain curved at top and bottom at oscilloscope window like old school, when we put a shower resistance plugged to the amp output, immersed into a barrel full of water (due to that big power), or are these impressive numbers sustainable for how many ms?
Thanks and regards,
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Old 2nd March 2012, 11:40 PM   #508
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Quote:
Originally Posted by PASC View Post
As I know little from this well named and expensive amp, and specs downloaded from factory site, and this one isn't tested by abeltronics, can you give me more details on it.
Like what I read on PDF:
Peak total output both channels driven - 9000W
Maximum output power P/C both working 4500W-2ohms, 3000W-4ohms, 1600W-8 ohms, 800W-16 ohms
Bridged...
I cannot read continues power.
But read "all the power all the time".
To also clear, is it continues (senoidal thru) measured WRMS, till senoidal signal remain curved at top and bottom at oscilloscope window like old school, when we put a shower resistance plugged to the amp output, immersed into a barrel full of water (due to that big power), or are these impressive numbers sustainable for how many ms?
Most high power amplifiers can not sustain full power without blowing a circuit breaker, the breaker value compared to the efficiency factor would determine how much power it can put out long term.

As an example, a QSC PLX 3602 would draw 63 volts at 120 VAC, though it can put out it's rated 3600 watts, it will blow it's breaker in about two seconds at rated power.
It will also blow the breaker when called to do really heavy compressed bass music in to 2 ohm loads.


Art
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Old 2nd March 2012, 11:47 PM   #509
Djim is offline Djim  Netherlands
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Quote:
Originally Posted by PASC View Post
Hi!
First time I see this 24LW2400 being mentioned.
This must move some air; but also the cone must weight a lot to not bend and sensibility should be lower. Own you the T/S.
Is it a new driver from 18 Sound as it not appears at their site yet? Will contact local dealer.
Regards,
Lol, sorry my typing mistake. Of course it should be 18LW2400. Maybe a couple of new drivers will be presented at the next Prolight + Sound convention in Frankfurt (21 till 24 of March). About the Labs, often they do even a little better as their specs suggest. For non commercial applications they are (too) expensive but they have their own quality. There are cheap Chinese clones of which a few seem to do a very similar job at a ridiculous low price.

Last edited by Djim; 2nd March 2012 at 11:50 PM.
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Old 3rd March 2012, 12:18 AM   #510
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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.

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.
Please do, I have a design using dual Lab12s in a tiny 83 liter box Hornresp predicts will do 124 dB flat 40 Hz to 100 Hz (half space full power, no HP needed) that I'd like to get right before cutting wood, as it won't allow adjustments after the build that the Keystone did.

I hate wasting plywood.

Art
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