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Ricci's CKRAM Subwoofer and Files

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Much more clear that makes sense.   I would just use the baffle screws into the inserts and foam tape between the baffle and front assembly, not bothering with the end grain screws and relying on the clamping force to damp any vibration.

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I'm going to adapt this design for my 15BTX100 so I have been going through it in order to understand things like how the bent port is altering simulation inputs.  Firstly I calculate the port area as:

13.5 * (60.96-(5*1.8)) = 701.46 

Based off the port height (13.5cm) overall width (60.96cm) and divider thickness (1.8cm) which differs from the Hornresp input for all vents open of 725.76, has the port area been increased to take into account viscus drag effects on tuning?

Secondly for the port length I get 102.97 cm using just the mid point and 100.99 cm using the advanced center line method but the input is 102 cm so what method was used to arrive at this?

 

*Also does anyone have complex inductance parameters for the 15BTX100? I'm having difficultly getting them my scales seem to have become inaccurate.

advance_center_3rd.webp

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Hey Kipman... the port area listed is exactly what the area of the vents are. There is no fudge factor. Your calculation must be off a bit. 24" width, two 18mm side panels and three 12mm vent dividers.

Length is 102cm effective calculated off of the sketches inside of Solidworks. Of the port calculation styles you linked only the 3rd and 4th from the left are worth using. Mixing #3 and #4 is worthwhile. The rest are inaccurate. I've designed, built and tested a bunch of designs with similar ports and that's how I've determined what results in a close match. Use #3 from the attachment for most cases.

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Great my mistake was that I thought the vent divers where 18mm not 12mm.  I used method 3 for the length but its within 1cm of your number so the discrepancy could just be metric US customary units conversion as I work in metric.  (although to be totally accurate Hornresps use of cm and cm^2 isn't metric...). 

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image.png.7b70a7f5ae830f042ffd1108c53ddf78.png

Simulating the CKRAM at full output with a 27Hz 4th order high pass I get ~35 m/S as the peak vent velocity.  Previous designs of mine have had peak velocities in simulation ~25 m/s which resulted in 1 - 2 dB of port compression.   Also my design for the 15BTX100 is coming out with 35 m/s vent velocity.  Looking as designs on data-bass such as:
https://data-bass.com/#/systems/5c48bfc611126b0004ca12eb?_k=sypf1q

I don't see much evidence of port compression at tune in the long term output graphs even though vent velocity must be high.  what kind of compression can we expect at 35m/s?

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With 726cm of vent area and 35m/s max velocity, port compression should be minimal. If I had to guess I'd say about 2dB port compression and that is only at maximum output. Reducing the output 3dB does wonders. I hope no one is running cabs at maximum! If you do you need more cabs. 

Airspeed will grow with the lower tuning options. There is nothing that can be done about it due to the physics. 

Have you read Collo's works and the JBL whitepapers on ports? One take away is that larger vent area will support larger air speeds with less chuffing and compression. 

With the modern high power drivers and tendency towards more compact enclosures it is impossible to keep vent velocities low. Especially with the low HT type tunings. The only way to do it is to make the enclosure unreasonably large, or limit SPL. Some of the speakers I've tested simulated to have >60ms velocity at maximum output. Some are approaching 100ms in the sims. More than a few of them actually. The cabs still work but a large amount of compression and noise is expected near max output. 

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37 minutes ago, Ricci said:

With the modern high power drivers and tendency towards more compact enclosures it is impossible to keep vent velocities low. Especially with the low HT type tunings. The only way to do it is to make the enclosure unreasonably large, or limit SPL. Some of the speakers I've tested simulated to have >60ms velocity at maximum output. Some are approaching 100ms in the sims. More than a few of them actually. The cabs still work but a large amount of compression and noise is expected near max output. 

I have experienced this with orbital shifters. There are videos with sheets waving in front of them from the air velocity. Looks cool, sounds like...

To each their own. 

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39 minutes ago, klipsch said:

I have experienced this with orbital shifters. There are videos with sheets waving in front of them from the air velocity. Looks cool, sounds like...

To each their own. 

 

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Keep in mind that the video above is one channel of the FP-13000 running full tilt into the impedance minimum of the 1/3 vent SKHorn there, which basically feeds it like 5KW since the two 21DS115-8 are in parallel. I never run into audible port chuffing during regular use, since I roll off the below 20Hz stuff usually.

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Haha nice video...

Yep. I can get almost any ported sub to make chuff noises with test signals and a big amp. If they say their sub won't they didn't try hard enough. With that said some speakers are a lot worse than others. Thankfully most of the time with music/movie/TV content it's triggered much less often. High power test tones at tuning will get them every time. 

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@Ricci Instead of the "8 point star" design as the throat braces, would a "tic-tac-toe" pattern work as well?   Something very rough like this?

ckram.thumb.png.149475df0e7fd74dc6f51c5d4d0091fb.png

 

 

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11 hours ago, klipsch said:

@Ricci Instead of the "8 point star" design as the throat braces, would a "tic-tac-toe" pattern work as well?   Something very rough like this?

ckram.thumb.png.149475df0e7fd74dc6f51c5d4d0091fb.png

 

 

Nice joints there! 😊

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12 hours ago, klipsch said:

@Ricci Instead of the "8 point star" design as the throat braces, would a "tic-tac-toe" pattern work as well?   Something very rough like this?

ckram.thumb.png.149475df0e7fd74dc6f51c5d4d0091fb.png

 

 

Sure... there are many ways to skin the cat. I encourage experimentation. 

I went with the star pattern for the simple fact that all 8 "exits" would be identical. It was easier to model in Akabak. Also it doesn't have the center "pocket" in front of the driver center. I thought this might cause turbulence. Does it matter? Probably not. The original front had this type of bracing pattern. 

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2 hours ago, Ricci said:

Sure... there are many ways to skin the cat. I encourage experimentation. 

I went with the star pattern for the simple fact that all 8 "exits" would be identical. It was easier to model in Akabak. Also it doesn't have the center "pocket" in front of the driver center. I thought this might cause turbulence. Does it matter? Probably not. The original front had this type of bracing pattern. 

Thank you Ricci. Guess I should try to learn akabak and hornresp and such to get a better idea of what I should expect with experimentation.  The tic tac toe pattern just seems easier to attach and remove. Maybe in practice, it is not. I still planned to put the small center circle in front of the dust cap as you've designed it. 

I was thinking of rotating the ckrams on their sides and using them as speaker stands.

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2 hours ago, klipsch said:

Thank you Ricci. Guess I should try to learn akabak and hornresp and such to get a better idea of what I should expect with experimentation.  The tic tac toe pattern just seems easier to attach and remove. Maybe in practice, it is not. I still planned to put the small center circle in front of the dust cap as you've designed it. 

I was thinking of rotating the ckrams on their sides and using them as speaker stands.

Should work just fine. 

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I have an unused 21SW152 8 ohm that is lonely and I haven't been able to sell it.

Thinking of maybe building 2 of these ckrams to be used as Left & Right speaker stands.  The current speaker stands are some "wasted space" of nicely painted 2x4s and plywood.  I'd need to buy another 8ohm 21sw152, but then the ckrams could be wired together for a 4 ohm load - running both off a single channel of a 20000q clone amp.  Turning these ckrams on their sides would maintain the proper height for the speakers.    Assuming this plan would work out ok - the the drivers/ckrams being about 15' apart from each other (on center) driven by 1 channel/signal.

As shown below, there isn't any internal bracing at this point.  I am wondering if the bracing may not be needed since the driver baffle, midbrace, vent-turn, etc. are all in notched .25" slots of the surrounding pieces.  Not sure if the small brace pieces would actually do anything more than the slots are already doing.  Any thoughts on that logic?

I apologize for destroying the star pattern and replacing it with the tic tac toe version.  I thought this way may lend itself better for what I was thinking with respects to different options of bolting the front panel.

 

 

 

ckramside.thumb.png.ac38cda382a23fde7f71c11be394f3da.png

ckramtopinside.thumb.png.7b1c2b3ce9e4fd27772400315f7be02a.png

ckraminside2.thumb.png.c65dfac6e95eb592a06996c598809a0d.png

 

 

 

 

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Looks ok to me. I don't think you need the center puck if not using the star pattern. It's only used to anchor and align the star pattern bracing. 

Personally I'd leave the small braces in. They are for locking the baffle in place with the main brace and the port panel. There's not a lot of baffle area there and the baffle is swiss cheese. Not critical but I like to be sure the cab's are rock solid especially the baffle area. YMMV 

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Hi Josh,

I'm building a couple of your CKRAM's.

Is it ok to use the circle cutout from  Baffle G (19.5") to use as Front Panel C (20.5")?

Or would this affect the response too much? Just trying to save some materials.

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On 5/9/2020 at 11:30 AM, Jesal said:

Hi Josh,

I'm building a couple of your CKRAM's.

Is it ok to use the circle cutout from  Baffle G (19.5") to use as Front Panel C (20.5")?

Or would this affect the response too much? Just trying to save some materials.

Should be fine. It'll only have a minor effect that would probably require measurements to notice. 

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On 8/20/2020 at 10:38 AM, Santiago G said:

Good afternoon I'm having trouble getting hornresp to work and was wondering if anyone had sim the BC115sd ? 

You mean the 18DS115? In this cab, or? I'd recommend the 21 for this cab. 

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