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Old 8th July 2017, 04:21 PM   #21
Brian Steele is online now Brian Steele  Grenada
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Quote:
Originally Posted by Circlomanen View Post
Attachment 624693

The blue line is with the microphone in the mouth of the ROAR12.
The red line is with the microphone at the exit of the tapped pipe section at the bottom of the front-resonator.
If the measurement was taken with the microphone in the mouth of the horn, that could tend to exaggerate its LF performance. I'm guessing that the purple line is a 1M measurement of the same horn? If so, the faster drop-off in FR is noticeable when you compare both lines on the graph. For my TH measurements, I've found that backing the mike off a bit so that it's about the same distance from the mouth as the effective radius of the mouth gives results that are a little more realistic without letting too much of the room get into the measurement. Some experimentation is required to get the best results though.

Measuring FR at various points *inside* the horn can be a illuminating exercise. I did the same thing with my THAM-like build, and the results eventually led to the "dogfood duct" "fix" I came up with to deal with the midbass notch in the THAM's response.

The ROAR12's "notch" is a pretty sharp one, but it's up @200 Hz, so it's a likely a bit less problematic than other alignments that have such a notch appearing considerably lower.

Interesting point on the symmetrical loading of the driver, BTW. I find it curious though that apparently none of the techniques used in car audio drivers to strengthen the driver's cone all the way up to its edge (where asymmetrical loading IMO will most likely lead to failure) haven't found their way to the pro audio subwoofer world. These include flattening the edge (Image Dynamics) or folding it back (JBL, Infinity), or even changing the entire geometry of the cone (Kicker Comp series). Maybe the problem isn't that significant?

What's the lowest resonant frequency of the ROAR12? What about its impedance curve? Comparing those two against the HornResp sim for it should give a pretty good idea of how close the sim matches the built system.
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Old 9th July 2017, 09:41 AM   #22
Circlomanen is offline Circlomanen  Sweden
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Quote:
If the measurement was taken with the microphone in the mouth of the horn, that could tend to exaggerate its LF performance. I'm guessing that the purple line is a 1M measurement of the same horn?
Yes, the purple line is at one meter from the mouth.
The driver is brand new and raw and I expect more LF performance once the driver has a few hours of a few hundred watts of workout. My neighbors protest whenever I fire up my old trusty QSC-amp for some nice punchy bass, so it might take a while before I can do proper measurements.
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Old 24th July 2017, 05:21 PM   #23
BesPav is offline BesPav  Russian Federation
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Hi, martinsson, am i right suggesting this kind of cutting for 1,5x1,5 meter sheets?

With my 18" drivers this bin could provide very good power conversion efficiency.

Frequency response can be easily corrected with Driverack PA. First parametric filter tuned up to -3,8 dB at 93 Hz, so there are a plenty of headroom for bass tweak.
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Last edited by BesPav; 24th July 2017 at 05:42 PM.
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Old 25th July 2017, 06:57 PM   #24
martinsson is offline martinsson  Sweden
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Hello BesPav

Thank you for taking an interest in the design, remember that the design is not yet built and so I cannot verify it's performance, but in theory it seems very promising, and the ROAR12 certainly made an impression if one can extrapolate on that (subjective impression only).

It's a bit difficult to make out the numbers in your cut sheet images, and I'll have to double check with the drawing detail dimensions, as far as I can see though the layouts seems good with as little waste a possible.

What kind of drivers do you have? from the simulations they seem very capable, I'm guessing 18SW115 or similar?
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Old 26th July 2017, 05:27 AM   #25
BesPav is offline BesPav  Russian Federation
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Quote:
Originally Posted by martinsson View Post
remember that the design is not yet built
Let me try.


Quote:
Originally Posted by martinsson View Post
I cannot verify it's performance
Doesn't worry, we can compare design ideas and performance graphs, but the most critical corner - the sounding can't be picked up from any kind of graphs or measurements.
So we have no other way than build and listen.

Quote:
Originally Posted by martinsson View Post
It's a bit difficult to make out the numbers in your cut sheet images
Yup... That's very simple cutting software, so let's check with school arithmetics.
960 mm (height of outer panels) + 564 mm (internal panels width) = 1524 mm

We just need cutting table with 1-1,5 mm thick saw, one cut and we're in.

Assume ply sheets are really square and precisely cutted at the factory.

Quote:
Originally Posted by martinsson View Post
What kind of drivers do you have? from the simulations they seem very capable, I'm guessing 18SW115 or similar?
This is RCF LF18X401, you can pick datasheet from official site here:
RCF - LF18X401

You are right, it's a hair lower or mostly similar to 18SW115 in performance terms, in the ocean of fake 18LW1400 they both are crusaders.
Last winter one of our local suppliers announced stock clearing and offer those drivers for my company for around $200. We could not resist and pick up large batch.
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Old 26th July 2017, 07:49 AM   #26
martinsson is offline martinsson  Sweden
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Quote:
Let me try.
If you decide to go ahead - thank you BesPav, it means a lot to us, it is not common that someone builds an unverified design, especially not one requiring this much effort and such an expensive type of driver.

Regarding the RCF LF18X401 in a rear mounting application, given the shape of the interfacing basket edge I have concerns that they might not seal properly towards the panel, which is very important that it does, do you share these concerns?

@ Mrcy - Apologies to the thread owner, thank you for your patience and please let us know if you feel that we should move this discussion to another thread.
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Old 26th July 2017, 11:22 AM   #27
BesPav is offline BesPav  Russian Federation
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Quote:
Originally Posted by martinsson View Post
If you decide to go ahead - thank you BesPav, it means a lot to us, it is not common that someone builds an unverified design, especially not one requiring this much effort and such an expensive type of driver.
He-he.
You know first hand, mr. martinsson, that all seems to be accurate to the contrary.
Members are often spoiled with approved designs, but where are a lots of backgroung estimating, calculating, simulation, modeling, labour samples and working prototypes, understanding in the end?
And even with huge support, mounting instructions and cutting sheets from time to time we have found gifted peoples doing things at unpredictedly wrong ways...


Quote:
Originally Posted by martinsson View Post
Regarding the RCF LF18X401 in a rear mounting application, given the shape of the interfacing basket edge I have concerns that they might not seal properly towards the panel, which is very important that it does, do you share these concerns?
Doesn't worry, RCF's datasheet keeps undisclosed hard polyethilene foam sealing ring at the inside bracket of the driver basket.
Your design with this driver could resist and dissipate around of 3 kWt power without risk of touching magnet system pole. Driver are well vented and symmetrically well loaded through the passband so cone stays inside Xmech even at rated program power.
I want to ask you about another concern, rear cover stiffness. I would prefer to keep two hardening brackets at the whole 928 mm length/height with a lot of confirment screws.

Last edited by BesPav; 26th July 2017 at 11:48 AM.
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Old 26th July 2017, 02:47 PM   #28
USRFobiwan is offline USRFobiwan
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Maybe put in a 45 degree triangle against the backwall to strengthen the back wall across driver cone. Does it need cone compensation?
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Old 26th July 2017, 07:48 PM   #29
martinsson is offline martinsson  Sweden
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Quote:
I want to ask you about another concern, rear cover stiffness. I would prefer to keep two hardening brackets at the whole 928 mm length/height with a lot of confirment screws.
The rear panel is 924x564 if built with 18mm plywood, and the bracing of the rear panel, and its connection to the driver baffle is one of the most difficult ones to get right, it is also one of the most exposed to pressure so bracing it is very important to get it right.

Interesting idea regarding the bracing (your concern) and your idea is not bad at all, but it means taking away the brace going perpendicular across the driver cut out, this brace was added since we believed it would act as a form of primitive divider, marking the start of the symmetrizing tapping sections.

Also, bare in mind that it might give rise to a local asymmetrical loading of the cone if you replace the four bracing pieces with two longer ones extending all the way along the rear panel and past the driver, in the THAM18 we suggested making holes in the two parallel braces to relive the potential pressure difference that might act on the cone (see THAM18 example picture below).

Click the image to open in full size.
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Old 27th July 2017, 10:51 AM   #30
martinsson is offline martinsson  Sweden
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Quote:
Maybe put in a 45 degree triangle against the backwall to strengthen the back wall across driver cone. Does it need cone compensation?
I think I can see what you mean, to integrate a cone compensation into the bracing is not a bad idea, I looked into it briefly, my idea was to make a really rough compensator doubling as a connector well, a box fitted to the inside of the rear panel at the center of the cut out for the driver, with a cutout in the rear panel slightly smaller, in which one could mount the speakons and prevent damage to the same should the slide of something.

The triangular or pyramid shape is not a bad idea, but it might be tricky get stable, but it should be possible to utilize it in pretty much the same way should one wish to do so.

I have not yet decided if cone compensators are necessary, so we left it up to the DIY'er to implement if he/she should feel it necessary, same as with the THAM designs, it would bring the design closer to the simulations but what concerns me is that I feel there is no harm with more air cone side, granted we already have very low compression, but still, it is also kind of tricky to make one static designs for all driver cones.
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