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Rock Block - a space saving sub
Rock Block - a space saving sub
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Old 11th July 2018, 07:12 PM   #11
Thijs666 is offline Thijs666  Netherlands
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Quote:
Originally Posted by Brian Steele View Post
Now that's some thinking outside the box..!
Pun intended?

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Originally Posted by Brian Steele View Post
The hornresp sim should probably be set to use PAR not CON segments for a little more accuracy, and if that's a 15" driver, Vtc should probably be a little higher (Vtc should include the volume contained within driver's cone as well as the volume between it and S2).
I've implemented cone correction. If you leave it out, the sim is quite worse. Haven't built a proto without cone correction though...

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Originally Posted by Brian Steele View Post
The main issue is likely to be panel flex and stability, as the bottom section isn't properly braced. Any squiggles or smooshed sections in the measured impedance curve that don't have analogues in the predicted curve are signs of panel flex affecting the output of the system. You could use impedance curve measurements as a "guide" to finding the optimal locations for clamps (to clamp the top section to the bottom section) and maybe a removable cross brace (for the bottom section).
True that! At the mouth panel flex is about a cm each way at 2000 watts . I've clamped it down at the mouth with two times two opposing clamps (so basically I created two braces) and what it mainly does is bring THD down (by quite a lot, I must add), especially second order, but it doesn't really alter the frequency curve by much. Just listening to the difference I would say it plays louder WITHOUT the braces, that's probably due to the second order harmonics.
I'm still thinking about the best solution for this. Maybe some sort of broomstick with bolts on both ends and a sunken metal dish in the sides of the mouth... Of course any bracing should be quickly installable and removable. That's kind of a challenge!

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Really interesting idea though!
Thanks!

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Did you do the FR measurements with the horns side by side like that? If so, that could affect the measurements and might explain that 52 Hz dip.
No. The Keystone was about 3m back with it's mouth to the ground.
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Old 11th July 2018, 07:24 PM   #12
Thijs666 is offline Thijs666  Netherlands
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Originally Posted by Jared View Post
I have been thinking of a similar idea for a much smaller blue tooth connected full range sound system for beach usage. I never would have thought of trying for a horn, I was more thinking of 3-4 telescoping tubes that could screw or lock somehow into expanded position. I like the hinge idea. Do you have wing nuts or the like to lock it together in the expanded configuration?
My first ideas were based on telescoping tubes, but in practice (I've built a proto) it proved too cumbersome. You would need to use a very rigid sliding solution AND come up with a decent way to seal the whole thing airtight when extended AND how to keep it all in place.

The hinges makes it really fast to 'unfold' the internal/top part and position it exactly right. But they must be very sturdy. I've used el cheapo ones and they just bend...

No, I don't have any locking implemented between the two parts yet. The top part holds the speaker and proved heavy enough to press down on the double weatherstripping to prevent any airleaks, good enough for a prototype. But indeed some sort of butterfly lock will need to be implemented.
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Old 11th July 2018, 07:31 PM   #13
weltersys is offline weltersys  United States
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Originally Posted by Thijs666 View Post
Yes, there are a few 'compromises', but for now I think it's a reasonable start. Excited for comments .
Thijs666,

Prototype seems to work well, especially considering the "C class plywood" ;^) !

Your BC18TBW100-8 loaded Keystone appears to roll off about 1/3 octave below my BC18SW115-4 loaded original version.

That said, using a BC18TBW100-4 in the "B-Low" version also did not perform as well as simulations predicted in the low end..

Back to the "Rock Block", other than the impedance response suggesting the horn being a bit shorter than the sim, it looks pretty close to the Hornresp sim.
Well done, very nice concept and execution.

Round the corners, fill in the voids, a few coats of "Turbo Blue", and off to the races!

Art
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File Type: png Lower Art's BC18SW115-4.png (209.9 KB, 89 views)

Last edited by weltersys; 11th July 2018 at 07:33 PM.
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Old 11th July 2018, 07:39 PM   #14
Brian Steele is offline Brian Steele  Grenada
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Originally Posted by Thijs666 View Post
I'm still thinking about the best solution for this. Maybe some sort of broomstick with bolts on both ends and a sunken metal dish in the sides of the mouth... Of course any bracing should be quickly installable and removable. That's kind of a challenge!
One or two flat panels that span the width of the mouth and a few butterfly screws might do it...
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Old 11th July 2018, 07:44 PM   #15
Thijs666 is offline Thijs666  Netherlands
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Originally Posted by Brian Steele View Post
The hornresp sim should probably be set to use PAR not CON segments for a little more accuracy.
Thanks. I just tried this and (luckily) there is hardly any difference. Nothing worthy of posting.

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Originally Posted by Brian Steele View Post
Export the impedance data from Hornresp and use REW to compare the measured impedance against the predicted one - that should give you a pretty good idea of how close the build is to the sim.
Rock Block - a space saving sub-impedance-sim-vs-measured-jpg

Could be better, could be worse...
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Old 11th July 2018, 07:53 PM   #16
weltersys is offline weltersys  United States
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Originally Posted by Thijs666 View Post
True that! At the mouth panel flex is about a cm each way at 2000 watts . I've clamped it down at the mouth with two times two opposing clamps (so basically I created two braces) and what it mainly does is bring THD down (by quite a lot, I must add), especially second order, but it doesn't really alter the frequency curve by much. Just listening to the difference I would say it plays louder WITHOUT the braces, that's probably due to the second order harmonics.
I'm still thinking about the best solution for this.
A fairly quick install could use flat metal strips routed flush on the cabinet exterior, with ratchet straps pulling wood braces in place between them.
The example below used a single vertical ratchet strap without wood braces for reference- seems there are some neophytes who have never encountered their many uses.

Art
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File Type: png Strapping.png (713.0 KB, 76 views)

Last edited by weltersys; 11th July 2018 at 07:56 PM.
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Old 11th July 2018, 08:09 PM   #17
Thijs666 is offline Thijs666  Netherlands
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Originally Posted by weltersys View Post
Thijs666,

Prototype seems to work well, especially considering the "C class plywood" ;^) !
Maybe even D class , but it was thrown away at my brother in law's company and this way it's had some more useful purpose before going up in flames

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Originally Posted by weltersys View Post
Your BC18TBW100-8 loaded Keystone appears to roll off about 1/3 octave below my BC18SW115-4 loaded original version.

That said, using a BC18TBW100-4 in the "B-Low" version also did not perform as well as simulations predicted in the low end..
Sadly I don't have the funds to buy the SW115 just to try it out . I would love to be able to check this. Or be able to measure a well-known industry sub side to side, just as a sanity check for my measurements.

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Originally Posted by weltersys View Post
Back to the "Rock Block", other than the impedance response suggesting the horn being a bit shorter than the sim, it looks pretty close to the Hornresp sim.
I thought the sensitivity was quite a bit lower than predicted. Hopefully this is mostly due to losses due to the bad plywood and a final version with proper plywood will improve this a bit. As I said, I guess this is a worst case scenario.

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Originally Posted by weltersys View Post
Well done, very nice concept and execution.
Round the corners, fill in the voids, a few coats of "Turbo Blue", and off to the races!
Thanks . Nah, this is just a proto. The OSB is really bad as cabinet material. It isn't even plywood. And it splinters badly . I was thinking to use Baltic Birch 12mm for the outside of the top part, poplar for the inside with a lot of bracing (to keep it light, as you will have to lift this part) and use 22 or 25 mm BB or douglas fir plywood for the bottom part, as there will be no internal bracing possible (only the front will probably be braced). But maybe glueing two different sorts of wood together isn't the greatest idea?
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Old 11th July 2018, 08:13 PM   #18
Thijs666 is offline Thijs666  Netherlands
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Originally Posted by Brian Steele View Post
One or two flat panels that span the width of the mouth and a few butterfly screws might do it...
I have been thinking about a grill or something with embedded long threaded bars, but I'm afraid this contraptions isn't going to be rattle free.
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Old 11th July 2018, 08:32 PM   #19
Thijs666 is offline Thijs666  Netherlands
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Join Date: Nov 2003
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Quote:
Originally Posted by weltersys View Post
A fairly quick install could use flat metal strips routed flush on the cabinet exterior, with ratchet straps pulling wood braces in place between them.
The example below used a single vertical ratchet strap without wood braces for reference- seems there are some neophytes who have never encountered their many uses.

Art
I've tried straps like this on a different prototype, but I have a couple of issues in this:
- The sheer force/pressure of the sound waves is so intense at the mouth, that the straps would have to bend the plywood so far inward, that I would fear for it to deform permanently.
- The movement that has to be stopped is two-way. Straps only prevent one-way. So the best solution I see would be a rigid construction to keep the sides from moving inward or outward. Luckily the forces applied to the sides are opposite to each other, so a simple threaded bar could in theory do the trick. (in practice it's a different story; I've tried )
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Old 11th July 2018, 09:38 PM   #20
Thijs666 is offline Thijs666  Netherlands
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Join Date: Nov 2003
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Quote:
Originally Posted by weltersys View Post
A fairly quick install could use flat metal strips routed flush on the cabinet exterior, with ratchet straps pulling wood braces in place between them.
The example below used a single vertical ratchet strap without wood braces for reference- seems there are some neophytes who have never encountered their many uses.

Art
Quote:
Originally Posted by Thijs666 View Post
I've tried straps like this on a different prototype, but I have a couple of issues in this:
- The sheer force/pressure of the sound waves is so intense at the mouth, that the straps would have to bend the plywood so far inward, that I would fear for it to deform permanently.
- The movement that has to be stopped is two-way. Straps only prevent one-way. So the best solution I see would be a rigid construction to keep the sides from moving inward or outward. Luckily the forces applied to the sides are opposite to each other, so a simple threaded bar could in theory do the trick. (in practice it's a different story; I've tried )
I'm sorry. I just now understood what you meant . With the wooden braces in between the sides and kept in place by the pressure of the straps... That might work. Though I've tried this on another sub with some serious wood clamps and they just weren't strong enough to keep the brace in place.
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