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Rock Block - a space saving sub
Rock Block - a space saving sub
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Old 10th July 2018, 08:33 PM   #1
Thijs666 is offline Thijs666  Netherlands
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Join Date: Nov 2003
Location: Maastricht
Default Rock Block - a space saving sub

As a ‘weekend warrior’ sound guy living in a smallish town in Europe I’ve always been struggling with space. Whether it is storage space or transport space, both are limited. Even the venue often has its limitations.

So I’ve been thinking about ways to slim down my hornloaded subwoofers. Since most of a horn consists of air, there surely must be a way to take advantage of this. I’ve tried a few approaches, but nothing really satisfying came out and I didn’t even want to post about it. But now I think I could be onto something and to be honest I am just wondering what you guys think . So here goes…

Design name: Rock Block
Design purpose: “small" form factor subwoofer for use with band/live sound
Design goals:
  • Small pack space
  • Loud
  • Capable of at least 50Hz, preferably lower
Design compromises:
  • Longer setup time
  • Louder instead of lower
  • Not a run-of-the-mill design
That said, here are the Hornresp sims:

Rock Block - a space saving sub-hr-parameters-png

Rock Block - a space saving sub-hr-frequency-curve-png

Rock Block - a space saving sub-hr-impedance-png

Rock Block - a space saving sub-hr-delay-png

Rock Block - a space saving sub-hr-max-spl-png

Based on this I designed a foldable prototype, measuring 76x66.5x48 cm (30x26x19 inch) on the outside.
And here are the measurements:

Rock Block - a space saving sub-rock-block-proto-2-vs-keystone-png
This is taken together with my Keystone loaded with an 18TBW100-8 for reference. Mind the 15TBX100-4 in my prototype is 4 ohms, effectively getting double the amount of watts. So no free lunch. But not bad either, right?

I'm not sure where the 52Hz dip is coming from. It was a ground plane measurement in open air on grass with no real buildings closer than 100 meters.

Rock Block - a space saving sub-rock-block-proto-2-impedance-png

Rock Block - a space saving sub-rock-block-filter-png
(some quick EQ I did based on measurements done inside combined with listening tests)

Rock Block - a space saving sub-rock-block-filter-thd-310-watts-png
(Measured at 10 meters with limited power, otherwise my measurement system would clip)

This is just a prototype, built with some C class plywood/leftovers, so I expect this to be a worst case version...
Attached Images
File Type: png Rock Block proto 2 vs Keystone.png (45.0 KB, 254 views)
File Type: png Rock Block proto 2 impedance.png (24.5 KB, 253 views)
File Type: png Rock Block+filter.png (37.5 KB, 254 views)
File Type: png Rock Block+filter THD @100W vs 310W.png (35.3 KB, 10 views)
File Type: png Rock Block+filter THD @310 Watts.png (59.3 KB, 253 views)
File Type: png HR Parameters.png (103.2 KB, 256 views)
File Type: png HR frequency curve.png (90.7 KB, 257 views)
File Type: png HR impedance.png (73.1 KB, 255 views)
File Type: png HR group delay.png (84.0 KB, 255 views)
File Type: png HR max SPL.png (102.3 KB, 255 views)
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Old 10th July 2018, 08:34 PM   #2
Thijs666 is offline Thijs666  Netherlands
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Join Date: Nov 2003
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What does it look like?
Attached Images
File Type: jpg IMG_20180708_160126.jpg (572.3 KB, 159 views)
File Type: jpg IMG_20180708_160059.jpg (584.3 KB, 169 views)
File Type: jpg IMG_20180708_155949.jpg (617.6 KB, 141 views)
File Type: jpg IMG_20180708_155942.jpg (537.1 KB, 136 views)
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Old 10th July 2018, 08:36 PM   #3
Thijs666 is offline Thijs666  Netherlands
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Yes, there are a few 'compromises', but for now I think it's a reasonable start. Excited for comments .
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Old 10th July 2018, 09:39 PM   #4
Cableaddict is offline Cableaddict
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I'll be watching this thread closely.

My main issue is weight, but packing size is also a factor, for sure.

I had previously floated the idea here of building a "medium sized" TH horn, then cutting it into 2 pieces so each would be easier for 1 man to move, then latching them together at the stage. I got a number of responses, all strongly negative. The basic opinion was that there is too much pressure inside a horn, or that the internal structure is too complex.

Well, Inever agreed with either point, seeing as one simply had to find the right spot. It doesn't have to be cut exactly in half, and you would try to separate at the area of lowest pressure. The particular horn design would of course be very important for this to work.

It looks to me like you found a very good spot.
---------------------------------------------------------


But now, if I were you, I'd ditch the hinges and make them 2 separate pieces. (Maybe with some nylon screening to keep bugs & debris out?)

Uses strong latches and a neoprene o-ring type seal, maybe like a Pelican case.

You could still put one part into the other, for transport and storage, but you'd also have the option of separate, lighter boxes for when you need to go up stairs, etc.
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Old 10th July 2018, 09:41 PM   #5
Cableaddict is offline Cableaddict
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BTW -

Is you Keystone accurate to Art's original plans?

I'll have to dig up the old graphs, (maybe I'm remembering wrong) but that LF response seems a bit shaky, even with a 15" driver.

Last edited by Cableaddict; 10th July 2018 at 09:43 PM.
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Old 10th July 2018, 10:40 PM   #6
Brian Steele is online now Brian Steele  Grenada
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Now that's some thinking outside the box..!

Very interesting idea. And I actually like the use of the hinges - should make setup time a little easier, amongst other things.

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).

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.

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).

Really interesting idea though!

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.
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Old 11th July 2018, 11:42 AM   #7
Jared is offline Jared
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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?
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Old 11th July 2018, 05:45 PM   #8
Cableaddict is offline Cableaddict
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Jared, I actually like your "tube" idea. Except, it COULD be a horn:

Imagine a 25' straight horn, just a continuous expanding diameter, made out of something very rigid. You could cut this into a bunch of smaller sections, and they would stack inside of each other quite nicely.

Once assembled, it could lay across the back (or front) of the stage, with the mouth on its side (towards the front.) Or heck, just add one 90º bend, and have the last third come forward, towards the audience. That way you could have one on each side.

Again, it would have to be REALLY stiff, so no internal bracing, or maybe run thin aluminum "box" channel down the length at a few points.
And if it were "round" like a large, straight trumpet, then that would add a lot of strength all by itself.

Hmmm .......
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Old 11th July 2018, 06:49 PM   #9
Thijs666 is offline Thijs666  Netherlands
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Quote:
Originally Posted by Cableaddict View Post
But now, if I were you, I'd ditch the hinges and make them 2 separate pieces. (Maybe with some nylon screening to keep bugs & debris out?)

Uses strong latches and a neoprene o-ring type seal, maybe like a Pelican case.

You could still put one part into the other, for transport and storage, but you'd also have the option of separate, lighter boxes for when you need to go up stairs, etc.
I have built a (way too big) prototype with exactly this idea, but the main problem was that it would take too long to put it together on the venue. With the hinges it takes about 30 seconds or even less. And also, I could not get the 'extender part' rigid enough without adding internal bracing. Believe me, I've tried lots of things and asked many people who I thought had a keen eye for constructions, but every solution was either not strong enough, too invasive (took too much space) or took too long to put together... I still have this prototype. It is really something else. The 15TBX100 is lower and louder in it than the 18NLW9600 is in my drumrizer sub.
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Old 11th July 2018, 06:50 PM   #10
Thijs666 is offline Thijs666  Netherlands
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Join Date: Nov 2003
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Quote:
Originally Posted by Cableaddict View Post
BTW -

Is you Keystone accurate to Art's original plans?

I'll have to dig up the old graphs, (maybe I'm remembering wrong) but that LF response seems a bit shaky, even with a 15" driver.
Yes, original plans, adapted for 12mm birch ply with LOTS of bracing, loaded with the B&C 18TBW100-8 (18", not 15").
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