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A Monster Construction Methods Shootout Thread
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Old 20th June 2020, 03:43 AM   #41
DonVK is online now DonVK  Canada
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Great idea , I'm looking forward to seeing the measurements.

I'll second an earlier suggestion to use common materials.
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Old 21st June 2020, 11:40 AM   #42
Baldin is offline Baldin  Denmark
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Quote:
Originally Posted by augerpro View Post
When I do the fill/lining I will mount the SB15 as a dummy woofer and measure what radiates through it.
Hi augerpro. Have been thinking about this. Are you sure it is a good idea to mount the SB15 unit?
I would think a lot of sound would be transmitted through it, magnitudes more/higher than from the panels/walls.
If this is the case then how will you determine what is what?

But maybe you mean you'll do all the material cabinet wall test first, without the SB15 mounted.
And then later moud the SB15 and see how much the inner filling will dampen the transmitted sound ... which is a good idea.

Looking very much forward to the results

Best regards Baldin
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Old 21st June 2020, 12:40 PM   #43
mayhem13 is offline mayhem13  United States
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Quote:
Originally Posted by Baldin View Post
Hi augerpro. Have been thinking about this. Are you sure it is a good idea to mount the SB15 unit?
I would think a lot of sound would be transmitted through it, magnitudes more/higher than from the panels/walls.
If this is the case then how will you determine what is what?

But maybe you mean you'll do all the material cabinet wall test first, without the SB15 mounted.
And then later moud the SB15 and see how much the inner filling will dampen the transmitted sound ... which is a good idea.

Looking very much forward to the results

Best regards Baldin
I shared a concern about this in another thread based on my experiences as a recording engineer with ISO CABS which are sealed boxes with speakers and microphones inside we use for tracking guitars when we donít want/need any room influence. My First round of testing would be the drivers inside the box and measure the sound outside the box......raw boxes. Then interior layer damping and then subsequent absorbants. Once peaks have been established as resonances of the box material, different damping materials can be applied to see what actually works with each box material. Different bracing methods could also be applied as test phases to determine effectiveness as well.
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Old 4th August 2020, 06:46 PM   #44
augerpro is offline augerpro  United States
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Measurements have started, need some feedback. Below is a measurement of the side panel and rear panel. Any reason to do one over the other? I'd rather not double my work by doing both, if possible. Will probably stick with 50ms gate, 1/6 octave smoothed, unless someone would like more accurate but messier plots, I can always reprocess past measurements so this is not something I need to decide now. Also, since there was some confusion on my test setup, here is a pic when measuring different materials and build methods. For the lining/fill tests there will be a dummy woofer below the source driver, and the mic will be nearfield on that dummy driver.

Click the image to open in full size.
Click the image to open in full size.
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Please help my waveguide and box construction research by donating to my gofundme via my website:Soma Sonus
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Old 5th August 2020, 02:05 AM   #45
454Casull is offline 454Casull  Canada
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If I had to pick one, I think the side panel would be more useful for most people. It tends to be larger and more of its sound will reach the listener (combination of both angle & distance).
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Old 5th August 2020, 02:46 AM   #46
augerpro is offline augerpro  United States
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That was my thinking too. But then I wondered if those additional peaks at 900hz and 1600hz would provide an opportunity to see how well certain materials/methods/linings would improve that, whereas with no high level peaks any improvements might not be so obvious.

EDIT: also one would suppose the rear panel response is similar to the front baffle, so that would be another reason to do the rear
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Last edited by augerpro; 5th August 2020 at 02:54 AM.
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Old 5th August 2020, 06:01 AM   #47
Baldin is offline Baldin  Denmark
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Great work augerpro

Three questions:
1. How will we from the graphs an readings know how severe it actually is? I mean it is a relative problem, og box radiation vs driver radiation. So how what is tha difference in db from the driver to the box?
2. I seem to recall someone suggesting that it is actually the corners and edges which radiate most energy in such a box. I can't really get my head around that, but it would be cool to verify either way, just on the first test box.
3. If you did the measurement in a hard surface room like a bathroom without any towels etc. you might be able to measure the total box radiation (power response).

Thanks for a great thread, and keep it up
BR Baldin
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Old 5th August 2020, 06:49 AM   #48
Nissep is online now Nissep  Sweden
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Please do a waterfall plot so it is clear how fast the energy is damped.
http://www.revintage.se/dga2.pdf

Top right corner of the document shows the difference between damped sandwich vs the same thickness but solid plywood.

And some inspiration from BBC http://downloads.bbc.co.uk/rd/pubs/reports/1977-03.pdf
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Old 5th August 2020, 10:58 AM   #49
andy19191 is offline andy19191  Europe
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Quote:
Originally Posted by augerpro View Post
That was my thinking too. But then I wondered if those additional peaks at 900hz and 1600hz would provide an opportunity to see how well certain materials/methods/linings would improve that, whereas with no high level peaks any improvements might not be so obvious.
It depends on how what you are measuring is related to what you want to know.

Clearly what you are measuring is not the sound radiated by a speaker enclosure at the listening position. The resonant motion of your box is also quite far removed from that of a speaker cabinet where the drivers play a major role in the motion. For example, of the small number of modes that need addressing with damping in a typical speaker cabinet the largest and lowest in frequency is likely to involve the low frequency driver bouncing/rocking on the baffle. This doesn't seem to be present in your experiment assuming my understanding of what you are doing is correct.

What you seem to be measuring is something approximately related to the motion of the box surface near the microphone. Some box modes will register and some will be missed as shown in your figure. The modes registering may be irrelevant at the listening position (e.g. a purely side-to-side motion will not radiated sound forward) whereas some of the missed ones may be among the few relevant ones that propagate significantly to the far field at the listening position. The energy in the sound waves in the near field does not all propagate to the far field with some recirculating (i.e. generated on one part of the speaker surface and absorbed on another).

Now I don't wish to be dismissive. With care I think your experiments may contain some guidance on speaker cabinet construction but it will be indirect and require some interpretation to read across. In your position I think before settling on a set of measurement positions on the surface I would first determine how well having the woofer present works and how well the box over the small driver is working. An alternative for the latter might be a long tube mounted on a stand rather than on the box with a large softish gasket over the driver. This would make the way the driver vibrates the box more representative of a real speaker cabinet. The air inside the box will almost certainly provide negligible forcing of the box walls at the significant frequencies in your figure.

BTW if measuring for high Q resonances use small frequency bins and don't average them since you are degrading what you are trying to measure. Ensemble averaging should preserve this information while reducing the grass and is likely supported by whatever measurement software you are using. As you mentioned above if the raw data is kept some of the mistakes we all tend to make when processing data can be fixed at a later date.

Quote:
Originally Posted by augerpro View Post
EDIT: also one would suppose the rear panel response is similar to the front baffle, so that would be another reason to do the rear
The motion of the rear panel is nothing like the baffle which has big holes and big heavy drivers bolted to it. And anyway, the large low frequency problematic modes tend to involve all the panels deforming together with the mode shapes involving individual panels resonating strongly occurring at higher frequencies, not containing much energy and tending to disappear when effective damping targeted at addressing the lower frequency modes is applied.
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Old 5th August 2020, 04:48 PM   #50
augerpro is offline augerpro  United States
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Baldin> here is a plot showing the relative levels of the bare driver vs box-only radiation. Both are 50ms gate and 1/24 smoothing, but the mic distance for bare driver was 33", while for the box-only is 1/2". I did some earlier measurements to determine SPL loss for these distances so the relative levels should be reasonably correct (for those confused why it doesn't follow 6db/distance doubling, this has to do with near field versus far field, and free field vs boundaried (the room)). I'll probably do another bare driver measurement in the near field and use that going forward, but you get an idea of the method behind the madness.

Click the image to open in full size.
Click the image to open in full size.

andy19191> here are two plots where the mic distance goes from 1/2", to 6", to 30". I assume by 30" you are comfortable we are seeing the far field response similar to the listening position (ignoring room contributions for argument)? The first plot is the raw response, the second is with some *approximate* SPL correction due to the increase in distance. I don't see anything standing out as fundamentaly different, other than the typical changes associated with room interaction vs the gate, moving from near field to far field, etc? I suppose this should be expected, since all of those issues you bring up would be potential whenever we do near field measurements of any driver, yet people just don't see them when doing near field measurements, other than high frequency differences typical of going from near field to far field. Measuring this box near field shouldn't be any different than measuring a woofer near field, correct? BTW, in previous experiments years ago, I really only found unusual effects (like you have identified) when moving *really* close to the diaphragm, like < 1/8"

Click the image to open in full size.
Click the image to open in full size.

EDIT: Re: smoothing hiding high Q peaks, I'm gravitating now towards 1/24" since it retains peaks well enough to see differences in materials/methods changes, while still producing a plot that is clean enough to be understandable to the human brain.

Re: applicability to real world, the source driver is screwed directly to the baffle, just like a normal driver. I agree we should include this direct driving of the baffle just as it would be in the real world. Overall, the entire point of this experiment is to recreate something with connection to reality, thus measuring SPL instead of accelerometers, etc.
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Please help my waveguide and box construction research by donating to my gofundme via my website:Soma Sonus

Last edited by augerpro; 5th August 2020 at 05:09 PM.
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