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doober View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote doober Quote  Post ReplyReply Direct Link To This Post Posted: 24 February 2021 at 9:12am
Originally posted by Elliot Thompson Elliot Thompson wrote:




Unless you are going into production with this design or, notice something is missing while playing music, you should not stress yourself about it. As your design offers a Multi-cellular concept, you will notice your mid range will be very prominent (in a positive way) when playing vocal and/or percussion tracks at a great distance.

You can research papers written by Don Keele. Don Keele was the first person to rectify the problem caused by multi-cellular lobbing and introduced various horns on the market around 50 years ago. Don Keele also created a line array in an angular fashion to reduce the lobbing affect caused by the majority of Line Arrays on the market today. This will allow you to prepare yourself for such objectives when the next project arise.

Best Regards,
 





I won't be going into production with this design or any others, I make boxes just for my own use. They do need to be a certain standard though as the competitors in the hire business around here are using some top level kit from well known brands. I can't sell my services off brand names, I have to keep up a reputation for providing good sound.

Prominent midrange certainly is a good thing, I see it as the most important part of music, it is where most of the information is.

I have read a few of Don Keele's papers, "What's so sacred about exponential horns?" was a particularly interesting read. It looks like I need to read (and understand) his many papers about CBT arrays. That should keep me busy for a while
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kipman725 Quote  Post ReplyReply Direct Link To This Post Posted: 24 February 2021 at 12:40pm
doober when you measure the box with it raised (perhaps you already know about this) you can time gate the measurements to eliminate the effects of reflections from the environment and obtain anercoic results (with limitations on how low the results go and low freqeuncy resolution dependent on how long the gate is).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 24 February 2021 at 7:48pm
Originally posted by doober doober wrote:

Originally posted by JulianDA JulianDA wrote:

I dont really understand why you put the horizontal dividers infront of the mid and hf sections. These will for sure cause resonances between the parallel faces (maybe you can spot the resonaces in your frequency response by calculating the corresponding wavelenghts with the distance of your dividers).


That is a good point, I was unsure whether to use them or not. They are not glued in, I might remove them to see if there is much difference.

The partial drawing below shows the box I intend to use below the current one, it is noticeable that the dividers make a series of horns which get progressively more vertical flare and less throat area from top to bottom. None of these pieces are actually parallel, although the top pair aren't far off. The idea is to create a system where the amplitude is asymmetric allowing less SPL difference between front and rear of the audience, with this achieved mechanically rather than using many amp and DSP channels.





Then I remembered this array from a few years back





No top or bottom horn walls at all on there. Presumably this works due to the physical displacement and the aim of the waveguides as they form a progressive curve. My mid and high components have a similar vertical curve, albeit on a much smaller scale.

One advantage of using the dividers is in construction of the side walls. The very slight angles between each section make it very difficult to build without the dividers to act as guides. I could always remove them after making the horn walls, gut some reinforcement would be needed on the back of the walls otherwise it would just be glued butt joints holding it in shape.


You might want to look at these:
https://patents.google.com/patent/US8422712B2/en
https://patents.google.com/patent/EP2060146B1/en?inventor=Rune+Skramstad
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Elliot Thompson View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 25 February 2021 at 3:18am
Originally posted by doober doober wrote:



I won't be going into production with this design or any others, I make boxes just for my own use. They do need to be a certain standard though as the competitors in the hire business around here are using some top level kit from well known brands. I can't sell my services off brand names, I have to keep up a reputation for providing good sound.

Prominent midrange certainly is a good thing, I see it as the most important part of music, it is where most of the information is.

I have read a few of Don Keele's papers, "What's so sacred about exponential horns?" was a particularly interesting read. It looks like I need to read (and understand) his many papers about CBT arrays. That should keep me busy for a while



I'm a strong believer of having custom products aimed solely for the designer and not for the masses. How can one be competitive if you have nothing unique to bring to the table that differs from the rest? The craftsmanship you've undergone, in designing that box, is far beyond what the majority of DIY box builders have done, when creating mid-hi cabinets. 

When you have time, watch the CBT Chronicles By Don Keele.

https://www.youtube.com/watch?v=WOBrPURqA-8&list=PLcuMvtBVm-LAQi1wZzoZOAIenpRTT8uyR


Best Regards,





Edited by Elliot Thompson - 25 February 2021 at 3:21am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote doober Quote  Post ReplyReply Direct Link To This Post Posted: 25 February 2021 at 8:54am
Toastyghost- I have seen the Danley patent before, it seemed to confirm that what I planned would work, especially this diagram which is very similar to my design, although it uses a planar source whereas I went with a curved source (at great effort, possibly for no gains...)





However looking at a later point in the article, it states:

"With the shaded amplitude lens there are two similar rules of thumb. The angle of the vane requires that the sound bend to accommodate a new angle. An important condition that should be observed, allows the sound to actually bend as desired. This condition defines the frequency point below which the passage way dimensions and bend angle have essentially no adverse effect. This would apply to conventional parallel plate lenses. FIG. 14 shows a planar wavefront entering one cell of a lens. In order for the wavefront to change direction and propagate perpendicular to the centerline, the difference in path lengths “A” where the angle changes must be less than ⅓ wavelength at the highest frequency of interest. Dimensions greater than that allow internal cancellation and ripples in the response as well as the possibility of propagating higher order modes (sound bouncing from wall to wall within a cell). FIG. 15 shows the exits of two adjacent cells where a second acoustic size rule should be followed. The difference between two adjacent cells where the radiations join can be no more than ⅓ wavelength as shown, at the highest frequency of interest."







I see why the vanes need to be close together to keep path lengths within 1/3 wavelength, however he is using a planar source which requires the wavefronts to bend. In my design they should already be heading in the correct direction from the source, and not need to bend.

This leaves me with more choices- I could take the vanes out of mine to see if it makes any difference (good or bad), or I could try adding a lot more to try and reduce reflections between them. If I add more they will have to be a thin material, using the same 9mm ply will soon fill the entire box and not let any sound through. I could try some 3mm ply, it won't be very stiff though.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote doober Quote  Post ReplyReply Direct Link To This Post Posted: 25 February 2021 at 8:57am
Originally posted by kipman725 kipman725 wrote:

doober when you measure the box with it raised (perhaps you already know about this) you can time gate the measurements to eliminate the effects of reflections from the environment and obtain anercoic results (with limitations on how low the results go and low freqeuncy resolution dependent on how long the gate is).


Yes I'm already aware of that, I've not looked into it in great detail, I haven't even looked at what the settings are in my software. Maybe it's time to do some more learning.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote doober Quote  Post ReplyReply Direct Link To This Post Posted: 24 March 2021 at 5:44pm
More progress. I've nearly finished the next box, just waiting for 12 drivers to arrive. This will go below the first one. I decided to leave out the dividers in the mouth for now and went for some small pieces to brace the 10" section instead.

It's currently upside down, it's easier building it this way.





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Post Options Post Options   Thanks (0) Thanks(0)   Quote JulianDA Quote  Post ReplyReply Direct Link To This Post Posted: 24 March 2021 at 7:42pm
Looking way better now without the dividers infront of the mf hf section, good work! Hopefully this will at least get rid of some resonances ;)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote imageoven Quote  Post ReplyReply Direct Link To This Post Posted: 25 March 2021 at 1:37am
It looks fantastic. You must have put some serious time into these.
Keep pushing on, things are gonna get better.
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doober View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote doober Quote  Post ReplyReply Direct Link To This Post Posted: 09 April 2021 at 8:53pm
I got the drivers, fitted them, and did some testing with both boxes. There was no wind when I started, later it was blowing towards the speakers and then across. The HF was getting reduced with the wind towards the speakers, but other than that there was little effect from the wind. The previous attempt with the vanes in the mouth sounded 'phasey' like an early line array in the wind, removing the vanes has fixed it.




I didn't get them as high as I would have liked, lower edge is 1.65m above the ground, 3m would be better.

Boxes close up





Video starting approx 35m away. This wasn't particularly loud, the -24dB (relative to limiter threshold) on the LMS were just flickering.





As the video shows the sound goes a bit screechy, too much upper mid, when close but still within the coverage of the top box. It sounds balanced again when within the coverage of the lower box. When the boxes are higher it won't be possible to be in the coverage of the top box when close to them.

I got loads of measurements taken at 4 distances on axis, mic on ground, 1m high and 2m high. These are averaged for each position, and shown below. There is a lot of smoothing, it makes looking at 4 traces on one screen much easier.





There's a bit of EQ to do, cuts around 1k and 4k will probably get it close enough.
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Elliot Thompson View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 10 April 2021 at 3:15pm

Here is what I am receiving on my end through the Youtube Recording.








The harshness you describe tends to be stemming from dips within in the following frequency ranges;



1.3 kHz

2.0 kHz

2.4 kHz

4.0 kHz


As those are very important vocal frequencies, try testing the box using female vocals. The old standard “The Hunter by Jennifer Warnes” should reveal any issues under the given circumstances, as her voice is not harsh nor hollow within the first verse of the track.


Best Regards,

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Post Options Post Options   Thanks (0) Thanks(0)   Quote doober Quote  Post ReplyReply Direct Link To This Post Posted: 11 April 2021 at 9:03pm
I wouldn't say it sounds harsh. It sounds fine at a distance, but close to the top box is out of balance- too much upper mid which sounds like it could easily be tamed with some gentle EQ. I should have filmed a bit longer and moved the camera down lower before stopping, that would have shown the difference better. The lower box sounds much smoother at the same distance. The upper box output will be going over the heads of the first 2/3 of the audience anyway, how it sounds at a distance is most important.

I can't work out why the upper mid would be more prominent close up, logic would suggest otherwise, that as the listener gets closer they hear less of the higher end due to the curvature of the exits and the smaller wavelengths.

The analysis of my video is interesting, I never would have thought to do that. It prompted me to do some analysing.

This is a transfer function of the audio from the youtube video used as measurement signal, and the audio of the same video straight from my phone as reference. Averaging is set to 5 seconds. One might expect it to be fairly flat...





Next is single channel amplitude of the same music, from an mp3 player, averaged over 10 seconds





I'm not sure what to make of any of this really.
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