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Post by gertman34 on Sept 26, 2018 19:16:08 GMT
Greetings!
My room is treated with Rockwool at first reflection points with 50g/cm3 density Rockwool 60mm thick, and 100g/cm3 100mm thick in corners for bass traps. The red graph shows the room response with no table in the listening position. The green graph is the room response with the table. I need a table for working on music, and need some ideas on how to reduce the comb filtering from the table. It is a standard wooden table, 60x120cm, with no cabinets or drawers. Just a simple slab on four legs. I only work with a laptop, software, a small audient ad14 interface, and a small midi keyboard, so I don't need much room. I have tried to tilt the speakers and the table, but that didn't seem to work. Placing a slab of rockwool on the table helped significantly.
The speakers are Eris E5s. These are active 5 inch active monitors. I have a subwoofer as well. However, it is disabled in the attached graphs.
Ideas 1. A table made of rockwool. How to make the surface firm and comfortable to work on?
2. A perforated table. What size holes? Should the holes be angled such that the sound can pass through more easily?
Thanks for your help.
All the best, Skyler
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Post by Hexspa on Sept 27, 2018 14:59:35 GMT
I'm not surprised to see this. Try to make a rockwool table - why not? Never heard of anyone doing it but maybe it's a profitable niche. The thing is, you're going to cover up most of it anyway. Why not just cover whatever area you can or just put the panel on your desk flat? You're up around 900Hz so even a 2" panel, forgive my lack of metric fluency, should do the trick. As far as a comfortable surface, maybe you can find some of that acoustically transparent film projector stuff and pull it really taught over some metal bars. Curious to see how you work this out.
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Post by gertman34 on Sept 27, 2018 20:26:13 GMT
I think you are right. I will try that, experimenting with different fabrics.
Of course, a more elaborate design could be to create a desk with diffusion on the surface. I am a bit skeptical on how effective that would be in comparison to an absorption panel desk. However, it would probably look really cool hehe. Also,I could do that using semi-firm materials (wood with deep grooves, perhaps with some softer material on the exterior). I think that would be more pleasant to work on. That would be quite difficult to make, but certainly a lot of fun.
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Post by pingpangpong on Sept 27, 2018 23:01:45 GMT
With minimal equipment why not get rid of the table, put the speakers on stands and design a smaller working suface, like one of those old hospital bed trays on wheels also height adjustable, Or glueing some thin carpet similar that used in cars to your table top, but guessing that if hexspa is talking 2" rockwool then the carpet wouldnt suffice, im going to be building myself a work desk soon and was planning on covering the outside with a thin layer of carpet, but not the work surface, so keeping my eys open for any desk tips.
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Post by Michael Lawrence on Sept 27, 2018 23:06:07 GMT
I don't have it in front of me, but the Master Handbook Acoustics has a bit in there on placing nearfields so there's no specular reflection off the desk that would get to the listener's ears. It's one of those "well why didn't I think of that" things. Definitely worth tracking down - many local libraries seem to have the book.
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Post by Ethan Winer on Sept 28, 2018 16:33:50 GMT
I think the key is to get the speakers off the table and put them farther back on stands, like this drawing from my Audio Expert book:
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Post by gertman34 on Sept 28, 2018 18:15:24 GMT
Thanks guys. Ethan, that's a nice simple solution. I also did not notice you have a book out. I will probably go buy that and have a read : ) It seems critical, based on the drawing, that some sort of barrier is present on the backside of the desk. The barrier, in this particular drawing seems to be about the height of the bottom of the speaker. My issue is that my room is only 4 by 4 meters. Therefore, 38% back from the front wall leaves only a small amount of space for my speakers behind, thus pushing my desk quite close to them. I could approach this by listening 38% in front of the back wall. Attachments:
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Post by rock on Sept 28, 2018 19:38:25 GMT
Along the lines of what pingpangpong said about a smaller table, what about NO table and just put your laptop and keyboard on stands.
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Post by Deleted on Sept 30, 2018 14:34:03 GMT
Thanks guys. Ethan, that's a nice simple solution. I also did not notice you have a book out. I will probably go buy that and have a read : ) It seems critical, based on the drawing, that some sort of barrier is present on the backside of the desk. The barrier, in this particular drawing seems to be about the height of the bottom of the speaker. My issue is that my room is only 4 by 4 meters. Therefore, 38% back from the front wall leaves only a small amount of space for my speakers behind, thus pushing my desk quite close to them. I could approach this by listening 38% in front of the back wall. Have you measured that 38% is even the flattest/best spot for you to sit ?
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Post by gertman34 on Sept 30, 2018 20:46:35 GMT
Have you measured that 38% is even the flattest/best spot for you to sit ? Good point. I moved the microphone to different locations in the room, and it seems that the bass response from 35 to 300 hz is the best around 38 percent
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Post by gertman34 on Sept 30, 2018 20:52:17 GMT
Along the lines of what pingpangpong said about a smaller table, what about NO table and just put your laptop and keyboard on stands. I like to drink coffee while working on music, and I like to have somewhere to put my elbows lol. I built this new table (attached), solved the high end comb filtering, and high mid comb filtering, but created a new problem in the low mids... (results attached). That is 50g/cm3 rockwool on the back walls of the table. I have a feeling the whole table is creating the problem. I bought the cheapest wood possible because I wasn't sure how this was going to turn out.
So two thoughts now
-Build as small a table as possible to minimize possible vibrations, or no table. But then nowhere to put coffee, pizza, drawings, etc...
-Drilling large holes in the current table everywhere. Perhaps this will eliminate possible vibrations.
My neighbors probably hate me. Building this stuff is loud.
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Post by Michael Lawrence on Oct 1, 2018 13:05:03 GMT
Here are my $0.02. Feel free to ignore: Without being in the room it's difficult for me to say but I think you're simply dealing with a specular desk reflection. Drilling big holes in your desk does not seem to be the best route forward. A great many recording and mixing rooms have desk/console reflections of some kind, so it's not the end of the world simply because great mixes are done every day in rooms with 'damaging' ER. Remember that we're dealing primarily with a time domain issue, which is CAUSING the frequency response issue you're showing, but the reference mic is omni and has no localization mechanism - it doesn't know the difference between that response created by a summation with an off-axis reflection, and that same response created by a lousy speaker under anechoic conditions. Our ears are a little better at this and can tell the difference between these two situations every time. Excellent data on this in Dr. Floyd E Toole's book "Sound Reproduction." Dr. Toole was one of the technical consultants on Ethan's book. It's important to use your ears, not your eyes, with this type of thing because our brain has some very very powerful auditory processing abilities. For example, go stand in your bathroom with a friend and have them talk while you record it on your phone. Then play the recording back with headphones. It sounds like there's WAY more reverb on the recording, but there's not. Your brain is just very good at interpreting the arrivals from the walls and ignoring them / integrating them into the source sound. Same thing happens all the time using a reference mic in a live performance space. There will always be seatback reflections and floor reflections and rear-wall reflections and they show up on the measurements but everything sounds just fine in the room because your brain is smart enough to process all those reflections. So we learn how to spot them on the analyzer (phase response helps with this, too) because we don't want to try to equalize something that's not a problem to begin with. This is a major area where "auto EQ" fails, by the way. Every single person in every single seat is going to hear the "sit dip effect" and the seatback reflections and so on, so it's a completely normal part of what sounds normal to us. It's like EQing to "fix" the equal loudness contours, or the 3k boost in the human ear canal. It's a natural part of how our hearing works. Messing with it creates an unnatural sound. I don't know if your desk reflection falls into that category or not, but I would say: how does it sound? Listen to some recordings you know very well, and if they sound good, leave it alone. If you legitimately hear a problem, then you can start worry about how to fix it. Have you thought about simply using EQ? www.prosoundtraining.com/2018/06/27/can-a-reflection-be-equalized/
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Post by Ethan Winer on Oct 1, 2018 15:24:03 GMT
Nice post Michael, and I agree with pretty much all you said.
I also agree with Rock that no table is the best table. Lacking that, the smaller the better.
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Post by Deleted on Oct 1, 2018 15:35:00 GMT
For example, go stand in your bathroom with a friend and have them talk while you record it on your phone. Then play the recording back with headphones. It sounds like there's WAY more reverb on the recording, but there's not. Unless, you block your other ear. Then you usually hear that reverb "live" too. (A good way to check how your recordings will sound). In my apartment the reverb is pretty horrible, but to notice it i need to block my other ear. OR if i've been the whole day in the studio (not lots of verb + critical listening whole day) I notice the reverb.
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Post by gertman34 on Oct 3, 2018 19:39:00 GMT
Solution to problem attached. I designed a slatted table in blender to reduce the surface area that could be vibrated, and the results are fantastic. I have no EQ applied at the moment. I may try to bring the highs up a bit using the speaker eq. Thanks for all your input guys. The smaller the better it seems : )
Somehow, it is actually better than with no table.
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