Monday, January 18, 2016


While on break I've been tweaking my sound system, and while looking for RTA software came across REW. REW is a pretty awesome piece of software, it runs on windows, mac, and Linux and it's free!

My PA speakers are pretty good, but do need a fair bit of EQ. I've been tweaking by ear, and got decent results, but it was also rather subjective, and time consuming. With REW I can run a frequency sweep in a couple of seconds and get a frequency response graph, and the parametric filters needed to correct it to the target frequency response! Alternatively you can use the generator tool to play pink noise through the system and adjust your equalizer until the RTA shows flat. I usually use the second method because I have a nice 31 band EQ, but my main system processor only has 5 PEQ filters. I do have a separate PEQ with something like 20 filters, but it's Behringer and has had some reliability issues, so I try not to use it.

Red is the raw speaker response, green is after correction. I should add, this is indoors in a room comprised almost entirely of hard reflective surfaces, and these are PA speakers, so the graph above is quite decent. Above is with 1/3 octave smoothing, below is the raw measurement:

There's another cool smoothing option called var smoothing which I really like. See below:

Anyway, enough distractions. Moving on.
Here's an example of the auto EQ feature:

The red trace at the top is the measured frequency response, below is the corrected (predicted) frequency response. Blue filled above are the filters needed to correct the response.

Not bad, except for that weird dip around 125, but some of that is due to mic and speaker placement too, when I was moving around it came and went to a degree. Here's an example of the format for the exact filter requirements:

Equipment: I don't have a dedicated measurement microphone, so I thought I'd try using my H4N and its built-in microphones. I measured, and corrected, and it did not sound right. Muted and muffled. I realized I should probably check how flat the frequency response on the H4N mics, and while not terrible, there's enough to make a significant difference.

So I don't have a calibrated mic, but I do have it's frequency response, and REW accepts calibration files, so if I can figure out the calibration file format I could hypothetically make my own calibration file for the H4N! So I looked up the file format, and it's pretty straightforward, arbitrary frequencies, space(s) or tab(s), and dB from reference. Eyeballing the chart, this is what I came up with:

"Sens Factor =-??dB, SERIAL NO: 0021####"
Calibration file for Zoom H4N
Calibration points are eyeballed from the 
manufacturer's provided frequency response chart.
10 -6
30 -3
40 -2
50 0
60 0.75
70 1
80 1.5
90 1.5
100 2
200 2.5
300 2.5
400 2.25
500 2
600 2
700 2
800 2
900 2
1000 1.5
1500 0
2000 2
2500 3.5
3000 3.5
4000 6.5
5000 4.5
6000 6
6500 6.5
7000 6
8000 5
9000 2.5
10000 2
12500 4.5
15000 4.5
17500 6.5
20000 -2.5

Which gives the graph below.

Not perfect, but within a few dB, and now calibration sounds great. This was a good learning experience, and now my system sounds great :)

I do enough sound work I figured it would be worth it, and I had a gift card, so I went ahead and got a real calibrated measurement mic. Dayton EMM-6. Came with a hardshell case, clip, and windscreen.
Not bad for $40, and it's been doing a pretty good job.

Tuesday, November 10, 2015

Sound and moon

My blog appears to be just about dead, but I'm keeping it hanging on every once in a while. I'd like to post more, but college and work are keeping me really busy.

Anyway, just ran across this, and thought it was a pretty good demonstration of a speaker for those curious.

Also, combo post! Here's a photo I took of the moon eclipse a while back.

Monday, June 29, 2015


I know I haven't posted here in quite a while...

Here's a visual representation of compression. This can be applied to audio too.

View full size!

Raw source (not really, but close enough)

Dynamic range compressed. Blacks flattened, loss of detail.

Data compression. This is why I don't like listening to MP3's in general.

Wednesday, May 20, 2015

Speaker progress - Almost done!

Almost done!

My little sister wanted to draw...

Prepped to paint

The finish actually looks pretty good for just unprimed plywood and spraypaint.

Inside done!
Sounds good too.
Trust me, it looks better in person.

Tuesday, May 12, 2015


Here are things that I find interesting or helpful, or both: 

     Blender is a free, full-featured, open source 3D suite. It has some amazing tools, and with a little work, you can make some pretty neat things. (
    Ninite is a great website if you want to do a batch install of a selection of common programs.
    Sadly it only works on Windows now.
    Grooveshark is a great free music streaming site with good variety and quality.
Stay away from their HTML5 version though. Last I checked it was awful.
The flash version is pretty good though. Grooveshark finally shut down :(
    Fun website if you like building computers. Targeted at desktop users, but there's a little bit of server class hardware on there too. You can also see price trends for the items you choose.
    Nothing special about the website, but it's really nice having the store nearby.
They have the absolute best prices on CPU's, and their motherboard combos are really good too. They've also been expanding into the DIY market some, they carry Raspberry Pi's, Arduinos, and Intel boards. They even have a model rocket section!
    Not cheap, but if you can afford it they have some really nice aluminum channel for building. Servo mounts, gears, driveshafts, gear chains, etc. Erector set on steroids.
    FreeBSD based OS for file servers.
I wasn't able to figure out how to set all the user permissions like I wanted when I was using it, but it keeps improving, and for a home NAS it could work pretty nicely. ZFS filesystem too.
    Students: Free Microsoft software.
    Schematic and PCB design software. This is what I use. Nothing fancy, but it does the job and it's free.
    Nice light photo viewer.
    For the Canon camera owners, this is a really cool website. RAW video on a 5D MKII(I)! Lots of added functionality. And if you do the raw video this is a nice viewer/converter:
    Free video editor. It's serious about the minimum specs though. While not strictly required, you should have at least 16GB of RAM and a good GPU for this.
    A good place to look for a new laptop. Some of the best prices, and lots of options.
    Horn loaded speaker website. Some really good info on there about sound in general too. I have a pair of the DR 250 and Titan 48 speakers, and I'm pretty happy with them.

This may be updated as I come across / remember other things.

Saturday, April 18, 2015


Aaahh! It's April already! Time is moving so fast it's scary. College is really hard.
Why must the nicest weather of the year coincide with exam study time?
I wrote this up a while ago, and am just now posting it in between studying for exams. I've been doing nothing but math for the past 6 hours, and I need a brain break or I think my brain will break.
I realized the other day that I haven't really posted any pictures from college, so I'll make an attempt to rectify that from now on. First though, new computer setup!

Never seen that error before...

It's working pretty nicely. The main reason I'm running Windows is that the free version of Davinci Resolve (Davinci Resolve lite) only runs on Windows. From what I can tell, the paid version runs on Linux, but I don't have $1000 to spare, and since I'm a student, I get Windows for free, so...
I'm really excited for DaVinci Resolve 12, I'll probably move to that as my primary video editor. (except on Linux...) Resolve can even do real-time optical flow interpolation, which is the coolest thing I've seen in a while.

New system specs: (Subject to change fairly often)
CPU: 2.5 GHz Xeon x8
GPU: Nvidia GTX 590
1 TB 7200 RPM SATA drive (Windows 7)
256 GB SATA SSD (Linux Mint)

So now I've got a good setup for CG and video editing, if only I had time to use it... I'm hoping to put it to use for the CRU VMA's next year. There are some nice computers in the video editing department at GMU, (i7 3770 with 16GB RAM), but they're rather lacking in terms of the GPU. (At least the ones I've tried, the mac pro computers may be better)

Anyway, photos!
Spring is beautiful.


 These are all raw, completely unedited, and some of them were taken with my phone. I did see enough good photo opportunities I've started bringing my camera. The Canon PowerShot G series is a really great all-around camera. It's small enough to bring easily, and still gives me all the control I need, and good photos. The new ones have HD video too. I'm very happy with my G10. I've put it through a lot, and it still delivers. I need to clean the lens though, as you can see in the photos above.
That's all for now.

Friday, March 13, 2015

Me and VMA shooting

Getting started on VMA's early this year...

Mostly generic guitar shots that could be used on various projects. I didn't realize until this project how nice the full frame sensor is on the 5D. I should have put magic lantern on it for this project, I'll try to do that for next time. It makes video shooting so much better. We didn't check focus except on the built-in camera screen for the first round, so we had to shoot that all again. 
Note to self: bring HDMI monitor next time, even if it's only a 5" screen, almost anything is better for checking focus than the 2" camera monitor. Magic lantern's focus peaking would have been very helpful.

We also did some other shots, I'm not sure how many of these will be used, they were more specific, but it was a very interesting shoot. Without revealing too much;

That is snow in the background, and the stick was an essential piece of equipment :)[]

Thursday, March 12, 2015

Speaker Progress 07

Amazing what can happen when I get time to work on things... With (a lot of) luck I could have it finished this week...

To date:

Trying out fitting for the back brace... Lots of routing on this piece.

Most of the (wood) parts for the tweeter module

I let my little sister have some fun with part of my speaker that doesn't show and won't get painted...

Marked for nailing

There's a minor problem...


Is supposed to look like this.

Much better. Glad I hadn't glued anything yet. Tack nails only so far. That will change soon.

I know, I said I should put this in slideshow format, but maybe next time. Or maybe long posts aren't so bad. It's late, that's all for now.

Speaker Progress 06

Ignore the sub next to it, it's just a freebie I'm using for testing purposes.

A critical listening test... ;)

Wednesday, March 11, 2015

Spring Break!

Hooray for Spring Break!
Even if it's only a week :(

None the less, I have plenty to do. (In addition to homework...)

(One of) My big projects for this week:

It's starting to make sense :)
This is a great mixer.
If everything goes well, it gets installed this week. Then I have to document and explain the new system. Should be fun, I've been working towards this for a while now, and I think it will significantly improve the church's audio system.

I also have a update on the speaker. I finished typing everything out, and then something weird happened and it all got deleted... So that should be coming soon, when I feel like typing it again.

It's hard to realize just how connected I am at college. It's just been a few days, and I'm already starting to miss some of my friends. On the other hand, I have enough to catch up on it's not such a bad thing. (my to-do list is about a page long, written in paragraph form...)

In unrelated news, I really like working with HDPE plastic. It machines very nicely, it's easy to work with, and finishes decently. I got about a 12" sheet a while back from, (good place for raw materials) and was able to use a scrap from that to hand make a replacement part for an old camera, but that's a different story.
Every time I work on something round like that I think I should make a lathe sometime. I've got a wonderful 3hp motor sitting around, and I could build a controller easily, but the chucks are quite expensive last I looked. GMU is planning a hackerspace, and I'm really looking forward to that. No timeline yet though. I put in a good number of suggestions for it :)
I like working with my hands. With (a lot of) luck, my speaker will be finished this week, and I can build the cabinet for a custom guitar amp I've been asked to make. If you're curious, I'm going to try the XF 212. It should be a fairly easy build, (all straight cuts) after what I've been doing. The custom electronics are a different matter. I have an idea of what I want to do, but I'm still working on it. All I really know at this point is that it will be a tube amp, and I want to try this: I built the SSE (Simple Single Ended) amplifier for a science fair project a few years back, and I still have it. I might use it on this project with an input transformer to drive the powerdrive board. I'll need to figure out power though. good HV transformers are expensive. I'll have to see if I can find a suitable one in my collection.

Anyway, more soon.

Monday, March 9, 2015

Ammo Can Radio thoughts

It's been a while (years!) since I posted anything about the ammo can radio. It was originally intended to be mostly analog, with just a digital frequency but I think at this point it would be best to at least have a digital VFO. The questions start...

  • How much digital control? Will there be any hard controls, or will it all be software? I'm fine with having software behind the controls as long as it's invisible. Menus I want to avoid.
  • Frequency range. With a digital VFO, DDS for example, an extremely wide frequency range is available.
  • Modulation modes. Somewhat dependent on previous question. AM, SSB, and CW are desired, digital and FM modes have yet to be determined.
  • Modularity. Basic module structure has yet to be determined.
  • Power structure / distribution. 13.8VDC bus + (5V bus?)
  • Structural considerations, aluminum vs. steel vs. plastic. What and where.
  • External connection options. (Can it operate when closed for waterproofing?)
  • Speaker(s) This probably won't happen, but a little internal horn loaded speaker would be fun...
  • Controller. I'm inclined to go with a Raspberry Pi 2 for the flexibility and horsepower this would provide. 40 GPIO should be adequate, and I can always expand that if needed.
  • Connectivity. I want this to be as versatile as possible.
  • Weight. For those people who know me, weight is pretty low on the list of concerns. Right now, my collected assortment of parts in an ammo can weighs about 25 lbs.

Digital control: If I use a Raspberry Pi (2), I could potentially make it a complete SDR. This opens up a lot of possibilities. On the other hand, I have a instinctive distrust of computers...
I don't know. If I used the raspberry pi, I could have a display port, and show a waterfall display, frequency, etc. on an external display. I could also potentially do some fancy audio filtering, but that requires more knobs unless I want to do software menus (I don't!) and I'm already short on front panel space.
Another advantage to using the Raspberry Pi is that it can be programmed in python. This is supposed to be an open project, when constructed, all schematics and source code will be released. I might sell plans and/or parts though. Python is very easy (relatively) to get into, so if people want to modify it, that's a plus. I hope to learn C (+, ++, ?) next semester though, and that's a more common language, so that's an option too.

Frequency range: Modern DDS chips can practically go the quintessential DC to daylight. For receive I know I want at least from the AM broadcast band to approx. 30 MHz. 6 meters would be a bonus, but not something I would focus on much. 2M would be very nice, but that's totally different from HF. If it goes to 2M, it needs to be able to receive the FM broadcast band, AM air stations, and the weather channels. 440 I'm somewhat indifferent to.

Modulation modes: Fairly simply, if it only does HF, it only needs to do AM, SSB, and CW. I know 10M has FM, but it's not worth putting in for one band. (Unless it's software and would be really easy to do) If it does anything above 6M, FM (narrow and wide) is a requirement. Digital modes are optional. Again, if using a Raspberry pi, there are a lot of options, but digital is close to the bottom of the list on things I'll be working on.

Modularity: I need to develop a good interconnection system. I'm thinking that each module should have access to a power bus, (see next point) the VFO, a discrete line to the controller, the previous module's output, and the next module's input. I'm not sure how I want to handle RF connections yet. I like BNC, but I think it's too big for this application. There are smaller versions of BNC, but I haven't found one I liked yet. I don't like SMA, but it might be a good fit for this, it's pretty small, and  readily available.

Power structure / distribution: My current plan is to use two nominal 12V, 7AH gel cell batteries. I plan to wire them in series when they are discharging, and parallel when charging. The reason for this is that DC-DC converters can be very efficient nowdays, and it's easier to build a converter that only has to downconvert instead of providing a regulated 13.8 VDC from a source that may be above or below the output voltage. Buck vs buck/boost. There will be a front panel meter to monitor voltage. I may make it switchable to monitor the battery voltage (should show around 24-28 VDC when discharging, 12-15 VDC when charging) I drew up a series/parallel switcher with a DPDT relay and a sense resistor, but I don't have a digital copy at the moment, I'll see if I can put that in later. For distribution power, I think one 13.8VDC bus would be adequate, but I'm also considering putting in a 5V bus. If I have a 5V bus I'll probably use a good switching converter, but if each module only has a 12V bus and has to internally convert to 5V, I'll probably just end up using a bunch of LM7805's.

External connection options: Ideally there would be external connections for a mic, speaker and an antenna, so that the radio could be sealed, waterproof, and still operate. Let's worry about that later. Maybe I could just make the whole thing water resistant when open. (Ammo cans are fairly waterproof when shut) That's probably the best/simplest plan.

Audio: Audio output will be via a 1/4" stereo jack. Audio will be mono (wait, maybe I could do stereo FM broadcast... hm...) anyway, I'm still trying to decide if plugging in a connection should automatically disconnect the internal speaker or if there should be a switch for that. Having a switch gives you more flexability, so I'll probably do that. If someone wants to have the speaker auto disconnect, that's easy to wire up. There will also be a switch to select whether you have connected a speaker or a pair of headphones. This radio should be very versatile. There will be an internal speaker, but you can only do so much with a given amount of space. A little horn loaded speaker would be fun, but I'm already tight on space, so I'll probably go with a simple direct radiator. Shouldn't be a problem to get a 10 or 20 watt 3" speaker or so. I think that should be adequate for most scenarios, and for anything else you'd need headphones.

Controller: The Raspberry Pi 2 is cheap, adequately powerful, well documented, and has good I/O. I even remember hearing something about it's PWM pins being able to output up into the FM broadcast band. Hm... with a little filtering, I might be able to use that... Now things are getting interesting. The Raspberry Pi (2) also has a display output, so I could possibly provide a front panel display jack for an external band display. Maybe a waterfall display like the Elecraft panadapter. It would be even cooler if I could mount a little display on the lid of the radio, so when you open it... I'm going a little overboard here, I'll back up.

  • Antenna: UHF (SO-239) and binding posts
  • Speaker/headphone: 1/4" jack
  • Mic: Undecided. May leave option open for people who already have Yaesu, Icom mics.
  • Power: IEC C-14 AC connector, Binding posts: 12-36V in. Bridge rectified and fused.
  • Potential: USB (Keyboard, software upgrades, etc.?), HDMI.

Weight. I'm not going to worry about it. This is designed to be rugged, reliable, and flexible, but not light. Which is too bad, as it would be a great backpacking radio otherwise, but I can only make so many tradeoffs. (Battery life, etc.) It might be a 20 or 30 pound radio, but the weight should be similar to an ammo can filled with ammo, so it's not too unreasonable...

In case anyone's wondering, yes, this is the sort of thing I think about in my free time for fun.
If anyone finds a flaw in my reasoning, or something that I should think about, feel free to comment!
I have a number of other considerations, schematics, etc., but those will have to wait for another day.

Monday, February 16, 2015

Speaker Progress 05

Speaker update. Lots of photos:

In case anyone's wondering, 1/8" plywood will easily bend to the radius specified by the plans, and quite a bit more! 



Generic multi-tool vs. Leatherman saw, the difference is amazing.

Bottom again

Side panels ready to go on

Sorry for the long post. I need to put these in slideshow format next time I have so many.