Frequency Response Spreadsheet & Measuring for Novices

Barista

Member
2002-03-27 5:27 pm
Hello,

This is my first post so take it easy on me! ;)

I've been fooling around with speaker design, basic electronics, crossovers, etc, etc. Well I’ve created this Excel template for mapping basic Frequency response. I've seen various threads asking "How can I measure the frequency Response of my new DIY project" so I figured someone here might find it useful as well.

From what I gather there is not any real "Standard", or at least inexpensive, method of doing this. However I think a lot of understanding and personal advancement can be gained by doing comparisons of like conditions using a somewhat scientific method.

It's nothing definitive, but does give you something tangible to work with when estimating Frequency Response in real world conditions, or for a said room. It might help you figure out where the dead spots are in your room or how to better you crossover to take the most from your finished enclosure, etc.

First thing to keep in mind! Be consistent! If you do a sweep reading at 1 Meter with [email protected] your baseline then make sure to do your next test under the exact conditions! Otherwise you'll be comparing apples to oranges, and that does nothing for you, except compare apples to oranges (shrug).

Here's the general idea.

Download a signal generator (or buy one if you got that kind of money for this kind of thing), http://www.esser.u-net.com/ttg.htm seems to work well enough for me. Remember we're playing around to learn and advance our personal skill and knowledge! We are not selling $15k speakers to someone based off this reading! At least I wouldn’t. Then again, if I could build a speaker someone would pay $15k for, I probably would! :)

Download the attached Spread Sheet (I also included an example XLS for your evaluation).

Get a SPL meter of your choice (Radio Shack has one for around $35 that will do fine for our purposes.)

Start by calibrating your speaker output and amp volume (You'll need to hook a computer up for this). Place the SPL meter at descent enough distance to get a clean 80db reading at 1000Hz (our baseline). Adjust your sound card output and amp accordingly. In my case, I am just goofing with a single 4" driver, so I can place the SPL meter about 10in away from the driver cone and get a nice reading. You NEED to support the SPL meter with a tripod, or set it one something (A small foam egg crate works nice) with the input unobstructed, preferably off the ground even with the driver or focal spot.

Then simply play each Frequency listed on the spreadsheet as Hz and record the value as +/- from 80db in the matching db cell. For axample if you play 100 hz, and get 75db reading, put in -5 (75db-80db =-5db difference)

When you map all 40 frequencies you'll have a neat little graph to print out and a baseline to work from. By studding the graph you can then determine where the holes are, and alter your EQ or crossover network to attain a response you are more satisfied with. Run a new sweep under identical conditions and you can directly see the results of your labor based off your previous reading.

Again, please don't consider this as a "standard" of any kind. Consider it a personal reference. It's simply something you can use to get baselines, and determine what you need to do to better your own personal project. As well, it’s a lot of fun, and that is why you are here anyway right? :)

I also started programming a signal generator that will measure output automatically for each frequency from the mic input and plot it in this spreadsheet. If anyone is interested, let me know and I will post a beta when I get something finished in a week or so.

I hope some of this is helpful, or at least as enjoyable for you as it is for me.

Later,
 

Attachments

  • frequency.zip
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This was posted in a public forum (somewhere) and might be of value to those using the ratshack meter.
==========
The Radio Shack meter is a wonderful unit. About a two and a half
years ago, I did a calibration curve for the RS meter using lab
equipment, with Eric Busch from DLC Design adding the low bass down
to 10 Hz. This was published in PSACS Sound Bytes in two issues.
These are the corrections that should be added to the meter readout
in order to achieve the correct SPL. These corrections are only
valid for the meter set to C weighting, using 1/3 octave pink noise
(easily available from various CDs), with the mic pointed at the
speaker.
Both my analog meters and my digital meter measured the same in
October, 1996.These are corrections, they are to be added to the
meter readout for the correct response in dB SPL.

10Hz +20.5
12.5Hz +16.5
16Hz +11.5
20Hz +7.5
25Hz +5
31.5Hz +3
40Hz +2.5
50Hz +1.5
63Hz +1.5
80Hz +1.5
100Hz +2

125Hz +0.5
160Hz -0.5
200Hz -0.5
250Hz +0.5
315Hz -0.5
400Hz 0
500Hz -0.5
630Hz 0
800Hz 0
1KHz 0

1.25Khz 0
1.6KHz -0.5
2Khz -1.5
2.5Khz -1.5
3.15Khz -1.5
4KHz -2
5KHz -2
6.3KHz -2
8KHz -2
10Khz -1

12.5KHz +0.5
16KHz 0
20KHz +1

<snip>

Michael Sims
Prairie State Audio Construction Society