The Beta-12s were indeed a significant upgrade (5dB greater at that 56Hz peak)Ģ. My amateur conclusions (comments and corrections welcomed):ġ. The orange line is the SWR Super Redhead 2x10 cabinet.
The yellow line is the 2x12 cabinet with Eminence Beta-12s. The purple line is the 2x12 cabinet with Oxford 12M6s. The green line is the measurement of the amp head via the DI box. Here's the plot of speaker responses, smoothed by 1/6 octave. (I know I have a room mode around 200Hz because I used that frequency to set levels and I could hear it.) However, since all the measurements were done in the same conditions on the same day, they should allow me to make some judgments relative to each other. My room is untreated so these plots include the room response. I chose a flat-ish tone setting on the bass channel and set the volume at 4 and then didn't touch the controls. Step 2 - I measured the speakers by setting each speaker cabinet on a stand in the middle of the room and pointing a calibrated measurement mic at them from a distance of 36 inches.
In addition to these two cabinets, I also measured the Bassman head hooked up to a Super Redhead 2x10 cabinet ('cause it's the only "modern" 4 ohm cabinet I have handy) I also bought a pair of re-coned Oxford 12M6s and put them in a '62 2x12 cabinet. Per billfitzmaurice's recommendations in the above-linked thread, I bought a pair of Eminence Beta-12s and put them in a '63 2x12 cabinet. So, having established what the tone controls were doing, I moved on to test speakers. Here is the same plot for the "Normal" channel: Here is that plot for the "Bass Instrument" channel of the amp (notice the 60Hz spike from my electricity complete with harmonics at 120Hz and 180Hz) : I left the Presence control set to 10 for all these tests. Since the Bassman only has Bass and Treble controls (and a Presence), I decided to raise Bass and Treble together one division at a time and plot the frequency sweeps. Step 1 - I measured the response of the Bassman head via a speaker-level DI box using the Quick Sweep in TrueRTA. I got to wondering about how much difference I would hear between various speakers and decided to measure. This started from a discussion of replacement speakers for my '62 Bassman with 2x12 cabinet in this thread:
Input on my methodology and results would be very welcome. In closing, TrueRTA is by all means a reliable and efficient application when it comes to studying sound generated by your audio system.This is my first attempt at measuring an amplifier and speakers using TrueRTA. You are also able to measure a loudspeaker’s frequency response and the noise from a given piece of audio equipment. With certain values for analysis parameters, TrueRTA can measure frequency responses using pink noise and quick sweep. Just like for the spectrum analyzer, you get a panel in the main window of the application which allows you to easily adjust these settings. TrueRTA enables you to set the oscilloscope time base, input voltage and allows you to choose between the left and right channels as the source for the sweep triggering.
Depending on your computer's hardware configuration, the application allows you to adjust the internal buffer size of the software so you can obtain the best possible synchronization between what you hear and what you see on screen.Īs far as the oscilloscope goes, you get to use and view a waveform of the input signal. Using this tool you can choose the audio device, select the channel, as well as the input and output sampling frequencies.
You get to control the generator from a simple panel and adjust its frequency, amplitude and wave type. TrueRTA offers you a generous display area for the available graphical representations of the analysis, oscilloscope and RTA modes. All of these come merged under a user-friendly interface which provides quick and easy access to all the features and functions you need. The application integrates a low distortion signal generator, a digital level meter, a crest factor meter, a dual trace oscilloscope and a high-resolution real time analyzer. TrueRTA is a powerful tool designed to help you test and run a detailed analysis of sound systems using your PC, a measurement microphone, preamp and a USB interface.