Semi scientific study of tuba bass output

[Shockwave]

I just got a handy new microphone, so I decided to test something I had always been curious about: differences in bass output between different tubas. I set up the microphone outside and recorded the tubas playing a descending Bb scale from about 50 feet away. Each instrument bell was aimed the same direction.

The horns are:

1924 King BBb sousaphone. 24" bell, .687 bore, old style wrap with tuning after the valves
1924 Conn 44k (converted to bell front) BBb jumbo sousaphone. 26" bell, .770 bore
1890 Leland BBb tuba. 18" bell, .738 bore
1926 Conn monster Eb tuba. 19" bell .689 bore
1850's E.G. Wright Eb saxhorn .655 bore 11" bell

The points on the graphs are notes of the Bb major scale, with pedal Bb on the left.

Notes between low F and pedal Bb were played with false tones

I performed a fourier transform on each note and recorded the strength of just the fundamental. The strength of the fundamental is fairly constant between dynamic levels, unlike higher harmonics.



My observations:

Tuba bass output seems to follow a 12dB per octave slope. Indoors the confinement of very large sound waves produces a bass boost making it seem more even.

A jumbo sousaphone produces about 4dB more bass than a 4/4 tuba, which is more than double the power.

A monster Eb is more powerful than a jumbo sousaphone on low C. It is also very uneven compared to other tubas.

An ancient saxhorn makes almost as much bass as a 4/4 king tuba down to Bb. It would probably be even better if I had a deep mouthpiece that fit the extra large receiver.

-Eric

[Wyvern]

Interesting! Thanks for sharing

[ckalaher1]

Very cool.

Lots of hard work went into that. At least from this scientifically inept point of view.

[Dan Schultz]

Pretty cool. But.... how did you control the input energy?

It's been my experience with my 'jumbo' that I tend to put more energy into the horn because it's difficult to judge the output level from behind the bell. To me.... these horns seem to be more efficient than they feel.

[iiipopes]

This is correlative with my subjective perceptions about my Besson, my 186 with either bell, and a 38K I used to play: the 38K had more fundamental, next the 186 with the front bell, then the 186 upright, and least efficient the Besson. But with the comp block and other variables, there were more reasons the Besson may have been inefficient by comparison.

I would also like to see the relative spectrum graph, kind of like Rick Denney did on his website with a York-Master, a 186, and a Yammy F.

[Shockwave]

I would be curious if your could normalize all these horns for total spectrum power, and after that normalization is done, compare each individual instruments fundamental, and first 3-4 partials. This study would allow people to compare the relative ratios of bass to total normalized volume of the instrument...

BTW, I'd love to hear the 1850's saxhorn!!!

That is possible, but where would you set the dynamic level? The saxhorn and the jumbo sousaphone can be played at subjectively equal loudness, but at the same time wildly different power outputs since the jumbo makes mostly bass to which the ear is less sensitive. A measurement of anything but the fundamental becomes very, very complicated. There is also the complicated problem of directionality of upper harmonics. I chose to compare the strength of the fundamental because it has vastly fewer problems in measurement. It is quite constant in strength from piano to fortissimo and it is omnidirectional. The difficult part that I learned measuring loudspeakers is that room resonances and microphone proximity effect ruin measurements, so I recorded outdoors at a distance.

Here's an audio file of the Bb scales. Not my best playing but it was good enough for a test. The order is King, Jumbo, Leland, Monster, Wright

http://www.supload.com/listen?s=iWkelk

Pretty cool. But.... how did you control the input energy?

It's been my experience with my 'jumbo' that I tend to put more energy into the horn because it's difficult to judge the output level from behind the bell. To me.... these horns seem to be more efficient than they feel.

Some quick measurements showed that the strength of the fundamental doesn't change much from piano to fortissimo, so I recorded at what felt like an ensemble forte on each horn. The jumbo is deceptively soft behind the bell, but the input power turns out not to matter much for this particular measurement.

I would also like to see the relative spectrum graph, kind of like Rick Denney did on his website with a York-Master, a 186, and a Yammy F.

There are so many variables when trying to compare instrument spectra that you need to decide exactly what you want to compare and exactly how. What measurement setup will work equally well for all horns? How will the volume level be set? One thought I had was to match the level of the third harmonic and compare spectra. I don't know if third harmonic level correlates to perceived loudness, but it might.

[DonShirer]

It is interesting how similar the curves are for the different instruments. I do have a question about the reproducibility of the results. No matter how careful a musician may be, I would guess that there might be a several db variation in output on successive notes just because of human variability. Did you make several successive trials with the same instrument to see how repeatable the output was? This could help tell you the expected standard error in these results.

[Shockwave]

I played some standard music on each horn before playing the scales, and compared the same notes at different volumes. It may seem counterintuitive, but the strength of the fundamental hardly changes from piano to fortissimo. There was only 2dB difference in the fundamental between very soft and very loud notes, and I kept the volume fairly constant on the notes I used for the test. Between the same notes of similar volume the spread was +- 0.3dB. For any higher harmonic there is almost no repeatability.

-Eric

[Søren]

Super cool. Thank you for posting.

I talked about doing this kind of analysis some years ago, but never got around to it. Is it some MatLab code you have put together for this analysis?

[toobagrowl]

Very interesting
Imo, the King BBb sousa has the best sound and scale of the samples given.

[DonnieMac]

Spectrogram is a tool that could reveal to you the frequencies generated by the several tubas, the strength of the fundamental and the array of overtones. Google "spectrogram" and pick off the free ware best suited to the project.

[Dean E]

That is an interesting chart. However, I'm wondering about the sense of pedal Bb, which I take to mean an octave below the Bb two ledger lines below the staff. I haven't been able to take an Eb [horn] that low, even with false tones.

[Donn]

That is an interesting chart. However, I'm wondering about the sense of pedal Bb, which I take to mean an octave below the Bb two ledger lines below the staff. I haven't been able to take an Eb that low, even with false tones.

I would interpret it like you, and like you I am not normally able to play it. It's in there though - not false, just a pedal note with a lot of valve tubing.

[finnbogi]

That is an interesting chart. However, I'm wondering about the sense of pedal Bb, which I take to mean an octave below the Bb two ledger lines below the staff. I haven't been able to take an Eb that low, even with false tones.

It is there, and doesn't need false tones. The notes from pedal Eb down to this Bb (on 4th valve) pop quite easily out of my Besson, the A and Ab are OK, but at G (124), the resistance due to the added compensating tubing makes things more difficult. I can usually touch that G, though, but the Gb only on a good day.