MAB
Major Contributor
Today I present measurements on a pair of Rauna Freja, aka affectionately as 'Swedish Tombstones'. They are a small 2-way in a concrete cabinet. I believe that Bo Hansson was involved with the design. I would appreciate any information members have regarding this nice little speaker.
These were made in the '80s, they are 100% original. Out of a discussion on another thread about the imagined virtues of avoiding measurements, I used the Rauna as an example of a speaker with weak bass but that still has a strong interaction with room modes and boundaries. Here I present a full set of measurements made in my shop using my simple loudspeaker testing rig; a stool with a plywood cutout graduated in 5 degree increments, a UMIK Microphone, REW, and VituixCAD. I will use the very good tutorial on how to roll-your-own spinroamas. I typically can get an acceptably close result as Amir or Erin when measuring the same speaker. You can too.
If you follow this post and the other thread on avoiding making measurements, I hope an appreciation will be for why even small speakers with limited bass output strongly interact with the room. In the case of measurements, I need to do some work to not have the room ruin the bass measurements below 300Hz. That same phenomena will cause the bass to vary by position in the room. And be really bad sounding in some places, and good in others.
I measured the woofer and port nearfield, and calculate an aligned sum to get in-room response free of the room boundaries as pictured below left. This is critical because we can't reliably measure bass frequencies as I just indicated above. I will later stitch the nearfield bass measures with 360 degree horizontal and vertical measurements as pictured below right, which need to be gated to filter out the room.
First the nearfield measurements of the woofer and port and the summed response:
The port is tuned super low, and is only2.5 4.5cm diameter. It provides a small boost in output at 33Hz, but the port resonance at 780Hz and higher harmonics is larger, wow! I am not sure this is a good application of a port. How audible the port resonance in far-field is unclear. These nearfield measurements show the resonance both in the direct woofer output and the summed woofer + port response. You can see that this speaker will not play much below 100Hz and the port barely helps, especially tuned so low. And the weak bass response it has will interact strongly with the room, as I show elsewhere.
I made a bunch of horizontal and vertical measurements at various angles, merging these in VituixCAD with the low frequency estimate, I obtain the following:
Aside from what I think is an odd port choice, the speaker has reasonably controlled directivity. Perhaps emphasized response in the 1.5-3kHz region. The notch at 780Hz caused by the port and its associated resonances at 1560Hz can be vaguely seen in the in-room response predictions. I am not sure if it is because of my method of stitching or if the port resonance shows up in the far-field.
Here is the estimated in room response based on the above measurements and my attempts to splice:
It's always been a pleasant speaker to listen to. I've called it congested in the past. I wonder if it's the port. Might be good to plug it and remeasure. That's in the future.
I use a DATS to measure the impedance:
Impedance trace shows two resonances at 350Hz and 450Hz, but not at the port resonance frequencies which makes me wonder if I am overemphasizing the effect of the port on the response. Not that it seems like a worthwhile port, but maybe it's effect is exaggerated, both in boosting bass and in generating issues at 780Hz and higher multiples.
The full spinoramas in horizontal and vertical:
Lastly, distortion at about as loud as I feel is safe.
I think you can see the port's resonance at 780Hz in the 5th and 7th HD peaks. Not that I am imagining that I can hear the distortion, rather the distortion indicates the resonance is there. No idea what the spike in even and odd distortion is at 300Hz, surround breakup? It is a 40+ year old speaker. I can't measure the woofer and tweeter separately, and can't demount the drivers to investigate further. I did measure both speakers to see if they match, here is an ungated on-axis measurement:
The output and distortion do match, including the HD peak at 300Hz. So they have aged equivalently, and don't appear broken.
That's the Rauna Freja. A bass-shy speaker that I measured. I welcome comments and input.
These were made in the '80s, they are 100% original. Out of a discussion on another thread about the imagined virtues of avoiding measurements, I used the Rauna as an example of a speaker with weak bass but that still has a strong interaction with room modes and boundaries. Here I present a full set of measurements made in my shop using my simple loudspeaker testing rig; a stool with a plywood cutout graduated in 5 degree increments, a UMIK Microphone, REW, and VituixCAD. I will use the very good tutorial on how to roll-your-own spinroamas. I typically can get an acceptably close result as Amir or Erin when measuring the same speaker. You can too.
If you follow this post and the other thread on avoiding making measurements, I hope an appreciation will be for why even small speakers with limited bass output strongly interact with the room. In the case of measurements, I need to do some work to not have the room ruin the bass measurements below 300Hz. That same phenomena will cause the bass to vary by position in the room. And be really bad sounding in some places, and good in others.
I measured the woofer and port nearfield, and calculate an aligned sum to get in-room response free of the room boundaries as pictured below left. This is critical because we can't reliably measure bass frequencies as I just indicated above. I will later stitch the nearfield bass measures with 360 degree horizontal and vertical measurements as pictured below right, which need to be gated to filter out the room.
First the nearfield measurements of the woofer and port and the summed response:
The port is tuned super low, and is only
I made a bunch of horizontal and vertical measurements at various angles, merging these in VituixCAD with the low frequency estimate, I obtain the following:
Aside from what I think is an odd port choice, the speaker has reasonably controlled directivity. Perhaps emphasized response in the 1.5-3kHz region. The notch at 780Hz caused by the port and its associated resonances at 1560Hz can be vaguely seen in the in-room response predictions. I am not sure if it is because of my method of stitching or if the port resonance shows up in the far-field.
Here is the estimated in room response based on the above measurements and my attempts to splice:
It's always been a pleasant speaker to listen to. I've called it congested in the past. I wonder if it's the port. Might be good to plug it and remeasure. That's in the future.
I use a DATS to measure the impedance:
Impedance trace shows two resonances at 350Hz and 450Hz, but not at the port resonance frequencies which makes me wonder if I am overemphasizing the effect of the port on the response. Not that it seems like a worthwhile port, but maybe it's effect is exaggerated, both in boosting bass and in generating issues at 780Hz and higher multiples.
The full spinoramas in horizontal and vertical:
Lastly, distortion at about as loud as I feel is safe.
I think you can see the port's resonance at 780Hz in the 5th and 7th HD peaks. Not that I am imagining that I can hear the distortion, rather the distortion indicates the resonance is there. No idea what the spike in even and odd distortion is at 300Hz, surround breakup? It is a 40+ year old speaker. I can't measure the woofer and tweeter separately, and can't demount the drivers to investigate further. I did measure both speakers to see if they match, here is an ungated on-axis measurement:
The output and distortion do match, including the HD peak at 300Hz. So they have aged equivalently, and don't appear broken.
That's the Rauna Freja. A bass-shy speaker that I measured. I welcome comments and input.
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