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The Tradenda Transmission Line Enclosure
This is the transmission line design I have so far for the bass section of my loudspeaker, which I have recently named the Tradenda, tradenda being transmission in Latin.
I’ll post a few images to explain the idea.
^ This is the schematic of the enclosure, the circles essentially represent where the loudspeaker sits. The dark grey area represents a certain density of mineral wool for absorption.
^ This is the estimated frequency response of the GRS 8sw-4 in the enclosure at the 50W signal I will be providing the driver. I know it’s very peaky, but luckily that can be solved with DSP, which will reduce the volume down to about 88db, however, luckily this is modeled in 2pi, or half-space (the equivalent of the speaker sitting in an infinite grass field). So it’s essentially the worst-case scenario in terms of output, so I’m pretty happy with that.
As for the higher resonances, most of those should be quite severely reduced in the fact that there will be a 180-degree bend in my transmission line, which has proved to damp higher-order resonances in the line quite well. This should also give us back a lot more high-frequency gain.
I will also be experimenting with thin layers of absorption on the walls, but I have a feeling all this will do is reduce the output and not much else, still worth a try though.
As you can see I have used the fact that the driver has such a high Qts to achieve a very low-frequency output, which when EQ’d should hopefully be flat down to 20hz. Not bad for an 8″ driver, eh?!
^ As you can see, even at 50W (my planned wattage) we are still below the 6mm xmax for this driver.
^ We are also below 10m/s for mouth velocity, which is literally inaudible, nowhere near chuffing territory.
^ Group delay may seem bad, but 30ms is the point at which group delay becomes audible and even then I plan to delay everything somewhat using my FIR filters to flatten the group delay. As for the giant peak at 20hz, that is pretty common anyway, but with everything getting flattened anyway the difference in group delay between 20hz and the rest will just be about 35ms, and it’s often said group delay is much less noticeable at low frequencies.
I think that’s everything, other than the fact it might be smaller than what you’d expect for 20hz. The line opening is just 52cm^2, with the maximum line cross-sectional area being 500cm^2 (about 22cm x 22cm, unless the fold makes it wider which is a possibility). Also, the height will be about 1m since it’s folded.
Ahah, yes. Just a quick sim of the power response if put between two walls (in a corner). This does however still disregard all other walls, this time the floor and ceiling too.
In fact this is probably louder than this speaker will ever run, an EQ’d state of about 95db, with the fact that due to the Harman in-room curve my bass will be 6db higher than the rest anyway, it means everything else is at 91db. 85 is too loud for me already XD. I think I’m happy with this, lets just hope that when I build it, it comes out this good.
Hope you enjoyed looking through the sim of my design!
Elliott
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