I put a damping layer in the front section by gluing a 60x40cm soft board below the front braces.
If I stagger the pipe output with the orginal unlined in green. Next up the red is with the lining around the driver. With the frontplate is at the top note that the brown trace, not that the trace is smoother than the other two.
If I alight the bass part of the traces on the big improvement was the felt and board lining. The added front board is icing on the cake and the knuckle rap test is much improved.
So to conclude I recomend the design. Building it from scratch I would line all parts in the closed en by felt before putting it all together. The front damping is also a good thing to have.
If I stagger the pipe output with the orginal unlined in green. Next up the red is with the lining around the driver. With the frontplate is at the top note that the brown trace, not that the trace is smoother than the other two.
If I alight the bass part of the traces on the big improvement was the felt and board lining. The added front board is icing on the cake and the knuckle rap test is much improved.
So to conclude I recomend the design. Building it from scratch I would line all parts in the closed en by felt before putting it all together. The front damping is also a good thing to have.
I had one final nagging question, does a final 90 degree bend reduce the 5th harmonic at 200 Hz. So at long last I cut out a hole of 190 cm2 in the back board and sealed the bottom of the box.
Impedance looks the same
Frequency response at the pipe end does not change. The measurements are months apart and the old one (blue) with the speaker at a wall and the new with the speaker in the middle of the room (green). That 200 Hz peak sure is persistent!
Then I have a new pair of Voigt pipes, designed by late Bosse Hansson of Opus 3 Records. They are designed for Lowther, with 19mm chipboard as the building material and 2x 19mm in front an back they are very different from the flimsy Deccas.
Tuning of the pipe is similar.
In both cases I used a Peerless 8" PP driver that works well in the pipes
Damping inside the pipes are similar with felt covering the walls of the first half of the pipes.
Listening to Adele 21 and some other records the pipes sound quite similar. Playing loud bass and the decca vibrates a lot not only the large front baffle but also the narrow top plate. The other pipe does not vibate at all or very little.
So that 200 Hz peak is not tamed with a new location for the pipe opening. Nor does the flimsy constructions cause the sound to radically different compared to a massive pipe of similar dimentions. The proper reference would be to build a second DCH but in much thicker material as baffle loadning and other factors comes into play here.
Impedance looks the same
Frequency response at the pipe end does not change. The measurements are months apart and the old one (blue) with the speaker at a wall and the new with the speaker in the middle of the room (green). That 200 Hz peak sure is persistent!
Then I have a new pair of Voigt pipes, designed by late Bosse Hansson of Opus 3 Records. They are designed for Lowther, with 19mm chipboard as the building material and 2x 19mm in front an back they are very different from the flimsy Deccas.
Tuning of the pipe is similar.
In both cases I used a Peerless 8" PP driver that works well in the pipes
Damping inside the pipes are similar with felt covering the walls of the first half of the pipes.
Listening to Adele 21 and some other records the pipes sound quite similar. Playing loud bass and the decca vibrates a lot not only the large front baffle but also the narrow top plate. The other pipe does not vibate at all or very little.
So that 200 Hz peak is not tamed with a new location for the pipe opening. Nor does the flimsy constructions cause the sound to radically different compared to a massive pipe of similar dimentions. The proper reference would be to build a second DCH but in much thicker material as baffle loadning and other factors comes into play here.
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