damping (BD-Design)

by GC, Thursday, August 04, 2005, 22:34 (4548 days ago)

Hello Bert,

I reported on finishing my BD-15 cabinets about one month ago. So by now breaking in of the units should be finished. Recently I played around with the amount and the position of the damping material (stiff plastic foam with rather open structure, it has a mixture of colors). I measured the impedance characteristic and found two maxima, at 21 and 67 Hz. The first one is 110 Ohm, the second one 185 Ohm and the minima are 15 Ohm. These values hardly changed during all changes, and also there were practically no differences in sound. In the past I used a few times far too much damping material. Am I too carefull now? I must add, nevertheless, that the sound is becoming very convincing by now. Speed and attack of bass drums and guitars are really getting to something that reminds of real instruments and that is indeed a big difference with all my previous bass speakers. Real deep bass is not available, the lowest audible frequency is somewhere just below 40 Hz. This is almost never a miss and the increase in clarity is much more important.

My TwinDac is also getting into shape. The first evenings I listened to it I was quite disappointed by the flat and uninvolved sound it produced. Only the bass sounded more detailed than from my Theta D/A converter. (This 15 year old converter probably suffers from worn-out capacitors in its power supply.) To my surprise the sound became gradually better and by now beats the Theta in all respects, even the width and the precision of the sound stage. Any idea what changes I can expect from replacing my CD-transport with a laptop?

The only problem remaining is the hum in my amplifiers. I tried many things with cables, grounding, shielding etc. Two days ago I suddenly got into a situation where this hum is inaudible at the listening position so for the moment I stopped to find the cause and I am enjoying many new details on old CDs.

Best wishes,
Eddie

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damping

by GC, Friday, August 05, 2005, 09:44 (4548 days ago) @ GC

Hi Eddie,

Damping material doesn't change the impedance much but if you want to have equal impedance peakes than play with the port length.

I always mix the direction but if you would close the port by 1/3rd and measure the impedance again then you'll see that it becomes more even or less even.

Adding too much damping material kills the liveness, as long as there is no hollowness heard then you have used enough, probaly a bit too much.

supply.) To my surprise the sound became gradually better and by now beats
the Theta in all respects, even the width and the precision of the sound
stage. Any idea what changes I can expect from replacing my CD-transport
with a laptop?

The used Black Gate capacitors need time to burn in before they perform optimal. Even when used and then not used for some time makes them more or less behave like new (needing time to burn in again).

What changes you'll hear depends on the quality of your transport... :)

You do have a PC and USB input so setup your PC and give it a try!

The only problem remaining is the hum in my amplifiers. I tried many
things with cables, grounding, shielding etc. Two days ago I suddenly got
into a situation where this hum is inaudible at the listening position so
for the moment I stopped to find the cause and I am enjoying many new
details on old CDs.

Most hum heard is in opposite phase so if both bass channels are equal and you're sitting in the middle then the hum is highly reduced...

Ciao,

Bert

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damping

by GC, Sunday, August 07, 2005, 16:14 (4545 days ago) @ GC

Hello Bert,
[image]

Most hum heard is in opposite phase so if both bass channels are equal and
you're sitting in the middle then the hum is highly reduced...

The hum has a standing wave pattern with minima and maxima only a few decimeters apart so I can sit with my head in a minimum. Since this is not a good long term solution I started yesterday evening again with a thorough check of all wiring. I was inspired by a well written story on ground loops, EMC, cables, etc., found on www.breem.nl (in Dutch).

I found something questionable which is drawn in the added image. As you can see both speakers and the bass amp are floating. Do you connect this the same way or do you ground it somewhere?


Best wishes,
Eddie

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damping

by GC, Monday, August 08, 2005, 11:06 (4545 days ago) @ GC

Hi Eddie,

I am not an electronical expert but with the BD30 amps I use there is no extra ground. The power supply of the BD30 amps is +35V, 0, -35V where the "0" is the "ground" connected to the ground (-) of the tube amplifier output.

Ciao,

Bert

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damping

by GC, Monday, August 08, 2005, 23:49 (4544 days ago) @ GC

Hello Bert,

I am not an electronical expert but with the BD30 amps I use there is no
extra ground. The power supply of the BD30 amps is +35V, 0, -35V where the
"0" is the "ground" connected to the ground (-) of the tube amplifier
output.

This connection is exactly the one that was missing in my system. So I just made it and to my disappointment and surprise it makes the hum considerably louder.


Best wishes,
Eddie

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