Dynaudio Subs

[pdjacob]

Hi

I am new to the forums and here is my first post asking for help.

Years ago I built a pr. of 100 liter sealed and stuffed cabinets to use with 17W-75 woofers. Madisound at the time suggested sealed alignments of 110-150 liter that would give an F3 in the 35-38 Hz range. Dynaudio suggested cabinets in the 20-60 liter range. Historically they were with a stereo amp and passive x-over. Life was simple.

Now they see duty being direct driven with an Adcom GFA 555 in stereo mode with movie soundtracks via sub out of my Anthem MRX 500 receiver. I do not feel we over drive these subs but hear a disconcerting "whack" during demanding soundtracks.

My question is: are they indeed under damped or is the Adcom not enough power. I have no intention of scrapping the cabinets but am willing to install better matched drivers and realize I will probably need to port them.

Thank You
Paul

 

[weltersys]

Now they see duty being direct driven with an Adcom GFA 555 in stereo mode with movie soundtracks via sub out of my Anthem MRX 500 receiver. I do not feel we over drive these subs but hear a disconcerting "whack" during demanding soundtracks.

My question is: are they indeed under damped or is the Adcom not enough power. I have no intention of scrapping the cabinets but am willing to install better matched drivers and realize I will probably need to port them.

Thank You
Paul

Some amps make a nasty sound when clipping, but more likely the disconcerting "whack" sound is the speaker hitting Xmech (also known as Xlim), the voice coil could be hitting the back plate, or the spider hitting the frame. The former can be fatal to the speaker, the latter annoying but can result in a ripped or separated spider.

If you can see the cone, put a white dot on it (silver Sharpie, White-Out) and measure the peak to peak movement during a demanding soundtrack sequence, if the p to p movement is more than double the Xmax rating (Xmax is one way) for the speaker, you need to turn the level down to avoid hitting Xmech.

Ported speakers suffer more from VLF over excursion than sealed cabinets, below Fb there is basically no air spring to resist cone movement.
If your Anthem MRX 500 receiver does not have a high pass filter (a low cut) set near the Fb of a ported cabinet, it will "whack" worse than a sealed cabinet.

Most music has little content below 25 Hz, some sound tracks have full scale output below 10 Hz..

P.S. Dynaudio suggested cabinets in the 20-60 liter range, your cabinet is almost double the higher suggestion, a smaller cabinet will keep excursion under control better, but will reduce LF output. You could put some bricks or canned food in the cabinets...
If you want more LF output in the same size box, you will need speakers with more Xmax potential.