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Velodyne HGS knock issue on low frequency/high output

956 Views 7 Replies 3 Participants Last post by  mjennings77095
I have recently acquired my 2nd HGS 15 subwoofer to serve as a companion to the one I've owned and enjoyed for the past 20 years. I wanted to explore a dual sub configuration, and was able to make a 'barn find' (not literally from a barn) of a lightly used HGS 15 that has been in climate controlled storage for 15+ years. The sub is emaculate - no chips, dings, snags, dents, etc. And it performs very well.....except when certain movie soundtracks or music reach a certain low frequency at earth moving volumes. When a certain frequency and amplitude is encountered, the sub will react with a 'knock' (or series of knocks).

My original sub continues to perform and does not exhibit the same knocking sound of its counterpart sub. The knock sound is not random, is not related to powering on and does not occur continuously. The knock sound occurs only during episodes of low freq/high volume - like an explosion (but not all explosions), very hard thump, etc. The issue can easily be reproduced when playing the same segment of music/soundtrack. The knock is mildly distracting, but generally doesn't occur frequently (depending on the authoring/content).

I've been trying to determine if this is a physical issue with the speaker (spider, surround, etc), with the plate amp, or possibly with the servo. The surround, dust cap and visible parts of the speaker inspect out fine. The speaker doesn't really look its age. But I can't speak for what may be behind the cone. I haven't inspected the amp for swollen capacitors or discolorations. I don't really expect to find anything since the subwoofer, in all other regards, performs perfectly. The cabinet is solid and the speaker and plate amp are all mounted tightly.

To try and determine if the issue is amp, servo or speaker related, and repairable, I have spoken to a local Velodyne repair center, as well Paul at ECB. The local repair center, understandably, won't say what the issue might be without putting it on their bench, and claim that if it is repairable, whether amp or speaker, they can fix it. Paul believes, based on my description, that it is amp related, but didn't offer any further detail or description of why he believes it to be amp related. I'm waiting to hear from him to see if it happens to be servo related, if it can be repaired (short of disabling).

I've done a lot of searching, but have found little that fits my issue from others who have posted Velodyne issues in the past.

I suspect, whatever the issue is, it can be repaired. But I'm not certain. It plays perfectly except for the instance I have described.

But I'm uncertain if the knocking is electronic or physical. I feel comfortable that the subwoofer is in its original condition and has not been tampered with. My guess is that sitting in storage for a lengthy time has resulted in one or more capacitors to dry and fail. If so, then it would make sense to have a professional identify the culprits and replace.

I was hoping someone on this forum could help with offering opinions and experiences with similar issues.

Thanks for taking the time to read through and respond.
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Seems like the driver is bottoming out. Your 12" sub may not have this issue because it might not be able to produce the frequency(s) that are causing the issue with the 15". You're just going to have to turn it down for the content that gives it trouble.
They are both 15". Both are HGS 15. The only difference is the sub I already have is a more updated amp (THX) and the one I just acquired is a little older (not branded THX). By most standards, they are the same from top to bottom.

I thought about the driver bottoming out, but not sure why it would do that (being the same sub) and how a driver that was truly hitting its limits would sound. I don't think I'm pushing either sub beyond its performance limits.

I have this same issue with my HGS 18!! Mine is also not branded thx, it did watching movies as well as with music at almost any low frequency, it behaves just like yours but pretty much at any any amount of gain. I figured it was the servo and disconnected it, which was better at producing those low end frequencies but not really, (it became a very unsophisticated sub, it couldn't really do anything well,) but just got a new driver with servo and it produces music wonderfully, haven't had any issues musically, but it still has that knock in the movies like you stated above. And I've had my amp serviced at EBC year and a half ago, just got the new driver and servo last week.
My issue went away on its own. When I bought the 2nd HGS 15, it had been in storage for a number of years. It seems it may have gone through a period of re-breaking back in after being stored for so long.
Fortunately my issue resolved itself over a few weeks of play. Sounds good and compliments the first HGS 15.
So did you just let it knock? Cause I'm hopeful now that I can actually listen to music and everythings fine. Trying to see if it's anything else, like cables, source,etc.
The knocking only occurred during high LFE on movies, when volumes were loud and certain types of explosions happened. Over a few weeks, it just stopped. That’s why I think it was just something readjusting itself after being in storage for so many years. But that’s just my speculation.
it may have happened with music when LFE was loud, but I don’t recall. I focused more on reproduce able parts of movies.
I still am aware and listen to see if it ever returns, but it’s been a very long time without any reoccurrence and have watched many loud movies and multi channel music during this time.
1 - 8 of 8 Posts