Subwoofer "popping" with new Denon AVR-590 (1 Viewer)

[Doug MacGregor]

My 8 year-old Mission 8" powered subwoofer has started popping under load.
I was watching a hockey game and the subwoofer started "popping" almost like it was clipping.
I checked the speaker cone and it was intact.
The crossover is set to 80Hz on the speaker and the volume control is set to about 60%.
Changing the crossover frequency did nothing...changing the volume control, however did. Higher, it popped more.
The Audyssey setup has already been run.
I ran the Test Tones and it "popped" as well.
Only noticed this once after I ran the Audyssey and ran the Test Tones, so I reduced the volume of the Sub.
The Sub never popped at any time in the last 8 years with my old JVC which had a fixed Subwoofer output signal and I ran it pretty hard over the years.
My old JCV was rated at 100 Watts RMS per channel...this one is rated at 75W but I don't think this refers to the Sub signal.
The Audyssey Dynamic EQ and Dynamic Volume were "on".
I also noticed that the cable connection on the receiver was quite loose...I could turn the RCA connector extremely easily.
Any idea what is happening here?
Thanks.

 

[Robert_J]

I would look at the RCA connector first. That is the easiest and cheapest fix. Use a different cable even if you have to move it closer to the receiver to test with. Make sure the RCA cable is tight on both the sub as well as the receiver. Use a quality cable. A composite video cable or a one of the cables from a component video cable is prefered. They are shielded and reject noise better than a cheap audio cable.

 

[Doug MacGregor]

Looks like you were right Robert. Being in Tech Support I always check the simple things first...just forgot that rule for some reason.
Thanks.

 

[Doug MacGregor]

It seems that this was not the end of the story.
Yesterday the subwoofer started popping every 3 seconds without any input.
The crossover and gain controls on the sub had no effect.
I unplugged it and after a few hours, plugged it in again.
After 90 minutes it started doing it again.
I opened the speaker and I found some light brown deposits on the circuit board in one small place.
I cleaned off the deposits and plugged in the sub and after 6 hours it had not done it again.
So far today it has not done it yet (after 12 hours) and I sent it a signal and it was smooth.
Seems like the earlier problem was just a symptom of coming attractions.
Thanks.

 

[Doug MacGregor]

Well, it looks like my subwoofer amp is on its way out.
Since the enclosure and speaker are just fine, I will be purchasing a Dayton subwoofer plate amp from Parts Express to restore this Sub to life.

 

[Robert_J]

Just remember that the factory amp may have built-in EQ to make the sub perform better. Adding a PE amp may NOT give you the best performance. If it is a ported sub, then you will also need to adjust the subsonic filter to the enclosure's tuning frequency.

 

[Doug MacGregor]

I appreciate that Robert but I don't have the money right now for a new sub so I'm going the PE amp way.
The enclosure and driver are in perfect shape and it would be a waste to throw them out.
I know it's kind of a "generic" solution but I'm willing to put up with it until I can get my hands on either an Energy sub or an SVS.
It is a ported enclosure (rear).
How do I adjust the subsonic filter?
Should I rerun the Audyssey Setup on my Denon AVR-590?
Thanks.

 

[Robert_J]

All PE amps come with a sheet of paper that lists two resistor values and the corresponding bass boost / filter frequency. You want to set the filter 2 or 3 hz below the enclosure's tuning frequency. How do you find that you ask? You measure the volume of the inside of the enclosure, subtract any braces, ports, driver motor structures, etc. Then you measure the internal diameter and internal length of the port(s). Post that information here and I'll figure the rest out. Or you can use the trial and error method with the port calculator at PSP-Inc dot com.

 

[Doug MacGregor]

I appreciate the help Robert.

The enclosure is 10.5" deep by 10.75" wide by 12" high or 0.784 cf. (inside dimensions).
The port is 2.5" in diameter and is 8" long.

I couldn't figure out the port calculator.

Thanks.

 

[Robert_J]

Based on your measurements (I subtracted the port from the overall volume), you have a .76 cubic foot enclosure. The 8" x 2.5" port means that it is tuned to 42 hz.

Looking at the PE amps, I can only find the filter table on the BASH model - http://www.parts-express.com/pdf/300-750.pdf but I can't find the appropriate values for a 40hz filter. You are missing an entire octave between where your sub cuts off and most others do at 20hz. Let me look deeper. I know there is a formula out there for this.

 

[Doug MacGregor]

Thanks Robert.
I appreciate this.

 

[Robert_J]

Here is the formula for the BASH 500 amp.
m=Q^2 * 4
R17=1/(2*pi*2.2e-7*fc*sqrt(m))
R18=R17*m

You can plug in different values and compare it to the sheet to make sure they match. You can then try the same thing on BASH 300 but the resistor numbers are different. I think the formula should work. In your case you want an Fc of 40hz and try a Q of .9.

 

[Doug MacGregor]

Excellent!
Thanks for taking the time to do this for me.
The PE amp I'm going for (the 100 A) is on back-order until Feb 20 so I'll let you know when I get it.

 

[Doug MacGregor]

I bought the subwoofer plate amp from Parts-Express this week and installed it.
It is the 100A Dayton.
It sounds pretty good although I will have to run the Audyssey setup on my Denon AVR-590 again.