Have a surround sound setup but haven't used it in ages.
Now with bigger/better tv, I am looking to set it back up.

The receiver is a Denon about 15+ years old as well as front/cent/rear and subwoofer.
A fiber optic cable is used for the audio.

The subwoofer isn't working and not sure if its the subwoofer or receiver.

Thinking of buying this subwoofer.
If it resolves the issue great.

If not, I would probably pickup this receiver.

Trying to keep costs down.
Not looking to upgrade the entire system.

Questions :
1 - Any major concerns with either the sub or rec listed above?
2 - What am I missing out by not taking advantage of the eARC technology?
3 - If I would switch to use the eARC technology I would have to upgrade all speakers?
4 - The sub/rec makes about a $500 expense. Anyway to switch to eARC for that price for the same amount to get the same or even better sound?

eARC is simply for getting audio from your TV to the receiver over HDMI, an alternative to the optical spdif you're currently using. The benefit over optical spdif is that it can do more formats including uncompressed 5.1 and Atmos/TrueHD.

ETA: Before you buy anything make sure your TV supports eARC if you want to use it

What size are your speakers set to?  If they are "large" then no bass is routed to the sub unless it is a 5.1 source.  If you set the speakers to "small" then all audio from about 80hz and lower goes to the sub.  So it could be as simple as a setting change.

Denon is a quality receiver but make sure it has an auto calibration setup.  That's worth the extra price in my opinion.

I'm not a fan of that sub but I'm a bass snob.  Look at the Dayton line from Parts Express and up your budget.

1.  Answered earlier.
2.  Nothing
3.  No.
4.  You are already using optical for a digital signal.  eARC is just another way to get the digital signal from your TV.

What I didn't ask is what are you using for a source?  If you use external sources and only use your TV as a monitor, then you never need eARC.  You would only need it if you use your TVs apps (smart TV) or its internal tuner.

After reading your reply I checked and they were indeed set to Large.
Was excited if this fixed it but after changing to Small, it did not help.
At least it is now set properly.

Do you have an alternate way to test your sub?  Another receiver?  Does the sub have speaker level inputs?  Even a friend with a working 5.1 system?

Do you have an alternate way to test your sub?  No
Another receiver?  No
Does the sub have speaker level inputs?  Do you mean these? Attached File

To be honest, I have no idea what those are for.
Even a friend with a working 5.1 system? Not locally.

Debating about buying a sub and receiver this weekend to test it out.
Found a sub and receiver on Amazon with "Free Returns".
Currently eyeing a Polk or Klipsch 8 inch (current one is 8 inch and plenty for the room)
This Denon receiver. Getting both should only be about $500 to get me back up and running.
Even less if one of the two items gets returned.

Yes, those are speaker level inputs.  You can run your speaker wire to them instead of your speakers and test your sub.  Make sure the speakers are set to Large.  Adjust the volume up on the receiver and the attenuation (incorrectly referred to as the Gain Knob) on the sub.  This will tell you if the sub is actually working and there isn't an issue with your cable or your receiver settings.

My expectations are too high for an 8" sub.  Heck, my wife has a custom built 12" (the driver was designed by David Moore of Pink Star Industries) and a 1,000w amp in her car.  But you do you and get your self an 8" sub.  You can definitely get some low end out of it although the output might be low compared to your mains.

@Robert_J

Thanks for all your help.

The Sub is a Definitive Technology SuperCube III
Definitive's smallest subwoofer, the SuperCube III provides huge bass performance in a compact, room-friendly enclosure that takes up less than a cubic foot of floor-space. The secret to its success is an active woofer/passive radiator combination that produces big sound despite the cabinet's small size. And a powerful built-in 650-watt amplifier really shows off this little sub's tight, accurate bass response.

I guess it isn't a typical 8 inch sub.

The wires were hooked up as seen on page 6

The speakers were tested as both Small and Large as well as the knobs were turned to min/max numerous times.
The front and center speakers still worked, but just no bass.

Based on this test, is the culprit the sub?
If I need to replace it, I don't believe a typical 8 inch sub will due it justice.
Its not too heavy, I may send it off for repair.

It's a ported 8" sub.  Nothing special at all.

I said "ported" but you are looking for the ports right?  It has 2 passive radiators which are the equivalent of ports.  Both are just Helmholtz Resonators.  A ported sub's tuning frequency is based on the air volume inside the cabinet, the diameter of the ports, the number of ports and length of ports.  In a small cabinet, you can't port it because the ports would be so long that they stick out of the cabinet.  That's where a PR comes into play.  Think of them as 8" ports.  In a cabinet that small, they would have to be about 10 feet long.  The air inside of each port will weigh about 120g.  If you disassemble each passive radiator and weigh the moving part, they will each weigh 120g.  NOTE - Those are not 100% accurate numbers.  I was just using them as an example.

Ported subs give you a lot of low end but once you reach the tuning frequency, the low end naturally rolls off at a very steep rate.  Sealed subs start rolling off at a higher frequency but their roll-off is a lot more shallow.  They also don't have as much low end unless you add some EQ into the mix.

If you feel like you have tested the sub then send it in for repair.  Def Tech is a very good brand and is still worth something on the used market.

Did you adjust the gain/volume/attenuator knob on the sub when testing?

Tested all 3 knobs individually as well as concurrently.
Also had the bass on the receiver turned all the way up as well as configured the sub to be +10 via the 5.1 setup.

Pull the amp out of the box and look at the components.  A bad capacitor is an easy fix.  Bad output transistors can be fixed if you have experience.

Tried opening up the box and there was a lot more going on internally than expected.
2 boards and couldn't fully remove the one cover to get a good look.
A bit over my head navigating the internals.
Thanks for the help.
I have opted to send off an e-mail to the company to see what what is the cost to troubleshoot and repair.
If too much, may give the repair another try myself before just purchasing a new one.

If it is only the amp that has gone bad and repair isn't in the budget, then you can replace the amp.  Chances of finding an exact replacement are slim but you can just add a set of terminals to the box and use an external amp.  If it comes down to that, I'll list your options.

@Robert_J

Quick question.
Called Definitive and can get the sub fixed for $280 which includes shipping to/from, diagnostics and any repairs.
I can get a new sub for $200.

Based on the specs of the existing and potentially new sub, is it worth it to pay the $280 to fix the old or only spend $200 for a new?
Not sure if the current sub is that much better to warrant the extra cost to get fixed.

Here are the 2 subs.

Current Sub


Potential new sub

The Def Tech plays a full octave lower.  The Klipsch goes down to 32hz and your sub plays down to 16hz.  Will you use that extra low end?  Not on every movie but if you like action movies, it will be worth the $80 difference.  At least to me.  I'm looking to get an octave lower and play down into the single digits.  8hz would give some killer tactile effects but only a few movies get that low.

For the Def Tech to play a 16hz sound at the same level the Klipsch plays a 32hz sound, the Def Tech sub has to move 4 times the amount of air.  It's already at a disadvantage since it only uses an 8" driver but that driver has a lot move travel (the cone moves in and out more) and the passive radiators fill in the lower part of the range as well.  Look up eBay item 254503539308 to see the driver.  254947055982 is the passive radiators.

Ran some tests (per the company) and appears the large amp is dead.
As mentioned above, the $280 is for the shipping, diagnostics and fix.
The concern is they no longer have this part in stock and there is a possibility it can not be fixed (per their own words).
If this happens, they keep $80 for the diagnostics and return the $200.

Instead of gambling I opted to buy new and narrowed it down to these 3 :

SVS SB-1000 which I could probably get for $399
Definitive Technology ProSub 800 for about $250
Klipsch Reference R-10SW  for $200

Snagged one of these 475 Watt 12" BIC subs for $209 a few months back. https://www.amazon.com/BIC-America-F12-475-Watt-Subwoofer/dp/B0015A8Y5M/ref=sr_1_28?_encoding=UTF8&c=ts&dchild=1&keywords=Home+Audio+Subwoofers&qid=1619609958&s=aht&sr=1-28&ts_id=172568

Honestly blown away by this little rinky-dink $200 sub. Every bit as good as the 18" 500 watt Bob Carver sub it replaced.

Checked the dimensions and it won't fit for what I need. The ones listed above are smaller is size due to location constraints.

SVS without a 2nd thought.

I have been a member of Home Theater Forum long enough to remember when Ron S. asked a question about building a cylinder sub and Tom V. answered.  Less than a year later, SV Subwoofers was born.

While they are no longer affiliated with the company, the current management team are long-time enthusiasts and well regarded in the industry.

Nice timing. I read your reply with about 20 minutes left on the clock before the deal expired.
Chatted with them on the phone and like the 45 day trial period and upgrade policy.