Axiom Home Page Forums General Discussion Technical Questions Understanding how a sub works

Hey guys,

I am trying to get my head wrapped around some subwoofer questions. I am sure someone will be able to help me out here...

When I am using a powered subwoofer with its own amp, I am sending pre-amp signal from my AVR to my sub, correct? Now this signal, does it only carry the frequencies (in the form of current) or information about the "volume" as well. What I am trying to say is that with the subwoofer volume at a certain level, how does it decide that the explsions are supposed to be louder than lets say a person falling on a wooden floor. What information does a pre-amp LFE signal carry to the amp of a power subwoofer.
Thanks

Hi geoffthemonk,

Welcome. You have some good questions -- as if there is any other kind... ha!

The signal your AVR sends to the subwoofer is tied to the volume knob, just as the rest of the channels are. All the level adjustment is done in the pre-amp stage before it is sent on to the amplifiers (internal or external). In that sense, the information the AVR sends to the sub is no different than the information it sends to its internal amps.

Does that clear it up?

Geoff, it's a widely varying voltage(not current)from the sub pre-out of the receiver that makes the difference in loudness. The output into the internal sub amplifier might vary from a full volt or a bit more down to a small fraction of a volt for more quiet moments. The sub amplifier then takes this voltage and increases it about 30 times(a "gain" of about 29dB)so that it's high enough to operate the subwoofer driver.

So here is my issue, my sub (an EP350) doesnt seem to be doing for me what I expect from it. I cant seem to be able balance it with my M60s. It is either too high or too low. I used YPAO that my Yammy 663 has. I am not getting the thum I am looking for. At lower volume, I am hardly getting any bass. I need to be above -20dB (receiver volume) before I start hearing any bass at all. I am attaching some pictures of how my room is layed out, It will be great if someone could help me with getting my sub to do what it must.
My home theater is in my living room. This first picture is taken from the left side of the room.

http://i310.photobucket.com/albums/kk429/geoffthemonk/IMG_2818.jpg

The three stackable table on the near side of the pic is where my sib is (shown in the next pic, this living room opens into a kitchen seen in the far side of the picture. The living room is 28' x 14'3". The TV and couc are on the width side of the room.
The kitchen is 16' x 9' (can be seen behind the staircase.
Here is the second pic that shows where the sub is right now..

http://i310.photobucket.com/albums/kk429/geoffthemonk/IMG_2817.jpg
The sub is under the tallest of the three stackable tables. This third picture is taken from the staircase side standing in the kitchen entrance....
http://i310.photobucket.com/albums/kk429/geoffthemonk/IMG_2819.jpg

It also shows where the M60s and VP150 are. This last one shows the QS8s.

http://i310.photobucket.com/albums/kk429/geoffthemonk/IMG_2821.jpg

Do you guys think my sub is just in a really really bad spot. Is it a must that I move it from where it is right now?

Thanks

Do you have your speakers set to "small" in the receiver setup? Often the auto setup in receivers turn your speakers to large. You want all speakers set to small with an 80hz crossover in the receiver. You want the crossover on the back of the sub cranked to the highest setting, to get it out of the way for the receiver to manage.

If you ran the auto setup, the sub and speakers should be calibrated to the correct SPL levels, but it might not be a bad idea to verify with a Radio Shack meter.

Do you have the distanc (delay) setting in the receiver correct for the sub. Looks like it would only be a few feet from the couch.

Have you tried adjusting the phase switch on the sub. Normally, you want it up near the front speakers for best blend, with a 0 phase setting. You might try adjusting this to see if it helps.

Keep in mind most music does not have lowwww frequencies, unless you listen to rap or r&b. What about movies with low LFE, how does it work for those?

Is this an older 350 or one of the new 350's? Either way you want it calibrated to the same levels with the receiver pink noise tests.

Great Advice!
Autosetup can play havoc with subs. Also look for any extra LFE settings that your Yammy might have.

My Denon, for instance, had a second setting (other than the main db setting for the sub) that was meant only to apply to DTS sound tracks. It was set for 10db in the difference and really confused me until I found it. This isn't exactly your issue but just an example of an extra setting that might not be so obvious.

sirquack, you are right, the YPAO sets mains to large but I always run them as small. My corssover is set at 80Hz, x-over on the sub is always all the way up (I adjust x-ver from the AVR), I do not have a delay settin in my receiver for the sub. I ave tried both 0 and 180 for the phase, not much affect. Like I said, the volume on my sub has to be fairly high to get any 'thump' from the sub. I have the sub volume set at about 12o'clock. Cranking it up helps a little but not a ton. Sub gain is set to 3.5 in my AVR. This is an EP350V2, not the V3.
Does anyone think/feel that 200W RMS amp just didint have enough juice to drive this 12-in driver and that is the reason why V3 has a beefier 300W RMS amp?

You should also double check that the sub is actually turning on at low volume; you may need to boost the output from the receiver and lower it on the sub to get enough signal at lower volumes to trigger the auto-on.

My thoughts exactly -- I've seen several reports of this happening.

Performance wise, I think there is a great difference between the 350v2 and v3. I've owned them both. The v2 did a respectable job in my larger room. However, the V3 has a different amp design and driver. I know in Alan's review, he said the new 350 was comparable to the EP500 in some respects.

So your receiver does not allow you to set the distance from the primary listening position to each speaker, or are you saying you just can't for the sub? This seems odd, even my old prologic receivers from the early 90's allowed for this delay setting.

Correct, sub doesnt turn on at low volumes but at higher than low volumes, it does turn on but doesnt have much thump, it isnt until I get to -20db or higher on AVR volume before I hear a bass to somewhat my liking.

Nopes, just the sub, I can adjust distance for all other speakers...

very strange...first time I've heard that on a receiver, that is a very important missing feature. ?

I don't have distance adjustment on my receiver for the sub, either.

So bump the output of the sub by a couple of dB in the receiver, see if you like it better.

double strange.

Geoff, the 663 does have manual distance adjustments available for all speakers, including the sub, but that wouldn't seem to be the solution for your complaint about the sub level. If the sub trim level on the 663 which showed after calibration(either by YPAO or manually)isn't high enough to send enough voltage to keep the sub amp "awake", you should turn the level control on the back of the sub down farther(say about 1/4th of the way up)and recalibrate(the 663 will have to output more voltage to compensate for the lower setting on the sub's level control).

Then of course, the "thump" that you say that you're looking for may not be a realistic expectation. A sub shouldn't be heard as a separate source; the impression should be that it isn't working but that the other speakers are putting out more bass.

Does anyone thing that the location of this sub is an is an issue? I have attached pictures in one of my previous posts. Itis by my couch, under a table...

It very well could have a LOT to do with your problem. As I mentioned above the ideal place would be up front, however, this is not always possible.

According to John, your receiver should have the distance setting for the sub as well as the other speakers. If this is not setup correctly, the sound from the sub will arrive at your ears incorrectly and skew the results.

A simple move of my sub from the middle front beside the TV, to a corner in the front amounted to a VERY noticeable difference in LFE in my main seated position. Not as drastic as your describing, of course, but there could be multiple things all adding up.

Can't remember if you said you talked to Axiom yet. I'm sure they could help confirm or rule out actual hardware issues.

Havent talked to Axiom yet, I was hoping someone from Axiom stumble upon my post. Hasnt happened yet.

You'll have more luck calling them, I suspect.

They have techs at the 800 that answer the phones until 11pm EST.

I wouldn't count on it, they do monitor the boards and occasionally post but they have the support line for issues. Posting in the forums is more for community support and thread hijacks.

Geoff,

If you want to be sure whether it is related to position, I'd recommend you get an SPL meter and run some sound signal sweeps. It could be that your listening position sits in a null for bass response. One good way to figure this out once you have an SPL meter is to use the free Room Equalization Wizard software (a google search will turn up a tutorial on the Home Theater Shack forums). It takes a bit of work to become familiar with it, but once you understand it, it is an incredibly valuable (and free!) tool.

This will show you if you're getting subpar bass response across the frequency range, or if you're experiencing nulls in common frequencies that may give make the bass less than you want it to be. In my room when I first set up the EP600, I was really disappointed, but after reading recommendations here, I ran the REW software and found that I had an enormous dip in volume at 60hz, which is where the bass was supposed to be for a lot of the music I listen to. (you can see a lot of these response curves if you go to the link in my signature) I repositioned the sub and also ended up using an equalizer to counteract my room's bass-numbing effects and now couldn't be happier. Your mileage may vary, but for me, it turned out to be a lot about position and room dynamics.

It's unquestionably more work to run through this experimentation, but it is a semi-definitive way to determine whether the problem is positional or just a matter of insufficient bass for your room.

Jason

I've been following the thread on you EP350 and you have been receiving solid advice. Positioning of your subwoofer is of importance and I would suggest that you pull away the tables from in front of the subwoofer. Since it is firing towards the mains set the phase to 180 to work in sympathy with your mains. If left at 0 you are actually cancelling bass.

As suggested, tweak down the volume on the subwoofer amplifier and add gain via the HT receivers menu system which will activate the sub at lower volumes. I would also recommend that you do utilize a SPL meter and set your system manually trying to achieve a blending of output throughout the speaker system.

After setting the crossover in the receiver bypass the crossover on the subwoofer.