Bass correction - the unexpected way.

[Davemcc]

I have to say that getting awesome bass has been a struggle but I think I have it solved in an unusual way. My room has a unique problem in that the bass response in relatively flat but I have a huge spike at 39Hz, something of the order of +30dB. Recently, I got an awesome little Era Sub 8 that was intended for the bedroom system. Then I got thinking...

I have my PB12-Plus and the Sub 8 co-located. The PB12 runs full range from 80Hz down to wherever it drops off naturally. The Sub 8's low pass is set for about 40Hz, the problem frequency, and runs 180 degrees out of phase. The Sub 8 drops out naturally about 30Hz by which point, the frequency issue is pretty much gone anyway. The frequency cancellation seems to work out quite well to tame that spike where nothing else has worked before.

So far, I've just sort of roughed everything in place as proof of concept. It seems to work out so well that I'm going to try to get a visual look at it with the SMS-1's mic and OSD. I'm still manually tinkering with relative volume levels between the two subs and tweaking the variable crossover of the PB12 a few degrees here or there. I think I've got a winner here, concept wise.

 

[Adam]

Very cool, Dave! If anyone had doubts about you being an AH, you buying a second sub and using active sound cancellation pretty much put those doubts to bed.

I feel like a jerk for not remembering which version of the PB12-Plus that you have. Does yours have the PEQ? If so, did that work at all for that spike?

 

[Davemcc]

Thanks Adam. I know it's hard to remember that I'm really an Audioholic since I only seem to post in OT these days. That's just because I haven't bought any gear this year, until now.

My Plus does have the PEQ. It worked to a certain extent and combined with the simple bass frequency EQ built into the Integra, it made a definitely passable combination. Then again, passable is hardly acceptable when it comes to bass. Awesomeness is the goal here. I'm getting there.

 

[Adam]

Thanks, Dave. I just saw your other thread. It's taking a while to catch up.

Excellent looking pair that you have. (Leave it alone, Alex. )

 

[Alex2507]

Thanks, Dave. I just saw your other thread. It's taking a while to catch up.

Excellent looking pair that you have. (Leave it alone, Alex. )

The one on the right is HUGE !!!

 

[Davemcc]

The one on the right is HUGE !!!

One side is always bigger than the other.

 

[Davemcc]

I'm really very confused right now. I did some sweeps with the SMS-1 and the baseline sweeps look nothing like the usual pattern I'm accustomed to seeing. This baseline is just the PB12 with all EQ's and everything else set to flat. In this configuration, I should be seeing my ever-present 39Hz spike but it's not there. Instead, what I see is a gentle climb to a +10dB peak at 50Hz that drops off slowly to a slight dip at 80Hz. This is outside the range of all previous experience.

To be fair, I have had the amp and driver in the SVS replaced and I haven't applied the SMS-1 to the new driver yet. On the other hand, this isn't the only sub I've measured in this location and the other sub showed the same 39Hz spike as well. The 39Hz spike was also confirmed mathematically by a resident AH acoustics guru based on my room's dimensions. So I don't know what happened to that spike.

Then it gets wierd. The only effect that the second sub can have is raise or lower the degree of the new 50Hz spike. It doesn't matter how the phase is set. It doesn't matter where the crossover is set. It doesn't shift the frequency of the spike or have any effect on any other frequency. It only increases or decreases the 50Hz range, even when the LPF on the second sub is set to 30Hz. The SMS-1 is only used as a measuring device. It's not connected to the subs. All the changes are made manually on the back of the subs.

I don't know what's going on. I do know I hate room modes. I hate subwoofers but I love good bass when everything is working and tuned right. I just don't know how to get there from here.

 

[Adam]

Did you move the furniture around? Are you using the microphone in a different spot?

 

[Davemcc]

Nope. Rooms the same. Mic location the same as last time. In fact, changing the mic location seems to have little effect of the pictured result.

I was questioning the accuracy of the SMS-1 when I went through my previous sub problems. That's why the sub is not running through it. I'm going to plot a graph manually with the Radio Shack meter and compare. I can't do it now because my wife is sleeping.

 

[Adam]

"Bring out the bass."

"Wife's sleeping."

"Well, I guess you're gonna have to go wake her up now, won't you?"

 

[Davemcc]

"Well, I guess you're gonna have to go wake her up now, won't you?"

I've learned not to poke a sleeping bear...metaphorically, you perv.

 

[Davemcc]

So I'm stumped. I ran some sweeps with the Avia disc and the SPL meter. They confirm the frequency response from the SMS-1. The massive room mode I've been dealing with ever since I got the PB12 is gone, vanished, dissappeared. I lived and fought with this thing for over two years and now that I think I finally have a solution, it's just gone.

Maybe it has something to do with the walls I removed in my basement?

 

[Alex2507]

Do you have a new amp and driver that could be acting differently?

 

[tcarcio]

Sounds to me like it had to be the wall removal if nothing else has changed.

 

[Davemcc]

Do you have a new amp and driver that could be acting differently?

I suppose it could be the new amp and driver. As I mentioned, I also measured my Hsu STF-3 in the same location with the same results as the PB12. This location has been sonically consistent until now. I can't scientifically rule out the driver change as the cause.

Sounds to me like it had to be the wall removal if nothing else has changed.

I'm thinking this. The basement walls under this room were filled with mineral wool acoustic insulation. So far, I've removed 4 insulated walls down there. A down firing sub driving towards a basement constructed of acoustically insulated walls could probably have a significant effect on the acoustics of the main room.

At any rate, it will be far easier to correct +6dB @ 55Hz than to correct +30dB @ 39Hz. Maybe I can even get rid of the corner traps.

 

[Davemcc]

So I'm back to the frustrating part. I brought the SVS and the Hsu together in the same room again. Starting to sound awesome again but needs some tuning. I measured the frequency response with the SMS-1 and found it was a bit heavy in the 30-50Hz area. So I re-hooked up the SMS-1 into the system so I could use it as an EQ instead of just a measuring device. I run the sweeps and get it looking something like this:

Then out of the blue right in the middle of a song I'm listening to, the bass simply drops out. I went back to the SMS-1 to re-graph what happened and here are the results of that:

Any suggestions why the SMS-1 would just drop out all the lower frequencies like this? It's very frustrating.

 

[lsiberian]

Forgive my conjecture, but it looks like you are getting a huge bump in the lower range. Perhaps it's placement issue. You might try moving your sub a little further from the wall.

 

[Davemcc]

Forgive my conjecture, but it looks like you are getting a huge bump in the lower range. Perhaps it's placement issue. You might try moving your sub a little further from the wall.

At his point it's not a tuning issue that's frustrating me.

The Velodyne simply drops all the lower bass right in the middle of a song for no reason. As you can see from the first graph, I can get a reasonably flat response. As you can see from the second graph, all the bass has been dropped out. There's no apparent reason and it happens right in the middle of a song or whatever. The only solution to getting it working again is to raise the output level of the SMS-1 until it kick starts itself back into action.

Now the worst part. In working out this issue, I just fried my SVS...AGAIN...about which I need to start a new thread.

 

[Alex2507]

I just fried my SVS...AGAIN...

Maybe that's divine reciprocation of the silent treatment.

Seriously, I'm really sorry to here that ... again.

 

[anamorphic96]

Dave,

Not sure if this will help but thought I would mention it. Does your SMS-1 have the latest firmware. 2.1.3 is the latest version. You might even want to call Curt over at Velodyne and see if he has anything to say. He's pretty helpful from my understanding.