Axiom Home Page Forums General Discussion Advice from Axiom Owners Help - M60 & VTF-2 bass rollercoaster

Greetings all. This is a call to owners of the goods in the title of this thread - I know you're out there. Disclaimer - this is my first home theater so please forgive questions of the obvious.

I just received AVIA in the mail last night and had a chance to try to fine tune the sub placement, M60 placement and crossover settings. I'm finding I have some huge bass humps - over 10dB in some areas and the whole sub sweep varies roughly between 75dB to 95dB from top to bottom in some areas. I've got the volume set to output at 85dB, everything is crossed at 80Hz right now. Bumping up the M60s to 100 seemed to tame the humps a bit, but then I really seems to lose volumes below 60Hz. This really doesn't make sense to me. Do I just have the room from hell?

I'm really at a loss for how to attack the problem other than random configurations. I've tried Alan's infamous crawling technique, though the differences in locations were very subtle. I've realized I'm learning how to listen and what to listen for. I'd appreciate some input on how owners of similar gear have their's configured - crossovers and levels. I know my room is the critical factor, but I guess I'm looking for a rough starting point, I feel like I'm grasping at straws.

I have the M60's with a VTF-2 as well. I have the cross-over switch on the VTF-2 turned off and use only the crossover settings of my Rotel. I've set the crossover at 40 and 60, depending on what I am listening to. 80 is quite high to be matched with the M60's.

I'd also drop an email to Dr. Hsu. He's very good about getting back to people with setup issues.

Good luck...once you get it right, the M60ti/VTF-2 combo is SWEEET!

That's so true. Dr. Hsu, whom I've met it person (at CES 2003), seems to be one of the most accessible "subwoofer celebrities" in the audio business.

Thanks for the info. I've got the sub crossover off as well. I'd started at 80, well, because that's what everyone says to do.

If I recall the big bass hump comes in the 60-80Hz region so I thought if I lowered the crossover on the M60s I'd just make things worse.

At one point (pre AVIA - tuning by ear) I'd tried a lower crossover point for the M60s to address some localized bass (the sub is right by the couch) but I started over once I got AVIA and I could actually determine the output for a given frequency.

I've seem glimpses of greatness, I know once I get it dialed in it should be awesome.

I think if you lower the x-over universally, the M60s might handle the 60-80hz range more evenly than the sub. I'd try tweaking your x-over through the entire 60 - 80Hz range to see which point gives you the smoothest response. Just keep your level calibrations the same throughout the tests.

Toby,
As Peter mentions, you can crossover the M60s with a sub. I have my EP350 set to about the 50Hz mark or so (M60s set to large in the receiver options) and i've found a smooth integration with the main speakers (gain set around the 10 oclock mark).

Your other option is to set the M60s as 'small' in the receiver options and then turn up the crossover on the subwoofer all the way in order to allow the receiver's built in crossover (usually around 80Hz but some are changeable) to handle the switching duties.

Chess...the Hsu crossover is defeatable to allow the receiver's crossover to handle the duties. No need to crank it up on the Hsu.

Defeatable?
You mean if it is kicked a couple of times the crossover shuts off?

Does it have a switch? That would be quite a handy feature, and more appropriate.

First off, thank you all for the quick responses and input. This forum is an awesome resource thanks to the likes of yourselves.

Yep, as spiffnme mentioned, the VTF-2 crossover can be turned off via a switch so everything from the receiver is output by the sub. I'm running everything with an HK 525 so I can set the crossover point for each set of speakers independently. I know I'll need to do some tweaking, just looking for suggestions of the best road to go down so I can stop fiddlin and start enjoying!

Toby, I don't know that you can effectively do much tweaking, absent an equalizer to work on the bass frequencies. Bypass the VTF-2 crossover, set all speakers small on the 525 and cross all at 80hz. Unless your room is cubelike, the smoothest and strongest(so turn it down)response is with the sub in the tighter corner behind the speakers.

Again...I personally felt that setting the crossover at 80hz with the M60's was too high. 40-60 was best for me. MAYBE 80hz for a movie, but for music, I'd keep it lower.

i have my 60's set to large, lfe to sub + mains on my yammi rxv1300. i have the volume on sub about 8 o'clock, and the x-over all the way clockwise. sounds good to me. is there a better way, or just preference?
dan

twodan,
I'm surprised that you haven't complained about 'muddy' sounding bass with your setup.
The idea about using one crossover is to blend the sound frequencies played by each driver. Since the crossovers form a declining curve, you would typically set the crossovers at the points where drivers 'interfere' with each other's sound frequencies the least and yet create as flat a frequency line as possible once the curves do collide. This is to eliminate any holes in the frequencies played back as well as eliminate or reduce the amount of material played by more than one driver.

In your case, by turning the M60s to large, they are allowed to play their full range of frequencies which according to the Axiom specs goes as low as 37Hz (+/-). By turning UP the crossover on your subwoofer, you are allowing it to play these low end frequencies right up to about the 120Hz mark overlapping the same notes the M60s are playing. Usually this makes the bass sound muddy, heavy or overbearing and not particularly defined.

Here's a suggestion to test, keep your receiver settings the same and try turning the sub crossover down to about the 80Hz mark. Compare this to the max value you are using now. Then turn the sub crossover down to 70Hz, then 60Hz then 50Hz mark and so on and listen to some music each time. Get an idea for how the effect sounds.
Pick the sub crossover setting that sounds good to you.

I have found with my room, system, that the ep350 crossover of around 50-55Hz works great with the M60s. According to the NRC graphs for the M80s (about as similar a comparison as possible), this appears to be the range in which the lower end of the speaker starts to dropoff so it all makes sense. You want the subwoofer to pick up the low end sound from the M60s as they begin to trail off due to their driver limitations.

The other method described for setting up a system is to set your speakers to 'small' in your receiver. This sets up the receiver's built in crossover (typically around 80Hz) for your speakers. Since the M60s and the subwoofer are now 'controlled' at the 80Hz mark it is often recommended you now turn up the crossover dial on your subwoofer to 'get it out of the way' of the receivers duties. Some subwoofers, as i have recently learned, have a switch to actually circumvent the subs' internal crossover completely.

Toby,

Those are room modes -- plus/minus 10dB swings are nothing rare, and unfortunately you have them. What are the approximate peak and valley frequencies, as judged with AVIA's low-frequency sweeps? Anyway, in order to simplify the trouble-shooting, I would do the following:

1) Set all speakers as SMALL; bypass the crossover on the VTF-2.
2) Set the subwoofer crossover on the receiver at 80Hz.
3) Try several feasible locations for the sub, testing it with the AVIA sweeps after basic calibration.
4) In each location, try both "max extension" and "max output" modes on the VTF-2 (one vs. two ports open) -- the sub has to be recalibrated after changing the setting.
5) In each location, try both positions of the sub's phase switch.
6) In each location, try several different sub crossover frequencies on the receiver.

I also second the suggestion that you FAX a diagram/measurements of your room to Dr. Hsu (see their web site).

Good luck!

i didn't think i could adjust the yammi rxv1300,; thought it was fixed around 90. am i wrong?
dan

First off, thanks again to one and all for the suggestions.

I spent some more time last night experimenting with various settings - M60s set to SMALL with several crossovers, M60s LARGE with sub set to varying crossovers and just LFE. With my HK 525 I can set the mains to SMALL and specify individual crossovers for mains and sub. With the mains set to LARGE I can set the sub to be SUB, SUB (LFE), or SUB + L/R, the latter having a synchronized crossover with the mains.

I am wondering if the crossover on my receiver is working correctly. With the M60s set to small and both the speakers and sub crossed at 80Hz (these can be set independently), a low freqency sweep produces a significant amount of air flow from the ports of the M60s below 40Hz. Could this be the M60 drivers responding to the air moved by the sub output?

Taking the advice from an earlier post I took a different approach to lowering the crossover - M60s set to LARGE and the sub set to 'SUB + L/R' with a 60Hz crossover - Holy S***! - serious difference in sound (very different with than having the M60s set to small with the same crossover)- much more transparent blend, much less localiztion, and MUCH more low end support. It was pretty late and at that point I just wanted to relish the new sound. I need to get AVIA back out and check the output.

Sushi,

I had submitted a diagram of my room to Dr Hsu prior to buying it and it's currently in the location he'd suggested. I've tried Alan's crawling method and tried a couple other locations and found this location produced the best output, but it could also be exaggerating the room nodes.

The nodes seem to differ between LF and RF, with a LF+SUB sweep, the big node come about between 70Hz and 80Hz, which lead me to believe it was a crossover problem. But with a RF+SUB sweep, the big node was up in the 90Hz to 100Hz. Then with both I seem to have a pretty significant (+10dB)dip between 40Hz and 50Hz.

I'll try moving the sub and further experiment with the output mode and phase options now that I've found a better speaker/sub configuration and see if that tames the nodes.

Thanks!

Dan,
There are 2 crossovers at work here, one is located on your Ep350 and the other is on your receiver.
When the main speakers are set to large, the receivers crossover is shut off.
When the main speakers are set to small, your Yamaha may have a fixed crossover, usually around 80Hz. My Onkyo 797 uses 80Hz but others can vary and higher priced models sometimes allow for a selection of 3 or 4 frequencies.

My suggestion was to set your main speakers to large (which is how i believe you already have them set), then play some music and change the crossover dial on your EP350 from higher to lower. This should give you a better idea as to how this dial changes the sound integration between your sub and your M60s.

Toby,

Your description of what happened when you set the M60s to "large" (with the sub supplementing below 60Hz) does make sense. It seems that, by driving the room from three separate locations (FR, FL, and Sub), you are canceling out the big room-mode dip at 40-50Hz to some degrees. So, maybe this is a good starting point for you for further tweaks.

The different peak frequencies you observed between the FL+Sub and FR+Sub sweeps are nothing surprising. Are these peaks seen with the M60s set to "large" and the sub added below 60Hz? Anyway, this strongly suggests that it is worth playing around further with the placement of the M60s as well, since your major room-mode peaks are above the sub frequencies.

Dan, this was also discussed about a month ago in connection with your "B" speakers hookup problem. As chess pointed out, you're still not getting proper bass management. You've made three settings which can be good, but not with each other. If you turn the sub crossover all the way up, and then you've also set the M60s "large" and the low frequencies "both" that means that both the sub and the mains are playing the bass all the way up from the bottom to about 150hz. Again, as I previously suggested, set the M60s "small" which sends the bass below the 90hz fixed 1300 cross to the sub. The low frequencies should not be "both" but just SBWF. Then, the sub crossover is correctly set all the way up to get it out of the way.

john, thanks, i'll set them to small, but where do you suggest i start with settings on the ep350?
dan

sorry, what about two channel? will it sound tinny, or is that what the sub is for?
humbly,
dan

Dan, as far as the sub crossover control goes, if you set all speakers "small" and the low frequencies are assigned to SBWF, not both, the sub crossover is unnecessary. Since the EP350 is one of the subs that doesn't have a switch or input that bypasses its crossover, the next best thing is to set it all the way up around 150hz, where it's out of the way of the 90hz crossover the 1300 does.

The sub level control doesn't necessarily have any good starting point. The idea is to set a proper sub level, either by ear or by meter. Both the control on the sub itself and the provision on the 1300 for changing sub level effect this. Some like to start with the sub control low and the receiver sub level around the middle. Then the sub control would be raised until the level on the meter or by ear is about right. Most subs are set too loud; they shouldn't be so loud that they draw attention to themselves. The idea is to give the impression that the sub is silent, but the other speakers are putting out more bass.

On two-channel, I don't quite follow, but the sub handles the low bass for that, just as it does in 5.1 play.

john, thanks. thought in the past, while watching tv, in 6 channel stereo, which my wife likes, something was lacking. as fot the a and b speakers, that was solved when someone, perhaps you pointed out that i was using the incorrect output on the receiver.
dan

Let me ask a question about the crossover settings for the receiver. When I have the main speakers set to SMALL and their crossover at 80Hz. I'm expecting nothing to be sent to the mains much below 80Hz. I understand there is a gradual rolloff. Is this the correct assumption?

When I ran the LF/sub and RF/sub low frequency sweeps on AVIA with the described setting I was noticing a serious amount of air flow coming from the ports of the M60s in the 40 - 60Hz range. Does this means the internal crossover in the receiver is not working propery?

Toby, my previous reply still stands, but I'll add more comments. "Gradual rolloff" is a correct assumption, "nothing" isn't. The 525 crossover(or filter)rolls off the response below the selected frequency at about 12db per octave. So, set at 80hz, 40hz should be about 12db down, which is a lot, but not to zero.So,it depends how "serious" the air flow at 40hz is. Try temporarily setting the cross on the 525 to 40hz; the air flow should be significantly stronger at 40hz if it's working.

So far as the heavy bass between 60 and 80hz, since you don't have the sub in the corner where it would excite all modes equally, it may be exciting the 70hz floor to ceiling mode(560hz/8')more prominantly. If you want to tinker with this, besides putting the sub into the corner, you can try 80hz and small on the 525, but put the VTF-2 crossover on and try to create a partial hole between 60 and 80hz by setting it at 60hz(if the marking is accurate, which it may not be).

John,

Thanks for the clarification on the crossover. I had no idea of the rate or magnitude of the roll-off.

Actually the sub is in the rear left corner of the room where Dr Hsu had recommended. I'll try your suggestion about creating a hole. Thank you.

Yes, judging from the published impedance curve of the M80, its ports are tuned at around 40-45Hz. So, M60's ports are likely tuned right at around 50Hz. I would expect lots of air velocity to/from the ports when driven near the resonance frequency, even if it is attenuated 8-10dB by the high-pass crossover on the receiver.

If you are still in doubt, just set the M60's as LARGE and see if the air flow further increases.