Axiom Home Page Forums General Discussion Technical Questions Sub setup + 6'

I think that I've read a # of times here that a good rule of thumb when setting up the sub is to add 6' to the distance. Is that correct and why?

I could be mistaken, but I think Jakeman has mentioned to add 3 ft to the actual measurement to account for the DSP circuitry in the EP subs. Also, if your using a Velodyne SMS-1 Digital EQ to flatten out your room response, add another 3ft for a total of 6ft. That is what I've done.

My Denon autosetup adds about 12ft to the actual measurement, so far I like Jakeman's suggestions better.

Charles, just to expand a bit on the point, the processing in the sub amplifier can cause a slight delay which makes the sound from the sub arrive as if it was significantly farther away than the measured physical distance. Auto calibration systems can measure this difference and my own view would be to rely more on that rather than arbitrary rules of thumb.

Maybe this is the answer to my "tightness" problem?

I didn't realize this when I started this thread, but the Emotiva doesn't have a distance setting for the sub so all settings are manual. Maybe the new LMC-2 will.

So how are you supposed to set the distance setting for the sub using an Emotiva? What do you mean by manual?

You can't set a distance for the sub on the LMC-1. There is a test tone (which doesn't work very well for the sub) and a trim level but you just have to use the volume on the sub to set it and blend it with the other speakers.

You are confusing volume with time delay (distance).

Distance is used to set the time delay for the sub and all of the other speakers. Since all of the speakers are not equidistant to you, the pre-amp adjusts for relative delays between the speakers so that sound will arrive at your ears at the same time from all speakers. In practice, this is never really the case but don't worry about that for now.

Volume on the other hand is ajusted using a set-up mic or, better yet, an SPL meter.

If you don't have a way to set distance for your sub, and it is more than a couple of feet further (or closer) from you relative to the front speakers, you may not experience the "tightness" that you should from your sub and it might sound "slow".

The other control to use is the delay setting in your receiver if it has one. Auto calibration in those receivers are very unreliable below 100hz owing to acoustical problems in room in the frequency and time domains. The small chips used in the receiver are not robust enought to quickly compute the many iterations required to arrive at accurate settings when using low frequency sine waves. Its more accurate to simply add 3 ft to for each processing step which accounts for the 2.5-3.0 milliseconds of delay before the signal reaches the drivers.

Imprecise auto-equalization below 100hz is something most software providers do not want to discuss in the manuals. The only one who does address the issue is Behringer in their DSP equalizers, who specifically warn against relying on auto settings in the low-mid bass region. Audessey is hoping to address this problem in their new unit which purports to make massive computations that adjust for phase and frequency. Without the use of far more computing power than found in a typical receiver or boxed equalizer I remain highly sceptical that will acheived. Over the years I have never seen any auto-equalized setting for subs that could not be improved with manual tweaking.

Back at the ranch, I've always found its best to shut off the auto-equalization for the low frequencies and rely on the above noted delay control along with manually tweaking room Q and level on parametric equalizers. Its those controls which make an SMS-1 such an effective tool.

To those who don't have an SMS I'd recommend taking measurements with an RS metre after manually adjusting delay/distance and experimenting with placement.

Sure. I use test tones and a SPL meter to set the speaker levels. I did think it interesting that there wasn't a sub distance on the processor. That is interesting about the def of "tight" & "slow". I hear that all the time but don't know what it means. I'm trying to tie the terms and the sounds together. Tight to me means crisp and not boomy. I don't know about slow in relation to bass. Does it mean that I hear the bass notes later than I should; that they are out of sync?

Everyone has a different definition for these terms, it is like "bright", "warm", etc...

Is this true for any sub or just Axiom subs with the DSP?

Only subs with DSP processing. In fact it applies to any DSP device you insert in the signal path. In Randy's case for example he also has a SMS digital equalizer in the subs signal path so he is delaying 6 ft, 3ft for the 600's DSP and 3ft for the SMS DSP. For subs without DSP use normal distance then experiment up and down a foot or two at a time and listen if the bass tightens up.

The distance setting will also depend on how much the sub is in phase with the main speakers. If you have the sub well calibrated to the mains, it should not sound much different from the normal distance (after adjustment for processing). If you find that the sub tightens up with a big variation from the normal distance, it is likely that you need to work on getting the sub more in phase with the mains.

I tried changing the distance on my sub setting from 0 feet all the way up to the max my receiver allows (28 feet I think) about a month ago. My ears could not hear a difference. I know I listened very critically but I will try this again when I get some time. By the way, according to my audiologist, within the limits of her equipment, my ears are "mutant-like" .

I definitely do hear a big difference when I adjust the delays on my surrounds though.

Any thoughts on why I don't hear a difference with different sub delay settings?

Are you listening with the mains on? If so you should hear the difference since you are adding much less delay as you increase distance. If your room is lively (ie very resonant)you will have a more difficult time hearing the best distance setting. As I recall from your pictures, you have bare walls in your HT so I suspect you are getting alot of LF reflections and standing waves in room. It will be more subtle, but there should be a setting where drums sound snappier and bass guitar notes decay more quickly. If you still can't tell don't worry about it and just leave it at the normal plus 3ft distance. It likely indicates a need for bass traps/room treatments.

Yes, I am listening with the M80s on and I am the one with the very live room. I also definitely do have standing waves. And I am the one who can't get a "snap" and chest punch out of my bass but I do have deep, transparent, gonad-tickling lows.

I'll experiment with the distance setting some more. Thanks.