Axiom Home Page Forums General Discussion Advice from Axiom Owners EP-500 Unequal Sound Pressures

Hi all, I discovered a problem with one of my two EP-500s today after fooling around with yet a new position for them. I seem to remember reading a thread quite a while ago with someone else that experienced amplification issues with their EP-500, but haven't been able to easily locate this thread (I'll keep looking :-). I have emailed support with the following message, but just curious whether any of you have some advice for me.

I recently (few months ago) purchased a second EP-500 (I can tell it's a newer model than my old one by the absence of a few fuses). I have been fiddling with placement of the two units ever since (not being displeased at all with what I perceived to be good sound quality). Today I decided to run them further away from my receiver and also to stack them and noticed a wide disparity between sound pressure coming from the respective subs. I may have overlooked this before, but I doubt it. The newer sub can barely give the same sound pressure as the older one at full dial compared to 9:00 position, respectively (as primitively measured by my fingertips on the suspension material). I have about a 25 foot run from my onkyo 876 to a y-splitter with 4 foot extensions to the subs. I have switched y-split leads to rule out faulty wiring. I used to have a much shorter run to both subs, but again, I can't say whether both subs were working at the same pressure at that time - besides wouldn't my previous experiment rule out cable run lengths?

In any case what troubleshooting do you suggest to address this issue?

Thanks,
Ian

P.S. I also traded line-in and line-out positions (since they are connected) on the plate just in case that might have been the issue - to no avail.

Contact Axiom. It is likely just that the dials (different age models) are not using the same position and scales.

You say they are stacked. Did you try switching there positions (which one was on the bottom)? I wouldn't 'think' that would make such a significant difference, but just another variable to check out. Are you testing their output with an SPL meter or by ear?

EFalardeau I have emailed and will phone them tomorrow - its holiday time in Canada today. I don't think it is a question of different dials especially if you consider that the newer one is maxed out just to match the 9 oclock position on the older one...IOW the older one has tones of additional headroom.

davekro, I guess I should be a little more scientific. I only performed the test by touch on the suspension material of the speaker. While this may sound like an incredibly gross way to do it, and now that I see it in print, is ridiculous, the difference in vibration is very distinct. I will switch positions as you suggested just so I can rule that one out - and see how my sound meter reacts to low bass differences.

Did you calibrate them one-by-one individually, then turn them both on,to get the same SPL?

sirquack, yes, though I have run out of testing license; unless I want to sleep in the garage tonight:-(. Here is my somewhat scientific testing results 2 inches removed from the centre of the speaker (flush plane) using a Scosche SPL1000 meter (zero boost from Onkyo sub calibration signal):

EP-500 Dial Position: @ zero: (old EP) 61; (new EP) 56
EP-500 Dial Position: @ 9:00: (old EP) 119; (new EP) 105
EP-500 Dial Position: @ max: (old EP) 126; (new EP) 119

And let me tell you, there is a very audible (palpable) difference between 126 and 119 dBC, even with industrial sound-proof headphones on!

Have you made sure too that the phase switch is in the same position as the other, or toggle it to a different position? I know in my basement it made a rather large difference. Also, maybe check your trim controls too to see if they might be in a different position then what you thought on the back of the EP500.

Yep, made sure that everything was exactly the same. However I did get a prompt reply from Brent at Axiom that goes some way to suggesting that I am getting worked up for no good reason:

"The current EP500 subwoofer does have the same output as the older EP500, however the output is not front end loaded like the older EP500. You will need to turn the volume higher on the current EP500 amplifier to match the output of the older EP500."

I will have to retest the upper end tomorrow because although the upper end of my test showed some convergence, it wasn't the same for both subs. But I will allow that my methods were a little unscientific.

In the end I guess a few dB difference is immaterial because I would never have either one cranked to the max anyway. Thanks everyone for your input.

Yes, Ian; on the older EP500 such as the one that I and several other members have, the volume control does very quickly drop the degree of attenuation of the voltage coming in from the receiver sub output. The result is that many of us found that a very low setting around 6-7 O'clock provided plenty of volume. Apparently in your newer unit the volume control(a variable resistor)has been re-calibrated so that it attenuates the voltage input more at low settings. This of course has nothing to do with the maximum "power" of the sub amplifier.

Be sure to restack the subs abd repeat your tests. Do this about 6-8 times and you will have your exercize for the day. Yuk. Yuk.

Hey Ian, I know I did at least 12 recalibration tests on both of my 500 (which I received about 6 months ago) and 350v3 to get them setup properly. They both have excellent output, but it took quite a bit of trial and error on moving them around to get the sound I wanted. My room is very square like with a bit of "L" on the back part.

I wonder if there's a possibility that he might be getting what sirquack was getting with some type of voltage loss?? Just a guess.

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Sorry for the period by itself in my post above. Seems I cannot conclude this thread with just a dot so I will just continue.

I also have dual EP-500s and experienced the same issue when one of my subs developed a problem with the amp and a replacement amp was sent. Please see this thread from several months ago. I was informed that the newer EP500 amplifier was redesigned to allow for greater adjustment on the volume control. Many customers apparently wanted more volume adjustment when coupling the subwoofer with brands other than Axiom, and hence the change. In comparison to the previous EP500 amplifiers, the output will not be the same at the identical positioning of the trim. However, maximum power output should, in theory, remain the same. I think Ian's finding and mine is that the maximum power output is lower compared to amps that had the older, higher-gain DSP programming. The newer subs still produce plenty of power and at the SPL levels that most owners use their subs, I think that the difference in maximum output is not likely to be of any practical importance.

Sorry I haven't been able to get back with some data but thanks very much for the advice. I have to wait until I have the house to myself and then I am going to create detailed calibration curves for each sub - if only to get good volume cross referencing. I agree that differences in maximum output would not be of any practical concern to me. Does anyone think I might blow one of these big boys if I run them at max power with the receiver calibration signal? I think I read somewhere that these things are indestructable?

Thanks
Ian

PS thanks ihifi I knew I had read your posts before.

The DSP keeps the sub in control so yes they are pretty much indestructible.

I finally got around to doing a little more testing with the two subs - with a little more precision. As pointed out by several of you, the subs have different scales. Two other interesting notes: as pointed out by ihifi the newer sub doesn't have as high a top end as the older EP-500, and second, both subs top out at the 12:00 position even though the dial has another 2:00 play before it reaches max. I don't see either of these factors having any effect on the way I use my rig. I am just a bit acedemically curious about what happened to the extra power on the new sub?

I didn't post the SPLs as it seems apparent that everyone would likely get different results for a bunch of different reasons. But if someone wants them let me know.

Thanks
Ian