Axiom Home Page Forums General Discussion Home Theater EP500 Response

I thought that I should clarify a bit on the first part of what I said... The THD will be higher in the lower frequency region because it requires more power for the same dB level. Thus, when pushed hard, it will distort the lowest frequencies first, making them appear to get a boost in amplitude. What is really going on is that they (the fundamental frequencies) do not actually go up, but rather their harmonics increase substantially.

DJ_Stunna thanks for the replies.

I think I understand what you're saying and it definitely fits what I'm observing. I'm not convinced though, the sub is actually being over driven or is clipping as I'm not seeing/hearing anything to give me the sense that this is occuring during the measurements.

I realize this is a bit of an unknown beast given the new technology in the sub and according to the Axiom literature the sub nor its amp can be over driven...

In reply to:

---

Its (EP500) special algorithm commands the subwoofer to deliver peak performance without ever being overdriven. And its maximum undistorted output of 120 dB is louder than a full orchestra in a concert hall.

---

And there's just no way I'm even approximating the limit of 120db anechoic in my little room.

I'm also very confused as to why I see no improvement/variation in smoothness from one position to another in my room as virtually everything I've read on the subject of sub placement suggests should happen. I definitely notice it louder in the corners but that's the only difference.

Well I'm still gonna work on this a bit more to see if I can figure out the "optimal" placement and it may be time to send a few queries to the Axiom experts.

I'll keep you all posted.

Thanks very much again, Jag

In reply to:

---

I'm also very confused as to why I see no improvement/variation in smoothness from one position to another in my room as virtually everything I've read on the subject of sub placement suggests should happen.

---

It's funny you say that. I have been talking to Tom from SVS over the last few day's yapping about placement etc. One of the things that came out of our conversations was the fact that by moving my sub around, I won't necessarily make it tighter, less boomy etc, all I'm doing is creating more db the closer I get to the listening position. I have been moving my sub all over my basement over the last few day's and it sounds the same no matter the location. I thought I was doing something wrong until Tom broke it down for me.

Sub placement seems to be something I always thought was an issue but I have now learned that as far as my room goes, I can drop it almost anywhere and it works more or less like the spot I had it in before. What got me on this path was the crazy thought of adding another SVS PC-Ultra to the back of my room. Here is a direct cut on a few of the things Tom had to say:

In reply to:

---

The room size and the distance between the subwoofer and the listening positions will largely determine how loudly the subwoofer will be able to play. In a larger room like yours, with the subwoofer about 5m from the key seating positions…the single PC_U will be capable of approx 109-115dB of clean output.(at the seating positions). But in a smaller room…say 20x14x8…with the PC_U 2-3m away from the seating positions…you could be looking at 115-121dB of output.(or, the amount of clean bass it would take DUAL PC_Ultras to produce in your room).

---

Jag:
I haven't had much time for these boards lately, but I DID want to mention that your plots certainly looked better than the ones I came up with for my JBL sub a couple of weeks ago (I haven't had a chance to do my new Axiom sub yet).

I had HUGE rises and dips, not all of which could be attributed to the room (for instance, I had a sharp dip of about 18db at 60Hz no matter what the position)!

Michael, while I agree with Will as to the general effect of subwoofer distortion as he clarified in his second post, upper harmonics added by possible distortion wouldn't explain the increase shown in the 10-20Hz octave. Also, the 100dB level, while quite high, should be well within the capabilities of the 500, as you point out. I find it hard to believe that the increase shown is "real", but just as hard to come up with a solid explanation. I wonder if the "correction" to the RS meter, which is actually an attempt to undo the C-weighted curve compensation for the Fletcher-Munson effect, is invalid at the higher level and that the correction should in fact be much less in the 10-20Hz octave.

Viewing the curves shown, one thought that struck me was that(if you aren't totally exhausted at this point from lugging the 500 all over the room)another position to try was the left front corner, but with the 500 turned around so that the driver cone faced diagonally into the corner and was about 1'-1 1/2' from each adjacent wall.

Woooowwww! This has exactly been my experience. I tried crawling around alot to see if I could hear a difference and just couldn't. I was thinking I just didn't have a good enough "ear" and this has been the reason I have gone to some effort to try and map out the In Room Freq Response. So perhaps I"m not so crazy after all . Well on second thought...

Seriously this is extremely helpful. I bet alot of what people hear as an improvement from one location to another by crawling around is simply differences in loudness. As is often pointed out here on the forum a speaker sounding just a little louder will sound "better". Perhaps this is what's going on when you crawl around?

Now that I've started though I"m still going to pursue the placement issue a bit more but it's certainly reassuring knowing that I may already be there.

Thanks alot NeverHappy, Jag

Hey JohnK, I'm definitely up for it! I agree with you I also have a hard time believing the higher output in the lower end and the compensation point is certainly possible. One thing to note though compensation aside the lower end was definitely higher when it was playing louder. Ultimately I'm just looking for the smoothest response and playing this loud certainly gets me there, but I just don't know how to use it. I was thinking something similar to your idea of facing the sub towards the wall thinking perhaps the sub would be driven a little harder but the loudness at the listening position would be more comfortable giving me the best of both worlds.

I'll give this a try in the next little while and let you know how it goes.

Thanks for the help, Jag

Hey Mark thanks, as I've never had a HT before I'm really in the dark of what a reasonable expectation for an In Room Freq response should be.

If and when you do have a chance to take your measurements it would be cool to also see them.

Thanks, Jag

Hey JohnK, I was thinking about your suggestion of the compensation issue and it certainly makes the point that the measurements could be in question with regards to compensation or the even worse the SPL meter itself.

I'm wondering is there any way I can cross reference the accuracy of the meter itself. One thought I had is to exchange it for a new one. At least that way I would feel more confident the meter was behaving properly.

Thanks, Jag

In reply to:

---

think I understand what you're saying and it definitely fits what I'm observing. I'm not convinced though, the sub is actually being over driven or is clipping as I'm not seeing/hearing anything to give me the sense that this is occuring during the measurements.

---

Yea - you won't actually hear the distortion until it reaches very high levels. This is typically 1-10% on higher frequencies but can be MUCH higher on bass notes (especially ones that are below audible threshold (under 20 Hz).

Also, just to point out... the 120 dB anechoic max is for one frequency - its peak frequency. There is no possible way that a subwoofer with an amp of only 500W, with only a 12" driver, and with a box that small will put out 120 dB C anechoic at 16 Hz. It would be a VERY impressive feat if it could do 120 dB anechoic at 22 Hz without distortion, but I imagine this peak output frequency will be more along the lines of 25-30 Hz. I suggest you use a decent quality microphone and download some RTA software and look at the different frequencies outputted when you run a specific test tone. I know there are a few websites online that offer 1/3 octave RTA software provided you have a decent mic. Alternatively, you can use your Rat Shack SPL meter AS a microphone (or so I hear), but I have yet to try with mine.