Axiom Home Page Forums General Discussion Advice from Axiom Owners Upgrade from EP350 to EP500?

Well, if you "want" dual matching subs, I think you've answered your own question.

Honestly, I think it's going to be difficult and frustrating to build 2 DIY subs that perform as well (or look nearly as good) as an EP350, especially at that price point.

If you are pleased with the Bic, why not get a couple more of those. Sell the 350 and you will darn near break even.

I currently have a BIC PL200 that I paid under $300.00 for that outperforms my EP350 at 1/3rd less volume on the dial!

the most logical step

Have you measured either sub in your room?

Those AE kits look really nice! I wonder what the tuning is on the pr subs.

I am interested in following your foray into DIY subs, be sure to post some pics(or PM me some) of the project along the way.

I also considered ED as well, but with the recent amp problems

Lets hope both of your ep500s amps fair well. If you haven't noticed Axiom too has had their share of amp problems.

Its interesting watching you go through the purchase decision. Those AE subs would have given you significantly more output than the EP500 as they are very efficient drivers AND they can handle a lot of power.

The question is, do you really need more output than the EP500s give you? Probably not.

you can tells your friends

Based on my experience, Dana, if something does go awry with one of your EP500's, it will be taken care of, and quickly at that.

Well, I got my Dual EP500's today, haven't had much time to get them dialed in yet.

But so far, it looks like I made the right choice. The difference between these and my EP350 and PL-200 is night and day.

I was debating between the dual EP500's or dual SVS PC12-Plus's. I don't know what the SVS's would of sound like, but I think I'm pretty happy with these.

Music listening especially is awesome. Haven't had a chance to play any heavy bass movies yet.

Once I get these dialed in with my SMS-1 they should sound really great! Thanks to all for the advice...

Dana

maintain the integrity of my sphincter...

Not sure whether to laugh or cry at that. At my age, I can't afford to lose any integrity of my sphincter!

Dana

Its nice to see your tinkering pay off. I wonder if the positioning of the subs and mains has something to do with why the system sounds better with the M80s handling the 50-80Hz region?

With receivers that offer individual cross-overs for each channel, I'd love to see a test where the center channel is set to 80 Hz, the mains to 60, and the surrounds to 100. Each speaker's distance should also vary slightly as it would in a real room. Then have a 50 to 150 Hz sine sweep played in phase through each channel simultaneously, and plot what is actually being output to the sub. I have a feeling it won't be pretty.

Considering your speakers, I'd suggest that the THX researched and recommended 80Hz crossover should work well for all of them, including the M60s. There shouldn't be a good reason for setting the M60s large.

Amazingly enough, non-localized frequencies when combined with the playback of their higher frequency harmonics really are localized by the brain to the speaker they were crossed from.

But my issue was not with that. It's that I'm wondering how the person programming the digital crossover maintains phase coherence when using different crossover points. People like to complain about comb filtering between individual drivers playing the same content. That's a measurement artifact which varies with mic placement. What about the comb filtering which results in a digitally summed signal comprised of out-of-phase components? There's no getting around that. The only reason wouldn't be noticed is that the bass content of the mains/center/surrounds isn't likely to be the same. But if it ever was and there is a phase mismatch in the cross-overs the resulting output to the sub would have serious artifacts.

Mixing high and low frequency crossovers in a multi-channel set up
Once you wrap your head around the fact that in most products you are setting a high-pass on each main channel and a single low-pass on the sub, the use of a different setting for each speaker (or pairs of speakers) no longer sounds like such a good idea (pun most definitely intended). Lets take an extreme scenario, just to illustrate the point.
We set the high-pass on the main left and right to 35 Hz because we think its in the best interest of our massive tower speakers. We set our center channel high-pass to 100 Hz because it isn't very big. What is the subwoofer low-pass in the processor going to be?
If set at 35 Hz to complement the main speakers, the center channel signal will have a huge hole from 35 Hz - 100 Hz. Whoa! Lots of bass on that channel we don't want to miss out on. So let's try setting the subwoofer low-pass to 100 Hz. Oops! Now we have IN-ROOM 6 dB too much from 35 Hz - 100 Hz on the main channels because BOTH the main speaker and the subwoofer are voicing it. You CANNOT correct for this. If you lower the subwoofer level, you lower it for everything, and now you don't have enough bass from the center channel.
By now some of you are thinking, "Why not low-pass a copy of each main channel at the various frequencies I want and sum that with the full LFE channel?". Possible, yes, and if fact there are some SSP models which do this, but at a price: doing so inherently results in frequency response aberrations due to phase issues. Bass is often common to the front three channels and even more often common between the LFE channel and the fronts. Summing different low-passed copies of the same material would by definition result in a messy frequency response. Take the ubiquitous 4th order low pass as an example: At the crossover frequency its phase has come around to 180deg, absolutely inverted (compared to material it is being summed with). Granted the relative amplitude of that low pass at the crossover frequency is down 6dB but is still enough to create the aberration.
The THX design manual references the Dolby Digital licensing manual which mandates that the subwoofer output be arrived at the way it does for these reasons. If there was a better way to do this, without adding a lot of cost and/or making the product overly complex, I think Dolby would tell us.
One alternative found in some decoders is to take a low-pass copy from the center (in our extreme example, at 100 Hz), add that to the front left/right and still high-pass those at 35 Hz, the balance going to the subwoofer (though you still waste 35 Hz - 120 Hz off the LFE channel). This can be both good and bad, depending on the rest of the design:

- Unless proactively addressed, you can still have the phase issues described above.

- When mixing channels digitally, S/N is lost (approximately 6 dB when two channels are added for example), because after the summing, the combined level has to be attenuated to the original level. Might not sound (pardon the pun) like much but its something a designer has to consider when weighing the pros and cons of doing something.
We acknowledge that a different crossover point for each speaker is a desirable thing from the point of view of real world acoustics and dynamics. The different positions of the speakers in the room virtually dictate it, and the various members of a mismatched speaker set will each have different points of intersection for increasing dynamic range and maximizing bass performance. But without also having a selection of slopes in the SSP and some VERY expensive measuring equipment, one is likely to end up further behind than ahead