Axiom Home Page Forums General Discussion Technical Questions EP subs sucking life (gain) out of the 350's....

I know mojo talked about this a long time ago, but today I noticed this to be a fact.

If I have the EP600 either daisy chained with my 350's, or if I use a splitter at the receiver it does not seem to matter, the 600 is dropping the dB's by about 6-7dB for each 350.

I thought the Line In and Line Out jacks were just a "pass through" type of connection, but this does not appear to be the case for the EP subs.

I found this out because I tried hooking up just 1 or 2 350s (daisy chained) with the 600 not in the loop. If I calibrate each sub to 75dB's individually, then turn them both on, I get about a 3dB+ increase, which makes sense. However, as soon as I incorporate the 600 into the daisy chain, or have it on its own line split at the receiver, the dB's for the 350's drop about 6-7dB's per the meter.

This explains why I have to have my 600 volume knob so lowwwwwwww (about 6 o'clock) and my 350's about 3/4 cranked to achieve the same dB reading on my SPL meter.

This seems crazy, and is causing habic with me setting up Audyssey. I may call Axiom to see what they have to say..

Randy

I don't see what the big deal is. That is what the gain knobs on the subwoofer are for.

If you run out of gain, it is a big deal. The 350's have to be pretty much maxed out to achieve the same SPL. It is pretty much impossible to calibrate to 75dB's with the 600 in the loop.

Do you frequently change the receivers trim for different sources?

I just talked to Axiom, it appears the output of the EP600 (and I assume 500/800) are great enough that other subs in the mix will require lots of gain to be equal. This can be a bit tricky. As most of you EP owners have realized, you have to keep the gain almost all the way down as a higher setting will require the receiver to be set down as low as -10to-12dB to compensate.

Then, to get the other subs at the same SPL, you have to almost max them out. You can't raise the receiver level to help, becauese this would require the 600 to be lower, and your out of room.

Maybe some day receiver manufacturers will figure out that independent multiple sub preouts are required.

I'm not as educated as others on this forum, but that doesn't seem right to me and would be frustrating.

In order to have seamless bass, you would need three EP600s. Jason, do you think this would apply when adding any other sub i.e. another brand?

No Dr, if you read what I've posted, the problem lies when trying to calibrate multiple subs, to the same SPL as your speakers. I never said that I change levels for different situations. Even the Audyssey setup guy recommends calibrating each sub independantly to 80dB's prior to combining theme and running Audyssey. Currently, this is not possible for me, so I have to use something lower like 70dB's. Anyway, Axiom confirmed my thoughts.

There are a lot of subs on the market Cam, lots with great output ability. I've never heard anyone on other forums having this issue, many people daisy chain subs. Maybe it is just the Axiom design, not sure.

I wonder if it would happen when daisychaining an Axiom sub that you mention with another brand.

The response from Axiom makes sense to me. The EP350 and EP600 will have different input sensitivity ( one will need more gain than the other) due to the amp design. Using them together in a multiple subwoofer setup will ultimately make calibrating more difficult. This is one of the advantages of using identical subwoofers.

Is it possible for companies to design all subwoofers so they have the same input sensitivity and amp design, thus eliminating this problem?

I'm not a subwoofer designer but the EP350 and EP600 are different animals all together. Taking into consideration the enclosure, driver, amp etc I wouldn't expect them to have the same senstivity (or any other similar specs) because they are entirely a different design with different design goals intended by the engineer.

Randy, have you tried to co locate the 350s to see if that would help with the proper amount of gain?

Randy, I think I've lost the picture here. Your original post indicated that *adding* the EP600 reduced the output of the EP350s, but later posts seemed to imply that the issue was "just" a difference in gain/sensitivity/whatever between the 600 and the 350.

From my understanding the EP600 needs much less gain from the reciever.

One way to test this is to calibrate the single EP600 by itself and see what the receivers gain is set at compared to dual EP350's (without the 3 way connection).

Hey John, hope I'm not confusing anyone, maybe my terminology is not accurate.

Lets say I want to calibrate all my subs to 75dB's and lets say currently one of my 350's is the only thing hooked to my receiver, this is not problem. I turn on the receiver test tones and adjust the volume (gain) knob on the sub to achieve 75dB on the SPL meter.

Now I want to add another sub, so I either use a Y adapter at the receiver, or just daisy chain my other 350 to the Line Out on the first 350, no problem. I turn the first sub off, calibrate the 2nd sub to 75dB's, now both subs are at 75dB's seperately and when both turned on get about 78-9dB's combined.

Now, I decided to add the 600 in the loop. I've tried using the Y adapter at the receiver, daisy chaining it at the end of the line, in the middle, or even as the first sub.

As soon as I plug in the Coax cable with the EP600 switch still turned off (AC plugged in though), and go back and independently measure each sub again, each 350 has dropped by 6-7 dB's, so they are no longer at 75dB, and are not reading 68dB.

To get them back in line, I have to crank the gain almost to the max. The 600 is another story, for me to achieve 75dB with the 600, the knob as to be very low, like 6 o'clock. Even at that the receiver still is like -6dB, which does not work well with the 350's. It is a crap shoot.

I'm hungry...later..

Wid, I suppose I could try that, but I'd have to move all my subs around again and put the 350's back up front. I kinda like having the 600 up front below my center as it is so big and since I got a horizontal design, does not look as nice standing up. The rubber legs look fugly.

Ok Wid, I moved things back the way they were months ago. Now I'm even more confused....

When I had my Denon 2805, I had the 350's up front below the screen between the 80's. My 600 was placed along the left side wall behind the listening area about 5 ft. The 2805 would always calibrate the distance to about 27ft. I was told this was due to the internal delay of a DSP based sub. However, if I just measured the 350's they would come out right on the money.

So, a few months ago, placed the 600 back up front, and placed one 350 to the right side of the listening area, and the other on the left wall where the 600 came from. Interesting, when I recalculated distance with the 2805, it came out about 13ft, which is about dead nuts for all 3 subs.

Jump ahead to a few nights ago. Audyssey had my subs at about 12ft which seemed fine. Tonight I have moved the 350's back up front, and the 600 back in the left wall, and guess what, I'm now getting 27.1 ft again for a distance (delay) setting.

It sounds great, but I'm trying to figure out if the 350's are being ignored or what..this is just to weird.

Ask axiom if it is safe/plausible to use a y-adapter on the subwoofer out and feed it into the R or L input on the EP350's in your multi sub configuration. In theory this can give your EP350 a signal boost without adjusting the receivers settings.

Randy, I'll more or less second John B.'s point: the fact that the EPs have higher amplifier gain(fairly obvious from the low settings on the level control that we use)doesn't explain why putting one of them into the circuit would drop the level of the other subs. Did Axiom seem to understand that this is what you were really asking about?

John, I called Brent, who called Tom C at Axiom. Brent called me back and said it had to do with the fact that the 600 has so much output, and that I will have to crank up the gain on the 350's. To me it is strange that even if I turn off the 600 using the power switch, it still reduces the 350's by so much, like it is reducing the signal?

Yeah, Randy; that reply from Axiom doesn't appear to be responsive to the problem. The difference in level settings required doesn't explain the drop in level when the 600 is connected.

I'm trying to understand it as well John, maybe Alan will jump in. The way I understood it is that the 600 requires more of the signal produced by the receiver, which would leave less for the other subs. I suppose I should have asked more questions.

Well, it shouldn't work like that with properly designed amplifiers(and the higher gain amplifier is the one that requires less voltage input, anyway). Typical amplifiers have an input impedance of 10K ohms or more. Preouts typically have an output impedance of a few hundred ohms. A common rule of thumb is that the input impedance of the amplifier should be at least ten times the output impedance of the preamplifier. When Mojo and I discussed a similar problem a little over a year ago both on the board and in PMs the results he was getting indicated an extraordinarily low input impedance in the Axiom switching amplifiers was causing a drop in voltage when the EP600 was connected. The question was never resolved.

I was having trouble with the volume knob having to be maxed out on my second EP800 to barely keep pace with the first one--it was actually just shy of the same SPL--but with the latest version of the amplifier, the volume knobs on both are very close to the same position to achieve equal levels. I assumed Axiom knowingly corrected this and it's not just a fluke.

I had the same issues Randy whenever I connected my old 350 with the 600, way low on the 600 with the 350 having to be turned way up ... I surely hope the same issue won't rear it's ugly head whenever a like sub is added to the 600.

There was most deinitely a problem with daisy chaining the EP600 when Mojo and I were doing the sub comparisons. It was thought that the latest batch of amps with the higher filter(150hz) on it and no by-pass mode solved the issue, IIRC. I seem to remember a couple of posts by a few owners with the newer amp design and they were able to daisy chain the 600 without the drop out of the other subs.

Just curious. Have you experimented with splitting the signal at the receiver so it's not being daisy chained? Excuse me if it's been covered, I reread the thread but only very quickly.

Same thing murph, I had a gold splitter adapter at the receiver. One of my 350's was on its own leg. I had it calibrated to 75dB's, but as soon as I plugged in the other line which included the 600, it dropped about 6-7 dB's.

Maybe Alan will see this thread and consult with Tom C. to give us a better understanding than Brent telling me the 600 has more output....

Well, this also solidifies that it is an electrical condition, not an output problem.

here is an oversimplified, probably silly thought. Could you use the equivalent of a fader device (instead of a splitter) to equalize the output to each sub?

Edited for second thought:
"Equalize" need not even be the goal here. You could use said device to tweak to whatever levels allows you to balance levels more easily without having to max out or minimize gain levels on each subs amp.

Mine never has been daisy chained, there's a splitter at the AVR and from there each sub cable gets plugged into a wall plate with individual cable runs going to each subwoofer location throughout the room.

I've never though too terribly much regarding the 600 and the 350 not playing well together because I knew bringing the old 350 into the mix was like bowling with a marble but if there is a problem with the 600's amp I sure would like to have it rectified.

Yeah, this seems to match what Randy is seeing as well, and it's one of very few explanations for how a sub on one side of a splitter could affect the output level of a sub on the other side of the splitter.

Here's a question... don't balanced inputs normally have a much lower impedence than single-ended inputs ? My mind keeps supplying "600 ohms" as the answer, even though I haven't asked it the question yet

Andrew, using a "Y" at the receiver sub out is electrically equivalent to using a "daisy chain" through the sub. The sub arrangement is an internal Y with one branch going straight through to the next sub and the other branch going into the sub amp. That's why Randy got the same result with both configurations. In both cases the two sub amplifiers are connected in parallel with the receiver preout, dropping the input impedance to 1/2.

This would exacerbate what may have been an unusually low input impedance on the EP600 amp, as Mojo and I had discussed. The output impedance of the preamp and the input impedance of the sub amp are in series and form a voltage divider. Unless the sub amp input impedance is much higher than the output impedance of the preamp(as was said, at least 10 times is suggested)a substantial drop in voltage from the preamp occurs, with a loss of volume, when the low impedance sub amp is connected. The modified amp in the EP600 may have corrected this low input impedance(if it in fact existed)and now the connection creates no significant volume drop. The change to a 150Hz brickwall filter instead of 100Hz would allow for better blending with small speakers that need crossovers above 100Hz, but wouldn't in itself change the input impedance of the amp. Randy might check with Axiom as to the possibility of installing the modified amp.

This 600 should have the modified amp. Less than a year ago, Axiom sent me a new amp as my original amp in the 600 was defective. When I would adjust the gain knob even the slightest, it would jump in output like 20+dB's. Also, if I pushed on the amp plate in a couple of locations, it would do the same thing. I believe this new amp does not have the brickwall filter.

Thanks John, you are most certainly correct. I need to re-open my text books.