Can I Increase Subwoofer Level?

[cwmcobra]

I have an all-Sherbourn system put together and can't quite get the subwoofer level matched right to the mains. With all adjustable volumes maxed for the subwoofers, their level is just shy of where I would like it. And I'd like to have a bit of "headroom" above where I currently like it in case I find a need to add more bass in certain situations, such as tuning for room correction in my under construction HT.

Here are my components:

PT-7030 pre/pro
PA 7-350 7-channel amp
4Z-75 four zone stereo amp (for subwoofers)
Klipsch La Scala LCR
Klipsch Heresy I side and back surrounds
A pair of Bill Fitzmaurice DIY Tuba Home Theater folded horn subwoofers

Current system connections:

-PT-7030 XLR interconnects to 7-350 mains and all surrounds driving all seven main and surround speakers
-PT-7030 RCA interconnects to 4Z-75 driving the two subwoofers.

Both master volume on the back of the 4Z-75 amp and the volume on the front are set at maximum. In the speaker setup of the PT-7030 the subwoofer level is set to MAX. The sensitivity of the subs seems pretty close to that of the Klipsch Heritage speakers. The levels can be easily matched if I use a commercial amp with higher gain and adjustable volume control. I just don't want any fans in the system and really like the look of the all-Sherbourn electronics in the rack.

I emailed Emotiva tech support and was told that the gains are very similar between the two Sherbourn amps. The 7-350 gain is 29 dB; the 4Z-75 is 30 db. So the gain structures are not favoring the 7-350. I have not set the main levels to their minimums in the PT-7030, since I don't currently have an HDMI monitor to hook up and play with the setup menus.

I can think of the following actions that might increase the relative levels of the subs vs. the mains:

1. Get into the setup menu on the PT-7030 and set the main and surround levels to their minimums. I assume this will attenuate them by 10 dB each. Reconfirm that the sub levels are set to MAX.
2. I believe I read that the XLR outputs on the PT-7030 put out a slightly higher level than the RCAs. If so, I am getting a bit of a boost to the mains and surrounds by using the balanced connections. So, I could use the unbalanced connections for all the channels and the subs to eliminate that level difference.
3. Can I achieve the same result as in no. 2 above by continuing to use the XLR connections for the 7 main and surround channels and buying XLR to RCA adapter cables to connect the PT-7030 to the 4Z-75? If the XLR outputs are at a slightly higher level than the RCAs, would using this adapter cable give me slightly higher output to the 4Z-75 sub amp?
4. If the adapter cable does slightly increase the level to the sub amp, would the maximum level increase be achieved by using the XLR outputs from the PT-7030 to the sub amp using the adapter cable and using the unbalanced connections for the main and surround channels?

The two critical questions for me are 1) confirm that the balanced outputs from the pre/pro do indeed provide somewhat higher levels than the unbalanced outputs and 2) will using the XLR to RCA adapter cable preserve the higher output to the sub amp (which doesn't have balanced inputs).

I'm ready to test out this approach if I can get answers to these questions. Any other suggestions to up the sub levels are appreciated.

Cheers!

Chuck

[cwmcobra]

Keith,

I think I've found where I got the idea that the output levels from the balanced connections would be slightly higher than the unbalanced and hope it saves you some time in searching for references. In the Do XLR connections make a difference to the sound?   thread, this question was posted:

"Thanks Keith L. What about the fact that the output voltage is doubled via the XLR outputs vs. the RCA outputs on the XDA-2"

Your response: "What about it?

There is no specific advantage to having a slightly higher output voltage. Both outputs carry the same exact audio signal, but it is buffered through two different buffer amplifiers; one is set to put out slightly more voltage, but they are otherwise the same - neither is "higher quality". (If you had a specific situation where the unbalanced output wasn't able to produce enough output voltage to drive a certain device, then the extra output voltage could be useful, but otherwise it doesn't matter. A balanced signal and cable reject noise because of the signal topology; the audio signal itself is no different.)"

And later in that thread you posted: "As we've been discussing, the input circuitry is slightly different for each input (on any device), so I can see how the two inputs on the 7-350 could sound slightly different - although I personally have never heard any difference. The actual wire used in the two different interconnects is also almost certainly different, which could produce a slight difference in sound (due to differences in resistance and capacitance.) You are also changing the levels slightly, which puts both units in slightly different parts of their gain range - but I wouldn't expect that to make much difference either."

So I guess a clearer question is, if the amp receives a higher voltage input signal from the pre/pro when using the XLR connection, does the gain structure in the amp then output a corresponding higher volume level?

Thanks again,

Chuck

[moovtune]

On my Emotiva amps I found there was a 6db difference in level being sent to the speakers between XLR ins to the amp and RCA ins to the amp. XLR ins creating a 6db increase in output. So changing to RCA connectors may give you the extra level you need ... if 6 db is enough. But I admit I've never heard of maxing out sub levels everywhere and still not getting enough low end.

[cwmcobra]

moovtune,

Thanks for the reply and the interesting information. This suggests to me that I have the potential to gain 12 db at the subs by reversing the connections between my amps. Connecting the 7-350 amp for the mains & surrounds to the unbalanced outputs of my 7030 and the 4Z-75 for the subs to the balanced XLR outputs using XLR to RCA adapter cables. Assuming, of course, that the 6 db difference works both ways. I think I will buy a pair of XLR to RCA interconnects to use with the sub amp and some good, but cheap RCAs, probably Monoprice. I have materials to make my own RCAs, but want to wait until I get the rack set up to customize lengths.

Of course, now I'm wondering if the 6 dB difference is a "standard" that is inherent to all balanced vs. unbalanced circuits or is unique to Emotiva amps and processors. Perhaps Keith can help with this question.

I was also surprised that there's not enough low end with this setup. My thought is that most subs are driven by plate amps and the plate amps must have more gain than a typical stereo or multichannel audio amp. Or, at least more than the Emotiva amps, but I doubt the Emo amps are unique.

Cheers!

Chuck

[Gary Cook]

Apr 3, 2014 20:43:57 GMT -5 cwmcobra said:

I was also surprised that there's not enough low end with this setup. My thought is that most subs are driven by plate amps and the plate amps must have more gain than a typical stereo or multichannel audio amp. Or, at least more than the Emotiva amps, but I doubt the Emo amps are unique.
Cheers!
Chuck

Hi Chuck, with the same sub woofer (driver and enclosure) I have used a 500 watt Class AB off the shelf plate amp, a 400 watt Class D stand alone DIY amp, a 400 watt Class AB stand alone DIY amp and an Emotiva XPA-100 (400 watts Class AB) and I can't say as I have noticed any volume changes. Sound quality is a different matter, the XPA-100 is streets ahead in that area.


Cheers
Gary

[moovtune]

I had a plate amp go out in my Epik Legend (2 12" drivers) and for about three weeks I was driving that sub with an Emotiva mini-100 (80 watts into 4 ohms) and only had the volume up halfway with the preamp sub output set at -4db. That's why I'm surprised you have to crank everything you have and still don't have enough level.

[cwmcobra]

Well, I guess I need to do a bit of "troubleshooting". I'll play with interconnects and see if that makes a difference. Thanks for the heads up guys. I appreciate it.

Cheers!

Chuck

[cwmcobra]

Results of brief testing; I changed main & surround connections from XLRs to RCAs (used some cheap patch cords I had laying around). This increased sub level, but not as much as needed or expected. I then played with the connections to the 4Z-75. Being a multi-zone amp it has (to me) unusual connections; four separate zones with two channels per zone.



I had my subs hooked up in a stereo configuration on Zone 1 (one connected to Channel 1 speaker outputs, the other connected to Channel 2 in Zone 1). I then changed the sub speaker connections connecting one to channel 1, zone 1 and the second to channel 1, zone 2. Now I have more volume and actually have reduced the volume control on the 4Z-75 amp. I don't understand the science, but it appears that I'm getting more amp gain by connecting the subs to separate zones in the amp.

This was a quick test, as I took a few minutes break from hanging drywall to test these changes. Back to hanging drywall now and the gear is turned off and covered with plastic to avoid that pesky drywall dust. I plan to do more detailed testing when the drywall dust has settled a bit.

I think I will also buy a pair of XLR to RCA adapter cables to hook up from the pre/pro to the sub amp to see if it will further increase the sub level. I'd like to have all the sub level that is possible and can attenuate it to suit my room and tastes.

Thanks again for your responses. It appears you got me on the right track.

Cheers!

Chuck

[cwmcobra]

Here's another thought. I assume that rear surrounds in a 7.2 setup would require the least amount of amp power of any of the channels. Again, assuming less volume and less dynamics. So, what if I run the rear surrounds through the 4Z-75 and the subs through the 7-350? With my highly efficient Klipsch Heresy surrounds, I have to believe that the 75-95 W/channel at 8 ohms from the 4Z-75 would sufficiently power the rears. That leaves 550 W/channel at 4 ohms for each of the subs. Way more than I need, but perhaps more importantly, a clean way to balance levels for the 7.2 channels and I could run XLR interconnects for all but the rears.

Any comments on this potential strategy? Am I underestimating the power needs of the rear surround channels? Any other downsides?

Thanks,

Chuck

[novisnick]

Apr 11, 2014 9:36:11 GMT -5 cwmcobra said:

Here's another thought. I assume that rear surrounds in a 7.2 setup would require the least amount of amp power of any of the channels. Again, assuming less volume and less dynamics. So, what if I run the rear surrounds through the 4Z-75 and the subs through the 7-350? With my highly efficient Klipsch Heresy surrounds, I have to believe that the 75 W/channel at 8 ohms from the 4Z-75 would sufficiently power the rears. That leaves 550 W/channel at 4 ohms for each of the subs. Way more than I need, but perhaps more importantly, a clean way to balance levels for the 7.2 channels and I could run XLR interconnects for all but the rears.

Any comments on this potential strategy? Am I underestimating the power needs of the rear surround channels? Any other downsides?

Thanks,

Chuck

I think that this solution makes perfect sence, rear surrounds   don't need that much power in my opinion.