Saturday, July 5, 2014

How good is the Logitech Z906 subwoofer as a...well, a subwoofer? A detailed look...

Hi guys, if you have read my previous update a few months ago, you would know that I did an experiment with the Z906 subwoofer that I have on my desktop. I took out the subwoofer and used it to temporarily replace my old Aiwa TS-W5 subwoofer that I had in my living room/home theatre. And as I said before, both are 8-inch subwoofers, but after some testing, the Z906 subwoofer sounds superior to the Aiwa sub, delivering deeper bass with much less distortion than the Aiwa one. But here's the more important part: It sounds even better than when I was using the Z906 as a complete set out of the box.

So after this experiment, I also mentioned that I want to upgrade my home theatre's subwoofer completely, that I want to replace the dying Aiwa sub with like a 10-inch or a 12-inch one. Unfortunately, the 10 or 12 inch subs are way beyond my S$500 budget. The retailer told me that a 10-inch sub would cost a minimum of S$600 or more. And I checked with the retailer about subwoofers like the B&W ASW-825 that one of the reviewers at uses, and that could cost S$4,000. What? And as I continue my research about the highest-end subwoofers in the market, a subwoofer like the THX-Ultra2 certified M&K X12 subwoofer, which I heard is used in Skywalker Ranch for Skywalker sound mixing rooms (don't know the authenticity of that information), that can cost a whopping US$3,200.

Ok, so forget about those subwoofers, it will take me ages to save up to get one of those. So I made the craziest decision with my S$500 budget: Buy another set of the Logitech Z906. But I'm only intending to use the subwoofer. So what about the other 5 satellite speakers in the box? I just keep them as spare speakers in case one of my speakers on my desktop goes down. Sounds pretty insane, right? Like why would I buy a S$500 product and just use only one of the many items in the box?

The Z906 subwoofer as a standalone subwoofer

Well, let me put it this way. The other high-end subwoofers cost a small fortune to get, and quite frankly, I'm already very satisfied with the performance of the Z906 when using it as a subwoofer by itself. Furthermore, the Z906 is also a THX certified product. Although it's certified only at a "THX Certified Multimedia Product" level and not at something like "THX Ultra2" level, the fact that it passed the certification process means that it surely can somewhat can deliver very good quality sound, and it's clearly evident when I tested it on my home theatre. And besides, THX Ultra2 is for viewers viewing their screens at 12 feet or more, and I'm only viewing my TV at about 10 feet, so I don't really need a THX Ultra2 certified subwoofer. Perhaps if you want to be really technical, then THX Select2 products would be more suitable for my setup as Select2 is for 10-12 feet viewing distance.

Now comes to the question: Why does the Z906 subwoofer sound worse when it's used directly out of the box, then when used as a standalone subwoofer with a separate receiver controlling the signal going to the sub? Well I hate to say it, but the in-built amplifier in the Z906 subwoofer is not ideal, at least to my liking. Why? It automatically crossover all the bass signals from the satellite speakers to the subwoofer (as per THX certification requirement), with no option on the control panel to turn it off. As a result, all this "crossover-ed" bass signals are louder than the discrete LFE channel (which is the channel containing all the deepest bass signals), thus overwhelming it. Of course there can be other factors like the placement of the subwoofer in the room, etc., but from my testing, this seem to be the primary reason. I'll be completely honest, I don't really like the fact that the THX certification requirement for amplifiers/receivers has a mandatory requirement that bass signals from the satellite speakers 80 Hz and below must be directed to the subwoofer channel. I feel that there must be an option in the receiver to turn this crossover setting on and off, so that we can choose to hear the sound mix as the sound mixers intended. Thankfully, the Denon AVR 1912 receiver that I use has this option to listen to the sound channels directly with "direct" mode. And one awesome thing that this Denon receiver has, but I'm not sure if other receivers have this option (I feel this option is a must in every receiver), is that you can set it in such a way that if the receiver detects stereo sound signal, it will automatically crossover the bass from the left and right channels into the sub, which is very cool because stereo content doesn't have a discrete LFE channel. But a standard 5.1 mix does have a discrete LFE channel, so I want to be able to listen to the channel purely through the subwoofer, and not have other bass signals from the other channels overwhelm it.

The Setup

Now, how did I connect and configure it? That's probably what you want to know, isn't it? So that you can create a nice home theatre setup without spending thousands of dollars on just a subwoofer. The main gist of this article is to tell you that if you are going to use the Logitech Z906 as an actually home theatre equipment, you definitely going to need to get a modern AV receiver, preferably with HDMI ports and support for lossless audio formats like Dolby TrueHD or DTS HD Master Audio (because the Z906 doesn't support sound from HDMI out of the box), like my Denon AVR 1912 receiver, for example. This receiver will allow you to hear the discrete LFE channel by itself on the subwoofer. You can even use the receiver to power the other 5 satellite speakers that came in the Z906 box.

First, you will need an RCA cable that has one jack on one end and then splits into 2 RCA jacks on the other end. 

On the above picture, the black RCA cable on the top is the signal cable coming from my subwoofer jack on my receiver. The 2 RCA connectors at the bottom of the splitter are the type of RCA cables that I mentioned earlier, the ones that split a mono input into 2 RCA jacks on the other end. The reason why there is a splitter before I use another splitting cable is to make room for dual subs, more on that later...
The next thing you may need is an RCA stereo to 3.5mm stereo jack converter, like this:

Why you may need to convert to a 3.5mm jack, and why do I need to split the subwoofer signal into 2? First, actually you may not necessarily need this RCA to 3.5mm converter because the Input 2 at the back of the sub is using an RCA connector. I use the converter because I want to plug in to my Input 1, which is actually the default input for the 5.1. I personally also want to standardise my input to Input 1 for both my living room's Z906 as well as my room's Z906 to facilitate the potential dual sub setup better. I plug the converter into the centre/subwoofer jack, which is the black/middle one:
I have this prediction that if you plug the RCA jacks into Input 2, the sound may be louder, because the 5.1 crossover for Input 1 is designed with the 5 satellite crossover signals in mind, so, from my experience, the crossover bass from the satellite speakers are softer, so that the 5 speakers' bass sounds will add up to sound louder. This is why I split the signal into 2 because if I just input the subwoofer signal into just one input, it's going to be very soft. With stereo, you only have 2 speaker signals to crossover the bass from, so I guess the amp will make the crossover bass signals louder. So my suggestion is to try and see for yourself which way to connect you prefer.
Finally, what volume level do I set it? This one, your results may vary a lot from different receivers, but from my Denon AVR 1912, with nothing touched on the subwoofer volume level on the receiver side, and with the exact same Z906 speaker balance levels as my desktop setup (one notch/light louder the satellite speakers for the subwoofer, as you can see in my previous Z906 review), this is my volume level:
Yup, so it's about two-thirds of the way maxed out. Again, this is for my setup with my receiver, test with different volume levels on your setup to see which one is preferable for you.
So that's how you use the Z906 as a standalone subwoofer. The results have been very nice for me, providing real deep, 80-90% cinematic quality bass for most movie soundtracks (except perhaps U-571, that movie still needs an insanely large and costly subwoofer to accurately reproduce that crazy depth charge bass), and if you want to have a home theatre, but don't have thousands of dollars for just a subwoofer, the Z906 is a great option to start. Just make sure you don't use the in-built amplifier, use a separate modern receiver and/or amplifier to control and power the speakers. Thank you for reading, and you can start building your affordable starter home theatre with this guide.
And remember, if a single Z906 sub isn't enough, get two, like my Titanfall setup! I sometimes take the second Z906 sub from my room into my home theatre for a dual subwoofer setup if want extra powerful bass from some movies (still not enough for U-571 though). Sure it may cost you about S$1,000, but it's still cheaper than the super high-end ones which cost 3 to 4 times as much! The best part? The one remote control can control both subs!

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