Subwoofer tuning for the laymen: the Room Analyzer
As some of you know, I have been digging deep into the subwoofer world since I decided to go for the SVS PB12plus early this year, and trying to learn as much as possible about it. It is of course a work in progress, and I am glad I have such a great source of information here in the AVForums. Thanks to all members, of course!
Few months ago, Rikard from XTZ in Sweden contacted me through the forum, after reading my guide regarding REW and subwoofer tuning. He offered me the opportunity to test their product "Room Analyzer" for some weeks and give him my feedback.
After some small problems regarding the delivery by the local service (DPD... stay away!), I finally got the package.
I have really enjoyed using this tool, although I could barely find the time because there was so much football on tv during that time
In the following, I want to inform you about the abilities of this tool, just in case you are interested. I am not going to describe every single menu and function, though. You can get an idea about them by reading the short and complete manual (if you can bear the funny English this should improved in the future), which also includes some good advice about room acoustics and speaker positioning. Pity it does not come in other broadly spoken languages like Spanish, French and German (this may be a problem for some potential customers, but if the local distributor is good, it shouldn't).
Please note that I do not have any business relation with XTZ and I am not being paid for this. I did not even know about XTZ before they contacted me for testing their "Room Analyzer".
2. Kit description and first impressions
The "Room Analyzer" consists of a software package, a calibrated microphone and an USB sound card, which allows to measure the frequency response and time decay of your AV system. One could think of it as a replacement of REW (or CARMA), a Radio Shack SPL meter and a bunch of cables, but there is more to it than that, and not only because it allows to simulate the effect of equalization in your room, measure the RTA and suggesting which equalization you should apply. But let me emphasize at this point that the Room Analyzer is not a parametric equalizer. You need to use it in conjunction with your sub's knobs, AVR equalizer, BDF...
The package design looks nice, modern and "professional". It came very well protected in a cardboard box. Moreover, the parts are protected inside the package, sitting in a foam piece with cut-outs for the different parts. The layout is tidy and simple.
It consists of very few parts:
2.1. USB sound card with microphone and line-out.
2.2. Heavy and solid plinth for the microphone which doubles as stable interface for the computer and the AV Receiver, with a nice padded bottom.
2.3. Line-level cable with RCA plugs
2.5. Male-male RCA adapter
3. Installing the software
No CD is delivered with the package, as you may have already realized above. You get a serial number, and can download the software from their web site. Although I do not like this approach, I do understand the argument of XTZ: this way, they ensure that every client always gets the newest version of the software and is informed about updates. A CD can be sent to you free of cost upon request.
Another thing I did not like so much was the need of giving my full personal data information in the web site in order to access to the download, but again I understand XTZ's concerns.
I found a little odd that no folder is given as default (and can't be created from the installation menu) for the installation, but this should be changed in the future. Otherwise, the installation was fast and easy.
4. Hardware setup
It can't be made easier (and it is described with a picture in the manual):
4.1 Plug USB card onto the plinth
4.2 Plug USB cable into the computer
4.3 Plug the line-out of the card to the AV receiver, or better yet, use the plinth loop to give additional stability
4.4 Set levels (for example, by playing some music, which you can do through the card). Start low with the first attempt, and increase them with care! For mic positioning, etc, refer to XTZ's manual and/or the REW guide in the “read first”of the subwoofer forum.
Note that no extra cables are required. Everything you need is included in the package.
The cables are long enough to allow plugging together PC, mic and amplifier even if they are not next to each other (for an average sized room): 5m to the receiver (analog audio), 3m (USB) to the computer.
The USB port also avoids the need of batteries.
5. Software setup
You can choose between default and advanced mode on the “setup” menu. That's it!
The "default" mode only gives you a superficial impression of the frequency response between 16Hz and 314Hz. It uses a “smooth RTA measurement”, according to XTZ. I pointed them out that this is not explained in the manual, so it will be hopefully added. Anyway, it is really too smooth, so I strongly recommend that you go to advanced mode without fear. It is dead easy!
Just to make it clear: no level adjustments, no mic calibration, no sound card calibration, no endless menus to configure the program. That's as close as it gets to “plug&play” in this arena.
6. Taking measurements
Again, it can't be made easier.
Just click on “measure” and choose the mode (3 point average or single point). Four short sweeps will follow (for the 3 point average, you need to acknowledge after each set of sweeps right after changing the mic position).
The results seem to coincide to a very good extent with manually taken data (RS meter) and REW result (I can't plot all curves together without great effort). No measurement tolerances are given, but I guess 1 or 2dB is realistic.
I had some problem with the scale, but you can use the mouse to read out values on plots (they are the raw values, not the smooth ones, I think). I have been told that this is the usual scale in audio engineering, based on octaves.
Regarding the 3 position measurement, I quote XTZ:
“The three position method should be used primarily. It is much more efficient when finding room modes. The single position measurement only gives a hint of the room at one point. It could look good but the room may still be a complete disaster a few feet away. The three position option makes sure the results is closer to reality throughout the room.”.
I only found a bit annoying that the 3 position measurement is always selected by default.
7. The perks.
7.1. Time-domain representation and analysis
This nice tool is more than a frequency response graph. By double clicking on the graph, you switch to a colorful representation of the time decay for all measured frequencies. I still have to figure out how to obtain this with REW. This helps you to identify problematic regions with ringing (that is, frequencies at which the emitted sound takes too long to fade out), but is also used by the software to identify room modes (remember, this is called “room analyzer”. These are listed in an excel-like box (room modes and normal response peaks are distinguished).
The program then calculates the optimal EQ to be applied, and can even simulate it in further measurements. A custom EQ can also be applied and simulated. The effect of the EQ is also shown in the graph.
7.2 Several degrees of curve smoothing available.
The least smoothed version seems to coincide with the “standard” 1/3 octave smoothing of REW.
The software has a RTA function, which measures the full range response with a more limited accuracy. Not much in the menus: scale range and top, output level and three functions: listen, pause and measure. You need to let the white noise play for a short while before pausing again to ensure accuracy. It works great. Additionally, you get a table below with the average (“ref” level and deviation from it at each frequency.
7.4 “listen” function (of the RTA tool)
This is great to measure your favourite movie scenes or music tracks, and find out which frequencies are involved and how loud they are. I had some fun with “Darla taps the tank” from “Finding Nemo” and the tripod coming out of the ground in “War of the Worlds”. The tripod beams have also great amounts of deep bass! Note that you can just plug the mic directly to the computer/laptop (and no need of further cables), making these measurements even faster!
7.5 EQ upload
If you happen to have a XTZ subwoofer, you can directly upload the EQ values to the sub, which is great.
7.6 Client Support
Finally, XTZ provides free email and telephone support for his room analyzer, even helping to interpret the results.
8. The Cons
Nothing is perfect. Although I have been very happy with this tool, I see room for improvement.
Some disadvantages are intrinsic to the simplicity of the program. You can't get a lot of flexibility, but this way you can't make anything wrong either. Maybe an additional mode should be added to the “advanced mode”, call it “expert mode”, for those who want to go crazy with this tool. But I fail to see why you'd need more than it already offers to get the job done.
In the following, I list my main "criticisms" and some answers from XTZ (underlined items are serious disadvantages IMO):
It can't measure above 250Hz (except with the RTA). XTZ told me that room modes are below 250Hz and the first priority of the program is to find these. Moreover, an acoustic software for fullrange costs a lot more. This is fair enough, considering that the kit is called "room analyzer" ;-)
When saving PIR and overwriting file, the program does not ask if I want to replace it. They will try to include a warning pop-up in the next update.
For some reason, when simulating EQ, the new curve appears about 3dB higher (unless I have done something wrong...)
A direct comparison of various measurements is not easy because the scale jumps from measurement to measurement, and also the color bar scale, even if you keep the volume at the same level (for example, if a given setting produces a big peak). This happens, I guess, because the software adjusts the range to the average SPL each time.
It is not possible to display more than two curves at once (may change in future versions).
Curves are saved in proprietary format, not exportable (so no chance to plot several curves, say with excel or so – may change in future versions).
No labels on RCA connectors (no real need, since it is just a loop) - no screw for tripod mounting. XTZ told me they will think about it for the future.
The lower range is limited to 16Hz. XTZ explained me the following:
- "To measure below 20Hz with accuracy, you need a sound card HIGH class, and those costs a lot of money. Even if we dont hear below 20Hz, there are infra sounds that will affect the measurement. Also the room has to be extremely large to house the wavelength. 12 Hz in a regular room is in my opinion "an utopia". The wavelength is way out of reach, ending up inside some of the neighbours rooms instead"
I did not know that measuring below 20Hz you need a better soundcard. I know that REW measures first the sound card response, and corrects the values accordingly. The newest version even does it in real time, while measuring, AFAIK. I wonder if that is pointless, then.
9. Some neutral observations
I also took some notes that are not negative, but cannot be classified as positive either (or the other way around):
There is no possibility to use the mic with other gear (response curve not public). I tried to use it with REW to find out (un-convoluting the resulting curves), but I can't, because it is a mic, and REW works only with line-in I could probably use CARMA, though (mental note!).
The USB stick easily slides out of the plinth when holding the assembly by the mic (I know everyone will do it, although it is not supposed to be done). A USB plug with screws would be a nice solution. It is not a downside, though.
No linux support.
Print out only in black and white, which should be improved in a new release.
10. A practical example: my setup
This section has little to do with the tool itself, but I know you want to look at some graphs
This is my former room response (taken with REW):
Fig. 1. Black, purple and green curves have -5dB, 0dB and +5dB respectively in the subwoofer gain. The crossover at 80Hz is noticeableYou can see that I have two main modes and the bass at 80Hz is reduced.
After leaving it like that for a while, I felt I could make it better, and I started thinking about my possibilities, after I learnt so much about the parameters to be adjusted in my first "encounter" with "room tuning". The obvious answer was an equalizer, but I wanted to exhaust all possibilities before (BTW, it is always better to avoid EQ if you can).
10.2. The Idea
I pondered that a lower crossover, at 40Hz, combined with a phase adjustment, could take care of the 55Hz mode, leaving the PEQ of my SVS for the mode at 31Hz. I would sacrifice headroom and a little bit of midrange clarity, as compared to an 80Hz crossover. But I never use the headroom anyway, and if the subwoofer is not well integrated, I will not use it for stereo either, so the midrange clarity should be equal or better than running the mains full range.
10.3. The measurements
I really wanted to try “The idea”... But I got shivers when I only thought about setting up REW again... Now, with the room analyzer, I even enjoyed it!
And here is the result:
Fig. 2. Improved response thanks to the optimized settings. 60dB (green) and 50dB (blue) curves shown. The Room Analyzer made it easier and faster than REW. On the top right corner, the time response is represented (double click for switching between time response and frequency response). Note also the window with EQ suggestions (editable), which can be simulated in a second measurement.The time response shows nasty resonances that last longer than 100ms: 16, 31, 63, 125.... See the pattern? And one at about 80Hz too. Even though they are not peaks in the response!
I still have the nasty resonances, but their level has decreased a lot and I have a more even response. My only trouble now (besides the longer decay times, which I can't solve) is the 125Hz region, quite enhanced. I can hear it, too.
A big advantage of this setup is that even in direct mode (no bass management for the main speakers), the response is even, since the speakers do not output much below 40Hz anyway. It is not as good, but enjoyable at least.
The RTA also looks quite nice:
Fig. 3. The green line shows the RTA. The blue bars show the noise nevel when I measured. A table below shows the "reference level" (average level) and deviations from it at each octave (it is called octave, right? ).
And I know you are waiting for this, so here you are:
- Darla taps the tank
Fig. 4. Darla taps the tank. This was about 15dB below reference level. Note the amount of bass at 25Hz. Note also that the dB scale is not that of Fig. 3.
- Tripod comes out of the ground
Fig. 5. Tripod comes out of the ground. I turned the volume down considerably, since it was getting late. Otherwise, it would reach the dB level of "Darla taps the tank".
- Tripod beams
Fig. 6. Tripod beams. Same volume level as in Fig. 5. Note that, in all three figures, every other sound is under 70dB. Nasty .
This is a great tool, but I think there is still room for improvement to cater a broader range of users, specifically regarding the flexibility of some functions. Its strength (simplicity) is also its major weakness.
If at least the measurement data could be saved as txt and then read with Excel, I would give it 9/10, because it is great for taking measurements. But I give it 8/10 due to the basic display capabilities. For 10/10, it would need to go down to 5Hz and up to 20k (adjustable), display several curves and allow different sweeps (but then, it would be a different product, wouldn't it?). This is a very personal evaluation, though, and the novice will find that the simplicity is all that matters.
At 230 euro (list price), I cannot judge if it is cheap or expensive because I am not aware of similar commercial solutions. But compare a Velodyne SMS-1 with the Room Analyzer+BFD, and the latter is way cheaper. Note also that the most basic SPL meter already costs 40 euro, and a decent one maybe twice that. You do not need to buy this if you have the Room Analyzer, so take it into account.
I only know a free software(REW) which I use with a regular, cheap SPL meter. REW is much more difficult to adjust/manage for the average user. I had my trouble with it (you can see it in my thread at AVforums), and I am a physicist... Another free software I recently discovered is CARMA, from Audionet. This is again very easy to use, and works with a mic-in, but displays the whole frequency range (20Hz-20kHz) and does not have all the perks.
I find the Room Analyzer very helpful, but I miss in XTZ's palette a standalone PEQ. I know their subs have it built-in, but I thought that there is no point buying the Analyzer if I have a subwoofer and no PEQ... XTZ could even make a bundle and compete with Velodyne's SMS-1. It is also known that SVS is working in a similar system based in Audyssey. Since XTZ's subs already have it built-in, offering a standalone PEQ shouldn't be such a big problem. And it has the advantage of a direct link with the software! BTW, I think they should find a different protocol for the data
transmission, RS232 is nice, but not everybody has a port at home (think about laptops...). USB to RS232 must be available and cheap...
I believe it is good knowing which problems your room have (Room Analyzer), but it is better to offer also a possibility to solve them (PEQ). XTZ has told me they are thinking about it.
Some interesting side notes I took while working on this:
A.1. By mistake, i made a measurement in Dolby ProLogic II mode, and it was also an interesting response, because the 55Hz peak was bigger, but the dip at 190Hz disappeared.
A.2. I found strange that my AV receiver in "5.1 stereo" mode only sends a signal between 120Hz and 8kHz to the center loudspeaker (I connected the center speaker to the left channel in order to measure its response properly).
A.3. I am liking this subwoofer/loudspeaker world so much, I start considering doing it for a living
I would like to thank Russ.will, who has proof-read the whole text and helped me improving my English and expressing better what I wanted to say (if you find any typos, grammar mistakes, etc... It is all his fault ).
Final note: if you are interested, XTZ have setup a powerbuy for the Room Analyzer here.