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The original was posted on /r/hometheater by /u/CalvinHobbesN7 on 2024-01-09 04:23:22+00:00.
Three weeks ago I wrote a post asking people for their opinion on running dual subs. I had the opportunity to buy a second matching subwoofer from a local guy at a very favorable price. I went for it! Because of the low price, I also opted to purchase a MiniDSP UMIK-1 to calibrate them properly for volume level and delay using REW and the MiniDSP 2x4 HD (which I already own for BassEQ). The following are the raw measurements of my previous single sub, the raw dual sub (calibrated for volume and delay only), and the calibrated dual sub via DIRAC Live in my Onkyo TX-NR7100.
The subwoofers are both SVS model PB-1000. These are not the "Pro" versions that are available on the market today. Still great subs though!
Before presenting the results, I just want to thank the YouTube channel, Home Theater Gamer, who's videos were astronomically helpful during this process. He has a 4-part series:
While great videos to get started, I want to add an additional note to his videos.
- On Windows, simply visit Control Panel / Sound / Select your output / Configure. From here, you can select what kind of output you want to send to your receiver. I opted for 5.1, and was able to select and output directly to the LFE track.
- Using "Direct" listening mode on my Onkyo receiver disabled the existing Dirac Live calibration, and used only the distance and level adjustments. The volume was set accordingly from there. NOTE: This leaves the LPF of LFE setting left on, disable it! (generally found in "Crossover" settings)
Now, on to my measured results.
You will notice three lines in each measurement chart. These are three seating positions on my straight 4-cushion couch, being the CENTER, the LEFT SEAT, and the RIGHT SEAT. The X axis is Hz, and Db is on the Y.
**Update: The same graphs have been updated from their original upload with new colors for improved readability against a dark backdrop**
Measurements - Single Sub (Front Left of Room) (RAW)
These measurements are taken from a single sub, in the front left corner of my room. This location was previously selected using the subwoofer crawl method (More on that in a future post). This measurement was taken RAW, with only level calibration utilized. No Digital EQ has been applied.
Measurements – Dual Sub (Front Left + Back Right of Room)
These measurements are taken from a dual sub configuration - the Front Left and Back Right corners of the room. This measurement is taken with both level and delay calibration for time alignment between the two subs in the MiniDSP. No Digital EQ has been applied.
As can be seen in these raw measurements, having dual subs levels out the response curve beautifully across every seat. Tones haven't only been amplified, they've been balanced out. My theater has a natural null from 70-140 Hz with a single sub in the front left corner. Having dual subs in opposite corners has raised and flattened those tones to elimiate the null and match the levels fairly consistently across the spectrum. With a crossover of 60-80Hz for my speakers the issues above 120Hz will be nonexistent.
The consistency from seat to seat has improved dramatically as well, even before the application of a Digital EQ. Which, speaking of a Digital EQ, now it's time to put DIRAC to work on my Onkyo receiver. Lets look at the results.
Measurements - Single Sub (Front Left) with DIRAC Digital EQ from my receiver
Measurements - Dual Sub (Front Left + Back Right) with DIRAC Digital EQ from my Receiver
For a single sub, this isn't too bad! Dirac did a very decent job leveling out the response curve, and each seat, while varying a bit, are still fairly consistent with this EQ. However, the dual sub configuration is much tighter aligned! It's great to know that all the main seats in the theater are getting a similar bass experience (within reasonable variation). Regarding the null at 130hz in the left seat with dual sub, no room can be perfect, but it should be largely inaudible due to the crossover. Other than that things look great.
You may wonder why I opted to use DIRAC Live to calibrate instead of the MiniDSP as others would assume. The reason is because of my other speakers. It's simply easier to run DIRAC and let it do its magic. In the future, as I have been having fun with this UMIK-1 calibration mic, I'll be writing a bit about DIRAC specifically. My next adventure will be to add a house curve using DIRAC manual adjustments in my receiver.
Evaluating my experience - Beyond the Measurements
Without a doubt, adding a second subwoofer has greatly enhanced my theater! After having friends and family sit in the seats and watch, it was collectively agreed that the bass felt deeper, however, it was also collectively agreed that the bass wasn't necessarily louder either. We watched a few different scenes to evaluate it:
- Frozen II - Earth Giants and Dam Burst (1:17:00)
- Master and Commander - First Naval Battle (with BassEQ) (0:06:00)
- Top Gun: Maverick - Final Assault (with BassEQ) (1:30:00)
That was the amazing thing though - it didn't feel like the bass was overpowering each scene of the movie, it was simply more present. After all, the subwoofers and the total bass level are calibrated to match with the other speakers. It's difficult to describe, but despite not being "louder" than the other channels, we now have more bass.
One significant thing to note is that the UMIK-1 microphone is measuring in mono. It can't record a stereo experience. Having dual subs in two opposite corners of the room made the source of the bass simply disappear into the room entirely. While it was difficult to pinpoint before with a single sub, it was impossible after the addition. The bass is everywhere, all at once.
I have been absolutely converted to multi-sub. My system went from sounding great, to sounding incredible.
Analysis of all 9.2 channels in the theater (Dual Sub - DIRAC). A crossover is applied for each speaker, which is the reason all speakers are showing a great response at 20Hz.
Speaking of opposite corners, lets segway into a fun experiment.
Bonus Material - Dual Subs placed in the same location (Spoiler: It was bad!)
Here is a chart with an amusing and unusual setup - stacking the two subwoofers on top of each other in the front left of the room, where I previously had one. My father was curious about my desire to run a 50ft cable to the back of my theater room and wondered "why not just put them in the same place? the cable is already there!" So, when you have a calibration microphone, why not experiment? I was curious too - but the results speak for themselves in case you were wondering if you could do the same.
Dual Subs, stacked on top of each other, in the Front Left corner of the room. If you have two subwoofers, this is likely a TERRIBLE position in your room. Both calibrated individually for level, with no delay difference.
As we can see, the listening experience has declined severely from seat to seat, with one listener experiencing severe nulls while another seat just a few feet away experiences a peak.
I hope this has been informative, and I'd like to thank you for reading.
