Earthquake Sound CP8 Subwoofer Review and In-Room Measurements
This is a brief review and some measurements of the Earthquake Sound CP8 "Couch Potato." This is a $250 subwoofer from Amazon that seems to perform far above its price point. While it's NOT the ideal subwoofer for cinema, it may be a great subwoofer for music for extended the frequency response of small bookshelf speakers at 76-86 dB. I thought about sending one to @amirm for measurement, but couldn't justify the shipping costs -- and you'll see why I didn't want to risk going dual subs.
Testing subwoofers can be tricky, so I ended up trying it in 4 different environments. I used a UMIK-1 that was disassembled to disable the +18 dB mic gain to allow me to record higher SPLs without clipping.
Room #1: Music Room (3m)
Here, you can see why it's impressive. This is in room #1 with a Bluesound Node Icon running Dirac. It's a giant open space, but the sub gets some wall reinforcement. I ran Dirac with the crossover at 40Hz and ran two sweeps. The magenta is what I get from the system, and then I unplugged the sub and ran the same sweep, getting me the green curve. This shows me what the subwoofer is adding. You can see that it still delivers 85 dB at 24 Hz.
Under CTA-2010A, for a Fundamental of 0 dB, you're allowed to have distortion that is 2nd order = -10 dB, 3rd order = -20 dB, 4th order = -25 dB, 5th order = -35 dB, 6th order = -45 dB
You can see that it passes the CTA-2010A threshold as low as 26 Hz. The region around 30-40Hz is definitely a lot higher in distortion, however the audibility of high distortion is more forgiving. If you were configuring this to only run for a 75 dB setup, it would let you be flat to 21.7 Hz. This is what Dirac shows in its sweep.
In terms of subjective experience, it clearly adds the last octave musically. While it is possible to hear differences at lower distortion levels, the overall "I just want to listen" experience is enhanced tremendously by having the extra response down low. In terms of what the threshold of audibility is, it's sort of a loaded question.
CTA-2010A and CTA-2010B have some standards for a goal of distortion that can be used for measuring subwoofers.
There is plenty of data suggesting that you might be able to hear much lower distortion than CTA-2010A/B.
www.audioholics.com
There is also data suggesting that you can tolerate much higher levels of distortion than you might expect below 40 Hz.
www.axiomaudio.com
This paradox can be explained by "I can hear the difference between subwoofer A and subwoofer B" in terms of distortion as well as "High distortion bass is preferred to no bass at all with no subwoofer."
Room 2: Non-DSP'd measurements (2m)
So, I then moved the CP8 to a different room and used a Fosi ZD3 directly into the CP8. Using REW "check levels" I measured 105 dB and 85 dB conditions. The 105 dB sweep caused clipping of my UMIK-1, so I dropped it down to 102 dB
Again, the numbers are pretty good. If you look at the 102 dB distortion measurement, it passes the CTA-2010A threshold for distortion even for 20 Hz. One weakness of CTA-2010A is that it doesn't capture resonances, port noise, etc. A lot of stuff was moving around in my room with this sweep, but clearly an impressive result for a $250 subwoofer.
Room 3: Trinnov Room, Position 1: Rear Wall (7 ft)
In this room,
S1 = Power Sound Audio S1813M at the front of the room
S2 = Earthquake Sound Supernova Luminous LU-15 at the front of the room
S3 = Earthquake Sound CP8. I placed the CP8 at the rear of the room, port firing against the wall. The port is about 1 ft away from the wall and this point of the subwoofer is about 7 feet from the microphone. You can see that the Level C (dBSPL) is 107.6 dB. Remember that this is the SPL of Trinnov's proprietary MLS not what you'd get from a sweep, but the Trinnov mic is capable of handling >120 dBC. The bandwidth goes down to 17.6 Hz. The Trinnov chart is at 1/6 octave smoothing. I used a REL wireless sub transmitter which explains the latency.
Room 3: Trinnov Room, Position 2: Under sofa (<1 m)
Again, in this room,
S1 = Power Sound Audio S1813M at the front of the room
S2 = Earthquake Sound Supernova Luminous LU-15 at the front of the room
S3 = Earthquake Sound CP8. This time immediately underneat the sofa.
Here the SPL jumps up to 108.7 dB, but look at that horrible frequency response! It only goes down to 41 Hz if you don't have the benefit of room/wall gain. I had actually expected this "nearfield" sub to be even better since the distance would be reduced, however you can really see how dependent this sub is on room gain.
Subjective Impressions
The Earthquake Sound CP8 is pretty impressive for music. Taiko drums, and classic audiophile test tracks with nice drum beats like the "Hotel California" from Hell Freezes Over works well. Movies are hit-or-miss. Some movies like Tiger's Apprentice or Top Gun: Maverick are really enhanced by the CP8 whereas other movies like Oppenheimer completely sound anemic.
Most mini-subs are designed with high SPL capabilities for movies, and although subsonic performance is some of the most "fun" for movies, real-world LFE special effects need to deliver content that's in the 40-70Hz range. Power Sound Audio likes to showcase this graph:
And so an 8" sub that has no meaningful output below 35 Hz is still pretty good. The very original THX and TH Select specification just needed subwoofers to hit 35Hz. Only the modern THX Ultra2 and Dominus spec looks for 20 Hz output. With the Earthquake CP8, it has a duality to it. It has a lot of output at that 40-60 Hz range, but also can dip down into the 20's for music, as long as you're just looking to hit 20 Hz at 75 dB. The wildcard is how much distortion you can tolerate and how much room gain you'll get in your own room.
When I saw some of the results in Room 1, I was super excited. Moving the sub to Room 2 showed me the limitations of the single sub, and that's when I considered a pair of these CP8 to get another 3 dB of headroom. But the CP8's strength is its size. If you can tolerate a bigger enclosure, something more proven like the RSL 10" or 12" subwoofer makes a lot more sense. Finally, when I took measurements in Room 3, I realized that it's so unpredictable to know exactly how well this sub will perform in-room, that I opted not to get a second CP8. Moving the budget up to $500 also opens up options.
Nonetheless, I came away very impressed with the CP8 and encourage you to give it a try if you want another octave of extension for not a lot of money.
Lastly, the RCA outputs have a 70Hz high pass filter at a 5 db/octave slope. This should make integration easy if you're not using a WiiM or Dirac-enabled Bluesound streamer. The speaker level inputs are only "rated" to 10V input, which might not be enough. I did not test this feature.
This is a brief review and some measurements of the Earthquake Sound CP8 "Couch Potato." This is a $250 subwoofer from Amazon that seems to perform far above its price point. While it's NOT the ideal subwoofer for cinema, it may be a great subwoofer for music for extended the frequency response of small bookshelf speakers at 76-86 dB. I thought about sending one to @amirm for measurement, but couldn't justify the shipping costs -- and you'll see why I didn't want to risk going dual subs.
Testing subwoofers can be tricky, so I ended up trying it in 4 different environments. I used a UMIK-1 that was disassembled to disable the +18 dB mic gain to allow me to record higher SPLs without clipping.
Room #1: Music Room (3m)
Here, you can see why it's impressive. This is in room #1 with a Bluesound Node Icon running Dirac. It's a giant open space, but the sub gets some wall reinforcement. I ran Dirac with the crossover at 40Hz and ran two sweeps. The magenta is what I get from the system, and then I unplugged the sub and ran the same sweep, getting me the green curve. This shows me what the subwoofer is adding. You can see that it still delivers 85 dB at 24 Hz.
Under CTA-2010A, for a Fundamental of 0 dB, you're allowed to have distortion that is 2nd order = -10 dB, 3rd order = -20 dB, 4th order = -25 dB, 5th order = -35 dB, 6th order = -45 dB
You can see that it passes the CTA-2010A threshold as low as 26 Hz. The region around 30-40Hz is definitely a lot higher in distortion, however the audibility of high distortion is more forgiving. If you were configuring this to only run for a 75 dB setup, it would let you be flat to 21.7 Hz. This is what Dirac shows in its sweep.
In terms of subjective experience, it clearly adds the last octave musically. While it is possible to hear differences at lower distortion levels, the overall "I just want to listen" experience is enhanced tremendously by having the extra response down low. In terms of what the threshold of audibility is, it's sort of a loaded question.
CTA-2010A and CTA-2010B have some standards for a goal of distortion that can be used for measuring subwoofers.
There is plenty of data suggesting that you might be able to hear much lower distortion than CTA-2010A/B.
The Audibility of Distortion At Bass Frequencies
Want to know how well your sound system reproduces bass? We discuss the audibility of distortion in bass and ways bass reproduction in audio systems can fall short of of a listeners expectations.
www.audioholics.com
There is also data suggesting that you can tolerate much higher levels of distortion than you might expect below 40 Hz.
How Much Distortion Can We Hear With Music?
How much distortion can we hear with music? An experimental study at Axiom.
www.axiomaudio.com
This paradox can be explained by "I can hear the difference between subwoofer A and subwoofer B" in terms of distortion as well as "High distortion bass is preferred to no bass at all with no subwoofer."
Room 2: Non-DSP'd measurements (2m)
So, I then moved the CP8 to a different room and used a Fosi ZD3 directly into the CP8. Using REW "check levels" I measured 105 dB and 85 dB conditions. The 105 dB sweep caused clipping of my UMIK-1, so I dropped it down to 102 dB
Again, the numbers are pretty good. If you look at the 102 dB distortion measurement, it passes the CTA-2010A threshold for distortion even for 20 Hz. One weakness of CTA-2010A is that it doesn't capture resonances, port noise, etc. A lot of stuff was moving around in my room with this sweep, but clearly an impressive result for a $250 subwoofer.
Room 3: Trinnov Room, Position 1: Rear Wall (7 ft)
In this room,
S1 = Power Sound Audio S1813M at the front of the room
S2 = Earthquake Sound Supernova Luminous LU-15 at the front of the room
S3 = Earthquake Sound CP8. I placed the CP8 at the rear of the room, port firing against the wall. The port is about 1 ft away from the wall and this point of the subwoofer is about 7 feet from the microphone. You can see that the Level C (dBSPL) is 107.6 dB. Remember that this is the SPL of Trinnov's proprietary MLS not what you'd get from a sweep, but the Trinnov mic is capable of handling >120 dBC. The bandwidth goes down to 17.6 Hz. The Trinnov chart is at 1/6 octave smoothing. I used a REL wireless sub transmitter which explains the latency.
Room 3: Trinnov Room, Position 2: Under sofa (<1 m)
Again, in this room,
S1 = Power Sound Audio S1813M at the front of the room
S2 = Earthquake Sound Supernova Luminous LU-15 at the front of the room
S3 = Earthquake Sound CP8. This time immediately underneat the sofa.
Here the SPL jumps up to 108.7 dB, but look at that horrible frequency response! It only goes down to 41 Hz if you don't have the benefit of room/wall gain. I had actually expected this "nearfield" sub to be even better since the distance would be reduced, however you can really see how dependent this sub is on room gain.
Subjective Impressions
The Earthquake Sound CP8 is pretty impressive for music. Taiko drums, and classic audiophile test tracks with nice drum beats like the "Hotel California" from Hell Freezes Over works well. Movies are hit-or-miss. Some movies like Tiger's Apprentice or Top Gun: Maverick are really enhanced by the CP8 whereas other movies like Oppenheimer completely sound anemic.
Most mini-subs are designed with high SPL capabilities for movies, and although subsonic performance is some of the most "fun" for movies, real-world LFE special effects need to deliver content that's in the 40-70Hz range. Power Sound Audio likes to showcase this graph:
And so an 8" sub that has no meaningful output below 35 Hz is still pretty good. The very original THX and TH Select specification just needed subwoofers to hit 35Hz. Only the modern THX Ultra2 and Dominus spec looks for 20 Hz output. With the Earthquake CP8, it has a duality to it. It has a lot of output at that 40-60 Hz range, but also can dip down into the 20's for music, as long as you're just looking to hit 20 Hz at 75 dB. The wildcard is how much distortion you can tolerate and how much room gain you'll get in your own room.
When I saw some of the results in Room 1, I was super excited. Moving the sub to Room 2 showed me the limitations of the single sub, and that's when I considered a pair of these CP8 to get another 3 dB of headroom. But the CP8's strength is its size. If you can tolerate a bigger enclosure, something more proven like the RSL 10" or 12" subwoofer makes a lot more sense. Finally, when I took measurements in Room 3, I realized that it's so unpredictable to know exactly how well this sub will perform in-room, that I opted not to get a second CP8. Moving the budget up to $500 also opens up options.
Nonetheless, I came away very impressed with the CP8 and encourage you to give it a try if you want another octave of extension for not a lot of money.
Lastly, the RCA outputs have a 70Hz high pass filter at a 5 db/octave slope. This should make integration easy if you're not using a WiiM or Dirac-enabled Bluesound streamer. The speaker level inputs are only "rated" to 10V input, which might not be enough. I did not test this feature.
