Learning about subwoofer specs

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shadyJ

Speaker of the House
Staff member
Hi Shady! It was your comment before that spurred me on to ask this. ;) How do I sift the chaff, or better yet, How do I recognize there is chaff to sift?
If you are asking how to tell if a sub is a good performer just from looking at measurements, there are a number of factors involved. One factor is cost; you can't expect a cheap subwoofer to perform as well as an expensive one, so the question then becomes how well does it perform for its price point? Another factor is size: small subs just can not match a large sub in terms of performance, but many people can not accommodate a large subwoofer, so the question is, how well does this sub perform for its size? Another factor is room size: the smaller the room, the more room gain will had, where sound pressure is increased from being contained in a smaller space, so the question then becomes will subwoofer X be able to meet your desired SPL in that space?

With that all being said, there are some things to look for in measurements to gauge the performance of a subwoofer. Here are some desirable subwoofer traits:
  • Flat frequency response
  • Dynamic range/ max SPL ability. This is a very relative metric, but I will say that, in terms of CEA-2010 measurements, 100 - 105 dB is fine, 105 - 110 dB is very good, 110 - 115 dB is excellent, and 115dB + is beastmaster mode. But this is relative to price, size, and frequency. For example, if a large, $10k subwoofer could only do 115 dB at 50 Hz, that is sadness, but if a medium sized $1k sub does 115dB at 50 Hz, that would be really good.
  • Low distortion. This is relative as well, with different factors affecting what should be looked for, but generally speaking, I would say if THD is under 10%, that is very good, and if it is under 5%, that is excellent. But there are a lot of factors involved in what makes one measurement better than another. The SPL of the distortion measurement has to be considered as well as the frequency, and even the harmonic composition of the distortion.
  • Low-frequency Extension. The importance of this is again very relative to personal desires, but if you want a sub that digs down to 16 Hz without problems, you should be looking for a sub that has a response that extends down to 16 Hz without rolling off too much by that point.
  • High-frequency extension. The importance of this is also very relative, but it's nice to have, and it is something I look for. Some subs roll off the high end after 80 or 100 Hz or so. I'd rather have a subwoofer extend a bit higher than that, even if that high frequency extension may not ever be used.
  • Time domain problems. This can be seen in the group delay measurements. If the sub manages to exceed 1.5 cycles above 40 Hz over a broad region, that would be cause for concern. I have never had a subwoofer that performed very badly. No competently built sub is likely to have a serious problem here.
  • Compression behavior. Steve81 touched on this, but if a subwoofer's response shape doesn't hold for much of its dynamic range, it will change the character of the bass depending on loudness level, and that is not a good thing. The less change of a subwoofer's response thoughout its dynamic range, the better.
There is a starting point, but these are very broad outlines. There are different performance targets for different needs, so if a subwoofer doesn't do well in one of these response, that doesn't necessarily that subwoofer is bad. Performance metrics have to be viewed in context.
 
ryanosaur

ryanosaur

Audioholic Overlord
If you are asking how to tell if a sub is a good performer just from looking at measurements, there are a number of factors involved. One factor is cost; you can't expect a cheap subwoofer to perform as well as an expensive one, so the question then becomes how well does it perform for its price point? Another factor is size: small subs just can not match a large sub in terms of performance, but many people can not accommodate a large subwoofer, so the question is, how well does this sub perform for its size? Another factor is room size: the smaller the room, the more room gain will had, where sound pressure is increased from being contained in a smaller space, so the question then becomes will subwoofer X be able to meet your desired SPL in that space?

With that all being said, there are some things to look for in measurements to gauge the performance of a subwoofer. Here are some desirable subwoofer traits:
  • Flat frequency response
  • Dynamic range/ max SPL ability. This is a very relative metric, but I will say that, in terms of CEA-2010 measurements, 100 - 105 dB is fine, 105 - 110 dB is very good, 110 - 115 dB is excellent, and 115dB + is beastmaster mode. But this is relative to price, size, and frequency. For example, if a large, $10k subwoofer could only do 115 dB at 50 Hz, that is sadness, but if a medium sized $1k sub does 115dB at 50 Hz, that would be really good.
  • Low distortion. This is relative as well, with different factors affecting what should be looked for, but generally speaking, I would say if THD is under 10%, that is very good, and if it is under 5%, that is excellent. But there are a lot of factors involved in what makes one measurement better than another. The SPL of the distortion measurement has to be considered as well as the frequency, and even the harmonic composition of the distortion.
  • Low-frequency Extension. The importance of this is again very relative to personal desires, but if you want a sub that digs down to 16 Hz without problems, you should be looking for a sub that has a response that extends down to 16 Hz without rolling off too much by that point.
  • High-frequency extension. The importance of this is also very relative, but it's nice to have, and it is something I look for. Some subs roll off the high end after 80 or 100 Hz or so. I'd rather have a subwoofer extend a bit higher than that, even if that high frequency extension may not ever be used.
  • Time domain problems. This can be seen in the group delay measurements. If the sub manages to exceed 1.5 cycles above 40 Hz over a broad region, that would be cause for concern. I have never had a subwoofer that performed very badly. No competently built sub is likely to have a serious problem here.
  • Compression behavior. Steve81 touched on this, but if a subwoofer's response shape doesn't hold for much of its dynamic range, it will change the character of the bass depending on loudness level, and that is not a good thing. The less change of a subwoofer's response thoughout its dynamic range, the better.
There is a starting point, but these are very broad outlines. There are different performance targets for different needs, so if a subwoofer doesn't do well in one of these response, that doesn't necessarily that subwoofer is bad. Performance metrics have to be viewed in context.
Very well stated, Shady. Thank you!
 
Steve81

Steve81

Audioholics Five-0
Truth be told, I'm not looking for an internal audio massage, or in quest of the mythical brown note...I'm dealing with 8312.5'3 room. And I do want 16Hz extension for pipe organ reproduction.
What kind of budget are we talking about?
 
Darenwh

Darenwh

Audioholic
Just my 2 cents, for what it's worth, probably a nickle less than that... The most likely reason not to bother with the sensitivity when referring to modern subs is that they are all powered by their own amplifier. Lets say you want your subs to play at a set volume based on the normal listening volume you use for the front speakers and you have very sensitive front speakers. If you think you need a sensitive sub to match it you would be wrong. Even if the sub you have is less sensitive all you need to do is adjust your amp section (turn the gain up) and you will have it performing just fine with the sensitive speakers being driven by your receiver. Now, if you have primary speakers that are not very sensitive and you try to run them on a receiver that does not have the power to run them at the level you are wanting to play them at then you are # out of luck until you can upgrade either the speakers or the receiver. In the end, the sensitivity of the sub is not really as much of an issue but the sensitivity of your other speakers can be.
 
ryanosaur

ryanosaur

Audioholic Overlord
What kind of budget are we talking about?
For subs, I'm hoping to keep it around $2K for duals, $3k on the high end. Point towards Hsu VTF15Hmk2 for coming in under budget. I really like the Outlaw X-13s and they have been my frontrunner thus far. Been impressed with SVS, but one of their reps suggested the 4000s (pb/pc) might not be the best match for my room, and the pb16u's are def over budget. Monoprice Monolith15" is impressive, but is that extra little bit of output a worthwhile trade off for poor customer service and the other intangibles?
Been familiarizing myself with Rhythmik and PSA... two FV15HPs could work, might be willing to stretch out for the FV18. Likewise, the V1510s or V1810s seem like they should fit my needs/wants.
I'm not necessarily opposed to ordering a single sub at my stated budget now and following up later next year, but would prefer to bring it all the way home in one fell swoop.
Id love to hear your thoughts on these, please. The ones I'm most familiar with, I'm comfortable that they are good little boxes. ;) The Rhythmik and PSAs I don't know very well yet. Perhaps you have some insight that might help me reframe my search?
Oh, usage is say 80/20 Music to HT.
Thank you!
 
Steve81

Steve81

Audioholics Five-0
Id love to hear your thoughts on these, please.
My initial thought had been the FV18, with a pair of the Rev 1 models running at 3,043.50 shipped to the continental US. Slightly overbudget, but not enough that you'd have to eat nothing but ramen for the next six months to compensate.

The tests done over at data-bass look nothing short of superb. Even with all three ports open to minimize chuffing / port compression, it's got enough extension and low end output for your purposes; distortion and compression are quite low up through the 110dB drive sweep, which is impressive. I also tend to prefer a cabinet that isn't particularly deep, both to keep the footprint limited and because it helps to mitigate some effects of placing the sub in a room (cancellation notches due to the Allison effect). Rythmik subs also have a decent amount of tuning options built in, which is always nice.
 
ryanosaur

ryanosaur

Audioholic Overlord
My initial thought had been the FV18, with a pair of the Rev 1 models running at 3,043.50 shipped to the continental US. Slightly overbudget, but not enough that you'd have to eat nothing but ramen for the next six months to compensate.

The tests done over at data-bass look nothing short of superb. Even with all three ports open to minimize chuffing / port compression, it's got enough extension and low end output for your purposes; distortion and compression are quite low up through the 110dB drive sweep, which is impressive. I also tend to prefer a cabinet that isn't particularly deep, both to keep the footprint limited and because it helps to mitigate some effects of placing the sub in a room (cancellation notches due to the Allison effect). Rythmik subs also have a decent amount of tuning options built in, which is always nice.
Couple questions please as I dig deeper into the Rythmik line:
For the FV18 rev2, with 4" ports: If I understand correctly, the larger the port, the more air can move, thus limiting chuffing and slightly increasing output? Please advise. Is there anything else different in the FV18.2 that I'm missing? (Right now, 2x FV18.2 = $1599ea. and if I pick up at the frieght terminal, $3098 total vs $2938 for the rev.1s)
Then, if I'm reading charts correctly when comparing the Frequency Response of the FV18 to the FV15HP, the 18 is outputting at roughly 12-13dB more than the 15, correct?

Thanks Steve!
 
Steve81

Steve81

Audioholics Five-0
For the FV18 rev2, with 4" ports: If I understand correctly, the larger the port, the more air can move, thus limiting chuffing and slightly increasing output? Please advise.
Yes, the larger port would limit chuffing, and be less susceptible to port compression, marginally improving output. It's probably a more valuable upgrade for those who want to plug a port for deeper extension than the native 16Hz tune.


Is there anything else different in the FV18.2 that I'm missing?
Not that I know of, though it wouldn't hurt to ask them.

Then, if I'm reading charts correctly when comparing the Frequency Response of the FV18 to the FV15HP, the 18 is outputting at roughly 12-13dB more than the 15, correct?
Nothing quite that extreme (a 12dB increase would be equivalent to a stack of 4 FV15HP's). Output capabilities are largely similar, except at the low end (25Hz and below) where the FV18 has a few dB more grunt. Rythmik's comparison is limited to 20Hz, but it reckons the FV18 has a 3dB advantage over the FV15HP there.
 
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shadyJ

Speaker of the House
Staff member
Yes, the larger port would limit chuffing, and be less susceptible to port compression, marginally improving output. It's probably a more valuable upgrade for those who want to plug a port for deeper extension than the native 16Hz tune.




Not that I know of, though it wouldn't hurt to ask them.



Nothing quite that extreme (a 12dB increase would be equivalent to a stack of 4 FV15HP's). Output capabilities are largely similar, except at the low end (25Hz and below) where the FV18 has a few dB more grunt. Rythmik's comparison is limited to 20Hz, but it reckons the FV18 has a 3dB advantage over the FV15HP there.
The FV18 does have less distortion than the FV15HP, but the FV15HP's distortion wasn't bad. The only real advantage that the FV18 has over the FV15HP is more deep bass output, from what I can see.
 
ryanosaur

ryanosaur

Audioholic Overlord
Yes, the larger port would limit chuffing, and be less susceptible to port compression, marginally improving output. It's probably a more valuable upgrade for those who want to plug a port for deeper extension than the native 16Hz tune.
See, I AM learning!
Not that I know of, though it wouldn't hurt to as
I did. There are no other differences. The guy at Rythmik said the inner port tubes are also not changed, if I understood correctly, just the front 6".
Nothing quite that extreme (a 12dB increase would be equivalent to a stack of 4 FV15HP's). Output capabilities are largely similar, except at the low end (25Hz and below) where the FV18 has a few dB more grunt. Rythmik's comparison is limited to 20Hz, but it reckons the FV18 has a 3dB advantage over the FV15HP there.
OK, teachable moment time, please:
As I look at the DataBass site for the FV18, comparable chart, selecting for the FV15HP 2port option, I see a very comparable graph for the CEA max burst test. Then scrolling down to the basic response graph, the two subs performances are separated by 12-13dB SPL with the larger FV18 on top. I understand the frequency response along the x-axis, but what accounts for the SPL difference along the y-axis, please?

Thank you!
 
ryanosaur

ryanosaur

Audioholic Overlord
The FV18 does have less distortion than the FV15HP, but the FV15HP's distortion wasn't bad. The only real advantage that the FV18 has over the FV15HP is more deep bass output, from what I can see.
And If I understood, the other key difference seems that the FV15HP has less upper frequency range too, correct? Starting to roll off between 80-100Hz to level out again, 10dB SPL lower at ~150Hz? Again, maybe I'm not quite grokking the SPL part, as per my question to Steve81 moments ago. :)
 
S

snakeeyes

Audioholic Ninja
If they are releasing a newer version of the FV18 with a larger port this soon, you can bet it’s an important improvement they made on the original one. :)
 
Steve81

Steve81

Audioholics Five-0
OK, teachable moment time, please:
As I look at the DataBass site for the FV18, comparable chart, selecting for the FV15HP 2port option, I see a very comparable graph for the CEA max burst test. Then scrolling down to the basic response graph, the two subs performances are separated by 12-13dB SPL with the larger FV18 on top. I understand the frequency response along the x-axis, but what accounts for the SPL difference along the y-axis, please?

Thank you!
Just ease of viewing to compare the base response curves. The CEA comparison and
Max Long Term Output graphs show the differences in output capability.
 
ryanosaur

ryanosaur

Audioholic Overlord
If they are releasing a newer version of the FV18 with a larger port this soon, you can bet it’s an important improvement they made on the original one. :)
How long has the FV18 been on the market?
 
ryanosaur

ryanosaur

Audioholic Overlord
Just ease of viewing to compare the base response curves. The CEA comparison and
Max Long Term Output graphs show the differences in output capability.
Cool. Confusing to see it like that, but thanks for pointing out the output on the other two graphs!
I should ask, then, does the y axis on a basic response chart have any importance than illustrating the amount of variation in bumps, dips and rolloff?
 
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shadyJ

Speaker of the House
Staff member
How long has the FV18 been on the market?
Not very long, that is a newish product. The FV15HP has been on the market for a long time though. It has been regarded as a top performer for many years now.
 
Steve81

Steve81

Audioholics Five-0
And If I understood, the other key difference seems that the FV15HP has less upper frequency range too, correct?
Sort of. Your interpretation of the graph is correct, but the observed roll off was a function of the amplifier. They’ve since been updated to include a LFE mode/input that doesn’t filter the top end (that particular FV15HP was measured ~7 years ago)..
 
S

shadyJ

Speaker of the House
Staff member
Cool. Confusing to see it like that, but thanks for pointing out the output on the other two graphs!
I should ask, then, does the y axis on a basic response chart have any importance than illustrating the amount of variation in bumps, dips and rolloff?
On a basic response chart, the Y axis is there just to show the shape of the response. Only on CEA-2010 graphs and long-term maximum output graphs does the Y axis also matter for SPL quantities.
 
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shadyJ

Speaker of the House
Staff member
I also tend to prefer a cabinet that isn't particularly deep, both to keep the footprint limited and because it helps to mitigate some effects of placing the sub in a room (cancellation notches due to the Allison effect). Rythmik subs also have a decent amount of tuning options built in, which is always nice.
Allison Effect boundary cancellations are not so much a factor in subwoofer band frequencies. The wavelengths are mostly too long for phase mismatch to really screw up the response at listening position. They are more a factor for mid-bass frequencies, and are especially a big deal in ground bounce from elevated woofers. As you know, a good way to address it is to have the bass drivers be placed very close to the ground and wall surfaces, but of course, that brings its own set of problems.
 
Steve81

Steve81

Audioholics Five-0
Allison Effect boundary cancellations are not so much a factor in subwoofer band frequencies.
It would indeed take quite the cabinet to have a problem even at 80Hz (~42" including space for cabling). OTOH, its helpful for a sub to maintain a reasonably smooth response a fair bit above its passband to ease integration with the other speakers. A larger cabinet like the aforementioned PB4000 (again, plus some distance for cabling) would have problems around 100Hz, which isn't terribly desirable IMHO.
 
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