As Tom seems to have cleared up quite well, a lot of comments in the AH review for the XV-15 and posted here are getting taken out of context and blown way out of proportion. Did the XV-15 exhibit a little port noise during the outdoor tests and with Pulse in the HT? Yes. Is this one of the few negative comments I could make about what this sub delivers for the price point it is at? Yes. Some of the comments here seem to give the impression that the XV-15 port is just chuffing left and right and is whistling Dixie whenever you are watching the nightly news. Pulse is incredibly demanding with a sustained 16-18Hz signal at high level with little other content in the soundtrack to mask any distress noises from the sub. It makes the majority of subs wilt completely when attempting to play it back at high level. This is also right in the port tuning range of a lot of vented commercial HT subs including the XV-15 so it produces chuffing when 99% of other tracks don't. In reality the test signals used for the outdoor measurements are absolutely worst case scenario. (Outdoors, no masking content from other speakers, no boundary reinforcement, pure test signals, sub driven to its very limits) Every single vented sub I have ever used will produce some port artifacts if pushed hard enough near tuning under these conditions. All of them. Some are better than others certainly. At the end of the day every ported sub mentioned in this thread will produce these noises to one degree or another if subjected to worst case scenario test signals at vent tuning. Part of my testing regimen is centered around identifying and quantifying the absolute limits of a system and its behavior when pushed there in a very unflattering environment. The typical use that the product might see is much much less demanding.
Bill have you even read what the testing procedures I use are?
It certainly seems like you haven't.
CEA-2010 specifically is for recording maximum short term output over a specified 1/3rd octave centered range and does not limit at a 10% THD threshold but is instead based on individual thresholds for each harmonic. The higher the harmonic the less distortion is allowed. The 2nd harmonic being largely inoffensive to the ear is allowed to be very high in amplitude compared to the fundamental where as the much more objectionable 5th harmonic is only allowed to be a fraction of the strength of the 2nd comparatively. The 2nd-9th harmonics and beyond are recorded. I know of no pro sound companies using this to report actual measured short term output data instead of the calculated sensitivity + peak power calculation which is common and allows room for a LOT of fudging. I wish some of them would take this up but I suspect that the reason they do not is because most looking at the specs to compare systems will not know the difference when looking at a claimed figure and an actual measurement and will assume the two are equal which will make the much higher claimed figure look better.
2m measurements are far enough away to allow most sub systems to integrate the various radiators output "enough" and to keep the effects from the cabinet faces on the output down somewhat. However there are still some differences of up to 2dB depending on cab size, geometry and orientation depending on how the cab is oriented relative to the mic. This is why I try every sub in a couple of orientations unless it is radiating from a single face. The XV-15 was tried with the bottom plate faced towards the mic but it did not significantly change the reading from normal downfiring. I did not remove the base plate because I felt it would be going a little too far in order to squeek out another dB or so and Tom did not mention it until later when we compared my measured results against their internal ones. I will add that this extra 1-1.5dB or so will show up in room because of boundary loading of the total output versus an unloaded condition with measurements taken from a single point in space. Please read the article on measuring dual opposed subs on DB. Anyway this is why it was mentioned in the review. Abnormally large cabs such as horn subs and cabs with drivers, PR
's or vents on multiple faces of the enclosure will show some response differences by rotating them at a distance of 2m. Some of them will even show a notable difference >1dB at 4m. In those cases it is a matter of picking the orientation that is "best" and rolling with it. Again most systems will have a 10m measurement to also compare to.
2m measurements also allow a better SNR in the outdoor measurement than a further distance which can often be a problem at LF's. Also it conveniently is roughly equivalent to a 1m anechoic measurement. Bill you mentioned Danley Labs and measuring at 10m distance. As far as I can tell they measure only 100w (28.3v actually regardless of impedance) sensitivity and the basic FR and phase at 10m for their cabs. You may have not known this but I measure every DIY and passive sub cab sensitivity at both 1w/1m and at 100w/10m the same as Danley does and also show the comparison of the 2. I also have response measurements at known input voltages at 2m and 4m. The rest of the tests are done at 2m as standard but I have the 10m measurements listed for easy comparison with the 2m ones so you can make an easy determination of how a 10m measurement would differ from a 2m one. Additionally I also do the CEA-2010 burst tests for maximum THD limited output, long term output compression and output by driving the cabs progressively harder until into clear compression and or showing signs of distress, distortion is shown at these same drive levels, etc...I even do high power impedance testing occasionally. Most commercial subs are internally powered so there is no reason for the impedance testing or sensitivity testing.
The reason that all tests are not done at 10m is simple. Firstly your SNR degrades 20dB by going from 1m to 10m (14dB from 2m to 10m) and this causes issues with accuracy especially in the deep bass unless the drive levels are significantly higher. I test everything from small commercial 8" sealed subs to massive horn subs for industrial type apps. At 10m most commercial subs simply don't have enough output headroom to get the output up out of the background noise floor. Again you lose 20dB of level at the mic element by moving it back 10x the distance however the background noise will still be the same level. So if the little 8" sub is producing 105dB at 40Hz at 2m, near maximum output, its level has dropped to just 91dB by 10m and that is with it being flogged for all it is worth. On the other hand my ACO Pacific mic rig and soundcard clip at about 140dB output from the speaker so I limit the input to about 135dB or so to ensure that the signal chain is not causing artifacts itself. With some of the big DIY or pro sound cabs this necessitates moving the measurement back to a 4m or even 10m distance to gain back some headroom in the signal chain for the CEA-2010 tests as they do start to approach 135-140dB at 2m. These longer distance measurements are then back calculated to a 2m result for easy comparison. 2m (and yes 4m) results are a good compromise of integration of the output from the cab and getting out of nearfield effects and maintaining decent SNR in the measurement for less powerful systems.