sealed vs vented subwoofers

Do the sealed subs produce a higher quality tighter controlled bass vs a more sloppy reverberating type of LFE out of the vented types?

Yes - just like most speakers - when a vent is used to extend the bass of a small box it increases the group delay and you lose accuracy. What most people are not aware of is that this ruins the lower midrange because a ported sub will "mask" other sounds that you would normally be able to hear.
(this can affect sounds several octaves higher than the sub and it is due to the way hearing works)

Compare the same sub from HT Shack Subwoofer Tests sealed versus ported.

Although the ported sub plays louder with lower distortion it goes on making noise (rings resonantly for up to three extra cycles). Note how the spectral decay plot has a camel hump - be wary of any sub or speaker that does this - it will tend to give you one note bass. (unfortunately it is the most popular design as it sounds impressive and fools people into a purchase based on a stereo showroom listening test versus more accurate speakers/subs)

To issue broad decelerations that one type of design
is better than another is almost always wrong.

It is simple physics. Sealed enclosures tend to produce tight, accurate bass
with a flatter frequency response curve. They are also generally the enclosure
of choice when looking for sound quality. Ported designs are more efficient
and give you more SPL output - they are generally the choice for higher
output when sound quality is less important. I explained why above but I'll try
further. More technically speaking it has to do with system Q....a ported
design tends to have much higher Q (underdamped) than compared to a
sealed design, again this is physics - the sealed box acts like a shock
absorber and dampens the movement of the cone - this makes the woofer
stop quickly when the power is removed whilst a ported design will just
waffle around even when power is removed. (Of course you have very sloppy
ported subwoofers with port tuned at 40 Hz and much better sounding ones
like the one I showed in the link above which can be tuned at 10, 15 or 20
Hz. Nevertheless, in a sub, the ported designs are always sloppier (higher Q)
than sealed - although a 10 HZ tune will have much better sound quality than
a 20 Hz tune)

You cannot ruin the lower midrange with a sub if you
cross it over properly and run it at the proper level

I guess it depends on your perspective. Most subwoofers typically add 20%
harmonic distortion anyway. There are some measurements on REL
subwoofers on the HT Shack website - so you can compare their
performance to other subwoofers.

Duke,

I am confused now because you say group delay is worse on sealed? You can clearly see on the links I gave how blocking the port reduces group delay - so how do you explain that? (My understanding is that the port radiates one full cycle out of phase at the tuned frequency - inevitably this implies poor group delay at the tuned frequency and can be seen on most plots on HT SHack website)

My guess is that kick drum sounds better on a sealed sub is probably again the higher group delay and possibly port ringing effects. (Port ringing may even affect mid bass quality)

Stan,

I agree with you that measurements are not everything. However I approach things differently from most - I try to start with good measurements to begin with and then listen for what sounds best to my tastes. It kind of weeds out stuff which simply sounds good but is actually adding coloration.

Have you ever had a pair of RELs in your house or did you dismiss them on the basis of some specification?

No. However I did not dismiss them - if you did go to the HT Shack website you will notice they have EXCELLENT extremely low group delay. Lord appears to design these deliberately with a very low Q and therefore they are not as efficient (play as loud with low distortion) as others but are probably much more musical sounding than many of the subs that were tested - especially on a kick drum. I suspect the REL's would work well with low Q speakers like ATC but I have not tried myself - so this is simply speculation based on the measurements. They also use Volt drivers that have a good reputation. I did not dismiss REL.

NO measurement or design principal has ever been
shown to give a close correlation with sound quality.

I agree in the sense that no single measurement does - it is usually a
combination of measurements and design principals that correlate to sound
quality. Often there is more than one way to skin a cat.

BTW - The student who ran these subwoofer tests in a parking lot has been
hired by Genelec - to
work in their R&D department. He will have access to anechoic chambers
now. I suspect the parking lot is just a way to get raw baseline comparable
measurements under controlled conditions - for sure these need to be
interpreted carefully. As Duke points out - a roll off is probably more
desirable than a flat response to 20 Hz - due to the in room wall boundary
boost effect.

Genelec is not well known to audio consumers but they have a strong
following in the music recording business.

Duke,

Thanks for the link - interesting reading. In simple terms, GedLee is saying
that higher order harmonic distortion is much worse than low order
distortion. This means 2nd order is better than 3rd order ...etc. etc. This jives
with everything we know - Class A amps sound better at low volumes - IMD
distortion is the worst - and that the "masking" effect means that
we may not hear nearby frequencies to a fundamental as easily as we might
hear a 9th harmonic (BAD).

This matches what Ralph has said so many times on these forums...high order
odd harmonics are bad - even in relatively much smaller amounts. To take
your example above, 30% second order harmonic distortion (barely or not
quite audible) may be akin or equivalent to 0.3% distortion in the 9th
harmonic. In that sense, an amplifier with THD of 1% all in the 9th harmonic
would likely sound much worse than an amplifier with 10% THD but all in the
2nd harmonic.

One could jump on this and say that all measurements are meaningless,
however, one must reflect that if an amplifier has a measured THD at full
power of less than 0.004% (vanishingly small) then it will likely sound good
anyway - irrespective of a GedLee higher weighting to the higher order
harmonic distortion (as, be it low order or higher order, the distortion is
simply very small).

Perhaps the problem (what listeners observe) begins when you hook up an
amplifier to a complex load and make the poor amp send bucketloads of
current to drive the woofer and then mere milli-amps to drive the delicate
little tweeter. When the rubber hits the road (in the real world and not a lab
test) the amp find itself being asked to perform two rather diametrically
opposing tasks: extreme butterfly wings delicacy and elephant brute force. A
case where IMD distortion seems inherently likely - so why does the industry
stick so vehemently to this design approach? And why is GedLee largely
ignored in manufacturer spec sheets?

I have never heard of Floyd Toole.

Then you might enjoy reading up and learning a bit more on the engineering of audio equipment. There are University accredited courses in the physics of applied acoustics and electrical engineering. It is not all smoke,mirrors and voodoo, as some of the journalists would have everyone believing.

Hawksford is an academic [as am I] but the serious work in sound reproduction is mostly being done at the practical rather than the theoretical end.

Stan,

It is a pleasure to have an academic researcher in audio engineering on these forums - what aspect of audio are you currently researching?

Dr. Floyd Toole's work was almost entirely practical - his research demonstrated strong correlations between loudspeaker measurements and listener preferences. He has written an excellent book - Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms.