Ported (Bass reflex) vrs Sealed enclosure Speakers
Craig Huggins
I am keen to hear what the difference one may expect in the sound
between a speaker system that is ported as opposed to one that is in a
sealed enclosure. Of course there is probably no two identical sets
of speakers in the world with the only difference being that one set
are ported and one set are not, so generalisations would be fine.
Why are speaker enclosures ported? And, with regards to your lsat
answer, why do some manufacturers then not port their speaker
enclosures?
Cheers
Craig Huggins
John Busenitz
On Tue, 14 May 1996, Craig Huggins wrote:
> I am keen to hear what the difference one may expect in the sound
> between a speaker system that is ported as opposed to one that is in a
> sealed enclosure. Of course there is probably no two identical sets
> of speakers in the world with the only difference being that one set
> are ported and one set are not, so generalisations would be fine.
I seriously doubt there is a general subjective difference between the
sound of a loudspeaker system with a vented enclosure and one with a
sealed enclosure, assuming both systems were properly designed and
constructed. Some people will tell you that vented enclosure systems
sound boomy, loose, muddy, slow, inaccurate, louder, etc., but this is
incorrect assumption on their part. There is a wealth of poorly designed
vented loudspeaker systems out there, more so than sealed enclosure
systems, which are much more lenient to mistakes and poor design.
> Why are speaker enclosures ported? And, with regards to your lsat
> answer, why do some manufacturers then not port their speaker
> enclosures?
One is not necessarily better than the other. Certain drivers work
best in a vented enclosure, and others are designed specifically for
a sealed enclosure. Some of the advantages of a vented enclosure system
are: greater efficiency and/or smaller box volume and/or lower cutoff
compared to an equivalant sealed enclosure system. Some disadvantages
are that they are more difficult to design, and below the system resonance
(dependant upon driver resonance, Q, box size and port acoustic mass)
the driver "unloads" (I don't know the best term for this) and starts
flapping around, which is very bad for the driver, wastes power, etc.
Disadvantages of a sealed enclosure system are that it will be larger,
more inefficient, and/or more limited in low bass response compared to
the vented enclosure system, and thus have greater distortion.
Some advantages of a sealed enclosure system are: ease of design and
sometimes better transient response/less group delay than a vented
system. I am not very sure about this last point, though. It is a
misconception that vented loudspeakers have poor transient response
and a lot of group delay; ie sound more muddy, tubby, boomy, etc.
However, I would guess that it is easier to get better transient behavior
with a sealed enclosure system than it is with a vented enclosure system.
Can a the vented enclosure system alignment with the best transient
response (SBB4, I believe) compare to a sealed enclosure system with
a Qtc of 0.5 purely in terms of transient response/group delay?
_____________________________________________________________
John Busenitz buse...@ecn.purdue.edu
P.U. ECE http://cernan.ecn.purdue.edu/~busenitz
Disclaimer: My statements do not represent Purdue University.
Axel Ridtahler HIT
In article <31984c88....@news.wn.iconz.co.nz>,
cr...@central.co.nz says...
>
>Why are speaker enclosures ported? And, with regards to your lsat
>answer, why do some manufacturers then not port their speaker
>enclosures?
>
(small)speakers to reproduce a little more bass. The enclosure and
the port together with the speaker-dates form some kind of filter
system whichreliefs a small bandwith of low-frequency sound of
through the port.This is the advantage.
The disadvantage : this output from the port has a shifting phase,
the waves coming out of the port and from the speakers cone area
mix and the result is not easy to describe. But what you hear is
more bass with less precision.This may be acceptable for small
speakers. If you are not limited in space a bigger and closed
enclosure stands for better precision.
Richard D Pierce
Well, I've been watching this thread, lurking in the backround, primarily
because of time constraints. Some of the "answers" have been, uh,
interesting, to say the least.
In article <4ncra8$j...@hdihp3.fzk.de>,
Axel Ridtahler HIT <axel.ri...@hit.fzk.de> wrote:
>In article <31984c88....@news.wn.iconz.co.nz>,
>cr...@central.co.nz says...
>>
>>Why are speaker enclosures ported? And, with regards to your lsat
>>answer, why do some manufacturers then not port their speaker
>>enclosures?
>>
>Making ported speakers, if the engineering is done right, helps
>(small)speakers to reproduce a little more bass. The enclosure and
>the port together with the speaker-dates form some kind of filter
>system whichreliefs a small bandwith of low-frequency sound of
>through the port.This is the advantage.
No, the advantages are far broader than this. For example, a properly
designed reflex system will reduce substantially the excursion of the
cone at those frequencies where it's least capable of low-distortion
motion. The net result is a dramatic reduction in the distortion at low
frequencies and high levels (because the port has taken over the primary
function of radiating the output of the system, the cone's output has
been reduced to a very low level, and the port is easily capable of
output higher levels at lower distortion). It substantially increases the
acoustic output capability at these frequencies because the system is no
longer suffering from excursion limiting.
Adding reflex tuning provides two extra degrees of design freedon. It
allows you, for example, to use a driver with a larger magnet. Normally, a
larger magnet, while it buys you increased efficiency, also increases the
low frequency cutoff point, reducing the bandwidth of the system. Using
the enclosure/port system to take over the radiation at the box frequency
extends the low frequency cutoff, allowing you to do things such as get
the same efficiency and cutoff from a smaller enclosure, take the same
enclosure size and efficiency and reduce the low frequency cutoff, and so
on.
>The disadvantage : this output from the port has a shifting phase,
>the waves coming out of the port and from the speakers cone area
>mix and the result is not easy to describe.
Wrong, absolutely wrong. There is no "shifting phase" problem as you
describe. The output of the port is constrained to a fairly small region
around the box resonant frequency. In that region, the output of the port
is in phase with that of the woofer. Outside of that region, the phase of
the two move away from each other, but the output of the port above Fb is
going away at 12 dB/octave, and below that, the entire output of the
system is going away.
>But what you hear is more bass with less precision.
As a general statement, this assertion has no basis in physical reality.
There are bad reflex systems that have low precision bass, but there are
bad sealed box systems that suffer from precisely the same problems.
>This may be acceptable for small speakers. If you are not limited in
>space a bigger and closed enclosure stands for better precision.
Again, as a generalization, you'd be hard pressed to come forth with
physical support for your statement. A sealed box system with a Q of 1.25
(which was typical of AR systems, for example), has a pretty ill-defined,
wooly bass, compared to something like a KEF RS104-aB.
Further, to achieve the same efficiency and bandwidth as a well designed
reflex, a sealed box system with a maximally flat response would have to
be 3 times the size of an equivelent maximally flat reflex system. Only
under such a circumstance could you make a valid comparison, then,
between, for example, the transient response of the system, where the
sealed would have a slight advantage. But comparing two systems of, say,
identical size and efficiency, with similar maxzimally-flat response, the
reflex system would have nearly half an octave greater bandwidth, and
would exhibit better transient response as a result.
--
| Dick Pierce |
| Loudspeaker and Software Consulting |
| 17 Sartelle Street Pepperell, MA 01463 |
| (508) 433-9183 (Voice and FAX) |
Greg Szekeres
In article <31984c88....@news.wn.iconz.co.nz> cr...@central.co.nz (Craig Huggins) writes:
>From: cr...@central.co.nz (Craig Huggins)
>Subject: Ported (Bass reflex) vrs Sealed enclosure Speakers
>Date: Tue, 14 May 1996 09:08:24 GMT
>I am keen to hear what the difference one may expect in the sound
>between a speaker system that is ported as opposed to one that is in a
>sealed enclosure. Of course there is probably no two identical sets
>of speakers in the world with the only difference being that one set
>are ported and one set are not, so generalisations would be fine.
>answer, why do some manufacturers then not port their speaker
>enclosures?
One usual difference in sound is the ability to hear low frequency
sounds in the closed box system. a ported box will often
completely cutout a sound which might be heard with a
closed system.
greg
John Busenitz
On Wed, 15 May 1996, Greg Szekeres wrote:
> One usual difference in sound is the ability to hear low frequency
> sounds in the closed box system. a ported box will often
> completely cutout a sound which might be heard with a
> closed system.
I would think this is a big "if". IF the closed-box system has a
lower cutoff than the vented box system, which if it is at the same
size and efficiency, it won't. Remember, if volume and efficiency
are equal, the vented box system will have the lower cutoff. And
thus it is easier to achieve lower response with a vented box (in
terms of physical tradeoffs) than with a sealed enclosure.
I guess my point is, that if you have a sealed enclosure capable
of reproducing a certain low frequency sound, will not the same
driver in a vented enclosure (properly designed) have a lower
cutoff, enabling the listener to hear the certain low frequency
sound, and even lower sounds?
Neil Brown
In article <gjs.209....@prophet.pharm.pitt.edu>,
g...@prophet.pharm.pitt.edu (Greg Szekeres) wrote:
>
> One usual difference in sound is the ability to hear low frequency
> sounds in the closed box system. a ported box will often
> completely cutout a sound which might be heard with a
> closed system.
>
> greg
>
How do you figue this? I have found vented systems generally have a better
but slower botten end!
Regards
Neil
Carlos Lorenzo
Many thanks for all the enlightening follow-ups, but, please, can someone
explain what the usually generous ammount of absorbent material is doing
inside a sealed box, if it's not dissipating thermically the energy radiated
by the back of the cone?
Thanks again in advance,
+-----------------------------------+
| BT NETWORKS CARLOS LORENZO |
| & SYSTEMS Satellite Systems |
| |
| IPSWICH, UK lor...@boat.bt.com |
+-----------------------------------+
Stewart Pinkerton
lor...@boat.bt.com (Carlos Lorenzo) writes:
>Many thanks for all the enlightening follow-ups, but, please, can someone
>explain what the usually generous ammount of absorbent material is doing
>inside a sealed box, if it's not dissipating thermically the energy radiated
>by the back of the cone?
Probably not, since that IS what it's doing :-)
--
Stewart Pinkerton | If you can't measure what you're making,
A S P Consulting | how do you know when you've got it made?
(44) 1509 880112 |
Richard D Pierce
In article <4nng60$p...@newsgate.dircon.co.uk>,
Stewart Pinkerton <a...@borealis.com> wrote:
>lor...@boat.bt.com (Carlos Lorenzo) writes:
>
>>Many thanks for all the enlightening follow-ups, but, please, can someone
>>explain what the usually generous ammount of absorbent material is doing
>>inside a sealed box, if it's not dissipating thermically the energy radiated
>>by the back of the cone?
>
>Probably not, since that IS what it's doing :-)
To be a wee bit more precise, what energy is being absorbed by this
material is being oncverted into thermal energy and thus is being removed
from the system for all intents and purposes as far as acoustic radiation
is concerned.
However, that is NOT to say that it is absorbing anywhere near all the
enrgy radiated by the rear of the cone. There is still a substantial bit
of reactance left in the box at low frequencies in the form of the
stiffness of the air, and even a theoretically perfect absorber cannot
cancel this reactance (enrgy storage, not energy dissipation), there is
plenty of energy left over to push back on the cone. At higher
frequencies, where the wavelengths are shorter the absorbtion is better,
but reactance plays a minor roll (the system is in the mass-controlled
region of its operation), but the absorbtion is still not complete.
Greg J Szekeres
In article <nbrown-1905...@news.wave.co.nz>,
I'm really listening for stuff between 20 and 30 hz. If you have a ported
system that is allready fairly low, much of this information is
still there to a certain extent. This works better compairing a box
with a higher than 40 hz cutoff. With a closed box of about the same
cutoff in this region, the bass all the way down is still there, just
attenuated. With a little room resonant boost and perhaps a little
bass eq, you have that capability to hear those lows. With a
ported system, forget it.
greg
Greg J Szekeres
In article <4nn937$b...@pheidippides.axion.bt.co.uk>,
Carlos Lorenzo <lor...@boat.bt.com> wrote:
>Many thanks for all the enlightening follow-ups, but, please, can someone
>explain what the usually generous ammount of absorbent material is doing
>inside a sealed box, if it's not dissipating thermically the energy
radiated >by the back of the cone?
>
Aside from modifying the tuning of the woofer, stuffing helps control
reverberation and other unwanted sounds which might be heard. It
also helps controll the way the box vibrates.
greg
Stewart Pinkerton
Neil Brown <nbr...@whispa.co.nz> wrote:
>In article <gjs.209....@prophet.pharm.pitt.edu>,
>g...@prophet.pharm.pitt.edu (Greg Szekeres) wrote:
>
>
>>
>> One usual difference in sound is the ability to hear low frequency
>> sounds in the closed box system. a ported box will often
>> completely cutout a sound which might be heard with a
>> closed system.
>>
>> greg
>>
>
>How do you figue this? I have found vented systems generally have
>a better but slower botten end!
I presume you meant bigger, not better! In their basic forms, one
essential difference between a sealed box speaker and a reflex design is
that the low-frequencly rolloff of a sealed box is -12dB/octave, while
that of a reflex enclosure is -24dB/octave. Clearly, an octave below the
cutoff point there will be a big difference in the amount of output
available from the two designs. I use 10dB of bass boost at 20-30 Hz in
a sealed box speaker (Tannoy 633) to lift film soundtrack effects nicely
without adding much boominess to music and speech. This just wouldn't
work with the equivalent ported speaker.
harding
>>Many thanks for all the enlightening follow-ups, but, please, can someone
>>explain what the usually generous ammount of absorbent material is doing
>>inside a sealed box, if it's not dissipating thermically the energy radiated
>>by the back of the cone?
>
As several people have said, the absorbent material is dissipating some of the energy which is radiated by the back of the cone.
The reason why it is there at all, however, has mostly to do with standing waves. The air in the sealed box has resonant frequencies=
determined by the distance apart of each pair of opposing faces. Resonances occur when lamda/2, lamda, 3lamda/2, etc, are equal to =
an internal box dimension, where lamda is the wavelength of the sound.
v= lamda x f
f= v/lamda
where v= velocity of sound, f = frequency
The speed of sound is about 1000 feet per second in air , though it changes somewhat in absorbing material.
So a box with sides 1 foot apart resonates at about 500hZ, 1khz, 1.5kHz etc. This can give an unpleasant honking characteristic to =
a speaker.
The purpose of damping material is to lower the Q of the resonance so that is less audible. It should therefore be located in the ce=
ntre of the box where the standing wave displacement amplitude is greatest. The simplest way to ensure this is to fill the box (thou=
gh you can have too much damping material, for other reasons. The final amount is determined by trial and error)
Other approaches to this problem include making a box with sides which are not parallel (e.g. Pentachord , Tannoy) , or putting a =
fresnel-lense shaped reflector on the sides which face each other so that sound is not reflected straight back to the other side ( t=
his is sold commercially as a Deflex panel).
The absorbent material should not be confused with Bituminous material which may be stuck to the panels. This is panel damping and i=
ts purpose is to lower the Q of resonances of the side panels themselves. The musical purpose is the same- reduce unwanted resonance=
s.
Hope this helps
John harding
opinions are mine, and not my employers...
Beakman
Stewart Pinkerton (pat...@popmail.dircon.co.uk) wrote:
: I presume you meant bigger, not better! In their basic forms, one
: essential difference between a sealed box speaker and a reflex design is
: that the low-frequencly rolloff of a sealed box is -12dB/octave, while
: that of a reflex enclosure is -24dB/octave.
A common misconception is that a a speaker achieves it's -xdB/octave
rolloff immediately below the point where the system begins to roll off.
In practice, these values are only reached asymmptotically, that is the
initial roll off is more gentle than the ultimate slope. Therefore, down
to a very low frequency (dependent upon the system , of course) a vented
system will still have more output. It doesn't really make much
difference if the sealed system has more output below 18 Hz.
David
--
______________________________________________________________________________
'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`
David Fokos Platinum/Palladium Photography & Workshops
bea...@netcom.com
______________________________________________________________________________
'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`
Neil Brown
> Neil Brown <nbr...@whispa.co.nz> wrote:
> >In article <gjs.209....@prophet.pharm.pitt.edu>,
> >g...@prophet.pharm.pitt.edu (Greg Szekeres) wrote:
> >How do you figue this? I have found vented systems generally have
> >a better but slower botten end!
>
> I presume you meant bigger, not better!
<deleted?
>
>
I guess better is opinion. Let me describe... My speakers have a KEF B139
driver, ported enclosure and material down below audible shakes the room.
The Sony test CD has subsonic tracks on it but other thsn watching the
cones who knows......
I have f ound notesso low on some CD's it is scary! without any boost!
Regards
Neil
Stewart Pinkerton
bea...@netcom.com (Beakman) writes:
>Stewart Pinkerton (pat...@popmail.dircon.co.uk) wrote:
>: I presume you meant bigger, not better! In their basic forms, one
>: essential difference between a sealed box speaker and a reflex design is
>: that the low-frequencly rolloff of a sealed box is -12dB/octave, while
>: that of a reflex enclosure is -24dB/octave.
>A common misconception is that a a speaker achieves it's -xdB/octave
>rolloff immediately below the point where the system begins to roll off.
>In practice, these values are only reached asymmptotically, that is the
>initial roll off is more gentle than the ultimate slope. Therefore, down
>to a very low frequency (dependent upon the system , of course) a vented
>system will still have more output. It doesn't really make much
>difference if the sealed system has more output below 18 Hz.
That's not generally true for commercial designs, which tend to have Qtc
factors of more than 0.7 to give 'impressive' bass and do therefore get
close to their final slope near to the cutoff point, certainly at the
level of reaching -10db/octave versus -22dB/octave in the octave below
resonance. Since the fc point is generally in the 50-100 Hz range except
for really big speakers, there is most certainly a noticeable difference
in the output at 25-35 Hz where differences can clearly be heard. In any
event, the end result depends on the overall system design, there's no
divine ruling that says vented enclosures give more bass - you don't get
many complaints about lack of bass from the NHT3.3 or Tannoy 636 f'r
instance. For a fuller explanation, read anything by Dick Pierce - who
knows, he may even dive in here with a complete exposition of relevant
theory!
Beakman
Stewart Pinkerton (pat...@popmail.dircon.co.uk) wrote:
: bea...@netcom.com (Beakman) writes:
: >Stewart Pinkerton (pat...@popmail.dircon.co.uk) wrote:
Stewart,
I have been professionally designing "commercial" loudspeakers for the
last 15 years -- . A lot of my systems have been vented designs. I have
never once designed for a Qtc of 0.7. I much prefer something on the
order of 0.57 - 0.60.
With a ceratin 10 inch woofer I have used frequently in vented systems I
get an anechoic -3dB point of 31Hz. when I tune the speaker the way I
like it. The same driver in a sealed box, tuned the way I like it, has a
-3dB point of 58Hz. Because the rolloff slopes are different, there is a
point where the sealed system begins to have more output than the vented
system. In this case that occurs at 17 Hz. where the output of the
driver is down 17dB from the passband.
I would like to gently suggest that in the future you try to avoid
generalizing as to what the entire "commerical" industry is doing; and
second, you might want to design a few more systems before you start
generalizing about system performance as well.
However, you were quite right when you said,"there is no divine ruling
that says vented enclosures give more bass", -- just as there is no divine
ruling that says sealed enclosures give more bass, Mr. Pinkerton.
Stewart Pinkerton
bea...@netcom.com (Beakman) writes:
>I have been professionally designing "commercial" loudspeakers for the
>last 15 years -- . A lot of my systems have been vented designs. I have
>never once designed for a Qtc of 0.7. I much prefer something on the
>order of 0.57 - 0.60.
Glad to hear it, should give nice clean bass with minimal boom. I like
'em lean and mean 0.5-0.55 but it's all a matter of taste. Pity more
people don't follow your example. Please note that I said it wasn't
generally true, not that it was never true, reputable companies such as
ATC and Tannoy also produce 'overdamped' alignments in reflex designs.
>With a ceratin 10 inch woofer I have used frequently in vented systems I
>get an anechoic -3dB point of 31Hz. when I tune the speaker the way I
>like it. The same driver in a sealed box, tuned the way I like it, has a
>-3dB point of 58Hz. Because the rolloff slopes are different, there is a
>point where the sealed system begins to have more output than the vented
>system. In this case that occurs at 17 Hz. where the output of the
>driver is down 17dB from the passband.
In which case, all other things being equal, the reflex design will be
superior for a CD source but the cone will flap horribly and cause
intermodulation distortion with a vinyl source. I'm not sure where
you're coming from here as I never suggested it wasn't possible to
design a reflex speaker with good deep bass extension, just that it
isn't usually done that way, especially at the lower end of the market
where the volume sales are. Also of course, you would be using the drive
unit in a less than optimal application in the sealed enclosure since
your examples indicate a drive unit with a Qms intended for reflex use.
>I would like to gently suggest that in the future you try to avoid
>generalizing as to what the entire "commerical" industry is doing; and
>second, you might want to design a few more systems before you start
>generalizing about system performance as well.
Been there, done that. If you wish to challenge my generalisation please
supply data to show that more than 50% of domestic reflex loudspeaker
production has a Qts of less than 0.707. I'd be happy if you could show
more than 25% by numbers sold (sigh). The truth is out there!
>However, you were quite right when you said,"there is no divine ruling
>that says vented enclosures give more bass", -- just as there is no divine
>ruling that says sealed enclosures give more bass, Mr. Pinkerton.
Well yes, logically that follows, doesn't it? You trade better power
handling and linearity in the pass band for uncontrolled behaviour lower
down. In fact, now that the horrible subsonic excesses of vinyl are
rapidly becoming a dead issue, the well-tuned reflex is seeing a
deserved revival. OTOH, my own pick - if you really MUST have a box
design :-) - will always be an active 3-way speaker with a sealed
enclosure, a Qts around 0.5 and electronically equalised bass response.
Having said that, the fully active ATC SCM100A is one of my favourites
and was designed flat to 20Hz with a reflex enclosure!
Having said all the above, I actually use large panel dipoles in my own
system, which is a whole other can of worms!
Regards
Stewart
Bob Neidorff
Stewart Pinkerton (pat...@popmail.dircon.co.uk) wrote:
: That's not generally true for commercial designs, which tend to have Qtc
: factors of more than 0.7 to give 'impressive' bass and do therefore get
: close to their final slope near to the cutoff point, certainly at the
: level of reaching -10db/octave versus -22dB/octave in the octave below
: resonance.
SMALL BOXES are often optimized with higher Qtc to get the most
realistic sound because they have no really low bass. A little
bass boom isn't ideal, but within the tradeoffs of small boxes,
it may be desirable. However, LARGE BOXES are optimized to Qtc
in the range of 0.7. Large boxes are capable of reasonable bass
extension without trading away efficiency, so there is little
benefit to higher Qtc.
Perhaps you are correct in the generalization if you are talking
about speakers in boxes smaller than 15 L or 0.5 cu ft. However,
for woofers in boxes 50 L (2 cu ft) or larger, this is a poor
generalization.
--
Bob Neidorff; Unitrode Corporation | Internet: neid...@uicc.com
7 Continental Blvd. | Voice : (US) 603-429-8541
Merrimack, NH 03054-0399 USA | FAX : (US) 603-429-8564
Earl Kiosterud
pat...@popmail.dircon.co.uk (Stewart Pinkerton) wrote:
>bea...@netcom.com (Beakman) writes:
>>I have been professionally designing "commercial" loudspeakers for the
>>last 15 years -- . A lot of my systems have been vented designs. I have
>>never once designed for a Qtc of 0.7. I much prefer something on the
>>order of 0.57 - 0.60.
>
>Glad to hear it, should give nice clean bass with minimal boom. I like
>'em lean and mean 0.5-0.55 but it's all a matter of taste. Pity more
>people don't follow your example.
Just a thought. This relates to your discussion on bass output vs. "boominess."
I suspect that if you design the system with a sufficiently low F3 point (20
Hz.), then a Qts around .707 will work the best. If the F3 point is up higher
into the audible band, then you get into Qts differences that trade output vs.
the slope below the F3. Then lower Qts values might be preferred. I have found
that the ear seems to "hear" a response slope and interpret is the way it
interprets a response peak, which of course has a slope on each side.
What I have suggested relates only to the sound quality. When we factor in cone
displacement issues and the related power handling limitations, it puts in more
demands, particularly with a very low F3.
Earl K. Virginia Beach, VA
Stewart Pinkerton
neid...@uicc.com (Bob Neidorff) writes:
>Stewart Pinkerton (pat...@popmail.dircon.co.uk) wrote:
>: That's not generally true for commercial designs, which tend to have Qtc
>: factors of more than 0.7 to give 'impressive' bass and do therefore get
>: close to their final slope near to the cutoff point, certainly at the
>: level of reaching -10db/octave versus -22dB/octave in the octave below
>: resonance.
>SMALL BOXES are often optimized with higher Qtc to get the most
>realistic sound because they have no really low bass. A little
>bass boom isn't ideal, but within the tradeoffs of small boxes,
>it may be desirable. However, LARGE BOXES are optimized to Qtc
>in the range of 0.7. Large boxes are capable of reasonable bass
>extension without trading away efficiency, so there is little
>benefit to higher Qtc.
>Perhaps you are correct in the generalization if you are talking
>about speakers in boxes smaller than 15 L or 0.5 cu ft. However,
>for woofers in boxes 50 L (2 cu ft) or larger, this is a poor
>generalization.
Accepted, my comments were indeed targetted at the two-way stand
mounting and compact floorstanding speakers which form the majority of
current production.
FWIW I think 0.7 is still too high as I like the detailed, fast bass
typical of Qts values in the 0.55 area, although this would be
considered very 'dry' by most listeners.
TBrown9000
My nit to pick:
.
.
Earl Kiosterud <ea...@livnet.com> writes:
>I suspect that if you design the system with a sufficiently low F3 point
(20
>Hz.), then a Qts around .707 will work the best.
pat...@popmail.dircon.co.uk (Stewart Pinkerton) writes:
>FWIW I think 0.7 is still too high as I like the detailed, fast bass
>typical of Qts values in the 0.55 area, although this would be
>considered very 'dry' by most listeners.
We're talking Qtc here, not Qts.
The classic Theile "B4" alignment has a Qts of .383.
Stewart Pinkerton
tbrow...@aol.com (TBrown9000) writes:
>My nit to pick:
>..
>..
>Earl Kiosterud <ea...@livnet.com> writes:
>pat...@popmail.dircon.co.uk (Stewart Pinkerton) writes:
Absolutely correct - grovelling apologies for temporary brainfade, it
should of course be Qtc, for which the maximally flat Butterworth 'B4'
value is 0.707. I still prefer <0.55 though :-)
Stewart Pinkerton
Earl Kiosterud <ea...@livnet.com> writes:
>pat...@popmail.dircon.co.uk (Stewart Pinkerton) wrote:
>>bea...@netcom.com (Beakman) writes:
>>>I have been professionally designing "commercial" loudspeakers for the
>>>last 15 years -- . A lot of my systems have been vented designs. I have
>>>never once designed for a Qtc of 0.7. I much prefer something on the
>>>order of 0.57 - 0.60.
>>
>>Glad to hear it, should give nice clean bass with minimal boom. I like
>>'em lean and mean 0.5-0.55 but it's all a matter of taste. Pity more
>>people don't follow your example.
>Just a thought. This relates to your discussion on bass output vs. "boominess."
>I suspect that if you design the system with a sufficiently low F3 point (20
>Hz.), then a Qts around .707 will work the best. If the F3 point is up higher
>into the audible band, then you get into Qts differences that trade output vs.
>the slope below the F3. Then lower Qts values might be preferred. I have found
>that the ear seems to "hear" a response slope and interpret is the way it
>interprets a response peak, which of course has a slope on each side.
I understand the accepted wisdom (with which I concur) to be the
opposite, i.e. high values of Qtc above 0.7 are acceptable only in a
system with a relatively high f3 point, as there is no real low bass
energy to cause excessive boominess. As the f3 value is reduced below
say 60 Hz there is so much excess bass energy in underdamped alignments
that values of Qtc below 0.6 are felt to give an improved perception of
bass extension and quality, while for very low f3 values below 40Hz it
is best to come right down to a Bessel alignment (my own preference for
filter alignments generally) with a Qtc between 0.5 and 0.55. These
figures apply both to sealed and vented enclosures.
>What I have suggested relates only to the sound quality. When we factor in cone
>displacement issues and the related power handling limitations, it puts in more
>demands, particularly with a very low F3.
Certainly the reflex design has advantages in LF power handling and
distortion, all other things being equal. I must admit I have never
designed an f3 value as low as 20Hz with a conventional passive speaker
system.
D.Kreft
> I have been professionally designing "commercial" loudspeakers for the
> last 15 years -- . A lot of my systems have been vented designs. I have
> never once designed for a Qtc of 0.7. I much prefer something on the
> order of 0.57 - 0.60.
Ummm, maybe either this is a poorly worded sentence or I'm mis-reading
this--are you saying that you're designing *ported* (bass reflex if you
will) enclosures with a Qtc of (insert favorite number here)?
If you are indeed implying this, how do you propose to obtain a Qtc
measurement for a ported alignment? Coulda swore Qtc was applicable to
sealed systems only.
Just wondering,
Dan Kreft
Web Developer
Kiwi InterNet Group, Inc.
-------------------------
me: http://www.kreft.net/
we: http://www.king.net/
Beakman
Stewart Pinkerton (pat...@popmail.dircon.co.uk) wrote:
[snip]
: bass extension and quality, while for very low f3 values below 40Hz it
: is best to come right down to a Bessel alignment (my own preference for
: filter alignments generally) with a Qtc between 0.5 and 0.55. These
: figures apply both to sealed and vented enclosures.
The Q of a Bessel system is 0.577.
Stewart Pinkerton
bea...@netcom.com (Beakman) writes:
>Stewart Pinkerton (pat...@popmail.dircon.co.uk) wrote:
>[snip]
>: bass extension and quality, while for very low f3 values below 40Hz it
>: is best to come right down to a Bessel alignment (my own preference for
>: filter alignments generally) with a Qtc between 0.5 and 0.55. These
>: figures apply both to sealed and vented enclosures.
>The Q of a Bessel system is 0.577.
That is correct for the classic D2 maximally flat delay response, I've
ben taught to regard these aligments as families, hence under 0.5 is
overdamped, 0.5 to 0.577 is Bessel, 0.577 to 0.707 is Butterworth and
higher values are Chebychev (spell it how you like) or just plain
underdamped, depending on order! However, you're right and it's not
worth arguing the toss, we all know the effect the Qtc value has on the
sound quality.
Richard D Pierce
In article <beakmanD...@netcom.com>, Beakman <bea...@netcom.com> wrote:
>Stewart Pinkerton (pat...@popmail.dircon.co.uk) wrote:
>
>: I presume you meant bigger, not better! In their basic forms, one
>: essential difference between a sealed box speaker and a reflex design is
>: that the low-frequencly rolloff of a sealed box is -12dB/octave, while
>: that of a reflex enclosure is -24dB/octave.
>
>A common misconception is that a a speaker achieves it's -xdB/octave
>rolloff immediately below the point where the system begins to roll off.
>In practice, these values are only reached asymmptotically, that is the
>initial roll off is more gentle than the ultimate slope. Therefore, down
>to a very low frequency (dependent upon the system , of course) a vented
>system will still have more output. It doesn't really make much
>difference if the sealed system has more output below 18 Hz.
The classic butterworth alignments are, essentially, at half their
rolloff rates at their cutoff frequency: in other words at the -3dB
point, a B2 alignment will have a slope of 6dB per octave on its way to
an ultimate asymtotic slope of 12 dB/oct, and a B4 alignment will have a
slope at the -3dB point of 12 db/oct on its way to an ultimate asymtotic
slope of 24 dB/oct.
There are classes of both 2nd and 4th order alignments whose slope in the
proximity of the cutoff is substantially less then their ultimate
out-of-band slopes. For example, the classic 2nd order bessels and the
so-called QB3 vented alignments take a LONG time to reach their ultimate
cutoff rates. I have built system with the latter alignments that people
have remarked sound remarkably like sealed box systems in terms of low
cutoff characteristics and, for a given box volume, all provided more
real bandwidth down to 20 Hz than an equivalently sized and efficient
sealed system.