I must say I had a feeling I would provoke the usual anti-OB suspect(s). Particularly concerning the bass.
The point is that you have a motor unit. This can drive a small cone in a reasonably-sized box, or a very large cone which isn't.
The large cone has intrinsically higher efficiency because it couples to the air much more efficiently. (But you can't put a large-coned unit in a box, because it will end up extremely large.)
The large diaphragm offsets the effect of low frequency loss of efficiency which results when you operate it as a dipole (and a dipole is something highly desirable because it negates undesirable room effects).
Practical OB bass units usually operate with a folded baffle, which increases effective baffle size ( and therefore efficiency) without increasing visual impact. I happen to operate mine without any baffle at all, which is a result of an aversion to anything woodwork. And with 2 cheap 12 inch drivers and 40W per side, I can can get thunderous bass when it's required, but, more to the point, it sounds much more natural than boxed bass units.
The only drawback is that they need about a metre of fresh air behind them. If you can accommodate that, you're onto a winner.
Plus OB midrange sounds superb (not very far removed from my ESL-57s).
The point is that you have a motor unit. This can drive a small cone in a reasonably-sized box, or a very large cone which isn't.
The large cone has intrinsically higher efficiency because it couples to the air much more efficiently. (But you can't put a large-coned unit in a box, because it will end up extremely large.)
The large diaphragm offsets the effect of low frequency loss of efficiency which results when you operate it as a dipole (and a dipole is something highly desirable because it negates undesirable room effects).
Practical OB bass units usually operate with a folded baffle, which increases effective baffle size ( and therefore efficiency) without increasing visual impact. I happen to operate mine without any baffle at all, which is a result of an aversion to anything woodwork. And with 2 cheap 12 inch drivers and 40W per side, I can can get thunderous bass when it's required, but, more to the point, it sounds much more natural than boxed bass units.
The only drawback is that they need about a metre of fresh air behind them. If you can accommodate that, you're onto a winner.
Plus OB midrange sounds superb (not very far removed from my ESL-57s).
Thanks, now is much more clear what is happening. All the nulls are still there and the "grass" above 1kHz is "trimmed".
IMHO, the rear waves are too low and have a too wide spectrum to be absorbed by the box.
The box resonate and generate harmonics... then we hear these "Woodbox vibrations".
🙄
boxes
There seems to be quite the mis-understanding of "boxes". I put "boxes" in quotes because the OB crowd will always use that term as opposed to "enclosure".
Did you realize that an unbaffled bass driver actually has a higher amplitude of resonance as compared to when it's placed in an enclosure ? The purpose of an enclosure is many-fold. The amplitude of resonance is reduced, but at the same time it's frequency is raised by the degree of the compliance of air verses what the compliance of the suspension is. The enclosure also prevents the front and back waves of the driver meeting and cancelling response. Damping material inside the enclosure is used to reduce/eliminate standing waves and echo. The action of the driver's excursion being transmitted to the enclosure, and to the extent of to what degree, is what results in the "boxy" sound, (or lack thereof).
A properly constructed enclosure is to many times more efficient at producing bass, as compared to an open baffle device, by it's very nature. Of course, then there's horn bass, which is altogether another beast and not really related to the topic here.
There seems to be quite the mis-understanding of "boxes". I put "boxes" in quotes because the OB crowd will always use that term as opposed to "enclosure".
Did you realize that an unbaffled bass driver actually has a higher amplitude of resonance as compared to when it's placed in an enclosure ? The purpose of an enclosure is many-fold. The amplitude of resonance is reduced, but at the same time it's frequency is raised by the degree of the compliance of air verses what the compliance of the suspension is. The enclosure also prevents the front and back waves of the driver meeting and cancelling response. Damping material inside the enclosure is used to reduce/eliminate standing waves and echo. The action of the driver's excursion being transmitted to the enclosure, and to the extent of to what degree, is what results in the "boxy" sound, (or lack thereof).
A properly constructed enclosure is to many times more efficient at producing bass, as compared to an open baffle device, by it's very nature. Of course, then there's horn bass, which is altogether another beast and not really related to the topic here.
I don't understand how the LF back waves can be absorbed.
"Damping material inside the enclosure is used to reduce/eliminate standing waves and echo" seem to impossible to me, the LF damping needs seems not compatible with a normal loudspeaker enclosure size.
"Damping material inside the enclosure is used to reduce/eliminate standing waves and echo" seem to impossible to me, the LF damping needs seems not compatible with a normal loudspeaker enclosure size.
This thread is quite informative and I have no desire to fan any flames but some of the very real limitations of the OB have been alluded to here. For those who can experiment with OB I envy you to an extent. My limitations occur with WAF and required distance to the back wall for best effect. My listening room, though rather large overall, is shaped and furnished in such a fashion that I am limited to speaker placement of no more than 2 ft (60 cm) from the back wall for the front baffle! My wife would never accept the look of wiring and speaker baskets hanging out the back of an OB. All of my speakers have to be finished like fine furniture for acceptance (not a problem for me as that is my habit anyway). Bass horns wouldn't work either due to their sheer size.
So I am limited to enclosed multiway or full range speakers with subwoofers masquerading as end tables or as stands for monitors. I accept those limitations because those are the parameters I cannot change. Every listening space is different and it's important to factor that into our designs whether for ourselves or for the people who receive our creations. Just my 2 cents/pence/shekels, etc.
So I am limited to enclosed multiway or full range speakers with subwoofers masquerading as end tables or as stands for monitors. I accept those limitations because those are the parameters I cannot change. Every listening space is different and it's important to factor that into our designs whether for ourselves or for the people who receive our creations. Just my 2 cents/pence/shekels, etc.
CraigSu, eg. LX521 or NaO multiway dipoles are not taller than a typical 3-way floorstander. They need a little more air behind them but less sideways! They are not so sensitive to furniture next and between them. But they don't look like conventional speakers and really need a (living) room instead of a man-cave.
This is the right speaker , the left one sits as mirror image to left of the 50" tv and it's measurements were posted yesterday. Willa is a wheaten terrier, weight 19kg (41lb)
This is the right speaker , the left one sits as mirror image to left of the 50" tv and it's measurements were posted yesterday. Willa is a wheaten terrier, weight 19kg (41lb)
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Please be kind, i've performed a lot of measurements in order to have reliable results.
Here is a graph of two dipolar subs with active filtering (HP24Db@30Hz and LP48Db@75Hz).
The blue one is two Visatons WS25E4
The green one is two Visatons WS20E4
We can clearly see my little room modes... (and why i've compartimented my system at the transition of the speaker mode and the room mode)
Raising the emmissive surface improve the the sub-bass response but also encourage the resonances of the room.
Here is a graph of two dipolar subs with active filtering (HP24Db@30Hz and LP48Db@75Hz).
The blue one is two Visatons WS25E4
The green one is two Visatons WS20E4
We can clearly see my little room modes... (and why i've compartimented my system at the transition of the speaker mode and the room mode)
Raising the emmissive surface improve the the sub-bass response but also encourage the resonances of the room.
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Disagree about the higher amplitude of resonance - an unenclosed driver will have a Qts equal to that quoted by the manufacturer (so most drivers will be distinctly overdamped, and OB designers will usually choose a driver with unusually high Qts for this reason). System Q rises as soon as you put it in an enclosure - the smaller the box, the larger the value of Q.
Obviously, OB bass is very inefficient, but who cares? Just use multiple large drivers, and sit back and enjoy the quality of the bass.
The dipole nature of the OB results in fewer room modes being excited, and I suspect that's why I (and many others?) find it superior. Here's a thread describing what you need to do to improve monopole bass:
http://www.diyaudio.com/forums/subwoofers/284221-multiple-subs-vs-bass-traps.html
At bass frequencies, the back waves are not absorbed - they're obliterated before they can form a wave. So, subwoofers typically don't need any damping material (though you may use it purely to increase the effective size of a closed-box design).
You do need damping material though, if the driver has duties extending toward the midrange. This because at higher frequencies, waves do indeed form, and can and will excite resonant modes within the enclosure.
Q verses resonance
System "Q" and driver resonance are not exactly the same thing.
Also, of special note is when di-pole type bass speakers are positioned and cantered out, many times the rear wave is focused into the room corners.
Look, I'm just discussing the basics and the differences between the 2 types, as was questioned by the original poster.
System "Q" and driver resonance are not exactly the same thing.
Also, of special note is when di-pole type bass speakers are positioned and cantered out, many times the rear wave is focused into the room corners.
Look, I'm just discussing the basics and the differences between the 2 types, as was questioned by the original poster.
Have you heard a pair of TAD 1601 or JBL 2226 in good enclosures ?
The LF waves can be propagated by the direct contact and the whole baffle is vibrating.
But the real problem is that a lot of membrannes are totally transparent to the LF (2mm of paper won't stop anything)... so at such frequencies your baffle is like an open cavity (helmotz resonator).
This resonator shoud be tuned low as possible (but its harmonics should pollute the whole audible spectrum) in order to avoid a "box sound"
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At low frequencies, the enclosure can deform slightly, I suppose, but all resonant modes will be at higher frequencies, so there won't be any frequency-dependent effect on response.
As for the speaker cone, at LF it is largely in control of its motion, thanks to the motor unit which vastly reduces compliance, thereby pushing any Helmholz-type effect up to a much higher frequency (in other words, out of the way).
Any flexure of the cone will be small, and any resonant mode of the cone itself will also anyway be at a much higher frequency.
"Box sound" is a term which applies only to the midrange.
As for the speaker cone, at LF it is largely in control of its motion, thanks to the motor unit which vastly reduces compliance, thereby pushing any Helmholz-type effect up to a much higher frequency (in other words, out of the way).
Any flexure of the cone will be small, and any resonant mode of the cone itself will also anyway be at a much higher frequency.
"Box sound" is a term which applies only to the midrange.
You are right and i’m ok with the theory but i’m in trouble with this concept since i’ve learn to make and made acoustic guitars.
The vibrations modes are very similar to a loudspeaker but all the parameters are optimized to maximize resonnances.
The guitar top is acting like a speaker membrane and the body like a bass reflex enclosure, the helmotz resonator (guitar body volume + hole) is tuned to add low notes on the bass strings but it have a very audible effect on all the strings and even the highest notes are inpacted.
There is no design on earth that can avoid that, even lattice smallman guitars with their super heavy and thick non resonant plywood body have audible impact on all notes you play on (you can be sure of that by obstruing the hole or fill the body with absorbant materials).
So i’ve read an engineer studie on the acoustic guitars resonnances modes complete analysis and it had confirm that all the ways.
Control the all the resonance modes of a speaker cavity seems to be an impossible challenge IRL and even the lowest frequency range notes can provide barely audible but audible midrange harmonics in their envelope.
The vibrations modes are very similar to a loudspeaker but all the parameters are optimized to maximize resonnances.
The guitar top is acting like a speaker membrane and the body like a bass reflex enclosure, the helmotz resonator (guitar body volume + hole) is tuned to add low notes on the bass strings but it have a very audible effect on all the strings and even the highest notes are inpacted.
There is no design on earth that can avoid that, even lattice smallman guitars with their super heavy and thick non resonant plywood body have audible impact on all notes you play on (you can be sure of that by obstruing the hole or fill the body with absorbant materials).
So i’ve read an engineer studie on the acoustic guitars resonnances modes complete analysis and it had confirm that all the ways.
Control the all the resonance modes of a speaker cavity seems to be an impossible challenge IRL and even the lowest frequency range notes can provide barely audible but audible midrange harmonics in their envelope.
Wow, you make acoustic guitars for fun! I'm very impressed - your woodworking skills must be top-notch. I'm sure getting the correct timbre is something of a black art - but very rewarding when you get it right.
As to a subwoofer (because that's what we're talking about here), don't forget that midrange harmonics will have been filtered out by the crossover.
I just measured the distance to the wall behind for my speakers and it's about 36 inches. I'm pretty sure you could take that down to 30 inches without many ill effects, which might just make it feasible for your room.
The LX521 and NaO have been mentioned, but you may also like to take a look at this much simpler and cheaper affair:
http://www.diyaudio.com/forums/multi-way/110583-fast-fun-inexpensive-ob-project.html
There still could be a problem in hiding the rears, of course - the difficulty would be in avoiding negative acoustic consequences.
Here is a measurement :
There is a tad of deviation of the the diplole sub response beacause i've displaced it for the test.
Yellow : two 20cm paper woofers in 20Liters (each) tuned@50Hz
Blue : WS25E4 dipole sub
Active filtering (HP24Db@30Hz and LP48Db@75Hz).
SL is talking about 6dB of room mode less excitation on his website...
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