Hi,
can anyone point out or link to the basic theory of an open baffle?
I know the benefits myself like low distortion and great impulse behaviour, but one of my colleagues who has always built ported speakers is a total non believer and just doesn't understand how a system like that can work.
I'm looking for text about full wavelength and when chosen shorter why it needs correction. Why there's so much less distortion.
can anyone point out or link to the basic theory of an open baffle?
I know the benefits myself like low distortion and great impulse behaviour, but one of my colleagues who has always built ported speakers is a total non believer and just doesn't understand how a system like that can work.
I'm looking for text about full wavelength and when chosen shorter why it needs correction. Why there's so much less distortion.
The fundamentals are explained by Linkwitz and Kreskovsky. That dipoles should have less distortion is highly disputable so ...
Thanks for your responses, I was under the impression that the distortion of OB was lower, but that probably is not right. Probably the lower distortion of many OB designs is due to the enormous amount of moving surface having to move only little. A direct comparison with the same moving surface in a boxed design shall probably have comparable distortion at the same level.
Correct me if I'm wrong, but this only counts for a baffle that is less than max. wavelength and is made linear by correction. When you for instance build the speakers in a wall or really large full wavelength baffle the SPL should be the same at the same power, only difference perhaps is the hub of the driver will run to it's limits sooner.
Most baffles were built with compromises between performance and practicality, I'm merely looking for theory here...
I have found the sheets written by mr. Linkwitz exactly what I was looking for, so basically my questions are answered here.
Thanks again!
cotdt said:
Correct me if I'm wrong, but this only counts for a baffle that is less than max. wavelength and is made linear by correction. When you for instance build the speakers in a wall or really large full wavelength baffle the SPL should be the same at the same power, only difference perhaps is the hub of the driver will run to it's limits sooner.
Most baffles were built with compromises between performance and practicality, I'm merely looking for theory here...
I have found the sheets written by mr. Linkwitz exactly what I was looking for, so basically my questions are answered here.
Thanks again!
For as far as I know (I'm no OB scientist, but I'm not entirely ignorant) this only counts for an OB with correction because you compensate the loss of low end output (due to acoustic short circuit at wavelengths larger than the baffle) by a bass-boost (the correction filter, similar to baffle step correction).
The bass boost certainly will introduce distortion, but a large enough baffle* needs no correction at all so should keep distortion at the same level or lower? Maybe due to the lack of air compliance you increase the excursion of the driver and at a certain point increase distortion. But as soon as you stay well within the mechanical capability of the driver I think the distortion should not increase.
*I've been told that ideally an open baffle should be at least as large as the max. wavelength and keep the frequency response straight and not decreasing towards the lower end like with the commonly used and more practical small baffles that need correction to compensate for this side effect.
The bass boost certainly will introduce distortion, but a large enough baffle* needs no correction at all so should keep distortion at the same level or lower? Maybe due to the lack of air compliance you increase the excursion of the driver and at a certain point increase distortion. But as soon as you stay well within the mechanical capability of the driver I think the distortion should not increase.
*I've been told that ideally an open baffle should be at least as large as the max. wavelength and keep the frequency response straight and not decreasing towards the lower end like with the commonly used and more practical small baffles that need correction to compensate for this side effect.
Personal opinion follows so be aware.
OB's greatest benefits are, it's cheap, they are great fun to build, they are very forgiving and sound quality is good.
Greatest drawbacks are lack of suitable high-power bass drivers and low WAF if baffle is made big enough as they do take up a lot of floor space.
I think that OB's are a build it and see/hear type of speaker, even a poor implementation can sound rather good.
The theory is covered quite well by GA Briggs in several of his books ( as far as I know all out of print )
Try local bookshops or Amazon for G A Briggs "Loudspeakers"
OB's greatest benefits are, it's cheap, they are great fun to build, they are very forgiving and sound quality is good.
Greatest drawbacks are lack of suitable high-power bass drivers and low WAF if baffle is made big enough as they do take up a lot of floor space.
I think that OB's are a build it and see/hear type of speaker, even a poor implementation can sound rather good.
The theory is covered quite well by GA Briggs in several of his books ( as far as I know all out of print )
Try local bookshops or Amazon for G A Briggs "Loudspeakers"
The benefits and disadvantages of the dipole polar pattern are controversial - and separate arguments apply to different parts of the spectrum. A dipole in the 1 ~ 5 kHz region is not the same as a dipole in the 200 Hz ~ 1 kHz region. It also has to be remembered that nearly all "conventional" direct-radiator speakers are omnidirectional below 250 ~ 500 Hz, despite what happens at higher frequencies.
Some people notice box coloration more than others; I personally consider box coloration important because it falls in a part of the spectrum where direct-radiator woofers and midbass drivers are intrinsically flat (piston band), the 200 ~ 800 Hz region. Although the drivers are inherently well-behaved, the box is not - the dominant up-and-down, side-to-side, and front-and-back standing-wave modes are only partially damped by foam, fiberglass, synthetic fiber, wool, and other filling materials. These materials absorb much more effectively above 1 kHz than below 1 kHz.
If you want to hear this box coloration for yourself, remove the drivers, and if there's room, put your head inside the box and listen for the droning coloration that is added to the ambient environmental sounds. Be careful about doing this little test - once you identify the coloration, you'll start noticing it in all box speakers! This is similar to learning to see the "rainbows" in a color-shutter projection TVs - once you see them, you'll be noticing them all the time in RPTV's!
If you're in an experimental mood, compare and contrast the box coloration with and without different filling materials. Although they will modify the droning sound in different ways, you'll find that none of them remove it completely, and some filling materials add annoying colorations of their own. There is such a thing as too much filling - if the filling is too close to the cone of the midbass driver, you start to get mass-coupling effects, and efficiency and midrange response will be degraded. There's a reason that choice of filling materials is still controversial after fifty years - none of them works all that well. So the radical alternative is no box, or at least no structure that will support standing waves.
The biggest downside of dipole speakers is massive loss of efficiency below the dipole peak (typically in the 200 to 500 Hz region). If LF equalization is applied, the driver excursion and resulting distortion goes up many times. The only counter to this is selecting expensive low-distortion drivers (2~3X improvement at best) and/or increasing cone area (loss of WAF, your choice on that one).
Some people notice box coloration more than others; I personally consider box coloration important because it falls in a part of the spectrum where direct-radiator woofers and midbass drivers are intrinsically flat (piston band), the 200 ~ 800 Hz region. Although the drivers are inherently well-behaved, the box is not - the dominant up-and-down, side-to-side, and front-and-back standing-wave modes are only partially damped by foam, fiberglass, synthetic fiber, wool, and other filling materials. These materials absorb much more effectively above 1 kHz than below 1 kHz.
If you want to hear this box coloration for yourself, remove the drivers, and if there's room, put your head inside the box and listen for the droning coloration that is added to the ambient environmental sounds. Be careful about doing this little test - once you identify the coloration, you'll start noticing it in all box speakers! This is similar to learning to see the "rainbows" in a color-shutter projection TVs - once you see them, you'll be noticing them all the time in RPTV's!
If you're in an experimental mood, compare and contrast the box coloration with and without different filling materials. Although they will modify the droning sound in different ways, you'll find that none of them remove it completely, and some filling materials add annoying colorations of their own. There is such a thing as too much filling - if the filling is too close to the cone of the midbass driver, you start to get mass-coupling effects, and efficiency and midrange response will be degraded. There's a reason that choice of filling materials is still controversial after fifty years - none of them works all that well. So the radical alternative is no box, or at least no structure that will support standing waves.
The biggest downside of dipole speakers is massive loss of efficiency below the dipole peak (typically in the 200 to 500 Hz region). If LF equalization is applied, the driver excursion and resulting distortion goes up many times. The only counter to this is selecting expensive low-distortion drivers (2~3X improvement at best) and/or increasing cone area (loss of WAF, your choice on that one).
I have not still decided which speakers should I use for my new apartment (kind of space limited). The last path I would like to take is a pair of two way bass reflex minimonitors.
By any means I do not listen to high levels, more or less normal TV levels, which is quite low. Could Open Baffle be the candidate? I can not accept anything wider than Manzanitas, for serious listening, I will have to move the speakers accordingly, otherwise for background listening they will be placed along the longer sidewall of a 3,5x4,5x2,4 m room.
Could some of the disadvantages be eliminated by near field listening?
How about hybrids with more traditional bass below the dipole peak? Is it worth trying?
My target is a relatively small system - is that contradictory to OB even if I consider the low listening levels?
By any means I do not listen to high levels, more or less normal TV levels, which is quite low. Could Open Baffle be the candidate? I can not accept anything wider than Manzanitas, for serious listening, I will have to move the speakers accordingly, otherwise for background listening they will be placed along the longer sidewall of a 3,5x4,5x2,4 m room.
Could some of the disadvantages be eliminated by near field listening?
How about hybrids with more traditional bass below the dipole peak? Is it worth trying?
My target is a relatively small system - is that contradictory to OB even if I consider the low listening levels?
pelanj,
low levels, I'd recommend full range drivers............
Nice dynamics without needing fireworks sound levels..........
What about a large open baffle with foam behind it against a wall ?
You wouldn't get the intoxicating dipole wall bounce, but you get excellent mids with complete lack of boxyness...............
I'm working on a 30" tall 36" wide dipole (working well above 200hz) then run a bass unit under that.....................
Norman
low levels, I'd recommend full range drivers............
Nice dynamics without needing fireworks sound levels..........
What about a large open baffle with foam behind it against a wall ?
You wouldn't get the intoxicating dipole wall bounce, but you get excellent mids with complete lack of boxyness...............
I'm working on a 30" tall 36" wide dipole (working well above 200hz) then run a bass unit under that.....................
Norman
Norman,
yes, I am interested also in fullrangers, however I am not able to incorporate such baffles into my living room. Then, there is the martyrium to choose one, that is available in EU. Whizzer cone or not, size, etc...Maybe some of the smaller ones with a sealed bass below. 12" inch wide baffle (wings are possible) is maximum, preferably less.
yes, I am interested also in fullrangers, however I am not able to incorporate such baffles into my living room. Then, there is the martyrium to choose one, that is available in EU. Whizzer cone or not, size, etc...Maybe some of the smaller ones with a sealed bass below. 12" inch wide baffle (wings are possible) is maximum, preferably less.
Actually I think it might work for you. My room is about 12' square which I guess works out to around 4m or so. I am sort of kludge bi-amping a 5.25" full range driver and a 10" high Q...
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=290-325
in a smallish baffle. The side panels are 1x6s which are about 5.75" in actual depth but they are biased forward to be even with the grill cloth so the sides are only about 4". The baffle width is about 13" if I remember correctly.
I use a homemade subwoofer to supplement the low end below about 60Hz but I had it disconnected the other day and they did pretty well on most music as is. Using a sub really makes it shine though. What I wanted to do bass wise was to be sure that the mains would cover the tympani which they do just fine and really cover most of the string bass quite well also.
I made the mains in the form of knick knack tables so they can be a couple of feet into the room without being intrusive. The wall behind the speakers is rather "busy" so the rear wave is nicely dispersed. The imaging and sense of presence of these things is incredible given that they are the cheapest speakers I have owned but the best sounding at the same time.
Attachments
Maybe somthing like this would interest you. This is a hybrid open baffle design that I'm currently working on. It is in the prototype stage with a pair built out of all mdf at this point. It uses a Lambda TD12H woofer in a 52 liter slot ported box with an open baffle mid, curently the B&C 6md38 and a Peerless HDS tweeter in a shallow waveguide. There is a thread going here that describes it more thouroughly. I'm starting you on page 6, since there isn't too much to look at prior to that.
BaSSlines
It is about 16" wide at the base, tapering to 7" wide at the top. I plan to used Lexan on the open baffle section to keep it looking smaller yet in the room. It is about 42" high.
Here is a mock up of what the final build is intended to look like:
BaSSlines
It is about 16" wide at the base, tapering to 7" wide at the top. I plan to used Lexan on the open baffle section to keep it looking smaller yet in the room. It is about 42" high.
Here is a mock up of what the final build is intended to look like:
v-bro said:
Ideally it´s just the other way round: A dipole should be kept in the 6 dB dipole loss ramp (equalized of course) and not be driven above the dipole peak since the radiation pattern will become wider above the dipole peak. Look at the ORION and the Nao with their narrow baffles.
JohnK gives an explanation.
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