Yep, that's the "dirty secret" of Open Baffle that most builders don't understand, or don't want to. The efficiency is limited to what the bass is. You could have open baffles losses as much as 10dB just to get a flat response. The room will give you some back in the power response. That's why most woofers are in a box. 
Some people think you can just boost the bass with EQ, which you can - but efficiency is still low. That's why more power is needed.
Some people think you can just boost the bass with EQ, which you can - but efficiency is still low. That's why more power is needed.
Hi Pano,
exactly. There are no realistic options to circumvent physics, sadly...
For passive OBs, certainly a Q of 0,6-07 works fine, much better than the weak Eminence drivers.
Pure Audio Project has nice 15-inchers for OB, made by Eminence as well. You will, however, end up with a relatively inefficient bass solution, the lower you want it to reach, the lower is the efficiency. Bigger baffle, better efficiency (slot loaded and H-baffles do their own tricks). More Sd (but NOT more Xmax) will raise efficiency.
I´m pretty conservative with regards to the Xmax race; have you tried to make an OB with, just as an example, two 12-inch-drivers with app. 200 gr. of mass, moving +- 1 cm or so? Doable, but not easy.
For active implementation, the choice of drivers is bigger, but those are NOT automatically more efficient, mostly the opposite. Of course you can pump up everything with 1000 watts of class-d power, but personally, I prefer the much more expensive passive approach... better for my ears (AE Dipole 18 in OB, passive filter). YMMV.
Regarding the crossover: If going passive, there´s no way to determine a correct filter without measurements at the real object. Simulation programs which work wit OBs might give a direction.OB filters are different from other filters, as you always have to deal with the 6-dB-dipole slope.
All the best
Mattes
exactly. There are no realistic options to circumvent physics, sadly...
For passive OBs, certainly a Q of 0,6-07 works fine, much better than the weak Eminence drivers.
Pure Audio Project has nice 15-inchers for OB, made by Eminence as well. You will, however, end up with a relatively inefficient bass solution, the lower you want it to reach, the lower is the efficiency. Bigger baffle, better efficiency (slot loaded and H-baffles do their own tricks). More Sd (but NOT more Xmax) will raise efficiency.
I´m pretty conservative with regards to the Xmax race; have you tried to make an OB with, just as an example, two 12-inch-drivers with app. 200 gr. of mass, moving +- 1 cm or so? Doable, but not easy.
For active implementation, the choice of drivers is bigger, but those are NOT automatically more efficient, mostly the opposite. Of course you can pump up everything with 1000 watts of class-d power, but personally, I prefer the much more expensive passive approach... better for my ears (AE Dipole 18 in OB, passive filter). YMMV.
Regarding the crossover: If going passive, there´s no way to determine a correct filter without measurements at the real object. Simulation programs which work wit OBs might give a direction.OB filters are different from other filters, as you always have to deal with the 6-dB-dipole slope.
All the best
Mattes
OB bass
It seems so many do not understand, or for what ever reasons, over complicate the basic design issues.
As I have said so many times... before you do anything, you need to set reasonable bass performance goals. Just like any other format. How loud do you need to realistically need to go? What low end cut off do you wish to do? What is the largest baffle you can tolerate? A good OB design, once you understand the physics is super easy to do. You can, for not much money, and work, design and build an OB that will embarrass nearly all box solutions when it comes to transparency and bang for the buck down in to the low 30's! Which frankly, most box solutions do not come close to getting down there. Simple passive crossover. Ask me a question, I will answer it.
It seems so many do not understand, or for what ever reasons, over complicate the basic design issues.
As I have said so many times... before you do anything, you need to set reasonable bass performance goals. Just like any other format. How loud do you need to realistically need to go? What low end cut off do you wish to do? What is the largest baffle you can tolerate? A good OB design, once you understand the physics is super easy to do. You can, for not much money, and work, design and build an OB that will embarrass nearly all box solutions when it comes to transparency and bang for the buck down in to the low 30's! Which frankly, most box solutions do not come close to getting down there. Simple passive crossover. Ask me a question, I will answer it.
If you want to stay in the 12" camp for the bass driver, never forget the Peerless SLS. The mentioned SB Acoustics has good spec, slightly better than Peerless, but the price of Peerless is just half of the SBA.
Also, the GRS driver used in Manzanita project, is now available in EU. SoundImports.eu - Your favorite one-stop-shop for DIY audio components - SoundImports
15PF-8 15" Paper Cone Foam Surround Woofer - Your favorite one-stop-shop for DIY audio components - SoundImports
Also, the GRS driver used in Manzanita project, is now available in EU. SoundImports.eu - Your favorite one-stop-shop for DIY audio components - SoundImports
15PF-8 15" Paper Cone Foam Surround Woofer - Your favorite one-stop-shop for DIY audio components - SoundImports
I will change the Alphas for 2x18". I will test some 18"s. What passive crossover points do you recommend? Thank you!
I will try 2x Beyma SM-118N8 ohm per side in an 60cm wide open baffle. What is the value for the big inductor that you recommend for 250Hz? Thank you!
Agree with John B and his assertion that good design is built around good bass.
My previous OB system was build around a quad of Goodwood 1858s in HFrames ala MJK. They were quite affordable and eye opening drivers. They allowed me to design a proof of concept. After getting those bass speakers to my liking, I was able to rotate in and out whatever upper range drivers I chose. Sometimes they were OB. Sometimes they were boxes. My friend seemed to also feel that different tops worked in different ways, but the bass was always there, loud enough and had definition that OB is known for.
It doesn't need to be super expensive IME. $750 drivers would be very nice but maybe a turn off to some. You can get plenty of decent bass speakers for a good price. Lots of folks have had success with all kind of bass drivers in OB. It just depends what you want to achieve. I feel like Open Baffle needs big bass drivers and a properly scaled midrange to hand off to. That is why I run 18's and 15's for my cones in OB. I have used 8" drivers and 10" drivers as well, and they did good jobs too, the 10" more so than the 8... So I feel there is merit in large cones.
I started with a pair of amps and PLLXO which was cheaper than a passive crossover. Then I went active now I run a 3 way with DSP. Could go back to OB and all analog in future but having fun with boxes ATM. I'm slowly beginning to realize how good and easy to integrate those 1858s were.
My previous OB system was build around a quad of Goodwood 1858s in HFrames ala MJK. They were quite affordable and eye opening drivers. They allowed me to design a proof of concept. After getting those bass speakers to my liking, I was able to rotate in and out whatever upper range drivers I chose. Sometimes they were OB. Sometimes they were boxes. My friend seemed to also feel that different tops worked in different ways, but the bass was always there, loud enough and had definition that OB is known for.
It doesn't need to be super expensive IME. $750 drivers would be very nice but maybe a turn off to some. You can get plenty of decent bass speakers for a good price. Lots of folks have had success with all kind of bass drivers in OB. It just depends what you want to achieve. I feel like Open Baffle needs big bass drivers and a properly scaled midrange to hand off to. That is why I run 18's and 15's for my cones in OB. I have used 8" drivers and 10" drivers as well, and they did good jobs too, the 10" more so than the 8... So I feel there is merit in large cones.
I started with a pair of amps and PLLXO which was cheaper than a passive crossover. Then I went active now I run a 3 way with DSP. Could go back to OB and all analog in future but having fun with boxes ATM. I'm slowly beginning to realize how good and easy to integrate those 1858s were.
Snake69fast Your Beyma 18 choice looks promising.. Assume you will wire in parallel... Something around 17-21 MH iron core in series should work. Also assuming a effective baffle width of 20-24 inches. May have to add a trap to offset the rising response. You want the electrical roll off to start somewhere around 65-75 Hz. What is best is to mount the drivers on a temporary baffle approximating the permanent baffle you intend to use (that can be heavy cardboard or similar) add about .75 ohms of series resistance and then measure the total effective QTS'. You then know where you really are and can fine tune to suit. John
Hi,
the Beyma SM 118 is no bad choice. Some simulations attached, and comparisons with a single AE Dipole 18 and the even cheaper (but nice, I have a pair) AD 1830.
Note that the Dipole 18 are my own parameters, not the manufacturers. Even then note, that the single Dipole 18 has better efficiency in the very deep bass and reaches an octave deeper...
The Beymas have much more headroom in the middle bass, but do you need that? However, they should give you a solid 92 dB/2,8 V and reach down in the middle 40s with a passive filter. Inductor question is also answered, but this is only the start. Single inductor will not work... you´ll need to measure and add parallel C, then you´ll need to care about the baffle hump and that loud 2-Khz region, possibly with a parallel notch.
Keep in mind that you´re dealing with few hundred grams of moving mass and make a very stiff and heavy baffle (60 kg or more), otherwise you´ll have unwanted resonances. CLD and mass are your friends here.
Those simulations have proofed to be quite realistic, but don´t trust them until the last single dB... they´re just simulations, if good ones.
All the best
Mattes
the Beyma SM 118 is no bad choice. Some simulations attached, and comparisons with a single AE Dipole 18 and the even cheaper (but nice, I have a pair) AD 1830.
Note that the Dipole 18 are my own parameters, not the manufacturers. Even then note, that the single Dipole 18 has better efficiency in the very deep bass and reaches an octave deeper...
The Beymas have much more headroom in the middle bass, but do you need that? However, they should give you a solid 92 dB/2,8 V and reach down in the middle 40s with a passive filter. Inductor question is also answered, but this is only the start. Single inductor will not work... you´ll need to measure and add parallel C, then you´ll need to care about the baffle hump and that loud 2-Khz region, possibly with a parallel notch.
Keep in mind that you´re dealing with few hundred grams of moving mass and make a very stiff and heavy baffle (60 kg or more), otherwise you´ll have unwanted resonances. CLD and mass are your friends here.
Those simulations have proofed to be quite realistic, but don´t trust them until the last single dB... they´re just simulations, if good ones.
All the best
Mattes
I have already a pair of Beyma SM-118N that measure like this:
Driver 1:
f(s) = 37.68 Hz
Q(ts) = 0.513
R(e) = 7.034 Ohms
Q(es) = 0.6096
L(e) = 0.8133 mH at 10kHz
Q(ms) = 3.238
Driver 2:
f(s) = 41.05 Hz
Q(ts) = 0.5291
R(e) = 6.756 Ohms
Q(es) = 0.6281
L(e) = 0.8159 mH at 10kHz
Q(ms) = 3.358
I hope the differences are not so big. I am waiting for a good deal for the second pair...
I'll start on Monday to cut the 60cm wide baffle and fix the drivers.
Driver 1:
f(s) = 37.68 Hz
Q(ts) = 0.513
R(e) = 7.034 Ohms
Q(es) = 0.6096
L(e) = 0.8133 mH at 10kHz
Q(ms) = 3.238
Driver 2:
f(s) = 41.05 Hz
Q(ts) = 0.5291
R(e) = 6.756 Ohms
Q(es) = 0.6281
L(e) = 0.8159 mH at 10kHz
Q(ms) = 3.358
I hope the differences are not so big. I am waiting for a good deal for the second pair...
I'll start on Monday to cut the 60cm wide baffle and fix the drivers.
It will be interesting to see where the Q goes once you have the woofers on the 60 cm baffle.Open Baffle 3 way
Mattes:
Could you look at the buyout 15" Eminence woofer on the diysoundgroup site, and comment on how it might work in a set-up such as this project? It is a very low QTS driver, however.
I bought a pair for a different project (sealed) but wonder if it would work decently for open baffle. The speakers he owns are made very close to where I'm located.
Thanks!
Mattes:
Could you look at the buyout 15" Eminence woofer on the diysoundgroup site, and comment on how it might work in a set-up such as this project? It is a very low QTS driver, however.
I bought a pair for a different project (sealed) but wonder if it would work decently for open baffle. The speakers he owns are made very close to where I'm located.
Thanks!
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