Dear Sirs,
i am a complete newbie related speaker design. Picture of my crossover is bellow - "current" part of the picture.
I am running an open baffle design with middle driver full range (type not known for now), tweeter is P Audio BM-D440S and woofer is SB Audience Bianco-12OB150. Sound is nice but i kind of would like to have more bass - not to much, just a little bit more (bass drivers are still preety new - maybe they need to work a little bit more to get to the level, i don't know)...
Right now the woofer board alone is not to big (can't go bigger because of the living room i have) so i was thinking to put maybe two 12OB150 drivers per side to enhance the surface area.
The problem is those drivers are 8 ohm... putting them in series is not an option so, if i put them in paralel i will have 4 ohm at the end... together with my 8ohm middle and a little bit more on the tweeter, i am worried if the overall impedance will be to low ... (my amplifier is class A F5 clone from Nelson Pass)..... so i am considering putting Rx resistors in series.... those Rx resistors from the "future consideration" part on the picture will have to be big (power related)?! what to choose to put there to get a good sound... type?
any thoughts for this case??
thank you
i am a complete newbie related speaker design. Picture of my crossover is bellow - "current" part of the picture.
I am running an open baffle design with middle driver full range (type not known for now), tweeter is P Audio BM-D440S and woofer is SB Audience Bianco-12OB150. Sound is nice but i kind of would like to have more bass - not to much, just a little bit more (bass drivers are still preety new - maybe they need to work a little bit more to get to the level, i don't know)...
Right now the woofer board alone is not to big (can't go bigger because of the living room i have) so i was thinking to put maybe two 12OB150 drivers per side to enhance the surface area.
The problem is those drivers are 8 ohm... putting them in series is not an option so, if i put them in paralel i will have 4 ohm at the end... together with my 8ohm middle and a little bit more on the tweeter, i am worried if the overall impedance will be to low ... (my amplifier is class A F5 clone from Nelson Pass)..... so i am considering putting Rx resistors in series.... those Rx resistors from the "future consideration" part on the picture will have to be big (power related)?! what to choose to put there to get a good sound... type?
any thoughts for this case??
thank you
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As a basshead and an OB fanatic, I’ll tell you what I do.
First of all, I often run a 4ohm bottom (single 4ohm driver or parallel 8ohms) in parallel with an 8ohm top. While the nominal impedance is 2.666ohm in the bass frequencies, in practice every amp I’ve tried has no problem with this. Between the series resistance of the inductor, the high-resistance resonance peak of the drivers, and the fact that only a small part of the audio signal is going that low, it hasn’t been a problem. That said, I typically use 10mH in front of the bass driver. With just 2.8mH you might need to be more careful.
I’d also recommend using a larger inductor on the bass driver and padding down the mid and tweeter. You can use adjustable l-pads to get the levels where you want them. You lose some efficiency by doing this but get more bass. I usually take this to an extreme, ending up with speakers around 70-75db in sensitivity but with bass extension down to the low 30hz with relatively small, flat baffles.
Another option would be to use a more conventional three-way crossover to reduce the amount of electrical and accoustic overlap of your three drivers.
Finally, look at Perry Marshall’s bass boost circuit. I haven’t tried it yet but I’ve read good things about it.
I’m wouldn’t do what you suggest in your “future” circuit because padding the bass driver is counterproductive IMO.
First of all, I often run a 4ohm bottom (single 4ohm driver or parallel 8ohms) in parallel with an 8ohm top. While the nominal impedance is 2.666ohm in the bass frequencies, in practice every amp I’ve tried has no problem with this. Between the series resistance of the inductor, the high-resistance resonance peak of the drivers, and the fact that only a small part of the audio signal is going that low, it hasn’t been a problem. That said, I typically use 10mH in front of the bass driver. With just 2.8mH you might need to be more careful.
I’d also recommend using a larger inductor on the bass driver and padding down the mid and tweeter. You can use adjustable l-pads to get the levels where you want them. You lose some efficiency by doing this but get more bass. I usually take this to an extreme, ending up with speakers around 70-75db in sensitivity but with bass extension down to the low 30hz with relatively small, flat baffles.
Another option would be to use a more conventional three-way crossover to reduce the amount of electrical and accoustic overlap of your three drivers.
Finally, look at Perry Marshall’s bass boost circuit. I haven’t tried it yet but I’ve read good things about it.
I’m wouldn’t do what you suggest in your “future” circuit because padding the bass driver is counterproductive IMO.
@gregulator is correct, 2.7mH looks too small for that driver in an OB. Here's a simulation of the response, assuming 0.3 ohms dcr for the inductor, and baffle 50cm by 90cm. -6dB looks to be about 80 Hz.
A 10mH inductor is probably a good call - simulation suggests the -6dB point will drop to about 52 Hz. (It's probably not realistic to go much lower with that driver (or two of them) as the Fs is 44 Hz.)
If you add a second woofer, a 5 mH inductor would give you a decent response, and keep the efficiency up around 93-94 dB/2.83V, at the cost of around 4 ohm minimum impedance. This is all simulation, of course.
(PS I also have an F5 clone and it has absolutely no problem with 4 ohm loads, in my experience.)
A 10mH inductor is probably a good call - simulation suggests the -6dB point will drop to about 52 Hz. (It's probably not realistic to go much lower with that driver (or two of them) as the Fs is 44 Hz.)
If you add a second woofer, a 5 mH inductor would give you a decent response, and keep the efficiency up around 93-94 dB/2.83V, at the cost of around 4 ohm minimum impedance. This is all simulation, of course.
(PS I also have an F5 clone and it has absolutely no problem with 4 ohm loads, in my experience.)
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Congrats! You just learned that one can violate any laws except the laws of physics. An open baffle will cancel out any LF with a wavelength bigger than four times the smallest distance between the driver and the baffle edge, regardless of how many LF drivers you use, of their efficiency, of the xover design etc. For signifikant LF response, you need to build an infinite baffle.
Best regards!
@Kay Pirinha Sorry, that's just wrong. OB can give excellent bass.
You invoke the laws of physics, but then immediately make false statements. (A surprisingly common move, on this forum, IME). Open baffles do not "cancel out" all sound below a certain wavelength. There is cancellation, yes, but it is partial, predictable and manageable, and can be designed around. It results in increased LF directivity, which some people find welcome.
You invoke the laws of physics, but then immediately make false statements. (A surprisingly common move, on this forum, IME). Open baffles do not "cancel out" all sound below a certain wavelength. There is cancellation, yes, but it is partial, predictable and manageable, and can be designed around. It results in increased LF directivity, which some people find welcome.
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The simplest thing you can do is add a subwoofer for below 100 Hz. A single 12OB150 is fine for 80 or 100Hz++, depending on baffle width, but needs help below 100. A 2nd 12OB150 won't do it. @perrymarshall uses 2 15's with wings. Speaking loosely, you can do as good or better with a sealed 12" sub, except it won't have OB directivity which arguably doesn't matter below 100 Hz
That's pessimistic, but fair. A sub is another good approach, but I don't think the 12OB150 is hopeless. It doesn't have a huge amount of linear excursion (6.79mm according to SB, but only 4.12mm if you go by gap length minus coil length/2.). But lets add some numbers. Here's the Basta sim I did of the 12OB150 on a 50 by 90cm baffle, with 10mH (0.5 ohm) and 50uF:
Sensitivity is 90 dB for 2.83V, and the -6dB point is 54Hz. You can't give it too much power before you hit the excursion limits - around 9 V, if you go by the more conservative linear xmax. But you are getting 100 dB in the passband, with that input. Now, if you add a second driver, and change the filter to 6mH (0.3 ohms) and 80 uF, here's what you get:
You're getting 94dB sensitivity, and response extends to 51dB, for -6dB. With 9V input you're getting 104 dB at 100 Hz. With a fairly low power amp, and so long as your room's not too huge, and you're not looking for huge volume levels, that looks perfectly usable to me.
Disclaimer: it's all just simulation, but I think it's not going to be too far away.
Sensitivity is 90 dB for 2.83V, and the -6dB point is 54Hz. You can't give it too much power before you hit the excursion limits - around 9 V, if you go by the more conservative linear xmax. But you are getting 100 dB in the passband, with that input. Now, if you add a second driver, and change the filter to 6mH (0.3 ohms) and 80 uF, here's what you get:
You're getting 94dB sensitivity, and response extends to 51dB, for -6dB. With 9V input you're getting 104 dB at 100 Hz. With a fairly low power amp, and so long as your room's not too huge, and you're not looking for huge volume levels, that looks perfectly usable to me.
Disclaimer: it's all just simulation, but I think it's not going to be too far away.
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An F5 should be able to do 1 ohm without issue....providing it has a properly designed power supply (Tranny VA and capacitance)
Right now i have two subwoofer boxes with bass reflex that i can use and it sounds really nice.... however, i would like to go full open baffle - this is why i am trying this ......
My room is around 16m2 and i have brick walls, floor is laminated wood and ceiling is concrete something....
The amount of bass right now as it is is almost the right amount.... it is just that on some songs i kind of think i would want to hear a bit more... so i am kind of there almost even with this simple setup...
Giving this is a temporary instalation and that the panel is just 60x80cm2 and 25mm thick mdf, i think when i go full thickness (at least 5cm) of baltic birch laminated, i might get a little bit more bass too