Allen, I would enjoy such a thread but Scott's hyperbole and straw manning was a turn off for me. I don't want to engage in emotional arguments over preference.
There is nothing wrong with simply stating facts politely and engaging in robust debate without referencing "cults" and assuming the person that has a certain preference is somehow inferior because it does not align with all-seeing (hearing?) savant's preferences.
There is nothing wrong with simply stating facts politely and engaging in robust debate without referencing "cults" and assuming the person that has a certain preference is somehow inferior because it does not align with all-seeing (hearing?) savant's preferences.
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OK, I'll accept the challenge. First principles:
Let's start with a given driver in an infinite baffle, in a large room. This may take the form of a simple baffle or a folded baffle - actually an infinite sealed box. Both will have cone movement largely determined by cone mass and suspension compliance, being mass-controlled above resonance. Both will radiate sound waves in an identical manner, noting that efficiency will be proportional to cone area.
As we make the baffle finite, and reduce its size more and more, the two models will start to diverge in their properties.
The boxed driver will have to start working to overcome the compliance of the air in the box. In order to minimise this, and to combat changes to cone resonant frequency, drivers intended for this mode of operation will have relatively small, heavy, cones. Both of these aspects reduce efficiency - cone size affecting the degree of coupling to the air, and cone mass reducing the amount of cone movement for a given motive force. The smaller the box, the lower the efficiency.
The other driver will operate largely as normal (mechanically) with a baffle of reduced size, but there will be less and less effective coupling to the air, as air is leaked around the sides of the baffle. This effect is worst at low frequencies - the lower you go, the more air is leaked. This can be compensated for electrically, but to attempt to regain efficiency, a driver with a large, light cone would be used for this application. But the smaller the baffle, the lower the efficiency.
So, drivers would ideally be optimised for one or other of the applications.
The other side of the story is how the two types couple to the air, and propagate sound waves in a room. The box will radiate sound as a monopole at low frequencies, and will tend to excite room modes all directions.
The open baffle will tend to radiate as a dipole, and excite only one or two of the room modes if standing vertically - but cannot propagate the lowest frequency sound waves unless the room is large enough to accommodate at least half a wavelength in the appropriate direction. Also, the back-wave can cause problems, being in anti-phase to the forward wave. The speaker cannot be positioned too close to the wall behind for this reason. Biggish rooms, at least in one direction, are required.
Well, that's a qualitative comparison of box vs OB. I'm sure there can't be any possibility of controversy...
Let's start with a given driver in an infinite baffle, in a large room. This may take the form of a simple baffle or a folded baffle - actually an infinite sealed box. Both will have cone movement largely determined by cone mass and suspension compliance, being mass-controlled above resonance. Both will radiate sound waves in an identical manner, noting that efficiency will be proportional to cone area.
As we make the baffle finite, and reduce its size more and more, the two models will start to diverge in their properties.
The boxed driver will have to start working to overcome the compliance of the air in the box. In order to minimise this, and to combat changes to cone resonant frequency, drivers intended for this mode of operation will have relatively small, heavy, cones. Both of these aspects reduce efficiency - cone size affecting the degree of coupling to the air, and cone mass reducing the amount of cone movement for a given motive force. The smaller the box, the lower the efficiency.
The other driver will operate largely as normal (mechanically) with a baffle of reduced size, but there will be less and less effective coupling to the air, as air is leaked around the sides of the baffle. This effect is worst at low frequencies - the lower you go, the more air is leaked. This can be compensated for electrically, but to attempt to regain efficiency, a driver with a large, light cone would be used for this application. But the smaller the baffle, the lower the efficiency.
So, drivers would ideally be optimised for one or other of the applications.
The other side of the story is how the two types couple to the air, and propagate sound waves in a room. The box will radiate sound as a monopole at low frequencies, and will tend to excite room modes all directions.
The open baffle will tend to radiate as a dipole, and excite only one or two of the room modes if standing vertically - but cannot propagate the lowest frequency sound waves unless the room is large enough to accommodate at least half a wavelength in the appropriate direction. Also, the back-wave can cause problems, being in anti-phase to the forward wave. The speaker cannot be positioned too close to the wall behind for this reason. Biggish rooms, at least in one direction, are required.
Well, that's a qualitative comparison of box vs OB. I'm sure there can't be any possibility of controversy...
Well considering how triggered young Scott became I think this deserves its own thread because there is some militant level hatred of open baffle "cults" here and maybe it should be fought out in a dedicated spot without spoiling the OP's thread. Poor OP was just looking for a new woofer...
Only this!
I remember reading some 'pampleths' about constructing boxes and
the main reason for building a box is to separate the front from the back emission. The following chapter usually talks about how to render soundproof the box ( remember the cavity for sand filling?).
Ohhh but this is old!
( just to say...from a mechanical POV all boxes made with wood are not-soundproof so the panels radiate...and they are dipoles! One could say that the panel's radiation is several dB down but...Oh! Panels....)
On topic.
I had Selenium WPU 1805-X U-frame bass, Qts 0.7, Fs 35 Hz, sensitivity 99 dB, Xmax 13 mm. I had it corrected flat to 25Hz. On my moderate comfortable SPL levels distortion is also moderate but rising lower than 40 Hz.
I am not sure is WPU 1805-X discontinued or not, Harman-JBL is now owner of Selenium, and lot of speakers are discontinued.
I had Selenium WPU 1805-X U-frame bass, Qts 0.7, Fs 35 Hz, sensitivity 99 dB, Xmax 13 mm. I had it corrected flat to 25Hz. On my moderate comfortable SPL levels distortion is also moderate but rising lower than 40 Hz.
I am not sure is WPU 1805-X discontinued or not, Harman-JBL is now owner of Selenium, and lot of speakers are discontinued.
Well that's engineering "truths" folks on this forum know well - in the abstract.
The question is behaviour in a room. Where's the evidence of how dipole bass plots?
If there is anybody out there with a dipole, please post some traces. Now... before we are exhausted from this arm-chair theorizing.
(Can somebody explain to frangus that free-floating (and repeated) abuse is not appropriate on the forum. His posts appear to be absent of substantive information.)
B.
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Um, in case you didn't notice, the first post was in 2011, ten years ago. The user's last recorded activity was from last November.
But the topic is certainly still a relevant one, so I suggest that we post about large format woofers for OB/dipole systems, and how they can be used (e.g. frequency range, type of baffle or nude, etc.) for a productive continuation of the original question.
Hi, I have found two different datasheet versions for this woofer. The first is saying Fs=41Hz, Qts=0.7 and the second Fs=34Hz, Qts=0.57.
What is right or wrong or did they change the design?
I have measurements somewhere, but it’s easier to just move from front of woofer an turn 90 degrees. There is absolutely no bass at 90 degree. Try the same with boxed speaker and There is still plenty bass at 90 degrees
Since this thread popped up again, I thought I would try to get back to the original question by giving some useful suggestions and listing some drivers.
I think one important aspect and requirement that will determine what "kind" of woofer is suitable is the bandwidth that the driver must operate over. This touches on OB design, and there are many different approaches. On the one hand, there are fullrange enthusiasts who would like to try an OB system. From my experience, these tend to turn out as a small-ish fullranger plus a "woofer", both mounted in a large planar baffle. Let's call these the Martin King type OB system. Next there are multi-way (more than 2 way) large planar or folded systems using one or more woofers or subwoofers. These might use a fullranger, horn, etc. but many use a midrange driver. Let's call this the Pure Audio Project type system. Next there are more compact or "minimal baffle" multi-way OB systems. The LX521 is a great example of this, so let's call this the Siegfried Linkwitz class of OB. Finally, there are "no baffle" multi-way OB systems. I am a proponent of this kind of build, so we could call it the CharlieLaub class if that pleases the court. All of the systems just described use a "woofer" and are OB systems, but each will have their own requirements for bandwidth, Sd*Xmax volume displacement, and voltage sensitivity. There is not one "best" driver that covers all the bases and fits all budgets
There are drivers that have been designed for OB/dipole use. For example the AE Speakers dipole driver line, and some new drivers from SB Audience (12OB150-01, 15OB350; both available from Madisound in the USA). These would be suitable for a large planar OB system or in a folded (U-frame, H-frame, etc) subwoofer for example. Sometimes a driver that is designed for "infinite baffle" use can also be a good candidate for an OB woofer or subwoofer. One example of this is the Fi Car Audio IB318v2, and I have built a large H-frame subwoofer around the driver that I am very happy with.
It's a good idea to consider motor/wind noises if you wish your OB woofer to reproduce the lowest octaves where excursion requirements are highest. I have tested several potential drivers only to find them quite noisy when driven during break-in with e.g. a 20Hz sine wave. Since the rear of the driver is open to the room, this can result in unwanted sounds during playback. Modern pro audio drivers with neo motors often have a ring of small holes that create turbulence and air flaw that helps to cool the voice coil, but these tend to cause noise issues. Drivers with a single pole vent tend to be much quieter. I would consider that point carefully when selecting your woofer.
In my design approach, the "woofer" only operates down to 80-100Hz and a dedicated subwoofer (not necessarily an OB/dipole sub) is used below that. I feel that the Eminence Deltalite 2515 is a great woofer when used in this way. This driver is not expensive, at about $170 each. The basket is very open and the motor is small quiet, since it uses a single pole vent. All in all it make a great woofer for OB dipole use, But because Xmax is only 4.5mm, Fs is not low and Qts is not high, it is not well suited for the lowest octaves. The 2515 is operated as high in frequency as is practical (its high end extends nicely to over 800Hz) until it crosses over to a midrange. The near-resonance region (around Fs) of a driver often has higher distortion than the mid passband region, and by operating only above 80Hz the driver is used where distortion is lowest. For this reason my designs tend to be a 3-way nude OB operating down to 80-100Hz, plus one or more subwoofers depending on the room size.
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GRS 12Sw-4 expriences
Hi
I bought some GRS 12SW-4 woofers to try out in an OB speaker I'm currently working on and I will share my experiences:
On paper the GRS 12SW-4 lookes ideal for Open Baffle:
Qts: 0,98
Fs: 29,6Hz
Xmax: 8,5mm
Impedance: 4ohm
They sound really good, with good definition and of course very little coloring. The will easily play down to 30 Hz. I am using a xover of a 12mH inductor and a 150uf cap to make a 2nd order filter. This yields a nice response from 30Hz-200Hz. All in all the woofers do as they promise. But it coms at a price: Loudness! They need a lot of power. I’m using 2 woofers per side in series to get 8ohm. This of course doesn't help on the loudness. I am thinking about using them in parallel to get 2 ohms, which my amp can handle, but it was not the idea from the beginning. My baffles are about 35cm wide with 8cm wings. Not the widest of baffles I know. They do play loud enough 95% of the time with my 50W First Watt F5t, but I’m missing some headroom before the amp starts clipping. Clipping occurs mostly on bass heavy electronic dance music though, so I can live with it
.
If there will be a next time, I would use at least 4 per side to get 4 ohm and an extra 6dB output, and consider using them in a folded OB, ripole or something like that.
So will I recommend them for OB use? Yes for sure, but be ware of the low output and the 4ohm impedance.
Mikkel
Hi
I bought some GRS 12SW-4 woofers to try out in an OB speaker I'm currently working on and I will share my experiences:
On paper the GRS 12SW-4 lookes ideal for Open Baffle:
Qts: 0,98
Fs: 29,6Hz
Xmax: 8,5mm
Impedance: 4ohm
They sound really good, with good definition and of course very little coloring. The will easily play down to 30 Hz. I am using a xover of a 12mH inductor and a 150uf cap to make a 2nd order filter. This yields a nice response from 30Hz-200Hz. All in all the woofers do as they promise. But it coms at a price: Loudness! They need a lot of power. I’m using 2 woofers per side in series to get 8ohm. This of course doesn't help on the loudness. I am thinking about using them in parallel to get 2 ohms, which my amp can handle, but it was not the idea from the beginning. My baffles are about 35cm wide with 8cm wings. Not the widest of baffles I know. They do play loud enough 95% of the time with my 50W First Watt F5t, but I’m missing some headroom before the amp starts clipping. Clipping occurs mostly on bass heavy electronic dance music though, so I can live with it
.If there will be a next time, I would use at least 4 per side to get 4 ohm and an extra 6dB output, and consider using them in a folded OB, ripole or something like that.
So will I recommend them for OB use? Yes for sure, but be ware of the low output and the 4ohm impedance.
Mikkel
Charlie,
The FICar Audio IB318 V2 specs state it's Xmax is 34mm "(one way!)", over 2.625 inches (68mm) peak to peak.
No Xlim or Xmech is listed as far as I've found.
Have you found the IB318 can actually move that far, and if so, is it still clean (low THD) at that excursion?
Have you found whether the suspension (surround or spider) or voice coil former hitting the back plate is the mechanical limit?
Thanks,
Art
A single 18" at 64mm peak to peak excursion used on an open baffle is unlikely to produce more than 106dB SPL at 20Hz at the listening position, perceived at about the equal loudness of an average conversational level of 60dB.
Rattles resulting from VLF (very low frequency) SPL may be annoying, but have nothing to do with whether the FICar Audio IB318 V2 output is still clean at that level.
Rattles resulting from VLF (very low frequency) SPL may be annoying, but have nothing to do with whether the FICar Audio IB318 V2 output is still clean at that level.
nice ,but in series you have a 90/91db and isn't good idea 2ohm on classA ,the OB bass need 6db min over the mid/tw ... biamp or go bigger 15/18 grsGRS 12Sw-4 expriences
Hi
I bought some GRS 12SW-4 woofers to try out in an OB speaker I'm currently working on and I will share my experiences:
On paper the GRS 12SW-4 lookes ideal for Open Baffle:
Qts: 0,98
Fs: 29,6Hz
Xmax: 8,5mm
Impedance: 4ohm
They sound really good, with good definition and of course very little coloring. The will easily play down to 30 Hz. I am using a xover of a 12mH inductor and a 150uf cap to make a 2nd order filter. This yields a nice response from 30Hz-200Hz. All in all the woofers do as they promise. But it coms at a price: Loudness! They need a lot of power. I’m using 2 woofers per side in series to get 8ohm. This of course doesn't help on the loudness. I am thinking about using them in parallel to get 2 ohms, which my amp can handle, but it was not the idea from the beginning. My baffles are about 35cm wide with 8cm wings. Not the widest of baffles I know. They do play loud enough 95% of the time with my 50W First Watt F5t, but I’m missing some headroom before the amp starts clipping. Clipping occurs mostly on bass heavy electronic dance music though, so I can live with it
If there will be a next time, I would use at least 4 per side to get 4 ohm and an extra 6dB output, and consider using them in a folded OB, ripole or something like that.
So will I recommend them for OB use? Yes for sure, but be ware of the low output and the 4ohm impedance.
Mikkel
PS1:NP have a boost jfet for ob bass....look
PS2: mod to SLOB ie one face to floor one to you slot load ....some db more
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