I've seen a number of open baffle builds that hang drivers, or attach them to flexible mounts to decouple them from the vibrations of other drivers. The LX521 uses a stand to decouple the subwoofer frame from the rest.
I have not found any measurements to show how useful this is. Does anyone have some measurements to show the difference this decoupling creates?
I have not found any measurements to show how useful this is. Does anyone have some measurements to show the difference this decoupling creates?
I have been wondering the same issue.
OB woofers must be large and have heavy moving mass and high excursion. Elastic mounting will make the frame to move because of counterforce, leading to loss ef efficiency(spl), added THD, IMD etc. No baffle means high dipole null and poor low freq spl.
Baffle/box will add effective baffle area, that helps low extension but harms upper usable limit. Installation should be firm and as high mass as possible. Opposing or v-shape installation of a pair of drivers like in LX521 will reduce inertia problems.
OB woofers must be large and have heavy moving mass and high excursion. Elastic mounting will make the frame to move because of counterforce, leading to loss ef efficiency(spl), added THD, IMD etc. No baffle means high dipole null and poor low freq spl.
Baffle/box will add effective baffle area, that helps low extension but harms upper usable limit. Installation should be firm and as high mass as possible. Opposing or v-shape installation of a pair of drivers like in LX521 will reduce inertia problems.
The best way to suppress vibrations is to weigh the OB with concrete or, in a less ideal way, to make shelves on which you can place pieces of granite. The bass then becomes monolithic and incredibly impressive.
Knock on wood with your finger and you will easily hear the transmission of sound, but knock on a stone wall and you will hear how the sound is greatly damped, so 20 cm thick concrete is best.
The baffle size (or existence) is different from what I'm asking about though. It seems like some people think the subwoofers move enough to introduce distortion into the mid(s) and tweeter? I am hoping to see some measurements that prove this one way or the other.
Having paired woofers that move in opposite directions makes sense for reducing vibrations, but again, idk if it makes a significant difference in practice.
I only want to spend the effort on decoupling if it is worth it, and I haven't yet seen any measurements to know if this is a real thing or not. I'm guessing it is only measurable if the woofers are causing significant movement of the baffle, and if that's the case then maybe reducing that movement with mass and spikes makes more sense than isolating the drivers with special mounts?
Having paired woofers that move in opposite directions makes sense for reducing vibrations, but again, idk if it makes a significant difference in practice.
I only want to spend the effort on decoupling if it is worth it, and I haven't yet seen any measurements to know if this is a real thing or not. I'm guessing it is only measurable if the woofers are causing significant movement of the baffle, and if that's the case then maybe reducing that movement with mass and spikes makes more sense than isolating the drivers with special mounts?
Sound in a cement OB and weighted with granite pieces. 1x18", 4x15", 2x10", 2x6.5", 2x tpl 150. This is acoustics from Russia:
When I built my OB three way speakers (picture, current state), I decided to mount the drivers with rubber o-rings on every screw and neoprene gasket on every driver, soft-coupling the drivers to the simple rectangular baffle. There are also rubber feet at the base. The whole system vibrates very little, just barely noticeable to the touch while playing. I would think this is less distortion than discernible vibrations from the panel. I could be wrong. Nevertheless, I think they sound fantastic. My Manzanitas, by comparison, vibrated quite a bit more. They still sounded great. Food for thought.
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I think the soft decoupling simple reduces the net excursion by a fraction. Cone moves forward e.g. 4mm. Frame moves backwards 4mm/ratio where ratio is the frame weight/(weight of cone +VC +?}. this is linear so it shouldn't add distortion. I did that once on a subwoofer and I could really feel the frame moving, but not the baffle, and I had no complaints about the sound.
I use decoupling in my dipole loudspeaker designs where there is not much mass to stability the drivers from moving from reaction force. You can probably envision the vibration from bass drivers pumping away feverishly to make up for dipole losses, but there is also some movement from a midrange driver that could modulate the tweeter output a bit. So I decouple.
In the LX521 the woofer box uses two SEAS 10" woofers that have a pretty substantial aluminum cone, and there is vibration generated even though they are mounted in a "V" configuration. Also, because OB speakers tend to be 2D structures (e.g. a planar baffle) these are very weak and subject to induced vibration and standing wave modes. Mass helps but in my case there is no where to put it.
Also vis a vis @Juhazi 's comment, a freely swinging driver will move/swing from the cone motion. I did an analysis on this for a paper I published last year. The amount of the loss in output is related to the ratio of mass of moving parts (cone, voice coil former) to the rest of the driver's mass and typically is much less than a dB, e.g. 0.1 dB. I'll take that.
In the LX521 the woofer box uses two SEAS 10" woofers that have a pretty substantial aluminum cone, and there is vibration generated even though they are mounted in a "V" configuration. Also, because OB speakers tend to be 2D structures (e.g. a planar baffle) these are very weak and subject to induced vibration and standing wave modes. Mass helps but in my case there is no where to put it.
Also vis a vis @Juhazi 's comment, a freely swinging driver will move/swing from the cone motion. I did an analysis on this for a paper I published last year. The amount of the loss in output is related to the ratio of mass of moving parts (cone, voice coil former) to the rest of the driver's mass and typically is much less than a dB, e.g. 0.1 dB. I'll take that.
Several speaker makers actually couple a woofer to the rear panel via a long screw. This image from the Linkwitz Orion shows a brace on the mid-woofer, and is an example of reducing the possibility of the dirver shaking the baffle if not the entire speaker assembly. IMHO, that's much more important than to leave a driver floating around.
The Orion is an interesting case. The earliest version had the 8" Seas mid attached to the baffle in the conventional way. Magnet mounting was a later development. As you say, 6thplanet, the bracket holding the magnet was mounted on the woofer box.
The idea was to have a foam seal between the mid driver and baffle, but no fixings. I acquired a pair of Orions, some years ago, and after a while I decided to adjust the mounting of the mid, so that it was pressing more tightly against the baffle (I was worried that it wasn't contacting the foam seal securely enough.) I found that the sound changed, and not for the better - a rather dull, dead quality in the mids. I readjusted it back to the way it had been, and everything was fine again.
I'm not sure what the lesson of that is, except that baffle vibration is definitely an issue, in OB speakers.
The idea was to have a foam seal between the mid driver and baffle, but no fixings. I acquired a pair of Orions, some years ago, and after a while I decided to adjust the mounting of the mid, so that it was pressing more tightly against the baffle (I was worried that it wasn't contacting the foam seal securely enough.) I found that the sound changed, and not for the better - a rather dull, dead quality in the mids. I readjusted it back to the way it had been, and everything was fine again.
I'm not sure what the lesson of that is, except that baffle vibration is definitely an issue, in OB speakers.
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But vibration from the woofers up into the mid is not? Is the baffle not connected to the woofer enclosure?
Regarding measurements, distortion (mostly H3) shows framework resonances best. Spl response has too many variables to be totally reproducible between evolution versions.
I think that the difference that ianbo heard was distortion peaks at certain frequencies.
My choice is sealed bow subwoofer, elastically mounter 12" low mid and planar magnetic upper mid and tweeter.
I think that the difference that ianbo heard was distortion peaks at certain frequencies.
My choice is sealed bow subwoofer, elastically mounter 12" low mid and planar magnetic upper mid and tweeter.
Hi, reasoning with radiating area vibrating baffle has likely more audible effect than vibrating mid driver alone, if I understood what you refer to. Another, shaking a driver would make the cone resonate at resonant frequency, except if it's connected to an amplifier it doesn't due to electrical damping. So, if mid woofer resonates due to bass, it has likely very little effect to overall sound, compared to if whole baffle was shaking.
Is there any FEM or other simulations about OB baffles resonating anywhere? It would be quite interesting I think. Trying to imagine shaking baffle is also a dipole sound source, but different parts in different phase so perhaps just "noise" like any resonance in any system, sound of the system and not sound of the music. Well, just speculating.
I agree with you. I don't really understand why magnet mounting made a difference. Woofer vibration was being fed into the structure, whichever way the mid was mounted, and the mid was connected to the whole structure, in both versions. Nor do I really understand why having magnet and rim in contact with the structure was less good. (But @tmuikku makes some interesting observations.)
I take your point on an intellectual level. What I can suggest is to get a big (12 or 15") driver in your hands, connect it (solidly) and wind it up playing live while you hold it by the basket near the surround and then hold it by the magnet. It's formative.
That's exactly what I'm going to do later. I did that a couple weeks ago while I was doing tons of tests and I don't remember the vibration being that intense, but I want to pay closer attention. Maybe I'll touch it to a baffle to find out how much sound that vibration makes.