No, it does absoluely not eliminate the wandering wandering of the sub because that would require a perfectly flat ground. P-P configuration only greatly (but not perfectly) reduces the movement in the P-P direction but not in the lateral or any uneven direction which is caused by a uneven floor. Have you ever encountered a perfectly flat floor? In over38 years I do have not. You need some kind of level adjustment and/or absorber. For both you need mass to be effective or extremely absorbant soft feet to compensate but even then the subs do not sound even close as precise and 'black' as sturdy, heavy subs. Your theory works on many tops or many fullrange speakers - which SQ could also be realized with heavy enclosures but with different measures and construction principles. For subs that's a different story and it's actually not that hard to keep the resonances below the reproduced range, even the room response is magnitudes above heavy enclosures resonances levels, ~30-40dB lower, you cant even remotely match that wit light enclosures which lose the precise sound reproduction by the impulses moving the enclosure or transfering (wasting) the signal impulse peak into an absorpton material and flatten the impulse response. Listen to a 'light' sub and then to the exact same sub in a really heavy enclosure, ie walkway cocrete tiles and the increase of resolution, blackness and unbeliveable authority will literally blow your mind. I know, none of that convinces you. Make an imulse response measurement of a 25kg sub and the same s50kg sub. No light sub can bring back that flattened impulse peak. Light subs are not your friend.
I agree there completely, the problem lays in the fact that many speaker builders connect the drivers too clse to each other (core piece bore air flow blocked or directly interacting) or mix a broken in driver with a completely factory fresh one. Both cases result in uneven behaviour. It's exactly the same as demonstrated on the experiment with the two balloons on a connected tube, one already blown up once (stretched), one fresh. When the tube is put under pressure, the already stretched will expand always first since it is already weaker. The same with the drivers, the (more) broken in will always stretch more. So it's not 90% but realistically about 70% (or less). Which makes it a lot less 'ignorable'.
Fortunately there are two extremely easy and cheap solutions for that:
- 'Break in' both for a long time so the compilance and fr are practically the same. Or...
- Build the enclosure with a wall between them. They can't influence each other anymore. Impulse compensation and everything else is the same and they will eventually break in to the same compilance and fs.
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Quite a few posts have emphasised the need to control panel resonances, and it's been suggested that light, stiff panels are good because they push resonances up, and increase the resonant Q, making it harder to stimulate the resonance. I've read similar points many times, in discussions of box construction.
I wonder if that's missing an important point, though? Speaker cabinets vibrate because of the vibrational energy imparted to them, directly or indirectly, by the drivers, and that vibration is not restricted to specific frequencies at which there's a resonance. When panel resonance happens it's a problem, of course, but it's not the only problem. Light, thin undamped panels will very easily be set in motion at a wide range of frequencies, even where there's no specific resonant problem. Think about how string instruments or keyboard instruments work - the principal sound generating element is a light, stiff panel of wood. These have to vibrate pretty evenly across a very wide range of frequencies, otherwise some notes in the scale would sound much more strongly than others.
Why do some speaker cabinets, such as those of the LS3/5a, use thin walls, then? Well, the BBC cabinet approach depends on the mass damping provided to thin cabinet walls by bituminous pads. Thin walls are preferred because thicker walls would be harder to damp.
As for subs, I've never tried one with thin, light walls. But I know that in buildings, thin stiff walls don't do much to hinder the passage of low frequencies from one room to another.
I wonder if that's missing an important point, though? Speaker cabinets vibrate because of the vibrational energy imparted to them, directly or indirectly, by the drivers, and that vibration is not restricted to specific frequencies at which there's a resonance. When panel resonance happens it's a problem, of course, but it's not the only problem. Light, thin undamped panels will very easily be set in motion at a wide range of frequencies, even where there's no specific resonant problem. Think about how string instruments or keyboard instruments work - the principal sound generating element is a light, stiff panel of wood. These have to vibrate pretty evenly across a very wide range of frequencies, otherwise some notes in the scale would sound much more strongly than others.
Why do some speaker cabinets, such as those of the LS3/5a, use thin walls, then? Well, the BBC cabinet approach depends on the mass damping provided to thin cabinet walls by bituminous pads. Thin walls are preferred because thicker walls would be harder to damp.
As for subs, I've never tried one with thin, light walls. But I know that in buildings, thin stiff walls don't do much to hinder the passage of low frequencies from one room to another.
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3. If you can measure T/S & match.
Given the wavekengths involved in a subwoofer the wall will not do anything but be a brace. Better if it has holes in it.
This is how we did it:
The brace leaves the VC vent clear, you will note the brace above which creates a cross. WXD are fairly tight to the driver asis the bottom so that provides pretty good coupling for “pull” cancelation.
2 SDX10s (traded for some drawings), in 44 litre sealed. Next one i’ll do the bit taller one. 15mm BB. Worked REALLY well (they got sold when i was in hospital, the new owner loves them). Got 4 more tucked away.
I could get the top to start moving at very high levels (had to turn the mains amp off, it was quite a bit liuder than i would ever play it), but i’m pretty sure the amp was clipping heavily which produces lot of HF crap. I’ve got some granit slabs i can put on the top of the next ones. Also helpswhen something wet is put on top.
If you search there are videos of people doing the glassof water test.
dave
Given the wavekengths involved in a subwoofer the wall will not do anything but be a brace. Better if it has holes in it.
This is how we did it:
The brace leaves the VC vent clear, you will note the brace above which creates a cross. WXD are fairly tight to the driver asis the bottom so that provides pretty good coupling for “pull” cancelation.
2 SDX10s (traded for some drawings), in 44 litre sealed. Next one i’ll do the bit taller one. 15mm BB. Worked REALLY well (they got sold when i was in hospital, the new owner loves them). Got 4 more tucked away.
I could get the top to start moving at very high levels (had to turn the mains amp off, it was quite a bit liuder than i would ever play it), but i’m pretty sure the amp was clipping heavily which produces lot of HF crap. I’ve got some granit slabs i can put on the top of the next ones. Also helpswhen something wet is put on top.
If you search there are videos of people doing the glassof water test.
dave
I have repeated it often. Finesse as aoopsed to brute force.
Motly from where the driver is connected to the box.
You are starting to get into the weeds, Strike a tuning fork with a broadband excitation and it only resonates at one very specific frequency
Thry developed their approach based on research that showed resonaces are not as audible at low frequencies so they pushed resonanes down. Problem is it is often audible. The research is all available on-line.
This works well if the resonances are below the speaker’s bandpass. For example: midrange boxes.
It is one approach. Others include the over the top like the Mrten’s, and constrained layer — probably achieves best results,but a whole lot of work and not that much, if any gain in typical dimestic situatiims. Carbob Fibte inner and outer skins with sfoamy stuff in between for example.
The first technique is a no brainer for subs, easy to push box resoances well abiove the speakers bandwidth. If it onlhy has woofers on one side you might having to take measures to minimize walking.
dave
In theory weight at the top 'might' be less good than the bottom. It wouldn't be restrained or damped by the floor so if it moves/vibrates at all then it could find a resonant frequency in combination with the cabinet. But in practice this may not happen to any noticeable degree, and would be fairly easy to test - so could be worth trying, especially if you want to avoid screwing the cabinet down.
Speaking of the Rogers a friend of mine added two nice bass boxes one per channel
We both understood that without subs we were listening to a radio
Imho the people who have lived with small speakers don't know what music is
It happened to me the first time i listened to a 12" woofer speaker
Modding Rogers could have a bad result in their resale value
Better mod something cheaper
We both understood that without subs we were listening to a radio
Imho the people who have lived with small speakers don't know what music is
It happened to me the first time i listened to a 12" woofer speaker
Modding Rogers could have a bad result in their resale value
Better mod something cheaper
Well, a tuning fork is about as different from a light stiff panel of wood as its possible to get. That's pretty much my whole point right there.
(To spell it out: a tuning fork is designed to resonate at one specific frequency, and it's pretty much impossible to get it to vibrate at any other frequency. On the other hand, a piano sound board, or a violin belly, can be easily stimulated into vibrating at a very wide range of frequencies.)
Regarding the BBC approach, I know the corporation's research is available, and I've read it. (And I've owned many speakers built that way, including some with impressive bass.) Can you point me to similar quality research that contradicts the BBC conclusions?
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I dampen and tune my sub boxes with turnbuckles and threaded rod. One assembly every 8 inches. Unlike a brace, the force won’t shift as the wood does and if the box wood shifts, the turnbuckles can be tightened to offset. Not cheap but not expensive either. I learned the method from a carpenter who specialized in building and repairing stairs.
I've heard people using the threaded rod technique claim the rods themselves causes resonances. Just something to keep in mind.
We did that in the late 70’s. That was when i figured out the top benefits a lot by the HP filter on the mains.
dave
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Huh. Resonanc wise, the tuning fork is the essence of a well built speaker panel.
A speaker is not a musicalinstrument. It should not be designed to purposely produce a wide range of choosable frequencies and charcteristic harmonics trains.
No, i can only say that most of the many built in such a way that i have heard have bass resonance issues. Some people like that.
And the whole box as a musical instrument is another school of loudspeaker box building.
dave
It can be an issue. Inside the box it shouldn’t be a big issue. The build i have planned that uses them outside will have shrink wrap on them, and given it is a subwoofer, if they are tight enuff the natural resonace fundemental should be well above the speakers bandpass.
dave
Dave, in post #2 you said light and rigid was best. Now you're saying a tuning fork (i.e. a heavy solid metal rod, resonating strongly at a specific frequency) is ideal. I'm not clear what you're really arguing for.
Moreover, you haven't actually addressed my main point, which was that light stiff panels vibrate easily at many frequencies, and do little to attenuate the passage of sound, including low frequencies.
You say a speaker is not a musical instrument. I never said it is! You're the one advocating resonant cabinets, not me.
Personally, for subs I'd lean towards stiff, cross-braced and heavy. I totally agree with dual-opposed drivers, but I'd prefer to connect them to each other, and decouple them from the cabinet. When I have a chance I'll build some of those. (I'm actually open, also, to trying the light and stiff school of thinking, but I have reservations, as I've made clear, and I'd like to hear more argument for, if I'm going to try it.)
Actually, it's the exact opposite. A well built speaker panel should not resonate, a tuning fork is made to resonate!
With the goal of making it a “tuning fork” high enuff in frequency it will be unlikely it ever gets set off.
Everything resonates. Light & stiff (with adequate bracing) pushes any fundemental resonances up in frequency. A panel willnot be excited below its fundemental resonance.
You implied it with the comment about pianos.
Mass on its own is no care. If you add mass without getting a coresponding increase in stiffness it will lower resonance frequencies. If more mass brings extra stiffness that is fine,it isn’t mass that is important. A 15mm BB sub will be better than a ¾” MDF one, both well executed. Because the BB is stiffer. That it is lighter is a bonus. And in a sub whw=ere you can easily take advantage of push-push to (largely) eliminate the injected into the box that causes resonance.
dave
The perfect enclosure does not resonate. In praxis, the goal is to make the best approach to it - instead of to make it willfully resonate 'like a tuning fork'. That's neither any speaker development goal nor rectifies/put right what you've wrote. Maybe you wanted to express something else - but you didn't and I don't know what else you could have meant. It's still not true, no matter how you defend it, in fact the, exact opposite. I don't mind someone making a mistake but the forum does not benefit from denying it.
If it's too hard to admit it, maybe just let it go?
Pretty much what i said.
The alternate to HF resonances is LF, that is more audible. Or lower Q, also more audible.
There is over the top, like the Rockport i mentioned earlier, or clever, elegant, and good enuff so it doesn’t matter.
Engineering or brute force. both can work. Oe engineering and brute force (and lots of effort and money),
How would you make a non-resonant box?
dave