subwoofers with dual opposed drivers

[SigbergAudio]

I was being sarcastic. dB is a relative value, what is your reference? Maybe you meant SPL which is a defined value.

Obviously spl yes, sorry. But some report CEA2010 results in RMS and some peak, and some 1m and some 2m, hence the specification of that to avoid confusion (or so I thought)

 

[sarumbear]

Obviously spl yes, sorry. But some report CEA2010 results in RMS and some peak, and some 1m and some 2m, hence the specification of that to avoid confusion (or so I thought)

SPL is an RMS value. It is a clearly defined unit. I urge you simply use SPL and just quantify the measurement distance.

Thank you for listening.

 

[Jinjuku]

I just wanted to chime in on DIYing my Dual Opposed subs: I liked that for a sealed alignment the construction is pretty easy.

I used the Infinity Kappa 120.9w's. Being fed by a fan and heatsink modded Behringer iNuke 3000DSP. I've no complaints for the $1K it ran me all in. I couldn't beat it commercially when I did them ~6 / 7 years ago and I doubt I could beat them now commercially for the money.

 

[SigbergAudio]

SPL is an RMS value. It is a clearly defined unit. I urge you simply use SPL and just quantify the measurement distance.

Thank you for listening.

Not in disagreement with that. The most used terms for these types of measurements are peak and rms so we've just followed suit, but I guess we could write both to cover all bases!

 

[gnarly]

I like dual opposed subs.
I run over the top levels of bass (and SPL in general), and the reduction in cabinet vibration really helps.
(And i should mention before continuing, i always use subs with xover no higher than 100Hz.)

For me, there's no need to measure or try to apportion room vibration or tactile feel, between air-born acoustic transmission or any floor talk/resonance from the sub(s).

I just run the subs alone at high SPL and listen.
If a sub alone can be aurally localized, either the cabinet is resonating and needs more bracing, or it's chattering against the floor surface.
(Localization is not prevalent if all content is below 100Hz.)

I've found no amount of bracing or cabinet weight can keep a good prosound 18" sub from wanting to walk around at high SPL.....hence the need for dual opposed.

fwiw, the "sub alone" listening test often makes me laugh at myself (and how crazed we as audio nuts, get with distortion specs).
The room can be freaking LOUD...at all kinds of resonant frequencies....... simply from subwoofer excitation.

 

[sarumbear]

Not in disagreement with that. The most used terms for these types of measurements are peak and rms so we've just followed suit, but I guess we could write both to cover all bases!

The issue is not terms, its the lack of any units. Will you say a power amplifier has 20dB output. dB by itself is not a unit, its a relative value. If used by itself it means nothing. You need to add a unit to the dB to make any meaning. dBV, dBSPL, etc.

 

[Chromatischism]

I cannot imagine how this can be true. Do you mean that the floor is generating half of the subwoofer output?

What? I responded to this:

Movement in floor and seating is induced from the acoustic sound energy in the room. It is the sound that acts on the surfaces that creates vibration - or movement, the mechanical vibration from a subwoofer contributes very little to this.

Depending on your construction, a good portion of the vibration or rumble you feel in the floor can come directly from the motion of the subwoofer box itself. You can test this yourself by swapping subs for dual opposed models as I did. Even with double the sound pressure as before I was barely able to get much rumble out of the floor. That is good for those wanting to reduce the effect, though you want it for movies and high-impact types of music.

 

[Chromatischism]

It is possible that the subwoofer acts like a shaker - on the house structure. Houses often has resonances in the structure in this frequency range, and with a very heavy moving mass - like the typical subwoofer has, then the effect may be noticeable. And this movement will disappear with dual-opposed. A scenario that fits well with your observation.

Exactly. I think the formula is low frequency output that demands some excursion thus moving mass, a box that's not too big or heavy to dampen it, and wooden subfloor construction, such as the 2nd floor of most houses in the United States. And I always run 2, so double it. And, I tended to be asking a lot of them. 102 dB is near their max 20 Hz SPL as a pair.

The effect will be much less on concrete, when using isolation products, when playing frequencies above ~30 Hz, or when using lower power subs.

 

[Chromatischism]

It has to have separate internal volume to achieve this not when they share the same internal volume.

That is probably the key. With the Rythmik dual opposed subs, the drivers share the internal volume sans some bracing. It's probably safe to assume PSA uses the same approach.

 

[Chromatischism]

fwiw, the "sub alone" listening test often makes me laugh at myself (and how crazed we as audio nuts, get with distortion specs).
The room can be freaking LOUD...at all kinds of resonant frequencies....... simply from subwoofer excitation.

Been there, done that. Have heard some really ugly things from my room that I can not un-hear now. Mostly between 80-100 Hz.

 

[pozz]

Some simulations here I always found interesting: http://elias.altervista.org/html/Dipole_vs_monopole_bass.html

 

[Ultrasonic]

Ah that's different then.

So lower distortion (yet producing lot's of distortion)

No, not necessarily producing 'lots of distortion' at all. Or rather, it very much depends on the sub(s) and what they're being asked to do.

 

[sarumbear]

What? I responded to this:

Depending on your construction, a good portion of the vibration or rumble you feel in the floor can come directly from the motion of the subwoofer box itself. You can test this yourself by swapping subs for dual opposed models as I did. Even with double the sound pressure as before I was barely able to get much rumble out of the floor. That is good for those wanting to reduce the effect, though you want it for movies and high-impact types of music.

You may have replied but not answered why you are saying that a good proportion of the subwoofer's output comes from the motion of the subwoofer box itself. The following link posted above shows a test that demonstrates that is not true. I am acoustician and I say it is not true either.

https://www.kvalsvoll.com/blog/2018/03/29/myth-or-fact-vibration-damping-platforms-for-loudspeakers/

 

[abdo123]

It has to have separate internal volume to achieve this not when they share the same internal volume.

Is it technically dual opposed if that’s the case?

 

[Chrise36]

Is it technically dual opposed if that’s the case?

Is there a formal definition of dual opposed? It has the same properties or even better regarding output and vibrations.

 

[Chromatischism]

You may have replied but not answered why you are saying that a good proportion of the subwoofer's output comes from the motion of the subwoofer box itself.

No, I am not saying that.

This is a simple physics problem. Newton's third law.

I guess if you want to argue semantics (which I'm not interested in), kinetic energy is transferred from the driver (where all of the force is generated) to the enclosure, which then transmits to whatever it is in contact with.

Dual opposed drivers eliminate this because they both provide equal force in the opposite direction of each other, canceling the effect.

 

[abdo123]

Is there a formal definition of dual opposed? It has the same properties or even better regarding output and vibrations.

How would the vibrations get cancelled if the sound waves of each driver never meet?

 

[Ultrasonic]

How would the vibrations get cancelled if the sound waves of each driver never meet?

Surely the principle argument for dual opposing designs relates to the mechanical motion of the drivers (and the corresponding effect on the cabinet), not acoustic waves within the cabinet?

 

[abdo123]

Surely the principle argument for dual opposing designs relates to the mechanical motion of the drivers (and the corresponding effect on the cabinet), not acoustic waves within the cabinet?

well the effect on the cabinet is because of the acoustic waves within the cabinet. At least that how i understood it.

 

[sarumbear]

Surely the principle argument for dual opposing designs relates to the mechanical motion of the drivers (and the corresponding effect on the cabinet), not acoustic waves within the cabinet?

I have never said anything about the waves within the enclosure.