How does Motor Force & power handling affect Vd?

[Cj Kumz]

Ok based on what I have learned so far, bass is all about air movement. So in GENERAL the more air movement you have the louder you will be.. Does this mean a 500rms sub vs a 1500rms sub with the same cone area and xmax (Vd) will the similar due to same displacement of air?? Or will 1 be louder. Same question with motor force (more vs less motor force but same Vd).

[alaskanzx5]

Still learning this one but I'm going to assume that since both would be displacing the same amount of air they should equally be capable of producing the same amount of volume.

However I think it would be easier to achieve more sound from the sub with a higher rms rating.

The subs with the higher rms rating would have more motor force behind it. Tires means that it would actually Be able to reach Xmax easier.

Even if two subs are identical in vd doesn't mean they will displace the same amount of air. The one with less motor force would most likely move less and see Xmax less often. Just better they birth have the potential to move displace the same amount of air doesn't mean they will.

[Triticum Agricolam]

Generally speaking, higher motor force will increase efficiency. However higher power handling almost always means higher moving mass, which decreases efficiency. Subs with higher motor force usually are higher power handling and the increase in moving mass has a bigger impact than the increase in motor force resulting in overall less efficiency. So in your example above, the 500 watt sub probably produces more dB per watt, but the 1500 watt sub probably has a higher dB potential.

So efficiency is something I've been thinking about a lot. How I see it is there are a couple ways to define efficiency, cost efficiency and space efficiency, and within those two groups we have per watt efficiency and max output efficiency.

Lower power systems almost always have a higher per watt cost and space efficiency than higher power systems. But when you look at max output efficiency the higher power systems win.

Ported boxes have higher space efficiency, but lower cost efficicny than more complex designs like band pass boxes.

I've started evaluating box designs based on the above metrics, it definitely lets you makes some interesting comparisons.

[Cj Kumz]

Thanks for your input. I soon wanna work on a build with about four 12s but was debating on the Vd of four 12s with lower motor force vs 2 15s with higher motor force. So based on the info you have given motor force is also another factor to look at too when selecting subs. I will try learn more on efficiency, that seems to be my weekness

[mikelbolton]

This will depend on the application... For example, I have 1-15" Ascendant Audio Mayhem on 4500 watts, and was able to pull a 150 on. I have the same setup on 1-15" Soundstream XXX, with very similar Xmax, but much higher power handling (8500 RMS). The Soundstream is about 4 dB lower.

The reason here is, although the Soundstream should effectively have more motor force, the same cone area and same excursion; it does not have the same suspension compliance, nor the same cone mass. The suspension compliance, is the amount of force that the suspension provides to the subwoofer to return to its natural resting position. When the amplifier signal is placed across the voice coil this causes the cone to move in and out of the resting position. The signal has to have enough force to overcome the compliance of the suspension, and reach full excursion. Effectively, the voice coils can handle 8500 watts RMS, and therefore the suspension has been designed to control the cone under this amount of power. Since I'm not giving the voice coils the full power, they are not able to generate the proper amount of force, and therefore struggle to completely overcome the compliance of the suspension. This means less excursion, and less displacement (and dB's).

With that being said, in a higher SPL setup, you will also want to ensure that there is enough suspension compliance, motor force, and power handling to overcome the compression that the subs might see. Flexing body panels, enclosures, and improper ports can contribute to the subwoofer seeing unequal pressure on one side of the cone. This can hurt efficiency, and potentially damage the subs.

So, to answer your question. A sub, with the same Xmax and cone area will in fact displace the same amount of air. Proper considerations should be given to match the subwoofer to the power and airspace available. These factors, along with compression can vary the output of the subs.

[magillaru]

Tuned in for the knowledge.

[Triticum Agricolam]

Thanks for your input. I soon wanna work on a build with about four 12s but was debating on the Vd of four 12s with lower motor force vs 2 15s with higher motor force. So based on the info you have given motor force is also another factor to look at too when selecting subs. I will try learn more on efficiency, that seems to be my weekness

Unfortunately you can't just look at motor force and be able to draw conclusions about efficiency. Mms, box design, suspension compliance, and a host of other factors all contribute to it. Your best bet is to use some kind of modeling software, such as WinIsd, Hornresp, term pro, etc. Due to the unpredictable nature of cabin gain, software cannot tell you exactly how a system will sound or how loud it will get, but it will allow you to compare different different system to see which should be more efficient/have more output. One thing to keep in mind though is the info you get out will only be as accurate as the data you put in, and not all manufacturers give you accurate T/S specs. Nothing is perfect, but it's better than nothing, or just guessing.

[Cj Kumz]

Bys why we need education to have a bass proffesion so we can become proffesors in it lol..

On a serious note ama start using winisd in more depth now

[Broke_Audio_Addict]

Vd?

Are we talking viral or bacterial?

[alaskanzx5]

Vd?

Are we talking viral or bacterial?

Lmao...

In short when looking at vd of a subwoofer even if it is the same as another it doesn't mean that they will perform the same. A stiffer sub with a 1500rms rating and 20mm xmax might get you a 143.2. the 500rms sub with 20mm xmax might get a 143.6.

Now that could be box design, placement, electrical, the subs might peak at different freq.

That or maybe the 500rms sub as a softer suspension and reaches full xmax off of the 578 watts it gets on a sine wave and the other sub only reaches 60% of xmax on the 1365 watts it gets on a sine wave. Since the higher power handling sub only reaches 60% of its xmax it was moving less air.