Coming soon, subjective SQ tests.

[Mark Seaton]

Ilkka wrote:

How many SGLC drivers or even XBL^2 drivers have you melted with clean music/movie signal? With a typical crest factor of 10 dB, 2.4 kW peaks cause a 240W RMS power in the VC. Naturally pure sine waves are a completely different matter. No VC will hold if much higher than RMS rated sine wave is run any longer than ~5-30s.

I don't have your experience with all sorts of drivers, but I would suspect it's not that easy to melt a VC with clean music/movie signal even though the peaks would go much higher than what the RMS spec of the driver is.

I am willing to eat my words after I've melted my first VC.

Give it time, you'll inevitably get there.

The longer-term, average power and the spectrum at which this power occurs all matters in the question of if you will be releasing the magic smoke. Even separately from excursion limits, many don't give much thought to the fact that the chosen box and driver combo have a significant effect on the input power handling of a driver as the heat generated by the same input signal will change with the box design. Remember that sensitivity and efficiency are two very different things. Efficiency is the one that has an impact on heat in the voice coil.

Even so far as bottoming the various drivers, you have to remember that BL is often about 70% the rest value and Vas 1/2-1/4 the rest value by the time you reach the commonly rated "linear" Xmax limits. Combine this with a good bit of mechanical headroom past "Xmax" and you can often safely get away with using more power than you might think. The point is not to want to use the driver past its linear limits, but in knowing that having only enough power to reach Xmax at some worst case will mean you run out of amplifier in other common conditions where the driver is still well within linear limits.

[SteveCallas]

Mark wrote:

The point is not to want to use the driver past its linear limits, but in knowing that having only enough power to reach Xmax at some worst case will mean you run out of amplifier in other common conditions where the driver is still well within linear limits.

Meaning what, uneven output capability across the frequency range, as in a high powered, small, sealed design? In my limited experience, music and movies don't push the limits of a quality sub in the higher bass frequencies in a home environment, they push the limits on the low end - and it's mostly from movies.

[Mark Seaton]

SteveCallas wrote:

Meaning what, uneven output capability across the frequency range, as in a high powered, small, sealed design? In my limited experience, music and movies don't push the limits of a quality sub in the higher bass frequencies in a home environment, they push the limits on the low end - and it's mostly from movies.

Hi Steve,

You're reading more into that than I wrote. The same case holds true for a big vented box as well, but for each box type the changing BL & Cms affect the response and resulting excursion differently.

The point I was making was that in a very large percentage of use, the subwoofer amplifier is driving a signal more complex than a single sine wave. If you examine the operation of the sub beyond a simple sine-wave condition, you see that many cases that will not drive past the excursion limits of the driver would justify more power than is needed to reach rated Xmax at some lower frequency.

Remember that music falls somewhere inbetween a sine wave and band-limited pink noise. If you drive a subwoofer with pink noise and keep increasing the volume until the driver would reach rated Xmax, you would find this to be notably higher power than is required from a single sine wave at the frequency where maximum excursion is reached.

[SteveCallas]

Mark wrote:

If you examine the operation of the sub beyond a simple sine-wave condition, you see that many cases that will not drive past the excursion limits of the driver would justify more power than is needed to reach rated Xmax at some lower frequency

Ok, but in the same respect, an amplifier will very likely be able to pump out more power then it's rated for with a brief, non-sine wave signal, no?

[Mark Seaton]

SteveCallas wrote:

Ok, but in the same respect, an amplifier will very likely be able to pump out more power then it's rated for with a brief, non-sine wave signal, no?

Being a sine wave vs. complex signal doesn't matter much. Time duration is a different factor that will entirely depend on the limiting factors of the amplifier. Once you hit the +/- Voltage rail, it won't go any higher, no matter how short a burst. You might get more in a burst where there is continuous current limiting from a smaller power supply, but then the question is how long, and how long is that relative to the program material. Burst power can be plenty useful at HF, but at lower frequencies things don't happen as quickly, so sometimes it's useful, sometimes it's not.

The point to realize is that while a 2.0V sine wave at some frequency into a 4 Ohm load is 1W, if you then add in sine waves at many more frequencies, each at 2.0V in isolation, your amp is now delivering much more than 1W. Pink noise is an extreme and randomized example of this with energy spanning all of the frequencies over some bandwidth. With such an input signal, now consider the excursion of the driver vs. the total power required from the amplifier.

[Ilkka]

I've been discussing about this with Mark already before. My 10-tone spectral contamination test is a good example of this phenomena. Even though many subs could output pretty high output figures when using a single sine wave/sweep, most of the subs struggled with the 10-tone test already at 100 dB total SPL (most of them couldn't do it). 100 dB total SPL means that the SPL of each single tone was only 90 dB.

Also notice what happens to excursion during multi-tone input. If 100 dB output at 20 Hz requires 20mm of excursion; when adding also a 40 Hz signal at the same level the excursion jumps to 25mm. Plus we also need 2x the power (not considering impedance). Add a 80 Hz signal, and we need 26.25mm of excursion and 3x the power.

[Mark Seaton]

Thanks for the added points of reference Ilkka. Using your example, we also see the case where you have a 3 fold increase in power yet only 30% increase in excursion, which is exactly the condition I'm referring to. The point is that unless you can already hit 125dB at every frequency you are covering with less power, there is usually benefit to having more power than models say is needed to reach Xmax at some frequency. Ideally you can make determinations as to how likely or even possible damage to the driver is with that much power on tap. This is where we need more manufacturers also inlcuding an Xmech spec that is simply the damage limit where parts are over-stressed or spiders or formers bottom.

[SteveCallas]

Ilkka wrote:

Also notice what happens to excursion during multi-tone input. If 100 dB output at 20 Hz requires 20mm of excursion; when adding also a 40 Hz signal at the same level the excursion jumps to 25mm. Plus we also need 2x the power (not considering impedance). Add a 80 Hz signal, and we need 26.25mm of excursion and 3x the power.

In such a case, should someone be more worried about not getting the absolute full signal reproduced or not frying their voice coil?

[Exocer]

Mark Seaton wrote:

Thanks for the added points of reference Ilkka. Using your example, we also see the case where you have a 3 fold increase in power yet only 30% increase in excursion, which is exactly the condition I'm referring to. The point is that unless you can already hit 125dB at every frequency you are covering with less power, there is usually benefit to having more power than models say is needed to reach Xmax at some frequency. Ideally you can make determinations as to how likely or even possible damage to the driver is with that much power on tap. This is where we need more manufacturers also inlcuding an Xmech spec that is simply the damage limit where parts are over-stressed or spiders or formers bottom.

This makes a lot of sense Mark.Would the damage limit reside somewhere between Xmech and Xmax? If it does, wouldn't it be relatively difficult to assign a given damage limit for drivers that will vary from one another (slightly) due to manufacturing differences?

[Mark Seaton]

Most high excursion woofers are limited by either the former hitting the back plate or the spider hitting the top plate. There are some rare cases where the spider isn't able to move that far, or the surround reaches full extension and deformation before those points. Hopefully you won't regularly drive a woofer to these limits, but it's more a matter of having safe operating area while adding to the performance in other conditions.

Of course the part to not overlook is the behavior of your design as you approach or exceed rated Xmax. There's nothing wrong with using less power for general safety. The trade off is that if you want more output you need another sub.

The reality is that driver manufacturers often build in a fair bit of mechanical headroom hoping that you won't use it, and not tempting you in telling you it's there as the general population of users tend to try some pretty dumb things.

[SteveCallas]

Mark wrote:

There's nothing wrong with using less power for general safety. The trade off is that if you want more output you need another sub

That's my train of thought. Amp limiting to xmax will not only keep the driver safer with low frequency material, it will also essentially force you to maintain generally cleaner bass as compared to other options, ie more power, by alerting you that you need more woofage. If your preferred listening levels result in active clipping lights, it's time to build another sub. It's almost like predictive maintenance By having enough woofage so that you never see the clipping lights with an amp limited design, you're basically sitting pretty in all regards.

[Exocer]

woofage woofage woofage woofage woofage :holycow:

[Exocer]

Well in any event, I plan on purchasing one of those Galaxy spl meters and running some relatively accurate sweeps of my system. Many of you guys were in doubt about my flat in-room measured response to the low teens without EQ, hopefully this new spl meter will yield the proper and similar results.

The Tumult currently resides in the 4ft^3 box, the Ava 15 takes a break. For power, an Ep1500 bridged. Finding Nemo chapter 25 (at -20db on my receiver) literally roundhouse kicked me in the chest. My mom heard it from the room directly below mine loud and clear.

I must re-iterate how drivers like the Ava 15 and Tumult 15d2 sound completely different from each other (in the same box), while their T/S would suggest otherwise.

[SteveCallas]

Can you elaborate on those differences some more? From what I recall, you said the Avalanche sounds lighter or something to that effect?

[Exocer]

The Ava 15 sounds "thinner" than the Tumult but thats clearly due to having a lower Q alignment. There is a bit more to it that I can't describe. Sweeps don't even illustrate much of a difference either. Maybe its just the tonal differences between two drivers.

[Mark Seaton]

Exocer wrote:

The Ava 15 sounds "thinner" than the Tumult but thats clearly due to having a lower Q alignment. There is a bit more to it that I can't describe. Sweeps don't even illustrate much of a difference either. Maybe its just the tonal differences between two drivers.

Here's what I might expect as the difference between the two drivers with the same 2.0V driving either in a 4 cu.ft. box. Long ago when they were new I tested the Avalanche 15 in a box about 1/2 this size from which the driver model is correlated to. I haven't measured any of the current crop of Tumults, so the inductive mound might be more significant than shown, but I did account for what Dan had posted in graphs before so far as the inductance at lower frequencies. If the published parameters are close to your driver, this should be pretty close.

[SteveCallas]

If the in room FRs are the same, which I believe they roughly were, the sound quality difference is gonna come down to non linear distortion. "Thinner" is a little telling in that regard - would you say the Avalanche lacks some of the "oomph" of the Tumult?

Mark, I recall you posting about that upper bass frequency rolloff a while back, but I still have yet to see it show up in any Avalanche project

[Exocer]

The inductive differences are something worth noting, indeed.

Here are some measurements taken a while ago with the Tumult/AVA in the same location in the same box...etc. NoEQ

Tumult

Ava


I'd like to re-test both of them and maybe even try the Galaxy spl meter (if/when I do purchase it).

[Exocer]

Note, those (above graphs) are with my doors closed. With the doors open FR looks like this

Tumult


My SPL measurements scream "ECM 8000 calibrated mic now please!"

Why would FR look so much better with my door open? Wouldn't a completely sealed room yield improved output down low? The exact opposite is demonstrated here.

[SteveCallas]

Lol, same here. To get my flattest response, I need to close the doors to my bedroom, bathroom, and laundry area, but I have to open the door to my office room, which is an extra ~1276 cubic foot chunk of space. Oddly enough, the region that opening/shutting the doors to my office room affects is only the <20hz region.