Originally Posted by splotten
Even if the voltages is not stated for the UXL, it obviously takes more (I’m guessing double) power for the single UXL than for dual Daytons to reach equal SPL. So, if anything it takes “double the amplification” with a single UXL compared to dual Daytons. No? In the CEA test at 20Hz and below, the THD limited results are less than 6db difference, not more than 6db. Does that not add up to dual Daytons having a tiny advantage in SPL, a large advantage in total power consumption and an even larger advantage in power per driver?
How do you get from there to stating that it takes another two Daytons (4 total) to equal the UXL. Going by the numbers and the actual information available it seems reasonable to conclude that 2:1 is a fair comparison. That is not to say that dual Daytons are a definite winner or that I would prefer multiple Daytons over half the UXLs as there are many other considerations.
You nailed it, and this is what's missing from these discussions; "there are many other considerations...".
Here's the first problem that's being skimmed over; I'm not aware of a variable voltage amplifier that somehow knows how to deliver safe voltage to a driver that can only handle 500W at 10 Hz but is amp limited with 12,000W at 80 Hz, and that's because it simply doesn't exist.
If a driver in a box gives optimal performance with 500W, then 500W is all you can give it. That means throw the CEA numbers for every result above 10 Hz out the window and recalculate them with 500W.
There are only 2 alternatives and they both require radically changing the FR of the system as levels increase. Maybe Seaton can chime in since we had this conversation last year. Employing a sophisticated limiter circuit like he has on the SM, and which is no trivial matter, allows you to utilize the top end while limiting the low end to safe operation overall. But, that means a radically changing FR (and thus, sonic signature) while playing a soundtrack with 30dB peak to average 3-120 Hz content. this, of course, is not an option for DIYers.
The more practical (and predictable results) method is to shrink the box, up the power and configure selectable curves, which I've been trying to say in every way the English language affords for a decade.
The bottom line is that you can completely disregard Josh's CEA results since they were arrived at with a 12,000W amplifier that was adjusted down to 30 volts at 10 Hz and ramped up to 300 volts at 80 Hz (see Josh's NOTE below). No system mentioned thus far in this thread has that capability with playback of actual source.
Another, and the most obvious, is that 16 Daytons requires 64 cubes of box while 4 LMS requires 14 cubes. If someone is suggesting that multiple placement of 16 boxes is a viable option, I'd like to see it. The end result is more likely that there are still only 4 placements of stacked boxes. I would also like to see some data proving the assumption everyone here is under that multiple placement means better FR. So far I've seen zero A/B comparison data.
Will any of the 16xDayton systems in this forum equal notnight's 8xLMS system? Yeah, I can't believe I'm even having to consider it. not has provided tons of data of the results of his system, so I know what it's capable of. The Dayton users? If there is any data of the results, please point me to it so that I can become as convinced as everyone else in this thread.
Originally Posted by MKtheater
After running many sims myself on what I have had and comparing them to what I get in room the one thing the sims don't account for is the rolloff of each driver or how each driver stays more linear down low. In Winisd all my 8x18 systems had more displacement and more spl according to Winisd at 10hz. This was not the case in my room at the seats!
Thank you. It matters coming from someone who has actually used a dozen systems in the same room with actual soundtrack content.
Originally Posted by Ricci
Move from single driver in a cabinet to a pair of identical cabinets and drivers and you pick up 3dB of output with the same input power as before. (Total system sensitivity and efficiency increased) However note that at the same time that the individual power seen by the original driver decreases to 50% and driver excursion drops by about 30%, so if the driver was moving about 20mm p2p before 50% power input will mean it is now only moving about 14mm p2p but with the second driver now utilizing the other 50% of the signal and also moving 14mm p2p the total displacement has increased to effectively that of a single driver now moving 28mm p2p and the result is about 3dB more system output. Doubling the power of the original signal will result in each driver now seeing 100% of the power that the original lone driver was seeing and both driver will now be at 20mm p2p and the SPL will be 6dB greater than the single driver alone. However to get to that point you have...
Doubled the drivers
Doubled the amplifier power
Doubled the enclosure volume
Now to compare the RS18 to the LMS using the measurements.
The LMS via CEA2010 produces about 6 dB more output than the Dayton RS18 10-20Hz. I did not record the actual voltages used but judging from the levels produced during the 130volt long term sweep it is safe to say that they are between 100-130volts over 10-20Hz. That corresponds to roughly 2-4,000watts input into a nominal 4 ohm load. Also the levels reached during the long term sweeps are fairly comparable over the 10-20Hz octave.
The Dayton RS18 does not handle power nearly as well which is not surprising. It has entered severe compression during the 73 volt sweep, partly due to the motor being out of force at the extremes of excursion and the coil probably being close to leaving the gap by that point. However if we look at the 41 volt sweep the driver is still behaving well. Also between 10-20Hz via CEA-2010 the input voltages required are similar and between about 40-45v. Into a nominal 4 ohm load this corresponds to about 400-500w.
we can see that since each Dayton only requires 500w for 90% of it's output 10-20Hz all you need add is another 500w. I don't see that as a requirement for another amp these days with cheap kilowatts everywhere. Meanwhile the LMS is already eating thousands of watts to produce its maximum output peaks in that octave. You can get most of what 4 Dayton's have to offer in the low bass with the power used for one LMS so there is no reason that the amp cost would not be exactly the same. (Note: That is in the low bass only and in the upper bass where excursion isn't the limiting factor the Dayton can take many hundreds volts short term just like most other drivers. If you want the crazy upper bass output numbers seen in the CEA-2010 testing of the drivers you will need insane amounts of power that really are impractical from a cost and driver safety standpoint.)
Don't forget that the Dayton's will require multiple times more real estate and enclosure volume than the single LMS driver and the enclosure costs will be commensurately higher too eating into some of the savings and taking more time to build as well. As always nothing is free.
Thanks, Josh. One correction; "Bosso is right that you have to double the power when you add another RS18 otherwise you will not get the full 6dB increase. However..." There is no "however". For the sake of this discussion, you have to stick to the facts as you stated in the first sentence. Mentioning various amplifier scenarios only muddies the water, especially when you consider the NOTE section of your post.
Also, when you go from one RS18 to two you have one choice; to go from 4 ohms bridged to 4 ohms per channel (or 8 ohms bridged, which is the same thing). You lose 1-3dB of amplifier, depending on the amp and there's no way around that.
Your NOTE section is the most important thing here and is completely glossed over in these discussions of systems comparisons-on-paper. A 4xLMS system can easily handle the voltage and the 8x Dayton system cannot, which changes the numbers dramatically in the real world DIY system.
96dB at 2M GP RMS at 10 Hz with 36% THD is an astounding achievement that gets tossed aside as though it's easily bested (because "there will be less distortion, thermal compression, smoother response from 2 subs...", etc.) by buying a pair of $250 drivers, while completely ignoring the rest of the picture.
The more power required for the LMS to achieve that 10 Hz stat, the better. Dunno why no one seems to grasp that.