burningdemons Show full post »
Djonyx
burningdemons wrote:

I didn't pay attention to what the ohm load was on their sheets. You're probably correct but in either case, the DBH218 can take 3,600 continuous wattage. So even if it was a 2 ohm load, that graph should look similar to its actual performance in the real world. Its peak is a massive 14,400 watts so it should be able to take 4,000 continuous. And it'll take 2,000 with ease. So if it was done in a 4 ohm load you just double the wattage I wrote and quadruple if it was done in a 2 ohm. The only that would remain to be corrected is the extra 3-4db that would not be there.

Strangely the TH221 takes less wattage than the DBH but it doesn't matter that much. Once you get past a thousand watts, it'll take 5-10 times that much power before you start getting noticeable increases in SPL. So the differences between a 2 ohm, 4 ohm, or 8 ohm load won't matter significantly in the real world.


I won't count on it! Remember those numbers are linear, you still have a mechanical limit. Real world test is the only answer to this.
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BASSBOSS - David Lee
I love talking about what happens in the real world!

First things first: Actually the woofer doesn’t simply move slower for lower frequencies. The amplitude required to produce the SPL drives the speed of the woofer’s movement. To produce a lower frequency the woofer has to continue moving in the same direction for a longer time. Thus the combination of the longer duration required for a lower frequency along with the greater amplitude required to produce high SPLs results in the demand for extremely large displacements and lots of quality power to manage and control the excursions.

You’re following the right path but people are apparently deliberately obscuring the way for you. You’re right to consider compression loss, but it may account for more than you think. The trouble with what you’ve done with that graph is you have taken a low-power measurement and assumed a 1-Watt power source and no losses due to heat and turbulence and transient overshoot or even amplifier output. The graphs I presented were actual real-world maximum power measurements.

As an example of what these thermal and power limit factors look like, below here is a set of measurements taken of a test enclosure. The first at 2V in blue, then with 33.8dB added to calculate for 2400W of power input in red, and the actual full-power sweep measurement in green. You’ll see about 6dB of difference between the calculated ideal between 30 and 35Hz and the measured response between 30 and 35Hz.

[Low-power_fullpower_calculated]   

As mentioned elsewhere, Danley does use the equivalent of 2.83V at 1M to derive their SPL figures. To their credit, Danley do measure at 10m and add 10dB of power, which pretty well eliminates the potential benefits of mic proximity. 2.83V output regardless of load impedance is the new industry standard. But that doesn’t restrict the measurements to 4 ohms and 2 watts.

This means, from what I can find in the documentation, the Danley DBH218 and the Danley TH221 are measured with 28.3V into a nominal 2 ohms. So because you’re starting with a 4-watt measurement, you have to back 6dB out of your maximum SPL calculations, and then you have to account for thermal losses etc., which would potentially take off another ~6dB at certain frequencies, especially at the power levels you’re discussing.  

One other detail is that the graphs you’re working from are measured without the “recommended processing”, which would pull 3dB out at 25Hz from the DBH, which would leave the response at 30Hz still down by about 2dB. The ZV28 is specified and measured with all processing engaged. If you re-draw that red line taking all these factors onto account I think it will reveal that the ZV28 is far from beaten by the DBH218.

Ultimately, in the real world, I think you will find it very hard to beat the ZV28 when it comes to most comparative metrics, especially when one of the metrics is low bass output and the others are either price or size or weight or even power consumption. Furthermore I think the ZV28 is more pleasant to listen to than any of the competing options, if that counts for anything.

From my experience you need 4 people or a forklift to move a TH221. The DBH218 is not as bad but still bigger and heavier and more expensive than the ZV28 and I’m very curious to see exactly how well they compare in a real full-power sweep test. You did note, as did the DBH218 spec sheet, that horn-loaded boxes work better in multiples, mostly increasing their low-bass output. The translation or corollary to that is that they don’t do low bass as well in singles. So if you’re looking for a smaller, more portable, more affordable source of high-output low-bass, the ZV28 is the one to beat., IMHO. [smile]

- David Lee
BASSBOSS
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burningdemons
Thank you. That explains a tremendous amount. It seems like this is something that one would have to take multiple classes on to understand. A thorough explanation is always helpful because it puts multiple things together adding coherency. I did not know that compression loss would account for so much. That's quite a bit of output that will be lost. It will be almost half as loud as my graph would be.

Compared to a single ZV28 it should beat it overall but it will sound a little more thumpy cause its highest sensitivity is up near the LS801's. Guess it was accurately named. Still a better option than TH118's, I've heard them in pairs and the DBH218 easily destroys them. It'd be 2.5-3 to equal the DBH218.

The TH221 is a monster. Seems like a good choice if you were going to install them. I laughed when you said it'd take a forklift cause it actually would. That beast is almost 500 pounds and not okay for mobile work. The DBH218 is fine for school gyms and big events cause you can just roll them in. And for steps it just requires 2 people to lift it up.

I've heard both but only used the DBH218 extensively. It is a monster, it's just the TH221 is a bigger monster. I have not heard another dual 18/21 come close to their output. Even with adding in 6-9db loss it'll still be louder than a pair of ZV28's in some frequencies. It comes at a price though and why pay the price if you can get it better for cheaper? The ZV28's seem to be that option. I will just have to weigh my options for which one comes in better for my planned budget compared to just upgrading to LS1208's for more low end and slightly more SPL. Right now I'm just working with a pair of LS808's and I sold my other pair. I'm trying to sell this pair and then purchase a monster sub after that can do what 4 could have done in just a dual 18 cab or single 18/21 cab. It took 4 LS808's to reach SPL's that worked with the ZX5's and it would take probably 5 or 6 of them before the ZX5's gave out and became overwhelmed. But the LS808 sounds like a boom box. The average person doesn't know the difference but artists do and they typically have little knowledge of PA systems so pleasing them can be tricky since they don't really count in cost, size, or anything. They just expect monstrous sound and meeting their demand means reoccurring gigs, more money, and a more friendly environment.
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