Interesting indeed. Man, I appreciate an answer that has actual data as its main body. Since I design and build all of my signal shaping circuits from close mic measurements, it will be interesting to see how the subs measure outdoors, GP.
Originally Posted by coctostan
I just read the whole thread and I'm pretty certain we have a combination of issues:
1. The Tumult has relatively high inductance, it is going show a hump and roll-off well beyond the simple Unibox model.
2. The AV15H is one of the lowest inductance subwoofers I know of and therefore should better match the simple Unibox model.
3. It appears your measurements are exaggerating the roll off above 40hz as the AV15H shouldn't be down ~8db by 100hz...could also be an artifact of close mic like Ricci suggested.4. You should expect some manufacturing variance along with some expectation that parameters can shift over 10 years of storage.
5. You mention a lack of punch and I believe that is easy to explain with your measurements showing a severe roll off likely due to inductance (and possibly combined with some measurement issues).
6. You could simply have a bad driver although I'm guessing that is not the case given that it is not far off what I would expect. Take Bosso's suggestion of a 100L sealed box for testing.
UniBox and WinISD models are only as accurate as the data that is used. In the case of low inductance drivers like the AV15H or many pro drivers you can be fairly confident when using a single inductance number. For long excursion, higher inductance drivers like the Tumult, the simple model will be off and I believe that is mainly what you are seeing.
A higher inductance driver like the tumult will require some amount of EQ to achieve the punch you would get from a lower inductance driver. That is the price you pay for the greater excursion. I'd suggest EQ'ing the Tumult to match the measured response of the AV15H and see how the sound differs. I'm fairly certain you will find the differences to be small assuming you are low passing around 80hz. The AV15H is likely a lower distortion driver above 80hz.You ask what drivers offer low inductance and high excursion. Well, that is basically what everyone seeks (aside from Bosso, although I'd guess all things being equal he wouldn't mind lower Le). Ultimately, this is expensive to execute and the market is generally small.
If you need the long excursion of the Tumult, I'd suggest EQ'ing. I don't know of a 15" that would replace it to your liking. If you are fine with the AV15H's excursion limits, stick to that.
As far as the reaction you've received, I think your title is at fault. First you trash a product without basis and then you suggest that either the specs or models are faulty. You were asking for assistance but you didn't exactly have an open mind.
Good post. I agree with all of it, except #4. My comments:
#4: inductance is the result of the amount of wire on the VC. I'm all but 100% certain that the VCs ordered for any sub of the Tumult caliber has virtually the same amount of wire and that can't change over time. This is the main reason I doubted the original posted measurements.
Regarding Le, I have not found that it matters much in the final analysis. The driver designers who know what they're talking about rarely state that they have gone with shorting rings (or similar measures) to flatten the high end response of their systems. Instead, they'll say something like "...to reduce some harmonic distortions".
I did not find the AV15H to be in any way superior to the Tumult. In fact, as I said, it takes a pair of the AV15H to match a single Tumult for clean output at 20 Hz... where it counts.
I would much rather have the available excursion <20 Hz and shape the signal and cross point to arrive at the required top end than to not have to shape the signal or cross point traded for 1/2 the power <20 Hz.
Have a look: Same placement, same input signal, same room, same mic distance and placement, same amplification, same # of drivers, etc., Tumult-based vs AV15H-based subs, same amount of boost in the signal shaper:
Can you tell which is which? Can you see a "hump"? Can you see a 12dB difference in top end? Etc.