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**Kornbread** · 08-08-2021, 02:44 PM

I thought dats didn't have enough drive to accurately measure larger subs?

**Chris Roemer** · 08-08-2021, 03:03 PM

I'd double-check your DATS by doing a Vas (and BL) calc. by using the "added mass" method.
I would not do this w/the driver "in box", or even on a baffle.

The DATS should be (basically) error-free running the Qs, and Fs determinations.
Really, only Vas can be (a bit) error-prone. Measure the surround "Dia." yourself and plug that in, then try a mass roughly equal to mms. If you go too light, DATS will tell you so. Generally, lighter is better (as long as the results are consistant and your Z-curve is smooth).

**camplo** · 08-08-2021, 03:35 PM

I finally tried a much heavier added mass and received BL measurements that made sense....Now the final MMS is not what you'd think it to be ...If I lower the added mass....then I get the correct MMS and incorrect BL

I thought dats didn't have enough drive to accurately measure larger subs?

- There must be something to this. What should I use if not DATS?

**camplo** · 08-09-2021, 01:53 AM

Does anyone know what formula DATS uses to calculate BL?

**johnnyrichards** · 08-09-2021, 08:16 AM

I think you are worrying about something not worth worrying about.

**dcibel** · 08-09-2021, 10:44 AM

Originally posted by camplo View Post

Does anyone know what formula DATS uses to calculate BL?

It's the same calculation as all T/S calculations. BL is dependent on cone size and weight, and Qe mostly. AE doesn't have spec listed for a 16 ohm TD15m, but I do see the 8 ohm and 4 ohm models and they list the same Qe and Qms for both models. Qe in the spec is much lower than your driver, as a result you have a high Qts of 0.66 vs the spec of 0.33. Simply put - your driver probably needs some break in.

People usually get too focused on this or that T/S parameter is different from the spec. It doesn't matter. You will see that when one parameter goes down, another goes up, the calculated values depended on each other. Why so much focus on BL when Qts is so far off? T/S is also dependent on drive voltage, ambient temperature and humidity will even make changes to measured results. If you really want to make comparison to the manufacturer spec, take your measured results and model them in a cabinet, and compare that model to what you get with the manufacturer data. If you get good agreement, enjoy your speaker and move on.

I would even recommend going as far to simply disregard manufacturer data altogether. You have a tool to produce T/S and impedance to know specifics about the driver you own, so determine if the driver is useful to you using that data, why should the manufacturer spec even matter at this point ?

**dcibel** · 08-09-2021, 10:47 AM

Originally posted by camplo View Post

There must be something to this. What should I use if not DATS?

If you want a higher test voltage, you can upgrade to V3 DATS or build an ARTA jig. ARTA jig is quite simple, just a few resistors in a box, then you can run through an amplifier and choose the test voltage at your discretion. Keep in mind, that T/S is defined as "at rest" parameters, as in low signal level.

**camplo** · 08-09-2021, 05:37 PM

BL is dependent on cone size and weight, and Qe mostly. AE doesn't have spec listed for a 16 ohm TD15m, but I do see the 8 ohm and 4 ohm models and they list the same Qe and Qms for both models. Qe in the spec is much lower than your driver, as a result you have a high Qts of 0.66 vs the spec of 0.33. Simply put - your driver probably needs some break in.

I'm using the v3 Dats but I don't know what this means for voltage...but you are making good points and thank you for your wise words.
According to John from AE the 16ohm driver Bl should measure ~23tm.... The comment you made about Qes suggesting the need for break in...can you elaborate on how this suggest that?

People usually get too focused on this or that T/S parameter is different from the spec. It doesn't matter. You will see that when one parameter goes down, another goes up, the calculated values depended on each other. Why so much focus on BL when Qts is so far off? T/S is also dependent on drive voltage, ambient temperature and humidity will even make changes to measured results. If you really want to make comparison to the manufacturer spec, take your measured results and model them in a cabinet, and compare that model to what you get with the manufacturer data. If you get good agreement, enjoy your speaker and move on.

I am learning. There is the idea that I designed cabinets based around the manufacturer specs....Motor strength and efficiency seem to matter if you paid for a specific level of performance. The QTS is not off for the 18H+ measurements yet the BL remains 75% of advertised spec. Isn't this like paying for a 400hp motor but receiving a 350hp motor?

**dcibel** · 08-09-2021, 06:18 PM

Originally posted by camplo View Post

I'm using the v3 Dats but I don't know what this means for voltage...but you are making good points and thank you for your wise words.
According to John from AE the 16ohm driver Bl should measure ~23tm.... The comment you made about Qes suggesting the need for break in...can you elaborate on how this suggest that.

Read the manual for your equipment, it should be capable of T/S measurement with a user adjustable voltage between 0.35V to 2V according to this:
https://www.parts-express.com/pedocs...hite-paper.pdf

Qts is higher than expected which is why I suggested break-in. Break-in lowers the Q.

For the other driver, if Qts is on-spec and so is Bl, how well does your Mms match up?

**camplo** · 08-10-2021, 12:06 AM

For the 18h+, I used specified mmd method...and Bl comes out to 19-21,,,it should be 27 according to spec....can you interpret this? Is this just a drover needing breaking in? DATS does not allow control of voltage for parameters btw....it only varies voltage for the linearity test

The 18h+ are mounted on a baffle that has the driver in a slot...likely lowering fs...I have the front baffles off to relieve box pressure.

**dcibel** · 08-10-2021, 12:34 AM

You have to measure T/S free air.

**DeZZar** · 08-10-2021, 12:42 AM

Originally posted by camplo View Post

The 18h+ are mounted on a baffle that has the driver in a slot...likely lowering fs...I have the front baffles off to relieve box pressure.

Not sure I'm visualizing this correctly but you should really take these measurements "free air". That's usually on a bench, face up, making sure any vents are not blocked.

Driver definitely needs break in. Having recently run this experiment myself, the trend is usually that all Q values will lower over the break in. I recommend playing a 20hz tone at close to x-max overnight (free air - not in a box or on a baffle unless you want to shake your house to bits the whole night). Let it cool and then measure again.

**camplo** · 08-10-2021, 12:56 AM

Here is the td15m in free after a break in session
fs-37...spec to be 34
qts should be 0.33
qms is spec to 5.09
Qes is double, do you think it really will halve itself? to 0.35?
Cms is within spec...should be .300
vas is shy of 315l

look at BL...it should be 23tm for 16ohm version

mmd and mms targets I got from AE, 16ohm version is not listed online....they come out to desired numbers

**DeZZar** · 08-10-2021, 01:46 AM

This is what happens to a Dayton woofer during/after break in:
https://techtalk.parts-express.com/f...69#post1474069

At the end of the day, the specs don't all align with the manufacturers. What's most important is that it models as close as possible to what the manufacturer states and in this case it does, even with different specs. If it didn't, there would be no way of really being able to reliably choose a driver for a project.

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