Ficar SSD18 Group Buy Thread - Page 18

Thanks, much appreciated!

A 7012 with 4012 preamp and a 511E calibrator. I'm having everything recalibrated by ACO and the power supply modifed a little. I also picked up a G.R.A.S. 40AM prepolarized capsule , which is the company founded by a few of the guys that defected from B&K when it was bought. They make precision capsules and preamps as well. Really good stuff. A 4048 preamp that I can use with a 48v source if I want to use a precision measurement mic without having to have the whole kit, a 4212 pre so I can use the 40AM with the 9200PS, etc...

That's what I thought you were getting at.

First, you can't eliminate a room mode with EQ. You pull down the peak with EQ, but you don't eliminate the stored energy. That's why you still see it in a waterfall graph.

A notch in the signal to the subs naked FR is a different situation. The peak from high inductance is not stored energy. It's what's left after the roll off above it.

I have disagreed with Seaton's 'fingerprint' theory simply because I've never seen any evidence of it. He says it rears its head when you 'push the sub to its limits', but any number of bad things (and/or changes caused by design, such as limiting) can happen anywhere in the chain when you do something like that.

In any case, I've heard dozens of subs in my room over the past 20 years. If there was any sort of ringing from the SSD-based subs, I would have heard it, rejected the design and not have ever suggested the SSDs to anyone.

On the contrary, other than lacking a few dBSPL below 20 Hz compared to other systems I've built using longer throw, lower Fs drivers, the system kicks serious a$$.

The Tumult MKI (and several other overhung, long throw, low Fs drivers I've used) rolled off -8dB from 50-100 Hz and I never experienced ringing after L/T signal shaping. (Instead of a notch, I used the L/T to treat the peak as a high Q sub, which gives a similar end result, but the price is that the L/T extends to above 200 Hz).

When most people say a sub is 'tight', they're usually referring to the fact that there is no low end. When I refer to a system as sounding 'tight', I'm invariably referring to the fact that there's no audible ringing because every system I design is flat to 4 Hz in my room.

I've read various opinions about high Q ringing and have since dismissed them as irrelevant to the 'after' notch with L/T response and its performance. When my systems are pushed to their limits, it's always below 20 Hz where the heaviest L/T boost is. Where the notch is, the system is doing the back stroke. Otherwise, you've designed a seriously flawed system.

Bosso

Now you're talkin'. I have the same ACOPacific system (7012, 4012, PS9200 and calibrator) since '04. When REW expanded to 2 Hz my whole world changed and then SpecLab added a whole new dimension.

Beyond reproach. Can't wait to read all about it. Congrats.

Bosso

Well said, Bosso and Ricci. Couldn't have said it better, myself and a large reason why I'm so picky these days.

Eric I put your info for the PSI recone 13AV2 on the Dizzle-Bizzle site.

Hey! Alright! Been waiting for the updates.... and you snuck in the MX18 from RE.

That was a personal...It made me curious.

Ricci did you ever do tests seeing if you could hear the loud knocking noise of the Q18/Xcon in the 4 cu ft enclosure through the cone??

That knocking seems insanely loud.

For the most part, issues below 100Hz are largely minimum phase, with some exceptions with long resonances, especially sympathetic, structural resonances. For such response issues, conventional EQ works very well. If you look into some discussions related to REW, you will see that taking the time to get the EQ to form a proper conjugate filter can make a noticeable difference vs. a response that is just in the ballpark.

A woofer's frequency response is entirely minimum phase, and correcting the frequency response does correct tails in the decay time. A decay type measurement will directly mirror the frequency response for subwoofers until you get into issues of pipe resonances and length/dimension resonances, which are often out of the subwoofer's operating band, but not always.


Once the peak is smoothed, a peaked/humped response from higher Le does not cause any time domain resonances. The bigger reason that high Le raises a flag is that the greater the Le, the more likely it will modulate with excursion. A changing Le means a changing frequency response around the inductance hump vs. coil position. This is not a certainty, nor an absolute. Once you see significant Le, then the next question is if it's a problem for your application, and how linear/consistent is that behavior. It is possible for a woofer to have significant Le, while also remaining fairly linear. The shorting ring Fi uses on the ID of the magnet is such a case where this mostly serves to reduce the increase in Le that typically occurs on incursion (due to more steel in the middle and around the coil).

This isn't all that different from BL linearity, where everyone likes to think of a driver perfectly following the small signal assumptions of T/S parameters out to Xmax. Woofers are often around 70% of specified Bl at Xmax and maybe 1/2 Cms. If you model such parameter changes, you can see these to be significant with the specific shape changes directly related to Fb, Qb and Le hump.

As bosso has pointed to many times, if you use 8-16 large woofers in most rooms, that change becomes rather insignificant. For those short of that or those who are using the full rated excursion potential of their woofers regularly, there will be some tell-tales between significantly different drivers. As Josh has been starting to report much more on, the self-noise of the driver's operation can make for yet another tell-tale fingerprint.

bosso, mark, thanks for the comprehensive replies.

As I've said before, there is no evidence. If you have that actual data, can you please post it?

Take a look at the SSD-15 dual opposed box. The notch is centered at 65 Hz. For 120dB @ 1M, you have approximately 8 mm of throw.

With Tumult MKI, the notch is lower due to a lower Fs. With prog sweeps, compare the high Le Tumult to the Flat to infinity LMS Ultra:



I have no reason to believe there would be a difference in the Tumults behavior with a notch in place, because, as I've said, I've seen no evidence of it in measurements or audibly. But, it certainly appears to me that the high Le driver in this comparison is the stable one as they're being pushed.

IOW, a) how do you push the driver to X-max at 65 Hz? You don't, regardless of how many drivers you use. So, sine wave testing isn't going to reveal this "fingerprint".

What I'm gathering from this is that it might be instructive to run a sine sweep, then run the same sine sweep while a 20 Hz sine, combined with the sweep, is pushing the driver to near X-max (or something around that) and look for a difference at the notch.

From my own experiences, I would have to guess that there will be a deviation in response anywhere BUT at the notch.

This should be simple enough to try, so I'll do it and post the results the next time I'm measuring stuff. If this isn't addressing the 'fingerprint' issue, what else might, in a format that we could at least see such a trend?

Bosso

On the surface that thought makes sense to my pea brain. It would mimic playback of most movies where multiple signals of varying frequency are coming in at one time.

Thanks for doing this bosso!

Would this result in some kind of Doppler effect occurring especially if you are pushing out higher frequency content?

Matt

You wouldn't see the effect with a sine wave sweep I don't think since that is only a single frequency at a time. This shifting of response shape would not show up since only a single frequency is measured at a time and at 40-80Hz there isn't usually a whole lot of excursion even at very high outputs as mentioned. You would need a more complex signal with higher frequency content on top of a low frequency carrier that provides a lot of excursion. This could show up as distortion, weird noises at excursion, or possibly shifting, or ???? Seems like John J also mentioned something about this long ago.

So how would this be tested? Generate a 16Hz-20Hz steady state sine to develop driver excursion and then run a sweep measurement through the system from 35-200Hz? Try varying levels of the low frequency tone for more or less driver excursion with varying levels of the upper bass sweep? Thoughts? Ideas? Stupid? (Edit I should have read the rest of Bosso's post first I see he is thinking the same thing.)

I actually think I might be able to pull this test off without too much trouble depending on whether I can get multiple programs to share the soundcard. I have multiple measurement or audio programs open all of the time but I haven't actually tried running the generator from one program in the background while running a test routine in another before.

thats what Bosso was stating, run a 20hz sine and then a sweep over top of it. So you guys seem to be on the same page

This is basically what I was suggesting.


You should not have a problem generating the LF tone from a different program and the sweep from REW at the same time. The mic will just pick up what's in the air.

I mentioned a sweep without the tone as a reference response. You would also have to test a driver with no Le hump vs one with and the one with after notch.

IOW,

a) Does the low Le driver behave differently in sweep vs sweep + tone?
b) Does the high Le driver behave differently in sweep vs sweep + tone?
c) Do the high vs low Le drivers behave differently in sweep + tone?
d) Does the high Le driver show this fingerprint when tested as above 'with notch' and, if so, at what excursion vs X-max?

Bosso

Right I didn't see that you had the same thought before replying. As Mark said it isn't necessarily about just the LE value. You can have a driver with a good amount of LE that still seems to control the change in inductance with stroke well. We need a couple of candidates. A driver with a ton of shorting rings and very low inductance. A driver with a shorting ring or 2 but a moderate amount of inductance nonetheless and one with no demodulation circuit at all and a lot of LE. Preferably all with similar stroke.

I don't really care about the EQ notch truthfully. I don't think it is going to show anything different tested with vs without, but I could be wrong. My gut tells me that the driving factor will be how much excursion the low frequency tone is asking the driver for more than how loud the upper bass sweep is. Again could be completely wrong though. Sort of uncharted territory.

I would probably do the same test at a couple of different excursion levels and sweep levels. Maybe low mid and high excursion and low mid and high output sweeps.

I know the mic won't care, neither will the driver or amplifier they just do what they are told. Sometimes there can be issues with a program taking control of the hardware which is outputting the signals and not allowing another program to share rights, I believe I have this taken care of though by now.

Right Josh. I never said that a single sine wave clearly shows a fingerprint. I said it could be an issue during real playback where real signals have high frequency events riding on top of low frequency effects.

You can likely do it in software, but alternately a DCX-2496 or anything with the capability to sum two inputs will make it that much easier. Then you also have a simple way to vary either signal separately.

I might try lower like 10Hz to make it easier to observe the excursion. A bigger box or free air will make it easier to get more excursion with less total power. The other way it can be investigated is using air pressure to displace the motor like the DUMAX testing used to do.

Mind you all of this has been studied extensively by Klippel, but more so for wide range drivers, not subwoofers, where the only question is the degree of audibility, and less so happens. To be honest this is much easier to probe about and empirically verify vs. displaying in a graph. Effects from Cms and BL change will be much easier to see as these are generally symmetrical where it falls with both incursion and excursion, so the Rms measurement will be lower, and distortion will be representative of a symmetrically drooping transfer curve. In cases where Le significantly increases on incursion and decreases on excursion, the net level measured likely won't change, but distortion profile will.

While this is a form of IMD, we are more specifically interested in the distortion of the test tone during specific and relative excursion levels, not simply the interaction of multiple frequencies. So it's an excursion modulation test with specific constants.

Right...As you say I'm not sure of an easy way to actually capture this with one simple and presentable metric. I'm not so sure that a FR sweep will show much of anything. Could try a distortion sweep. What about dumping it into spectrum lab? I am going to try a few things and see what happens. It will be a couple of weeks though.

Dave or somebody else for that matter give it a shot if you have time I'd be interested to see what results there are if anything.

Hey, Silly question what should i expect from my replacement Q18...Scott said it is gonna be designed for my 5.5 cubic foot sealed box?

You should probably ask Scott but I would guess you will be getting the High QTS option which I was told is better for small sealed enclosures.

Bump...To continue on this topic.

I can easily run a measurement sweep with a steady state sine wave so that is no problem. I did a very quick measurement with a sealed woofer just as a sort of gauge but as Mark points out I'm not sure if this sort of thing can be easily presented on one graph or how to show it in a useful manner, what levels to use, signal, etc...So the question is how or what to do with this type of measurement, if anything at all. I'm open to experimentation to see if it can provide something worthwhile if anyone has ideas.

Attached is just a couple of basic results. A regular distortion plot with FR and also a capture of the woofer output into SL both with just a reqular sine sweep and the same sweep signal with a high level steady state 10Hz tone playing to provide a large amount of cone excursion. Should be pretty obvious which is which.



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Hi Josh,

Thanks for the exercise.

Having a tough time with your SL scale. Is that 100dB in the middle of the color scale?

Bosso

Sorry about that. I didn't put much time into getting the settings dialed in. I think it is 70-140dB overall scale. I haven't messed with SL in a long time, since learning how to calibrate the SPL level back when I received the dts10 kit I think.