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Fi Car Audio SP4 18D1 Sealed Measurements Discussion


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Typical Fi frequency response and mechanical noise during operation. Ugh.

 

Can't say it'd be my cup of tea either... The burst numbers from 16-31.5Hz are impressive, but the inability to post a 10Hz passing score and the mediocre top end sensitivity stick out compared to high performers like the UXL.

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Thanks Josh! This is a driver that had piqued my interest.

 

Looking at what you've shared, I'm not thrilled with the hump in the response, or the fact that it made your K20 cranky, which is more troubling IMO. 

 

Any chance you'll post up the Thiele-Small parameters? I'd like to see if the hunch I have is valid.

 

EDIT - like 3 minutes later...

 

And - that's what I get for not checking before I posted... Nevermind...

 

Hunch = valid. Le / Re is nearly 2 mH/Ohm.

 

Pity. 

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When you compare this to big hitters like the LMS, HST18, UM18, RE XXX, etc. this thing is looking really good. Sure, the native response has a huge hump in it, but do we care?

 

The amp shut down thingy is alarming. Not really sure if I'd feel comfortable risking my amp with that possibility. Would be nice to know what it is exactly. I'd personally go with a UXL cause I'm in Canada though, so just mental interest is all.

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Sure, the native response has a huge hump in it, but do we care?

 

Depends on the application I suppose. Obviously you can use EQ to tame the hump, and if you have enough amp the drop in top end sensitivity doesn't matter quite so much. OTOH, if you're crossing over at 120Hz and attaching it to one channel of an iNuke 3000, it might matter a little more.

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Depends on the application I suppose. Obviously you can use EQ to tame the hump, and if you have enough amp the drop in top end sensitivity doesn't matter quite so much. OTOH, if you're crossing over at 120Hz and attaching it to one channel of an iNuke 3000, it might matter a little more.

 

This is my pick out of all the Fi drivers I've tested. It's the cleanest and has the most headroom. Still not the driver I'm looking for personally but I've pretty much given up hope that someone will design that one anyway. I don't like the issue with causing the amps to protect. It is odd. Only happens if you are really pushing it for all it is worth. My hunch is it has something to do with the design of the driver. The owner has 4 of them and I think is using Inukes and has had the same thing happen a few times with his other ones. I recall some of the other Fi drivers having issues if you pushed them too far which I had thought was actually the leads contacting the frame on the 12 spoke but that's not happening here. I'm not sure a bridged Inuke 3K has enough juice to run into this issue unless the driver is free air or something. I have also wondered if there is stray flux at the bottom of the gap by the back plate that is opposite polarity of the actual gap but I don't know what they have going on inside those steep back plates.

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Hi Josh,

 

Any thoughts on using this driver full bandwidth given the lack of a 10Hz passing response? I know that THD is a relatively minor concern at that point given that cabin gain will end up reducing effective distortion in room. At the same time, it doesn't inspire much confidence about how the driver will hold up an octave below that.

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This is a really wacky problem that I would love to understand the reason for. 

 

"While doing the burst tests and edging up to the limits of the SP4 driver the sound would abruptly change to an odd overtone  and the K20 amp would suddenly protect and mute the outputs for about 2 seconds."

 

-The odd overtone seems to be the biggest clue we have

 

"This was with the amplifier signal lights indicating that the output was well below clipping the amplifier output stages. At first it was thought that this may simply be too much current demand from the amplifier since it is being bridged into a load with a minimum resistance of less than 2 ohms. However after observing the behavior this seems unlikely as the Powersoft K series amplifiers have never exhibited this behavior with burst testing or even when completely destroying a driver resulting in a shorted load during a measurement sweep. Nor has it been observed when bridged into other 2ohm nominal loads. If the signal level was backed off what would be 0.3dB or so, the issue would go away. This behavior was repeated at all of the lowest frequency bands from 10Hz up to and including 50Hz. Looking at the impedance curve of the SP4 in the sealed test box it can be noted that the impedance between 25-40Hz is actually about 6ohms or higher which should not pose a problem. At the 31.5Hz band the impedance is about 15 ohms before any heating of the system, which should pose no problem at all for the amplifier so this points to something occurring with the driver itself."

 

-Right, so it's definitely not protecting itself from overcurrent

 

Perhaps the coil was contacting something in the motor or a lead wire was shorting.

 

"the Powersoft K series amplifiers have never exhibited this behavior with burst testing or even when completely destroying a driver resulting in a shorted load during a measurement sweep."  -So it would seem unlikely that this would be the problem if the Powersoft did not go into protect mode when the driver was destroyed and shorted. 

 

Whatever the cause it is clearly the limit of the SP4 driver. After talking with the owner of the driver he commented that he has seen this issue himself with the other SP4 drivers he owns and with a different amplifier powering them, so it is a driver related issue it seems. Perhaps a short that develops at high excursion or some sort of motor design property.  However this issue was only when driving the SP4 to extreme excursions that were close to some sort of mechanical limit for the driver anyway so it should not be an issue in any normal use.

 

-I'm curious what kind of rig/situation caused the problem with the owner and if the same overtone sound was heard. 

 

How does that amp handle a DC offset getting sent to it?  Any idea what the output impedance of the amp is for the frequency band in question? 

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I've learned (from experience) to avoid drivers with a "specific inductance" (my own term, defined as Le/Re) greater than 1.4 mH/Ohm or so when I am messing with complex, multi-resonant cabinets (like I do). Things just don't tend to work right, and I have a hard time making the math match the measurements. Others have adjusted the parameters in the model to "compensate" for the effects of inductance, and while I understand the approach, it seems somewhat backwards to change the part that we can accurately measure to make the model match measured results. That just sort of goes against my grain, I have a hard time changing the things that I can measure accurately to explain things I don't fully understand, and I'm certainly not smart enough to think I should be questioning the accuracy of the math used in the simulation software.

 

Generally speaking though, this hasn't been an issue for me, as I just haven't gone there. Most of the drivers I work with have a "specific inductance" that is less than 1.0 mH/Ohm, but then, none of the drivers I work with can do much more than an inch linear. This will change soon, I am planning on playing with some heavier hitters for the cabinets in the new theater. Still, as I tend to run higher impedance drivers, it is easier to keep the coil inductance levels reasonable, I doubt that an 8R coil in the same motor would have an inductance of 16 mH. 

 

Though it is just sitting there, gathering dust now, I've never seen my iNuke go into protect when it was in use. I've pounded on it pretty hard, and I was on marginal wiring and I've fan-modded it. I am running the amp bridged into an 8R nominal driver in a tapped horn though, so my current expectations are probably more in line with what the amp can actually deliver. The minimum impedance of the cabinet (15-120 Hz) is more like 9.5 ohms, the average is over 20 ohms.

 

edit: Typo

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This is my pick out of all the Fi drivers I've tested. It's the cleanest and has the most headroom. Still not the driver I'm looking for personally but I've pretty much given up hope that someone will design that one anyway. I don't like the issue with causing the amps to protect. It is odd. Only happens if you are really pushing it for all it is worth. My hunch is it has something to do with the design of the driver. The owner has 4 of them and I think is using Inukes and has had the same thing happen a few times with his other ones. I recall some of the other Fi drivers having issues if you pushed them too far which I had thought was actually the leads contacting the frame on the 12 spoke but that's not happening here. I'm not sure a bridged Inuke 3K has enough juice to run into this issue unless the driver is free air or something. I have also wondered if there is stray flux at the bottom of the gap by the back plate that is opposite polarity of the actual gap but I don't know what they have going on inside those steep back plates.

 

Just thinking out loud after reading this re: the Inukes. I think it would be fun to incorporate into your testing running all these drivers with "normal" amps. We all know the k20 is not....But basically it would be fun to see how the individual drivers operate on your normal "Run of the mill" 15-20a 120v outlet and a crappy ass inuke.  Obviously the REAL testing would be left to the big boy, but would be fun to see exactly how much worse the numbers really would be on your everyday budget amp. It'd likely make a lot of people question the "power" they have in the rack currently. 

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Fwiw I used to run an sp4 15 and I remember it produced a most offensive noise on one occasion doing some compression tests. It didn't repeat under similarly aggressive sweeps powered by my speaker power amp though. I assumed I was clipping the amp at the time but perhaps it was a similar situation to your test.

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Just thinking out loud after reading this re: the Inukes. I think it would be fun to incorporate into your testing running all these drivers with "normal" amps. We all know the k20 is not....But basically it would be fun to see how the individual drivers operate on your normal "Run of the mill" 15-20a 120v outlet and a crappy ass inuke.  Obviously the REAL testing would be left to the big boy, but would be fun to see exactly how much worse the numbers really would be on your everyday budget amp. It'd likely make a lot of people question the "power" they have in the rack currently. 

 

That would be really cool but it would require so much more work on Josh's end. And that would be even just for one amp let alone several.

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That would be really cool but it would require so much more work on Josh's end. And that would be even just for one amp let alone several.

 

 

Oh I'm not talking anything extensive, and just for maybe one single amp. Like maybe just a single sweep at max level and compare it to how the drivers do on a "real" amp. 

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"-I'm curious what kind of rig/situation caused the problem with the owner and if the same overtone sound was heard. 

 

How does that amp handle a DC offset getting sent to it?  Any idea what the output impedance of the amp is for the frequency band in question?  "

 

Matt who I believe goes by the handle PDXrealtor over at AVS is the owner. Perhaps he will chime in.

 

As far as the Powersoft's go so far they've been very reliable amps. They don't seem to care what's connected to them really. They have DC protection and every other fail safe known to man and the higher the back EMF on the driver the better as that is recycled. That is sort of what I was thinking though was a huge DC offset or some sort of current spike or a short of some kind. Let me see if I can get Kyle to offer some thoughts. He's an actual transducer engineer so he has better knowledge on this than most of us.

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Oh I'm not talking anything extensive, and just for maybe one single amp. Like maybe just a single sweep at max level and compare it to how the drivers do on a "real" amp. 

 

Sounds reasonable to me but might be a real PITA for Josh doing the amount of extensive tests with his "normal" rig. I doubt it would be a simple 'plug in and get quick data' kind of situation but I don't want to speak for the guy.

 

Not sure if doing that for every driver really meets the philosophy of this website. Maybe it would be a good thing to do as an article as he has written several extremely interesting and useful tests that are more like one-offs. He could choose a system of to his liking and put through some tests that check the response of the whole system and put the amp through the wringer. Then swap out the K20 (used as the reference) and then plug in other popular amps like the EP4K, inukes, Peavey's, Cerwin, Crest, etc, etc. That doesn't sound so bad doing a day of testing with one system but doing something like this with every system sounds like a huge time sink. Interesting but exhausting.

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I'm actually planning something similar with an SP2-12000 and one of my K20's soon. This type of thing would have to be a 1 time deal with a few different amps. I do have an inuke 6K sitting around. The problem is I want to test 1,2,4,8 ohm nominal loads to see how each amp behaves, so I need at least 4 different loads or wiring schemes and they need to be able to reliably handle the amount of power on tap without being severely heated or over driven. That is a big problem for the big SP and PS amps. I tried doing it at the house with the XXX's but it was too much. Had to abort mission. Have to do it outdoors.

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"-I'm curious what kind of rig/situation caused the problem with the owner and if the same overtone sound was heard. 

 

How does that amp handle a DC offset getting sent to it?  Any idea what the output impedance of the amp is for the frequency band in question?  "

 

Matt who I believe goes by the handle PDXrealtor over at AVS is the owner. Perhaps he will chime in.

 

As far as the Powersoft's go so far they've been very reliable amps. They don't seem to care what's connected to them really. They have DC protection and every other fail safe known to man and the higher the back EMF on the driver the better as that is recycled. That is sort of what I was thinking though was a huge DC offset or some sort of current spike or a short of some kind. Let me see if I can get Kyle to offer some thoughts. He's an actual transducer engineer so he has better knowledge on this than most of us.

 

 

I can post the links to the troubleshooting threads over on AVS if that's OK, Josh.  JD over at Peavey was involved and we played with all sorts of things. In any event they're over on AVS.

 

The short of it was the Peavey IPR2 7500s power supply could not keep up with the highest of demand when driving both chanels driven @ 2ohms/each. This was with (if memory is correct) 7 lbs of boost down low and 9 lbs of boost a bit higher in the form of a shelf filter to create the house curve.

 

Once the IPR2 was only driving one driver it did not shut down, and the driver ran more controlled and tighter. Beast experienced this with both his Crest and Peavey amps as well although I think he had some other things going on too.

 

Antoher option was to remove the boost and the ability to run both channels of the amp returned.

 

When the amps did shut down, it was only during the most demanding material. WOTW for example.

 

 

 

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"-I'm curious what kind of rig/situation caused the problem with the owner and if the same overtone sound was heard. 

 

How does that amp handle a DC offset getting sent to it?  Any idea what the output impedance of the amp is for the frequency band in question?  "

 

Matt who I believe goes by the handle PDXrealtor over at AVS is the owner. Perhaps he will chime in.

 

As far as the Powersoft's go so far they've been very reliable amps. They don't seem to care what's connected to them really. They have DC protection and every other fail safe known to man and the higher the back EMF on the driver the better as that is recycled. That is sort of what I was thinking though was a huge DC offset or some sort of current spike or a short of some kind. Let me see if I can get Kyle to offer some thoughts. He's an actual transducer engineer so he has better knowledge on this than most of us.

 

 

I can post the links to the troubleshooting threads over on AVS if that's OK, Josh.  JD over at Peavey was involved and we played with all sorts of things. In any event they're over on AVS.

 

The short of it was the Peavey IPR2 7500s power supply could not keep up with the highest of demand when driving both chanels driven @ 2ohms/each. This was with (if memory is correct) 7 lbs of boost down low and 9 lbs of boost a bit higher in the form of a shelf filter to create the house curve.

 

Once the IPR2 was only driving one driver it did not shut down, and the driver ran more controlled and tighter. Beast experienced this with both his Crest and Peavey amps as well although I think he had some other things going on too.

 

Antoher option was to remove the boost and the ability to run both channels of the amp returned.

 

When the amps did shut down, it was only during the most demanding material. WOTW for example.

 

 

 

 

7lbs and 9lbs of boost?

 

We talking about amplifiers or forced air induction systems?   :P

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