Uuummmm,

I’m finding it very interesting that the reason the Inf 8V2 appeared louder than the other amp is due to a lack of cone control with the Inf 8V2. It’s too easy a thing to say to stop losing face. Ok the Inf 8V2 is not the best amp I’ve ever tested when it comes to cone control, but its not the worst and I would have to put it in the top 20% of amps I’ve tested. So in reality there are more amps that have worst control than better.

Only real way to put a lid on this and that’s with a scientific test with validated measurements people can see and touch. A standard real world test would require two tests to be preformed at once. The first test would be to place an accelerometer capable of 500G onto a cones surface and measure the Xmax, velocity and acceleration of the cone with varying power levels right up to an amps max output. The enclosure housing the driver would obviously remain the same and in the same position throughout the test, the only thing that would be changed is the amplifier. The second test requires a laser to be fired at a white spot painted onto the centre of the drivers dust cap. The changes in cone position can then be calculated very accurately by recording the reflected light. This test can provide force factor, electrical capacitance representing moving mass and mechanical resistance measurements.

The SPL would need to be recorded during the test and also the output voltage of the amps would need to be matched at each power level to determine which amp has greater control. The amp that produces greater acceleration, velocity and lower Xmax for the same amplifier output voltage has better control. The test would be run from 5Hz up to 50Khz and would need to be repeatable my other test labs.

Now all we have to do is find a test lab with all the suitable equipment and both amps and its put straight once and for all. I have all the suitable equipment to perform both tests, but strangely have forgotten how to use it all in the last week.

I’m going to sit on the fence with the pro soundman vs roots soundman debate. I will state an observation from watching both for many years though. Pro soundmen will tend to use cabs where the drivers can’t be seen because of horn loading or because of grill foam, and roots soundmen will use cabs where you can see the driver moving all the time. Pro soundmen will sit at FOH mix position some 30 to 50 meters away from the system or if they are a system tech, get pissed in the back of a van nearby and roots soundmen will have the control tower within range to spot or hear any problems. Pro soundmen will never go right up to the bass stacks during a gig to check how its sounding, they will just access how the bass is sounding via the overall sound quality and maybe if they can be arsed have a look at the clip lights occasionally. Roots soundmen go out to see and hear how the bass is sounding often and have the bass amps right next to them at every gig.

So when it comes to an amp test and I have been to both types many times, I would say that a group of people that are used to watching cone movement often, know how clip lights interact with the distortion they are hearing because they are close to both amps and speakers all the time during a gig and actually have cabs that allow the cone movement to be observed might have more awareness to perceived loudness vs cone control.

I would have to call anyone out that has only ever used cabs where you can’t see the drivers cone and are 50 meters away from the amps if they said they know more about cone control than a group of people that spend half there lives standing in front of drivers and amps.

I am not a roots soundman but I do pay attention to the driver excursion on my cabinets (I run front loaded reflex boxes and the foam is easily peeled back from the velcro) and probably spend more time than I should away from the mix position watching the processor and amplifiers.

I think this phenomenon has more to it than pure 'cone control' because the Inf8V2 is a pretty decent amp. I would very much love to see some tests using accelerometers and laser interferometry, I was going to post that they were the only way to settle the argument but you beat me to it Rog.

Ultimately without seeing for myself exactly how the other amp tests were carried out, I don't really have enough information to go on.

Incidentally, if there is to be some comparision between the two amps, I'm pretty certain the PKN would come out on top in the case of a poor mains supply. The active PFC not only gives it a perfect power factor at full power but also will boost a low voltage or sagging supply, while the very high efficiency makes good use of what is available.

Rog Mogale wrote:


There it is right there...

Rog, please also mention I'm "not" a Void salesman, and have no vested interest in mentioning here, what many witnesses saw & heard that day.

Rog Mogale wrote:


To be honest, I'm wondering if some people have just plain forgotten how tell if one amp is just "louder" than another on the same subs.

Was far from scientific test, but it couldn't have been more realistic in terms of a gig.

John Newsham has already commented on the quality of sound Ren can extract from his system, something it seems people keep forgetting.

Huge venue, power perfect for 4x subs, 2x different rigs, each using 2x of the most popular drivers on sub. Amps tested on one rig, then moved along conveyor belt to the other. 2x amps were found to be in the premier league, the rest were just found to be average lightweights that don't measure up to their specs.

If an amplifier runs out of headroom, driving 2x PDs per channel, 35-90hz, it is obviously not performing to spec down to the lowest notes. So simple. Even an EV P3000 can perform this task without thermalling.

chaudio wrote:


First time I saw PKN in action in Roots arena, was at venue with notoriously saggy mains.

Had previously heard Inf8Mk2 in there, and only problem with that rig was, the "operators" were seriously in danger of blowing all their subs, as the Inf8Mk2 exhibited no early limiting due to mains.

Again PKN used across 4x 1850 scoops, however SPL & Pressure was massive, but was not doing anything below 50hz, which is quite noticeable in the Roots scene. The reason, Engineer showed us the amp, and it was again fully opened up, limiting, and he said HPF was raised to 50hz, otherwise amp would have thermalled.

I’m also having trouble believing that amps with worst cone control, i.e. ones that have poor damping factor possibly due to higher negative current feedback, raise the perceived level of bass from a driver. You will get a change in response with decreasing DF, but I’m not sure you will get more SPL.

A lower DF will not produce the same transient response that an amp with a high DF will, but my tests have always concluded that there is no more SPL possible with very low DF values. Its also difficult to see how more SPL can be available when the driver used at the amp test was a PD1850, which due to its very low mechanical Q doesn’t have a lot of flyback current compared with mush motors that have high Vas and mechanical/electro Q values. Any amp/system with poor damping is also going to get into trouble very quickly with a PD1850 as the back plate sits very close to the coil. If you can’t put the brakes on quick enough you’re hear the coil hitting the back plate. A simple but by no means conclusive test as the coil is out of the gap at this point is to play 2 amplifiers at the same output voltage and see which one makes a PD1850 coil hit the back plate first. Your need around 100 volts or more to do it, but all serious contenders should be able to offer this. If both amps are reading 100V out and one amp makes the coil hit the back plate then that could be down to poor damping.

I’ve also done many club installs where the amp room has been a long way from the bass stacks. I remember one club where I installed 70 meters of 4mm cable per bass cab. Each cab contained 2 x 8 ohm 18” drivers in a 6th order BP enclosure. Each cab was fed from one channel of an amp, so the amps were seeing 4 ohms per side. I turned the system on and began tuning. It didn’t take very long to realise there was no kick in the system and that the output from the bass cabs was very low. I just could not get the system to work how I knew it should of in that venue. I did some calculations and worked out the DF was below 20, which is a point I would always want to be above. I could not run more cables to the bass stack as the drywall had gone in, so the only thing I could do was open up each bass cab and change the wiring from parallel to series. So each cab was now 16 ohms. I still feed each bass cab from one side of an amp as before. I then turned on the system and could not believe how much louder the bass was in that room. It was tight, had a great transient response and was a lot louder than before. I know this as I had to turn the gain down on the LMS to the bass amps. Each driver was now getting around 500 watts compared to 3 times as much when the bass cabs were 4 ohms.

So from situations like this, I’m not sure that lower DF or a lack of cone control will result in higher SPL’s or perceived levels of bass. I’ve seen and heard the effects of poor damping many times and have never thought that it sounded better or gave an increase in output to the system.

If you want proof, get 100 meters of 2.5mm cable and wire it up to a 4 ohm bass cab. You will need an accurate SPL meter to increase the power to match the output of the cab driven from the 100 meters of cable due to resistance losses. Then compare the 100 meters to a 3 meter 4mm cable going to the same 4 ohm bass cab. What you have done is lower the DF with the 100 meters of cable. See which has the better transient response and cone control. And which will play louder, even though you have made up for the decrease in output for the 100 meters of cable.

its an interesting one, as lev said he witnessed a pkn not being able to power 2 1850 drivers... Ive witnessed the same amp, driving 8 1850's, 4 a side, smoke 4 of the 1850's drivers, it sent them into thermal meltdown....... The cab the drivers were used in was a cubo 18 extended version.... and yes they were spanked way too hard... power wise they were run from a 13amp plug......... yes operator error was too blame for blowing them as we just pushed them too hard...... just to confirm amp was not in clip, but very near to full power just off clip...... music on the night was the harder edge drum and bass.

For a switching amp[having a switching power supply and class-d output stage] to handle lows around 20 to 40hz region, it needs loads of power supply capacitance which is a big deciding factor in amplifier's performance in sub-bass region. I am yet to see any 1U rack size switching amplifier whose secondary capacitance exceeds 10000MFD per channel/per rail. Same goes for primary bulk capacitance, its also vanishingly low in such amps[less than 6000 MFD usually]. Don't forget that you still have 50/60HZ mains power source which is rectified and converted in to DC for primary side in SMPS. Having a PFC in frontend doesn't means that one can get away with less number of primary bulk capacitance storage, PFC helps in fluctuating mains or varying mains but for SUB BASS demands nothing replaces the amount of capacitance.


my 2 cents
Kanwar

I don't think it's entirely true that PFC can't help with power delivery. The whole principle of it is to make use of more of the mains cycle to continually fill the primary reservoir rather than it just being topped up at the peak of the waveform.

Conventional toroidal amps will suffer from the same problems because they can only top up their secondary bulk storage when the mains waveform is at a peak which means that the transformer and secondary rectifiers are doing all their work in fairly short pulses. The difference is that conventional amps have no option to do it using the 'brute force' approach and massive reservoir caps.

The easy solution to this is to use three phase power....

chaudio wrote:


Well it doesn't help the PKN in this area. 1st & 2nd time I heard them in gigs, they did the same thing, 1st venue had dodgy power, 2nd venue power was great, even allowed the '8 to draw almost 20A at one stage whilst powering the 4x Turbomax.

chaudio wrote:


Except that there are many town halls, function halls in UK that don't have 3x phase power, or dedicated 16A+ spurs.

To be honest as some keep pointing out, "Most" people would be happy with lightweight, 1u sub amp, that can pummel buildings/people, at @ 4 ohms stereo, down to 50hz.

For those who require more, there is still the PL9, K10.

In a previous post I said how I thought that roots soundmen were in a good position to judge an amps ability in the real world. That’s not changed and probably never will for me. But I also have to say a bit in the defence of the PKN amp.

I’ve meet Peter a few times and can honestly say the man has no need to lie about the specs of his products. As you get older its gets a bit easier to read people and from our chats and meetings I have to say I think he’s a totally honest man that would not mislead anyone. So I think saying the specs are lies is a bit over the top.

One the other side of the coin, if a group of experienced people who make a habit out of comparing and pushing equipment to the edge say it didn’t perform, they I have to believe them. So what can explain this. A product that is proven in many people’s hands yet doesn’t stand up to the expectations of others. Here’s my theory.

I own a couple of very hi performance race bikes, the kind of bikes that would have won the 2005 –2006 SBK races, so a little shy of 200 BHP at the rear wheel. I ride them a lot and you get to know about different suspension and ECU mapping combinations to get what you need from the bike. I’m by no means a race bike rider, I just like to push a bit on some of the best roads I’ve ever seen which are luckily around where I live. For most people a bog standard Honda 600 or 1000cc bike is all they will ever need and they will probably never play with suspension settings or try different tyre combinations. I see this quite like the difference between people who make there living from sound who need reliability and predictable performance. They will never push there equipment to the edge or expect the last ounce from it as its has to work for them for many years to pay for itself. The other side is the formula 1 crowd (roots soundmen) who just need the drivers to last to the end of the session. They compete against other teams and push because there reputation is on the line. This is exactly like an F1, Motogp or SBK team. So here’s the problem. If I change the ride height or rake angle of by bike even a little bit it feels and rides completely different. So different that if I was on a track I might lose 2 seconds per lap. It would be the same with different tyre combinations. If I did those tweaks to the average person who rides to work everyday or just at the weekends for fun then they would probably not even notice anything was different.

So when you change from one amp to another and leave everything before and after the amp the same that will only work for people who make a living from their system and don’t expect too much from it. They won’t notice too much difference or really care as long they can still carry on making a living. But if you push and compete you would have to change many other things before and after the amp to get the best from it. Just like changing the rake angle on my bike requires a different damping setting on the front suspension. One cannot be done without other adjustments to bring the whole thing back into alignment. I feel this is the same with any system that is pushed right to the edge or where you expect or need the ultimate level of performance. So its not really fair just to swap an amp and say it didn’t make the system better. At that level its never going to be that simple. Any system requires all its parts to work together with each other in an extraordinary way if you are going to win. The best teams know this and would never just throw in or change a part just before a race.

So in a way amp shootouts are misleading for the F1 teams of reggae. But I get the feeling that that’s half of the charm of the events…..

Lies maybe a strong term to use, but I would feel exceptionally deceived, if my new lightweight rated at 2x3600w per channel at 4 ohms, could not meet or exceed the 4R performance of an 8', or PL9, both rated well below it, yet able to pound 2x drivers per channel effortlessly.

Not all Reggae/Root systems have sponsorship or can afford for drivers to just last till the end of the night.

Recently went to Scala, to hear mate's PL9 pound 6x 1850s all night, culminating in all out war 5am onwards, yet none of his drivers were burned, or ever came close to distorting. Because amp, drivers, cabs, outboard, engineer, all chosen carefully, all able to do what they say.