What sub would be better with PR 15’s?


  • Member
    Paul K. on #82

    What would give me a lower F3, and give me more SPL?
    My current setup is a 2.5 cu ft box with two PR15’s at 1400g each and a Fosgate RFR3112 sub. Can someone run this through WinISD or similar program and post it please?
    Thanks!

    Rockford Fosgate Power HX2 RFR3112
    Fosgate specs:
    Re 2x 2.12
    Fs 26hz
    Qts .34
    Qes .37
    Qms 5.637
    SD 84″ 2
    Vas 1.15′ 3
    Cms 1.06E-04 m/N
    Mms 350g
    Vc Dia 4″
    Vc ind 1.78mH
    Bl 13.88Tm
    Xmax 19mm
    SPL 85.3dB
    PE 1KW RMS

    Same box with a Stryke AV12
    AV12 specs:
    Fs (Hz) 24.85
    Qms 6.456
    Qes .486
    Qts .452
    VAS (ltrs) 48.44
    Zn (ohm) 4
    Re (ohm) 2.79
    Le (mH) 3
    Rms (Kg/s)
    Mms (g) 286.6
    Cms (mm/N) .143
    Bl (N/A) 16.04
    Sd (cm²) 488.4
    2.83V SPL (dB) 88.42
    Pe Cont (W) 500
    Xmax (mm) 23
    VC diam (mm) 2″
    VC length (mm) 2.1″
    Gap height (mm) .385″

    Same box with a Brahma 12D2
    Brahma specs:
    Fs 19Hz
    Qes .41
    Qms 11.6
    Qts .39
    Vas 92.3 L
    Re 2x 1.4ohms
    Le 2x .5mH
    Bl 12.8 N/A
    Xmax 28.5mm
    Sd 436cm2
    SPL 83.8 dB
    Pmax 600W


    Member
    R. Buszka on #1554

    With two PR15-1400 and the current generation AV12, you can get down to 19.8 Hz, though you may run out of excursion on the PRs when at very high volumes down around the tuning frequency. I’ve only been able to do this with a test tone nd by maxing out the amp’s gain, but the driver will never exceed Xmax if you keep it under 500 watts.


    Member
    Paul K. on #1555

    Thanks,

    If I was to go that route, I would most likely go with two AV12’s and series wire the Vc’s on each one to give me a 1KW 4ohm load. I’m using a Crown K2 to power the Fosgate, and I think it might be a bit much for one AV12.


    Member
    R. Buszka on #1556

    I think you can still only pump 500 watts into one AV12, which would be 250w/coil, though John or dB could provide a more definitive answer. 500W is the maximum thermal dissipation.

    Oops, read your post. yeah, that would indeed be 1kW between the two AV12s, but you would have a 2-ohm load instead of a 4-ohm load.

    Addendum: Is this for a car audio application? PRs are a bad idea for use in cars since there are other forces that screw up the operation of the passive radiators and eventually damage them.


    Member
    dB on #1557

    You’re better off to have too much power available then too little. Amplifier clipping kills more drivers than over powering them.

    500 watts continuous spread over 2 hours with pink noise using 6dB crest factor, 12dB butterworth filters set from 25-250hz, and duration of 2 hours with no measureable dammage post cool down.

    Short periods of time more than 500 watts is acceptable. If you’re running a continuous sine tone at very very very high levels with 1kw, you will kill the drivers pre-maturely – but with typical music content – the time constant is fairly short durration A.V. 12’s in automotive use have survived for years with 1kw amplifiers.

    Passive Radiators are perfectly aceptable in automotive use – and in fact are my preffered implementation 🙂 (yes I’m a bass head) No port noise, small boxes, low-ish tuned freq’s. :):):):):):):)


    Member
    Admin on #1558

    R.Buszka,

    Typically you’d want PR’s with the softest suspension possible to get you the most output. In a vehicle you need to have a slightly stiffer suspension to keep the Pr’s from moving due to the forces of acceleration/decelleration and cornering. The tradeoff is a little loss of output at the lowest frequencies with the stiffer PR’s but you still have a big advantage over small ports in terms of output.

    The other problem is the effect of the PR’s moving the enclosure too much and shaking the vehicle. Putting the PR’s on opposing sides of the enclosure is the best way to eliminate this.

    John


    Member
    dB on #1559

    Don’t forget the effects of the vehicle’s transfer function. I’ve measured over 30 different vehicles – outside of minivans, and the average increase in SPL at 20hz vs 80hz reference level was around 28dB. Put a flat sub in a car – it will become a massive one note boomer on the bottom end.


    Member
    Paul K. on #1560

    Thanks for the replies guys. This is definately home audio use, not car audio although I’m using a car audio sub. Reason being is I already had the sub before I found AV12’s or I most likely would have gone that route.

    I was under the impression that a single AV12 had dual 500 watt coils, thus running them in series would give a single 4 ohm 1KW load.

    Here is my current setup:


    Member
    Travis Gibby on #1561

    @db wrote:

    You’re better off to have too much power available then too little. Amplifier clipping kills more drivers than over powering them.

    I’m not trying to look like a smart a** here. There is no question that dB, Dan Wiggins, and Tracy Focht know more about subwoofers in general than I do.

    There was a lengthy debate about this on the Ford-Trucks.com forum in which Tracy Focht, of Kicker Car audio (and Dan Wiggins agreed), said that there were only two ways to blow a subwoofer:

    1) over powering a sub

    2) pushing a sub past it’s mechanical limits

    He said if your 25 W amplifier blows your 100 W subwoofer, then you should look at the build quality of your amp.

    Would you agree with this dB? I will see if I can find Dan and Tracy’s post, but I was under the impression that you were safe as long as you keep the the gain, and volume control at reasonable levels.

    I am trying to gain a better understanding on this subject. Assuming that Dan Wiggins and Tracy Focht are correct, then I don’t understand how clipping by itself could destroy a driver. If an amp is pushed into clipping than it is producing more power than it’s nominal power rating, so you could exceed the thermal power rating in this way. However, if the clipped signal is greater than the drivers’ thermal power rating than the unclipped version must exceed the thermal power rating to an even greater degree (the more powerfull the amp the easier it is to exceed the drivers thermal power rating).

    With tweeters and mid-range drivers, it’s a different story. As many of us know. When a signal is clipped odd-order harmonics are generated increasing the power at high frequencies. Although your speaker may be rated at 100 W, the tweeter ‘sees’ just a small portion of that power. The speaker may be rated at 100 W, but that does not mean that the tweeter can handle 100W of power. Powerful harmonics of a lower frequency signal may find there way though the crossover and cause the high-frequency driver(s) to fail.

    If anything I have said is incorrect, please let me know.

    Thank you,

    Travis


    Member
    R. Buszka on #1562

    Well, if you give a subwoofer too much RMS power over a very long time, you will kill it (as dB mentioned — this would be accomplished with a full power sine signal or some other signal producing full RMS power of the amplifier), but by that point in your particular box, you would have the passive radiators getting blown off their suspensions before you would kill the driver, down around the tuning frequency. Driver power handling is usually a thermal phenomenon if the enclosure loads the driver well enough that Xsus is not reached. Think about the heating element on your stove, if you have an electric stove. When you apply the voltage, you know from experience that it takes a while for the heating coil to get red-hot. If you just turn it on for five seconds and turn it off again, the burner may still be hot to the touch but it won’t be red-hot, or hot enough to cook anything. The same thing works with speaker drivers receiving a music signal, which is of a very dynamic and transient nature (which is why the transient response of a driver becomes important for audio.) Another factor to consider is, how compressed (dynamically) is the signal? A compressed signal has a more continuous loudness level, which is used in recording to increase the apparent loudness of the overall sound by making the difference between loud and soft sounds less dramatic, but in a case like this, it is behaving more and more like the sine wave signal in terms of the power being dumped into the driver. The copious amounts of compression of commercial recordings has been a gripe of audiophiles for quite some time, as recording studios try to make their recording sound “louder” on the radio than the last song that played. In pro audio the situation is different, and it is not uncommon to drive a speaker with twice its RMS power, and most pro sound manufacturers even routinely list program power in addition to program power. Usually this is found by just multiplying the RMS power by two, but Community Light and Sound, Inc. of Chester, PA (a pro audio manufacturer known for its rigorous testing and very truthful/honest measurements and measurement standards of its Community loudspeakers) generally lists program power ratings that are generally 2.5 times the RMS value, which suggests more than just a “rule of thumb” treatment.

    It used to be my understanding that an amplifier put out direct current over the clipped portion of the waveform (think about an undefined function), and that was how it would blow drivers, but in order to do that, it would have to actually distort the frequency over the clipped portion to 0 Hz, so my understanding can’t be right. A 25-watt amplifier couldn’t produce enough voltage, even if it hit the rails, to heat a modern subwoofer’s voice coil to thermal failure. Of course, if the driver isn’t in a box, it could only take 25 watts to force the driver to Xmax, and that would be a different mode of failure.

    The RMS power handling of a driver is the maximum thermal load that can be dissipated by the coil and thermal management scheme. The thermal handling of one coil may be more than half the RMS power rating, but it’s generaly not a good idea to driver a dual voice coil driver by only one coil because it really does weird things with the T/S parameters. Even in the case of the Parts Express DVC woofers (which are like the older Adire Audio Shiva drivers), the RMS power is 600 watts, but each coil can technically handle 350 watts when driven on its own. So don’t pump more than 500 watts total into the current generation of AV series woofers. I recommend the 500-watt class G amplifier Parts Express sells. It does a very good job on my AV12 driver.


    Member
    Travis Gibby on #1563

    Thank you Buszka,

    I find this topic very interesting. It seems that even the experts have differing opinions on this subject.

    @R. Buszka wrote:

    Well, if you give a subwoofer too much RMS power over a very long time, you will kill it (as dB mentioned — this would be accomplished with a full power sine signal or some other signal producing full RMS power of the amplifier), but by that point in your particular box, you would have the passive radiators getting blown off their suspensions before you would kill the driver, down around the tuning frequency.

    That is true, but if the clipped signal exceeds the thermal limit, then shouldn’t it exceed the thermal limit unclipped, only more? After all, a clipped signal will still be on and off just as often as an unclipped signal, but the peak amplitude of the unclipped signal will be greater (assuming the same level of gain).

    @R. Buszka wrote:

    Another factor to consider is, how compressed (dynamically) is the signal?

    I don’t believe that compression in and of itself of the dynamic range can harm a speaker. If the driver itself is compressing then damage might occur but the damage and compression both are the result of pushing the driver past it’s mechanical limits.

    Earlier I suggested that harmonics generated by clipping may destroy high frequency drivers. Dan Wiggins thinks so too:

    Hi all,
    Power is power. The speaker doesn’t know if it’s clipped, clean, or what. It knows there is power. And power is what kills speakers.
    One thing to correct – a clipped signal does NOT create DC; this is an oft-repeated myth that should be eliminated. When you clip a signal, you actually INCREASE the HIGH frequency content! DC would be the opposite – removal of high frequency signal content.
    In fact, the ultimate clipped signal would be strikingly similar to a square wave. A square wave is nothing more than a set of harmonically related sine waves – there is no DC component present. It is all AC.
    This is, in fact, why clipped amps are literally murder on tweeters. Clipped signals contain much more high frequency energy than unclipped signals. This is readily passed by the high pass filter of the tweeter, and means the tweeter can receive 2-10X as much power as anticipated, and quickly blows out.
    Anyway, too much power – clipped or unclipped – is what kills speakers. You can toast an speaker with clean or clipped signals. Just give it too much power.
    To answer the original question, you can push the driver to its full limits with that amp, so I’d recommend running the gains down a bit, and if you hear nasty bumps/distortion from the sub, turn it down even more.
    Note that you won’t get more SPL from ANY driver once you’re at its limits, regardless of how much more power you pour on. The nice thing about larger boxes is that you need less power to reach the limits. Would you rather hit full output with 100W or 1000W? Personally, I’ll take the 100W, since it’s less thermal strain on the driver and amp, and less draw on the alternator.
    Once you’re at the limit, you’re there. More power won’t help.

    – Dan Wiggins, CEO Adire Audio

    my emphasis

    Everybody knows this, but I just read an article that suggests that may in fact be FALSE:

    http://www.rane.com/pdf/note128.pdf

    The article suggests that it is compression of the audio spectrum that blows high frequency drivers and not odd-order harmonics caused by clipping. In other words if you turn up the volume untill clipping occurs, then you have effectively limited the low frequencies (since this is where most of the power lies in program material). If you continue to turn up the volume the power keeps increasing in the high frequencies but not in the low frequencies. The article suggests that this is why tweeters are the first to blow when the amplifier is driven beyond it’s limits.

    Travis


    Member
    Travis Gibby on #1564

    I found that thread on the Ford-Trucks forum. It’s relatively long (~390 posts) so I will try and sum it up with a few quotes from Dan Wiggins and Tracy Focht:

    @Tracy Focht wrote:

    >>There is Tracy’s post. He works for Kicker.
    >
    >Doing what? Sweeping floors for all I know. He is your
    >friend and will side with you no matter what Kicker’s stance
    >was. rbrendel has said he called Kicker and talked to a
    >tech and the tech support my claim. So, at best, your
    >friend has been negated.

    On many of your ‘beliefs’ and post, you are wrong…I will not sit here and argue with them, as I am in the industry you argue about.
    I am the Distribution Director for Kicker, and 5th in senority ad have been happily employeed here for 15 years.I’ve been around car audio for quite some time, and so happen work with some of the larger names in car audio. Mark Eldridge is one, and he was a co-worker with Richard Clark.

    We find no evidence that underpowering speakers is a cause for a premature driver loss. Like i stated in my earlier post, it is usually from
    a) overpowering
    b) pushing past mechanical limits

    I could really care less what others might find, if so, they may want to look at build quality if 25 watts kills a 100w woofer.
    Clipping, or pushing a cheaper, smaller amp past it’s limits, will hurt the driver. A true mis-conception that it was because it was underpowering.

    And other, you state that no car audio manufacture will warranty these such claims, you again, are wrong. We even ( as well as other car audio manufactures)do cover factory defect, customer abused subs. A majority of the ones turned in are customer abuse. And this is not just us, we have rep’s that used to work for Alpine, Rockford, eclips, etc…so they know the industry.

    If you want to continue to belive that low power kills speakers, by all means, go ahead. But without long history and dat, you can’t get me to swing, to that belief.

    have a nice day.

    Tracy Focht
    Kicker Car Audio
    http://www.kicker.com

    @Dan Wiggins wrote:

    – Underpowering destroys drivers. I believe Tracy (hi Tracy! Missed you at CES; I’m still here in LV, enjoying a bit of sun…) summed it up correctly: underpowering isn’t a problem. Overpowering or overexcursion are.

    A driver’s excursion is a function of the current flowing in the motor AND the stiffness of the box behind it. A larger box means less current flow required (less power, since power is current squared times impedance) to reach a given excursion level. In fact, you can push just about any driver to full linear excursion with a couple hundred watts, depending upon the box and signal used.

    Overexcursion is bad for a sub in two ways. The first is physical damage. You can snap tinsel leads, bottom the voice coil, wedge the voice coil on the top plate (if you walk it out the front of the gap; a common occurance with flux modulation effects), tear spiders, etc.

    The second problem with overexcursion is reduced cooling. Over 90% of the heat dissipation in a driver comes from air movement in the motor, not conduction through the pole, top plate, etc. When you linearly scale air motion with power – like when a driver is still within it’s linear range of motion – you’re generally OK. But when you reach the suspension limits and keep increasing power, you get into trouble. It’s like restricting the cooling air to the motor; akin to placing a restrictor plate in front of the radiator in your car. As you run with more and more motor output, heat builds up. And if you restrict the cooling – or hold it’s level constant – you can’t remove the heat as effectively, meaning a meltdown in imminent.

    As far as damaging from underpowering, it really can’t happen. It can happen if you CLIP the amp, but that’s not from the amp being underpowered; it’s from the amp generating even more power. Please see the eatel.net site for a VERY good description of the way the power envelope increases from a clipped signal. It’s not the fact the amp is underpowered; it’s the fact that you are increasing the power to the speakers, usually beyond it’s rating.

    @Tracy Focht wrote:

    >
    >Here’s a good summarization:
    >
    >The less power you present to a subwoofer, the safer it is
    >for your subwoofer… although you will also have less
    >output, the lower you go.
    >
    >If you clip your amp, you could send up to two times the
    >rated RMS power of the amp through your subwoofer…
    >(although in reality it is less than that)
    >If that clipped power exceeds your subwoofer’s RMS power
    >rating, you could indeed cause thermal damage to the
    >subwoofer..
    >But that’s not because you were using too small of an amp,
    >it’s actually because you made your amp put too much power
    >through the sub… not too little.
    >
    >However, if you have a very small amp, and you are clipping
    >it.. but even the clipped power doesn’t exceed your
    >subwoofer’s power rating (and as long as the sub is in a
    >proper enclosure), you simply won’t harm it.
    >
    >But you shouldn’t clip your amp anyways, because it sounds
    >bad.
    >
    >

    >So, it’s not that “too little power” kills subwoofers at
    >all..
    >In fact, the less, the safer.
    >
    >It’s not “clipping causes damage” either, because you could
    >clip the snot out of the amp, and still not harm the sub, as
    >long as the clipped power remained at safely low enough
    >power levels for the sub to handle.
    >
    >There’s only two things that kill subwoofers:
    >1) Too much power (causing thermal damage).
    >2) Too much excursion (user error – enclosure/music/power
    >level issue, causing mechanical damage from bottoming or
    >other physical collision)
    >
    >Concise? That really does sum up what we have discussed.
    >
    >

    IMHO, this post should be closed, as this most certainly cleared it up….can’t get any better discription that this…….

    (the person he quoted here is a user that goes by “Geolemon”)

    If anyone wants to read more here is a link to the thread:

    http://www.ford-trucks.com/forums/showthread.php?t=74578&page=14&pp=15

    Travis


    Member
    R. Buszka on #1565

    yes, it seems that the notion that clipping can kill a subbass driver isn’t true, and the notion that clipping can kill a speaker applies to the term “speaker” in the sense of an integrated full-range system, incorporating a tweeter that can be easily fried. Thermal power handling isn’t a function of frequency any further than the impedance might be different at that frequency. Thermal power dissipation by a resistor (in this case, the voice coil) has to do with a relationship between voltage and resistance, current and resistance, or voltage and current. A voice-coil still takes some time to heat up, which is why the notion of musical power or “program power” handling is still valid. In order to blow a driver, you’d need to exceed its RMS rating for a long period of time without rest. If you’re supplying power just a little over RMS, this could be hours, but if you’re way over RMS, this could be just a few minutes. A Watt is one Joule per second, or J/s, or one newton-meter per second (Nm/s). There is also a thermal definition for Joule as well. So power dissipation has something to do with how long the motor is applying force to the driver, which is roughly proportional to the input voltage for a small signal, so therefore it has to do with how long the voltage is applied across the driver’s terminals. An amplifier doesn’t actually supply “power”, just voltage. The “power” number comes from a calculation of the dissipation of heat from the applied voltage and the resistance (in this case, impedance) of the voice coil of the driver. That is why amplifiers list different power ratings into different impedances. So an amplifier simply supplies voltage, but a Watt of power is still a Watt. So it seems to me that the idea here is that a more powerful amplifier can supply the higher voltage over a short period of time without distorting the waveform, and yet with a music signal the driver won’t be asked to dissipate its full wattage rating. I don’t know, I’m not an engineer yet. Time to go have lunch.

    This discussion is really leading me to question some of the basic assumptions of power handling of drivers.


    Member
    Travis Gibby on #1566

    Yeah, another thing I find confusing is Tracy seems to contradict himself when he says:

    Clipping, or pushing a cheaper, smaller amp past it’s limits, will hurt the driver. A true mis-conception that it was because it was underpowering.

    I can only assume that he meant that a 100 watt amp can overpower a 150 watt speaker if you drive it into clipping, because he later agrees with Geolemon when Geolemon says:

    The less power you present to a subwoofer, the safer it is for your subwoofer… although you will also have less output, the lower you go.

    and:

    If you clip your amp, you could send up to two times the rated RMS power of the amp through your subwoofer… (although in reality it is less than that) If that clipped power exceeds your subwoofer’s RMS power rating, you could indeed cause thermal damage to the subwoofer.. But That’s not because you were using too small of an amp, it’s actually ecause you made your amp put too much power through the sub… not too little.

    However, if you have a very small amp, and you are clipping it.. but even the clipped power doesn’t exceed your subwoofer’s power rating (and as long as the sub is in a proper enclosure), you simply won’t harm it.

    But you shouldn’t clip your amp anyways, because it sounds bad.

    So, it’s not that “too little power” kills subwoofers at all.. In fact, the less, the safer.

    It’s not “clipping causes damage” either, because you could clip the snot out of the amp, and still not harm the sub, as long as the clipped power remained at safely low enough power levels for the sub to handle.

    Travis


    Member
    TeeCee on #1567

    Here are two ways in which I can see support for the clipped signal = damaged sub argument.

    (1) An uncorrected clipped signal will in fact approach a square wave. You can view it with a scope if you don’t believe me. It will approach a square wave until the point at which some component fails (internal wiring, fuses, power supply components).

    A square wave at say 100Hz with a peak to peak swing of say 10 volts (as limited by a given amp’s voltage rails) is indeed a more powerful signal than a 100Hz pure sine wave with a peak to peak swing of 10 volts. The power of the square wave is equal to the power delivered by a 10 volt DC signal (but is not DC). RMS calculations do not apply as all of the area under the voltage rails is signal. The power delivered by a clipped signal will be somewhere between the square wave power and the pure sine power, but will be greater than the sine wave power. So you are delivering more power to the sub with a clipped signal.

    (2) It seems that many who know agree that a clipped signal introduces high frequency content. This is also a fact.

    As stated in a previous post, a square wave is composed of a series of sine waves starting at the square waves base frequency and effectively continuing upwards infinitely (actually up to a real world limit). Think of it this way, the transition from smooth sine wave to hard clip is a very fast transition – a high frequency transition.

    Seeing as many sub designs incorporate a crossover before the amp, not after, this high frequency content is delivered to the sub.

    Note that some amps have soft clipping and the like to soften the transition. MacIntosh (sp?) used to do this with a phototransistor that would limit the input signal as the amp approached it’s maximum output. I believe some of the Parts Express amps have built in limiting.

    So, a clipped signal output from an amp delivers both more power and higher frequencies to a sub than a clean sine wave would.

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