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High x-max vs. high sensitivity

Years ago i had a 15" JBL subwoofer in a ported box in the rear of a camaro. It was running off a rockford fosgate punch amp and was receiving 200 watts rms. This set up worked great and was able to hit 133db with this basic installation. The sub only had a "x-max"of 8.5 mm but had a sensitivity rating of 97db.
My question is this----There are a lot of subs on the market that have a high "x-max" rating of 20-30mm yet have a low sensitivity of 85-90db.If you had 2 choose between the following setup,which would yield the highest bass output and spl in a ported box.>>>A)-15" subwoofer receiving 300-400 watts rms."x-max"-12mm,sensitivity 98db.>>>B)-15" subwoofer receiving 300-400 watts rms. "x-max"-24mm,sensitivity 87db.

Would appreciate any input from anyone out there, especially all the "bassheads"

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Sensitivity is a representation of efficiency. The higher the efficiency, the better the sound quality.
Xmax is a measure of the "throw of the cone peak to peak. This is a direct representation of the volume of air the subwoofer will displace..
A High X.Max subwoofer will displace more air - and therefore produce more SPL in a vented enclosure.
Sensitivity on these subs aren't crucial, because the customer is looking for LOUD and will purchase a large class D Mono amplifier to power it - characteristically low in sensitivity as well due to the way the power is inverted. Highly efficient, yet low sensitiviy.
I am definately a basshead! My show car has (4) 15" Cerwin Vega Stroker PROs. (one of the most highly EFFICIENT high xmax subs available) (86dB). (36-44mm Xmax (adjustable for SQ or SPL)
High x-max vs. high sensitivity - ea141e4.jpg If you are looking for SPL, High XMax, Low sensitivity, and lots of power is the way to go. Generally, to increas SPL by 3dB, yuo must either increase surface area of driver 2x or double the input power. Slot ports, aeroports, and loaded horn ports can also increase your dB level by up to 3dB as well.
Properly constructed enclosures have an effect as well. Instead of wasting some of your power on vibrating the enclosure, it should be braced properly to reduce the wasted energy.
All of these tips will add tou your satisfaction of the product. You can make a $100 sub sound phenomenal in a proper enclosure, and a $400 sub sound like $hit in a prefab or poorly constructed one.

Your original question - with all things equal except the subwoofer, the subwoofer with the higher Xmax should yield the most SPL - due only to the fact of air displacement.

If you have additional questions or need clarification dont hesitate to ask.

Posted on Jan 15, 2009

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  • BassMutt Feb 12, 2011

    Pure Bs , using speakers with high sensitivity will require less power to achieve higher volume.
    The total SPL is limited by the Number of drivers and the available space, If you wanted to go higher than 133dB you would have to add more Drivers. If you had a pair of drivers rated each at 96dB it would take around 400 watts to reach 130dB.......thats inside a small to med car, the cabin gain adds some SPL. A pair of speakers rated at 86 dB would require well over a 1000watts to reach 130dB.......Cone excursion at 400watts= 9mm, Cone excursion at 1000 watts = 26mm , so you can see both systems will both reach their xmax and power handling and still get the same SPL. The big benefit of using high Xmax drivers is clean, tight accurate bass at " normal " listening levels......If you want high SPL you need high SPL drivers...and a high spl driver will have less xmax, so more likely to hit distortion, if you still want high SPL and low distortion you need to use more drivers....such as 4 instead of
    2 speakers, each at 97dB with 400 watts = 127 dB with cabin gain 130 to 136dB
    4 speakers, each at 97dB with 400 watts = 131 dB with cabin gain 134 to 140dB

  • adam eldridge Jan 09, 2012

    yur right and wrong 2 10'' subs at 400w rms = 146.7 db learn how to install before u act like u know sumthin i have beatin 2000w multi driver systems with a mere 600w on a single sub rightn now im running a 50 dollar kicker with a 300 w amp and my dbs are touching 129 and thats country music but yes higher eff. levels equal more db with less power

  • amoctez2
    amoctez2 Apr 16, 2013

    You add 6dB when you double power(dB is measured as ratio of powers not voltages!). But at high powers, efficiency is lowered (the nonlinearity depends on the sub you are testing). Therefore, all those theoretical calculations just give approximations. There's nothing like measuring at the resonant frequency.


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