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Old    Claudiu Barbura (claudiub)      Join Date: Apr 2008       04-16-2013, 6:19 PM Reply   
I recently purchased a set of MB8 frmo Earmark Marine to complement my Pro80 setup.
I have the Pro80 hooked to a JL XD400/4 amp bridged to 2x200W RMS. I like turning down the amp output so I can lower the HP filter to 50Hz, for a deeper bass without distorsion.
I am planning to connect the MB8 to a P300.1 RF amp (2ohm 1x416W RMS according to its birth certificate).
Question is: should I reverse the amps and use the classAB RF for the Pro80 and the class D JL for the MB8s? I need more sound quality than just sheer volume, since I will have plenty of power I am sure.
Old    Earmark Marine (david_e_m)      Join Date: Jul 2008       04-16-2013, 6:54 PM Reply   
Claudia,
JL Audio doesn't do birth certificates but when tested the bridged XD400/4 will deliver 2 X 280 watts into a 4-ohm load with a 14.4 volt supply. Typically a JL XD amplifier is rated conservatively enough that it will produce its 14.4 rating with a 12.5 volt supply, which is very impressive.
The Pro80s and MB-8s have the same size midbass driver with the same size voice coil in the same displacement pods. So at first glance you would think they deserve symmetrical power. However, the Pro80 will be reproducing more bandwidth which takes more power to stay clean. Also, the Pro80 has insertion losses due to the more complex internal high/lowpass passive crossover. Plus, you are going to be more sensitive to distortion at higher frequencies above that which the MB-8 will reproduce. So based on all the above, I would recommend using the bridged XD400/4 on the Pro80s and the RF 300.1 to the MB-8s.
50 Hz is too low for either 8-inch to deliver IMO. The pod displacement ultimately will determine the low frequency cut off point. To my ears, 80 Hz is a good minimum highpass number. I would be surprised if you hear more bass extension below that frequency selection. Narrowing the bandwidth cleans everything up. And, you always want to tune a system for the maximum volume used rather than the minimum.

David
Earmark Marine
Old    Claudiu Barbura (claudiub)      Join Date: Apr 2008       04-17-2013, 9:51 AM Reply   
David,

helpful as always, thank you!

What is the frequency range these MB8's can reproduce?
I will set the HP filter at 80Hz, as you suggested and listen to the udner 80Hz frequence range from the JL sub.

Thanks,
Claudiu
Old    Earmark Marine (david_e_m)      Join Date: Jul 2008       04-17-2013, 10:41 AM Reply   
Claudiu,
A - 3 dB 80 Hz crossover point is a good number for an 8-inch speaker in a sealed pod. Actually that is on the low side. As the amplitude increases the bandwidth will narrow related to the bass extension. So you might get low frequency reproduction that is too low in amplitude to be useful. Past a point the speaker and amplifier are wasting too much energy trying to reproduce the deeper lows at an insufficient amplitude. By removing that lower region, the speaker and amplifier play much cleaner over the remaining range. A person who only listens at lower levels in close proximity at rest can use a slightly lower crossover frequency that one who listens at wake range. To maximize output and increase projection you raise the crossover thereby narrowing the bandwidth. You have to find the balance for your particular usage. When you get to the point of lowering the crossover without hearing a difference in the lower bass extension then you have gone too low. And you have to tune for the loudest volume you are likely to use.

David
Earmark Marine

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