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  1. #11
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    Wired in series, that amp should have no issues driving 4 pair, but its pushing a lot with too chnls at 1.33 nominal impedance. During normal listening, this 1.33 will actually drop lower. This should put any 2 ohm stable amp into protect mode.

    If the amp actually delivers its advertised 4 ohm and 2 ohm output, then I would suggest rewiring the 2 pairs of polks, to series. You will likely not have a noticeable drop in volume, but may actually pick up some sound quality at the higher impedance.

  2. #12

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    This is not a step by step professional tuning prescription like you would get from Odin at Earmark Marine. Odin is a masterful acoustic engineer and walks his customers through a real pro tuning process. He can also dumb it down if you don't have the tolerance for the technical, however, he will take everything into consideration on his own as he instructs you. The following is just a few of the guidelines a pro might consider in making your particular crossover selections.
    Alpine says that your woofer in your box will have a gradual deep bass roll-off starting at about 60 Hz, be at half power at 45 Hz, and roll-off rapidly below 45 Hz. Not bad for that small of a box. A typical active crossover is at half power at the crossover frequency so it also begins to roll-off gradually outside/lower-than the crossover region. The 'meat' of the bass is in the 50 to 80 Hz region ('meat' denoting the range that is perceived to be the loudest). So you are beginning to roll off on the bottom end below 60 Hz by nature of the enclosure/driver. If you select a lowpass crossover of 90 Hz for example you are beginning to gradually roll-off the top end of the sub below 90 Hz. That doesn't leave much bandwidth. Again, this would have you at half power at 45 Hz on the low end and at half power at 90 Hz on the top end. That is less than one full octave. That is also beginning to infringe on the power bandwidth of the bass (in other words the 'meat'). A 'Qtc' of 0.81 in your case will also generate a small peak in the response about an octave above the system (woofer in box) resonance. That becomes an accentuation of what could be an already pronounced peak by nature of the lower end and upper end roll-offs. So with what I am sharing with you, your conclusion should be that you do not want to crossover your sub below 90 Hz.... period. It's also to your advantage to have the lowpass of the subwoofer and highpass of the coaxials as close together as possible. Otherwise, as you spread the crossover points apart you get farther and farther out of phase with one another and any degree of coherency becomes impossible.
    So why is coherency important and why do I place so much emphasis on having the best possible phase relationship? Because you are very dependent on your coaxials and the relationship between the sub and coaxials for bass tonal construction and pitch accuracy. Want proof? Easy. Just run your subwoofer in isolation in the lowpass mode and without the benefit of the coaxials or other fullrange speakers. No matter which sub you have it will sound drunk, soggy and muddy. Add the upper harmonics back in from the coaxials and you will find that structured bass tones actually are formed again.
    If we change equipment or even change the sub enclosure we might be changing the crossover selection. It's a sequential process, a step by step prescription, and not a simple set of numbers that are commonly used and that would apply to all systems. And I've only scratched the surface. For a music lover it's a crime to simplify it.
    But when tuned correctly the identical equipment can perform at twice the perceived level.

  3. #13
    Join Date
    Jul 2009
    Location
    Marquette, Michigan
    Posts
    141

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    Quote Originally Posted by David Analog View Post
    This is not a step by step professional tuning prescription like you would get from Odin at Earmark Marine. Odin is a masterful acoustic engineer and walks his customers through a real pro tuning process. He can also dumb it down if you don't have the tolerance for the technical, however, he will take everything into consideration on his own as he instructs you. The following is just a few of the guidelines a pro might consider in making your particular crossover selections.
    Alpine says that your woofer in your box will have a gradual deep bass roll-off starting at about 60 Hz, be at half power at 45 Hz, and roll-off rapidly below 45 Hz. Not bad for that small of a box. A typical active crossover is at half power at the crossover frequency so it also begins to roll-off gradually outside/lower-than the crossover region. The 'meat' of the bass is in the 50 to 80 Hz region ('meat' denoting the range that is perceived to be the loudest). So you are beginning to roll off on the bottom end below 60 Hz by nature of the enclosure/driver. If you select a lowpass crossover of 90 Hz for example you are beginning to gradually roll-off the top end of the sub below 90 Hz. That doesn't leave much bandwidth. Again, this would have you at half power at 45 Hz on the low end and at half power at 90 Hz on the top end. That is less than one full octave. That is also beginning to infringe on the power bandwidth of the bass (in other words the 'meat'). A 'Qtc' of 0.81 in your case will also generate a small peak in the response about an octave above the system (woofer in box) resonance. That becomes an accentuation of what could be an already pronounced peak by nature of the lower end and upper end roll-offs. So with what I am sharing with you, your conclusion should be that you do not want to crossover your sub below 90 Hz.... period. It's also to your advantage to have the lowpass of the subwoofer and highpass of the coaxials as close together as possible. Otherwise, as you spread the crossover points apart you get farther and farther out of phase with one another and any degree of coherency becomes impossible.
    So why is coherency important and why do I place so much emphasis on having the best possible phase relationship? Because you are very dependent on your coaxials and the relationship between the sub and coaxials for bass tonal construction and pitch accuracy. Want proof? Easy. Just run your subwoofer in isolation in the lowpass mode and without the benefit of the coaxials or other fullrange speakers. No matter which sub you have it will sound drunk, soggy and muddy. Add the upper harmonics back in from the coaxials and you will find that structured bass tones actually are formed again.
    If we change equipment or even change the sub enclosure we might be changing the crossover selection. It's a sequential process, a step by step prescription, and not a simple set of numbers that are commonly used and that would apply to all systems. And I've only scratched the surface. For a music lover it's a crime to simplify it.
    But when tuned correctly the identical equipment can perform at twice the perceived level.
    Makes sense. Thanks. After a little trial and error based on a starting point of 80 HP on the cabin speakers and 80 LP on the Sub, I ended up at about 100 on the cabin speakers, and about 100 on the Sub and it sounds pretty good and fairly seamless. In fact, I found myself putting my ear down by the sub to make sure sound was coming out. It basically just sounded like all the bass was coming from the cabin speakers.

    I'm going to change my speaker wiring to series and see how it sounds.
    2019 Moomba Mojo

  4. #14

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    Quote Originally Posted by yooper View Post
    Makes sense. Thanks. After a little trial and error based on a starting point of 80 HP on the cabin speakers and 80 LP on the Sub, I ended up at about 100 on the cabin speakers, and about 100 on the Sub and it sounds pretty good and fairly seamless. In fact, I found myself putting my ear down by the sub to make sure sound was coming out. It basically just sounded like all the bass was coming from the cabin speakers.

    I'm going to change my speaker wiring to series and see how it sounds.
    Yeah man!!! When the sub localization disappears and you have plenty of bass you have really accomplished something.

  5. #15
    Join Date
    Jul 2009
    Location
    Marquette, Michigan
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    Cool. I'm there. I switched the 4 main cabin speakers to series, which now means the Amp is seeing 5.4 ohms from those 4. The two bow speakers are just wired directly to the amp.... 2.7 ohms. All things being equal, the bow speakers should now be louder, right? Would it make sense to bump the sensitivity up a touch for the 4 that are in series?
    2019 Moomba Mojo

  6. #16
    Join Date
    Oct 2010
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    Lake Wylie NC Area
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    Quote Originally Posted by yooper View Post
    Cool. I'm there. I switched the 4 main cabin speakers to series, which now means the Amp is seeing 5.4 ohms from those 4. The two bow speakers are just wired directly to the amp.... 2.7 ohms. All things being equal, the bow speakers should now be louder, right? Would it make sense to bump the sensitivity up a touch for the 4 that are in series?
    And you can easily dial back the bow chnl gains to reduce their dominance.

  7. #17

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    I totally agree with MLA on avoiding a 1.35 impedance which actually is lower at some frequencies as that is just the nominal impedance. It could pass thermal but it's better for sound quality to run it higher.

    Whenever the output impedance load is high you will need a little more rotation on the input gain with the inverse being true at a lower impedance load.

  8. #18
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    Jul 2009
    Location
    Marquette, Michigan
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    141

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    Quote Originally Posted by MLA View Post
    And you can easily dial back the bow chnl gains to reduce their dominance.
    Except the fact that both gains are all the way down.... so the only way to equalize them would be to bump the 4 speakers up, rather than the bow speakers down.

    Which brings me to another question.... should the gains be all the way down? Or should I lower the gains on the ZLD so that I can turn up the amp gains a little?
    2019 Moomba Mojo

  9. #19
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    Oct 2010
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    Quote Originally Posted by yooper View Post
    Except the fact that both gains are all the way down.... so the only way to equalize them would be to bump the 4 speakers up, rather than the bow speakers down.

    Which brings me to another question.... should the gains be all the way down? Or should I lower the gains on the ZLD so that I can turn up the amp gains a little?
    There is absolutely nothing wrong with having the amp gains bottomed. Now, wide open is another story. The lower the gains, the lower the noise floor. I would not lower the EQ's gains, simply to raise the amps' gains, this is counter productive. Raising the gain on the chls driving the 2 pair, in order to balance thier output to the bow pair is fine, providing you are not exceeding the pre-clip level, over driving the speakers, or getting to a point that gain hiss is introduced. Once balanced, then use the EQ's volume to do the rest. If the balance you seek can not be achieved without the main cabin gain being to high, then a simple RCA line level controller can be put in after the EQ, prior to the amp, with a dedicated set of RCA cable to the bow chnls. This would allow for further control.

  10. #20
    Join Date
    Jul 2009
    Location
    Marquette, Michigan
    Posts
    141

    Default RCA wiring my new amp.

    Here's what it looks like now:



    2019 Moomba Mojo

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