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Old 6th January 2005, 06:50 AM   #11
Ranthum is offline Ranthum  United States
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Here's the link to the PE amp: http://www.partsexpress.com/pe/showd...number=300-794
and the MCM amp: http://mcm.newark.com/NewarkWebComme...U=50-6281A&N=4
For the MCM amp details, you have to search for it and click on tech info. I was leaning toward the Rythmik amp based on price and my first impression but I haven't ordered it yet. If I do get the rythmik amp, what would be the rumble filter setting I need for a 214L box tuned to 15.4hz? thanks.
Josh
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Old 6th January 2005, 06:36 PM   #12
BassAwdyO is offline BassAwdyO  United States
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The amps are very similar, except you can adjust the rumble filter on the rythmik and it also has higher S/N ratio. The PE and MCM amps also do not advertise dampening factor, which rythmik does indicating that their amps probably perform well in that area, while the others might not
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Old 6th January 2005, 07:11 PM   #13
directservo is offline directservo  United States
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Quote:
Originally posted by Ranthum
Here's the link to the PE amp: http://www.partsexpress.com/pe/showd...number=300-794
and the MCM amp: http://mcm.newark.com/NewarkWebComme...U=50-6281A&N=4
For the MCM amp details, you have to search for it and click on tech info. I was leaning toward the Rythmik amp based on price and my first impression but I haven't ordered it yet. If I do get the rythmik amp, what would be the rumble filter setting I need for a 214L box tuned to 15.4hz? thanks.
Josh
Our rule of thumb: set the rumble filter to same as the box tuning frequency. You don't really have a choice here. Set the rumble filter too high, roll off the bass too early; set the rumble filter too low, not enough protection for the driver. The only thing you can play with is Q value. Now, the real concern I have is the box size and the efficiency that come with it. To give you a rough idea, the box you have 214L can be up to 4 times more efficient (in terms of power) than a 100L box (at the tuning frequency and below). That means if you are using 350WRMS amp, the person with 100L box will need 350Wx4=1400W RMS amp. Above tuning frequency times 1.4, the efficiency is limited by the driver. With such a high efficiency, 350WRMS is definitely too much. I would recommend you to scale down the power and pick and amp that is flexible in setting up rumble filter. Or use one amp to drive 2 boxes.

Brian Ding
Rythmik Audio
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Old 6th January 2005, 07:41 PM   #14
BassAwdyO is offline BassAwdyO  United States
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Looking at WinISD specs it seems that 350watts would be just about perfect. Max power of the tempest is at 750watts. WinISD's max power simulation shows a dip centered at about 25hz that has a local minimum of 320watts. 350watts would probably be nice for a little extra headroom there. How much power do you suggest Brian?
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Old 6th January 2005, 08:18 PM   #15
Ranthum is offline Ranthum  United States
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I was thinking of getting the 250 watt model. That shouldn't be too much power with a tempest should it? Do you have a phone number that i could reach you or somebody else at rythmik to discuss/order an amp? I want to make sure i'm getting the right amp with the right settings to get the most of my sub while still protecting it.
Josh
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Old 6th January 2005, 08:45 PM   #16
directservo is offline directservo  United States
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Quote:
Originally posted by Ranthum
I was thinking of getting the 250 watt model. That shouldn't be too much power with a tempest should it? Do you have a phone number that i could reach you or somebody else at rythmik to discuss/order an amp? I want to make sure i'm getting the right amp with the right settings to get the most of my sub while still protecting it.
Josh
Josh,

You can give me a call at (714)612-2590. 250WRMS will be more reasonable. Even that you need to resist the temptation of cranking up the volume. In the previous post, I mainly just wanted to caution you the potential problem. The numbers that I quote you were more of a guideline. Now, you would like to tune it to 15hz which is quite low. If you compare a simulation of the same box tuned to 20hz, you may find the excursion requirement of your enclosure is larger. If you don't push the amp into clipping, the rumble filter will be very effective. However, when the amp clips, the output from the amp contains spectral components that are not in the input signal. These newly introduced components are hard to predict. But if they happen to have components at the frequency that the enclosure is most susceptible to over-excursion, it can easily overload the driver. In short, a rumble filter protects the driver from the signal that you feed the amp, it does not protect you from the clipped waveform created from amp when it is into clipping.

Brian Ding
Rythmik Audio
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Old 6th January 2005, 09:10 PM   #17
directservo is offline directservo  United States
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Quote:
Originally posted by BassAwdyO
Looking at WinISD specs it seems that 350watts would be just about perfect. Max power of the tempest is at 750watts. WinISD's max power simulation shows a dip centered at about 25hz that has a local minimum of 320watts. 350watts would probably be nice for a little extra headroom there. How much power do you suggest Brian?
Mike,

I would recommend no more than 250WRMS output. Another thing I would like to point out is over-excursion has little to do with power in vented box. It is kind of hard to read from simulation. First, if the simulation result does not include the effect of rumble filter, you will see tremedous excursion below box tuning frequency. So that does not tell you the acutal excursion when one adds a rumble filter. On the other hand, if the simulation does include the effect of filter, it is hard to see the weak spot of the driver when the amp is overloaded. Plus there are some drivers that are well behaved when the voice coil is over driven to out of the gap and others that a small overload can cause the voice coil "slide" to reach the suspension limit. It is a matter of spider design.

Brian Ding
Rythmik Audio
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Old 7th January 2005, 06:28 AM   #18
simon5 is offline simon5  Canada
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Hi Brian, I just did a EBS Shiva box (142,5 liters tuned to 18,4 Hz) with your 250 W RMS amplifier. You have your rumble filter set at 12 Hz. As I can see, I will run in overexcursion under 16 Hz. You think it would be worth it to modify your stock rumble filter? You know, I don't want to break something and lose the warranty on your amplifier but I don't want to break the Shiva!

If I tune the rumble filter at 18 Hz to protect the driver, I lose 2 dB at 20 Hz which is not acceptable, since I want to beat a SVS PB10-ISD in linearity, distortion and loudness.
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Old 7th January 2005, 08:17 AM   #19
directservo is offline directservo  United States
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Quote:
Originally posted by simon5
Hi Brian, I just did a EBS Shiva box (142,5 liters tuned to 18,4 Hz) with your 250 W RMS amplifier. You have your rumble filter set at 12 Hz. As I can see, I will run in overexcursion under 16 Hz. You think it would be worth it to modify your stock rumble filter? You know, I don't want to break something and lose the warranty on your amplifier but I don't want to break the Shiva!

If I tune the rumble filter at 18 Hz to protect the driver, I lose 2 dB at 20 Hz which is not acceptable, since I want to beat a SVS PB10-ISD in linearity, distortion and loudness.
Keep in mind, a rumble filter protects the driver from signals below box tuning frequency and it does not have any effect on a clipped output signal from power amp. So the most important thing is keep the volume at reasonable level so that the amp will not be driven too much into clipping (slight clipping is ok). For a movie track, the sound engineers are supposed to filter out the signals below 20hz (or something a bit lower than that), not for our benefits, but for the speakers in movie theaters. Those speakers are most likely ported. Heavy signal below 20hz can overload them. That is one reason that some people are ok with their vented box even without a rumble filter. But you cannot count on that for all movies because some of them do not follow this guideline. As for the rumble filter, a Q value of 1.0 is in general good. It has a small boost of 1db in the passband, and at the same time have a sharp roll-off below corner frequency. The lower the Q, the more gradual the roll-off. So it may be worthwhile to put a filter with Q=1.0 or 0.9 if you like, that just starts to roll off at 20hz. So there is no attenuation at 20hz (or above). It is definitely doable.

Brian Ding
Rythmik Audio
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