TOPIC:

After reading some discussions I need clarification. I have a LMS5400 sealed sub + a Marathon Ma5050 amp (4000Watts). I will be using the MiniDSP to create an LT for my sub boosting the low end so my sub can play flat down to 15Hz.

What are my limits with the inputs/outputs?

In answer to your questions, your limits are as per the miniDSP spec sheet. If we're talking of the miniDSP Unbalanced kit or 2x4 in a box:
- Inputs: 0.9Vrms or 2Vrms depending on the version you're using
- Outputs: 0.9Vrms for the outputs

Whether you will overdrive the outputs or not will depends on how much EQ'ing you're doing...
It's actually real easy to see if you're saturating or not. Simply connect the outputs of your miniDSP (with your source as it is supposed to) to a PC measurement system (e.g. REW or Arta). Have a look at the THD measurements. When you start to see all the harmonics coming out (e.g. 1kHz tones showing huge peaks on the 2k, 3k...) then you're close to saturation.

Hope this makes sense.

Thank you, I will test the distortion using REW.

I have ten db boost at 20Hz. Its not overloading. Its the only big boost in my setup. I am using Emotiva equipment.
Its amazing the bass that my 15 year old NHT 1259s put out.

Neat... Glad to hear you're having fun with your Sub and miniDSP combo!

penngray wrote:

After reading some discussions I need clarification. I have a LMS5400 sealed sub + a Marathon Ma5050 amp (4000Watts). I will be using the MiniDSP to create an LT for my sub boosting the low end so my sub can play flat down to 15Hz.

What are my limits with the inputs/outputs?

Hi, I did a little bit of math, and perhaps this is of some help:

according to the spec sheet I found on your amplifier, it has selecatble 1.0V input sensitivity (which is probably the best match for MiniDSP's 0.9V output), but 5000W into 4Ω bridged, which equates to 141V output voltage. That means 20*log(141V/1.0V) = 43dB of voltage gain.

So, if you are worried about saturating your output, consider building the filter with attenuation instead of boost. That is, instead of adding 12dB of boost at 15Hz, add -12dB of EQ everywhere above 15Hz ( something like this ).

Even then, you've still realistically got 31dB of gain for the high frequencies, which would take you to 32V output with your amp turned up to max. That's 256W into 4Ω, which means 3*ld(256/2) = 21dB louder than then quoted sensitivity, or 109dB SPL.

As it is, SPL is excursion limited to 107dB at 15Hz, so if you're aiming for a -3dB point at 15Hz, you won't be able to go louder than 110dB SPL anyways.

Or, if you're not happy with having your amp turned up full blast, perhaps consider a compromise - 6dB of boost at low frequencies, 6dB of attenuation at high frequencies, but turn the amp down 6dB to remain at the same level. As reports in this thread have confirmed, you probably won't have any trouble with some boost at low frequencies, but to be absolutely on the safe side, only use attenuation, no boost.

Oh, and one more thing, as far as I'm aware you can't enter any values lower than 20Hz into the MiniDSP, so boost at 15Hz might be tricky. On the other hand, perhaps it's possible to circumvent this limitation using the advanced coefficient entry function. I cannot confirm this, as my order has not shipped yet, so I don't have the software available to look at.