Finding Center Frequency - No Label, how do i do this?

[Decado 10+ year member]

On my new hcca-d2400, for the lpf, it just shows the minimum (30) and the maximum (250), is there some way that i can set this accurately? Because eyeballing it just isnt going to work. Also, how can i set the subsonic filter accurately?

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[helotaxi 5,000+ posts]

RTA would be the easiest for both.

 

[thch 10+ year member]

step 1. turn SSF to lowest setting, preferably off.

step 2. play a test tone at the desired cutoff frequency.

step 3. turn up volume until you get 1.414V out on the DMM, measuring AC Volts.

step 4. adjust ssf until the DMM reads 1.00V or so.

if you want to improve on this, try setting the SSF at the minimum and the LPF at the maximum, and playing a tone at 100hz or so, and setting the 1.414V reference this way

 

[Decado 10+ year member]

step 1. turn SSF to lowest setting, preferably off.
step 2. play a test tone at the desired cutoff frequency.

step 3. turn up volume until you get 1.414V out on the DMM, measuring AC Volts.

step 4. adjust ssf until the DMM reads 1.00V or so.

if you want to improve on this, try setting the SSF at the minimum and the LPF at the maximum, and playing a tone at 100hz or so, and setting the 1.414V reference this way

Uhh, when you say turn up volume until i get 1.414v what do you mean by volume, on the HU, or the gain? Also, how do i find the center frequency with the lpf?

Another question, what would be the best setting for the lpf and the ssf with a port tuning of 33 hz?

 

[helotaxi 5,000+ posts]

Uhh, when you say turn up volume until i get 1.414v what do you mean by volume, on the HU, or the gain? Also, how do i find the center frequency with the lpf?

Actual volume, he's assuming that your gains are already correctly set. You have to determine what center frequeny you want and then the process is the same as for the SSF. Start with the freq at max and dial it down until you get 1V.

Another question, what would be the best setting for the lpf and the ssf with a port tuning of 33 hz?

SSF about 30 Hz. LPF depends entirely on the rest of the system. I would suggest setting the LPF by ear so it sounds good to you.

 

[thch 10+ year member]

Uhh, when you say turn up volume until i get 1.414v what do you mean by volume, on the HU, or the gain? Also, how do i find the center frequency with the lpf?
Another question, what would be the best setting for the lpf and the ssf with a port tuning of 33 hz?

turn down the volume on the HU or the gains. your amp shouldn't be clipping at 1.4V. (you can also use 14V or anything else really). if you have the gains set, then it will make the most sense to adjust the HU.

the reason for all of this is because 1.000V is -3dB down from 1.414V. so if the test tone normally creates a 1.414V signal at some frequency, then a filter will be affecting this signal by -3dB when the measured signal is 1.0V. that is, 1 is 70% of 1.4. 70% correspondes to -3dB.

the alternative method is to play a 20-25hz test tone at full volume. set the SSF all the way at max. then lower the SSF frequency until the excursion reaches a point you concider to be excessive. this method has an advantage that is is actually relevant to the system and not based on some folk-lore "5hz lower" or "1/3rd octave lower" myth/method. it will not limit low frequency extension more then necessary, nor will it allow overexcursion. its also easy.

 

[Decado 10+ year member]

Ok, now when i set the lpf, lets say I set it at 70hz, do i then use a 70hz tone to set the gain again?

 

[thch 10+ year member]

Ok, now when i set the lpf, lets say I set it at 70hz, do i then use a 70hz tone to set the gain again?

it really makes the most sense to remove the filtering. if you apply a 70hz LPF and test the gain at 70hz, you will end up with higher gain settings then you were supposed to have. but really it shouldn't matter to much. its equivilent to testing with -3dB (or -6dB for linkwitz riley) test tones.

since mild clipping is generally harmless, this shouldn't be an issue. if it is an issue, it can be solved by turning down the volume by 1 to 3 clicks.

 

[Decado 10+ year member]

it really makes the most sense to remove the filtering. if you apply a 70hz LPF and test the gain at 70hz, you will end up with higher gain settings then you were supposed to have. but really it shouldn't matter to much. its equivilent to testing with -3dB (or -6dB for linkwitz riley) test tones.
since mild clipping is generally harmless, this shouldn't be an issue. if it is an issue, it can be solved by turning down the volume by 1 to 3 clicks.

Well, the LPF cant be turned off, and I already set it with -6. So if I want a 70 hz lpf frequency, i set the lpf and then the gain? Or the other way around? I guess I dont see how i'd end up with a higher gain setting if i just set the lpf and then set the gain afterward.

 

[thch 10+ year member]

the cutoff frequecy of a filter is normally defined as being -3dB down. Linkwitz-Riley crossovers are defined by being -6dB down at the cutoff frequency.

if you use a 70hz lpf, and a 70hz tone for testing, you will be effectively testing with a tone which is -3dB from what you wanted.

if you set the crossover to the furthest setting, or off, you can test at a frequency which is in the middle of the band, which will be at -0dB. afterwards, you can adjust the lowpass filter down.