FMOD high pass filters?

[aerochrome2]

I re-ran the ARC calibration with the PEQ eq turned off on the sub. As expected, the peak from 50 to 100 dropped a few DBs.

 

[Maginness]

I've used both the inline ones and adjustable one. Very happy with both.

Currently running a MiniDSP Flex (wanted balanced connections and moved to a 2.2 system I wanted DSP and lots of tuning for).

 

[aerochrome2]

I've used both the inline ones and adjustable one. Very happy with both.

Currently running a MiniDSP Flex (wanted balanced connections and moved to a 2.2 system I wanted DSP and lots of tuning for).

Thanks. Since I already run ARC room correction, I definitely wanted something passive if possible. A miniDSP would add an extra ADC conversion. So far, I am happy with the FMOD as well.

 

[Maginness]

Thanks. Since I already run ARC room correction, I definitely wanted something passive if possible. A miniDSP would add an extra ADC conversion. So far, I am happy with the FMOD as well.

This thread reminded I have the adjustable FMOD set up in my garage system. But I have a currently unused minidsp DDRC-24 laying around. Obviously the garage "needs" DSP too and I now know what today's project is. Oh wait I have a Topping E30 laying around too. Darn it. Today's project is now MiniDSP vs DAC + FMOD. It's a sickness. A fun sickness though.

 

[dlaloum]

I wanted to experiment with BiAmping... my speaker has a crossoverless connection to the woofer as an option - but to make best use of it you need to LP the woofer, and HP the rest...

It worked as described on the box, I ran the inline FMODS before the power amp inputs with y Splitted - sadly BiAmp did not do much for my speakers (didn't degrade things, but didn't improve things either...) - so I put them aside.

I later tried the BiAmping / Crossover options on my AVR, and also on my power amps (which also have a crossover DSP for that purpose) - results were pretty much the same.

So yes the FMODS do the job and do it well - whether it is of any benefit depends on your setup, speakers, purpose and use....

 

[Head_Unit]

PFmod, it's an 18dB/oct

Really? I didn't catch that in the product blurb. I'd love to see THAT thing measured, see if the slope and frequencies are accurate at all. (Hint to @amirm ).

 

[EJ3]

Does anyone have first hand experience with these?

https://www.hlabs.com/products/crossovers/index.htm

Do they actually work as advertised? Any attenuation, distortion, noise issues?

I am mainly interested in an inexpensive way to filter out bass at line level (RCA) going from preamp to my amp and bookshelf speakers.

Also, am I right to assume that a typical 100 Hz high pass filter with a 12 dB/octave slope is already down 3 dB at 100 Hz? Trying to decide if a 70 Hz one or a 100 Hz one would be better for my PSB Alpha B speakers (5.25" drivers), which are rated ±3dB from 65-21,000Hz.

Thanks!

I Use this from them. It works well and I can select my frequency crossovers. I run a tri-amped system
(one stereo amp with over .6 KW a channel for the 2 subs [2 ohm] and one .5 KW amp for each of the left & right channels [4 ohm])

 

[DHT 845]

Therefore, if I understand correctly, the selection of RC elements depends on 1. the output impedance of the preamplifier and 2. the input impedance of the power amplifier. Does anyone know of a useful online calculator for calculating resistor and capacitor values with assumed impedances and a given crossover frequency and slope?

I assume that the 18db/Oct slope will be a CRC system, right? But how to calculate these values depending on the impedance of the devices? I cannot find any online calculator for inline crossovers. Please help.

 

[DHT 845]

Anyone could help?
What RC values are needed for Hi-pass from 70Hz, Preamp: 20 Ohms output impedance, Amplifier: 100 kOhms input impedance.

 

[DHT 845]

Could someone on this scientific forum at least verify the schematic?

 

[Sokel]

Could someone on this scientific forum at least verify the schematic?

You have to include the upwards and downwards impedance as well.
In pre's case it may not be the same as levels change (depending on how it makes VC) .

 

[DHT 845]

You have to include the upwards and downwards impedance as well.
In pre's case it may not be the same as levels change (depending on how it makes VC) .

So how to do it? Simple inline hipass filter for god's sake. I don't even ask for 18dB/oct or 24dB/oct . Impedances 20 Ohms (Pre) and 100k Ohms (Amp).

 

[NTK]

So how to do it? Simple inline hipass filter for god's sake. I don't even ask for 18dB/oct or 24dB/oct . Impedances 20 Ohms (Pre) and 100k Ohms (Amp).

Below is from the Harrison Lab web site (source).


Beyond that, I don't think they has provided enough information to calculate the response given the specific source and load impedances. I found their information confusing. In this page they said the filters are 12 dB/oct (2nd order), but the FR plot they showed on the page looks like to me it is 20 dB/decade = 6 dB/octave = 1st order filter.

 

[DHT 845]

Right, they provide little information because they want to charge 28 USD for a cap and resistor

 

[Oski1928]

Would I be able to use these between a streamer and an integrated amp? I see most people talking about them between a pre amp and a power amp

 

[NTK]

Right, they provide little information because they want to charge 28 USD for a cap and resistor

Didn't read this thread carefully enough. Not knowing that you simply asked for the R & C values of a high pass first order RC filter. Here is the frequency response plot:


The source impedance doesn't affect the filter frequency. The corner frequency of an RC filter is given by (Wikipedia):
fc = 1/(2π R C)

Choose C = 0.47 μF. As fc = 70 Hz, the value of R = 4837.54 Ω.

Since R is R2 parallel with R_load, therefore R2 = 1 / (1/R - 1/R_load) = 1 / (1/4837.54 - 1/100000) = 5083.45 Ω
Round to the nearest available value = 4.7 kΩ.

Solution: R_filter = 4.7 kΩ; C_filter = 0.47 μF

 

[DHT 845]

Choose C = 0.47 μF. As fc = 70 Hz, the value of R = 4837.54 Ω.

Since R is R2 parallel with R_load, therefore R2 = 1 / (1/R - 1/R_load) = 1 / (1/4837.54 - 1/100000) = 5083.45 Ω
Round to the nearest available value = 4.7 kΩ.

Solution: R_filter = 4.7 kΩ; C_filter = 0.47 μF

Thanks a lot,
I found calculator yesterday:

RC, RL, LC Passive Filter Calculator | DigiKey Electronics

Calculate the -3dB cutoff frequency of RC, RL and LC circuits for both Low and High Pass filters using DigiKey’s passive filter calculator.

www.digikey.com

I'm just wondering what would be the difference (if any)...
And what type of filter and combination of values would be optimal in my case?

1. using other RC combinations, for ex. R_filter = 22.7 kΩ; C_filter = 0.1 μF (or) R_filter = 294 kΩ; C_filter = 7733 pF
2. using RL filter (instead of RC), for. ex. R=10Ω; L=22mH
3. using LC filter (instead of RC), for ex. L= 50mH; C=100uF

Especially I wonder about LC filter because of it's natural similarity to speaker level crossovers... For example Marchand Electronics makes passive line-level filters with inductors,
and even very large inductors like 11.8H.

Is it any "sonical" benefit using more expensive LC instead of RC? I could use 50mH air coil and 100uF mkp cap (actually I got 2 of them). I don't understand why in RC filter coil (large inductance) can be replaced with just a resistor (with negligible inductance)???

 

[DHT 845]

Anybody could answer above?

 

[NTK]

1. using other RC combinations, for ex. R_filter = 22.7 kΩ; C_filter = 0.1 μF (or) R_filter = 294 kΩ; C_filter = 7733 pF
2. using RL filter (instead of RC), for. ex. R=10Ω; L=22mH
3. using LC filter (instead of RC), for ex. L= 50mH; C=100uF

1. The corner (or cutoff) frequency of a 1st order RC filter is inversely proportional to the product of the capacitance and resistance. Therefore as long as the product of the capacitance and resistance has the same value, the corner frequency does not change.
   The consideration is load and source impedances. Since your load has an input impedance of 100 kΩ, the effective R in your filter is the resistance value of the filter resistor in parallel with the load impedance, and the effective R will never be below 100 kΩ. To reduce the effects of the load impedance, since it may vary a bit with the signal frequency, the value of the filter resistor is often chosen to be significantly less than the load impedance.
   When considering the filter as a load to the source, in the pass band where impedance will be lowest, the impedance of the filter is the effective R, therefore the filter R needs to be large enough that it does not pose a problem to the source. This together with the previous consideration give the range of the practical filter R and C values.
   
   
2. The reason I chose RC filter was to keep a similar form factor as the Harrison Lab ones. Inductors suitable low frequency applications are usually significantly larger than the capacitors or resistors (for line level signals).
   
   
3. A LC filter is second order (12 dB/oct slope), and is more desirable IMHO for this application.. However, a purely LC filter will have a very high resonance peak (high Q) at the cutoff frequency, and adding a resistor into the circuit (see below, source: Wikipedia) will let you adjust the Q.
   The problem is, when you plug in the numbers, a 70 Hz cutoff high pass filter will require a huge inductor, e.g. when C = 10 μF, the required L = 0.52 H, which is going to be pretty big.

Is it any "sonical" benefit using more expensive LC instead of RC? I could use 50mH air coil and 100uF mkp cap (actually I got 2 of them). I don't understand why in RC filter coil (large inductance) can be replaced with just a resistor (with negligible inductance)???

When implemented properly (by choosing the appropriate values with the appropriate type of components), they should sound the same.

 

[Ron Texas]

Right, they provide little information because they want to charge 28 USD for a cap and resistor

Most of the cost is putting the components in an enclosure which connects to RCA male plugs on each side.