Please feedback on high pass filter

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Hi All,

After having worked with a miniDSP I have decider I cannot get rid of the noise/hiss this introduces and want to try another way.
I would like to add a high pass filter to my open baffles (Tangband full range w8-1808 and double Eminence Alpha15) to cut the frequency for the Tangbands at 120Hz.
My double Hypex DS4.0 amps will then drive the woofers from 120Hz and lower.

I have tried to design a high pass filter based on what I have learned from this forum and the internet and this is what I have come up with

High pass filter 2nd order Butterworth
Speaker 8 Ohm, Freq 120Hz, C = 117,10, L - 15,01.

The parts I am thinking of using are:
Air Core Inductor Crossover Coils in the Speaker Components Department at Parts Express | 297

100uF 100V Electrolytic Non-Polarized Crossover Capacitor

15uF 100V Electrolytic Non-Polarized Crossover Capacitor

Audyn Cap Plus 2.2uF 800V Double Layer MKP Metalized Polypropylene Foil Crossover Capacitor

For further details see the drawing.
Hope you can give me feedback on the design and it's parts because I have no expertise on designing crossovers.
Thank you
Jock
 

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Why don't you look at line level analog filters? When built with the right components (metal film resistors for low noise and film capacitors) they work great. Low noise op amp is a good idea too.

Here's a circuit with a chart of values for different crossovers. It doesn't get any simpler. Project 123

Your passive crossover is interesting. I like how you staggered capacitor values. Have you tried using three equal value caps? Lower esr and less inductance than one big cap. Three 40 uF caps paralleled by one 4.7 uF cap would probably work better and still retain the benefit of staggered values.
 
Your passive highpass filter won't give you the response you expect because of the mechanical resonance of the W8-1808. Note in the datasheet how the impedance rises to over 20ohms at 45Hz:
http://www.parts-express.com/pedocs/specs/264-894-tang-band-w8-1808-specifications-46404.pdf

As a result, instead of getting a 2nd order rolloff the response will peak up again as the frequency approaches 45Hz.

To use a passive highpass filter you therefore need to add a series resonant filter to flatten the impedance of the driver so it looks more like a constant 8ohms to the crossover
http://www.mh-audio.nl/RLC_Series_Resonant_Calculator.asp

Most of the time people complain about hiss with the MiniDSP it is because they have their system gains set wrong. Ideally, you should have whatever comes before the DSP set to maximum volume (or as high as possible without clipping the input of the DSP) and then adjust the volume after the DSP. This maximises the signal to noise ratio. If your volume control can't be before the DSP then you need to reach a compromise - basically your amplifier gain/volume must only be set as high as necessary to minimise the amount of hiss while the system is idle while still reaching an acceptably loud volume. If your amplifiers have their gain/volume controls set at max and you are adjusting the volume before the DSP to a really low level to prevent the system blowing your ears off then that is the cause of your hiss problem.
 
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Thanks for your replies.

Fast Eddy, since my main amp to drive the Tangbands is an integrated tube amp (Melody MI880 and pending a SimpleSE) I don't think the line level approach is going to be the way to go. Using a MiniDSP, also to regulate the overall volume and using the integrated amp as a non integrated amp, didn't give the best results. I will keep this in mind for future projects.

Sreten and TMM. I'll need to study on you input. My first impression of the quarter wave is I need to crossover at a higher frequency which means I cannot use the low pass of the plate amp.

Some additional information on what I am trying to get working together is in the drawing

Specs for the Hypex DS4.0
  • 400 Watt Class D subwoofer plate amplifier with active filtering.
  • Continuous output power (8 Ohm): 210 Watts (+0, -0.5dB)
  • Continuous output power (4 Ohm): 400 Watts (+0, -0.5dB)
  • Subsonic-filter: 12Hz / -3dB, 24dB/Octave
  • Phase: 0° - 180°, 180° - 360°
  • Crossover frequency subwoofer: 30Hz - 120Hz, 18dB/Octave
  • Bassboost: 20Hz - 50Hz
  • Bassboost level: 0dB - +6dB
  • Damping factor: 1000
  • Protection: Output shortcut / DC-error
  • Crossover filtering: Linkwitz-Riley, 18dB/Octave
  • Input impedance RCA: 10kOhm
  • Input impedance high level: 1kOhm

Jock
 

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Hi All,

After having worked with a miniDSP I have decider I cannot get rid of the noise/hiss this introduces and want to try another way.


In all fairness to the miniDSP, yesterday I learned that the miniDSP was not introducing any noise.
From youtube I learned that what I was hearing was a 60hz hum. Temporarily changing the amp with a T-amp took away the hum. This hum can be caused by a bad tube but since I have replaced all of them it had to be something else. In the end it was a faulty ground from my power socket was causing the tube amp to hum. When I used a socket from another group it was dead silent
 
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