FMOD high pass filters?

[escape2]

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!

 

[Blumlein 88]

I've seen them used. They work well. You are correct about the 3db down.

You do need to look at input and output impedance, but working with memory I don't think it's a problem usually.

 

[Head_Unit]

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?

Back in the day I measured a couple FMODS. What I recall most distinctly was the 100 Hz model was like -7 dB at 100, and -3 around 155 Hz. Due to shape I'm size, I'm quite certain that inside you'd find 2 stacked RC 1st order filters, making a filter with Fc=100 and a Q around 0.5 (except it won't be perfect, and it will depend on input and output impedances of what is connected).
I'd get the switchable frequency version; it hardly costs more. But right now Safari nor Firefox can find hlabs.com

 

[ruinevil]

I have a pair to cut signal to a pair of Magnepan LRS. The crossover slopes weren't steep enough to be useful there. The LRS loses all dynamics if it is told to play < 70 Hz. Dynamics speakers don't fail that hard when given something they can't play.

Since they are line level devices, you just increase the power at the amplifier, so the attenuation isn't an issue.

 

[Blumlein 88]

Back in the day I measured a couple FMODS. What I recall most distinctly was the 100 Hz model was like -7 dB at 100, and -3 around 155 Hz. Due to shape I'm size, I'm quite certain that inside you'd find 2 stacked RC 1st order filters, making a filter with Fc=100 and a Q around 0.5 (except it won't be perfect, and it will depend on input and output impedances of what is connected).
I'd get the switchable frequency version; it hardly costs more. But right now Safari nor Firefox can find hlabs.com

Seems to be working fine now.

https://www.hlabs.com/

You can get them at Parts Express too.

 

[Ron Texas]

For small speakers get the 100 Hz filter and set the low pass on your sub to around 100 Hz.

@Blumlein 88 I could not find Harrison Labs on Parts Express this week but the manufacturer now has a store on Amazon.

 

[escape2]

For small speakers get the 100 Hz filter and set the low pass on your sub to around 100 Hz.

How do you define "small speakers"?

@Blumlein 88 I could not find Harrison Labs on Parts Express this week but the manufacturer now has a store on Amazon.

They also have an ebay store:
https://www.ebay.com/sch/hlabsusa/m.html

 

[Deleted member 2944]

https://www.parts-express.com/search?keywords=harrison labs

The problem with the Hlabs gadgets are that the impedance levels are scaled so low. This so you won't have differing response with a wide range of load impedances. Thus you have increased insertion loss and/or potential problems with sources that have high output resistance.

The innards here are so simple in concept that I don't understand why folks pay money for these and not construct their own filter/attenuators with optimized components. A good learning experience and much cheaper too.

Dave.

 

[pjug]

I was recently looking at these so I thought I would add that they do give info on the variability due to different amplifier input impedance, which should be good enough to dial them in if you know your amplifier impedance:

From https://www.hlabs.com/products/crossovers/index_files/Page446.htm

 

[Head_Unit]

The innards here are so simple in concept that I don't understand why folks pay money for these and not construct their own filter/attenuators with optimized components. A good learning experience and much cheaper too.

Are you serious? I can't tell. If so the reason is, it is more work and messier. And most folks would have zero idea how to design these, zero idea how to make these, and no capability to measure input and output impedances. Now sure if you can do that stuff you could make a more precise solution and power to ya!
- The one time I measured a set of FMODS with MLSSA, the 100 Hz highpass was -3 dB at around 155 Hz and -6 at 100 Hz. The lowpass was -3 around 70 and roughly -6 at 100.
- I'd pay a bit more and get the satellite/subwoofer parametric for adjustability, even if you don't use all the outputs.

 

[chang]

Are you serious? I can't tell. If so the reason is, it is more work and messier. And most folks would have zero idea how to design these, zero idea how to make these, and no capability to measure input and output impedances. Now sure if you can do that stuff you could make a more precise solution and power to ya!
- The one time I measured a set of FMODS with MLSSA, the 100 Hz highpass was -3 dB at around 155 Hz and -6 at 100 Hz. The lowpass was -3 around 70 and roughly -6 at 100.
- I'd pay a bit more and get the satellite/subwoofer parametric for adjustability, even if you don't use all the outputs.

What parametric are you referring to? I'm looking to set a HPF on a 2.1 system (the sub has built in LPF).

 

[pjug]

https://www.parts-express.com/search?keywords=harrison labs

The problem with the Hlabs gadgets are that the impedance levels are scaled so low. This so you won't have differing response with a wide range of load impedances. Thus you have increased insertion loss and/or potential problems with sources that have high output resistance.

The innards here are so simple in concept that I don't understand why folks pay money for these and not construct their own filter/attenuators with optimized components. A good learning experience and much cheaper too.

Dave.

I made a 6dB version (just a cap!). But even with my best effort shielding with a good wrap of grounded copper foil, I was getting more pickup of 60Hz compared to running without the filter. I couldn't hear the difference but it was about 4dB worse or something like that. With the fmod, I don't see any difference in the 60Hz pickup with the filter compared to without, plus it is a 12dB filter. You could probably build something as good using a nice shielded box, but then the fmod's small size is a big advantage over that.

 

[Head_Unit]

What parametric are you referring to? I'm looking to set a HPF on a 2.1 system (the sub has built in LPF).

https://www.hlabs.com/products/crossovers/index_files/Page384.htm
It says "electronic" but it's passive. Adjustable, and hardly costs more than the fixed frequency.

 

[chang]

https://www.hlabs.com/products/crossovers/index_files/Page384.htm
It says "electronic" but it's passive. Adjustable, and hardly costs more than the fixed frequency.

Is something like this needed with a built-in LPF on the sub? I guess I'm really just looking for a HPF for the bookshelf speakers

 

[aerochrome2]

Is something like this needed with a built-in LPF on the sub? I guess I'm really just looking for a HPF for the bookshelf speakers

Trying to solve for the same issue. Sub has a low pass filter but want a high pass filter for the speakers. This seems like a good, simple option?

 

[Head_Unit]

Trying to solve for the same issue. Sub has a low pass filter but want a high pass filter for the speakers. This seems like a good, simple option?

Yes but the values are off, I measured "100 Hz" -3 dB at 155. Get the adjustable one and just don't use the lowpass part, it's barely more expensive. https://www.hlabs.com/products/crossovers/index_files/Page384.htm

 

[aerochrome2]

Yes but the values are off, I measured "100 Hz" -3 dB at 155. Get the adjustable one and just don't use the lowpass part, it's barely more expensive. https://www.hlabs.com/products/crossovers/index_files/Page384.htm

Thanks. I just ran a quick measure comparison with my ARC (room correction software) to see if I got the same results as you. I am by no means and expert, so curious to see what you think of the difference (or can see where mine are measuring). See attached.

I am also uploading my actual ARC curves when I add the subwoofer back in with a 110Hz low pass. As you can see, my room is awful, but I don't have any ability to add room treatment (I am in a sunroom with glass walls on 3 sides and I cannot add room treatment due to room (and family) constraints (it is a shared space).

If I am not getting the right values, I would be happy to try the one you linked, assuming it is still passive/not adding distortion, etc. (it is labeled as "electronic" but I assume it is not digital).

 

[Head_Unit]

As you can see, my room is awful, but I don't have any ability to add room treatment (I am in a sunroom with glass walls on 3 sides and I cannot add room treatment due to room (and family) constraints (it is a shared space).

That is called "real life"
Room treatment won't help bass problems. However, curtains might be acceptable to all depending if that is even possible. A friend has acoustic foam panels he brings out for serious listening then stows away for normal times. From your curves, I can see the FMODs are knocking down the low bass. With ARC at hand, I'd say good enough* and the corrected curves are actually really smooth, maybe too perfectly so. I haven't compared ARC Genesis post-curves versus "real" measurements. (The designers of both ARC and Audyssey would say the post-curves are an average of sorts so not directly comparable to single-point raw microphone measurements; critics says they are glossing over and results are not so perfect).

*well, if you unplug the subwoofer and crank your favorite bass-heavy stuff, how do the mains sound? Distorted and overloaded? Or pretty clear? Are the woofers pumping like crazy?

 

[aerochrome2]

That is called "real life"
Room treatment won't help bass problems. However, curtains might be acceptable to all depending if that is even possible. A friend has acoustic foam panels he brings out for serious listening then stows away for normal times. From your curves, I can see the FMODs are knocking down the low bass. With ARC at hand, I'd say good enough* and the corrected curves are actually really smooth, maybe too perfectly so. I haven't compared ARC Genesis post-curves versus "real" measurements. (The designers of both ARC and Audyssey would say the post-curves are an average of sorts so not directly comparable to single-point raw microphone measurements; critics says they are glossing over and results are not so perfect).

*well, if you unplug the subwoofer and crank your favorite bass-heavy stuff, how do the mains sound? Distorted and overloaded? Or pretty clear? Are the woofers pumping like crazy?

Thanks! I'll check out the mains without the woofer in a listening test. Good idea.

Subjectively, I think everything sounds really good, so I'll probably stick with this all for now and eye some drapes down the line.

*I realized I do need to re-run ARC. I realized I left a few small PEQ bass bumps in the SVS turned on during the calibration, so those peaks are being knocked down too far.

 

[Calleberg]

I have used their PFmod, it's an 18dB/oct HP/LP model, but I only used the LP outs. Was in a pinch and borrowed one from a friend . Had low expectations but loved it so much I ended up buying three of them for myself.