Why preamps or DACs really should have high pass filters

[dougi]

My solution has been to use a passive High Pass Filter in the cable from the balanced output of the RME ADI-2 DAC to the power amplifier, in the same way as the Harrison Labs Fmods. The subwoofer with its own Low Pass Filter uses the RCA output of the ADI-2.

You could use the headphone output with it's seperate EQ for the sub, but it would look ugly!

 

[dougi]

You could use the headphone output with it's seperate EQ for the sub, but it would look ugly!

PS the ADI-2 does have high pass, for filter 1 only. At least it does in the pro:

 

[Filio45]

PS the ADI-2 does have high pass, for filter 1 only. At least it does in the pro:

Also the non pro ADI-2 has the same. Good to know!.

 

[Godataloss]

Maybe I'm just hopelessly old school, but I never considered a speaker driver smaller than 12" a 'woofer'. At least that's the way it was in my formative years.

I must be slightly less hopeless. I'm ok with an 8 or 10 inch woofer though and 8 incher would undoubtedly be classified as a lowly bookshelf.

 

[EJ3]

I must be slightly less hopeless. I'm ok with an 8 or 10 inch woofer though and 8 incher would undoubtedly be classified as a lowly bookshelf.

My Dahlquist M-905 (bought new in 1990) has a ported 8" woofer/mid (this is a 100% stock speaker, no mods except replacing the xover caps with modern ones of the same value). The speakers advertised response is 40 HZ-24 KHz. No Db spread given.
The measured response is 26 Hz-20 KHz +-2 Db.
It was my first proof that less than a 12 inch can get down low. Prior to that I had been using 15 inch (or 18 inch) for subs & 12 for low-mid.
I do, however, augment the Dahlquist's with a pair of custom built (by me) ported 12 inch dual 4ohm voice coil (set up to operate on 2 ohms) speakers which cover <20 Hz-80 Hz.
I was once one of the hopeless, too. Jon Dahlquist (working with Saul Marantz) proved me wrong back in the 1980's.

 

[Chromatischism]

But let's stop calling these 4"-6.5" drivers "woofers". They aren't. They are mid-bass drivers at most. They aren't even good at midrange.

SB Acoustics SB17NRX2C35-4​

SB Acoustics SB17CAC35-4​

Raw response looks pretty decent to me.

 

[Godataloss]

My Dahlquist M-905 (bought new in 1990) has a ported 8" woofer/mid (this is a 100% stock speaker, no mods except replacing the xover caps with modern ones of the same value). The speakers advertised response is 40 HZ-24 KHz. No Db spread given.
The measured response is 26 Hz-20 KHz +-2 Db.
It was my first proof that less than a 12 inch can get down low. Prior to that I had been using 15 inch (or 18 inch) for subs & 12 for low-mid.
I do, however, augment the Dahlquist's with a pair of custom built (by me) ported 12 inch dual 4ohm voice coil (set up to operate on 2 ohms) speakers which cover <20 Hz-80 Hz.
I was once one of the hopeless, too. Jon Dahlquist (working with Saul Marantz) proved me wrong back in the 1980's.

That's quite a claim. I had DQ 10s for over a decade. Excellent speakers, but I don't think they even hit the low 30s with a 10 inch driver in a much larger sealed box with gobs of power applied. And that's in a 5-way. Great speaker designers, but they weren't magicians. If it's hitting that low, it's breaking down elsewhere.

 

[EJ3]

Most proper old-skool preamplifiers and integrated amplifiers had two low filters and two high filters. The low filters were infrasonic and another filter around 70-80Hz- primarily for hum issues, but quite usuable with modern 2 way baby speakers that are so popular these days.

But let's stop calling these 4"-6.5" drivers "woofers". They aren't. They are mid-bass drivers at most. They aren't even good at midrange.

TRUE! Using my APT/Holman Pre as an EXAMPLE:
Frequency Response

20 - 20,000 Hz ±0.5 dB, with ultrasonic and ultrasonic filters active.

RIAA EQ ±0.5 dB 30 - 15,000 Hz.



Selectable 15 Hz Infrasonic filter (rear panel switch)

Within 0.5 dB at 20 Hz, -3 dB at 15 Hz and > -30 dB at 5 Hz.

Group delay 4 mS at 50 Hz.

If the filter isn't selected, the -3 dB point is 8 Hz.



Ultrasonic Filter (automatically engaged when Tone Controls active)

Within 0.5 dB at 20 kHz, -3 dB at 40 kHz, and -18 dB at 100 kHz.

Group delay 7 µS.

Interchannel delay: < 0.5 µS. (the limit of audibility is 10 µS.)

When the tone controls are defeated, the -3 dB point is 150 kHz.



High Filter (only active with Tone Controls selected)

-3 dB at 8 kHz.

 

[EJ3]

That's quite a claim. I had DQ 10s for over a decade. Excellent speakers, but I don't think they even hit the low 30s with a 10 inch driver in a much larger sealed box with gobs of power applied. And that's in a 5-way. Great speaker designers, but they weren't magicians. If it's hitting that low, it's breaking down elsewhere.

That is according to Stereo Review (Julian Hirsch, Hirsch-Houck Laboratories) magazine issue 10 OCR pg 0044-46 1987.

 

[dougi]

I am afraid you are misunderstanding what I wrote. I use the unfiltered full range output from the ADI-2 into a cable with FMOD equivalent High Pass filter. The ADI-2 does not do any High Pass filtering, which is not to say that it is not a great DAC.

Filter 1 on the rme can be set as a high pass. If you rig up the headphone output for use as a line-out, you can then have matching HP and LP for a sub-sat combo.

 

[EJ3]

Filter 1 on the rme can be set as a high pass. If you rig up the headphone output for use as a line-out, you can then have matching HP and LP for a sub-sat combo.

That is great to know, 'cause after some long studying, the RME ADI-2 PRO FS R ADC/DAC is an upgrade that I want to do next year. Thank you.
I want to run it in my external processor loop.

 

[Head_Unit]

Some Spendor speakers have quite low port tuning frequency for the price. Low port tuning frequency means less over excursion problem.

Well somewhat.That excursion minimum gets moved down to where there is little energy coming below the port tuning so yeah-though now with the port effect moved to a lower frequency there will be more midbass excursion. Still likely better than something tuned up like to 70 Hz, where any low bass gets into that region where the port unloads the woofer which goes nuts.

A first order filter won't be as effective as a second order, but yes easier to make. If you plug the port, the box becomes second order, total 3rd order with a highpass capacitor.

Harrison Labs are good for what they are, though the frequencies are off. My "100 Hz" were -6 dB at 100, -3 dB at 70 and 155 lowpass and highpass. I'd get this one because it is more flexible and barely more expensive http://www.hlabs.com/products/crossovers/index_files/Page384.htm
or perhaps better there are some inexpensive Rolls active models (search "rolls crossover")

Oh, I almost forgot to rant how STUPID it is that 2-channel equipment rarely has a highpass filter, and double public caning and tarring and feathering on those that have a "subwoofer" output with no highpass.

 

[EJ3]

Well somewhat.That excursion minimum gets moved down to where there is little energy coming below the port tuning so yeah-though now with the port effect moved to a lower frequency there will be more midbass excursion. Still likely better than something tuned up like to 70 Hz, where any low bass gets into that region where the port unloads the woofer which goes nuts.

A first order filter won't be as effective as a second order, but yes easier to make. If you plug the port, the box becomes second order, total 3rd order with a highpass capacitor.

Harrison Labs are good for what they are, though the frequencies are off. My "100 Hz" were -6 dB at 100, -3 dB at 70 and 155 lowpass and highpass. I'd get this one because it is more flexible and barely more expensive http://www.hlabs.com/products/crossovers/index_files/Page384.htm
or perhaps better there are some inexpensive Rolls active models (search "rolls crossover")

Oh, I almost forgot to rant how STUPID it is that 2-channel equipment rarely has a highpass filter, and double public caning and tarring and feathering on those that have a "subwoofer" output with no highpass.

I have had good luck with the PFMODS but do mot know if the exact crossover points are actually exact.

 

[dshreter]

Sonos Amp is a nice option that when the subwoofer output is turned on it implements a high pass to the mains. The crossover frequency and phase are both configurable.

 

[zeluxao]

Filter 1 on the rme can be set as a high pass. If you rig up the headphone output for use as a line-out, you can then have matching HP and LP for a sub-sat combo.

How do you "rig up the headphone output for use as a line-out"?

 

[EJ3]

How do you "rig up the headphone output for use as a line-out"?

I only use cordless headphones, (old Sennheiser TR180's I bought new many, many years ago [it is not my main way of listening, speakers are) but the RF unit plugs into any line level Pre out.

 

[zeluxao]

Well somewhat.That excursion minimum gets moved down to where there is little energy coming below the port tuning so yeah-though now with the port effect moved to a lower frequency there will be more midbass excursion. Still likely better than something tuned up like to 70 Hz, where any low bass gets into that region where the port unloads the woofer which goes nuts.

A first order filter won't be as effective as a second order, but yes easier to make. If you plug the port, the box becomes second order, total 3rd order with a highpass capacitor.

Harrison Labs are good for what they are, though the frequencies are off. My "100 Hz" were -6 dB at 100, -3 dB at 70 and 155 lowpass and highpass. I'd get this one because it is more flexible and barely more expensive http://www.hlabs.com/products/crossovers/index_files/Page384.htm
or perhaps better there are some inexpensive Rolls active models (search "rolls crossover")

Oh, I almost forgot to rant how STUPID it is that 2-channel equipment rarely has a highpass filter, and double public caning and tarring and feathering on those that have a "subwoofer" output with no highpass.

Are the ins and outs of the pfmod all rca?

 

[EJ3]

Are the ins and outs of the pfmod all rca?

yes, all RCA.
And I would go with this recommendation from zeluxao. This is how I run mine using the PFMOD that zeluxao suggests (& have been for many, many years:
Using it in my Tri-Amped application: One NAD 2200 on each main,& one NAD 2200 running 4 ohms stereo on the pair of subs.:

I use these amps Tri-Amped-1 on each main speaker (using the 8 OHM setting, as the speakers are 6 OHM at their lowest point).
& one running stereo 4 OHM for my woofers, which are 4 OHM each.

Per Amirm (on one of my personal NAD 2200's):

Note the differences in the frequency response plot and the SINAD.
They are both better when you run it using the LAB INPUTS (that is true whether you are running bridged mono or not) :

NAD 2200 Vintage Amplifier Review​

Wow, we have one kilowatt of power coming out of this amp in short duration!

I was surprised that the frequency response was not flat but was relieved to see later in the thread that this is due to insertion of low and high pass filters. So here is the frequency response with Lab input that doesn't have such a filter:

Response now (in green) as it should be, ruler flat to below 10 Hz, and well extending past the 40 kHz limit of this measurement.

I figured the filters may be adding some noise/distortion so re-ran the dashboard again:

Distortion doesn't change but if you look at the noise floor at 20 Hz, it is down by some 10 dB. That improves SINAD a couple of dBs, making the amplifier stand out even more!

Zoomed:

And signal to noise ratio:

Conclusions
Nice to see innovation like this from equipment that is over 30 years old! Shame on manufacturers that produce amplifiers for much less power, more distortion and higher prices these days. No, you don't get a fancy case here and sheet metal is strictly budget category. But you are not going to sit on the amp. The guts are where it matters and NAD 2200 delivers.

NOTE: the output relay on stock 2200 gets corroded and fails over time. There are videos and DIY threads on how to upgrade the relay there to fix the problem. The unit tested here has that fix. Other than that, there are not reports of many other reliability issues even though NAD products are often said to be less reliable than other brands.

Overall, I am happy to recommend the NAD 2200. I almost gave it the highest honors but given the upgraded nature of the test unit, and the fact that used amps may have issues, I avoided that. But you could have easily pushed me to give it the golfing panther

 

[Head_Unit]

Are the ins and outs of the pfmod all rca?

Good question, I cannot find a real image of that. All their other stuff is RCA so I am certain the PFMOD as well.