Speakers reproducing freq's way too low

[phorensic]

I often notice my Paradigm Monitor 3's (should have a sig describing system by now) reproducing WAY subsonic freq's pretty often. My amp is a Jolida 1701 and the source is a PC. Somewhere along the line this is no subsonic/high pass filter intervening. Is this bad for the Paradigm's? Should I actively seek out a way to filter the low end?

It's pretty amusing to play this certain track by Pink Floyd or some other random band and see the 8" woofers move in this huge rhythmic motion completely independent of the music :D

[HiFiber]

the source is a PC.


:scratch2:

[bigphil]

.... 8" woofers move in this huge rhythmic motion completely independent of the music :D

this may not be because of your source, but simply the recording. I can think of a few bob marley songs (specific ones) that make the woofer move as if its out of time with the music... this can be destructive for some woofers, so be careful.

oh, and please please please get a better source than your PC for that Jolida amp.

[Dusty Chalk]

So you can see them move? Sounds like maybe a DC problem...

[Whitehall]

If they're moving it means that current is flowing through the coils. This produces heat in the coils and wastes amp power.

Is the Jolida a hybrid or a tube amp? If the former, it could be DC offset "hunting." If the latter, the output transformers would not pass any power close to DC

[Mike Caldwell]

Just about any sound system large or small benefits from a high pass filter. It will tighten up the low end, increase your amps head room and my very well save the life of your speakers.
I have the schematic to a active high pass filter network that Urie Electronics had available about 25 years. In addition to the original I bought I must have built 4 or 5 of them for different projects.
I will try to find it and scan the page to post here. It's easy to build with easily obtainable parts.

Mike Caldwell

[phorensic]

It's not DC offset guys. This is sub 20Hz going right to the woofers. I have a couple movies on my HDD that are known to contain information down to ~15Hz. I also have a couple bass test CD's that have tones below 20Hz also. They pass right on through to my Paradigm's, even though they are WELL below my in room freq response that is in the high 30's. As Mike said, this is wasting my amplifier power, and possibly affecting the higher freqs (higher as in high 30's on up, not as in 1KHz and up). I'm just surprised there is no highpass in the whole system.

"Is the Jolida a hybrid or a tube amp? If the former, it could be DC offset "hunting." If the latter, the output transformers would not pass any power close to DC"

The Jolida is a hybrid amp. Tube input, SS output. Explain to me what DC offset hunting is. This just looks like very low freq sine waves. It doesn't happen randomly or all the time, it happens when there is clearly a low frequency meant to be played in the source material.

Mike, I would very much appreciate a schematic for an active high pass. I love DIY as well, having soldered together a good amount DIY amplifiers/circuits in my time.

[House de Kris]

Attached is a hi-pass filter, courtesy of the National Semiconductor Application Handbook (and slightly modified by me). It has a 3dB down point of about 17Hz.

Now, why is it you think this information should be filtered out? I guess I am asking, how do you know you are NOT supposed to be trying to reproduce these low frequency signals? Is this a digitized version of one of them black rekkids?

[phorensic]

Now that I think about it, there is no reason Jolida should put a highpass filter in my amp at ~20-30Hz, because what if I had some floor standers with 18" woofers? They don't know that I'm going to be using bookshelf's. I guess my complaint then lies with Paradigm for not putting a highpass filter on the woofer to keep it from trying to play freqs well below what could possibly be heard in any room on these things.

I'm talking HUGE x-max low freq sine waves with no audible or physical effects when the rest of the material is playing at around 90dB. It just seems like a total waste, if not damaging, to the speakers. I mean, its hilarious to be watching a movie, never seeing the woofers even budge, and then all of a sudden there is an event that happens that you think might have some deep bass, but you can't hear it, or you can only hear the somewhat higher remnants of the sound, and you see the woofers moving like MAD in and out! I mean it even happens on scenes that don't look like they would have any bass at all. The same goes for music.

Maybe I'm a little naive in thinking that there aren't any other mid to high end bookshelf speakers that don't have some sort of highpass?

Maybe this means I have to buy a subwoofer now? :scratch2:

[Mike Caldwell]

Hello
If your speakers are not designed to reproduce say 20hz and are only rated to a -3db at 50hz there is nor sense in sending them a full power signal with really anything much below around 40hz. It wasting power, potentially damaging the speakers and coloring the sound as they are trying to reproduce the signals below the speakers cut off point.
I'll get the schematic I have posted in a couple of days.

Mike Caldwell

[RichPA]

Now that I think about it, there is no reason Jolida should put a highpass filter in my amp at ~20-30Hz, because what if I had some floor standers with 18" woofers? They don't know that I'm going to be using bookshelf's. I guess my complaint then lies with Paradigm for not putting a highpass filter on the woofer to keep it from trying to play freqs well below what could possibly be heard in any room on these things.

I'm talking HUGE x-max low freq sine waves with no audible or physical effects when the rest of the material is playing at around 90dB. It just seems like a total waste, if not damaging, to the speakers. I mean, its hilarious to be watching a movie, never seeing the woofers even budge, and then all of a sudden there is an event that happens that you think might have some deep bass, but you can't hear it, or you can only hear the somewhat higher remnants of the sound, and you see the woofers moving like MAD in and out! I mean it even happens on scenes that don't look like they would have any bass at all. The same goes for music.

Maybe I'm a little naive in thinking that there aren't any other mid to high end bookshelf speakers that don't have some sort of highpass?

Maybe this means I have to buy a subwoofer now? :scratch2:

Actually, I have never heard of a bookshelf speaker that had a highpass filter built in - that would be very unusual, not to mention difficult and expensive to do at speaker level.

[phorensic]

So what's with these bookshelf speakers all over the place having in room freq response in the 40-50Hz range trying to belt out ~10-40Hz when there is no hope?

I know Mike has been saying it's a waste and colors the sound. Anyone else have any experience to share on this? Any articles on the net I can read? I'm a techie kind of guy, so numbers helps me even more.

Now, If I do plan on building a crossover, and keep in mind I am a purist/perfectionist, what type of crossover would degrade the signal the least? Maybe I shouldn't ask that question, because I would love one that I could adjust.

[Mike Caldwell]

Hello
Attached is the schematic and response curve for the Urei high pass filter. The op-amp is a quad op-amp and can be just about any of the varieties that are available today. The ones I built I used the low noise FET models.

This filter is for line level use between the preamp and power amp.

Let me know if you have any questions on building it.
If you want I could send a larger sized schematic directly to you.
Thanks
Mike Caldwell

[RichPA]

Unless you're playing near the speaker's loudness limit, the low-frequency stuff is usually not a major problem. But one simple and relatively inexpensive thing to try is these (an example, also available for other frequencies): http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=266-250

Edit: Oops, that's the low pass, you want high pass: http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=266-270

[ron-c]

Sounds like your amp has a low frequency oscillation or high IM distortion. may be a beat frequency from the power supply ripple and the music. This is not normal or good. It should be checked out in my opinion.

Thanks,
Ron-C

[Cloth Ears]

So what's with these bookshelf speakers all over the place having in room freq response in the 40-50Hz range trying to belt out ~10-40Hz when there is no hope?

Now, If I do plan on building a crossover, and keep in mind I am a purist/perfectionist, what type of crossover would degrade the signal the least? Maybe I shouldn't ask that question, because I would love one that I could adjust.

Mostly, the bookshelf speakers are designed so that excursion of the bass driver tends to flatten out below the tuning frequency. How much below is a function of the box tuning and the size of the enclosure. The actual 'bass' response has been 'going down' at about 24dB/octave since the tuning frequency. Yes, it's a waste, but having a 900uF capacitor to roll-off the lower frequencies is also a waste (at 20Hz with a 8ohm woofer).

You could always try a highpass filter INTO your amplifier. I think the Jolida 1700 has input impedance of 47Kohm (and that's constant - no having to worry about impedance changing with frequency), so all you need is a .10uF cap in series with both your inputs to get a 6dB roll-off that is -3dB at 34Hz. Then you can spend quite a bit on your 2 caps and on the method for doing it (maybe something along the lines of those MIT Terminator cables from a few years back). This is not one of those applications that you can adjust, unless you use a .15uF (23Hz), a .10uF (34Hz), a .082uF (41Hz) and a .068uF (50Hz) with an attached switch.

But, also try another source (other than your PC). Just in case. And it doesn't even have to be much good. Possibly your PC's power supply is reacting strangely when the grid is under heavy load?!?

[Aage]

Try putting the covers back on your speakers (so that you can't see the woofers).

It may solve the problem...! :D