[pstrisik]

From some reading, it seems generally accepted that limiting low frequency input to a driver helps it to produce cleaner sound with greater headroom in the remaining range.  Does this work in practice?

Would it be beneficial to use, say, a 50Hz high pass filter between preamp and amp?  This is assuming, of course, there is ample subwoofer support below the cutoff frequency.

If so, what would be good ways to accomplish this?  The cheapest would be using Harrison FMOD filters at ~$25 pair.  Much higher end would be the $3000 JL-Audio subwoofer crossover unit.  There is the First Watt B-4 at $1500.  There are pro-audio products like the Behringer CX-2310 at less than $100. 

Anyone tried something like this?  Opinions from Louis/Rob? 

Since this kind of HPF would act on line level and not speaker level, I would think it wouldn't interfere with the design philosophy of no crossover components at the speaker. 

Thanks........  Peter

[rollo]

   A good idea to try. IMo the most affective is to add a resistor at the input of the amp to get the desired crossover point. relieving the speaker from not producing a frequency range it cannot handle.
   The Harrison F-Mods are OK but bright in character. Make a high pass filter as described and check it out. Louis can guide you as to the desired crossover point. No Berhinger either sounds processed IMO.


charles

[pstrisik]

I am far from an electrical engineer, but I've thought that it is a capacitor inline with the positive signal that would create a high pass filter.  In order to calculate the proper cap value, I would need to know the resistance going into the amp.  I don't have that spec.  Can it be measured with an multimeter? 

I clearly know just enough to be dangerous! 

I did this with my supertweeter project, but that was at speaker level where I could measure the resistance across the terminals of the tweeter and calculate (eg, 6 ohm tweeter, 1 mF capacitor to make a first order HPF at ~22kHz - IIRC).

.......Peter

[DBC]

pstrisik wrote:

From some reading, it seems generally accepted that limiting low frequency input to a driver helps it to produce cleaner sound with greater headroom in the remaining range.  Does this work in practice?

Based on my experience using a high pass filter works better on paper than it does in practice assuming you have good quality system components to begin with. I experimented with the Paradigm X-30 crossover unit (no longer manufactured to the best of my knowledge) some years back. This box had connections for input from your pre and then 50hz, 80hz or 120hz output RCA's. In my system sound quality seemed to be degraded more by the added interconnects and electronics. In other words I got no improvement and felt clarity and dynamics suffered.

At that time I was using: Oppo BDP-83se > Paradigm X-30 > Decware Zen Amp > Klipsch RF-7 Mains with a Sub. In my case I was attempting to relieve the 2 watt Decware amp of low frequency duty and let the sub handle that exclusively.

I assume most here with Omega speakers are running them full range ???   If not then I would be interested in their approach.

[pstrisik]

Based on my experience using a high pass filter works better on paper than it does in practice assuming you have good quality system components to begin with. I experimented with the Paradigm X-30 crossover unit (no longer manufactured to the best of my knowledge) some years back. This box had connections for input from your pre and then 50hz, 80hz or 120hz output RCA's. In my system sound quality seemed to be degraded more by the added interconnects and electronics. In other words I got no improvement and felt clarity and dynamics suffered.

At that time I was using: Oppo BDP-83se > Paradigm X-30 > Decware Zen Amp > Klipsch RF-7 Mains with a Sub. In my case I was attempting to relieve the 2 watt Decware amp of low frequency duty and let the sub handle that exclusively.

I assume most here with Omega speakers are running them full range ???   If not then I would be interested in their approach.

Thanks for sharing your experience DBC.  The quality of the HPF components is a concern, particularly since it is directly in line with the main driver.  I'm tempted to try the HSU crossover unit as it is only $100, but that price also probably indicates that the components could be improved.  The Paradigm unit sounds flexible with three frequency settings.  Did it plug in or was it electronically passive?  Do you recall its approx price at the time?

.......Peter

Edit:  Found that it retailed for $149 and did have power to it.  Three separate outputs rather than a selector switch which might be a positive.

[DaveC113]

Yeah, it's going to be a trade-off and unless you need the extra volume it won't be worth it. I'm doing the 50 Hz xo because I'm using the Crown, which has a digital xo built in and it converts the signal to digital anyway. I'm not sure it's ever converted back to analog until the final output stage, it's hard to say exactly what Harmon did there.

One issue with a PLLXO (passive line level xo) beside the added complexity is a first order slope at 50 Hz may not do a whole lot, it'll only be 6 dB down at 25 Hz, this may not be enough to control excursion caused by frequencies below the tuning frequency of the box. The Crown has a 24 dB filter which is pretty steep. The only other way to achieve this without an overly complicated and sonically harmful 4th order xo would be using DSP of some sort, they are getting good enough that high end models are transparent, but then you're adding another component.

One thing I was going to try but never got around to it, was adding an output to my preamp that uses an output capacitor sized to roll off the low end, this would give you a PLLXO without adding any additional parts. You could also do this if your amp is cap coupled with the cap in between the driver and output stage.

[pstrisik]

Yeah, it's going to be a trade-off and unless you need the extra volume it won't be worth it. I'm doing the 50 Hz xo because I'm using the Crown, which has a digital xo built in and it converts the signal to digital anyway. I'm not sure it's ever converted back to analog until the final output stage, it's hard to say exactly what Harmon did there.

One issue with a PLLXO (passive line level xo) beside the added complexity is a first order slope at 50 Hz may not do a whole lot, it'll only be 6 dB down at 25 Hz, this may not be enough to control excursion caused by frequencies below the tuning frequency of the box. The Crown has a 24 dB filter which is pretty steep. The only other way to achieve this without an overly complicated and sonically harmful 4th order xo would be using DSP of some sort, they are getting good enough that high end models are transparent, but then you're adding another component.

One thing I was going to try but never got around to it, was adding an output to my preamp that uses an output capacitor sized to roll off the low end, this would give you a PLLXO without adding any additional parts. You could also do this if your amp is cap coupled with the cap in between the driver and output stage.

Probably a bit difficult for my skill level unless I could simply add a cap after one of the preamp outputs.  I need to output from the preamp to subs as well.  If first order, I would make the cut higher.  That's what I found with the supertweeters.  I used a 1mF cap which sets the cut at 23kHz, but it is still audible so it clearly plays well below the cutoff (especially with my ears!).

.......Peter

[DBC]

pstrisik wrote

Thanks for sharing your experience DBC.  The quality of the HPF components is a concern, particularly since it is directly in line with the main driver.  I'm tempted to try the HSU crossover unit as it is only $100, but that price also probably indicates that the components could be improved.  The Paradigm unit sounds flexible with three frequency settings.  Did it plug in or was it electronically passive?  Do you recall its approx price at the time?

Seems to me the X-30 was around $250 10 years ago ???  The unit is powered via a wall wart. About the same time I borrowed a friends $3,000 B&K preamp processor that did high pass in the digital domain. So I had Oppo BDP-83se via digital coax  > B&K preamp processor via interconnects > Decware Zen Amp. Again to my ear the B&K did more harm than good.

[pstrisik]

Wow, if the B&K still caused harm, there seems to be little hope!  However, I guess it would undo whatever was good about DAC that preceded it in the chain.

I've emailed Dennis Had, the designer and builder of my pre and amp to get his thoughts. 

.......Peter

[DBC]

pstrisik,

I don't want to discourage you from trying, your results in your system and for your taste may be different.

My system is so simple (Oppo BDP-105D direct to my Decware Super Zen amp) and high efficiency speakers (Klipsch RF-7 at 102db) that even the fine Decware CSP Tube Preamp that I own will diminish clarity & detail a tad when in the chain (the reason I don't typically have it in the system).

[DaveC113]

Probably a bit difficult for my skill level unless I could simply add a cap after one of the preamp outputs.  I need to output from the preamp to subs as well.  If first order, I would make the cut higher.  That's what I found with the supertweeters.  I used a 1mF cap which sets the cut at 23kHz, but it is still audible so it clearly plays well below the cutoff (especially with my ears!).

.......Peter

If you have a cap coupled tube pre (most likely unless it has output transformers) you would be placing 2 capacitors in series as there will be a coupling cap right before the RCA jack:

http://www.allaboutcircuits.com/vol_1/chpt_13/4.html

So it would be more ideal to simply replace the output cap in the preamp with one of lesser value, the value depending on the input impedance of the amplifier and desired cutoff frequency. If you want to just add a cap in series, figure out the value of the preamp's output cap and calculate the equivalent capacitance that you'll need using the series capacitance formula in the link.

Another option would be to add a 2nd output to your preamp so you have both a full range and high passed output.

Unless you are running into issues with excursion limiting your desired SPL levels then trying this may not be worth the time and expense... I will say that I can play bass heavy music louder and clearer using the high pass xo in the Crown amp though. 

[FullRangeMan]

From some reading, it seems generally accepted that limiting low frequency input to a driver helps it to produce cleaner sound with greater headroom in the remaining range.  Does this work in practice?

I dont recommend it, Omegas are too good for being paired w/caps,filters etc
But answer the question it works only when you listen deep bass music.

[DaveC113]

I dont recommend it, Omegas are too good for being paired w/caps,filters etc
But answer the question it works only when you listen deep bass music.

It might be cool to add a cap or even a higher order PLLXO that could be switched in and out of the preamp circuit, which you would only use if you want to listen to music with low bass at higher volumes. I think you could do this with inconsequential harm to the sound when run full range, a good switch won't be too bad.

[pstrisik]

I've officially gotten in over my head!   

I should probably stick to a finished product to experiment with (like the HSU).  My Omegas are 93db, so your point is well taken about the difference in sensitivities. 

My pre does have two outputs, so I could conceivably alter the output of the one that goes to the main amp.  The other goes to a Crown that powers the supertweeters.  I will need to split it further, if using a splitter for that output is ok to do, as I'm hoping to add powered mid-bass modules.  That's what started me down this road.

If I'm lucky, Dennis will tell me the cap value to use between the pre and amp as he knows the design of both.

......Peter

[FullRangeMan]

It might be cool to add a cap or even a higher order PLLXO that could be switched in and out of the preamp circuit, which you would only use if you want to listen to music with low bass at higher volumes. I think you could do this with inconsequential harm to the sound when run full range, a good switch won't be too bad.

If a FR is used w/a tube amp isnt the OPT doing the work of bass attenuation?
Since tube amps arent makers of earthquakes.

[tvyankee]

Hey.

I think you could try a speaker level crossover at the back of the speaker input . There are cheap and at least you can get a taste to see if you want to go any furthur . They have them at parts express and they come in different values.

They won't break the bank either.

good luck.

[pstrisik]

Hey.

I think you could try a speaker level crossover at the back of the speaker input . There are cheap and at least you can get a taste to see if you want to go any furthur . They have them at parts express and they come in different values.

They won't break the bank either.

good luck.

It's an interesting idea, but flies too directly in the face of the single driver design by adding electronics to the speaker level signal.  That's why I'm looking at the active xover approach (line level).

Thanks........Peter

[tvyankee]

Ok,

I don't see a big difference but some are made better then others and some are variable and some are fixed. They are all in line in some form or fashion but i guess you gotta do what ya gotta do.

I my opinion i think you should try something. In The pro world crossovers used correctly do make a lot of speakers sound better .

Good Luck

BTW it's Dave

[pstrisik]

Ok,

I don't see a big difference but some are made better then others and some are variable and some are fixed. They are all in line in some form or fashion but i guess you gotta do what ya gotta do.

I my opinion i think you should try something. In The pro world crossovers used correctly do make a lot of speakers sound better .

Good Luck

BTW it's Dave

Hi Dave,

If I was going to do the minimal expense trial, I would buy a pair of Harrison FMODs that would go in line between pre and amp.  They are something like $25/pair.  Second would be the HSU High Pass Filter at $100.

[DBC]

This might be of interest:

With so many people using home theater systems, we're used to seeing preamps and processors that have a subwoofer out; often called the 0.1 channel or LFE output. But we're not looking to discuss subwoofers in a multi-channel setup here... we're more interested in two-channel with this tutorial. In a regular stereo amp that has no surround processing, if you see something marked "subwoofer out," it's typically another preamp output. In essence, nothing more than voltage signal coming from the preamp, fed to the woofer's amplifier.

SO WHAT HAPPENS IF YOU DON’T HAVE A PREAMP OUT?
Most subwoofers are designed to handle this situation. They have a high-level input (sometimes called speaker-level input) that hooks up to the speaker taps of your amp. All you do is run another pair of speaker cable from the output taps of your amplifier into the high-level input on your subwoofer. This connection works the same way as a preamp/subwoofer output: It takes the voltage from the amp as the signal and sends it into the subwoofer.

This does not cause a power draw on the amp you hook up to. It is merely sharing the signal with your main speakers, not the power of the amp. This means there is no power draw, and the impedances all remain the same.

In fact, even if your preamp or integrated has a preamp/subwoofer output, you may want to consider using the high-level connection method. The most prestigious subwoofers in the industry are made by REL of England. They are the “Gold Standard” of the industry and priced accordingly, topping out at $9,000! REL recommends using the high-level input for all of their subwoofers. The reason they recommend this type of connection is as simple as it is logical: it ensures your subwoofer is seeing the EXACT SAME SIGNAL as your speakers. If you use the preamp/subwoofer output from your preamp or integrated, the signal seen by your subwoofer does not include the tonal balance and timing cues created by the amp. By using the high-level connection, the subwoofer gets the same signal as your main speakers, keeping them in better synch with each other, thus improving sound quality.

One snippet of information: Often times subwoofers will allow you to hook them up to the speaker taps of the amp and to cross-over the main speakers, restricting how much low information they get. Don’t assume this is a benefit. It may allow the mains to play louder as they are not having to move as much air, but the downside is you can lose some clarity. Experiment as different products work different ways.

http://www.upscaleaudio.com/pages/Using-a-Subwoofer-in-a-System-with-no-Subwoofer-Output.html