General passive-line level filtering issues.

Hi All,

At this moment I am spending my time to do some work I should have done some time ago. In the past years I have learned several ways to build a crossover for systems based on the Compact, Basic and Ultra bass systems in combination with Oris horns and the Orphean.

I will have the first basic crossovers done soon (for using the Orphean MkI and Orphean MkII on top first). The principle used will be almost similar as done before (using the signal from the main amplifier to feed the filter and the amplifier for the bass).

These filters still have some ways implemented to change for personal taste/room but it would be very handy for me if people would report back to me their prefered settings. With this information I would not only save a lot of time to try the filters myself elsewhere, it will also give me usable information to proceed with the Oris based systems.

Please don't ask me about other bass systems or other principles to use than the ones mentioned as it is impossible for me to give usable suggestions to optimise those. Implementations for those systems have to be figured out by yourself.

Stay tuned...

Bert

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BD-Design - Only the Best!

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Hallo Bert!
I know that You use the filter at the speaker terminals of the main amp, to keep the general characteristic of that dominant amp.
I went a different way: As main amp I use a SET-amp. The biggest amplitude is in the bass - so if there occurs clipping it will happen there first and produce harmonics. So I filter the main-amp at the input, that it has to produce no bass.
That means I´ve to split the line signal before the main amp, which I do with a passive network, like the one published in the forum.
For my system, that works very well. The network was tuned to the drivers in use, so slightly different to Your Oris set-up. To get symmetrical responses I used a 18 dB filter..
Maybe a path worth a try for You?
Best regards
Stephan

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Hi Stephan,

That means I´ve to split the line signal before the main amp, which I do
with a passive network, like the one published in the forum.

This might work if you have a preamp with a very low output impedance, it will not work with a TVC or even tube pre-amp as their output impedance is a lot higher that your 40ohm pre-amp. So, that is not the path I will walk simply because most people do not have such a pre-amp... :no:

Bert

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BD-Design - Only the Best!

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Hallo Bert!

You are right of course - my concept needs a low impedance preamp. Neither a valve- amp nor a TVC has a low enough impedance.
Some years ago I build a valve-amp, which could drive a 75 ohms load, but it was a lot of expensive parts used...
Best regards
Stephan

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Stephan,

You said:

"The biggest amplitude is in the bass - so if there occurs clipping it will happen there first and produce harmonics. So I filter the main-amp at the input, that it has to produce no bass."

I'm not sure how your system is set up but for most of us we have speaker level outputs into solid state bass amps. There is a passive filter between the main amp and bass amps. So the bass that the main amp is producing is into a very easy, high impedance load. The bass character is heavily influenced by the main amp, but the main amp will never strain to produce bass frequencies.

It works very well unless there is too much low frequency noise in the system, since any noise will be amplified by the main amp and bass amps.

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There is a somewhat related discussion on line level vs. speaker level outputs going on in the Diy HiFi Supply Forum over at AA.

Brian mentioned that the rolloff of the output transformer (if there is one) can be a factor on whether line level or speaker level outs are preferred. To quote: "many OPTs are already rolling off at 40hz".

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Stephan,

You said:

"The biggest amplitude is in the bass - so if there occurs clipping it
will happen there first and produce harmonics. So I filter the main-amp at
the input, that it has to produce no bass."

I'm not sure how your system is set up but for most of us we have speaker
level outputs into solid state bass amps. There is a passive filter
between the main amp and bass amps. So the bass that the main amp is
producing is into a very easy, high impedance load. The bass character is
heavily influenced by the main amp, but the main amp will never strain to
produce bass frequencies.

It works very well unless there is too much low frequency noise in the
system, since any noise will be amplified by the main amp and bass amps.

Hi,

I agree with this. Additionally it may be good for understandings that the amplitute -like Stephan mentioned- from bass waves is not larger at all (opposed to the higher frequencies). For this matter IMO clipping won't be a problem, or no "additional" problem anyway. What would be true though, is that bass waves sustain longer, and therefore require more power in one go (large elco's etc.). But, power for what ? these waves are just passed through to the bass amp, and no large stiff diaphragm has to be sustained in any position etc. by the main amp. So indeed, there is no load.

Peter

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Hi Cappy,

It works very well unless there is too much low frequency noise in the
system, since any noise will be amplified by the main amp and bass amps.

True but there is one problem with amplifiers who care about impedance changes (like most tube amps) when connected to an unfiltered Oris system (Lowther, AER, Fostex, etc.) which do have a relative big impedance hump in the lower frequencies. Where that hump is depends on the way the back of the chamber is closed, partly closed or not.

At the "hump" frequency the main amplifier (sensitive to impedance changes) will give a higher output picked up by the line level filter which is the main cause for a less controlled bass. When the Oris horn is filtered then the amplitude changes gradually and gives hardly a problem to tune it all in (but also the reason why passive line-level filters have to be tuned at home).

Bert

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BD-Design - Only the Best!

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...to which I seem to come back all the time for the Orphean with Compact bass system (using the BD15 of course..).

[image]

Note: Check the polarity of your connections, the grounds (-) of the drivers (midrange and BD15) should be connected.

Tune in the volume for the bass in a way that the lower midrange sounds in balance and then listen for a few days. Let me know how this works out in your situation (MkI and MkII) and report back so that I can give usable suggestions so that you can tune it optimally.

Bert

--
BD-Design - Only the Best!

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I hve one suggestion about the 100 k pot in Berts drawing:
Install it in the first tests, till You are satisfied with the reproduction.
Than measure the values and replace it either by two resistors, or a two pole rotary switch with some values ,narrowly spaced arround the first measured value. I did this with my amps and the reproduction is better than with a pot!
One of the easy tweaks!
Best regards
Stephan

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Bert,

What do you mean by a bipolar 100uF cap? Electrolytic so as to be cheaper?

There are 100 uF film caps about albeit they kind of expensive. I guess one could get a cheaper electrolytic (if that is what you mean) and once one is happy with the bass filter swap it out for a film cap or caps.

Also, I wonder how using a few 47 uF film caps doubled up would work? Have you ever tried that? Diy HiFi Supply has some nice sounding Obbligatos for $16.75 U.S. each.

Regarding the inductor -- you show <0.5 for the DCR. Is lower better? I see a Solen 3.6 mH 12g with a DCR of 0.47. Northcreek can wind a 0.33 ohm one but it would be more expensive.

Also, for my current bass filter I am using an air coil inductor. These work well for midrange and treble, but I think it is holding my bass back a bit. The next one I get won't be air coil.

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Hi Cappy,

What do you mean by a bipolar 100uF cap? Electrolytic so as to be
cheaper?

Yes but also having some internal damping lowering the Q. You can try a film type later and see if you like it better though...

Also, I wonder how using a few 47 uF film caps doubled up would work?

Yes, that is close enough to try.

Regarding the inductor -- you show <0.5 for the DCR. Is lower better? I
see a Solen 3.6 mH 12g with a DCR of 0.47. Northcreek can wind a 0.33 ohm
one but it would be more expensive.

Higher than 0,5 ohm will hold back the bass but the 0,47ohm will do for now. You can always try other things later to see if it brings improvement as changing the DC resistance changes the Q of the filter at the same time...

Also, for my current bass filter I am using an air coil inductor. These
work well for midrange and treble, but I think it is holding my bass back
a bit. The next one I get won't be air coil.

I don't think it is because of the air, perhaps the resistance was a bit too high and/or the value was doing the wrong things.

Bert

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BD-Design - Only the Best!

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What do mean "having some internal damping lowering the Q". What kind of electrolytic cap did you use?

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What do mean "having some internal damping lowering the Q". What kind of
electrolytic cap did you use?

I use a relative cheap electrolytic capacitor (not the cheapest) which have internal losses (resistance) compared to foil types and that gives a lower Q.

Bert

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BD-Design - Only the Best!

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So does that mean a more expensive film cap could sound worse, as far as damping goes anyway?

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So does that mean a more expensive film cap could sound worse, as far as
damping goes anyway?

Yes, it can sound worse easy as it will change the amplitude/phase.

Especially when the designer (generally speaking) of a filter is preferring them for the sound (not costs) within a certain system then an "upgrade" can sound worse.

Most people who upgrade their speakers have no clue what is happening in reality and rave about "improvements" pretty quickly to find out later that the old parts didn't sound that bad when these are connected again to check...

Bert

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BD-Design - Only the Best!

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Whoops, didn't mean air core, meant copper foil, i.e. Alpha-Core.

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Whoops, didn't mean air core, meant copper foil, i.e. Alpha-Core.

Ah, okay. Then use a normal air coil (and keep it away from metal as this will change its value).

Bert

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BD-Design - Only the Best!

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I can't find any Air Coils in stock in 3.6/3.7 mH.

So unless someone posts a source I missed it's going to be a few weeks minimum before I can try the new filter.

I did receive the other parts though.

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Hi Cappy,

I can't find any Air Coils in stock in 3.6/3.7 mH.

Didn't think about availability at all, I usually unwind higher valued coils until I have the value I need. This way I can always make a perfect pair with one longer wire "attached" to the coil too (one solder connection less this way...).

I just measured the value of the coils I am using and printed that on the schets.

Bert

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BD-Design - Only the Best!

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They exist in those sizes, there is a Solen 3.7 mH perfect lay and a Solen 3.6 mH hepta-litz, for example. Erse has a 3.6 mH perfect lay.

Everyone is just out of stock. Madisound said there has been a run on those values lately.

So what do you do, measure your final induction value with an LCR meter? I could do what you do, get a larger size, it seems like a good idea, but I don't have any way of measuring the inductance that I know of, without buying a meter or signal generator.

Actually, I just checked, and there is this technique which measures the voltage drop across a resistor:

http://wiki.4hv.org/index.php/Inductor

I'll think about it. :cool:

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...unless 109 Euro is too much?

[image]

Perhaps I should add that one to my on-line shop for situations like this... :grin:

Then you can measure while unwinding the coil at the same time, make matched pairs of C's, L's and R's and even have a diode tester for free! And use it anytime in the future if things change...

You can then even see what is happening when you place 2 coils too close to eachother (or wrongly) or close to some iron and learn from that.

Bert

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Perhaps I should add that one to my on-line shop for situations like this...

... :grin:

Click here: Other Goodies (DIY-Section)

Bert

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BD-Design - Only the Best!

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Bert

I'm not using the exact set-up you mention with the horn amp driving the bass amp but I do use the passive filter values you gave to me with 150s and compact bass cabs. As you know, I use an amp that is specially designed to drive the 150s directly, without a filter. It has the output chokes and transformers wound to roll off at 150hz. I use a line level Y with one leg going from the source directly to the 150 amp and the other leg going to your passive filter, which is built onto an RCA plug that fits into the bass amp. An autoformer does the volume control for the CD player and the phono stage. This works pretty close to perfect. I realize that it has been said in this thread that this connection method will not work well but all I can say is my usual response,"Just listen to the system". We all know how critical(read negative) hifi guys can be. I've had many guys sit in the listening chair and, although it is easy to see that they are trying their best to come up with something to say, not one of them has been able to come up with a single negative critique of the sound of this system. That pretty much says it all. The system has it's own sound, of course, but I agree it is hard to find anything negative to say about the sound of this system. This set-up seems to simply work. I have an active crossover that I initially used. Aside from the passive filter being quieter, I couldn't tell any real difference so I went with the simpler and quieter solution. Overall, the system is essentially silent.

The sound of your bass cab, and it's ability to integrate with the horn, is surprisingly good. I always knew the horn would be fine but I had concerns about using a reflex bass. It sounds a lot better than I imagined. I also listen to a full range electrostatic/ direct drive system so I know what integration sounds like. Even with the electrostats in the same room as the horns, I have no problems with the bass from your horn system.

I have also bought some Orpheans, just had to try them, but - and a BIG but it is - they have been lost in transit for a long time now. Honestly, I don't think I'll ever see them. If the Orpheans do show up, I have always planned on hooking them up in essentially the same manner as the 150s, with the addition of a filter on the Orphean and different bass filter values, obtained from you, of course. The last paragraph in your post seems to say you will not support someone using your horn and your bass cab in the same configuration. You certainly helped me in the past when you gave me the filter values that I am currently using. This is of particular importance to me as I still hold out some hope that the Orpheans might arrive. If they ever do show up, I'd want to use your filter values for the Orphean/Compact system and for the Orphean high pass filter. I bought the Orpheans thinking that I'd get the filter values from you, just as I did for my Oris horns.

While on the filter subject, how much, if any, does the distance from the horn to the listener, and the distance from the bass cab to the listener, figure into the filter design? I have been thinking of ways to further fine tune the system. Moving the bass cabs away from the horn, closer to the listener, is something that I have been thinking about. Is there a formula for determining the best relationship between the horn, the bass cab, and the listener? Also, when the horn is atop the bass cab, what the best horn driver to bass driver center to center distance? If the bass cab was moved closer to the listener, or if the horn center to bass driver center distance is changed, would the same filter values be correct? I'm just looking to do things as well as I can. I know that I could try moving things around and hear what happens but I don't want to be trying to reinvent the wheel when you have already figured all of this out.

Thanks

Tom

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Hi Tom,

filter values, obtained from you, of course. The last paragraph in your
post seems to say you will not support someone using your horn and your
bass cab in the same configuration.

It should read that no support can be given for a system not delivered and tested for suitability by me in person. Any combination with the BD15 in their suggested enclosures and any Oris or Orphean horn in combination with those will be supported as I can check myself. Own designed bass systems or horns or used drivers are unknown to me, how can I be of help there anyhow?

With some luck the same filters work out okay on other systems too but I can't guarantee that this is the optimal situation.

While on the filter subject, how much, if any, does the distance from the
horn to the listener, and the distance from the bass cab to the listener,
figure into the filter design?

The filters I use myself and suggest are for the systems placed as shown on the related picture (in case of the Orphean Compact you have to look look at the picture on that page). The timing is not always perfect but fiddling with the filter gives pretty good results with a "normal" visible placement of the parts.

Optimal would be to have the drivers more in line, similar distance from the driver to the listener with usually the basses a bit to the front as these are "slower" before they are on level...

Bert

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General passive-line level filtering issues. (BD-Design)