Analog Bass Management Anyone?

[davee70]

Has anyone tried using external crossovers to take care of bass management duties?

My Oppo player will not direct bass to the subwoofer, at least not on 5.0 SACD discs, no matter what I do (I assume because of DRM issues). So, I'm thinking that I could put a high-pass filter (e.g., Marchand 12db/oct passive filter (XM46XLR-A)) between the pre-outs and the amp (and on to my speakers) and run the full scale line level signal to the subwoofer (Velodyne DD-15), which is made to handle it.

I've got a quad arrangement with two floorstanders in front and two bookshelf speakers for the surrounds. The multichannel preamp (Parasound P7 analog - no processor) has RCA and XLR outputs, both of which are active, so I figure I could use both: run the XLR's to the high-pass filter and the RCA's to the subwoofer. The sub has a standard set of stereo inputs, so I would have to combine signals from the surrounds with the fronts somehow so as not to affect the XLR outputs.

I'm confident the crossover would work on the fronts because I'm doing essentially the same thing now (the DD-15 has a 6db/oct pass-through, which I'm currently using) but it requires a lot of cabling: from the pre-outs to the sub and back to the amp. And, of course, it doesn't help me any on the surrounds.

Anybody adventurous enough to try something like that?

I know I could use a processor to handle it but that's not the road I'm on.

 

[jostenmeat]

Forgive me if I am incorrect in any way, as I've never had DVDA/SACD capability. It appears that somehow you can route the center channel to your mains, and I guess your player can do this.

I'm not quite sure what you are doing now, nor what you are exactly considering, but 6db/oct xover seems to be very shallow to me, and especially if the xover point is not rather low. Oh wait, is that slope for the sub or the mains? (I was under the impression that most subs do not do anything for the speaker outs, but maybe this one is approximating a 2nd order acoustic xover when the natural rolloff of the speaker is considered. OK I'm blabbering.)

You want an Outlaw ICBM. The problem is that they've been discontinued for a good long while now. You need to keep tabs at all the major classified sections, and when one pops up, jump all over it. From my impressions, they are not often on the classifieds anymore, and when they are, they're gone in a heartbeat.

There might be another solution for you, assuming you simply must require analog, but I don't know want that might be.

 

[TLS Guy]

Has anyone tried using external crossovers to take care of bass management duties?

My Oppo player will not direct bass to the subwoofer, at least not on 5.0 SACD discs, no matter what I do (I assume because of DRM issues). So, I'm thinking that I could put a high-pass filter (e.g., Marchand 12db/oct passive filter (XM46XLR-A)) between the pre-outs and the amp (and on to my speakers) and run the full scale line level signal to the subwoofer (Velodyne DD-15), which is made to handle it.

I've got a quad arrangement with two floorstanders in front and two bookshelf speakers for the surrounds. The multichannel preamp (Parasound P7 analog - no processor) has RCA and XLR outputs, both of which are active, so I figure I could use both: run the XLR's to the high-pass filter and the RCA's to the subwoofer. The sub has a standard set of stereo inputs, so I would have to combine signals from the surrounds with the fronts somehow so as not to affect the XLR outputs.

I'm confident the crossover would work on the fronts because I'm doing essentially the same thing now (the DD-15 has a 6db/oct pass-through, which I'm currently using) but it requires a lot of cabling: from the pre-outs to the sub and back to the amp. And, of course, it doesn't help me any on the surrounds.

Anybody adventurous enough to try something like that?

I know I could use a processor to handle it but that's not the road I'm on.

I think you are making this too complicated.

Your problem is not a DRM issue. On most SACDs, there is no 0.1 LFE channel.

You can't record a sub channel and have to derive one. The LFE channel is primarily for effects. When a multichannel music disc either BD or SACD has a sub channel in my experience the results are not good and I usually don't use the sub channel (0.1). The problem is issues of phase.

So I would drive all you speakers full range with SACD, I would use a Y-connector on the left front and rights and send a left and right signal to your sub. The sub will buffer the left and right to mono in the sub only. Set the sub crossover at X2 the F3 of your mains and you will be set.

If you had a processor and used bass management it would convert the SACD stream to PCM. You can't process DSD. That defeats the rational of SACD.

If you put crossovers on all speakers, you will need five high pass filters and five buffer amps summed to mono for the sub feed.

If you are asking the question, I doubt you can accomplish it.

In my rig I have a switch that does change to analog crossovers when playing SACD or BD with no LFA channel or when there is an LFE channel and I don't want to use it. However, my speakers all handle full range signals without distress and I have seven active crossovers in the rig already as a lot of the crossovers are active.

In your situation, my recommendation will work the best unless any of your fronts have poor bass power handling.

 

[davee70]

jostenmeat,

In doing my research on external crossovers I did come across the Outlaw ICBM but at the time I wasn't sure it was what I needed and in any event it is discontinued, as you say. If I'm remembering, it's an active crossover, which could raise the noise floor, but I'll take another look.

The flaw (I guess I should say a flaw) I can see now in my thinking was in viewing the balanced and unbalanced pre-outs as independent circuits. No doubt they share the same (+) signal and I would end up with multichannel mono to my speakers if I did what I suggested in the original post. (Any bets?)

I now think I will need to add a pair of two-channel low-pass filters (also available from Marchand) before combining the signals on route to the sub. If I set the low-pass crossover at 80 Hz like I do now, I could then disable the electronic crossover in the sub, like you would for a regular LFE channel. (Since I use no EQ on the DD-15, it would almost be like having an analog sub!)

The DD-15 has built into it a fixed 6 db/oct high-pass stereo line level filter crossed over at 80 Hz, which I have been using on my mains, with the crossover on the sub also set at 80 Hz but with a slope of 24 db/oct. This combo blends together well, as indicated on the DD-15 video display, and is pleasing to the ears. (I can attest it is way better than running the full scale signal to the mains without the high-pass filter, no matter how low I set the crossover on the sub.)

The low slope of the DD-15 high-pass filter (which is fixed) takes advantage of the low extension of the front floorstanders while the high slope of the low-pass filter avoids interference with the speakers above the crossover point.

Marchand, who has a reputation for making fine crossovers, only makes the 12 db/oct high pass with the XLR connections I need. I think a 12 db/oct slope should work almost as well with the front speakers and maybe better on the bookshelf speakers I'm using as surrounds. So I think that is consistent with what you were saying.

 

[davee70]

If you put crossovers on all speakers, you will need five high pass filters and five buffer amps summed to mono for the sub feed.

What are the buffer amps for? Could the low-pass passive filters accomplish the same thing per my previous post?

In my rig I have a switch that does change to analog crossovers when playing SACD or BD with no LFA channel or when there is an LFE channel and I don't want to use it.

I want to know the particulars of your rig! Come on, don't hold back.

 

[TLS Guy]

What are the buffer amps for? Could the low-pass passive filters accomplish the same thing per my previous post?



I want to know the particulars of your rig! Come on, don't hold back.

I doubt you can combine the outputs of all those low pass amps, without a problem. You will have to ask Marchand. It all depends on the output impedance of the outputs of the low pass crossover.

Generally you want low output impedance and high input impedance. So it is likely you would need buffering to sort out the impedance issues.

The other issue is you don't need more than one two channel crossover low pass crossover. You will need 12 db per octave high pass filters to all of your speakers, judging by your last post.

Bass is omnidirectional, and the bass from all channels will be present at the two fronts.

Combining the outputs of two low pass crossovers without buffering will be no problem.

12 db high pass with 24 db low pass works best and is what you need.

You definitely want 24 db per octave low pass to the sub.

From what you say it seems your mains can not handle bass at power, other wise you would have had no problem.

You can link to my rig in the links in my signature.

There is no sub as such, as the mains are truly integrated full range speakers and so are the rear backs. The center and surrounds handle bass without problems.

The other thing you might keep in mind is that mastering standards, for SACD are different in North America and Europe.

In North America the mix is done with the surrounds as rear speakers. In Europe the rear channels are in the position if the rear backs of a 7.0 or 7,1 system. This is another problem that has to be designed for. If you get that wrong the perspective is upset.

This is one of many issues that make SACD problematic. Moving to BD audio only would make life easier.

 

[Pyrrho]

Has anyone tried using external crossovers to take care of bass management duties?

My Oppo player will not direct bass to the subwoofer, at least not on 5.0 SACD discs, no matter what I do (I assume because of DRM issues). So, I'm thinking that I could put a high-pass filter (e.g., Marchand 12db/oct passive filter (XM46XLR-A)) between the pre-outs and the amp (and on to my speakers) and run the full scale line level signal to the subwoofer (Velodyne DD-15), which is made to handle it.

I've got a quad arrangement with two floorstanders in front and two bookshelf speakers for the surrounds. The multichannel preamp (Parasound P7 analog - no processor) has RCA and XLR outputs, both of which are active, so I figure I could use both: run the XLR's to the high-pass filter and the RCA's to the subwoofer. The sub has a standard set of stereo inputs, so I would have to combine signals from the surrounds with the fronts somehow so as not to affect the XLR outputs.

I'm confident the crossover would work on the fronts because I'm doing essentially the same thing now (the DD-15 has a 6db/oct pass-through, which I'm currently using) but it requires a lot of cabling: from the pre-outs to the sub and back to the amp. And, of course, it doesn't help me any on the surrounds.

Anybody adventurous enough to try something like that?

I know I could use a processor to handle it but that's not the road I'm on.

What Oppo player are you using? All of the Oppos that I have seen have bass management that applies to the multichannel analog outputs. You might want to consult your manual, and if you cannot find the information you need in there, you might want to contact Oppo. I think you probably have the settings set wrong.

 

[jliedeka]

If you do end up needing an external crossover, I'd really recommend active over passive. Yes, an active can add to the noise floor but if it is well designed, it should be inaudible. Passive crossovers have another set of trade-offs. They have resistors which will waste some power and inductors which will add some non-linearities aka distortion.

I'm pretty sure you just need to set your speakers to small and set the crossover frequency in the player. It should take care of bass management before converting to analog.

Jim

 

[davee70]

What Oppo player are you using? All of the Oppos that I have seen have bass management that applies to the multichannel analog outputs. You might want to consult your manual, and if you cannot find the information you need in there, you might want to contact Oppo. I think you probably have the settings set wrong.

I have the BDP-95. Just got it a couple weeks ago.
The menu does give me the option decoding DSD directly or converting to PCM. I chose the former. However, like I said nothing came from the sub with the speakers set to small and xover to 80 Hz. So I chose large and used the crossovers in the DD-15.

TLC says,

You can't process DSD.

so that explains it. The manual says something about choosing which one you prefer, the sound from the DSD option or the PCM option but it is silent on the bass management question. If I select PCM, from what you are saying the player should handle the low frequencies and send them to the sub. Is that right? I can give that a try.

I do know one thing, the DSD direct on Shostakovich's Symphony No. 5 with the Russian National Orchestra (Pentatone PTC 1586 096) was an epiphany of sorts for me.

My main speakers have never sounded better (that is, using the hi and lo-pass crossovers in the sub).

My main speakers do ok on bass by themselves but they sound much better with the sub handling the low bass duties.

 

[TLS Guy]

What Oppo player are you using? All of the Oppos that I have seen have bass management that applies to the multichannel analog outputs. You might want to consult your manual, and if you cannot find the information you need in there, you might want to contact Oppo. I think you probably have the settings set wrong.

You can not use bass management in an Oppo player without having the player do a PCM conversion. No bass management is possible within DSD.

 

[davee70]

I doubt you can combine the outputs of all those low pass amps, without a problem. You will have to ask Marchand. It all depends on the output impedance of the outputs of the low pass crossover.

Generally you want low output impedance and high input impedance. So it is likely you would need buffering to sort out the impedance issues.

The other issue is you don't need more than one two channel crossover low pass crossover. You will need 12 db per octave high pass filters to all of your speakers, judging by your last post.

Bass is omnidirectional, and the bass from all channels will be present at the two fronts.

Combining the outputs of two low pass crossovers without buffering will be no problem.

I'm having some difficulty following this. Assuming I could work out the output impedance issue, why don't I need more than one two channel low pass crossover? I am using bookshelf size speakers for the surrounds. Don't I also need to route the bass from those with a second two channel low pass crossover?

In the Shostakovich 5.0 SACD I mentioned in the previous post, the listener is positioned not in the audience but in the center of the orchestra (in the round I guess you would say - the feeling is terrific). There are oodles of low frequency harmonics in the surround channels on that disc.

If combining the outputs of two low pass crossovers without buffering is no problem, do you mean the two outputs of a two channel crossover? So then, I would need buffering if I tried to combine the outputs of more than two channels?

What kind of buffering do you mean? To me buffering is all about pH.

Seriously, what kind of device would I need to buffer 4 or 5 channels? Are those the buffer amps you mentioned in your earlier post? Is something like that commercially available or is that getting into some kind custom electronics?

 

[TLS Guy]

I'm having some difficulty following this. Assuming I could work out the output impedance issue, why don't I need more than one two channel low pass crossover? I am using bookshelf size speakers for the surrounds. Don't I also need to route the bass from those with a second two channel low pass crossover?

In the Shostakovich 5.0 SACD I mentioned in the previous post, the listener is positioned not in the audience but in the center of the orchestra (in the round I guess you would say - the feeling is terrific). There are oodles of low frequency harmonics in the surround channels on that disc.

If combining the outputs of two low pass crossovers without buffering is no problem, do you mean the two outputs of a two channel crossover? So then, I would need buffering if I tried to combine the outputs of more than two channels?

What kind of buffering do you mean? To me buffering is all about pH.

Seriously, what kind of device would I need to buffer 4 or 5 channels? Are those the buffer amps you mentioned in your earlier post? Is something like that commercially available or is that getting into some kind custom electronics?

First lets take he buffering. Say the output impedance is 200 ohms say. If you combine four low pass filters each will see an impedance of 50 Ohms, so you probably won't have much output and it will likely be clipped.

You would have to design and build your buffer amp from op amp chips. You would need a quad opamp chip and design for high output impedance so you could mix them plus likely add a little gain.

However all of the low stuff below 80 Hz, will be on all channels. Bass is not directional. So getting your below 80 Hz feed from the left and right channels, will be more than sufficient. It will sound exactly the same as getting it from all the channels. It will, I can be certain of that. So you don't need to over complicate your set up.

 

[davee70]

If you do end up needing an external crossover, I'd really recommend active over passive. Yes, an active can add to the noise floor but if it is well designed, it should be inaudible. Passive crossovers have another set of trade-offs. They have resistors which will waste some power and inductors which will add some non-linearities aka distortion.

My experience with passive is limited to the 80 Hz, 6 db/oct high-pass one in the Velodyne DD-15. It really improved things when I ran the front pre-outs through them and set the active crossover in the sub to 80 Hz, 24db/oct. Of course, that was a Velodyne high-pass filter.

I do know one thing, I don't want a high-pass filter that mucks things up like your typical tone control on receivers
of yore. Is that the kind of distortion you mean? That would defeat everything (no pun intended ).

I looked at Rane, Behringer, and dbx and on first impression, none seemed like something I would want. I thought the Marchand passives would be more transparent. They do make active ones. They're a bit pricey, especially if you need more than one.

 

[davee70]

First lets take he buffering. Say the output impedance is 200 ohms say. If you combine four low pass filters each will see an impedance of 50 Ohms, so you probably won't have much output and it will likely be clipped.

I got you. Ohms law.

You would have to design and build your buffer amp from op amp chips. You would need a quad opamp chip and design for high output impedance so you could mix them plus likely add a little gain.

I wish Parasound would have done that already.

However all of the low stuff below 80 Hz, will be on all channels. Bass is not directional. So getting your below 80 Hz feed from the left and right channels, will be more than sufficient. It will sound exactly the same as getting it from all the channels. It will, I can be certain of that. So you don't need to over complicate your set up.

Do you mean that in the recording studio (as for example with the Shostakovitch disc) the low bass harmonics from the instruments behind you would be on the front channels when played back? Is that just because that is the way things are mixed in the recording process? Or is it because that's the way the acoustics work in the performing venue?

 

[davee70]

Marchand XM-46 specs

FYI. Here are the specs on the Marchand passive crossovers.

SPECIFICATIONS:
Frequency response: DC to 100 Khz,+/-1 dB
Crossover frequency: 50Hz - 20KHz
Insertion gain: -1 dB
Filter slope: 24 dB/octave standard (1st, 2nd, 3rd or 4th order can be provided)
Harmonic distortion at 1 KHz: Less than 0.01%
Signal-to-noise ratio: Much better than 110 dB
Input impedance: 1K Typ.
Output load capability: 10 KOhm min.
Maximum input voltage: 10 V RMS

http://www.marchandelec.com/xm46.html
Note: the high-pass filter box w/ XLR connectors is available w/crossover frequency of 80 Hz or higher, slope 12 db/oct.

TLS Guy, would 4 ea 10,000 ohm output load => 2,500 ohm low-pass be ok? Of course, I don't really need it, as you point out.

jliedeka, does the harmonic distortion look ok to you?

 

[TLS Guy]

I got you. Ohms law.

I wish Parasound would have done that already.



Do you mean that in the recording studio (as for example with the Shostakovitch disc) the low bass harmonics from the instruments behind you would be on the front channels when played back? Is that just because that is the way things are mixed in the recording process? Or is it because that's the way the acoustics work in the performing venue?

It has nothing to do with the mix, but the wavelengths of the frequencies involved. For instance a 50 Hz tone has a wave length of 22 ft and a 25 Hz tone 44 ft. So the wave will cover all conceivable mic layouts.

So you do not need all those crossovers, you actually only need one low pass filter from 1 channel.

The 10 k Ohm is the impedance that the crossover must see. The output impedance of each crossover will be much lower than that, likely between 200 and 600 ohms. So if you sum the amp then it will see the output impedance of the other amp.

If the output must see 10 K ohm minimum, I doubt you could combine even two filters without buffering. So you could get a zero sum buffer amp to combine two filters, like the ATI L200.

In fact using low pass filters on all channels would actually be a detriment, as you would have some phase cancellation due to mic spacing.

So the adage, keep it simple stupid applies.

The harmonic distortion is miniscule and of no consequence.

 

[davee70]

So you do not need all those crossovers, you actually only need one low pass filter from 1 channel.

The 10 k Ohm is the impedance that the crossover must see. The output impedance of each crossover will be much lower than that, likely between 200 and 600 ohms. So if you sum the amp then it will see the output impedance of the other amp.

If the output must see 10 K ohm minimum, I doubt you could combine even two filters without buffering. So you could get a zero sum buffer amp to combine two filters, like the ATI L200.

In fact using low pass filters on all channels would actually be a detriment, as you would have some phase cancellation due to mic spacing.

So the adage, keep it simple stupid applies.

The harmonic distortion is miniscule and of no consequence.

I'm hesitant about relying on only one channel for the sub, though I don't dispute what you're saying. Otherwise, I think I follow you.

I would prefer to use the balanced LFE input on the sub if I can, to avoid problems with hum. Going back to an earlier post of yours, you say I could use Y-connectors on the front two channels of the pre-amp and run one side of each to the two channel, 12 db/oct high-pass filter (Marchand XM46XLR-A). I guess I could then run the other side to the ATI L200, which I would need to set to work as a summing amplifier, and then run the mono signal to the crossover in the sub.

Alternatively, I could take the front two channel RCA pre-outs (both the RCA and XLR pre-outs on the P7 are active) and connect them directly to the stereo inputs of the DD-15.

Or, I could run the front two channel RCA pre-outs to a separate 24 db/oct low-pass filter (Marchand XM46SB) and turn off the digital crossover in the DD-15. I suspect that would qualify as stupid.

The surround pre-outs I would need to connect to another two channel 12 db/oct high-pass filter.

All crossovers would be set to 80 Hz.

Cost of crossovers and amp, about $550 (or $800, if I'm really stupid )

 

[TLS Guy]

I'm hesitant about relying on only one channel for the sub, though I don't dispute what you're saying. Otherwise, I think I follow you.

I would prefer to use the balanced LFE input on the sub if I can, to avoid problems with hum. Going back to an earlier post of yours, you say I could use Y-connectors on the front two channels of the pre-amp and run one side of each to the two channel, 12 db/oct high-pass filter (Marchand XM46XLR-A). I guess I could then run the other side to the ATI L200, which I would need to set to work as a summing amplifier, and then run the mono signal to the crossover in the sub.

Alternatively, I could take the front two channel RCA pre-outs (both the RCA and XLR pre-outs on the P7 are active) and connect them directly to the stereo inputs of the DD-15.

Or, I could run the front two channel RCA pre-outs to a separate 24 db/oct low-pass filter (Marchand XM46SB) and turn off the digital crossover in the DD-15. I suspect that would qualify as stupid.

The surround pre-outs I would need to connect to another two channel 12 db/oct high-pass filter.

All crossovers would be set to 80 Hz.

Cost of crossovers and amp, about $550 (or $800, if I'm really stupid )

I would try and get your bass from the two front L/R channels. High pass 12db per octave to all speakers. You could then send right and left signals to the sub, which contains a buffer amp, and use the 24 db per octave crossover in your sub.

That is the least costly and simplest solution and will almost certainly be the best.

 

[jliedeka]

I think the PCM/DSD setting refers to digital outs (HDMI/toslink) so that doesn't really apply here. If you are using the analog outs, the Oppo has to convert the DSD internally before converting to analog.

I would really try to do this without adding more electronics. I think if you just set the crossover in the Oppo and set your speakers to small it should direct all low frequencies to the subwoofer channel.

Jim

 

[davee70]

I think the PCM/DSD setting refers to digital outs (HDMI/toslink) so that doesn't really apply here. If you are using the analog outs, the Oppo has to convert the DSD internally before converting to analog.

On the BDP-95, the Audio Format Setup allows the user to choose DSD over PCM. It says:
"For the analog audio outputs, DSD data is converted to analog signal directly by the internal DAC." (pg. 62)
In addition, the LPMC rate limit setting affects the analog sound. The manual says:
"Setting to 192K may help to get the best audio quality." (pg. 62)

This should not be that surprising since the whole point of the BDP-95 was to give the best analog sound they could achieve.

Personally, I think they're being modest. See my Shostakovich post!

I would really try to do this without adding more electronics. I think if you just set the crossover in the Oppo and set your speakers to small it should direct all low frequencies to the subwoofer channel.

I have no doubt now that is the case. However, I am going to try what the TLS Guy suggested in his last post. It will only cost me $300 for the two passive filters. Marchand claims they use only "high quality inductors and capacitors" on their balanced boxes. If I don't like it, I can remove them from the mains and go back to the 1st order high-pass filter in the DD-15, which I have already been using. Are Velodyne electronics better than Marchand? I really don't know.

And as you point out, I can always convert to PCM.

I'll tell you, that DSD direct sure is sweet.