robbie010

Active / DSP / EQ / WTF?

Recommended Posts

I initially used v cheap xlr to rca leads off eBay 😀

Share this post


Link to post
Share on other sites
Super Wammer
5 minutes ago, MF 1000 said:

I initially used v cheap xlr to rca leads off eBay 😀

That is what my first thought was. 

Do you think that setup would work to give me a flavour of what going active can do?

Maybe do:

Passive pre - DCX - 6 Channel Amp - drivers 

I also have a friend locally who has a umik microphone and knows how to use REW software so I’m sure he would step in and help. 

Share this post


Link to post
Share on other sites

No reason why it shouldn’t work Simon 

  • Upvote 2

Share this post


Link to post
Share on other sites
Super Wammer

Take it slowly Simon and try and learn a little about reading the REW measurements along the way , you can then explain them to me as I can do a full REW session and generate lots of pretty graphs but I would be hard pressed to tell you what any of them mean.

With regard to amplifiers again I like to go for the simple and easy option (all of you shouting that's because your simple and easy Andrew get a gold star ) . So in my case for the Two Way I use I have always used matched pairs of stereo amplifiers Quad 405 to start with and currently NVA 20 power amps .

As a result I currently have have two excellent Fidele Audio modified Quad 405 amplifiers sitting doing nothing and you would be more than welcome to lend them to try out getting your speakers active . As the Quads are nice and compact they could easily be hidden behind your speakers and they would deal with the Bass and Mid Range you could then use your current amplifier for treble only . Couple that with Keiths Beringher and you have a full active set up to listen to and decide if this active lark is for you . Let me know if you are interested as either I could collect the Beringher and deliver the lot to you or Keith can collect the Quads and do the same .

  • Like 2

Share this post


Link to post
Share on other sites
On 28/10/2020 at 23:14, robbie010 said:

....... is it always going to be an improvement when changing passive to active?

This is a key question. Which I've covered recently on this forum when I said:

===================================================

If you have a speaker that is:

high efficiency

has an amplifier friendly impedance curve

has bass drivers that have about the right amount of total damping when used with a passive crossover and with whatever amplifier will be used with them

first order passive crossovers with inductors that are properly specced for the speakers

a relatively neutral frequency response

then I can't think of a single benefit to going active. I can only think of downsides.

.

If on the other hand you have a speaker that is:

low efficiency

has an unfriendly impedance curve

has bass drivers that would benefit from all the electrical damping they can get

has bumps in the frequency response around the crossover region(s)

Then that would be an ideal candidate for conversion to active.

==========================================================

.

Over the years I've seen a lot of rather one sided marketing for active speakers. Where the advantages are put, whilst the disadvantages are blithely ignored. The disadvantages coming from the number of active amplification devices they add to the signal path - usually transistors, but sometimes valves or analog to digital converters and digital to analog converters or a combination of all these.

Which translates, listening wise, in my (small sample size) experience to the addition of transistorised hash and possibly a reduction in dynamic freedom to the music.

It's all ifs and buts and it depends on the actual active crossover. But some of them do add a huge number of transistors to the signal path. We can be looking at taking a system from about 8 transistors in passive form to over 50 in active form. Which is quite shocking when you think about it. Especially if you are in the "less is more" school of system building.

I've used 2 active crossovers on my Bozaks: a 4th order Ashly. And a variable order 1970's Pioneer. The Pioneer sounded better - more transparent - and is used with the first order setting.

I'll copy and paste the opening post from this thread:

https://www.avforums.com/threads/the-big-technical-downside-to-active-crossovers.2183729/

=================================================

Let’s have a look at what’s inside a “simple 3 way analogue active crossover”.

3-Way+Active+Crossover+Circuit.jpg

 

If we trace the signal path from the input to the midrange output we can see that it goes through IC1, IC4A, IC4B, IC5A, IC5B, IC7A.

Looking at the parts list for this circuit we can see that that’s 1 x TL071 and 5 x TL072’s.

If we then look at the Texas Instruments Functional block diagram on page 32 of their TL07xx series Data Sheet:
http://www.ti.com/lit/ds/symlink/tl071.pdf

we can see that the signal passed through something of the order of 8 transistors in each TL071 or TL072 op amp.

(also check out figure 6-19 on page 30)

This means that this active crossover adds 48 active amplification devices (transistors) to the signal path!

For reference purposes, passive crossovers add 0 active amplification devices to the signal path.

For further reference purposes, my Phillips CD753 CD player has a DAC chip and then an analogue section that consists of half an op amp per channel. So let’s call that 4 active amplification devices. In my main system I have a stepped attenuator (passive) pre-amp with 0 active amplification devices and then a SET amplifier with 4 active amplification devices (2 x valves and 2 x transformers) in the signal path. If I were to use a solid state integrated amplifier I’d have something of the order of 8 active amplification devices in the signal path, in addition to the 4 from the CD player.

My conclusion from this is that when comparing active to passive crossovers, one should be aware of the SHOCKLINGLY HUGE number of amplification devices that active crossovers may add to the signal path.

OK that was one example of a 3 way active crossover. In a 2 way 4th order active crossover we can expect to have 4 op amps (c32 transistors) in the signal path. Whilst a 2 way 8th order active crossover will have 8 op amps (c64 trasnsistors) in the signal path!

Please feel free to examine the circuit diagrams of any active crossovers that you may own to determine how many active amplification devices your active crossover is adding to the signal path.

=================================

  • Like 1

Share this post


Link to post
Share on other sites
8 hours ago, bencat said:

Take it slowly Simon and try and learn a little about reading the REW measurements along the way , you can then explain them to me as I can do a full REW session and generate lots of pretty graphs but I would be hard pressed to tell you what any of them mean.

I'd strongly recommend learning about REW and getting some measurements done BEFORE you start messing about with the DCX.

Really important in my opinion.

Share this post


Link to post
Share on other sites
Super Wammer
1 hour ago, Psilonaught said:

I'd strongly recommend learning about REW and getting some measurements done BEFORE you start messing about with the DCX.

Really important in my opinion.

I have already spoken to my friend who knows how to use REW and has the umik mic, he is going to come and help me take some initial measurements next weekend. 
 

1 hour ago, lindsayt said:

This is a key question. Which I've covered recently on this forum when I said:

===================================================

If you have a speaker that is:

high efficiency

has an amplifier friendly impedance curve

has bass drivers that have about the right amount of total damping when used with a passive crossover and with whatever amplifier will be used with them

first order passive crossovers with inductors that are properly specced for the speakers

a relatively neutral frequency response

then I can't think of a single benefit to going active. I can only think of downsides.

.

If on the other hand you have a speaker that is:

low efficiency

has an unfriendly impedance curve

has bass drivers that would benefit from all the electrical damping they can get

has bumps in the frequency response around the crossover region(s)

Then that would be an ideal candidate for conversion to active.

==========================================================

.

Over the years I've seen a lot of rather one sided marketing for active speakers. Where the advantages are put, whilst the disadvantages are blithely ignored. The disadvantages coming from the number of active amplification devices they add to the signal path - usually transistors, but sometimes valves or analog to digital converters and digital to analog converters or a combination of all these.

Which translates, listening wise, in my (small sample size) experience to the addition of transistorised hash and possibly a reduction in dynamic freedom to the music.

It's all ifs and buts and it depends on the actual active crossover. But some of them do add a huge number of transistors to the signal path. We can be looking at taking a system from about 8 transistors in passive form to over 50 in active form. Which is quite shocking when you think about it. Especially if you are in the "less is more" school of system building.

I've used 2 active crossovers on my Bozaks: a 4th order Ashly. And a variable order 1970's Pioneer. The Pioneer sounded better - more transparent - and is used with the first order setting.

I'll copy and paste the opening post from this thread:

https://www.avforums.com/threads/the-big-technical-downside-to-active-crossovers.2183729/

=================================================

Let’s have a look at what’s inside a “simple 3 way analogue active crossover”.

3-Way+Active+Crossover+Circuit.jpg

 

If we trace the signal path from the input to the midrange output we can see that it goes through IC1, IC4A, IC4B, IC5A, IC5B, IC7A.

Looking at the parts list for this circuit we can see that that’s 1 x TL071 and 5 x TL072’s.

If we then look at the Texas Instruments Functional block diagram on page 32 of their TL07xx series Data Sheet:
http://www.ti.com/lit/ds/symlink/tl071.pdf

we can see that the signal passed through something of the order of 8 transistors in each TL071 or TL072 op amp.

(also check out figure 6-19 on page 30)

This means that this active crossover adds 48 active amplification devices (transistors) to the signal path!

For reference purposes, passive crossovers add 0 active amplification devices to the signal path.

For further reference purposes, my Phillips CD753 CD player has a DAC chip and then an analogue section that consists of half an op amp per channel. So let’s call that 4 active amplification devices. In my main system I have a stepped attenuator (passive) pre-amp with 0 active amplification devices and then a SET amplifier with 4 active amplification devices (2 x valves and 2 x transformers) in the signal path. If I were to use a solid state integrated amplifier I’d have something of the order of 8 active amplification devices in the signal path, in addition to the 4 from the CD player.

My conclusion from this is that when comparing active to passive crossovers, one should be aware of the SHOCKLINGLY HUGE number of amplification devices that active crossovers may add to the signal path.

OK that was one example of a 3 way active crossover. In a 2 way 4th order active crossover we can expect to have 4 op amps (c32 transistors) in the signal path. Whilst a 2 way 8th order active crossover will have 8 op amps (c64 trasnsistors) in the signal path!

Please feel free to examine the circuit diagrams of any active crossovers that you may own to determine how many active amplification devices your active crossover is adding to the signal path.

=================================

I have asked the question over on the US Klipsch forum and the response regarding the Behringer was very similar i.e. people have gone active but struggled with the Behringer due to the analogue sections. However, they have used it to get a flavour of what going active can do and then switched in favour of the minidsp unit or some other unit. 

Share this post


Link to post
Share on other sites
23 minutes ago, robbie010 said:

I have asked the question over on the US Klipsch forum and the response regarding the Behringer was very similar i.e. people have gone active but struggled with the Behringer due to the analogue sections. However, they have used it to get a flavour of what going active can do and then switched in favour of the minidsp unit or some other unit. 

That was exactly what I did. Keith's Behringer was instrumental in getting me started with an active setup and then I bought an analogue crossover.

Share this post


Link to post
Share on other sites
5 hours ago, lindsayt said:

This is a key question. Which I've covered recently on this forum when I said:

===================================================

If you have a speaker that is:

high efficiency

has an amplifier friendly impedance curve

has bass drivers that have about the right amount of total damping when used with a passive crossover and with whatever amplifier will be used with them

first order passive crossovers with inductors that are properly specced for the speakers

a relatively neutral frequency response

then I can't think of a single benefit to going active. I can only think of downsides.

.

If on the other hand you have a speaker that is:

low efficiency

has an unfriendly impedance curve

has bass drivers that would benefit from all the electrical damping they can get

has bumps in the frequency response around the crossover region(s)

Then that would be an ideal candidate for conversion to active.

==========================================================

.

Over the years I've seen a lot of rather one sided marketing for active speakers. Where the advantages are put, whilst the disadvantages are blithely ignored. The disadvantages coming from the number of active amplification devices they add to the signal path - usually transistors, but sometimes valves or analog to digital converters and digital to analog converters or a combination of all these.

Which translates, listening wise, in my (small sample size) experience to the addition of transistorised hash and possibly a reduction in dynamic freedom to the music.

It's all ifs and buts and it depends on the actual active crossover. But some of them do add a huge number of transistors to the signal path. We can be looking at taking a system from about 8 transistors in passive form to over 50 in active form. Which is quite shocking when you think about it. Especially if you are in the "less is more" school of system building.

I've used 2 active crossovers on my Bozaks: a 4th order Ashly. And a variable order 1970's Pioneer. The Pioneer sounded better - more transparent - and is used with the first order setting.

I'll copy and paste the opening post from this thread:

https://www.avforums.com/threads/the-big-technical-downside-to-active-crossovers.2183729/

=================================================

Let’s have a look at what’s inside a “simple 3 way analogue active crossover”.

3-Way+Active+Crossover+Circuit.jpg

 

If we trace the signal path from the input to the midrange output we can see that it goes through IC1, IC4A, IC4B, IC5A, IC5B, IC7A.

Looking at the parts list for this circuit we can see that that’s 1 x TL071 and 5 x TL072’s.

If we then look at the Texas Instruments Functional block diagram on page 32 of their TL07xx series Data Sheet:
http://www.ti.com/lit/ds/symlink/tl071.pdf

we can see that the signal passed through something of the order of 8 transistors in each TL071 or TL072 op amp.

(also check out figure 6-19 on page 30)

This means that this active crossover adds 48 active amplification devices (transistors) to the signal path!

For reference purposes, passive crossovers add 0 active amplification devices to the signal path.

For further reference purposes, my Phillips CD753 CD player has a DAC chip and then an analogue section that consists of half an op amp per channel. So let’s call that 4 active amplification devices. In my main system I have a stepped attenuator (passive) pre-amp with 0 active amplification devices and then a SET amplifier with 4 active amplification devices (2 x valves and 2 x transformers) in the signal path. If I were to use a solid state integrated amplifier I’d have something of the order of 8 active amplification devices in the signal path, in addition to the 4 from the CD player.

My conclusion from this is that when comparing active to passive crossovers, one should be aware of the SHOCKLINGLY HUGE number of amplification devices that active crossovers may add to the signal path.

OK that was one example of a 3 way active crossover. In a 2 way 4th order active crossover we can expect to have 4 op amps (c32 transistors) in the signal path. Whilst a 2 way 8th order active crossover will have 8 op amps (c64 trasnsistors) in the signal path!

Please feel free to examine the circuit diagrams of any active crossovers that you may own to determine how many active amplification devices your active crossover is adding to the signal path.

=================================

Hi,

I can see the logic that more components will degrade the sound, and this is true - if they are sub-optimal. The TL072 opamp is an old design and there are much better performing opamps as per the 1980's NE5532, and lately the LM4562.

I posted on another thread that Bob Carver solved the sound characteristic heard in an amplifier, which is determined by the amplifiers distortion profile. It does not matter how many transistors there are in the path, but what does matter is the distortion profile.

In this thread i have seen references to analogue crossovers, which i have not purchased, but did design my own based on a reference design - but i have yet to implement the PCB manufacturing.

I would use a DSP based solution, such that it is a fully digital process until the last point which is the DAC IC with analogue output stage.

Digital active system does restrict you to the DAC selected by the vendor - but it is possible to use a solution that has the digital outputs for you to connect to your own DAC solutions - but i have not seen such a solution.

One aspect i think i missed in reading, is that a 3-way system requires 6 amplifiers, and their power consumption idle can be quite high, unless class D is used.

Regards,

Shadders.

Share this post


Link to post
Share on other sites
1 hour ago, Shadders said:

Hi,

I can see the logic that more components will degrade the sound, and this is true - if they are sub-optimal. The TL072 opamp is an old design and there are much better performing opamps as per the 1980's NE5532, and lately the LM4562.

I posted on another thread that Bob Carver solved the sound characteristic heard in an amplifier, which is determined by the amplifiers distortion profile. It does not matter how many transistors there are in the path, but what does matter is the distortion profile.

In this thread i have seen references to analogue crossovers, which i have not purchased, but did design my own based on a reference design - but i have yet to implement the PCB manufacturing.

I would use a DSP based solution, such that it is a fully digital process until the last point which is the DAC IC with analogue output stage.

Digital active system does restrict you to the DAC selected by the vendor - but it is possible to use a solution that has the digital outputs for you to connect to your own DAC solutions - but i have not seen such a solution.

One aspect i think i missed in reading, is that a 3-way system requires 6 amplifiers, and their power consumption idle can be quite high, unless class D is used.

Regards,

Shadders.

Please feel free to include a complete circuit diagram of any active crossover that you use. Including the internal circuit of any ADC and DAC chips - which may well include transistors.

You may think that it's possible to create a circuit with transistors that is the equivalent of a "straight wire with gain." I don't think that such a thing has ever been achieved. Audible distortion in amplifiers and active crossovers can come in many different forms. Some of them difficult or impossible to measure with laboratory equipment.

It is also a relative unknown as to how transparent the ADC and DAC's in digital crossovers are. It would be a huge assumption to make that they are sonically transparent - in terms of them not damaging the audible reproduction of the music.

You could also turn around your statement on it not mattering how many transistors there are in the signal path of active crossover by saying "In a passive crossover, it doesn't matter if a passive crossover has capacitors, resistors and inductors in them. As long as the distortion profile is at least as good as any given active crossover alternative."

Share this post


Link to post
Share on other sites
2 hours ago, lindsayt said:

Please feel free to include a complete circuit diagram of any active crossover that you use. Including the internal circuit of any ADC and DAC chips - which may well include transistors.

Hi,

The circuit is essentially as per the example design in Doug Self's Active Filter book - i changed a few things, but the basics are there.

For ADC's and DAC's, i don't have the specific circuit diagrams, but some DSP books and literature on the internet describe the structure.

2 hours ago, lindsayt said:

You may think that it's possible to create a circuit with transistors that is the equivalent of a "straight wire with gain." I don't think that such a thing has ever been achieved. Audible distortion in amplifiers and active crossovers can come in many different forms. Some of them difficult or impossible to measure with laboratory equipment.

I never stated you can create a circuit that is a wire with gain. The low levels of distortion available from some amplifiers do go quite some way to achieve this though.

I am interested in audible distortion that cannot be measured - do you have links to the articles ?. Thanks.

2 hours ago, lindsayt said:

It is also a relative unknown as to how transparent the ADC and DAC's in digital crossovers are. It would be a huge assumption to make that they are sonically transparent - in terms of them not damaging the audible reproduction of the music.

In my current project, i will implement an ADC, but the primary design is digital input, which passes to the ADAU1452 Sigma DSP IC for active filter, volume control and time alignment of the drivers - DAC's are the PCM1795 32bit from Texas Instruments - 3 DAC's for 3-way design.The ADC is just in case there is a source that is not digital.

The filters in DSP are sonically transparent as it is just maths. The transient responses and cross over functions are the same as analogue design, but without any of the losses, or non-linearities due to coupling of inductors etc.

2 hours ago, lindsayt said:

You could also turn around your statement on it not mattering how many transistors there are in the signal path of active crossover by saying "In a passive crossover, it doesn't matter if a passive crossover has capacitors, resistors and inductors in them. As long as the distortion profile is at least as good as any given active crossover alternative."

Agree - a poorly designed active crossover is poor and a passive crossover well designed using air cored inductors, spaced/oriented accordingly, will exceed an analogue active crossover.  I personally would not purchase an analogue active crossover, so would design my own, but they are then difficult to modify - replacing resistors to change the crossover frequencies will be a pain - in DSP is it a few mouse clicks away.

The cost and amount of board space for an analogue active crossover is high compared to a DSP solution, and a DSP solution is vastly more configurable too - different filters easily implemented.

I think analogue active crossovers are old, but easily implementable for a quick design and solution that has been designed without too much tweaking.

Regards,

Shadders.

Share this post


Link to post
Share on other sites
Super Wammer

There are a lot of topics covered here and the risk is that none get the attention they deserve, but let me pile in on the only topic I can talk with any knowledge of: active speakers.

I am sure you can do all sorts of clever stuff with dsp etc but to me the most fundamental difference will be with active vs passive speaker topologies. I'm not sure what active and passive speakers @lindsayt has heard but, whatever some theory or other might suggest, the sonic difference between passive and active ATC SCM40/A is huge, regardless of the quality of amplification used with the passives. As Andrew @bencatsays, the key differentiator is the sequence of crossover>amps>drivers in the actives vs amps>crossover>drivers in the passives. Analogue vs digital crossover? I suspect that's far more a matter of personal taste (and of course the attraction with digital of being able to reconfigure as required) than of anything inherent in the different types.

Get that fundamental structure right (actives, for the avoidance of doubt!) and then, as @bencat, @MF 1000 and others have found, you not only have something which will give you £-for-£ more sonic gorgeousness than the equivalent passives, it can be the start of a journey of learning, and tweakery, and joy and no doubt heartache along the way...

Edited by TheFlash
  • Upvote 2

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Recently Browsing   0 members

    No registered users viewing this page.