Author Topic: Digital speaker crossovers and room correction discussion  (Read 2380 times)

Offline steve

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Re: Digital speaker crossovers and room correction discussion
« Reply #15 on: August 20, 2017, 06:09:31 PM »
The equivalent is a peaking filter that has both gain and attenuation.  You set the gain(or attenuation in dB) center frequency and Q you want.  You can measure the original analog crossover and then adjust parameters in the software.

It does not simulate the crossover at the RCL level like SPICE. 

Amplitude adjustments in the scaling blocks are floating point math precision.

Setting the Q and center frequency is a resonant type circuit. I don't see how it will mimick a zobel network.

Below shows the difference between a Zobel impedance curve and 2 resonant circuits impedance curve (2 different Qs). Please excuse the quick hand drawing.

Cheers
Steve
« Last Edit: August 20, 2017, 06:22:50 PM by steve »
Steve Sammet (retired, but manufacturing "V" ics again)

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Offline HAL

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Re: Digital speaker crossovers and room correction discussion
« Reply #16 on: August 20, 2017, 06:54:43 PM »
A driver driven by an amp directly without the digital crossover feeding the amp will not be flat response.  It will be the response of the driver. 

If the Zobel network is being used to give the driver flat response as a compensation for a driver impedance causing resonances, the digital peaking filter driving the amp can be used to compensate for the resonance.  That has amplitude change in 1dB steps for the peak/dip.  Center frequency is in 1Hz steps.  Q is in 0.1 steps.

Another option is using a single biquad digital filter with the parameters to simulate an impedance compensation network for the driver response.  That gives the finest control over the filter response.  Then you have 32bit floating point precision on filter input values.   Each channel is independent, so drivers can be worked individually.  This requires measurements of the individual drivers.

Another option is using a short convolver with specific driver measured data from both drivers to invert their responses for flattening. 

The last two methods are available, but measurement tools are not built into the unit.  I have tools that can be used to do them with correct measured data.

Both the A/D's and D/A's in the unit all run at 24bit/192KHz for DSP processing and without using linear phase filtering. The unit uses AKM AK5397 and AK4495S units for their analog performance for sound quality.  Much improved audio performance over the digital crossover units I mentioned earlier. 

I have used the system as a digital crossover and compensation for a Dayton Audio PS220-8 full range driver to 3x8" servo subs in an open U-baffle with very good results.  I used the peaking filter method above for compensation and also with a Butterworth filter for crossover to the subs.
 


Offline HAL

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Re: Digital speaker crossovers and room correction discussion
« Reply #17 on: August 20, 2017, 07:04:14 PM »
The R and C of the Zobel network with the RLC of the driver builds a resonance circuit for compensation.  The Zobel Network RC is calculated to work with the driver impedance (RLC parameters) 

If it is a parallel circuit usually for impedance flattening for easier amp/passive crossover design and drive.

Offline HAL

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Re: Digital speaker crossovers and room correction discussion
« Reply #18 on: August 20, 2017, 07:11:18 PM »
A schematic for the Zobel's implementation with the driver might be helpful.  Can be a series or parallel network with the driver feed.

Offline steve

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Re: Digital speaker crossovers and room correction discussion
« Reply #19 on: August 20, 2017, 07:15:40 PM »
The R and C of the Zobel network with the RLC of the driver builds a resonance circuit for compensation.  The Zobel Network RC is calculated to work with the driver impedance (RLC parameters) 

If it is a parallel circuit usually for impedance flattening for easier amp/passive crossover design and drive.

I beg to differ, a zobel network is not a resonant circuit for compensation. Check the impedance curves I posted in my last post. A zobel network is simply to reduce "flatten" the impedance of a speaker, to flatten the frequency response. In fact, one can cause the frequency response to drop as the frequency rises.

Cheers

Steve
Steve Sammet (retired, but manufacturing "V" ics again)

SAS Audio Labs Test Phono Stage
SAS Audio 11A Preamp
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Offline steve

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Re: Digital speaker crossovers and room correction discussion
« Reply #20 on: August 20, 2017, 07:17:54 PM »
A schematic for the Zobel's implementation with the driver might be helpful.  Can be a series or parallel network with the driver feed.

A zobel network is always across the driver itself. I think you are confusing a resonant circuit, often called a notch filter, which you described in an earlier earlier.

Cheers

Steve
Steve Sammet (retired, but manufacturing "V" ics again)

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Offline HAL

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Re: Digital speaker crossovers and room correction discussion
« Reply #21 on: August 20, 2017, 07:32:56 PM »
Parallel Zobel network for flattening driver impedance is not possible.  Biquads in this system simulate series style filters.

That style of network affects the electrical impedance load of the driver which has no effect on a digital crossover.  It affects the driver load on the amplifier.   


Offline steve

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Re: Digital speaker crossovers and room correction discussion
« Reply #22 on: August 20, 2017, 07:48:07 PM »
A driver driven by an amp directly without the digital crossover feeding the amp will not be flat response.  It will be the response of the driver.

The amplifier is virtually never accurate, and its output impedance also contributes to poor response. But you are right in that a driver's response is not a flat.

Quote
If the Zobel network is being used to give the driver flat response as a compensation for a driver impedance causing resonances, the digital peaking filter driving the amp can be used to compensate for the resonance.  That has amplitude change in 1dB steps for the peak/dip.  Center frequency is in 1Hz steps.  Q is in 0.1 steps.


What you are describing is often called a notch filter, which has a resonant and Q. It is in series with the driver. I believe you are confusing it with a zobel network, which is a CR and across the driver. I posted the two impedance curves for a notch filter and zobel network in one of my previous posts.

Quote
Another option is using a single biquad digital filter with the parameters to simulate an impedance compensation network for the driver response.  That gives the finest control over the filter response.  Then you have 32bit floating point precision on filter input values.   Each channel is independent, so drivers can be worked individually.  This requires measurements of the individual drivers.


That sounds promising if it truly is similar to a zobel network, and not a notch filter. However, the sensitivity of the adjustment is still my question. Can the adjustments to the frequency response be so small as to be around 105db down from the fundamental/midband? (For the general public, we are discussing frequency response, tonal balance, not SPL changes across the entire audio band like a voluime control adjustment.)

Quote
Another option is using a short convolver with specific driver measured data from both drivers to invert their responses for flattening. 

Not good enough for what I am doing.

Quote
The last two methods are available, but measurement tools are not built into the unit.  I have tools that can be used to do them with correct measured data.

It appears I am working with such minute adjustments that a digital won't be able to obtain the ultimate "blending" the drivers. But then I am really delving into "deepest crevices" for maximum accuracy/naturalness.

Quote
Both the A/D's and D/A's in the unit all run at 24bit/192KHz for DSP processing and without using linear phase filtering. The unit uses AKM AK5397 and AK4495S units for their analog performance for sound quality.  Much improved audio performance over the digital crossover units I mentioned earlier. 

I have used the system as a digital crossover and compensation for a Dayton Audio PS220-8 full range driver to 3x8" servo subs in an open U-baffle with very good results.  I used the peaking filter method above for compensation and also with a Butterworth filter for crossover to the subs.

I am glad to hear of your success Hal. Sounds like you have been doing some fine work. As I mentioned I am delving into that last bit of territory to discover what can be obtained in matching woofer/full range drivers, and sonic purity; maximizing drivers. I will probably have to test the digital crossovers myself to see the absolute maximum capabilities I can obtain.

Cheers and thanks for the information Hal. Keep up the good work.

Steve
Steve Sammet (retired, but manufacturing "V" ics again)

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Offline steve

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Re: Digital speaker crossovers and room correction discussion
« Reply #23 on: August 20, 2017, 07:58:02 PM »
Parallel Zobel network for flattening driver impedance is not possible.

Are saying the digital xover cannot simulate a zobel network? If so ok.

If you are saying a zobel network cannot flatten the driver impedance, what the amplifier output sees, yes it can quite well, but not perfectly. I have been using it for a long time to "flatten" the response of the speaker. But one has to use great parts.

Quote
That style of network affects the electrical impedance load of the driver which has no effect on a digital crossover.  It affects the driver load on the amplifier.   

Correct, a zobel will not affect the digital xover. The zobel network affects the load that the amplifier sees.

Cheers
Steve
« Last Edit: August 20, 2017, 08:00:32 PM by steve »
Steve Sammet (retired, but manufacturing "V" ics again)

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Offline dBe

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Re: Digital speaker crossovers and room correction discussion
« Reply #24 on: August 20, 2017, 10:15:52 PM »
Parallel Zobel network for flattening driver impedance is not possible.

Are saying the digital xover cannot simulate a zobel network? If so ok.

If you are saying a zobel network cannot flatten the driver impedance, what the amplifier output sees, yes it can quite well, but not perfectly. I have been using it for a long time to "flatten" the response of the speaker. But one has to use great parts.

Quote
That style of network affects the electrical impedance load of the driver which has no effect on a digital crossover.  It affects the driver load on the amplifier.   

Correct, a zobel will not affect the digital xover. The zobel network affects the load that the amplifier sees.

Cheers
Steve
I always use zones on drivers with large peaks @ FS because I do not know of any amplifier that does not benefit from a flat impedance curves.  Especially tube amps in the contexts of tube life, punch and timbre.

Offline steve

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Re: Digital speaker crossovers and room correction discussion
« Reply #25 on: August 22, 2017, 11:48:04 AM »
I have a NOS pair of System Audio 1270 speakers with a notch filter at ~6500hz. I call them NOS because I do not have 100 hours on them, maybe not 50 hours. Got them out this morning and I am so so impressed with them. Claim to fame is that the membrane is 1 gram. So one only has to worry about the mass of the voice coil. Quick, natural sounding, dynamics, that notch filter does wonders to tame the upper mids/lower highs that 5 1/4" drivers are known for.

Cheers

Steve
Steve Sammet (retired, but manufacturing "V" ics again)

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Offline HAL

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Re: Digital speaker crossovers and room correction discussion
« Reply #26 on: August 22, 2017, 11:58:20 AM »
I like open baffle planar/ribbon line arrays using servo sub arrays.  No Zobel or Thiel networks needed for the solid state Class AB amps driving either the ribbons or the planars. 

Been very happy with the dspMusik as the DSP crossover, A/D's and D/A's with my PC Music Server for room correction.




Offline steve

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Re: Digital speaker crossovers and room correction discussion
« Reply #27 on: August 22, 2017, 02:28:24 PM »
I like open baffle planar/ribbon line arrays using servo sub arrays.  No Zobel or Thiel networks needed for the solid state Class AB amps driving either the ribbons or the planars. 

Been very happy with the dspMusik as the DSP crossover, A/D's and D/A's with my PC Music Server for room correction.

Glad it is working out so well for you Hal. I did own some used maggies some years ago and loved them. I did have a break in a lead wire that I had to repair. Other than that, I really liked them.

I did have some problems finding a nice capacitor for my zobel, but now am very happy. These days, it is difficult to find a great, accurate capacitor due to all the mis-testing procedures used. I have not listening tested the expensive caps so I cannot say if they are good. Just too expensive to test them in the size needed.

Anyway, the walls just disappear, music is in space, and very dynamic and live sounding.

Cheers and continued good work Hal.

Steve
Steve Sammet (retired, but manufacturing "V" ics again)

SAS Audio Labs Test Phono Stage
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Offline doug s.

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Re: Digital speaker crossovers and room correction discussion
« Reply #28 on: September 01, 2017, 10:54:03 AM »
hi hal,

i have a deqx 2.6, and i think it makes a nice improvement to most any speaker i tried it with.  in fact, it made a cheap pair ($25) of craigslist sansui sp2500's sound damned close to some speakers considerably more expensive.

but, i have a few issues with it.  it's only a 3-way; i'd like the ability to have a 4-way.  and, if i want to cross over to subs, say at 60hz, i cannot then cross over at 150hz to a midwoofer; next lowest x-over point is 300hz.  finally, it's not very user friendly, regarding measuring drivers, correcting them, and then  measuring/correcting the room.

what improvements would i gain by going to a dspmusik system, re: sonics, ease of use, etc?  and, what sort of cash outlay would i be looking at?  i have no desire to use any preamp features; this would be strictly for implementation between preamp and amps as active x-over/dsp.

thanks,

doug s.

Offline HAL

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Re: Digital speaker crossovers and room correction discussion
« Reply #29 on: September 01, 2017, 11:53:12 AM »
Doug,
I have a DEQX 2.6p and it is a good unit.  I did not like the sound of the ADC and DAC's or linear phase filters, so that was my problem with it. 

The dspMusik has better ADC's and DAC's to me using the AKM AK5397 and AK4495S units.  It has the capability for being used as a preamp, but can be set for 1:1 operation and not used. 

The dspMusik has 8 outputs that are independent, so can be used as a 4-way stereo crossover.  As long as 4 channels of crossover covers all the drivers per channel, it will work. All analog inputs and outputs are balanced, but adapters for single ended can be supplied.  For longer runs balanced really helps with noise reduction and ground loop elimination.   Crossover points for subs are variable in 1Hz increments.  Low pass filtering can be set independently of the high pass frequency if needed or can be the same.

The measurement system is not integrated like DEQX.  I prefer to have the customer make the measurements needed with my Audiomatica CLIO pocket system and PC I send and then I do the build of the crossover software.   Once completed, the dspMusik is programmed and sent for trials.  If you already have a crossover design and parameters from DEQX, those can be used and no speaker measurements needed. 

MathAudio RoomEQ only works with digital file replay, so room correction is not available as a standalone box.  A Music Server is needed to use with either Foobar2000 or JRiver or other player that uses plug-ins for processing.   Until the next generation ADSP21469 dspblock is available from Danville, not enough memory to do room correction. 

The dspMusik programmed for customer use is $2000.00 + shipping.  This covers the CLIO measurement system being sent and returned for data collection.  The dspMusik system can be reprogrammed at any later point if the speakers change for an additional cost. 

Hope that explains the system.

Rich Hollis