To Sub Or Not To Sub, That Is The Question

[Musical Bass]

@Musical Bass

If you've really been able to make any sort of progress and innovation here, that's awesome! But you need to stop expecting people to just believe it because you say it, and listen to the feedback you get.

Go back and take proper measurements to prove your claims, then I think both sales and forum discussions will be much easier afterwards.

The web response file for passive sub is full range 6th Oct smoothed apology issued! It was webmaster choice!

The attached files are associated with the MS-6P to illustrate why we are making our claims. We have a typical impedance graph for a ported subwoofer attached! If someone can present a better example please do. The amplifier only has a direct connection to diaphragm (VC) at the box frequency. If the amplifier doesn’t control the driver it invites modulation from external pressures ( room modes). This will be for most of this conventional systems frequency range.

The other graphs are of our MS-6 passive (or active) impedance vs response (not smoothed) and with better resolution. The response and distortion is also plotted both at 2W input with a 32gram moving mass! If you notice the impedance is low over a broad range meaning the amplifier is controlling the driver over the concerned low frequency range making it resistant to external modulation (room modes). The drivers Q is high with little effect on response. The port low frequency response extends below the port peak (no -24db rolloff here) while it outputs energy beyond 200Hz with little error. ! When I use the word grounding it refers to broadband loading of the driver. Minimizing the reactive loading reduces the coupling effects that room modes have on the diaphragm motion.

 

[Musical Bass]

The web response file for passive sub is full range 6th Oct smoothed apology issued! It was webmaster choice!

The attached files are associated with the MS-6P to illustrate why we are making our claims. We have a typical impedance graph for a ported subwoofer attached! If someone can present a better example please do. The amplifier only has a direct connection to diaphragm (VC) at the box frequency. If the amplifier doesn’t control the driver it invites modulation from external pressures ( room modes). This will be for most of this conventional systems frequency range.

The other graphs are of our MS-6 passive (or active) impedance vs response (not smoothed) and with better resolution. The response and distortion is also plotted both at 2W input with a 32gram moving mass! If you notice the impedance is low over a broad range meaning the amplifier is controlling the driver over the concerned low frequency range making it resistant to external modulation (room modes). The drivers Q is high with little effect on response. The port low frequency response extends below the port peak (no -24db rolloff here) while it outputs energy beyond 200Hz with little error. ! When I use the word grounding it refers to broadband loading of the driver. Minimizing the reactive loading reduces the coupling effects that room modes have on the diaphragm motion.

The driver excursion is at a minimum at box frequency only in typical reflex designs. Our MS-6 design keeps the driver motion at minimum over several decades eliminating the resonance factor normally associated with ported designs. Box vibration is also at minimum while the internal pressure is regulated by an isolated volume utilizing viscous isothermal dissipation.

 

[Musical Bass]

The driver excursion is at a minimum at box frequency only in typical reflex designs. Our MS-6 design keeps the driver motion at minimum over several decades eliminating the resonance factor normally associated with ported designs. Box vibration is also at minimum while the internal pressure is regulated by an isolated volume utilizing viscous isothermal dissipation.

Minimum excursion with a low mass driver means quick response times that can match the speed of electrostatic, magnetic planar, low mass stand mount dynamic systems and other designs not utilizing excess mass to extend the low frequency response!

This is not a one off! Our goal is to extend the design to larger drivers keeping the mass/diameter ratio similar with as much as 75% reduction in enclosure dimensions!

 

[sigbergaudio]

The web response file for passive sub is full range 6th Oct smoothed apology issued! It was webmaster choice!

The attached files are associated with the MS-6P to illustrate why we are making our claims. We have a typical impedance graph for a ported subwoofer attached! If someone can present a better example please do. The amplifier only has a direct connection to diaphragm (VC) at the box frequency. If the amplifier doesn’t control the driver it invites modulation from external pressures ( room modes). This will be for most of this conventional systems frequency range.

The other graphs are of our MS-6 passive (or active) impedance vs response (not smoothed) and with better resolution. The response and distortion is also plotted both at 2W input with a 32gram moving mass! If you notice the impedance is low over a broad range meaning the amplifier is controlling the driver over the concerned low frequency range making it resistant to external modulation (room modes). The drivers Q is high with little effect on response. The port low frequency response extends below the port peak (no -24db rolloff here) while it outputs energy beyond 200Hz with little error. ! When I use the word grounding it refers to broadband loading of the driver. Minimizing the reactive loading reduces the coupling effects that room modes have on the diaphragm motion.

Thank you for sharing more graphs.

To be able to judge the level and distortion at 2W against anything else, you'd need to specify the distance between the microphone and the sub, and ideally use a standardized distance like for instance 1 meter or 2 meters. To still be able to get the response of the sub and not the room, the measurement should be done outside with what is called a ground plane measurement. 2.6% THD at 2W sounds high, but I guess that can be expected from a 6.5" driver.

The m6responseimp-graph is now less smoothed, which is good, but the Y-axis is still very wide, which in itself ends up smoothing the result / removing detail. 45-105dB is more or less "the norm" for these types of graphs. Your graph is -100 to +175dB. So the resolution should be 60dB, not almost 275dB.

 

[Musical Bass]

Thank you for sharing more graphs.

To be able to judge the level and distortion at 2W against anything else, you'd need to specify the distance between the microphone and the sub, and ideally use a standardized distance like for instance 1 meter or 2 meters. To still be able to get the response of the sub and not the room, the measurement should be done outside with what is called a ground plane measurement. 2.6% THD at 2W sounds high, but I guess that can be expected from a 6.5" driver.

The m6responseimp-graph is now less smoothed, which is good, but the Y-axis is still very wide, which in itself ends up smoothing the result / removing detail. 45-105dB is more or less "the norm" for these types of graphs. Your graph is -100 to +175dB. So the resolution should be 60dB, not almost 275dB.

Please focus on low mass and broadband loading for a wide range. No resonance, wide-band loading, low Xmax these are the things to consider when integrating a sub and low distortion. The mic is at the port to keep the room out of the mix! The graphs are detailed as requested to include impedance plot. This is perhaps the most important measurement to be had for a subwoofer design. If you can duplicate the impedance plot by any design please upload the graph. It is very important that the amplifier maintain control of a low mass diaphragm for ideal integration with mains. The room modes modulate the diaphragm over most of the range in conventional reflex design!

 

[Musical Bass]

Please focus on low mass and broadband loading for a wide range. No resonance, wide-band loading, low Xmax these are the things to consider when integrating a sub and low distortion. The mic is at the port to keep the room out of the mix! The graphs are detailed as requested to include impedance plot. This is perhaps the most important measurement to be had for a subwoofer design. If you can duplicate the impedance plot by any design please upload the graph. It is very important that the amplifier maintain control of a low mass diaphragm for ideal integration with mains. The room modes modulate the diaphragm over most of the range in conventional reflex design!

One more graph showing impedance relative to resistance and minimum phase shift that all amplifiers love.

 

[DonH50]

Please focus on low mass and broadband loading for a wide range. No resonance, wide-band loading, low Xmax these are the things to consider when integrating a sub and low distortion.

Most subwoofers these days are active so driver impedance is irrelevant to the user (not to the sub designer, of course).

The mic is at the port to keep the room out of the mix!

You said that the subwoofer reduces or eliminates room modes everywhere in the room. You also said you had compared to a swarm of subs. Can you plot in-room response from several positions showing how your design mitigates room modes? I showed the 1 m measurements of my subwoofer's frequency response earlier. Other manufacturers provide similar data but I've little interest or incentive to search and post them. Many subs exhibit good frequency response and low distortion for close-in measurements, but none claim to mitigate room modes.

You seem to be claiming that your innovation mitigates the modulation of the driver by room modes impinging on its surface and thus reducing distortion, but it is not clear that is a significant distortion mechanism for most subs, and most importantly how that leads to suppressing their (room modes') effects on frequency response in the rest of the room.

The graphs are detailed as requested to include impedance plot. This is perhaps the most important measurement to be had for a subwoofer design. If you can duplicate the impedance plot by any design please upload the graph. It is very important that the amplifier maintain control of a low mass diaphragm for ideal integration with mains. The room modes modulate the diaphragm over most of the range in conventional reflex design!

See above -- it is not important to owners of active subs, and since most are active, there is no impedance plot available since it is an internal design parameter. What users see are distortion over frequency and output (anechoic SPL) sweeps. The innovations you claim, as I understand them, will provide lower distortion and the ability of a single sub to mitigate room modes.

 

[sigbergaudio]

Please focus on low mass and broadband loading for a wide range. No resonance, wide-band loading, low Xmax these are the things to consider when integrating a sub and low distortion. The mic is at the port to keep the room out of the mix! The graphs are detailed as requested to include impedance plot. This is perhaps the most important measurement to be had for a subwoofer design. If you can duplicate the impedance plot by any design please upload the graph. It is very important that the amplifier maintain control of a low mass diaphragm for ideal integration with mains. The room modes modulate the diaphragm over most of the range in conventional reflex design!

With a 6.5" driver and low xmax you are unlikely to compete with anyone on low distortion. But I am still interested to see proof that your subwoofer is not affected by room modes.

 

[Musical Bass]

Most subwoofers these days are active so driver impedance is irrelevant to the user (not to the sub designer, of course).


You said that the subwoofer reduces or eliminates room modes everywhere in the room. You also said you had compared to a swarm of subs. Can you plot in-room response from several positions showing how your design mitigates room modes? I showed the 1 m measurements of my subwoofer's frequency response earlier. Other manufacturers provide similar data but I've little interest or incentive to search and post them. Many subs exhibit good frequency response and low distortion for close-in measurements, but none claim to mitigate room modes.

You seem to be claiming that your innovation mitigates the modulation of the driver by room modes impinging on its surface and thus reducing distortion, but it is not clear that is a significant distortion mechanism for most subs, and most importantly how that leads to suppressing their (room modes') effects on frequency response in the rest of the room.


See above -- it is not important to owners of active subs, and since most are active, there is no impedance plot available since it is an internal design parameter. What users see are distortion over frequency and output (anechoic SPL) sweeps. The innovations you claim, as I understand them, will provide lower distortion and the ability of a single sub to mitigate room modes.

Your assessment of powered subs being benign in the impedance is wrong! The active subwoofer is using an amplifier that also loses control of the driver at any frequency other than the box frequency. There is no amplifier compensation possible if the driver is only well connected at the box frequency! Look at the conventional impedance curve that I attached earlier and realize this fact that reactive elements are associated with the diaphragms motion at other than the minimum saddle frequency.

 

[DonH50]

Your assessment of powered subs being benign in the impedance is wrong! The active subwoofer is using an amplifier that also loses control of the driver at any frequency other than the box frequency. There is no amplifier compensation possible if the driver is only well connected at the box frequency! Look at the conventional impedance curve that I attached earlier and realize this fact that reactive elements are associated with the diaphragms motion at other than the minimum saddle frequency.

Read my post again. To the user, the consumer, the person buying an active sub, the amplifier/driver interface is part of the design they do not see or control. I did not say they were benign; the subwoofer designer must deal with them, but that is outside the user's control. Impedance is interesting but irrelevant to the user, at least from the consumer's driving side, which is a line-level interconnection.

Feedback (usually called servos for electromechanical interfaces) can allow the amplifier to compensate driver motion. Published distortion measurements are available for many commercial subwoofers and do not indicate the amplifier "loses control of the driver at any frequency other than the box frequency". That statement implies a high level of distortion and undamped cone motion not seen in practice.

Acoustic resonance of the box and port lead to mechanical coupling to the driver that affects the measured electrical impedance irrespective of reactive circuit elements. I suspect a translation issue.

 

[Musical Bass]

With a 6.5" driver and low xmax you are unlikely to compete with anyone on low distortion. But I am still interested to see proof that your subwoofer is not affected by room modes.

When you hear a conventional resonate subwoofer design operating under the impedance conditions described it is more annoying than any THD distortion less than 10% at very low frequencies. It’s all about timing when it comes to integration and the MS-6 disappears acoustically becoming an image where the fundamental appears to be with the harmonics coming from the mains. The result is a bass image that appears to be a part of the soundstage.

 

[Musical Bass]

Read my post again. To the user, the consumer, the person buying an active sub, the amplifier/driver interface is part of the design they do not see or control. I did not say they were benign; the subwoofer designer must deal with them, but that is outside the user's control. Impedance is interesting but irrelevant to the user, at least from the consumer's driving side, which is a line-level interconnection.

Feedback (usually called servos for electromechanical interfaces) can allow the amplifier to compensate driver motion. Published distortion measurements are available for many commercial subwoofers and do not indicate the amplifier "loses control of the driver at any frequency other than the box frequency". That statement implies a high level of distortion and undamped cone motion not seen in practice.

Acoustic resonance of the box and port lead to mechanical coupling to the driver that affects the measured electrical impedance irrespective of reactive circuit elements. I suspect a translation issue.

Well the amplifier (any amp) is looking for a load to deliver power directly to the driver. If it’s 4ohms then a good load little reaction involved. When the frequency changes in either direction from the box frequency the impedance rises rapidly meaning the motion is now controlled by reactive elements with less current through the VC. The amplifier now has less control and the driver is sensitive to internal and external pressures that can exaggerate the natural small room modes.

 

[Musical Bass]

Well the amplifier (any amp) is looking for a load to deliver power directly to the driver. If it’s 4ohms then a good load little reaction involved. When the frequency changes in either direction from the box frequency the impedance rises rapidly meaning the motion is now controlled by reactive elements with less current through the VC. The amplifier now has less control and the driver is sensitive to internal and external pressures that can exaggerate the natural small room modes.

Yes to your question of eliminating the need for multiple subs. You can use two subs if very high crossover frequencies are involved and the wavelengths are short. This is common when using with panels or very small dynamic systems that have limited acoustic output below 100Hz. You can also use multiple subwoofers to increase the pressure in very large rooms or those with high ceilings.

 

[Musical Bass]

Well the amplifier (any amp) is looking for a load to deliver power directly to the driver. If it’s 4ohms then a good load little reaction involved. When the frequency changes in either direction from the box frequency the impedance rises rapidly meaning the motion is now controlled by reactive elements with less current through the VC. The amplifier now has less control and the driver is sensitive to internal and external pressures that can exaggerate the natural small room modes.

.

Read my post again. To the user, the consumer, the person buying an active sub, the amplifier/driver interface is part of the design they do not see or control. I did not say they were benign; the subwoofer designer must deal with them, but that is outside the user's control. Impedance is interesting but irrelevant to the user, at least from the consumer's driving side, which is a line-level interconnection.

Feedback (usually called servos for electromechanical interfaces) can allow the amplifier to compensate driver motion. Published distortion measurements are available for many commercial subwoofers and do not indicate the amplifier "loses control of the driver at any frequency other than the box frequency". That statement implies a high level of distortion and undamped cone motion not seen in practice.

Acoustic resonance of the box and port lead to mechanical coupling to the driver that affects the measured electrical impedance irrespective of reactive circuit elements. I suspect a translation issue.

Why would you publish a situation that you have no control over. If there are no technological challenges why be concerned unless a new reference is presented. There is no substitute for solid low resistance control of the driver! Expensive cables etc. What you describe above the use of electronic means cannot replace the losses incurred. Current must flow through the VC for the amplifier to maintain control even if electronic manipulations are required. It’s that current (that we refer to as grounding) that keeps the driver insensitive to room modes.

 

[sigbergaudio]

When you hear a conventional resonate subwoofer design operating under the impedance conditions described it is more annoying than any THD distortion less than 10% at very low frequencies. It’s all about timing when it comes to integration and the MS-6 disappears acoustically becoming an image where the fundamental appears to be with the harmonics coming from the mains. The result is a bass image that appears to be a part of the soundstage.

Our subwoofers also result in a bass image that appears to be part of the soundstage. We build speaker systems where the subwoofers are an intergrated part of a 4-way system, so a subwoofer behaving as you claim traditional subwoofers do would not cut it.

The problems you describe do not exist in a modern subwoofer with a modern class D amplifier. Such an amplifier stays linear irrespective of changes in impedance. There are no resonance issues or timing issues.

 

[Musical Bass]

Our subwoofers also result in a bass image that appears to be part of the soundstage. We build speaker systems where the subwoofers are an intergrated part of a 4-way system, so a subwoofer behaving as you claim traditional subwoofers do would not cut it.

The problems you describe do not exist in a modern subwoofer with a modern class D amplifier. Such an amplifier stays linear irrespective of changes in impedance. There are no resonance issues or timing issues.

All quality amplifiers have a low output impedance and if the load impedance increases less current will flow through the voice coil. Type of amp doesn’t matter as a linear power delivery means a constant resistive load regardless of frequency!

 

[DonH50]

Well the amplifier (any amp) is looking for a load to deliver power directly to the driver. If it’s 4ohms then a good load little reaction involved. When the frequency changes in either direction from the box frequency the impedance rises rapidly meaning the motion is now controlled by reactive elements with less current through the VC. The amplifier now has less control and the driver is sensitive to internal and external pressures that can exaggerate the natural small room modes.

These are the numbers for an amplifier and speaker test pulled from an old article. It is not a class D amp and was full-range; class D subwoofer amplifiers usually have lower output impedance. DF is the amplifiers specified damping factor into 8 ohms, which I converted to magnitude Zout (output impedance). A 1 V signal was used for reference. The hybrid speaker (ESL with conventional woofer) ranged from 2 to 50 ohms (Zspkr) over the frequency range from 10 Hz to 10 kHz.

For this example there is virtually no change in signal at the speaker (Vspkr, in volts and dB) until the highest frequency where the amplifier's output impedance has increased significantly due to its output filter and reduced feedback (loop gain) while the speaker's impedance has fallen. In the bass region, where amplifier impedance remains low, there is little change in voltage despite the large change in load impedance. This does not measure cone movement or acoustic output, but speakers are generally designed as voltage-driven devices (at least this one was), so a perfect voltage source provides flat output.

 

[sigbergaudio]

What is most confusing in this whole debate is that I have completely failed to identify what you present as a big problem during development of our subwoofers. If it is such a huge problem, surely I would have encountered this and found it to be problematic. But that has not happened.

So, I am not completely sure what is happening.

 

[Musical Bass]

These are the numbers for an amplifier and speaker test pulled from an old article. It is not a class D amp and was full-range; class D subwoofer amplifiers usually have lower output impedance. DF is the amplifiers specified damping factor into 8 ohms, which I converted to magnitude Zout (output impedance). A 1 V signal was used for reference. The hybrid speaker (ESL with conventional woofer) ranged from 2 to 50 ohms (Zspkr) over the frequency range from 10 Hz to 10 kHz.

For this example there is virtually no change in signal at the speaker (Vspkr, in volts and dB) until the highest frequency where the amplifier's output impedance has increased significantly due to its output filter and reduced feedback (loop gain) while the speaker's impedance has fallen. In the bass region, where amplifier impedance remains low, there is little change in voltage despite the large change in load impedance. This does not measure cone movement or acoustic output, but speakers are generally designed as voltage-driven devices (at least this one was), so a perfect voltage source provides flat output.

View attachment 135363

Flat output can occur with reactance involved it’s the drivers velocity that’s now a concern. Current due to the incoming signal carries the detail in the bass. Reactance mixed with resistance cannot provide the control detail or prevent reflected signals from modulating the diaphragm. The diaphragm has to follow a velocity to make sound! If the response measures flat with a sweep or noise source will it remain flat as the velocity changes! Internal compression and room reflections alter the velocity response of the driver if it is not critically loaded.

 

[Musical Bass]

Flat output can occur with reactance involved it’s the drivers velocity that’s now a concern. Current due to the incoming signal carries the detail in the bass. Reactance mixed with resistance cannot provide the control detail or prevent reflected signals from modulating the diaphragm. The diaphragm has to follow a velocity to make sound! If the response measures flat with a sweep or noise source will it remain flat as the velocity changes! Internal compression and room reflections alter the velocity response of the driver if it is not critically loaded.

Amplifier damping factor is moot if reactance is involved with the load.