Ascend Sierra Luna Mini-Monitor Review

[amirm]

If the worst problems are caused by the port, maybe trying blocking it and retesting them to see how much they improve?

Happy to oblige if you deposit $1,000 in my paypal account. Otherwise, I have other speakers to test....

 

[tktran303]

Amir is measuring speakers performance OOTB.
And often shows an attempt to EQ it for better performance.

The (reverse) engineer types want a deconstruction, what went wrong, or play by play analysis. But probably because they are interested in how to improve the gem in the rough.

The curious thing for me is that a great deal of ported/passive radiator speakers, when measured by Amir’s Klippel NFS, show interferences between these two acoustic sources- the driver and the port/PR

These are not always apparent in the design phase; probably because the acoustic sources are Modelled or summed mathematically?

I mean, how do you measure, (without a $20K NFS) everything 20Hz to 1KHz- the port/PR + the (mid)woofer driver, and the effects of the baffle step, as well as all the distortion products down to about -50dB to see if anything funny is going on...

 

[ctrl]

These are not always apparent in the design phase; probably because the acoustic sources are Modelled or summed mathematically?

With appropriate effort, a loudspeaker can be completely simulated in software, with resulting port resonances and their effects on the overall system.

Depending on the software used, it can be as complex as desired and can also include damping.
A simplified BR-speaker example, HxWxD 0.7x0.45x0.44 m, BR-port length is 0.12m.

Simulated (low resolution) result.
The blue curve shows the sound pressure inside the enclosure between the rear panel and the vent.
The red curve shows the sound pressure at the port opening.
The green curve shows the sound pressure of the entire loudspeaker at a distance of 1m at the height of the woofer chassis.

If you don't simulate, you build a prototype to see if there are any problems and revise the design if necessary.

I mean, how do you measure, (without a $20K NFS) everything 20Hz to 1KHz, to simulate Tt capture the port/PR + the (mid)woofer driver, and the effects of the baffle step, as well as all the distortion products down to about -50dB to see if anything funny is going on...

This can be done easily. All you need is a simple measuring system (optimal is to measure "phase correct", e.g. via dual channel measurement).

Near-field measurement of all ports (<0.01m distance), near-field measurement of all woofers, after sound pressure correction of the sound sources based on their radiating area, the corrected measurements are summed. Performing the baffle step correction on the summed measurement - that's it. With large enclosures you can also set appropriate delays to improve the validity to high frequencies (in this case always <400Hz).

Sounds complicated, but it is not. The results correspond quite well with reality (as represented by the NFS) - <400Hz.

UPDATE: With a good measuring microphone, distortion can be measured close to the chassis and thus reliable distortion values can be obtained even at low frequencies.

 

[andreasmaaan]

I could see why the slot port may have a higher chance of resonances due to being essential a very short port. My understanding is that shorter ports are more susceptible to resonances in the midrange area. I might be wrong though as I am still just learning to really the fine tune in my own designs.

The longer the port, the lower in frequency the pipe resonances will be. So actually longer ports are more likely to have their resonances excited, as the resonances are (a) more likely to be within the passband of the woofer and (b) less likely to be damped inside the enclosure.

 

[aarons915]

If the worst problems are caused by the port, maybe trying blocking it and retesting them to see how much they improve?

I know that sounds logical but looking at the bass response, it already needs a sub crossed around 100-120Hz, if you block the port you'd have to cross them over at 150-200Hz, resulting in localization of the sub.

 

[hardisj]

I mean, how do you measure, (without a $20K NFS) everything 20Hz to 1KHz, to simulate Tt capture the port/PR + the (mid)woofer driver, and the effects of the baffle step, as well as all the distortion products down to about -50dB to see if anything funny is going on...

Ground plane measurement. It's quite easy. Just time consuming unless you are only measuring a single axis (which doesn't help identify absolute resonances). Only good up to about 500/600Hz in most cases due to aiming or poor SNR if the mic is placed far away to eliminate aiming concerns.
Nearfield response of each component (drive units, ports, etc).

 

[pjug]

Do the Ascends have damping material at the back end of the port? The WOW1 port goes straight to unpadded MDF. I might try putting some damping material on that back surface to see if it makes a difference. My Usher V601 have a lot of damping material there.

Edit: damping material against the back wall of the WOW1 port just muted the low end without doing anything for the resonance.

 

[ROOSKIE]

The longer the port, the lower in frequency the pipe resonances will be. So actually longer ports are more likely to have their resonances excited, as the resonances are (a) more likely to be within the passband of the woofer and (b) less likely to be damped inside the enclosure.

Howdy, I can't tell for sure but it sounds like you are confirming that short ports are more likely to have resonances in the midrange area. (I get that longer is more likely to have a pipe resonance in general but am wondering about the slot port short-comings)
If so and if that slot port is poorly designed and the cabinet doesn't use proper stuffing than it is likely those midrange resonances could be due to the short port? Trying to hone in on this so I make less mistakes when building stuff. I also realize those resonances could be due to all kinds of driver/cabinet/port relations.

 

[napilopez]

A better comparison from KEF size and price wise might be the LSX. From stereophile:

A clear port/cabinetr esonance, and it's about 5-6dB higher than this if you factor baffle step in, but still much better controlled

Edit: One thing I'm honestly not sure of: do these port problems become directional at higher frequencies?

The port is obviously omnidirectional at its intended low frequency peak, what about problems at higher frequencies? If your port shows a midrange problem escape, are you better off just sticking it in the rear where it will less affect the direct sound? Or if it's a cabinet resonance, are we looking at omnidirectional behavior?

Anecdotally, it seems to me that I've noticed more midrange problems from speakers with front ports.

Perhaps someone with speaker building experience can chime in. @ctrl?

 

[andreasmaaan]

Howdy, I can't tell for sure but it sounds like you are confirming that short ports are more likely to have resonances in the midrange area. (I get that longer is more likely to have a pipe resonance in general but am wondering about the slot port short-comings)
If so and if that slot port is poorly designed and the cabinet doesn't use proper stuffing than it is likely those midrange resonances could be due to the short port? Trying to hone in on this so I make less mistakes when building stuff. I also realize those resonances could be due to all kinds of driver/cabinet/port relations.

Lol, yeh I think we may well be talking about the same thing

I guess I’m just not sure I’d say “short” ports are more likely to have pipe resonances in the midrange. If we define the midrange as 200-2000Hz, then a port of length roughly 85cm will have its first pipe resonance at 200Hz and subsequent resonances at multiples of that. I’d say a port of this length would have the most resonance throughout the midrange. For the first pipe resonance to occur above the midrange (if we define that as >2000Hz), the port would need to be 8.5cm or shorter.

Most ports, of course, will fall somewhere between these two lengths.

What software do you use to model these things? VituixCAD has a good quick and basic calculator to check where your internal standing waves and port pipe resonances will be and to make sure these overlap as little as possible. Hornresp is also pretty good for getting a rough idea of not only where some of these resonances will occur, but also their approximate magnitude. Next step would then be either prototyping and refining, or using more sophisticated modelling software like ABEC, similar to what @ctrl mentioned.

 

[Dennis Murphy]

A better comparison from KEF size and price wise might be the LSX. From stereophile:

View attachment 90826

In preparation to bring back one of my speakers as a kit, I noticed a port resonance very similar to this one. The cabinet is part of a commercial kit that I modded, and it wasn't practical to change the basic port dimensions or cabinet size. So I tried stuffing the port tightly with soda straws (paper, not plastic) that ran the length of the port. Proac did this with their Tablette mini's, which I always thought were exceptionally clean in the midbass. That way you end up with a gazillion very long ports in relation to diameter, and the total output should be close to the untreated port. The result was effective suppression of the port peak, a virtual elimination of port noise at low frequencies (34 hz), and a small drop in the tuning frequency that may or may not be a problem. I still have to do more comparative listening and make sure there aren't in unintended side effects, but so far it seems like a viable solution for certain BR designs.

 

[BYRTT]

I ran into issues with the typical gated measurements I use for crossover development not picking up the severe port resonances in the Helium design also reviewed here. I suspect this "quasi-anechoic" graph was done similarly, with low frequency response spliced in. I was able to pick up the resonances with an ungated close-miked measurement of the port.

For Sehlin Helium DIY build maybe try what Dennis suggest below and lower crossover region to 3500Hz area ..

In preparation to bring back one of my speakers as a kit, I noticed a port resonance very similar to this one. The cabinet is part of a commercial kit that I modded, and it wasn't practical to change the basic port dimensions or cabinet size. So I tried stuffing the port tightly with soda straws (paper, not plastic) that ran the length of the port. Proac did this with their Tablette mini's, which I always thought were exceptionally clean in the midbass. That way you end up with a gazillion very long ports in relation to diameter, and the total output should be close to the untreated port. The result was effective suppression of the port peak, a virtual elimination of port noise at low frequencies (34 hz), and a small drop in the tuning frequency that may or may not be a problem. I still have to do more comparative listening and make sure there aren't in unintended side effects, but so far it seems like a viable solution for certain BR designs.

Thanks ..

 

[DDF]

In preparation to bring back one of my speakers as a kit, I noticed a port resonance very similar to this one. The cabinet is part of a commercial kit that I modded, and it wasn't practical to change the basic port dimensions or cabinet size. So I tried stuffing the port tightly with soda straws (paper, not plastic) that ran the length of the port. Proac did this with their Tablette mini's, which I always thought were exceptionally clean in the midbass. That way you end up with a gazillion very long ports in relation to diameter, and the total output should be close to the untreated port. The result was effective suppression of the port peak, a virtual elimination of port noise at low frequencies (34 hz), and a small drop in the tuning frequency that may or may not be a problem. I still have to do more comparative listening and make sure there aren't in unintended side effects, but so far it seems like a viable solution for certain BR designs.

The old straw trick will reduce the organ pipe resonance with a slight reduction in tuning frequency, but has a couple other drawbacks: increase in acoustic resistance which lowers port gain and broadens its response, and the added flow resistance can also limit the maximum output before it becomes non laminar (chuffs earlier). All in all maybe not a bad tradeoff for a badly resonant port.

Paper straws will be good so they flex, similar in idea to KEFs lossy rubber section in their ports (strategically placed at resonance points vs distributed like a straw).

Another trick I've heard of but not tried is using a mylar sheet bent into an s and inserted in the port (attribution: Jon Risch).

 

[ctrl]

So I tried stuffing the port tightly with soda straws (paper, not plastic) that ran the length of the port.

Another trick I've heard of but not tried is using a mylar sheet bent into an s and inserted in the port (attribution: Jon Risch).

Another trick is to drill holes in the BR channel halfway along (across the channel), e.g. 8mm drill bit with 8mm space between the holes.
This increases the BR tuning frequency slightly, so it would have to be compensated by a slightly longer BR channel.

You can also use an internal Helmholtz resonator (a tube closed on one side, slightly filled with damping material), which is tuned to the unwanted resonance frequency and placed in the BR channel, to fight the resonance.

Edit: One thing I'm honestly not sure of: do these port problems become directional at higher frequencies?
The port is obviously omnidirectional at its intended low frequency peak, what about problems at higher frequencies? If your port shows a midrange problem escape, are you better off just sticking it in the rear where it will less affect the direct sound? Or if it's a cabinet resonance, are we looking at omnidirectional behavior?

A resonance at 1kHz should already show a clear directivity.
If the BR-Port is placed in the back instead of the front, the phase of the BR-Port resonance shifts. With a 0.2m deep speaker cabinet and a 1kHz BR-Port resonance, the phase is reversed - this would be positive if it would create a dip instead of a hump.

 

[andreasmaaan]

A resonance at 1kHz should already show a clear directivity.

I don't know that I would agree 100%, although I admit I haven't looked at this rigorously before. But my general starting point would be to consider the port exit as a plane circular source, with directivity obviously proportional to its diameter. Do you see any problem with this?

Using ABEC to do a quick and dirty model of a 7cm-diameter port (pretty average for a bookshelf speaker), I get this (normalised) directivity profile (on an infinite baffle):

Quite omnidirectional right up to 4 or 5kHz.

Admittedly, I don't usually try to model ports in this way... Perhaps my starting assumptions are incorrect?

 

[napilopez]

Another trick is to drill holes in the BR channel halfway along (across the channel), e.g. 8mm drill bit with 8mm space between the holes.
This increases the BR tuning frequency slightly, so it would have to be compensated by a slightly longer BR channel.

You can also use an internal Helmholtz resonator (a tube closed on one side, slightly filled with damping material), which is tuned to the unwanted resonance frequency and placed in the BR channel, to fight the resonance.


A resonance at 1kHz should already show a clear directivity.
If the BR-Port is placed in the back instead of the front, the phase of the BR-Port resonance shifts. With a 0.2m deep speaker cabinet and a 1kHz BR-Port resonance, the phase is reversed - this would be positive if it would create a dip instead of a hump.

I don't know that I would agree 100%, although I admit I haven't looked at this rigorously before. But my general starting point would be to consider the port exit as a plane circular source, with directivity obviously proportional to its diameter. Do you see any problem with this?

Using ABEC to do a quick and dirty model of a 7cm-diameter port (pretty average for a bookshelf speaker), I get this directivity profile (on an infinite baffle):

View attachment 91030

Quite omnidirectional right up to 4 or 5kHz.

Perhaps my starting assumptions are incorrect?

I appreciate this discussion, as it's something I worry about with nearfield port/woofer summations and then splicing. Not been a huge issue so far, but I'm always trying to refine my methodology given ground plane isn't an option where I live

 

[Mudjock]

For Sehlin Helium DIY build maybe try what Dennis suggest below and lower crossover region to 3500Hz area ..

The straws would be interesting as the port has a 90 degree elbow. I wonder how much good straws in half the length would do?

I can get a similar response to the original with a crossover around 4 kHz. That solves some, but not all issues. For the Helium woofer, I would really like to get the crossover down to about 2-2.5 kHz, which would allow a really flat response through the lower midrange, but would require a different tweeter. If the current tweeters have inconsistent response, which I suspect is the case, a different tweeter might be a good thing...

The 4" woofer from the same series as the 3" Helium woofer can do about 80 Hz f3 sealed in a small enclosure, which might be a better solution overall.

 

[ctrl]

I don't know that I would agree 100%, although I admit I haven't looked at this rigorously before. But my general starting point would be to consider the port exit as a plane circular source, with directivity obviously proportional to its diameter. Do you see any problem with this?

I have to admit that I have not been interested in the BR-Port's directivity in such detail too (I try to avoid BR-constructions at all times). We have @napilopez to thank for this!

Would, naive as I am, distinguish two cases. One is the general midrange "mess" that comes from the rear radiation of the woofer chassis. Since it is not possible to simulate the BR port without radiation from the driver, in this case I placed the membrane directly to the BR channel (an approximately 2'' diameter) inside the speaker - this should reflect the "evenly" distributed sound in the loudspeaker cabinet..

The second case are the BR-Port resonances. The BR-Port resonances are created in the channel, so I would, as you suggest, make the sound radiation directly aligned with the baffle (for these frequencies).

Let's take a look at what the computer has spit out as a result. Shown are the spectrograms normalized to the axis frequency response with +-180° horizontal for our two cases with an approximately 2'' diameter BR-Port, the cabinet is about 9'' wide. (Please note the scaling of the x-axis, only the frequency range 200-3000Hz is considered):

At least these simulations confirm the listening experience of @napilopez . In both cases one can assume that the midrange frequencies, around 1kHz, are attenuated by about 12dB 9-12dB with a rear BR port (compared to the front one). Of course without considering possible reflections from the front wall.

Quite omnidirectional right up to 4 or 5kHz.

I re-enacted your case in Axi-Driver (on an infinite baffle). I got a slightly different result, but even there the membrane is omnidirectional up to more than 2kHz (+-90°).
It seems, the influence of the baffle plays a major role.

 

[napilopez]

I have to admit that I have not been interested in the BR-Port's directivity in such detail too (I try to avoid BR-constructions at all times). We have @napilopez to thank for this!

Would, naive as I am, distinguish two cases. One is the general midrange "mess" that comes from the rear radiation of the woofer chassis. Since it is not possible to simulate the BR port without radiation from the driver, in this case I placed the membrane directly to the BR channel (an approximately 2'' diameter) inside the speaker - this should reflect the "evenly" distributed sound in the loudspeaker cabinet..
View attachment 91126


The second case are the BR-Port resonances. The BR-Port resonances are created in the channel, so I would, as you suggest, make the sound radiation directly aligned with the baffle (for these frequencies).
View attachment 91127

Let's take a look at what the computer has spit out as a result. Shown are the spectrograms normalized to the axis frequency response with +-180° horizontal for our two cases with an approximately 2'' diameter BR-Port, the cabinet is about 9'' wide. (Please note the scaling of the x-axis, only the frequency range 200-3000Hz is considered):
View attachment 91128
View attachment 91129

At least these simulations confirm the listening experience of @napilopez . In both cases one can assume that the midrange frequencies, around 1kHz, are attenuated by about 12dB 9-12dB with a rear BR port (compared to the front one). Of course without considering possible reflections from the front wall.



I re-enacted your case in Axi-Driver (on an infinite baffle). I got a slightly different result, but even there the membrane is omnidirectional up to more than 2kHz (+-90°).
It seems, the influence of the baffle plays a major role.
View attachment 91125

This is very insightful, thank you! This seems to give some defense for rear mounted ports.

I'm going to through some of my measurements and compare the results for speakers with rear ports vs front ports and make sure it's true that it is more common for front-mounted ports to show midrange problems.

 

[andreasmaaan]

I have to admit that I have not been interested in the BR-Port's directivity in such detail too (I try to avoid BR-constructions at all times). We have @napilopez to thank for this!

Would, naive as I am, distinguish two cases. One is the general midrange "mess" that comes from the rear radiation of the woofer chassis. Since it is not possible to simulate the BR port without radiation from the driver, in this case I placed the membrane directly to the BR channel (an approximately 2'' diameter) inside the speaker - this should reflect the "evenly" distributed sound in the loudspeaker cabinet..
View attachment 91126


The second case are the BR-Port resonances. The BR-Port resonances are created in the channel, so I would, as you suggest, make the sound radiation directly aligned with the baffle (for these frequencies).
View attachment 91127

Let's take a look at what the computer has spit out as a result. Shown are the spectrograms normalized to the axis frequency response with +-180° horizontal for our two cases with an approximately 2'' diameter BR-Port, the cabinet is about 9'' wide. (Please note the scaling of the x-axis, only the frequency range 200-3000Hz is considered):
View attachment 91128
View attachment 91129

At least these simulations confirm the listening experience of @napilopez . In both cases one can assume that the midrange frequencies, around 1kHz, are attenuated by about 12dB 9-12dB with a rear BR port (compared to the front one). Of course without considering possible reflections from the front wall.



I re-enacted your case in Axi-Driver (on an infinite baffle). I got a slightly different result, but even there the membrane is omnidirectional up to more than 2kHz (+-90°).
It seems, the influence of the baffle plays a major role.
View attachment 91125

Interesting that there’s still a bit of a discrepancy between our two models, but this does seem to explain things for the most part, ie it’s primarily the rear panel of the enclosure that controls the port’s directivity in your sims, rather than the port itself. Certainly a good illustration though of why (at least for a two-way system) rear porting is likely to be a better choice.