Question of speaker designers: How important is Q for midrange speakers and their box sizes?

I am asking for a friend who is designing a three way 10/5/1 Satori speaker.
He is measuring Q with a view to the size of the midrange enclosure. He is within 5% of the SB parameters published.
The question is how much Q should be designed for, and why. 0.5? or maybe 0.75?
What would be the differences and how would this affect the size of the enclosure?
Thanks in advance; I'm a newbie here........
HD
 
I am asking for a friend who is designing a three way 10/5/1 Satori speaker
I'm a newbie here........
Your friend could consider joining the conversation 😉

The question could be: why is he concerned about the Qtc of the mid? Followed by: what is his idea on combining electrodynamic filters with electric ones and the resulting system Q? And, also important, which other considerations have to be attended to in designing a mid enclosure?

In the end, Allen is completely right. But it might take some contemplation to get to the same conclusions.
 
  • Like
Reactions: witwald
Hi Hugh, I'm noob, too. In Vituixcad, I selected the Satori MW13P-8 and changed its closed box between a q of 0.5 (pink) and 1.0 (black).

mid box q 0.5 vs 1.jpg


Looking simply at bass response and impedance, there are teensy variations (and also to phase response), but given that the midrange will be crossed over way higher than this frequency range (I assumed a second order high pass of 500hz), there's not much to sleep over here, other than the box volume for 0.5 = 7.5 litres and for 1.0, it's 2.35 litres.
 
Last edited:
T&S paramaters don't tell anything about the internal reflexions, the loudspeaker have a Q and the box have another Q and you have to keep the two mathematically combinated peaks mathematically inaudible, it is a rough starting point for a design.
Not the most important parameter IMHO.
 
Last edited:
Hi,
if all this feels very mysterious with Q and impedance and all the details, here is simplified way how to visualize/imagine how the system works and what Q is and how it relates to anything and basis how to understand all the other comments 😀

Woofer moving parts are a spring mass oscillator, like a weight at the end of a spring. Visualize spring hanging from ceiling and a some mass at the end of it, if you poke it with a finger it would start to oscillate up and down at some frequency which depends of weight of the mass and stiffness of the spring (constant). No matter how "fast" you poked it, it always ends up resonating at that particular frequency, as it is the low energy state for the system. Any other frequency movement would require constant poking as it would be doing work against the spring or mass.

Resonant system means in general, that when ever it is poked it likes to resonate as the mass is canceled by spring and it's just prone to resonate at that particular frequency. Q is simply how much damping there is for this resonance, which means how long it oscillates after being poked before settling down to rest. The more there is damping (the smaller the Q), the faster it settles down. Without any damping (losses) it would oscillate seemingly forever (very high Q). From wikipedia the Q is just how many cycles it takes the resonance to die down. Q = 1 means one cycle.

Now turn this into loudspeaker context: Think a power amplifier is finger that pokes the system, and usually frequency response is constant voltage sweep, meaning that the system is poked with same intent on all frequencies. Frequency response is basically measurement all sound that hits microphone within some time window, which basically how much and how long the cone moved when poked, so the longer the system resonates the more it seems to have output at resonant frequency, which shows as peak in frequency response if it's long enough. So the longer the system resonates it is higher Q (low damping) the higher frequency response peak there is, at the resonant frequency.

Take this into practice like so: a loudspeaker box the air inside the box is part of the spring, hence shrinking the box size reduces air volume inside making it stiffer and it stiffens the (total) spring and resonant frequency of the system goes up. If you add damping material inside the box it literally dampens the spring and Q goes down. There is also electrical damping which is the driver dampens itself at the resonance through back EMF making opposing current, so Q goes down when there is low impedance in series with the driver, and Q goes up if the impedance is increased.

To think this stuff with the mid range driver context that operates mostly above it's resonant frequency: when ever the amplifier poking stops the driver will return to rest position at the system resonant frequency and would make sound at that frequency. Since the resonance is at much lower frequency than the pass band, it would need much more volume displacement to be as loud as the passband, so even if it oscillated few cycles (high Q) before settling to rest the sound would be so low in SPL that it would make almost no sound so doesn't really matter. Oscillating less than one cycle certainly is very low output, Q < 1. This is all is just the frequency response.
 
Last edited:
  • Like
Reactions: AKSA and mayhem13
Hi MotoKok (Bob?),
Many thanks this is very helpful, thank you.......
I checked Chat GPT and got these results:
Cheers,
HD

Result from Chat GPT:


How does Q affect the size of a midrange driver enclosure and what are the results for 0.4Q, 0.5Q and 0.8Q?

ChatGPT said:​

The Q factor (or quality factor) of a driver, including midrange drivers, significantly impacts the design of its enclosure, particularly its size and type. The Q factor indicates the damping of the driver’s resonance and affects the frequency response, efficiency, and transient response of the speaker system.

Effects of Q on Enclosure Size​

  1. Q Factor Basics:
    • Q < 0.5: Low damping, typically leads to a larger enclosure. The driver will produce a broader, less controlled bass response.
    • Q = 0.5: Moderate damping, offering a good balance between size and performance. This is often considered a good compromise for many applications.
    • Q > 0.5: High damping, results in a smaller enclosure. The driver can produce tighter bass with better control but may have a limited low-frequency extension.

Enclosure Size Recommendations:​

  • 0.4Q:
Enclosure Size: Larger than average; often requires a vented or ported design to enhance bass response.
Result: A smoother, more extended bass response but potentially less precise, with some risk of resonances.
  • 0.5Q:
  • 0.8Q:
    • Enclosure Size: A moderate size; commonly used for many applications. Can work well in both sealed and ported designs.
    • Result: Balanced performance with good low-frequency extension and reasonable transient response.
    • Enclosure Size: Smaller enclosure is often acceptable; suited for sealed designs.
    • Result: Tighter bass response with better control, but potentially reduced low-end extension.

Summary​


Choosing the Q factor affects not just the enclosure size but also the overall sound characteristics of the midrange driver. Lower Q values require larger enclosures to manage resonance, while higher Q values allow for smaller enclosures with tighter bass. Understanding the desired sound profile will guide the optimal Q selection for your design.
 
  1. Q Factor Basics:
    • Q < 0.5: Low damping, typically leads to a larger enclosure. The driver will produce a broader, less controlled bass response.
    • Q = 0.5: Moderate damping, offering a good balance between size and performance. This is often considered a good compromise for many applications.
    • Q > 0.5: High damping, results in a smaller enclosure. The driver can produce tighter bass with better control but may have a limited low-frequency extension.
Lol, thanks.

(for others who may be new to this, ChatGPT has no idea.)
 
while higher Q values allow for smaller enclosures with tighter bass
Just that midranges don't reproduce bass and their useful range is usually (far) above resonance frequency, which is impacted by Q (Q has little/no influence the farther you go above fc).
So I suggest to make the enclosure big enough to keep fc (resonance frequency of speaker in the enclosure) an octave or so below woofer/midrange crossover frequency.
 
Hugh, you may as well ask chaptgpt if all solid state amps should use a symmetrical topology, cause that's what sounds best, innit?

In context of a cone midrange in a 3-way, crossing to a 10" which will be providing the bass, and the midrange highpass filter of the crossover point is way above the range where the mid enclosure size or q makes bugger all difference, except for its size.

Have a look at the mid box for one of Troels' Satori 3-ways; there's nothing fancy about it regarding q. https://www.troelsgravesen.dk/SBA-941.htm

What's more important is minimising internal reflections (use non-parallel walls and damping materials).
 
  • Like
Reactions: AKSA and witwald
Just that midranges don't reproduce bass and their useful range is usually (far) above resonance frequency, which is impacted by Q (Q has little/no influence the farther you go above fc).
So I suggest to make the enclosure big enough to keep fc (resonance frequency of speaker in the enclosure) an octave or so below woofer/midrange crossover frequency.
You should be carefull if you use a very low efficiency woofer crossed with a medium efficiency wide band midrange, the mess in the lows will be audible even with the highest slopes filters (uncorrectible design fail🙁)
 
  • Like
Reactions: stv
I am asking for a friend who is designing a three way 10/5/1 Satori speaker.
He is measuring Q with a view to the size of the midrange enclosure. He is within 5% of the SB parameters published.
The question is how much Q should be designed for, and why. 0.5? or maybe 0.75?
What would be the differences and how would this affect the size of the enclosure?
Thanks in advance; I'm a newbie here........
HD

The high pass filter for a midrange makes the Q of a well designed midrange enclosure irrelevant. This is good because the Q is for a resonance and in the presence of a resonance the midrange cone will be weakly track the input signal. So a well designed midrange enclosure is large enough for the resonance to be well below the passband and hence largely unimportant. It is also large enough so that there is enough stuffing in the enclosure to absorb the low frequency end of the passband to a reasonably high degree.

Note that chatgpt has generated misleading information which is common when it comes to technical matters.
 
  • Like
Reactions: witwald
Makes one wonder where ChatGPT is right... I grinned upon reading the answer above. But the first reply still has about all the right answers. Funny how that 'Q-voodoo' keeps on popping up from time to time.

There are plenty of audiophile subjectivists that derive pleasure from things that are incorrect or don't matter in a cold dry technical sense and they tend to chat about it a lot on the web and in audiophile publications. Chatgpt hasn't got a chance of being technically correct given that technically incorrect/misleading information came to dominate the home audio sector after the mid-to-late 70s when the audiophile subjectivist "view" was adopted by the majority of the home audio mainstream in response to the decline after the stereo boom. Nonetheless if something is technically incorrect but widely accepted as true by the technically uninformed majority it becomes to some extent true(ish) socially.
 
Thanks guys. I checked out Troels website and in truth his SBA 941 is exactly the speaker were are designing!
Effectively, he has done most of the work for us....... and his comments reflect that our choices were excellent.

Hugh
That’s an interesting summation of midrange enclosure Q and why one would select a desired enclosure size 🤔. Between AI and Troels, the universe is revealed. Lol
 
Low Q mid, when we include baffle step will have natural roll of, let say to early. Imho, first order HP filter on the mid is bad thing, because there will be hump at driver resonance fr. Then 2 nd order electrical topology is needed.With low q mid driver you end up with huge value of coil around 8mH, so you have to decide air coil (huge) or core ( distortion).

Actve x over could easy fix this, but with passive it could be problem to get proper integration with woofers.