Group delay improvements 24" vs 32" vs 50" sealed Subwoofers

[CameronHamill]

Hi Members,

 

Just analysing the group delay on this 24" Subwoofer tested by Josh from data-bass.

"DIY Stereo Integrity HS-24 Sealed Group Delay" 23.0 ft3 cabinet.

From 10 Hz through to 120 Hz the group delay is less than one cycle for this Subwoofer.

Incidentally one cycle in milliseconds for each of these Hz frequencies is:

10 Hz (100ms)

20 Hz (50ms)

30 Hz (33.33ms)

40 Hz (25ms)

50 Hz (20ms)

60 Hz (16.66ms)

70 Hz (14.28ms)

80 Hz (12.5ms)

90 Hz (11.11ms)

100 Hz (10ms)

120 Hz (8.33ms)

 

So that tells me this subwoofer is quite fast.

 

My question is how much faster might a 32" or 50" Subwoofer be across the 10Hz to 120Hz range?

 

Ascendo talks about their 24" subwoofers as having good group delay and are suited to movies and music.

They also have a 32" and 50" version targeted for home and commercial cinema. Again they state the group delays are even better.

 

Deep Sea Sound has a 24" sealed sub as well. They don't mention the group delay specifically but they mention it's a fast sub.

 

Basically my point is let's say a 24" sealed sub will generally have good group delay figures. How much better might a Mach 5 32" be or one of these Ascendo 32" or 50" ones be?

 

I'm mainly interested in music more than home theatre but I'm interested in the fastest subwoofers with the largest woofers.

 

Edit:

 

I just saw on YouTube the owner of Ascendo state his 50" subwoofer can achieve a group delay of 6ms at 30Hz. Lol. That's incredible.

 

The video is titled: "50" SUBWOOFERS? Talking Subwoofers w/ Ascendo Immersive Audio" on the Spare Change Podcast channel. From the 16 minute mark on the video.

Edited March 17, 2021 by CameronHamill

[Kyle]

The size of the driver does not make it fast or slow. In this case, you have low delay because its a sealed box. The HS-24 would perfectly fine for music, but you do need to couple it with a large box because of its higher Q of about 0.5. A big sealed box would be perfect for this driver.

Also, to understand why group delay is a much more apparent with a port / horn (compared to just a driver in a sealed box) because the port, unlike the driver acts like a spring mass system. When you apply a voltage to the driver, its ridge and starts to accelerate more or less as a rigid body. But when you apply a force to a spring-mass, then it acts differently compared to the input signal. I'm honestly not sure how group delay is perceived in terms of subjective sound quality -- I hope some others chime in.

[Ricci]

Hello Cam,

To add a bit more to Kyle's post, group delay is WAY over rated when it comes to subwoofers. Lower is better make no mistake but the perception of it at low frequencies has not been shown to be very audible unless it gets very bad. Studies have shown that as frequency decreases we are more tolerant of large GD and it is much more difficult to distinguish. Personally I don't worry about it below 30Hz. 20ms at 50Hz is probably not worth worrying about. 20ms at 200Hz on the other hand should be quite audible. This is why group delay is often represented as a percentage of a cycle vs frequency. 

With subs I only have concern if the delay is not uniform (spikes, sudden increases in certain frequency bands above 30Hz, the delay exceeds 1.5 cycles > 30Hz, or a combination of both. If the GD is relatively smooth over the primary bass range and remains below 1 cycle I don't worry about it. Room acoustics tend to do horrible things to the time response at the listening position that dwarf the native GD of the sub anyway. 

[SME]

I'll just add that subwoofer responses are mostly minimum phase (MP).  What this is implies is that the magnitude frequency response (FR) essentially *determines*, the phase and group delay response.  They are mathematically interchangeable.  If you have a MP system and you have perfectly flat FR, then the group delay (GD) will be perfect *by definition*.  Real subs always have at least a low-end roll-off somewhere, and you will usually see group delay rise and peak in the area of the roll-off transition.

The most notable exceptions to "mostly minimum phase", where subs alone are concerned, is when you have multiple radiators (like a driver and its vent) that are physically far apart.  Other potential causes are design / build quality problems like resonating panels, badly designed vent systems, etc.

Now, once you cross over (XO) to speakers, the resulting response is likely not MP anymore, at least for frequencies in the XO region, because of the physical separation involved as well as some excess GD from the summing in the XO itself.  Likewise, the room itself has a substantial effect on the measured responses, and the contributions may or may not be MP, depending on the configuration, frequencies considered, measurement location chosen, etc.   Note that in general, in-room FR from a sub varies *a lot* vs. location as a consequence of the acoustics.

With all that said, what makes bass sound "fast" or "tight" is mostly a question of *neutrality* across the low frequency spectrum, and that depends at least as much on the room as the sub.  If the sound has audible resonance at some mid-bass or sub frequency, then it will tend to overhang or "boom" there.  Small listening rooms in particular often have strong standing wave resonances that can contribute a lot of slop and boom to the sound.  These resonances can quelled or eliminated with skillful application of EQ (which is typically MP, by the way), but results vary a lot depending on the particular approach.  The best sounding systems are almost always tuned by hand beyond some point.  You can also try using an auto EQ product like Dirac, Trinnov, Audyssey, etc.  I won't endorse or recommend any of these, but they are popular and offer rudimentary hand-tuning functionality.  I'm working on my own auto EQ technology that I believe to be capable of achieving outstanding low frequency neutrality in a variety of listening rooms, but it's not ready for public release yet.

Sorry I can't offer more specific tips, but bass quality in small listening rooms is fundamentally tricky, and the particular sub choice is probably not as important as other factors.  The main thing with choosing subs is ensuring you have enough headroom for the SPL you want for the frequency range you want, and ensuring the FR (outdoors) is reasonably clean to a high enough frequency, something like 1/2-to-1 octave above where you intend to cross it over.  If you are looking at 24" and 30" subs, enough headroom is not likely to be a problem unless you want it *really really* loud.  Less compression and lower distortion at medium output levels are also a plus.  Don't ignore or skimp on the speakers either.  Bass doesn't stop at 100 Hz, and bass up to 200 Hz and beyond can be very tactile if the sound is neutral enough to perceive it.  Too many systems with big subs are woefully inadequate in the crucial upper bass region because the are too small to keep up with the subs.  This is all the more important for a "tight" sound.

 

[Camplo]

Hello, I'm new to the forums but not to loudspeaker design....Its funny how many people don't know what the think of group delay, what it is and what it means to Sound Quality....I'd like to believe that I am one of the first people in recent times, within the DIY community to make connection between the Group Delay Curve and the Time to Peak energy curve...the trend of both lines. 

 

When it comes to describing a sub as tight...No one is ever specific enough of what they are talking about...imagine that....If I say I want a tight woofer....am I speaking of time to peak energy or time to -25db energy? Both ..... Now that I have made known the to aspects of Time distortion....it must be made known that inside of a "room"...the room dominates all of these specs (Phase, FR, GD and Decay times).....phase can cause strange anomalies.....you can only expect direct energy measurements to be more faithful in a faithful within a nearfield situation but within 1 meter measurements of my current home system incorporating dual 12"s, I have anomalies non the less....as if near field didn't matter lol.

 

Regarding driver size....everyone that the epitome of Sound Quality is low excursion......See it move....see it distort. So a large driver needs to move less in order to achieve the same spl as  a smaller driver thus distortion is less.....Multiple drivers can be using to increase accumulated surface area for a range of spectrum. These multi drivers boost efficiency and drive down excursion resulting in the same lowering of distortion.

 

If your driver only has to move a few MM to achieve desired output, you no longer have to worry about thd or dynamic compression/power compression

 

Quote

 Bass doesn't stop at 100 Hz, and bass up to 200 Hz and beyond can be very tactile if the sound is neutral enough to perceive it.  Too many systems with big subs are woefully inadequate in the crucial upper bass region because the are too small to keep up with the subs.  This is all the more important for a "tight" sound.

Agreed, I've been taught by the guys at Diya and over and over its touted that a 15" is the apex midrange. I also agree with much thats said in the above post, just wanted to add my 2 cents 😃

 

Oh ya! another thing! vented boxes tuned lower, will have lower group delay in the areas away from the tuning note. The lower you move the tuning note aka Fb.....the better group delay is in the area in perspective to the tuning note....I'm not looking at horn resp right now but I think the same trend will happen with Sealed boxes as you move the Fc lower via Box size....