"Fast" woofers.

[PDS]

I'm considering adding some subwoofers to my system, which consists of LRSs, a Minidsp SHD, and an Adcom 535II amp. The system sound very good in my smallish room, roughly 11'5", 13'6", 8'6". The LRSs are a "fast" sounding speaker. There is very minimal resonance type artifacts. Many people say that it's hard to match subs to them, claiming that either one should use a small sub, a dipole sub..... Well, I'd prefer to not put more boxes in my room, and so I'm considering buying some Fi Audio 18" woofers spec'd for an infinite baffle installation, using a manifold in the floor to mount the woofers. On the one hand, I've been told that smaller woofers, especially with a feedback circuit, will mesh better than bigger speakers. On the other hand, some have told me that a modern woofer with a good motor won't be a problem. I expect I'd cross over at about 60hz. Thoughts? Do modern small woofers really sound "faster" than bigger woofers? I guess that means that they'd have better transient response?

 

[AdamG]

Welcome Aboard PDS.

 

[alex-z]

"Fast" subwoofers are not a thing, bass wavelengths are long and therefore take time to propagate, 12.5ms at 80Hz, 25ms at 40Hz, etc. All subwoofers are slow by nature. Ported vs sealed vs infinite baffles are not changing the speed of the driver, but rather how it interacts with the room.

The primary performance factors of a subwoofer are smooth frequency response and low distortion. If you can achieve those 2 things, it will sound good. Infinite baffle subs are a good solution for someone with power to spare and EQ. Group delay and resonances cannot be entirely discounted, but those are easy things to get right simply by designing the correct enclosure.

I assume you have seen the ASR review of your Magnepan LSR? You probably want to crossover at 80 or 100Hz, distortion rises quickly in the bass region.

 

[MZKM]

Data-Bass has measurements, an 18” Rythmik is not going to be audibly “slow”, so if they can do it, others can to.

A lot of the time people say smaller subs are “faster” because they don’t have much extension. The deeper the bass, the more room modes and reverberation you will have. Take an 18” sub and cut the bass below 30Hz, it will sound “faster” and “tighter”.

The main thing you want it to time/phase align your subs at the crossover point, which is not an issue if you use the MiniDSP.

 

[PDS]

I appreciate the comments!

By "fast" I meant not playing higher frequencies but being able to start and stop quickly. Some subs, for example, have a "one note" quality, all of the bass sounds similar, no matter what instrument makes the sound. I expect that MZKM is right, and in many cases room modes cause the problems. Another way to say this is, does what Danny says in this video make sense, or is it more snake oil?

Regarding the LRSs, all I can say is that in my room they sound much better than Polk LSI15s. My wife thinks so too, and she has no idea about the different technologies, price points...., and she has better hearing.

 

[alex-z]

Subs with "one note" quality are simply bad subwoofers, not the fault of the sealed/ported/infinite baffle design. Room issues can also play a huge role, hence the importance of good placement, multi-sub configs, and EQ.

A lot of what Danny says is pure non-sense. Good crossover designer, but when he strays outside his realm of expertise it is painfully obvious.

The ability of a driver to stop/start is called the damping factor, and the ratio is determined by the impedance of the speaker vs the amplifier impedance. Modern amps have such low output impedance this is a complete non-issue.

 

[PDS]

That's good to know. Thanks!

 

[GDK]

I was kind of hoping this thread would be about that gorgeous dog in your avatar...

 

[PDS]

 

[Erici]

Sweetchaos has put together an excellent page on subwoofers:

https://www.audiosciencereview.com/forum/index.php?threads/subwoofer-comparison.20494/

 

[Erici]

Erin has also tested many subwoofers:

https://www.erinsaudiocorner.com/subwoofer_testing/

 

[ppataki]

This is covering this topic pretty well:
https://www.audiosciencereview.com/forum/index.php?threads/step-response-question.15375/

the tldr version:
1cm measurements about my SVS SB-1000 and my DIY sub based on Dayton Audio RSS315-HF-4 (both are sealed boxes and 12")

SVS:

Dayton DIY:

As you can see there is a dramatic difference in the fall time meaning that the Dayton comes to a rest way faster than the SVS
So there can indeed be huge differences between speakers when it comes to 'speed' (which is not speed but transient response really)

 

[Frgirard]

The boxe resonance.
Fast woofer? Test in the same box, same crossover & in the same location.

 

[witwald]

The ability of a driver to stop/start is called the damping factor, and the ratio is determined by the impedance of the speaker vs the amplifier impedance.

Some quotes from "Damping, Damping Factor, and Damn Nonsense", by Dr. Floyd E. Toole (AudioScene Canada, February 1975, pp. 16–17) may help to shed some light on this issue:

"The first, and perhaps the most important, observation to be made regarding damping factor in amplifiers is that it has really rather little to do with the damping of anything."

"The damping factor (DF) which appears in the spec sheets of hi-fi amplifiers is an expression of the ratio of the nominal amplifier load to the internal impedance of the amplifier (in reality this impedance is complex but normally it is blindly assumed to be resistive). For example, taking a nominal load of 8 ohms, an amplifier with an internal impedance of 0.08 ohms would be said to have a damping factor of 100."

"Another way of saying all this is that tight, incisive, well-damped sound is the result of good speaker design not a high amplifier damping factor."

 

[witwald]

As you can see there is a dramatic difference in the fall time [between the SVS SB-1000 and a DIY sub based on Dayton Audio RSS315-HF-4] meaning that the Dayton comes to a rest way faster than the SVS.
So there can indeed be huge differences between speakers when it comes to 'speed' (which is not speed but transient response really)

The Thiele-Small parameters of the RSS315-HF-4 are such that it has a rather high F3 (–3 dB cut-off frequency) when placed in a sealed enclosure, of around 50 Hz. That's why its step response function decays so much faster than that of the SB-1000, which is much more extended in the low-frequency range.

It should be kept in mind that the step response function of a subwoofer can generally be obtained from a knowledge of the subwoofer's frequency response function. It's that simple. If two subwoofers have the same upper and lower cut-off frequencies, and the same low-frequency and high-frequency roll-off rates, then their step responses will be identical, irrespective of their size (e.g. 8", 10", 12", 15", 18"). Of course, that assumes that they are linear transducers, but for smaller input signals that's usually not an issue.

 

[tuga]

Some quotes from "Damping, Damping Factor, and Damn Nonsense", by Dr. Floyd E. Toole (AudioScene Canada, February 1975, pp. 16–17) may help to shed some light on this issue:

"The first, and perhaps the most important, observation to be made regarding damping factor in amplifiers is that it has really rather little to do with the damping of anything."

"The damping factor (DF) which appears in the spec sheets of hi-fi amplifiers is an expression of the ratio of the nominal amplifier load to the internal impedance of the amplifier (in reality this impedance is complex but normally it is blindly assumed to be resistive). For example, taking a nominal load of 8 ohms, an amplifier with an internal impedance of 0.08 ohms would be said to have a damping factor of
100."

"Another way of saying all this is that tight, incisive, well-damped sound is the result of good speaker
design not a high amplifier damping factor."

I agree that Damping Factor may be a misleading, perhaps worthless metric but wouldn't you agree that amplifier/speaker interaction issues with high output impedance amplifiers are real?
The dummy load used by JA when testing amplifiers seems to indicate that the combined amplifier/speaker response can be greatly affected depending on the output impedance of the amplifier.

PrimaLuna ProLogue Premium, 8 ohm tap, frequency response at 2.83V into: simulated loudspeaker load (gray), 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta), 2 ohms (green) (1dB/vertical div.).
https://www.stereophile.com/content/primaluna-prologue-premium-integrated-amplifier-measurements

Modified Kantor speaker simulator, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).
https://www.stereophile.com/content/real-life-measurements-page-2

 

[Willem]

What people call slow bass is almost always interaction with the room, i.e. room modes lingering on. There are three cures: bass traps (large and ugly), dual/multiple small subs instead of one large sub, and dsp room equalization. The combination of multiple subs and dsp eq is usually highly effective. There is a lot of literature on this, but see here for starters: http://archimago.blogspot.com/2020/05/musings-measurements-subwoofers-to.html

 

[PDS]

Well, I'm happy to use multiple subs, and I use REW for positioning, along with Dirac 3.

 

[tuga]

What people call slow bass is almost always interaction with the room, i.e. room modes lingering on. There are three cures: bass traps (large and ugly), dual/multiple small subs instead of one large sub, and dsp room equalization. The combination of multiple subs and dsp eq is usually highly effective. There is a lot of literature on this, but see here for starters: http://archimago.blogspot.com/2020/05/musings-measurements-subwoofers-to.html

Not an issue with subwoofer because the tuning frequency will be below 30Hz but what about bass reflex particularly in small-ish loudspeakers, couldn't that be a cause for perceived "slow" bass?

 

[vavan]

Not perfect now, but better

right, it just became faster lol