Sub Sound Quality

There are a couple of things that come to mind when people talk about a sub's Sound Quality.

1. What is sub Sound Quality'?
2. Without the right conditions', does it make any sense to compare the sound quality of one sub versus another?
3. If you can't directly compare sub sound quality, what should you look for to determine if the sub has good sound quality?

I'll take a stab at this at answering these based on what I've learned from AV forums. I'd like to hear other opinions as well.

***Note, the below assumes you are comparing subs with similar output capabilities.

1. What is sub Sound Quality'?

To me, sound quality is just the subs ability to reproduce a reference (e.g. flat) frequency response with minimal distortion. It needs to do this at the output you desire, extend to the frequency you desire, and do all this while remaining consistently 'flat' regardless of dynamic volume changes in the content (music or HT). Sound Quality is based off a Reference (flat frequency response), and NOT based on Preference (e.g. I like more midbass slam, or I like more ultra low frequency). A flat frequency response is the best Sound Quality' metric because it reproduces the content exactly how the content producer (director, artist, etc.) wanted you to hear it.

2. Without the right conditions', does it make any sense to compare the sound quality of one sub versus another?

The biggest impact on sound quality for a sub is the ROOM. Every room will wreak havoc on a sub's frequency response. If you take different subs, put them in the exact location in the same room and level match the subs, and then try to compare the subs with their natural in room response, any differences you hear in sound quality' between the subs are because each sub will have a different frequency response based on how it interacts in the room. It has nothing to do with the subs ability to reproduce a flat frequency response.

Since the subs aren't FR matched, the SQ comparisons will be largely influenced by the different FR's each sub exhibited. So when the claim is made that one sub has a better SQ over the other, it's primarily because of the reviewers preference for the FR of that particular sub in that particular room, not necessarily it's SQ.

Here's an example that may make more sense: Blind fold the listener. Tell him that you're testing 5 different subs. Take 1 sub and hook it up to a 12 band sub EQ. Play the same song/movie 5 different times. Each time, adjust the FR bands slightly. At the end of the comparison, the listener will claim that the first time perhaps it sounded tighter, the second time perhaps it had great low end extension, the third time perhaps a lot of mid bass slam, etc. etc. At the end of it, the listener will pick a 'perceived sub' that had the best sound quality. They are really just picking the FR he preferred as set by the EQ. This is why it is important to FR match the subs to really make it an apples to apples comparison.

So unless you level match AND try to EQ all the subs to the flattest frequency response that their able to achieve, you can't really compare the sound quality (the subs capability to play flat') between the subs.

Let's suppose you do this with some sort of EQ (audyssey, etc.) to make it as flat as possible, better sound quality' will start to show its head in the following areas based on a given output level:

- Flat Response: The sub with the flattest response will contribute the most to achieving the best sound quality.

Assuming that they all are able to get relatively flat frequency responses, other things start to contribute to sound quality;

- Extension: some subs may extend lower than others based on how they handle the EQ, assuming that we can hear or feel the difference of that lower extending sub, that sub may sound' better
- Distortion: if the subs have the same extension, one may have lower distortion than another making it sound' better
- Consistent frequency response: I don't really know how you would measure this, but when you play back music or HT content, any difference in sound could be attributed to how the sub maintains its flat' frequency response based on the sources dynamic content...perhaps contributing to a better sounding' sub.

Having said all that, it will take an incredible amount of time trying to get these right conditions' and most will NEVER try and do this test, and if they do, without special equipment, environment, etc. the margin for error is high. So if you can't do that, then I'm not sure it even makes sense to compare the sound quality between subs

3. If you can't directly compare sub sound quality, what should you look for to determine if the subs has good sound quality?

Since the biggest driver to a subs sound quality is its capability to play a flat frequency response, and the best way to get a flat frequency response is via EQ and multiple subs, should we then look at how a sub can handle EQ? A subs ability to handle EQ is directly related to its headroom as using EQ will reduce its headroom. When you reduce headroom, you potentially can't achieve the output you want and your distortion rises. So a sub with more headroom can handle EQ better and can get us a flatter frequency response. How do you tell if a sub has more headroom than others? I believe output and amplifier power is a good indication. What I mean by this is that if a sub can hit 125db and you normally never listen to it over 115db, you've got that extra headroom to eq to a flat response while maintaining clean output at the levels you want. The best way to add headroom is to buy multiple subs.

You can also look for the physical characteristics like xmax, xmech of the sub to determine how it will be able to handle those ultra low frequencies. And yes, (dare I say), you can look at the close mic and ground plane measurements as well (Stay on topic please).

I'm sure there are a ton of other factors, but I think this covers the major ones. Does this make sense?

EDIT: If great Sound Quality for a sub is just a function of how well it can produce a flat frequency response, than it would seem that you don't actually need to 'hear' the sub to determine its sound quality. All you need is good data about some key measurements (mentioned above).

Thanks.

Yes, you are right that different people will have their own preference when it comes to the sound they like to hear. And no one can debate someone's preference (and win), that's for sure.

Unfortunately, preference has no reference; so comparisons from a preference perspective are even more difficult (I'm not suggesting that you're saying we should compare them this why...just sayin).

I too am a bass head. My subs are about 7db hot. However, I do like a flat response for my sub frequencies (10hz to 80hz) and then level off for the rest of the audible spectrum...

I've often that this as well...but have never determined what the 'inherent sound qualities' are?

Can you put more color around what you mean by this?

If 4 Lava's and an AS-EQ1 get you a flat response at the output you want it and extends to the frequency you want it to, then what else would you want from a sound quality perspective?

What I think typically happens is that 4 Lava's don't give you the output you want especially at lower frequencies. That's where upgradeitis sets in, and your back to the forums.

That's a great comment about REW.

The question is, what things can't we see with software like REW that impact sound quality? I don't know, but would like to if someone knows...

Do those subs have similar output capability and similar extension?

I understand the point you're trying to make...I've always thought that way myself. But have never been able to figure out what makes them sound different?

Perhaps this is a better question (sorry if this comes off as Nietzsche like):

If two different subs have the exact same output at all frequencies, have the exact same frequency response, have the exact same distortion levels, and are able to maintain these characteristics exactly the same based on dynamic output changes....will they sound exactly the same? And if not, what makes them sound different?

Just as an FYI, my point of this thread is about learning, not about defending...

That's a good link...and I did watch the Complex Sound section.

But, I'm not sure how that specific example applies to subs. In other words, they talk about how different instruments can play the same frequencies, but they all sound different. Your reason above about multiples and different proportions of those frequencies demonstrate how the instruments/voice sound different makes sense.

But for subs, they are just replicating frequencies they are told to replicate from the source content. In other words, they don't have a choice to sound different like instruments/voice. In my theoretical example above, if both subs (with different drivers, cabinet designs, amplification) have the exact same frequency response, output, etc. etc., then any multiples of all those frequencies should all sound the same I would think.

Maybe to drill down even further...

Does a 50hz sine wave of two different subs (with different drivers, cabinet designs, amplification), played at the same output, in the same location (etc. etc.) sound exactly the same? And if not, what makes them sound different?

Sound preference and sound quality are different things.

A flat frequency response is the Reference for sound quality. There are an infinite number of sound preferences, but only one reference.

When comparing sub sound quality, if you aren't comparing from a reference point, then the comparison doesn't really make sense.

Typically, when people make comments about how this sub has better SQ than this sub, they are comparing from their own sound preference, not sound quality reference (flat frequency response). In fact, I would go on to say that most have never even heard a true flat frequency response, let alone remembering how flat' sounds and comparing it with another sub.

So I guess I'm back to one of my questions, given that we'll likely never have the time or tools to get the correct environment to make a valid sound quality comparison, does it even make sense to make compare sound quality between subs or should you look to other characteristics of the sub that help indicate that it has the capability (flat response, headroom, output, extension, etc.) to have good sound quality?

I did cover the room in my first post. See my answer to the second question.

Great point. Group delay as I understand would certainly play a part in SQ. It contributes to the 'tightness vs loose' sound of that of a sub. Perhaps the term 'stopping on a dime' is also related to group delay.

In laymen's terms, how does power compression affect SQ?