Understanding subwoofer specification

Dave Lobster

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While reading the specifications of some subwoofers, I came across

Lower Frequency Response in Room: 22Hz at -6 dB

While the 22Hz frequency is fairly self explanatory, I'd be grateful if someone could explain what this means in relation to "at -6 dB".
 
Hello. If we look at a subs response it will start to roll off. Meaning the lower the frequency required it becomes harder for a sub to create the said frequency at a given volume. If a sub is set to say 75db and we run tones through it, it will start to produce less volume as it goes lower.

So at say 22hz, it is starting to struggle, and at 20hz it is 6db lower in volume as compared to say 80hz.
 
The spec is saying the sub's output volume (i.e. sound pressure level) at 22hz is 6db lower than the level it can reproduce for certain higher frequencies that it can reproduce the loudest. It's an indication of the flatness of the speaker's frequency response and is often quoted as a "+/-3db" deviation for a lower and upper frequency range. Is that clear?
 
Thanks for the helpful explanations. I was familiar with the +/-3dB. Is there a reason a manufacturer would choose to quote at -6dB rather than some other figure (such as +/-3dB)? Am I correct in thinking that 3dB is representative of a typical minimum discernible volume difference for human hearing?
 
With subs its more common to sack the -3db reading as the lower fr looks to be lower when quoting -6. As it makes it look like the sub goes lower.

3db is roughly twice the given output perception.

So say 100hz at 90db you would certainly notice the difference if 100hz was played at 93db.
 
You need a much more powerful sub than that one OP.
 
Still if there was one post I wanted my Wife to see...... :devil:
 
Thanks for the helpful explanations. I was familiar with the +/-3dB. Is there a reason a manufacturer would choose to quote at -6dB rather than some other figure (such as +/-3dB)? Am I correct in thinking that 3dB is representative of a typical minimum discernible volume difference for human hearing?
The spec is based upon the frequency response of the subwoofer. Ideally you want the subwoofer to reproduce a perfectly flat response. No subwoofers can do this, and you dont actually want a flat response from the sub itself, rather you want a flat response in room. Low frequencies enjoy room gain, which boosts low frequency output, so you actually want a subwoofer to roll off at the low end to account for this boost to give you a flat end frequency response when listening to the system.

The stated response is telling you at what point the response is dropping off from the range where its response is flat. Rather than saying it starts to roll off at say 40Hz, they will instead state a -3 or 6 db figure so they can make the subwoofer look like it goes lower, but also so you can get an idea of where its output is actually rolling off and to what degree. If you know about your room gain properties, it can also help you choose a subwoofer suitable for your room. Almost no one has a true idea of this. To put things into perspective, every 3dB increase in output requires a subs amplifier to double its output power.

You will see different manufacturers state different figures, basically playing with numbers, as all manufacturers do. If you see -6 used, this will be at a lower frequency than a -3 figure, so it makes the subwoofer seem like it goes deeper. If you see in room stated, you know the subwoofer can only hit this frequency response with the help of room gain as well. People will argue as to whether a sub has been designed with room gain in mind, or if numbers are being jumbled to make a product look better than it is. In reality, unless you really know your stuff so you can pick the data apart and then use it to compare one product to another, then the figures are simply a rough guide, and not necessarily representative of how good or bad a subwoofer is.
 
How do you work that out ?
I can post some really boring graphs and charts up if you like?

Actual power required is dependant on the driver used and the cabinet its employed into. The OP tells us nothing of the subwoofers actual output capability, only its frequency response, and it doesnt even stipulate and anechoic, ground plane, or in room factor for for that frequency response.
 
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I can post some really boring graphs and charts up if you like?

Actual power required is dependant on the driver used and the cabinet its employed into. The OP tells us nothing of the subwoofers actual output capability, only its frequency response, and it does even stipulate and anechoic, ground plane, or in room factor for for that frequency response.

No thanks - I've got REW for that ;)

...but seriously I think I now understand that aspect from your more recent posts :)

Jim
 
No thanks - I've got REW for that ;)

...but seriously I think I now understand that aspect from your more recent posts :)

Jim
Just bear in mind REW only tells you about your room, and a measured subwoofers in room response. It can be used to extrapolate other useful data about your sub, like distortion and output capability in room, but it wont tell you things like how much power is being used or needed for example.
 
Just bear in mind REW only tells you about your room, and a measured subwoofers in room response. It can be used to extrapolate other useful data about your sub, like distortion and output capability in room, but it wont tell you things like how much power is being used or needed for example.

Thanks - I appreciate that - at the moment I'm trying to get my sub tuned with it's limited placement options and also looking at using a dual sub config. with both subs basically in the same location - possibly stacked or side by side... both subs are DF and an upward facing driver isn't an option due to "Pet Involvement" :facepalm: - both subs are Tannoy TS10 models.
 
Thanks - I appreciate that - at the moment I'm trying to get my sub tuned with it's limited placement options and also looking at using a dual sub config. with both subs basically in the same location - possibly stacked or side by side... both subs are DF and an upward facing driver isn't an option due to "Pet Involvement" :facepalm: - both subs are Tannoy TS10 models.
Stacking dual DF subs isnt an issue as long as you make sure the top one doesnt move, assuming there is no fixing kit solution available. There isnt for your subs.Having a top one firing at the bottom one wont be an issue. Stacking, while it has benefits, I have tested a system with a full stacked system in one corner that still didnt have as a smooth a response over more listening positions as split dual subs had. Stacking drives the room in a certain way that can give very good performance, but rooms can still be unpredictable, and if your response issues arent related to height modes, stacking wont make them go away.
 
Stacking dual DF subs isnt an issue as long as you make sure the top one doesnt move, assuming there is no fixing kit solution available. There isnt for your subs.Having a top one firing at the bottom one wont be an issue. Stacking, while it has benefits, I have tested a system with a full stacked system in one corner that still didnt have as a smooth a response over more listening positions as split dual subs had. Stacking drives the room in a certain way that can give very good performance, but rooms can still be unpredictable, and if your response issues arent related to height modes, stacking wont make them go away.

Thank you - very useful to know about the need to immobilise the top sub.

Any thoughts about "side by side" with both on separate marble plinths and the possibility of using both with an Anti-Mode ?
 
Thank you - very useful to know about the need to immobilise the top sub.

Any thoughts about "side by side" with both on separate marble plinths and the possibility of using both with an Anti-Mode ?
The will act as a single dual driver sub effectively, but they need to be gain matched as per the post in your other thread.
 
Thanks AudioVisualOnline for the explanation of "in room".

I'm somewhat surprised that the frequency response of many subs at -6dB is only in the order of 10Hz lower than that of 'normal' speakers. e.g 37Hz for KEF R700 at -6dB vs. 26Hz for the R400b sub. Admittedly, the 11Hz difference is a substatial percentage difference, but if I understand it correctly, this is less than an octave.

Do such subs really make a noticeable difference?
 
Thanks AudioVisualOnline for the explanation of "in room".

I'm somewhat surprised that the frequency response of many subs at -6dB is only in the order of 10Hz lower than that of 'normal' speakers. e.g 37Hz for KEF R700 at -6dB vs. 26Hz for the R400b sub. Admittedly, the 11Hz difference is a substatial percentage difference, but if I understand it correctly, this is less than an octave.

Do such subs really make a noticeable difference?
Frequency response alone doesnt tell you a great deal, it would be akin to buying a car blind based on nothing more than its top speed. The information gives you something to work with, but without more information its actually not a whole lot of use.

A speaker thats rated down to say 30Hz in room @ -6 might only be capable of 80dB max output at full power. If a subwoofer can go to 20Hz @ -3dB in room with a max output of say 100dB, then the reality is the subwoofer outputting frequencies the speaker cant even manage, and at crazy output levels comparatively speaking. You need to double input power for every 3dB more output you want from a speaker, so you can see what 20dB more output would take. If the speaker was using 50 watts for that 80dB of output for example, then the figures alone tell you theres no way it could ever hope to achieve that, even without going to lower frequencies. The end result is that a subwoofer just reproduces low frequencies in a different way.
 
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