How Audioholics Determines Bass Output Ratings in Subwoofers

[westcott]

At what distance was that sub measured? Are those RMS or peak #s? What brand of sub is it? I may request a review sample if its a current model and have it shipped to Josh for testing.

I will have to dig up the article, if it is still available on their site but I am sure I can get the data to you on testing procedures by Tom Nouissane. It is made by Klipsch and yes, it is discontinued but I am sure if you talk to Amy, she might be able to locate one for testing for you.

http://www.nousaine.com/pdfs/behindthenumbers.pdf

Here is a link to his testing procedures. They are near field measurements and uses a maximum length sequence signal generated by a DRL Labs signal generator which eliminates all frequencies above 200 Hz thereby reducing secondary reflections. Measurement are taken every 1/3 octave through out their range. The subs are tested in a 7000ft3 room and placed 2 meters from the optimal corner. All measurement are averaged SPLs. A 1 watt (2.83volt) pink noise input is used. Since the signals are averaged, I have to assume they are given in RMS. (No sense publishing the numbers if they are not, right?)

 

[gene]

I will have to dig up the article, if it is still available on their site but I am sure I can get the data to you on testing procedures by Tom Nouissane. It is made by Klipsch and yes, it is discontinued but I am sure if you talk to Amy, she might be able to locate one for testing for you.

http://www.nousaine.com/pdfs/behindthenumbers.pdf

Here is a link to his testing procedures. They are near field measurements and uses a maximum length sequence signal generated by a DRL Labs signal generator which eliminates all frequencies above 200 Hz thereby reducing secondary reflections. Measurement are taken every 1/3 octave through out their range. The subs are tested in a 7000ft3 room and placed 2 meters from the optimal corner. All measurement are averaged SPLs. A 1 watt (2.83volt) pink noise input is used. Since the signals are averaged, I have to assume they are given in RMS. (No sense publishing the numbers if they are not, right?)
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Unfortunately Tom's measurements are all done in-room so its difficult to impossible to correlate them with outdoor groundplane.

We have Klipsch's latest sub offering in for testing. We don't test discontinued product. We know how Klipsch rates max output of their subs so it will be interesting to compare their spec with our test results. I have to credit Klipsch for how they spec their in-room output as its partly how I came up with our in-room projected outputs based on outdoor groundplane technique.

 

[westcott]

Unfortunately Tom's measurements are all done in-room so its difficult to impossible to correlate them with outdoor groundplane.

We have Klipsch's latest sub offering in for testing. We don't test discontinued product. We know how Klipsch rates max output of their subs so it will be interesting to compare their spec with our test results. I have to credit Klipsch for how they spec their in-room output as its partly how I came up with our in-room projected outputs based on outdoor groundplane technique.

I don't believe Tom has tested their latest subwoofers but the RT12D design that came afterwards was no match for the RSW15. Tom's testing in some ways is more conservative than your testing procedure because the sub placement is geared more for a flat frequency response in his room, rather than all out reinforcement with corner placement (and you have to admit, thats a lot of cubic feet). There is a list floating around that lists all the subs he tested and how they compare against one another. Since all were tested with the same criteria, it does provide a reference point for which they can be fairly compared against (one another). May be something you may want to reexamine. As we both know, flat frequency response is the ideal goal.

 

[gene]

Tom's testing in some ways is more conservative than your testing procedure because the sub placement is geared more for a flat frequency response in his room, rather than all out reinforcement with corner placement (and you have to admit, thats a lot of cubic feet). There is a list floating around that lists all the subs he tested and how they compare against one another. Since all were tested with the same criteria, it does provide a reference point for which they can be fairly compared against (one another). May be something you may want to reexamine. As we both know, flat frequency response is the ideal goal.

I'm sorry but your dead wrong about this. An In-Room measurement can NEVER be more conservative than an outdoor groundplane measurement which takes the entire room out of the equation. It's impossible to get a flat frequency response at bass frequencies in anything but an infinitely large room (anechoic chamber, room without echoes). You can accurately measure a subs frequency response nearfield in a room if its not ported and has only one driver but you can't get Max SPL in such test conditions without over driving the mic.

 

[westcott]

I'm sorry but your dead wrong about this. An In-Room measurement can NEVER be more conservative than an outdoor groundplane measurement which takes the entire room out of the equation. It's impossible to get a flat frequency response at bass frequencies in anything but an infinitely large room (anechoic chamber, room without echoes). You can accurately measure a subs frequency response nearfield in a room if its not ported and has only one driver but you can't get Max SPL in such test conditions without over driving the mic.

I must have missed the outdoor measurement statement. I though you were adding several dB to your equation to make up for corner placement/reinforcement that Tom is not doing.

"Choosing a Common Subwoofer Distance
So we now know that simply adding +12dB to our 2 meter groundplane SPL data will give us an equivalent corresponding corner-loaded room output at 2 meters. Again, this does not factor in any room resonances which varies from room to room depending on room dimensions, position of the listening seats and room furniture, ceiling contribution, and the quality and kind of construction of the room.

It is reasonable to assume the subwoofer will be (on the average) at a fixed distance of 4 meters from the listening area.

So in order for us to translate our 2 meter groundplane data to a corresponding 4 meter corner-loaded approximation, we can simply add 6dB (+12dB for two additional surfaces and -6dB for doubling of distance) to our SPL data. IE. If a sub measures 110dB 2 meter groundplane, the corresponding in-room output if the sub was corner-loaded would be roughly 116 dB at 4 meters."

 

[gene]

I must have missed the outdoor measurement statement. I though you were adding several dB to your equation to make up for this.

"Choosing a Common Subwoofer Distance
So we now know that simply adding +12dB to our 2 meter groundplane SPL data will give us an equivalent corresponding corner-loaded room output at 2 meters. Again, this does not factor in any room resonances which varies from room to room depending on room dimensions, position of the listening seats and room furniture, ceiling contribution, and the quality and kind of construction of the room.

It is reasonable to assume the subwoofer will be (on the average) at a fixed distance of 4 meters from the listening area.

So in order for us to translate our 2 meter groundplane data to a corresponding 4 meter corner-loaded approximation, we can simply add 6dB (+12dB for two additional surfaces and -6dB for doubling of distance) to our SPL data. IE. If a sub measures 110dB 2 meter groundplane, the corresponding in-room output if the sub was corner-loaded would be roughly 116 dB at 4 meters."

We are measuring the sub outdoor via 2 meter groundplane first to get the most accurate response. We are then adding +6dB to those measurements to simulate the output one could expect if the sub was corner loaded in room and sitting 4 meters from the sub. This is actually how Klipsch comes up with their max SPL spec for their subs. They do it at 30Hz whereas we are doing it from 25Hz to 80Hz.

 

[westcott]

I'm sorry but your dead wrong about this. An In-Room measurement can NEVER be more conservative than an outdoor groundplane measurement which takes the entire room out of the equation. It's impossible to get a flat frequency response at bass frequencies in anything but an infinitely large room (anechoic chamber, room without echoes). You can accurately measure a subs frequency response nearfield in a room if its not ported and has only one driver but you can't get Max SPL in such test conditions without over driving the mic.

First, I would like to say that I have the utmost respect for your knowledge in the audio profession. That is the reason I have been a participant of this forum for many years and I would like to think that I have treated you as a professional. Having said that, I am not sure to be insulted or just disappointed that you would think that I do not understand the effects of an enclosed space on a speaker/subwoofer vs. an open space. I would like to think that I had earned your respect throught the years with my participation. I would never make such an absurd statement that in room measurements do not have a greater effect on bass reinforcement than open air measurements. I just suggested that since Tom Nouissane did not corner load the subwoofers he tested, his numbers may be more conservative than the ones you arrive at as defined by the protocols you outlined.
I quote, " To measure bass limits, I place subwoofers in the corner of the room, which I determined by measuring the performance at many different locations. In my (Tom's) room, the optimal listening position happens to be 2 meters from the optimal corner."
I stand by my original observation that his measurements may be more conservative than the ones you arrive at because your error correction factor is for corner loading. Yes, there will still be some bass reinforcement in his room (that is obvious) but not as much as if one were to test the subwoofer directly in the corner.
I am an enthusiast, not a professional. I do not own 5 or 6 (money) digit audio testing equipment and would never assume to understand the limitation or nuances of the hardware required. I leave that up to the professionals in the business who actually have experience in the field using it. I also feel uncomfortable defending someone elses testing methodology but you asked and I tried to accomodate you. I come here to learn from you and others whos input I value on this site. I find that an admirable trait in anyone on any subject. I hope in the future you take my comments here into account.

 

[gene]

First, I would like to say that I have the utmost respect for your knowledge in the audio profession. That is the reason I have been a participant of this forum for many years and I would like to think that I have treated you as a professional. Having said that, I am not sure to be insulted or just disappointed that you would think that I do not understand the effects of an enclosed space on a speaker/subwoofer vs. an open space. I would like to think that I had earned your respect throught the years with my participation. I would never make such an absurd statement that in room measurements do not have a greater effect on bass reinforcement than open air measurements. I just suggested that since Tom Nouissane did not corner load the subwoofers he tested, his numbers may be more conservative than the ones you arrive at as defined by the protocols you outlined.
I quote, " To measure bass limits, I place subwoofers in the corner of the room, which I determined by measuring the performance at many different locations. In my (Tom's) room, the optimal listening position happens to be 2 meters from the optimal corner."
I stand by my original observation that his measurements may be more conservative than the ones you arrive at because your error correction factor is for corner loading. Yes, there will still be some bass reinforcement in his room (that is obvious) but not as much as if one were to test the subwoofer directly in the corner.
I am an enthusiast, not a professional. I do not own 5 or 6 (money) digit audio testing equipment and would never assume to understand the limitation or nuances of the hardware required. I leave that up to the professionals in the business who actually have experience in the field using it. I also feel uncomfortable defending someone elses testing methodology but you asked and I tried to accomodate you. I come here to learn from you and others whos input I value on this site. I find that an admirable trait in anyone on any subject. I hope in the future you take my comments here into account.

Westcott, I appreciate your contribution to this site and apologize if my responses have come off abrasive to you. The wonderful world of the internet can be quite dispassionate and impersonal at times.

Subwoofers measured in a room will typically give you far more output than the +6dB correction factor I am adding to simulate corner loading. I have a real problem with how Tom measures subs and so did the manufacturer whose product I set him up for review as a result. I don't mean this as a negative against Tom as I acknowledge his respect and contribution to the industry.

However, I am quite meticulous how we measure products, especially when dealing with their max output capabilities. Heck one particular manufacturer is even more meticulous than me, hence why they reject a proven and reliable method of measuring subs via groundplane technique.

Measuring max SPL of a sub in-room is next to impossible to achieve accurate results. If a correction curve isn't introduced into the measurement to remove the room effects, I'm afraid its pretty impossible actually.

 

[Ricci]

I just suggested that since Tom Nouissane did not corner load the subwoofers he tested, his numbers may be more conservative than the ones you arrive at as defined by the protocols you outlined.

I quote,

" To measure bass limits, I place subwoofers in the corner of the room, which I determined by measuring the performance at many different locations. In my (Tom's) room, the optimal listening position happens to be 2 meters from the optimal corner."


I stand by my original observation that his measurements may be more conservative than the ones you arrive at because your error correction factor is for corner loading. Yes, there will still be some bass reinforcement in his room (that is obvious) but not as much as if one were to test the subwoofer directly in the corner.

Hello Westcott.

I highlighted some parts in the quoted text from Tom...Seems to me that he is saying that he corner loads the subwoofer after determining it was his best placement option and that his listening position is only 2 meters from the sub placement corner. That is just how I read it...

I would tend to agree with Gene that a 2m outdoor test +6db will usually be the more conservative result versus an in room result even at a 4m listening distance from the sub, let alone a 2m listening distance which is what it appears he used. Truthfully without knowing exactly what affect Tom's room was imparting on the sound arriving at the measurement mic we are all of us just giving our best guess. Guessing at what any random rooms acoustics will be is an inexact thing at best. Either way we can't really directly compare outdoor ground plane tests to Tom's results. What we can do is compare all of the subs that Tom himself tested in the same manner with each other though, as many have for years. I have the utmost respect for Tom and have followed his tests, reviews and work for many years.

 

[westcott]

Hello Westcott.

I highlighted some parts in the quoted text from Tom...Seems to me that he is saying that he corner loads the subwoofer after determining it was his best placement option and that his listening position is only 2 meters from the sub placement corner. That is just how I read it...

As you say, it is hard to understand what he said in this sentence. I have a hard time figuring out how the primary listening position in a room 7500 ft3 could be 2 meters from the subwoofer and corner loaded given the conventional starting points for speaker placement and seating distance in a rectangular room. His further description of testing different positions kind of seems long winded just to stick it directly in the corner anyway (I did give this some thought, believe it or not). Having a similar sized space, 2 meters from the corner turned out to be the best place for overall room frequency response for my subwoofer placement with extensive testing with a signal generator and an oscilliscope. This still does not conflict with my premise that if he did not corner load the subwoofer, the dB level would be less than if he had. I agree that as long as the testing procedures are consistent for all subwoofers tested with a given methodology (as long as the measurement method is relevant, done with precision and a reasonable amount of accuracy) a relative comparison would still be valuable tool.

 

[DangeRuss]

My puny subs

As part of our new powered subwoofer measurement protocol, we will be offering a room size recommendation for each subwoofer tested based on the data gathered from our exhaustive CEA SPL vs frequency and distortion output testing. It is our hope that the methodology we chose in determining the room size capability for subwoofers can be a useful general rule of thumb for an end user attempting to determine which model is right for their listening space. We always recommend multiple subwoofers for more overall output and smoother bass response from seat to seat. The goal for a great A/V system is lots of clean output and a similarly good listening experience for all listening seats in the room, NOT just the money seat. See if your favorite subwoofer will get our "Bassaholic" recommendation.

I will be reading this thread religiously from this moment forward. There seems to be alot of useful information being shared here. Although most of it is way over my head (I'm a newbie). I do however have a question about were my puny subs would rate in the "Bassaholic" scheme of things..... I have a pair of the latest edition SVS PB10-NSD 's ( with the STA-400D DSP amps) in a 1824 cu. ft. room with a large opening to the rest of the apartment. After purchasing more room treatments and an AS-EQ1 , I have been toying with the idea of going larger

 

[DangeRuss]

I will be reading this thread religiously from this moment forward. There seems to be alot of useful information being shared here. Although most of it is way over my head (I'm a newbie). I do however have a question about were my puny subs would rate in the "Bassaholic" scheme of things..... I have a pair of the latest edition SVS PB10-NSD 's ( with the STA-400D DSP amps) in a 1824 cu. ft. room with a large opening to the rest of the apartment. After purchasing more room treatments and an AS-EQ1 , I have been toying with the idea of going larger

Anyone........ ?

 

[its phillip]

What exactly is your question? Should you get more capable subs? If you want to, sure.

 

[DangeRuss]

What exactly is your question? Should you get more capable subs? If you want to, sure.

Well sort of..... I'm really happy with the PB-10's yet wonder if there's something I'm missing. But what I want to know is how does my present sub system rate in the Bassaholic scheme of things being that my room is relatively small - medium (1825 sq.ft.) or would it rate a badge at all ?

 

[mike c]

Well sort of..... I'm really happy with the PB-10's yet wonder if there's something I'm missing. But what I want to know is how does my present sub system rate in the Bassaholic scheme of things being that my room is relatively small - medium (1825 sq.ft.) or would it rate a badge at all ?

output-wise even a single pb10 is overkill in your size room.
what you get from getting a better model is better SQ and lower extension, something you don't get even if you had 10 of the lesser sub.

 

[NuTReez]

Great article!!!

Most informative. Thank you for the detail.

 

[Jor4President]

question regarding the size rating protocol

I understand the target max rl spl output @ 4m is >115db for a large room (or >109 @ 25hz) in order to have that big bass pressure/tactile feedback. Will a 'Bassholic Certified Medium' sub at -6db below 'Certified Large' output be able to provide the same pressure/tactile feedback in a medium room?

Another question. My living room is a hair below what is considered to be 'Large' at 2987ft^3. I have windows along an entire wall on one side and curtains in front of the windows. The sub will be in one of the corners opposite the curtains. How significant will the effect of the curtains be on the room gain? Is this negligible enough that a 'Certified Medium' sub will be able to provide enough bass or will the room require a 'Bassholic Certified Large' sub?

 

[Steve81]

I understand the target max rl spl output @ 4m is >115db for a large room (or >109 @ 25hz) in order to have that big bass pressure/tactile feedback. Will a 'Bassholic Certified Medium' sub at -6db below 'Certified Large' output be able to provide the same pressure/tactile feedback in a medium room?

A lot really depends on the situation/room, but I think it's fair to say something like a Hsu STF-2 would compare well in a smaller room versus say, a VTF 3.4 in a fairly large room.

How significant will the effect of the curtains be on the room gain?

Curtains won't make a bit of difference.

Is this negligible enough that a 'Certified Medium' sub will be able to provide enough bass or will the room require a 'Bassholic Certified Large' sub?

My advice: if you can reasonably afford a larger subwoofer, and you like you bass (who doesn't like bass )...get the larger sub

 

[Jor4President]

Thank you for your reply.

Unfortunately budget is an issue. I'd rather not spend more than I need to get that audioholic approved sound, but I will spend enough to get it. (If I had the means, yes I would definitly buy the bigger sub regardless of room size.)

I guess I'm trying to convince myself that the Bassholic Medium/Small rating the best thing since sliced bread for those on a budget and living small(er). And those new cute SVS subs are now also available in europe.

 

[Steve81]

I guess I'm trying to convince myself that the Bassholic Medium/Small rating the best thing since sliced bread for those on a budget and living small(er). And those new cute SVS subs are now also available in europe.

They're certainly a useful starting point. I owned a PB10-NSD for several years that I thought gave a good accounting of itself in a fairly open floor plan room in an apartment and in my current room which is ~2500 cubic feet; I'd expect the new PB1000 to carry on that tradition reasonably well.