Subwoofer specifications vs. "in room"

[Boomzilla]

I'm confused -

How can Emotiva (and the vast majority of other manufacturers) claim an "in room response" of 20 Hz. if the actual product is -20 decibels at 20 Hz.?

I realize that there is no "standard" for measuring subwoofer response as there is for "normal" loudspeakers. The normal measurement criteria is for the microphone to be at the vertical and horizontal center of the speaker cabinet, at one meter distance, and with one watt of input (adjusted for the average impedance of the speaker). For subwoofers, there is no standard. This seems understandable because there is no "standard placement" for subs. Some are set out in the room, some at a floor/wall junction, and some in corners. Placement would make a HUGE difference in frequency response.

Nevertheless, it seems inappropriate for ANY manufacturer to claim an in-room response frequency that is actually -20 decibels on the subwoofer output curve.

The issue is further complicated by the fact that specifications sell speakers. Some "spec-readers" conclude that because one sub claims 20 Hz. response and another only 30 Hz. that the one with the lower published response must be the better of the two. Some companies are notorious for using their (misleading) specs to sell product (cough, cough - DefTech).

I'm very disappointed in Emotiva, though, to see them doing what I perceive to be the same thing.

What assumptions are made for a system with -20 decibels of actual output at a certain frequency to claim "room response" to that frequency?

[garbulky]

It's called Fudging. Didn't you see the movement of the speaker cone. There....solid full range response ;D
As for room response, the room did respond. It just didn't have very much to say. ;D

[Boomzilla]

For standard speakers, even floor-standers, the typical spec is -3dB for lower usable bass response. How does that become -20 dB for subwoofers. Fudging, indeed!

[garbulky]

Haven't you heard the bigger number is better. See all I see is DASH 20 db. I don't know where you got your minus from. Why would anybody want to subtract sound?!

[DYohn]

No it's not called fudging. It's called physics. Do some research on boundary gain or room gain.

[Boomzilla]

Apr 1, 2013 9:23:23 GMT -5 DYohn said:

No it's not called fudging. It's called physics. Do some research on boundary gain or room gain.

Yes - Room gain is there, but there's no standard way to quantify it. How big is the room? Is the sub in the corner, the wall, or a null point? How lossy is the room for standing waves? What frequencies are reinforced or cancelled by the room dimensions?

No matter how you cut it, it seems dishonest to claim a response when the actual radiator is 20 decibels down at that frequency. To say "everybody else does it" is no excuse.

[DYohn]

It's not dishonest and it is absolutely a predictable effect you can calculate. It is a standard industry practice. No excuse necessary: that some users don't understand it is not the manufacturer's problem.

[Boomzilla]

If there's no standard way to compare, then there's no way for "some users" to understand it at all.

Without the data to understand the specification, then it's ALL "fudge."

[DYohn]

You believe what you want to believe. But I really do suggest you research the effects before you begin condemning standard industry practices.

While it is impossible to know precisely what is going on in any user's room, it is absolutely true that there will always be low frequency gain in ANY room. Predicting what is likely and normal for any system is part of the design process. Listing those predictions as "in-room" output is the most useful parameter to any user. You do not listen in an anechoic chamber, you use the system in a real living space with walls and floors and ceilings. It is absolutely correct to list predicted in-room output for a subwoofer (or for any loudspeaker system) and this will always be +3 to +20db over the anechoic output below about 80Hz depending on the system.

[Boomzilla]

The classical theory states that the effective gain realized from incoherent summing due to radiation confinement is +3dB for each additional boundary, and that +9dB relative to the free-field response can be achieved by “corner-loading” a loudspeaker.

9 decibels is still a mile away from 20. I don't where YOU get the 20 decibel figure, but "standard industry practices" are ANYTHING but standard.

[DYohn]

I get my information from the work of Dr. Floyd Toole of Harmon Industries. You?

[gregd]

Apr 1, 2013 10:16:48 GMT -5 Boomzilla said:

If there's no standard way to compare, then there's no way for "some users" to understand it at all.

Without the data to understand the specification, then it's ALL "fudge."

You just need to by this kit so that you can get a flat frequency response down to 20 hz and below:
emotivalounge.proboards.com/index.cgi?board=emporium&action=display&thread=29949
;D

Me, I'm going to buy subs that someone else says they like. The numbers aren't so meaningful to me.

Of course, you'd need to add a sub. Too bad nobody makes a sub that looks like a large flower pot so you could sneak it in.

Are you _sure_ you couldn't hide one inside the sofa?

My wife doesn't much care what I put in the family room with the rest of the stereo system but she made it very clear that she won't be happy if I start any new projects (like building sub cabinets) until the bathroom remodel is done.

[Boomzilla]

Apr 1, 2013 10:46:31 GMT -5 DYohn said:

I get my information from the work of Dr. Floyd Toole of Harmon Industries. You?

In fact, you don't.

From Dr. Floyd Toole's paper here: www.harmanaudio.com/all_about_audio/loudspeakers_rooms.pdf

Dr. Toole specifically states:

"Reducing by a factor of two the solid angle into which a loudspeaker radiates, can result in an increase in sound pressure of a factor of two, or 6 dB, measured at a particular location. This is entirely consistent with the notion of the sound power radiated by the loudspeaker into the reduced solid angle being increased by a factor of two, or 3 dB."

This is EXACTLY what I stated earlier from this website: www.synaudcon.com/site/author/pat-brown/how-boundaries-affect-loudspeakers/

Which was:

"The classical theory states that the effective gain realized from incoherent summing due to radiation confinement is +3dB for each additional boundary, and that +9dB relative to the free-field response can be achieved by “corner-loading” a loudspeaker."

Now, Mr. Yohn, either you are mis-referencing Dr. Toole, whom you obviously haven't bothered to read or else you are "inventing" statistics.

Which is it?

Cordially - Boomzilla

[DYohn]

I never claimed that you get +20db from corner loading. I just said that if the manufacturer is claiming +20db from room gain (which Emotiva is not) that would be within the realm of possibility.

[Boomzilla]

Apr 1, 2013 14:38:26 GMT -5 DYohn said:

I never claimed that you get +20db from corner loading. I just said that if the manufacturer is claiming +20db (which Emotiva is not) that would be within the realm of possibility.

It is nowhere near the realm of possibility.

Emotiva claims +20 decibels from room effect in their own specifications.

You have used an ad-hominem argument against me in claiming that I am somehow not competent to understand Dr. Floyd Toole's very clear explanation of room reinforcement.

Emotiva's own plot for the X-Ref 12 DSP powered subwoofer (acoustic response with all filters set to flat) clearly shows -20 decibels at 20 Hz.

Emotiva's own plot for the X-Ref 12 DSP powered subwoofer (using their parametric EQ settings one or two) clearly shows even more level reduction at 20 Hz.

Yet Emotiva's specifications for the sub say "Typical in-room frequency response: 20-200 Hz."

There is no credible room placement that will compensate the 20 Hz signal more than 9 decibels (per Dr. Floyd Toole). Even that is a "best-case" scenario.

Emotiva's specifications for this subwoofer are lies.

Your accusation that I don't understand the physics is similarly a lie.

You are entitled to your own opinions, but not to your own facts.

Boomzilla

[DYohn]

Wow, dude, chill out. You absolutely can get +20db from room gain. It's not typical perhaps, but I've seen swings of + and - 30db due to room modes... but hey, whatever, if you want to get on your high horse enjoy the ride, and if you have an issue with Emotiva's specification I suggest you take it up with Lonnie.

[Boomzilla]

Apr 1, 2013 10:46:31 GMT -5 DYohn said:

I get my information from the work of Dr. Floyd Toole of Harmon Industries. You?

It's this sort of snide comment that I object to. I don't claim to have an exclusive on the facts, but when you imply that I'm creating garbage when you don't seem to have bothered to even look at the authority you're citing, it rankles.

In fact, the statement I copied was EXACTLY what Dr. Toole himself stated in his article. Why, then, would you wish to claim that your source (Dr. Toole) is the gospel when you haven't even bothered to verify the source? Your statement further implies that I'm somehow either ignorant or incompetent.

It is your attitude, David, that provokes such responses. This is truly a shame, because you are exceptionally knowledgable and very generous with that knowledge.

I, myself, have benefitted several times from your sharing. I have also been provoked several times by your statements which imply that I (and often, others as well) are somehow ignorant or incompetent.

I'll try to be less sensitive if you'll try to be less arrogant.

Deal?

[garbulky]

Boom, I guess the real question is is the response of the emo x-ref 12 sub able to actually do useful relatively even output at 20hz in a "typical" room as they advertise. Does it have it or not...
For instance an axiom ep600 (which is admittedly a very different design) has anechoic +/-1.5db @ 19hz at around 90db volume, +/-3db @ 17hz and then there typical room response (+3,-9 db) gets it to 15hz. If you notice that is about 4 hz below it's anechoic level as I assume it gets tougher to move air as you get down low. I have a hard time believing that a typical room will give you a 20hz response when the sub is rolling off in the low 30's anechoically. But then again, I haven't heard it but I know that my car can't do 200mph even when rolling downhill even on a windy day.

[Boomzilla]

A comment from Lonnie on the provenance of Emotiva's "20-200 Hz" specification would be welcome.

Lonnie?

[GreenKiwi]

Actually, I think that the problem might simply be that all the charts that we're seeing on the X-Ref 12 page that shows -20db at 20Hz is the chart for the X-Ref 10 (looks like it falls fast from 35Hz) (Keith or someone else at Emo, you might want to fix the links)
emotiva.com/resources/media/xref10/acoustic_flat.jpg

Now, the XRef 12's chart is only a bit better, it appears to be down about 15-16db (Looks like it falls from 30Hz)
emotiva.com/resources/media/xref12/acoustic_flat.jpg