How do I properly read an SPL vs. Freq. Chart?

[Alamar]

I'm a little confused by some of the reviews that I see when SPL vs. Freq. charts are published.

For example let's look at the SPL vs. Freq. Chart here: SPL vs. Freq chart

From reading the graph it looks like I see the following:
1. From 70Hz to 20KHz I see several readings down to 80 ish db.
2. From 70Hz to 20KHz I see a couple of peaks around 90 ish dB.
3. From 70Hz to 60Hz there is a steep drop-off in SPL db.

From a newb viewpoint it looks like the speakers are flat within +/- 5db from 70Hz to 20KHz based on the measurements takein in that specific environment from that specific distance.

However the article, which I'm of course assuming is correct, says:

"I did a quick and dirty in room response measurement of the TK-5Cs at ½ meter. What I found was that the -3dB point as confirmed by the frequency response and saddle point on the impedance graph is around 60Hz just as the manufacturer claims. They maintain a linear response of +-3dB throughout the entire audio range but do tend to favor the lower midrange in the 1kHz to 3kHz region just like my listening tests confirmed."

Based on the above it seems like the reviewer is saying that the units are flat +/- 3dB from 60Hz to 20KHz. When checking the manufacturer's web site they say: Frequency Response: 60Hz-20kHz (±3dB)

My problem is that I don't see, based on the chart, how that conclusion is arrived at. What am I missing or not taking into consideration? Is the reviewer saying that +/- 5dB from 70Hz to 20KHz in his [imperfect] room is close enough to +/- 3dB from 60Hz to 20KHz [perfect conditions] for government work?? Is the reviewer throwing out some of the higher peaks in the mid range????

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Edit: I did see a chart on the manufacturer's site that [to me] does look flat +/- 3dB from 60Hz to 20KHz so I guess that I can read the chart. Now my question is why did the reviewer says that the review unit seemed to meet specs? .... Was it close enough for his imperfect room to assume that it was otherwise fine????

 

[Alamar]

I saw a sticky in another forum and I'm sure that I read the chart right. I guess that I will have to assume that the person doing the review knew that their room was cause this level of distortion ...

 

[jcPanny]

Frequency response

Based on your quote from the review, it looks like this is an in room frequency response measurement that incorporates the speaker and the room. The +/- 5dB is a very flat in-room response which is likely due to Gene's treated HT room. It is easy to get 10dB nulls in a regular untreated room.

A manufacturer's frequency response chart is typcally done in an anechoic chamber or other measurement technique so that the "room" does not effect the results. This measurement is used to derive the +/- 3dB spec. On the in-room response it is easy to see the speaker roll off below 60 Hz and how it corelates with the manufacturer's spec.

 

[Jeff Straight]

Frequency response

Based on your quote from the review, it looks like this is an in room frequency response measurement that incorporates the speaker and the room. The +/- 5dB is a very flat in-room response which is likely due to Gene's treated HT room. It is easy to get 10dB nulls in a regular untreated room.

A manufacturer's frequency response chart is typcally done in an anechoic chamber or other measurement technique so that the "room" does not effect the results. This measurement is used to derive the +/- 3dB spec. On the in-room response it is easy to see the speaker roll off below 60 Hz and how it corelates with the manufacturer's spec.

This is where the confusion comes from. According to my eyes that chart starts rolling off at about 70 hz. Just like the Alamar said. jcPanny, are you looking at the same chart Alamar posted?

 

[mtrycrafts]

This is where the confusion comes from. According to my eyes that chart starts rolling off at about 70 hz. Just like the Alamar said. jcPanny, are you looking at the same chart Alamar posted?

That's a 10 year old post. Who knows where those posters are today.

 

[panteragstk]

That's a 10 year old post. Who knows where those posters are today.

I've seen some forums that have auto-close on threads that don't get responses for x amount of time. Think that'd be a nice feature to stop this sort of thing.

 

[PENG]

I saw a sticky in another forum and I'm sure that I read the chart right. I guess that I will have to assume that the person doing the review knew that their room was cause this level of distortion ...

I think you read the chart right so I think the comments probably referred to a different chart.

 

[jslivingston]

The conundrum is that we want to read consumer measurements because we might be skeptical of the manufacturer's claims. But the manufacturer's are performing their measurements in anechoic chambers that basically suck all reflections out of the room and scatter anything left over to where it doesn't have enough energy to matter.

Consumers MIGHT have some acoustic treatment in their room, and even when they think they have a ton, it's not enough to make a conclusive measurement. Most don't even realize you need to tune your room with your treatment as well. All of the reflections bouncing around create constructive and deconstructive interference, which makes peaks and nulls that change even depending on where you're measuring from. The slightest movement in a poorly treated room can drastically change the measurement.

So yeah, you're reading it right. Plus-or-minus 3 dB is extremely flat in response, but you may not see that level of flatness without referring to a professionally measured graph, as you ended up noting.