Discrepancy speaker Specs vs Measurements

[manu3l]

Hi wonderful audiophile people, so nice to have such valuable info and feedback on this forum.

Been researching speakers that go deep in low frequencies and found discrepancies across both tests and specs.
Notably about mean on-axis levels as well as frequency response range.

1. How can a manufacturer claim 39hz but be tested at 64??
Namely the Polk XT20, S20 and ES20 which are rated 38, 39 and 44hz at +/-3dB respectively.

2. Does lowering the mids via EQ effectively raises the lower frequency threshold?

3. What else can I use as a cue whether a speaker can produce acceptable levels at 40-50hz?
4. As a side question, should I bother with 2 x 6" drivers for a wide and open room or go with 2 x 8" speakers, this is for a sub-less application.

 

[mhardy6647]

1) Loudspeaker performance is oh-so-dependent on environment.
2) "Standards" and/or apparatus for testing vary.

 

[fpitas]

The size of the drivers is a big clue about bass reproduction. Small drivers can dig deep, but at whisper levels. I wouldn't go less than 8" for 40 - 50Hz at realistic levels.

 

[mhardy6647]

The size of the drivers is a big clue about bass reproduction. Small drivers can dig deep, but at whisper levels.

... and/or require lots and lots of watts (and/or esoteric enclosure designs) to reproduce respectably low bass at "usable" SPL.

That said, there are practical limits to cone excursion, so high levels of low frequency sound is are more sensibly achieved with a large woofer, I'd agree.

 

[fpitas]

... and/or require lots and lots of watts (and/or esoteric enclosure designs) to do it.

That said, there are practical limits to cone excursion, so high levels of low frequency sound is more sensibly achieved with a large woofer, I'd agree.

At least a 15, I'd say

 

[mhardy6647]

At least a 15, I'd say

Total of four 15 inch drivers dedicated to the cause at my house in toto (i.e., counting the subwoofer).

 

[fpitas]

Total of four 15 inch drivers dedicated to the cause at my house in toto (i.e., counting the subwoofer).

I make do with two 15s, propping up their MTMs. But I think you have a bit larger room.

 

[staticV3]

"Total Frequency Response" is a meaningless metric.
Polk could've claimed 20Hz - 40kHz and it still would've been technically correct (and equally useless).


Instead, better to look for manufacturers that specify frequency response like this (8020D):

 

[mhardy6647]

Well, two of the four aren't really woofers by modern standards...



but we digress

Back to the OP (if he/she/they're still out there): loudspeaker and driver specifications (still) tend towards modern short fiction as opposed to expository prose.
Go with established brands, models, and designs. Even though price and value are different (and non-identical) parameters, quality doesn't tend to come cheap.

 

[fpitas]

"Total Frequency Response" is a meaningless metric.
Polk could've claimed 20Hz - 40kHz and it still would've been technically correct (and equally useless).
View attachment 241141 View attachment 241140

Instead, better to look for manufacturers that specify frequency response like this (8020D):
View attachment 241143

Yes that, and an output level.

 

[fpitas]

Well, two of the four aren't really woofers by modern standards...



but we digress

Back to the OP (if he/she/they're still out there): loudspeaker and driver specifications (still) tend towards modern short fiction as opposed to expository prose.
Go with established brands, models, and designs. Even though price and value are different (and non-identical) parameters, quality doesn't tend to come cheap.

Hard to go wrong with those. New from GPA?

 

[LTig]

Hi wonderful audiophile people, so nice to have such valuable info and feedback on this forum.

Been researching speakers that go deep in low frequencies and found discrepancies across both tests and specs.
Notably about mean on-axis levels as well as frequency response range.

1. How can a manufacturer claim 39hz but be tested at 64??
Namely the Polk XT20, S20 and ES20 which are rated 38, 39 and 44hz at +/-3dB respectively.

It depends on how the frequency response is measured. Standard is in an anechoic room.

2. Does lowering the mids via EQ effectively raises the lower frequency threshold?

???

3. What else can I use as a cue whether a speaker can produce acceptable levels at 40-50hz?

Look for low distortion at high SPL below 150 Hz

4. As a side question, should I bother with 2 x 6" drivers for a wide and open room or go with 2 x 8" speakers, this is for a sub-less application.

Bigger woofers are better for low frequency playback but then you better get a 3-way speaker to prevent directivity problems, or a 2-way with a big waveguide for the tweeter.

 

[DVDdoug]

In general, I don't fully trust the manufacturer's specs but I wouldn't expect Polk to fudge too much.

+/-3dB could mean mostly-flat (flattish?) and then -6dB at the extremes, or maybe just at the low-end. I assume most manufacturer's move the +/-3dB range up and down for the "best" reported results. And since it says 3 and not 3.0 they could be rounding from +/-3.4dB or 3.499.

Namely the Polk XT20, S20 and ES20 which are rated 38, 39 and 44hz at +/-3dB respectively.

2. Does lowering the mids via EQ effectively raises the lower frequency threshold?

If you look at most frequency response graphs, you'd usually have to lower almost everything except the deep bass. And you still might be limited by "physics".

 

[manu3l]

The size of the drivers is a big clue about bass reproduction. Small drivers can dig deep, but at whisper levels. I wouldn't go less than 8" for 40 - 50Hz at realistic levels.

Ok thank you. If the graph shows levels within 3dB then the bigger driver still has the advantage over a small one and will fill the room better or no?

"Total Frequency Response" is a meaningless metric.
Polk could've claimed 20Hz - 40kHz and it still would've been technically correct (and equally useless).
View attachment 241141 View attachment 241140

Instead, better to look for manufacturers that specify frequency response like this (8020D):
View attachment 241143

That is the +/-3dB rating.

???

The way I understand is that the +/-3dB range is calculated off of the mean level between 300 and 3000hz.

Look for low distortion at high SPL below 150 Hz

Ok, especially around the level of intended use.

Bigger woofers are better for low frequency playback but then you better get a 3-way speaker to prevent directivity problems, or a 2-way with a big waveguide for the tweeter.

Thank you.

In general, I don't fully trust the manufacturer's specs but I wouldn't expect Polk to fudge too much.

+/-3dB could mean mostly-flat (flattish?) and then -6dB at the extremes, or maybe just at the low-end. I assume most manufacturer's move the +/-3dB range up and down for the "best" reported results. And since it says 3 and not 3.0 they could be rounding from +/-3.4dB or 3.499.

Namely the Polk XT20, S20 and ES20 which are rated 38, 39 and 44hz at +/-3dB respectively.


If you look at most frequency response graphs, you'd usually have to lower almost everything except the deep bass. And you still might be limited by "physics".

Excellent, appreciate the response. So it's still a bit more vague than measurements would indicate, haha!

The one point that I miss clarification on is that if I lower via EQ everything above 300Hz (theoretically), am I in essence raising the lower frequencies and therefore the speaker will play bass at a higher level?

 

[fpitas]

Ok thank you. If the graph shows levels within 3dB then the bigger driver still has the advantage over a small one and will fill the room better or no?

Yes. Within reason, bigger is better. A big driver will start beaming earlier than a small one, but otherwise can put out more power, all things (like Xmax) being equal.

 

[staticV3]

That is the +/-3dB rating.

38 Hz -> 40,000 Hz is not the ±3dB rating.
57 Hz -> 26,000 Hz is the ±3dB rating.

 

[manu3l]

Yes. Within reason, bigger is better. A big driver will start beaming earlier than a small one, but otherwise can put out more power, all things (like Xmax) being equal.

Ok I read about driver speed, that's what they were alluding to then,

38 Hz -> 40,000 Hz is not the ±3dB rating.
57 Hz -> 26,000 Hz is the ±3dB rating.

View attachment 241190

Doh!!!! Makes way more sense. The RTI A3 has 40Hz response but 50Hz at +/-3dB which is better than the XT20.

 

[fpitas]

Ok I read about driver speed, that's what they were alluding to then,

Doh!!!!

Driver speed is some audiophile buzzword. If such a thing even exists it's fully expressed in the frequency response at the listener.

 

[manu3l]

38 Hz -> 40,000 Hz is not the ±3dB rating.
57 Hz -> 26,000 Hz is the ±3dB rating.

View attachment 241190

But where did you get this classified info? I looked around on Polk's site and 3rd-party's no luck.

 

[staticV3]

right here on Polk's website: