Usefulness of In-Room LF Measurements vs. No Measurements (ref FH)

[planet10]

Originally Posted by Ultralight

For example, one can say, 'In my room of 15 x 20, and 12 inches from back wall, I measured 35hz at 3db down....."

For example somone reported 35 Hz with a set of Fonken, a speaker that does more like 60-65 Hz. Room is totally dominant. The only measure that makes any sense for you is the one made in your room and even then...

dave

[planet10]

Originally Posted by xrk971

Well if someone wanted an *idea* of the sort of response they can get if they were to build it and if it was placed in a corner in their room at the same distance from the corner, sure it is a useful measurement.

And given the quality of today's sim sw that is just as, if not more, useful

dave

[xrk971]

The title of this new thread is confusing, what is meant by "lf measures ref fh"?

[freddi]

for a really rough idea, besides listening perspective, a mic at the floor boundary at the listening point - my Klipschorns look real good from this perspective and must have some room "gain" but sound awful as there's resonant wall flex which is excited even with acoustic guitar - they've not been played more than a few minutes total in years I have a little BK20 which can measure ok with a few drivers - but is subjectively very weak on drums - mouth sounds "out of phase" with direct.

sims should show extension - look at power handling across the bass to midbass frequencies and if experienced, make some guesses as to whether the speaker under question can handle the music. Is very subjective. (that should be a K33 - CTS below - my later lumbercore K-horns have K33E)

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here's a graph of the La Scala sent to me from Paul Klipsch - he took the time to pencil in
his Klipschorn's response - great support from that company in those days.

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[Ray21]

Originally Posted by planet10

More likely confusing.

The FHs use variable damping to tune the bass, the design uses the room as part of the design, so any measure is only applicable to the specific build and the room it is in. Take the room out and you are hobbling the speaker. So measures are only useful to the guy tuning it in hid toom

And knowing those that treasure their measures and give them toomuch creed they would take what they see and generalize it well beyond their applicability.

dave

I'd have to agree with this.

I take measurements so I can apply EQ and fine tune necessary phase and time alignment between the speakers and the sub. But it is really just not applicable to suggest that my measurements will be what someone can expect to achieve in their environment.

And I like to see other peoples in room measurements....

What I think matters more, or is more relevant, to someone that takes measurements is how a simulation fleshes itself out in your particular room. Then you can get an idea of how something else may measure in your particular environment.

[xrk971]

And I like to see other peoples in room measurements...

Yes, I do too, which is why I asked in the first place. This is DIY where info and images are all welcomed. Not providing a measurement of one's system because of fear it may not apply for someone else's measurement of the same speaker in their room would be like saying I won't post photos of my build of this speaker because someone else's build may not look like mine (because they use different wood, construction technique, finishes, etc). "Oh gee, I can't post photos of my bubinga veneered 15-coat of hand rubbed varnish speaker because it is not representative of some other poor guy who can't afford this level of finish and care in construction of the speaker."

We are all big boys and understand the applicability of a measurement to a particular room. That should not stop us from sharing what our measurement looks like in *our* room. And as Freddi shows above, there is a way to minimize the effect of the room by keeping the mic either closer to the speaker or by using a ground-plane measurement. But if you have room-effects, they really are effects below 300Hz, there is still a lot going on that is *speaker-design-dependent* and not room-dependent that is of interest. These effects are intrinsic to the driver in that cabinet as a result of acoustical interactions, baffle edge diffraction, and of course, the driver's intrinsic response.

Take for example my measurement previously posted for one of my builds from this thread:
http://www.diyaudio.com/forums/full-...-bandpass.html



Sure, it's got warts and is not the smoothest response above 300Hz (where it is really all due to the speaker and not the room - and I think sharing this helps folks see that this speaker does indeed color the sound, independent of the room), but I think it gives readers a whole lot of info of whether or not they should pursue this particular build with this driver in this cabinet. Is this measurement worthless? It shows the bass extension possible, the variation of frequency response vs off-axis listening angle, and it shows that although not flat, it is overall, a rather balanced presentation as there is no huge rising response that will sound like shout, and that there is some body to the bass because the response is flat down to 55Hz. More data is always better than no data.

[freddi]

here's an in-room comparison of a Fostex BK20 back loaded horn loaded with an inexpensive Sammisound wideband 8 inch speaker, augmented with a ST324 Selenium helper tweeter. The other speaker in direct comparison is a Klipsch Heresy I. The back loaded horn would appear to be quite a bit better but with wall mounting and a single ended amp, I prefer the 3-way and think other than the woofer to midrange blend, that it sounds more coherent than some fullrange' so in this case I prefer the worse looking graph speaker when driven by the SE tube amp. (BK20/Sammi was not auditioned with that amp) Both speakers were about in the same spot but the Heresy was elevated off the floor. This cheap Sammi 8 which cost me $12.80 has a calculated efficiency of about two percent. Selenium's ST324 slot loaded tweeter imo was a very good helper tweeter.

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[Greg B]

Originally Posted by xrk971

We are all big boys and understand the applicability of a measurement to a particular room. That should not stop us from sharing what our measurement looks like in *our* room.

Exactly. If a speaker is designed for corner placement, fine, we understand that an ideal speaker for this might be perceived to have poor response by a newbie. Why worry about this? A measurement at least gives us a starting point. Besides, all the info above 200hz matters too.

Anyhow, all speakers are heavily affected by the room. To decide that one is exempt from the importance of measurements because it is room dependent is ridiculous.

That said, I'd be the first to tell you that frequency response measurements are far from everything, and you can only tell so much from charts. There are plenty of perfectly flat horrible sounding speakers.

[xrk971]

I think a speaker that does not measure flat can sound good, but a speaker that measures flat in frequency and phase, has a clean impulse response, and relatively low harmonic distortion will not sound bad, and actually will most likely sound good with all genres.

My experience has been that if it measures well for all four things: FR, phase, impulse, HD - I know it will sound good with music.

[Greg B]

Fair enough. I was referring entirely to frequency response measurements. I've been doing this hobby for a while, and for years people obsessed over FR, primarily in my view because it was the one thing people could measure.

I also like to look at CSD, but few manufacturers will publish it for full range drivers.

I think our ears compensate psychoacoustically for quite a bit of variation in frequency response, as it was important to hear a bear or a voice whether it was in a cave or in the woods. Besides, to some degree you can fix it with EQ. Distortion and impulse response - not so much. (though wesayso's recent experiments have been pretty interesting)