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In Reply to: RE: The best bass (below 100 Hz) you have heard posted by beppe61 on November 30, 2014 at 04:31:10
I also greatly value piano recordings as litmus tests of speaker fidelity.I often hear the kinds of problems with speaker playback that you (and others) have brought up.
Principally I hear problems with the crossover between the mid-range driver (woofer) and tweeter and also problems with break-up modes of the mid-range driver not being fully fixed by the crossover. These issues over-lay and color the sound of reproduced piano.
Yet I think the issue that you brought up...problems in the bass are not solvable by subwoofers (which typically function below 100 Hz). Moreover, as has been pointed out, most speakers, even minimontors can reproduce flat anechoic response down to below 100 Hz.
Edits: 12/02/14Follow Ups:
Hi and thanks for the advice
It seems that more than i sub i need a real bass
A good pair of 12" woofers ... crossed to satellites.
I have seen something done for the Rogers ls3/5a (see picture)
A smart concept to follow ?
Kind regards,
bg
Above: Power (in-room) response curve of Focal Grande Utopia BE courtesy of Stereophile.I have experimented with subwoofers and have come to the conclusion that though they can enhance the sounds of explosions and dinosaur foot thumping (sounds occuring below 60 Hz), they don't do much to enhance the realism of recorded piano.
The problems that you have addressed must be happening at a higher frequency. The problems are exacerbated by the modern habit of mounting speakers on stands out near the middle of the room. What I am referring to is known as the "Allison Effect."
Duke discussed how room coupling produces "shelving bass boost" below the frequency at which bass reflections from the room's boundaries and the primary output of the woofer re-inforce each other.
Yet, just above the frequency of "shelving bass boost," there is a region where bass reflections from the room's boundaries and the primary output of the woofer (being out of phase) cancel each other, producing a deep null, a suckout.
The frequency of these nulls can be determined using the following formula:
Frequency of null = 1130 (velocity of sound)/distance (in feet) x .3 (quarter wave co-efficient).
Using this formula you can determine that given the dimensions of a standard room and the habit of mounting speakers on stands, away from boundaries, quarter-wave nulls usually occur in region of 250 Hz to 300 Hz.
A deep null, a suckout (of the speaker's in-room response) between 250 Hz to 300 Hz is particularly destructive of piano music and is the principal reason that the piano ends up sounding denuded and "miniaturized"...you are only hearing the piano's upper notes, it's bottom registers (overlapping with the null) are sucked out of the in-room response.
Furthermore, the primary wave-front of the woofer does not just interact with the reflections coming off the room's boundaries but in a stereo pair of speakers, each speaker's primary wave front will interact with that coming from the other speaker producing the same kind of "shelving bass boost" and quarter wave nulls. In effect, the half point of the distance between the speakers in a stereo pair acts as another boundary.
When the frequency of these boundary induced quarter wave cancellations overlaps, the resulting nulls can be both wide and deep, as can be seen in the linked page of power response measurements of various speakers (courtesy Stereophile).
The trick to minimizing the severity of quarter-wave cancellations is to make sure that the speakers are a different distance from each room boundary (and 1/2 the distance between the speakers) and that none of the distances are multiples of any other.
Edits: 12/02/14 12/02/14
"Duke discussed how room coupling produces "shelving bass boost" below the frequency at which bass reflections from the room's boundaries and the primary output of the woofer re-inforce each other."Yet, just above the frequency of "shelving bass boost," there is a region where bass reflections from the room's boundaries and the primary output of the woofer (being out of phase) cancel each other, producing a deep null, a suckout."
Sorry if I wasn't clear, but I was talking about a general trend due to boundary reinforcement, and of course that general trend is marred by peaks and dips. I can promise you that the anechoic curve of that Focal system exhibits neither the peaks nor the dips that the in-room curve does south of 150 Hz. If you mentally draw a straight line from about 150 Hz down to 20 Hz (which is probably down in the pressure zone), that's an indication of the general rising trend I was talking about (assuming the speaker isn't really +4 dB anechoic at 20 Hz!). The 100 Hz dip, and the 50 and 30 Hz peaks, are the sort of peak-and-dip pattern I was talking about.
The curve you show is one speaker in one location. Add three more in dissimilar locations (different distances to the room boundaries) and you have four dissimilar curves. Their sum will be significantly smoother than any one alone. Also, peaks and dips in the summed curve will be more numerous and closer together, so the ear/brain system's 1/3 octave averaging characteristic will probably work in our favor. And any significant remaining peaks in the response will tend to be global rather than local, and so are good candidates for correction via EQ.
(The dotted-line curve is the speaker with its internal subwoofer disconnected. It looks to me like the designers either had a much bigger room in mind, or under-estimated the effects of boundary reinforcement by about 4 dB. Or maybe they just wanted a big low end.)
In-room curves really do look as bad as that graph in your post shows. It is a fundamental acoustic problem of small rooms, and distributed multisubs with room-gain-complementary response curves would be an acoustic solution. In this case the dip at 100 Hz is centered north of the region typically covered by subs, so we may need to call on other techniques to address that issue (cough cough bipolar cough).
Imo, ime, ymmv, etc.
Duke
Me being a dealer makes you leery?? It gets worse... I'm a manufacturer too.
Edits: 12/02/14 12/02/14
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