method for vented speakers

Foreword
The need to succeed in placing their speakers without having to make hundreds of tests and experiments is certainly one of the springs that I was straining to try to combine the experiences of 25 years of listening to the checks (instrumental) in the last year 'sphere of 4 rooms with different speakers and testing the frequency response of the same to changing their positioning in the environment.
For these tests I used a generator on a PC and an FFT precision sound level meter B & K2206 (with microphone with high linearity of frequency response) or through your existing preamp output lets you scan (using sound card ultralinear) on the pc 'pattern of frequency response using spectrum analyzer.
I state, however, that the instrumental measurements have been used more than anything else to confirm that instead of listening impressions together theoretical approach had fundamental importance.

Purpose
Leaving aside the desirability of theories have room or not square with the appropriate proportions in order to limit the occurrence of standing waves because I guess nobody wreck his room to build an ad hoc ....!! (If anyone here is interested in an article in this regard here) then you will get from your real listening room the best obtainable from the standpoint of timbre.
The aim is to obtain the response in environment as possible with linear diffusers air suspension (sealed box) from the pedestal or floor (obviously excludes bookshelf positioning given the constraint imposed by the shelf itself) use by the 'install only one instrument (or almost): the metro!
The fact that this method is declared only for speakers in air suspension should not be construed as limiting but rather as an index of accuracy: there can be installed in the same position in an closed box speakers, dipoles and reflex! Proponents make an obvious and superficial generalization.

Reverb
The absorption capacity increased gradually starting with frequencies of about 500Hz from materials commonly found in more or less normal furnishings (curtains, carpets, etc..) Makes the environment of speaker placement must be chosen depending on the frequency below 500Hz where the main differences on the response are caused by the walls (even a couch or a bookcase to affect these frequencies to a lesser extent than they can the walls of the room).
To get an accurate result from the application of the method described later (which in fact it will establish the location where to install the diffuser) as it should be "properly prepared" the room so as not to have loss of definition due to reflections in range midrange.
Here it should clarify a point, historically, often because of disputes between those who considers it important to reflected sound (as the live sound he shall consist of majority) and those who do not.
If we expect to hear from a recording the information "environment" that is generated by the reflections of the environment in which sound is recorded (which are sometimes exaggerated for " 'effect" by some engineers with the addition of echo) everything will be added to these discussions will be recorded loss of definition, the only reflections "good" are those already recorded on the disc that have a sense of harmonic richness and depth of environment.
Obviously making absorbent at all frequencies (type anechoic chamber) a normal domestic environment would be impossible (as well as disadvantageous in low range as described below normal listening environment may result in the extension of benefits in frequency) for which we seek to obtain an average absorption and absorption to avoid unbalancing the sun too high frequencies.
With regard to the considerations on the reverberation time to see here
The "break" with appropriate diffrattori "natural" (furniture) the reflected waves from walls also leads to substantial suppression of resonances and / or otherwise waves often found in rooms of regular proportions.
To combat the steady state can use some pipe foam cushions are marketed as commercially dall'Ikea and it is very good order (although very cheap) seats in the corners: a pair stacked in every corner of the room.
Must therefore be at home trying to deal with these considerations is normal with sofas and armchairs furniture both treatments.
Wall will be completely stripped easily attributable to a loss of definition and therefore should, if possible to avoid this condition. If you have pictures would be appropriate to avoid the safety glass (if he were to ruin your vs.figlio lithograph vs.Rembrandt preferred not blame me .....). A carpet to dampen the reflection of the wall more frequently station (the floor) etc etc.
In short a richly decorated environment is the best you can do.
In the case of wall acoustic treatment advice remains the far wall (the rear speakers), especially if the installation is done like case B (see fig.sotto) and possibly the rear to the point of listening to do this (for those does not like to resort to unsightly cartons for eggs ....) may be used (more efficient) tents or similar heavy velvet or polyurethane material suitable for this purpose and / or foam (high thickness).
In general, a room filled with sofas and furniture will be better sounding of a half-empty with many bare walls.

Considerations
In the method above, for conceptual simplicity, the reflections have been neglected in the low range higher than the first (which, though still influential people have less energy and thus disrupt the first reflection on the response in less environment).
Like any method that has the theoretical basis that too is reflected in certain conditions, here they are:

1) air suspension speakers
2) installation on the local rectangular
3) Knowledge of the resonant frequency of your speaker
4) placement of a distance between them not less than 1.2 m.
5) placement of the listening point at a distance not less than 1.8 meters from the speakers

Point 5 is set at the minimum distance for distances less because you might not yet have a coherent summation of the issue of individual speakers (tw and mr above) and consequently the distance of point 4 is the obvious consequence for not have a stereo too little "stereo" with a picture that is not credible in width.
Average is rather a shared proportionately between the speaker-to-point distance and distance between the speakers listening of 1.5.
The limitation due to the type of room (rectangular parallelepiped) is obviously dictated by the impossibility of analyzing the infinite variations that may in some cases home be even better.
One of the few serious studies on the experimental frequency range of from 20 to 500Hz from the past is that of Roy Allison, however, that had other purposes than what we aim: Allison tried to get a speaker that would result in the maximum linearity of frequency response if properly installed, but we find ourselves in the opposite condition of having already built a speaker and having to adapt to the best in the listening room.
I state that I personally feel perfectly shareable (as also perfectly supportable theoretically) by Allison experiences regarding the only bass, but do not share the position that it was therefore to have Mr. Allison on the speakers and tw .... .... but that's another story. Since the reflections of the walls are added in step or direct-pull with the signal depending on the wavelength of the reproduced signal, we will have in your listening irregularities due precisely to the vector sum of these sounds. The solution found on the speakers Allison was pretty simple: eliminate the reflections PushPull due to nearby walls (floor and wall and in the case of "three" even than the side) by simply placing the wf next to these walls and thereby obtaining reinforcement of the entire bass range (up to about 400Hz in the case of these speakers).
To better understand the concept of "reinforcement" should mention the application of acoustic emission solid angle: the space that determines the acoustic load that the speaker is to have a function of frequency emitted.
A solid angle is measured in "steradian" emission free field that would have a spherical solid angle of 4π steradian, half sphere = 2 π steradian, 1 / 4 of a sphere = π steradian, 1 / 8 of a sphere = π / 2 steradian
So for example in the case of corner placement (3 wf as on the walls next to Allison three) is changed from a solid angle of 4π steradian (referred to free field) to one of π / 2 with a considerable increase in efficiency of the release wf of: for each wall is a reinforcement of theoretical 3dB for a total of 9dB!
There will therefore be a reflection PushPull frequencies with a wavelength dx 4 (d = distance from the wall) to be followed by a partial cancellation of the wave emitted), whereas ADX 2 we have a reflection in phase with its strengthening. In reality, these effects are reduced by the overlapping pressure waves (with different phases) from the other walls, but ........
for all frequencies with wavelengths equal to or greater than 8 ADX reflection is still in phase (with phase error of 90 ° from the frequency and tends to zero as f tends to zero) and the acoustic impedance from view ' speaker comes to changes found to emit a sound on an area "seen" as a smaller (half the previous sound power which is thus a double) which includes the aforementioned then reinforced with an asymptotic maximum of 3 dB for f tending to zero.
Whereas in fact only the primary reflections (for conceptual simplicity) being mainly responsible for the evolution of the frequency response in the environment, we have (for each speaker) primary reflections as there are so many walls
the ns. room: six!
Should be established:

1) at what height to put the speakers
2) how far to put the listener from the rear wall (understood as the one behind the listening position)
3) how far to put the speakers from the back wall (in the sense that behind the speakers)
4) how far to put the speakers from the side walls (and hence the distance between them)
5) at what height to put the listener (ie ears) from the floor
6) In relative distance from the ceiling of the room.

How obvious prerequisite to everything that follows should be taken into account as the influence of the walls is proportional to the incident acoustic pressure: the higher the pressure wave incident with the wall, the greater the amplitude of the carrier "wave reflected" that we add direct wave.
Then the walls will be more distant from the source emission weaker their influence in terms of amplitude of reflection.
 

Fig.1 answer with a reflective wall as a function of Report wall distance / wavelength	Fig.2 response with 3 walls spaced in proportion wall distance / wavelength

As you can see from the graph of fig.1 the influence of the wall is greater than the wavelength of the frequency reproduced is large compared to the distance to that wall.
In Fig.2 one can observe the influence of 3 walls placed equidistant from the source of issue: as you can see this is the worst case and may also lead to fluctuations in response to 20dB!
It may be noted however that the ripples caused by the graph ratio x / λ (where "x" is the distance from the wall and λ is the wavelength) equal to or greater than 0.5 are minimal, and then to install the speaker keep account of this factor.

If you can not have your system off-side but less than P L has the following considerations are equally valid with the exception of the distance Y because of the greater influence of the side walls, see "Distance from the side walls" to Following
All the measures referred to below are believed to be related to the center of the woofer
So for the measure compared to the far wall there is also half the width of the front panel (if the wf is mounted in the middle panel of course ....) whereas the shortest path that the pressure wave must make to get to the back wall, so if the speakers are angled toward the listener must add half the panel to the distance between rear and front edge "inside" of the speaker.

Distance K
That is the height of the listening position.
This distance can vary depending on the type of sofa / chair / chair uses the same size as a function of partial reflection and absorption can be made: for example a couch sitting on the same plan involves a partial reinforcement to the distance between the plan itself and ears .... not by chance use a sofa comes greater fullness in the low range compared to the use of a common chair ....
The fact remains, therefore, that this distance will be less certain because it is subject to many variables but be aware that any event will provide reinforcement distributed attenuation-frequency: distance between ear and floor, between ear and back and between his ear and a floor but with certainty but only the latter will lead to a safe distance reinforcement for f tending to 0 for which we will average: K = 100cm
average distance can be checked by sitting on a comfortable sofa / armchair and whose ripple for λ / 4 is (partially) compensated by reinforcement (partially mitigated by the characteristics of sound absorption of the sofa) due to the distance floor-ear is just about half K.
The distance K not determined with precision can not however be taken as a reference to determine the remaining distance.

Distance Z
Ie the distance from the floor.

Speakers pedestal
Knowing the resonant frequency fr and its assumption that the speaker is properly designed with Qt close to unity, we can first establish the frequency fz start floor reinforcement.
To compensate for the depression caused by reflection on the floor that we see at the distance equal to 1 / 4 λ (see previous graph in fig.1 and fig.2), the ideal would be just to have a speaker with Qt = 1 with the excitement typical "centered" around that dip.
That excitement is not exactly twice the fr but it is tolerable simplification in asking: fz = fr
from which a distance: Z = (344/fr) / 8

If we consider for example the resonance characteristic of a loudspeaker as the Grundig Box 850th equal to 72Hz we applying that   Z equal to 60cm.
The ground clearance is achieved by raising the speaker with stand 40cm.

Floorstanding speakers and speakers to "full-range"
If wf extension greater resonance at 40Hz for example with the installation by this method would lead to a ground clearance equal to 344/40 x 8 = 106 cm. This distance itself bears considerable wf ear height (or higher ....) and the group midrange well as high (thus causing an unnatural increase in the image) and causes increased irregularity your answer in the very "significant" of 70-150 Hz, for this reason almost all the speakers with such an extension in frequency are (also having regard to the mole) from the floor or still have calculated taking into account the presence of the reinforcement (due to the fact floor) which starts from an average of 150-200Hz down (wf distance of 30cm from the floor equal to or less) for which the lift from the ground would lead to inevitable loss of "body".
For these speakers we will have to adapt to the installation height "from project" as he tried to raise slightly the WF but never exceed 35-40cm from the ground (always referred to the center of the WF).

Distance X
Both the rear wall (in the sense that behind the listener) and the wall (in the sense that behind the speakers) provide reinforcement following the same rules already seen before: as regards the back wall you can regard the wave as be made by a fictitious source coincident with the point of listening and then do the calculation is equivalent to that already seen.
Although quite similar results obtained with installation type A than type B there are, obviously, differences mainly on the yield of the midbass range that if B is (on average) more cohesive but making it essential to acoustic treatment of the posterior wall speakers should be as absorbent as possible for frequencies above 400-500Hz to avoid flattening the image and loss of definition.
The case A (sofa near the wall) is preferable in case of facilities where the rear speakers is not acoustically treated or only partially.
The cases analyzed are those that most frequently occur at home and obviously you can not just revolutionize the layout of the room: for every decor its place .....
We can now determine what will be the distance X of the point of listening from the back wall in case A (in case B this distance is the distance the speakers from the back wall).
Having to take advantage of 4 appropriately distributed reinforcements have been recovered by 12dB and then extending in an octave (I remember that below resonance diffuser air suspension reduces the output level with a slope of 12dB/oct) will act as follows .
Both Speaker Pedestal for both floor-standing speakers, we can calculate the distance X whereas we already have a reinforcement due to Z and one due to K and then identify a strap attached 1 / 2 octave above the fr (both maximum and to be able to exploit both to comply with the response curve Moeller ...) in third followed by reinforcement (distance Y) set at 1 / 2 octave below the fr.

fx = fr x 1.5 (in our case = 108Hz)

which

X = (344/fx) / 8  then

X = Z / 1.5

for a distance of 40cm is the case here.

Distance Y
We shall therefore such reinforcement 1 / 2 octave below fr.
then:

fy = fr * 0.75 (in the example on the 850th we 54Hz)

which

Y = (344/fy) / 8

or simply

Y = Z / 0.75

for a distance in the case of our example of 80cm

The determination of the distance and the distance X Y affects the way speakers on the distance-point of listening and then to check the maintenance of a ratio distance loudspeaker-listening point / distance between speakers tolerable around 1.5 (say 1, 3 to 1.7 approx.)
Discourage the equilateral triangle "classical style" to avoid excessively dilated images with classic "hole" between the speakers.

Considerations
Given the above example with the distance and K equal to 100cm examined to determine the quarter, we reinforced the box850a (speaker resonance at 72Hz) the following distances:
Z = 60cm
X = 40cm
Y = 80cm
And 'interesting to note that in this case thus made the 4 reinforcements are distributed distance of 20cm from each other and therefore obtaining appropriate compensation while avoiding the deficiencies that occur in response to the case of two walls placed at same distance.
Thus the speaker in question is to extend its response in an octave of Ben!

Very important thing to emphasize is that these 3 distances that concerns only the low range (on the upper midrange of course much depends on the acoustic treatment of the various walls) are interchangeable depending on their needs for furniture.
Clearly all this is in agreement with the nearest side wall that must lie at a distance of not less than 120cm otherwise you can still apply this method but should be replaced with one of these distances on the side wall of the station (although in this case reinforcement is relative to the low range of a single speaker).
If the installation of speakers with an appropriate extension in frequency distances capacity calculation, as an obvious consequence, to a location (bonds) in rooms large. The choice of these speakers should be made only if you have the availability of large spaces, in a small room a full-range speakers would only lead to a marked exaltation of bass.

Distance from the side walls
Regarding the distance from the side walls you may find (depending on the type of room you have available) in two different conditions:
1) distance d2 greater than K
2) Distance d2 less than K
In the first case, we are probably in the presence of availability of sufficient size, at least in width, which allows better and better application of the method in the latter case we should instead consider that the distance d2 must be changed to Y (that is, to what is the maximum distance of the three above, ZXY) by placing a higher value as a distance Y of K not less than 110 cm (for K = 100cm).
To have the least influence of the side walls, in terms of linearity of bass response, we may ask the speakers so that the length L divided into three equal parts: each speaker will then be L / 3 from the closest wall and to 2 / 3 of L compared to the far wall (of course L / 3 is also the separation between the two speakers). This distance would compensate (as guessed) at least in part the primary reflections in the low range side.
But such a place brings the listener exactly the same distance from the two side walls, creating irregularities on the response especially if these walls are bare or at least close to the listening point (narrow room).
Then choose always the asymmetric (cases A and B) even if the narrow room (in which case the asymmetry will be very small matter given the closeness to the speaker of the side walls and should be verified experimentally) so as to avoid further such irregularities .
As an experiment I could draw as relations between distances (seen good in the rooms where I have checked this method) the following:
d1 = 4 / 7 L or in case of very large room and particularly resonant on the low d1 = 3 / 7 L
d2 = 3 / 7 d1
d3 = obviously obtained as an interim step to d1 and d2 (axis of symmetry with respect to the speakers, is still between 1/3L and 3 / 7 L)

Distance from ceiling
Considering the wf floor height not exceeding 70-80cm away from the ceiling will have a greater than or equal to 2m which would involve a possible reinforcement 344 / (2 * 8) = 21.5 Hz that although there may be pleasure in theoretically no effect (as far as the only reinforcement) largely on the overall result.
It appears however very influential if it is tilted (see lofts) and smooth (if you already different speech beamed) and substantially affect the result if not acoustically treated in mid-high range.

Examples
With reference to the following table as seen for example in the case of SL1000 distance calculated by the method Z is exchanged with the distance Y, since it coincides perfectly with the average height from the floor of the two woofers. The color identifies the data available, while the calculated column identifies what distance (between Z, X and Y) is more appropriate to use as high in the case.
As for the DSL is not exactly the height calculated with the real height because of the particularities of the project that needs a little reinforcement in advance: do not go absolutely raise more!
Calculated values in parenthesis beside the real ones.
 

distanza\diffusore	Grundig box850a	Grundig box1500a	Grundig Box2500a	Grundig SL1000	LT DSL	Rogers LS3/5a	Dahlquist DQ10
fr (Hz)	72	70	58	95	61	80	45
Z (cm)	60	61	74	60	62,5 (70)	70	*      35 (63)
X (cm)	40	41	**      49	30	46	**     36	95
Y (cm)	80	82	98	45	93	53	126

* height woofer from the ground with legs raised with the original speaker.

** In these two cases (indeed quite rare ...) this distance should not be considered as such speakers from the project have already provided an exaltation in the same area of frequency of reinforcement for beginning the distance. In such cases you should therefore take into account the remaining 2 distances (with the other walls placed at greater distance of course).

Conclusions
The method described is not intended to be neither perfect nor final, may even undergo further refinements, not even pretend to be reflected in all cases (the furniture can make significant variables) - Council to mark the floor so the position of the speaker before application of that method (sore is going back .....) - but I think provides a clue other than the usual and a good basis from which to install your system.
I am available to discuss the various aspects within the forum with those who want to bring their experience and their advice in order to refine the writing, applicability and understanding.

                                                                                                      Massimo Ambrosini

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Choosing speakers / room

DIFFICULTIES 'INSTALLATION
In this part, I tried to analyze the difficulties encountered in obtaining the best results from each speaker.
As for Multi-Fix is obviously greater because the tilt of the speaker toward the listening point also involves a different issue at the speaker side by side (MR and TW), and then ..... need some more proof.
We must also take into account the limited dispersal of some speakers in the high midrange (especially DSL and ESL63) from which a most difficult setup to get the "right" sum of emissions from two speakers in that range and especially in the case of the dipole also considerable weaknesses in order to obtain proper consistency bass and midbass.
The vote was then the lower the higher the difficulty of installation.

ROOM VOLUME
Since you can not provide measures of minimum and maximum for each speaker, I preferred the very least provide an indication of "rough" that can still be completed with the application of the method of "installation speakers".
Broadly speaking the term "small rooms" within the local 10mq, "medium" between 10 and 20sqm and "large" than 20sqm.
 

loudspeakers system	timbre respect (see note 1)	ability to disappear	dynamic capacity (see note 2)	installation difficulties	room volume
box300 (on bookshelf)	9,5	9,5	7	8	small
box400 (on bookshelf)	9,5	9,5	8	8,5	small/medium
box500 (on bookshelf)	9,5	9,5	8	8,5	small/medium
box650prof	9	8,5	8	8	small/medium
box850a prof	9,5	9	9	8,5	medium
box1500a prof	9,5	9	9	8,5	medium/large
box2500a prof	9,5	9	9,5	8,5	large
SL1000	9,5	10	8	8	small/medium
aktiv20 mod LT	10	9,5	9,5	8,5	medium
aktiv30 mod LT	10	9,5	9,5	8,5	medium/large
aktiv40 mod LT	10	9,5	10	8,5	large
LT DSL	9,5	10	9,5	9	medium/large
Telefunken TL800	9,5	9	9	8,5	medium/large
Rogers LS3/5a15ohm	9	9	7	9	medium
Quad ESL63 mod CCI	9*	7*	7,5	6	medium
B&W DM6 prima serie**	8,5	8.5	8,5	8	medium/large
Dahlquist DQ10	9	9	8,5	8	medium/large

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