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Audio Pro B2-50 Subwoofer Bassystemet that goes nail straightlily down to 20Hz with extreme low distorsion


   “You´ve done the impossible”

AUDIO PRO B2-50 was shown for first Dr. R.H. Small in Australia has teore-
past on an of the world's bigliest audiomäs- tiskt proven that the is impossible to do kon-
sor - Consumer Electronic show - ventionella speakers that both have good
in Chicago, 1978. effectiveness, moderate carton size and straight
Namnkunniga konstruktörer and kriti- frequency time long down in the basis.
ker within HiFi listened, looked, sitdowned in A way to come past this begräns-
in konstruktionen - och listened again! ning is then to do a specialsystem for
Chefredaktören for an of USA ' s most the basis, a system where the speaker and pre-
well-known audio-tidningar listened and pre- the pc renown vats that run the to be seen as an unit
vånades also he, so to that degree that he and dimension avalanches ihop - en so called active
called on an of audiovärldens well-known hög- speakers. Additional effect can then be allocated the
talarkonstruktörer. The editor wanted to have lowliest tonerna -där the behövs - och on so
professional and impartial help that few pre- ways can the basis area be increased.
coped with that the he consulted actually each  
physical possibleily, for never earlier had A NEW, UNIQUE TECHNOLOGY
he consulted so clean and considerable basis with so little The does not be sufficient however with straightening fre-
distorsion and the explanation to why the kvenskurvan with an active system. High
came so powerful basis from a so small carton set sound pressures, with low distorsion, must can
all established högtalarbegrepp on the head. be brought forth which sets requirements on that the system
The editor might gradually clearlily for will pumpkin big quantities air. About one
itself that this not only each possible, without also will can to bring forth 100 dB right to down to 20 Hz
a revolutionerande new ways to tackle with an end högtalarsystem, willed hög-
basis depiction. The each then he fälla kom- talarelementet need to last 24 inch (60 cms)
meaning taking clean in the section. in diameter about the could hit ±4 mm. Dess-
Behind Subwoofern and the patented except willed the be required a big högtalarlåda
world the unique method as done the possible and a lot of considerable effect an amplifier.
stands a Swede konstruktör and inventor, If one uses a basreflexlåda
Cold Ståhl. So here describes you bak- instead for an ends, decreases these requirements
the basis: strong. So far has the however not existed
You can höra - och känna- tonerna down some active method that functions together with
to approximately 20 swings per second. basreflexsystem and both gives straight frekvens-
If you have a pair good speaker functions time and slimmed-down distorsion.
the perhaps down to 50 Hz in the basis. Then The is where my new method comes in.
farms utnivån to sink quicklily and distor- The is called for ACE-Bass, uttytt Ampli-
sionen increase strongly. fier Controlled Euphonic Bass. The method is
A subwoofer is used in order to reproduce patented or patent applied for in most big
tonnes from 20 Hz up to approximately 100 Hz while the industrial countries and Audio Pro has exclusive
one lets common speakers or side systems correct to the method.
takes hand about the rest of the frequency area. ACE-Bass, that is the basis and förutsätt-
A good subwoofer does not give only an utsträckt ningen for Audio Pro B2-50, is therefore an active
basis depiction without also an a lot of good method in order to good basis few depiction. The
depiction and an entire new experience in the functions excellentlily both with closed cartons
the low registers. and with basreflexlådor. The principle is that
Since the does not exist some stereo- ACE-Bass the amplifier checks hög-
information (direction feeling) in those low tonnes talarelementens mechanical parameters
as a subwoofer reproduces, is sufficient the with oscillated mass, moderation and fjädring/'
such a in a högtalarsystem.

                                  Audio Pro B2-5Q

The combination of straight frequency time down to 20 Hz and capacity to high sound pressures with low distorsion does that Subwoof ern is entire without competition. Corresponding performance does not go to achieve to be itself with conventional methods or with other active methods, since these does not function together with basreflexlådor.

A COMPLETE BASSYSTEM to use subwoofers is quite new in Europe, but in USA has the occurred in several years. Those speakers that exist do not come however in the vicinity of B2-50 ' s performance. Moreover has early subwoofers, apart from the actual speaker, often required additional effect an amplifier and separate division a filter. The has given costly and clumsy systems as not always functioned that one desired itself.

B2-50 Subwoofer solves also these problems. Both an effect amplifier on 80 Woch an a lot of flexible electronic division filter exists integrated. Delningsfiltret does that Subwoofern can work fairly together with side which system as entire pcs.

You can part's adapt Subwooferns sound volume to side system even, part's to determine how far up in the frequency Subwoofern will work. Moreover, you can cut of the low basis in the side systems, since the most often is irregular in frequency past and has high distorsion.

Subwoofern is connected just rightest between preamps and effect stages. Goes the not to detach them in your plant so can Subwoofern also is connected to the common högtalarutgångarna.

ÖVERLÄGSNA PERFORMANCE Audio Pro B2-50 Subwoofer has two paragraphs specialgjorda högtalarelement with big magnet and extreme long stroke, ±9 mm. Through doing a basreflexsystem, as been optimized with help avACE-Bass-metoden, so needs the elements not to last bigly than 6,5 inch!

B2-50 Subwoofer has straight frequency curve bottom down to 20 Hz and the can cause high sound a lot of pressures.


The unique subwoofern.

The unite högtalarelementet is turned bak- och - forward (the electrical connection has of course also been turned). The means that the to unite the element “threads”, concurrent that the other “shoots”, whereupon a big part of distorsionen släcks out. Along with ACE-Bass-metoden that additional decreases distorsionen, gives this Subwoof ern unique good distorsionsdata, also at low frequencies and high sound pressures.

That we achieved all this with net carton a volume on only 50 liters are a performance that does Subwoofern still more unique.

MANY FINESSES B2-50 Subwoofer is a worked through and precise uttestad structure with many finesses.

The sophisticated integrated end the stage has among other thing active mjukklippning, which means that you not sheep some interfered bee sounds if you willed run the system over its ability (överstyra the).

A special filter in the amplifier limits högtalarelementens konutslag during 20 Hz.

Special weight has to be placed at formulation of the carton and basreflexröret - that ends in botten - för att entire to eliminate blås- och murmur sound even at the low frequencies and the high sound the pressures.




The is the new ACE-Bass the method as done B2-50 Subwoofer possible. The method exits on giving högtalarelementets mechanical parametrar - svängande mass, moderation and fjädring - the new host through running the with an amplifier with a lot of special utimpedans.

That the does not go to do systems that B2-50 Subwoofer with conventional methods has we already mentioned, but the exists of course other active methods than ACE-Bass, for example re-engage systems as MFB or servosystem. These can however only be used along with closed cartons, which sets almost unreasonable requirements on högtalarelement and förstärkareffekt. Systems that only increase frequency huddling used to in the basis and in this way utsträcker the frequency area exists also. Distorsionen becomes however an easy problem in such systems and the is sensitive for discrepancies in the natural frequency the curve.

ACE-Bass is widelily divided from the above methods and functions excellentlily both with basreflexlådor and closed cartons.

A speaker's properties are decided to a large extent of högtalarelementens mechanical parameters. Since these is checked through ACE-Bass so can one few both straight frequency time and low distorsion, concurrent as the system becomes okänsligt for variations at högtalarelementen.

ACE-Bass was presented of cold Ståhl at Audio Engineering Societys 61:a konvent in New york in November 1978. If you want to can you few a copy of preferred (on English) from 3Dgruppen ab.

LITTLE HÖGTALARTEORI in order to explain how the method functions must we first go through little högtalarteori.

A speaker's electrical impedance is shown in character 1.

Re is talspoleresistansen and Zb is a mechanical impedance that depends on the carton and the ambient air.

Högtalarelementets the cow and number bobbin has a certain weight, the so the called oscillated mass Mm. The sexes' upphängning has a certain fjädring cms and moderation Rm. These mechanical parameters give parallellreso-nanskretsen, where A is the element's force factor (also called Bl-faktör).

We can in fig 1 see that the mechanical parameters influence the electrical impedance. With ACE-Bass does we tvärtom - vi influences the mechanical parameters through the amplifier's electrical utimpe-dans.

We can also consider högtalarsystemet from the mechanical side and may then the ekvivalenta the schedule in fig 2.

Fig 2. Equivalent schedule for a högtalarsystem seen from the mechanical side.

Tune you is not misleaded of that the mechanical components here be represented with electrical symbols. The depends only on that the is easy to draw these.

F is that force that to be brought forth of the amplifier's ut-spänning U and Ru is the amplifier's utresistans.

We can here see that apart from the true moderation Rm exists an additional “electrical” moderation

.Normalt is the amplifier's utresistans Ru~0, but through doing the barrel organ or negative can one to give the total moderation a rather arbitrary value. This is old well-known technology that in certain case has been used early. The new with ACE-Bass is that we on similar way also can to determine the oscillated mass and fjädringen.



ACE-BASS - TO TAME A SPEAKER's MECHANICAL PARAMETERS in order to achieve this control of all the three mechanical parameters uses we an amplifier according to fig 3b, unlike the conventional amplifier in fig 3a.


Fig 3b. ACE-Bass amplifiers.

ACE-Bass the amplifier comprizes a negative resistans Rs, new parallel a circuit and a driven power generator instead for excitement generator.

Then we mesh ACE-Bass the amplifier in fig 3b with the speaker in fig 1, may we the schedule in fig 4. Since the amplifier's negative utresistans takes out talspoleresistansen so ends up the new parallel the circuit - comprizing CP, RP and LP - analog with the old as being given of högtalarelementets true mechanical parameters.


Fig4.Ekvivalent schedule for ACE-Bass, seen from the electrical side.

Fig5. Equivalent schedule for ACE-Bass, seen from the mechanical side.

Sees we same system from the mechanical side sheep we in the schedule in fig 5, that will be compared with the conventional system in fig 2. We find then that the total oscillated mass has ökat with A2CP and the moderation with AVRP and that fjädringen become rigid through Lr/A2. Through choosing CP/RP and LP in the amplifier's end impedance on appropriate way can we therefore few those mechanical parameters that we desire.

These rail only mechanical parameters that we achieve through ACE-Bass the amplifier's ut-impedans is actual so apparent that about a mekanist



willed measure up högtalarelementens mechanical parameters with the amplifier tillkopplad so willed he find the rail only and not the true parameters.

ACE-BASS THE AMPLIFIER ACE-Bass the amplifier according to fig 3b must be done with special methods, among other thing because negative resistanser does not exist as components. A good way to do the amplifier on being shown in fig 6.

Fig 6. Blockschema for ACE-Bass amplifiers.

The power through the speaker feels of with R and the positive återkopplingen about the effect amplifier gives the negative resistansen while the negative återkopplingen about the band passport filter gives the parallel circuit.

ACE-BASS in B2-50 SUBWOOFER in B2-50 Subwoofer uses we ACE-Bass in order to do basis a system with straight frequency time down to 20 Hz with least 100 dBspl out. We want to moreover to have moderate carton size and förstärkareffekt and low distorsion. In order to achieve this has we done a 6:e the order's Butterworth-system. The means that the speaker is a basreflexsystem - as here been optimized with ACE-Bass - and that a 12 dB/oktav filters exist in the amplifier in order to decrease högtalarelementens konutslag during 20 Hz.

This optimum systems do that we can to fulfil the lined up, hard, the requirements with two specialgjorda 6,5 " högtalarelement.

For these elements, we have through ACE-Bass reversed the oscillated massan - för both elements tillsammans - från 38 to 260 g, the moderation from 25 to 56 kg/s and f jädringen from 0,45 to 0,25 mm/N.

Such values can one not give the true mechanical parameters and although one could the so willed the effectiveness become unacceptableily low.

LOW DISTORSION that we already mentioned gives ACE-Bass low distorsion. The depends on that the through ACE-Bass syntetiserade the mechanical parameters are more linear than the true parameters. Of course more the syntetiserade the parameters dominate over the true, the low distorsion may one. In B2-50 Subwoofer has we a select solution where the syntetiserade the parameters considerable dominates the true and Subwoofern has therefore extremelily low distorsion. Moreover, the system becomes through this solution okänsligt for variations in the true mechanical parameters.



Frekvensgång: 20-200 Hz within ±1,5 dB from the curve below, 6:e the order's Butterworthsystem with - 3 dB at 20 Hz, the upper boundary frequency adjustable 40-200 Hz. Ljudnivå out: least 100 dBspl on 1 meters' distances in half held (2tc steradiancrs volume angle). At high frequencies than the very lowliest can up to 10 dB high sound pressure be received. Normal location on the floor against a wall gives considerablily highly sound pressures.

Känslighet for 96 dBspl: adjustable 50 mV to 2,5 V for förförstärkaringången, >10kohm inimpedans, and


Frekvensgång ' at different attitudes of the upper boundary frequency.

“the curves are measured with Bruel&Kjaer mätutrustning in a big, approximately 1000 m3 echo free rooms. 3 mm/s sweeping speed, 100 mm/s writing speed and clean sinuston has användts.


1 to 50 V for effektförstärkaringången, >20 kohm inimpedans.

Avskärningsfilter for the side speakers: 6 dB/oktav inställ-bart between 50 and 250 Hz, strengthening 1, <200 ohms utimpedans, maximum signal >5 V, upper boundary frequency>500 kilohertz, maximum excitement derivative 13 V/|ice, distorsion <0,02% (the filter is only active then förförstärkar-ingången is used).

Measures: spread 46 cms, increased 54 cms, deep 45 cms. Folded: 28 kg net.

Typical distorsion * at different sound levels, 2a+3c harmonious övertonerna.

Distorsion is measured with tersoktavfilter, why low distorsion than approximately 0,5% cannot be measured.

Audio Pro B2-50 is produced at Lövånger electronics Ltd


   They who did it

The world unique Audio Pro B2-50 Subwoofer each developed in Sweden of 3Dgruppen. The replied moreover for a row other innovations and unique audio-konstruktioner that market was pursued during Audio Pro-märket. Here is seen from left Ola Malmefeldt, Ingemar Hartwig and Bengt Svärdström from 3Dgruppen in chats with Subwoofcrns konstruktör cold Ståhl.



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