There was an article to relate the concern between element of audio of a few influences and objective index and electroacoustic products plan, craft before. Share electroacoustic parts of an apparatus to affect audio to everybody now index of a few technologies.

 

We still are with loudhailer exemple will show this issue. Here we promote the “ class ” of electroacoustic parts of an apparatus, we

 

Will study the technical index of the loudspeaker that Hi-Fi acoustics uses.

 

The loudhailer nature that friends use to Hi-Fi acoustics is not new. When we choose a loudhailer, loudhailer manufacturer nature is met

 

Provide a few parameter and test data. The manufacturer that bear the blame can offer commonly:

 

Impedance, power

Noisy curve of sensitivity, frequency

Curve of F0, impedance

A few common T/S parameter are like Qts and Xmax, the data such as BL.
 

Actually, parameter of the noisy curve of such as frequency that a lot of manufacturer offer, impedance curve, T/S, the circumstance of lack fidelity ” of the “ beautification ” with exist certain and “ . Even if is relatively elder has a fever friendly, build a frequency to check a system to be like LMS by oneself, basic also upper limit at checking above parameter accurate just. However, more and more practice prove, pay close attention to above index merely, still can’t decide the stand or fall of monomer of a loudhailer. That is to say, pay close attention to above index only, it is insufficient actually. But regret is, electroacoustic architect mixes current great majority have a fever friendly, it is to be in be based on the function index with narrow above to undertake designing, having toing say is a kind of regret.

 

Below, tiger 180 won’t pay close attention to commonly with respect to a few everybody, but very useful to the design a few parameter and data, one by one describes:

 

One, THD

 

THD is the abbreviate of English “Total Harmanic Distrotion” . Ring with frequency the curve is similar, in different frequency point, the THD of loudhailer is different also. Because this THD can generate a curve. And in the norms of general loudhailer, all do not have corresponding description to THD curve. But actually, THD is great to listening to move impact. Brief for, the loudhailer of THD overall on the high side, its sound scarcely is like the nature that the loudhailer of overall on the low side comes to THD.

 

The noise of a frequency that next graphs are typical loudhailer and THD curve. From inside the graph we can see, THD curve is in low frequency part, especially under syntonic frequency when, can have relatively substantially carry litre. In frequency of prep above resonance when drop all the way. In certain frequency dot, accompanying frequency noisy curve rise and fall, THD curve also arises rise and fall.

 

 

THD curve around low frequency F0 carry the internal cause that promote basically comes from Yu Yangsheng implement amplitude. Because loudhailer is near syntonic frequency,basically be, amplitude is increased, those who bring about phonic film fold annulus and centering to raise piece etc those who cause is lack fidelity. Cause this lack fidelity origin to still have a factor, that is magnetic circuit of symphonious circle cooperate. If phonic group brought about the flux with phonic located group to have bigger change in the displacement in magnetic circuit, what also can cause bigger low frequency is lack fidelity.

 

THD curve is in high frequency paragraph ” of “ peak value and brace up Buddhist nun of velar appearance, internal resistance closely related. Often go up in this frequency dot, because high frequency sound wave is in brace up the transmission on film, brought about brace up ” of “ standing wave arises above film, make then nod in certain frequency, brace up certain place of film is out of shape apparent, reflect go up in index, it is the peak value of THD. Hereat corresponding, also often can behave the cereal that it is a peak on frequency noisy curve, affect then listen feeling.

 

Further analysis is lack fidelity, still can be opposite according to rank number lack fidelity do fractionize. Pursue as follows, right 2 rank and 3 rank lack fidelity show respectively.

 

 

Those who need an attention is, THD index is the frequency that works with loudhailer and susceptive power closely related. Broke away from designation frequency or power, talking about THD is theoretic. Curve of the blue in pursueing on is the THD curve when 2W, and the THD curve when maize curve is 0.5W. The loudhailer that sells on market, a lot of do not give the data that gives THD, because traditional large loudhailer produces business,that is, take THD seriously not quite, the test equipment of a lot of manufacturers even cannot accurate measure a THD curve! And accompanying a mobile phone to wait for the promotion that consumes kind of product frequency design, of system of test of frequency of enharmonic of B&K, Soundcheck guide, THD got the attention of a few manufacturer. What need points out is, loudhailer power is lower, THD is smaller; In 1-2K frequency paragraph, the THD of loudhailer also is comparative and inferior. A few manufacturer claim oneself loudhailer THD can accomplish <5% even <3% , look seemingly very low, but if do not specify power and the word that specify frequency dot, basically be no point. The sort of so-called oneself THD can be accomplished 1% even 0.5% the following, basically mix mountebank as good as. . . If need to pay close attention to THD, the proposal pays close attention to the THD curve below rated power, such meetings are a few more objective.

 

2, T/S parameter

 

T/S parameter is the basic parameter of the model of loudspeaker system maths that offers above all by THIELE and Mr SMALL. T/S parameter is the basic parameter of the model of loudspeaker system maths that offers above all by THIELE and Mr SMALL. T/S parameter is comprised by parameter of 4 small signal and parameter of 2 big signal.

 

Small signal parameter includes 4 basic parameter:

Fs is the syntonic frequency of loudhailer unit.

Vas is the equivalent cubage of loudhailer unit.

Qes is the electric Q value of loudhailer unit.

Qms is the mechanical Q value of loudhailer unit.
 

In applying actually, classics regular meeting encounters Qts parameter, its token loudhailer is in low frequency paragraph the size of syntonic peak. Qts is the paralell connection of Qes and Qms.

 

Big signal parameter includes two basic parameter:

Pe (Max) heat up ability place to decide to loudhailer comes loose unitly most high-power rating.

Vd is loudhailer unit brace up the volume that film drives when the biggest amplitude.
 

T/S parameter is in process of electroacoustic system design, need is judged neatly according to actual condition. The applied setting that we often encounter is not had outside two kinds. The first kind of setting: As it happens of our at hand has monomer of a horn, we hope to design a sound box that can be used at bass replay with it. The 2nd kind of setting: We use the need of setting according to making, the plan does the casing with a long more affirmatory aspect ratio, even the blueprint paper that we had considered casing, decided the acoustics structure of casing, we hope to choose an appropriate horn monomer to cooperate our casing. No matter be the sort of circumstance, there is the ” effect of ideal of a “ in our memory, our design should be close to the ” effect of this “ ideal as far as possible. Right now, t/S parameter can help us make certain judgement. Make we obtain a low frequency to answer the system of the ” of “ ideal effect that is close to us.

 

Try with 2 for exemple, summarize this process to be as follows:

 

Assume we need to make the sound box of an airtight casing, loudhailer caliber 4 inches, hope acoustic quality is good, move of low frequency volume is highlighted as far as possible, how should design?

 

According to the physical meaning that Q is worth, hypothesis Qts is Qes and Qms paralell connection, syntonic peak of taller low frequency jumps over Qts big, low frequency measures the word that feels outstanding, we should the trumpet with first selection high Qts? When be being designed actually, often not be such. The first pace when the design often can consider syntonic frequency Fs first, because syntonic frequency Fs is displacement amplitude,obtain even frequency to respond the turning point that gains even frequency to answer with acceleration amplitude. Fs is lower, mean even frequency to answer a curve to be jumped over to low frequency Duan Yanshen much. Contrary, fs is taller, mean in the frequency under Fs paragraph, acoustical pressing will drop according to exponential rule, obtain good low frequency not easily to answer. To 4 inches of loudhailer, the common limits of Fs is between 60-90Hz, low Fs conduces to the promotion of low frequency.

 

After the loudhailer that has chosen appropriate Fs, we just need to go to those who consider other parameter and casing matching. Here when, the element that we need to consider has: 1, airtight sound casing accumulates what after antrum forms to compress ” of air “ bedspring, the meeting is right loudhailer brace up ” of damp of velar generation “ . This damp can bring about systematic resonance frequency to lift, loudhailer low frequency paragraph amplitude is reduced. . The.2, effect that considers this damp, need loudhailer monomer checks mode to work to owe the state of damp ” in “ in baffle, hind of put on an act uses air damp to achieve correct “ damp to answer ” thereby. . Problem of ” of speed of “ of.3, loudhailer. In this design, need to ensure above all listen feeling, namely dimensional feeling and career move, ensure voice is fresh, not slow, not laggard also. Go after flat frequency to answer again next. Right now, the QMs parameter of loudhailer with respect to the use on the clique. Enough the design of big Qms (be like Qms>2) it is the key that acquires tut show. . Of noisy curve of.4, frequency flat. Traditional sound box devises theory, be designed according to this train of thought, can take the place of to examine. If need to adjust, in ensure the premise of Fs, speed falls, the adjustment that can design through BL and diaphragm will be optimized further. Common law is: Increase BL, qms promotion, qes and Qts drop.

 

3, time domain and transient state are answered

 

Paragraphic in front mention, the problem of ” of loudhailer “ speed, this answers a question with respect to the time domain that is loudhailer and transient state actually. Also be to decide to listen to a of feeling very main factor. The time domain of loudhailer and transient state are answered, in traditional loudhailer and acoustics the domain that make is talked about very little, but if do not pay close attention to,dig the design of this kind of index greatly, the component that wanting to obtain good audition to feel can be ” of “ try one’s luck only is a few bigger.

 

The time domain of loudhailer and transient state are answered, having system of very much electroacoustic test can complete a test. Commonner electric sound measurement software Soundcheck, the 2006th among them module—Time Selective Response, can finish corresponding measurement. Be like again free acoustics measure software REW (Room Eq Wizard) , also can measure such as TimeDomain to answer.

 

In be being answered with transient state in loudhailer time domain, graph of three-dimensional spectrum accumulative total is a kind of our more familiar logo. More moment, he has more the name with popular image: Fall plan.

 

 

Fall plan has 3 dimension to spend form, it is frequency, sound pressure level and time respectively. Inside the plane of time =0, the noise of stable state frequency of the loudhailer that be measured can be regarded as the first curve. And after passing interval of period of time, the odd frequency noisy curve of the loudhailer that be measured can generate the 2nd curve again. Repeat this one process, can get on different time coordinate a lot of curve. Right now, the leftover frequency noise of loudhailer is characteristic with respect to take in everything in a glance.

 

Good attenuation character is complete frequency of course paragraph even attenuation, and attenuation is splitting. But in fact, loudhailer won’t stop immediately in the motion after drive disappears, so we can be retreated only and beg next, from the attenuation time of loudhailer and attenuation uniformity two dimension are spent will ask.

 

4, phasic character

 

In a good linear system, if we define output to did not produce the delay time of any deformation and time to inputting signal, criterion a frequency of this system and photograph frequency curve are flat. And actually, the output signal of loudhailer is existence deformation and delay time to inputting signal. Among them, because be apart from brought defer, it is a fixed cost. And after eliminating this fixed cost to affect, we still can get an opposite phase shift curve.

 

 

The phasic wave motion in the curve of opposite phase shift of loudhailer, often mix the wave motion of a frequency curve is one to one correspondence. Loudhailer unit serves as a the smallest phasic system, the photograph frequency character that its do not take group of delay time is OK Xibaite changes a frequency classics and get by its. These are fluctuant, often can make a mark that loudhailer changes tinnily. Exemple as above pursues medium, group the wave motion between the 5-6KHz of the token in defer curve, extent curve, phasic curve.

 

Notable is, in scale down design, also need relatively of consideration loudhailer of the system join phasicly. If join occurrence problem, corresponding frequency noisy curve also can appear fluctuant, and audio quality also can be affected.

 

In addition, loudhailer still has the index such as such as directivity to need to pay close attention to. The friend that these index have fun at can consult by oneself relevant data.

 

(author: Ge Hu)