Hardware manual

NexSys v. 3.0 Crest Audio Inc.

band, number of sample points, number of cycles per sample point, and test signal attenua-

tion. Once this data is entered a test sweep may be conducted by clicking on the sweep but-

ton located below the graph. When the reference curve is completed you may elect to save

the reference which means that that exact curve will be used as the baseline for all subse-

quent tests.

Entering Test Parameters

Remember that the test signal is generated at the ampliﬁer, so any limiters, crossovers, etc.,

at the head end will be out of the signal chain. First, enter the pass band of the test- if you

are testing compression drivers with a response range of 800Hz - 10kHz then this same

range should be entered. Next, enter the number of sample points. The maximum number

of points is 200 and this will produce the most detailed results- but it also takes the longest

time to perform and the detail it provides may not be required. Try using 50 sample points

ﬁrst. If the detail of the curve is acceptable then leave that as a default value. If the 50 point

curve takes longer than desired then try a smaller number bearing in mind that the resolu-

tion of the curve will decrease.

Next set the samples per point parameter. This deﬁnes how may samples per discrete fre-

quency will be acquired, averaged and then reported to the host computer. Typically a value

of 3 yields consistent results without taking excessive time that additional samples would

require. Using larger numbers to acquire more samples will deﬁnitely slow the process.

Always enter an attenuation value that is high (30 dB for example) until you determine how

the system will respond. The reason is very simple- the test inserts pure tone into the ampli-

ﬁer which may result in some very high SPL as compared to dynamic program material.

Always start with a large number for this selection. After running your ﬁrst curve you must

determine if the amount of attenuation is correct for the test. Excessive attenuation may not

exercise the drivers (especially LF drivers in reinforcement systems) sufﬁciently to have the

test yield results that would indicate a failure. If the initial attenuation levels are high try

additional tests entering a lower attenuation value so that the drivers are fully exercised but

are at levels that are not painful to humans and other living things.

Distributed high impedance systems typically do not require the detail of testing or the

sound pressure levels that reinforcement systems do. With careful attention and some exper-

imentation on how to best set these parameters, impedance sweeps can take place largely

unnoticed. This testing procedure will however, be more effective if conducted at realistic

sound levels and duration.

Care must be taken when initiating an impedance sweep. Excessive duration or

sound levels could cause speaker damage or personal injury.

If any of the sweep parameters require changing you may either abort the sweep (click on

the abort button) or ﬁnished the test and select a new reference. You may need to run the

reference sweep several times in order to determine the optimum setup parameters. Once

you have determined the proper test settings save the reference. This will automatically use

the same parameters on all subsequent sweeps.

Be sure the reference sweep is done on the system when all speakers and speaker wiring is

working properly. This will ensure a proper reference sweep.

Page 15.2 Software Manual