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Dayton DS90-8 driver does not measure up

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  • Dayton DS90-8 driver does not measure up

    I have a problem with the portable Bluetooth speaker I am building at the moment. I have measured the speakers and that endeavour has been documented in another thread. However, I feel the problem I am having now is too far removed from the initial problems I have documented in the other thread an that they warrant a new one.

    To describe my problem. I have build a Bluetooth speaker using the Dayton DS90-8 and the Dayton ND16FA. I have just started doing measurements of frequency response and impedance response. From my measured responses I have found a quite large discrepancy from my simulated response for the DS90-8 in VituixCAD and my actual measurements.

    I have made a bass reflex enclosure, and to add more confusion Parts Express recommends two different enclosure volumes for the DS90-8. One of the recommended volumes is 3.39 l (0.12 ft3) and a port of diameter 2.54 cm (1 in) and length of 15.2 cm (6 in). This is supposed to give an f3 of 73 hz. On the other hand, a volume of 1.41 l (0.05 ft3) with a f3 of 80 hz is also recommended. Port diameter and length is not specified for this enclosure volume.

    My Bluetooth speakers is made of two separate chambers with a volume of 1.56 l (0.055 ft3) and with a port each with a diameter of 2.4 cm (0.95 in) and length 11 cm (4.3 in). The simulated response of this enclose gives is:
    • fb = 82 hz
    • f3 = 80 hz
    However, my measured response of the driver in this enclosure gives:
    • fb = 113 hz
    • f3 = 115 hz
    This is far from the measured response. So I though that since the product information page gave two different recommended enclosure volumes, then perhaps the T/S parameters on the product page was wrong and the driver had been updated without updating the information. So I measured the T/S parameters of the DS90-8, but they were quite similar to the product specs. Of note is that I have not broken in the driver.
    Parameter Manufacturer Measured
    Sensitivity 84.1 dB @ 2.83V/1m 82.9 @ dB 1W/1m
    DC Resistance (Re) 6.3 ohms 7.35 ohms
    Voice Coil Inductance (Le) 0.56 mH @ 1000 hz 0.312 mH @ 2643 hz
    Resonant Frequency (Fs) 81.4 hz 79.2 hz
    Mechanical Q (Qms) 2.19 2.78
    Electromagnetic Q (Qes) 0.53 0.58
    Total Q (Qts) 0.43 0.48
    Diaphragm Mass Inc. Airload (Mms) 3.8 g 3.96 g
    Mechanical Compliance of Suspension (Cms) 1.02 mm/N 1.018 mm/N
    Surface Area Of Cone (Sd) 31.2 cm² 31.2 cm²
    BL Product (BL) 4.76 Tm 5.01 Tm
    Compliance Equivalent Volume (Vas) 1.31 l 1.43 l
    Driver's Mechanical Losses (Rms) -- 0.709 kg/s
    Here are some pictures of the enclosure I have build from the front and the back.

    Click image for larger version  Name:	image_79000.jpg Views:	1 Size:	85.8 KB ID:	1409450Click image for larger version  Name:	image_78999.jpg Views:	1 Size:	80.3 KB ID:	1409451

    Here is a graph of the simulated and measured impedance of the DS90-8.

    Click image for larger version  Name:	Dayton_Audio_DS90-8_Impedance.png Views:	1 Size:	25.0 KB ID:	1409453Click image for larger version  Name:	impedance_ds90-8_ported.jpg Views:	1 Size:	57.9 KB ID:	1409452

    The discrepancy between the simulated and the measured responses I find very frustrating. For the past year I have been reading up on the theory behind loudspeaker construction. It is one of the hardest subjects I have tried to teach myself. And it is made even more frustrating if I can't trust my simulations to give me a design which will perform similar to my simulations in real life. Any input or suggestions to solve this is much appreciated. If you need ny more info I will gladly supply it if you ask me in a post.