tuning bass reflex according to the driver's frequency response - diyAudio
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Old 21st March 2016, 10:08 AM   #1
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Default tuning bass reflex according to the driver's frequency response

Hi

I'm designing small full range speakers, using winISD. According to the driver's spec sheets, its frequency response starts dropping at 150hz :

Click the image to open in full size.

I need to tune the bass reflex to about 85-95hz.
In WinISD, do i need to tune the bass reflex for a flat curve, or with a peak to compensate the natural drop of the driver? (to get a flat response at the end...)

Thanks

Last edited by gougigaga; 21st March 2016 at 04:23 PM.
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Old 21st March 2016, 11:25 PM   #2
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If you simulate a flat curve using the T/S parameters, the driver's natural response will already have been taken into account into the system's total response. However tuning to 85-95Hz may not allow flat response. Which driver is it?
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Old 22nd March 2016, 12:05 AM   #3
Ron E is offline Ron E  United States
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The manufacturers driver response curve is often taken on a large baffle, or mounted in one wall of an anechoic chamber. Sometimes with a small box fitted behind baffle or wall. You cannot know unless measurement conditions are stated. That "specified" response curve does not impact box design.

Use measured T/S parameters. Take Mfg values with a grain of salt.

If you can measure actual response in your box, you might want to account for frequency response in some cases, but not in the way you guess. Most likely you will not be pleased at how box diffraction impacts response.
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Old 22nd March 2016, 11:11 AM   #4
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The driver is the Vistaton FRS-8, 4ohm : FRS 8 - 4 Ohm

I want to build a 3L enclosure for it, although i know it's smaller than the optimal value

Click the image to open in full size.


For baffle diffraction, i plan to add a baffle-step compensation before the amp (they will be active speakers) and doing a 2cm chamfer to the front edges.

Seems reasonable ?

I'll try to measure read T/S parameters when i receive the drivers, i already did that (with my computer and the "added mass method")
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Old 22nd March 2016, 01:51 PM   #5
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The attached vented sim is based on Vb 3L, Fb 90Hz, Dv 1.12", Lv 2.92", HP BW4 75Hz, EQ1 (-2dB, 72Hz, Q2) and EQ2 (+3 db, 90Hz, Q1). F3 is 83Hz, F6 is 78Hz and F10 73Hz.

Problem with tuning as low as 85-90 Hz is the limited power handling (mecanical/Xmax limit). Max power to hit Xmax+15% in the sim is 12W. Max SPL is 97dB allowing about average listening levels of about 80dB (1m).

With a Qts of 0.69 you will find it difficult to get away from the hump in a vented enclosure. Could you go sealed and use a sub instead? Or FAST? The attached sealed sim is based on 3L and HP LR4 140Hz (after equalised flat to 30Hz with LWT). F3 is 172Hz, F6 is 139Hz (xo point) and F10 is 115Hz. You hit Xmax+15% with 25W for max SPL 99dB.
Attached Images
File Type: gif WBCD5_FRS 8_vented_90_FR.gif (25.0 KB, 92 views)
File Type: gif WBCD5_FRS 8_vented_90_Xmax.gif (10.8 KB, 90 views)
File Type: gif WBCD5_FRS 8_vented_90_PS.gif (9.3 KB, 89 views)
File Type: gif WBCD5_FRS 8_vented_90_IR.gif (8.5 KB, 8 views)
File Type: gif WBCD5_FRS 8_vented_90_GD.gif (11.9 KB, 10 views)
File Type: gif WBCD5_FRS 8_sealed_FR.gif (25.0 KB, 9 views)
File Type: gif WBCD5_FRS 8_sealed_Xmax.gif (10.5 KB, 10 views)
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Old 22nd March 2016, 02:10 PM   #6
TBTL is offline TBTL  Germany
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The Visaton FRS8 has an Xmax of +- 0,5 mm (taken from Boxsim), so the sound pressure level will be even lower. The value of +-2,5 mm refers to the Xmech. I own a set of these drivers and they start to distort badly beyond +- 1 mm. Distortion at frequencies below 200 Hz is high anyway.

Last edited by TBTL; 22nd March 2016 at 02:13 PM.
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Old 22nd March 2016, 02:24 PM   #7
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Ouch... fuhgeddaboudit then

.. and just use it as it was meant to be used (sim attached, w/HP LR4 400Hz).
Attached Images
File Type: gif WBCD5_FRS 8_sealed_FR.gif (25.6 KB, 14 views)
File Type: gif WBCD5_FRS 8_sealed_Xmax.gif (9.4 KB, 14 views)
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Old 22nd March 2016, 05:42 PM   #8
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mmh... on paper, i like those drivers for their balanced frequency response and ability to get some bass in a small enclosure. This distorsion problem is annoying tho, but isnt it the same for most 3" drivers ?
If you think about a better driver for me, i'm open to any suggestions i'd like one with an overall balanced response (but it's not important if it doesnt go up to 20khz), and some bass (80Hz -3db would be nice)
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Old 23rd March 2016, 09:36 PM   #9
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Staying with the brand, the Visaton B80 is a better-quality full-range driver but with similar specs and limitations to produce distortion-free bass in small conventional box alignments.

If you can go up a litre or two in volume and add a tweeter, the W4-1720 is quite the performer.
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