21DS115-4 6th order bandpass design - port flares
Printed From: Speakerplans.com
Category: General
Forum Name: Advanced Discussion
Forum Description: Advanced discussion area for higher lifeforms
URL: https://forum.speakerplans.com/forum_posts.asp?TID=109482
Printed Date: 26 March 2026 at 12:35pm
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Topic: 21DS115-4 6th order bandpass design - port flares
Posted By: Larry23
Subject: 21DS115-4 6th order bandpass design - port flares
Date Posted: 21 March 2026 at 12:48pm
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Hi folks, I’ve been working on a design for a new 6th-order series bandpass enclosure using the 21DS115-4, and I’m pretty happy so far. The design is relatively compact out of necessity, with a total internal volume of around 200 L including ports, driver, and bracing. -3 dB points are roughly 35 Hz and 110 Hz. I’ve started looking more closely at the port design. Air velocity isn’t an issue, but I’d like to incorporate something more than simple, straight rectangular ports. Many commercially available designs, and those from 18 Sound/B&C etc. incorporate angled or flared sections within the ports, both internally and at the exits. Is there a reliable way to sim/calculate how these affect tuning? I’m considering an exit with a 10 cm, 45° flare on one side leading onto the front baffle, while the other side remains flush against the side panel. Is there a method to predict how this kind of asymmetric flare would influence the effective port length/vol and tuning frequency? Thanks in advance |
Replies:
Posted By: DMorison
Date Posted: 21 March 2026 at 1:24pm
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AFAIK, the only freeware tool for working with flared ports is the optimiser developed by user "stv" over on DIYAudio: https://www.diyaudio.com/community/threads/investigating-port-resonance-absorbers-and-port-geometries.388264/" rel="nofollow - https://www.diyaudio.com/community/threads/investigating-port-resonance-absorbers-and-port-geometries.388264/ I don't know if it works with the specific combination of shapes you describe or not though. HTH, David.
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Posted By: Larry23
Date Posted: 21 March 2026 at 1:35pm
Amazing, thanks David.
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DMorison wrote:Posted By: snowflake
Date Posted: 25 March 2026 at 12:35am
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what's going on with the specs for the 21DS115 ? B&C have updated the specs for the 8-ohm version and removed the spec sheet for the 4-ohm version. The 8-ohm spec sheet now says the Fs is 36Hz but the impedance plot shows it is 30Hz. https://www.bcspeakers.com/en/products/lf-driver/21/8/21DS115" rel="nofollow - 21DS115 8Ω - LF Drivers - B&C Speakers |
Posted By: Contour
Date Posted: 25 March 2026 at 6:01pm
| Spec sheet on website states fs = 34 Hz, this matches peak in impedance plot in same spec sheet. |
Posted By: snowflake
Date Posted: 25 March 2026 at 6:05pm
they must have updated them both last night  . 4 ohm page is back up too.
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