Short answer. An automatic door bottom houses a bar that drops as the door closes; a door shoe is a fixed bottom-edge housing with a flexible insert; a corner pad addresses a localized junction at the bottom of a jamb. They are not substitutes for one another, and a component's acoustic marketing does not grant a sound rating to an untested doorway.
How to recognize the mechanism without dismantling it
Look at the exposed lower edge with the door at rest and, only when safe and authorized, observe a normal close from outside the sweep path. A housed automatic bottom can show a jamb-contacting plunger and a movable drop bar. A door shoe typically remains mechanically fixed to the door leaf and makes contact via its own flexible edge. A corner pad is a small element at a junction, not a full-width bottom seal. Do not put hands under a closing door or defeat closers and panic hardware for a test.
Pemko describes the 4301 automatic bottom with a drop bar activated by a jamb-contact plunger. It offers model-dependent surface or semi-mortise mounting. [F16] The 412 series is expressly a handed surface-mounted automatic bottom. [F17] So it is unsafe to say “all automatic bottoms reverse without handing” when ordering a replacement or copying an installation video.
Acoustic assembly is not a single part
Pemko's PEMKOSTCSET-1 acoustic single-door seal-set family describes combinations of an STC411_PK automatic bottom, ACP112 corner pad, and selected perimeter gaskets across multiple variants. [F18] The useful lesson is not that every automatic bottom has a universal STC score; it is that the cited result is tied to the combination and test setup.
Before discussing “acoustic,” specify the actual complaint. Is it a bright line under the door, hallway speech, a draft at the bottom corners, or a rubbing sweep at a carpet transition? Photograph the closed leaf from the room side and the floor across its width. Mark whether the greatest gap is under the middle, near one jamb or where a floor transition changes height. Uneven floor contact may require trained alignment/threshold review, not simply a thicker shoe insert.
A comparison to send to a door-hardware supplier
| Field observation | Investigate | Verify before selecting |
|---|---|---|
| Housed bar moves down upon closing | Automatic door bottom | Exact model, handing, permitted mounting face, activation and approved gap |
| Fixed metal shoe stays on bottom edge | Door shoe / fixed insert | Width/thickness of door, shoe retention and insert geometry |
| Small pad sits at bottom jamb corner | Corner pad in possible seal set | Location, material, matching set and condition of adjacent seals |
| Surface contact changes where carpet starts | Floor/threshold interface | Verified floor elevations, applicable door hardware and opening requirements |
On a carpeted opening, do not assume that a brush insert is the same as a fixed shoe or that either is specified in the tested acoustic kit. Product-specific instructions matter. Keep the path of travel, accessibility, egress, latching and any fire-door label intact.
Finish the identification, not a speculative order
Gather the series marking, photos of the entire bottom and plunger, door thickness and visible mounting position, threshold/floor type, and exact project requirement (draft control, privacy or an independently specified acoustical target). Ask Pemko/dealer for the current cut sheet, permitted installation and tested system—not just a product with “acoustic” in its name. This guide expands on, but does not replace, the existing site's generic threshold versus door-bottom and door-shoe identification pages; it is not evidence of exact fit.
Source links and source-bound facts
- [F16] 4301 automatic door bottom has an enclosed drop bar activated by jamb-contact plunger and may be face-mounted or semi-mortised in listed versions. Pemko, Undated currently published 4301 Series product page; locator: Features / Product Overview. https://www.pemko.com/en/products/door-bottom-and-top-solutions/automatic-door-bottoms/product-details.aehpdp-4301-series-ag_pemko_12038 (accessed 2026-10-12).
- [F17] 412 is a handed surface-mounted automatic door bottom, so general assumption that all ADB are non-handed is unsafe. Pemko, Undated currently published 412 Series product page; locator: Product Overview. https://www.pemko.com/en/products/door-bottom-and-top-solutions/automatic-door-bottoms/product-details.aehpdp-412-series-ag_pemko_302357 (accessed 2026-10-12).
- [F18] Pemko acoustic single-door seal-set variations combine an automatic bottom, corner pad and selected perimeter gaskets; system test not single-part performance. Pemko, Undated currently published PEMKOSTCSET-1 product page; locator: Product Overview > Features / Models. https://www.pemko.com/en/products/acoustic-products/product-details.aehpdp-pemkostcset-1-series-ag_pemko_302488 (accessed 2026-10-12).