I see some pics of moderators (Donny FL) and they have vent holes in the forward section of the moderator. I see some companies with vent holes near the rear of the moderator. Is there a practical explanation for the differences, or just aesthetics?
Moderator vent holes
- Thread starter Corvid_hunter
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Depends where you want the air to blow out the front won't blow dust up if your shooting off the ground
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It is easy to understand why a smaller front cap bore would slow down air exit and have less noise escape from the moderator. With that as a foundation, it is my contention that any side vent holes, with a combined area large enough to flow enough air, to reduce the report coming from the front cap bore, would increase the noise towards the sides of the muffler. Any collection of side vents so small that it does not increase the noise level towards the sides, will subtract nothing from the noise exiting the front cap bore.
Anyone that points out the myriad of well vented tubes inside a engine muffler, needs to understand that those flow into an enclosed casing. That there are never any "side vent" holes on the outer casing of an effective engine muffler. In similar fashion, the metal screen that hold felt or foam inside a DFL moderator is acting like the vented tubes inside an engine muffler. Those work because the vent gas from one internal space through a partial restriction, into another internal space.
The vents on factory made airgun moderators use a few very tiny holes, mostly blanked off by felt on the inside. So practically speaking they don't flow enough air in the few tenths of a seconds that an airgun moderator does most of its work to make any difference. Their effect is mostly psychological. And their primary function to get you to buy a sophisticated looking device. A such, it matters not if the vent holes are at the front or rear end of the muffler. Nor if the holes are placed in straight or curved lines; flush with the OD, or sunk into shallow grooves. As long as they look groovy; mission accomplished.
Anyone that points out the myriad of well vented tubes inside a engine muffler, needs to understand that those flow into an enclosed casing. That there are never any "side vent" holes on the outer casing of an effective engine muffler. In similar fashion, the metal screen that hold felt or foam inside a DFL moderator is acting like the vented tubes inside an engine muffler. Those work because the vent gas from one internal space through a partial restriction, into another internal space.
The vents on factory made airgun moderators use a few very tiny holes, mostly blanked off by felt on the inside. So practically speaking they don't flow enough air in the few tenths of a seconds that an airgun moderator does most of its work to make any difference. Their effect is mostly psychological. And their primary function to get you to buy a sophisticated looking device. A such, it matters not if the vent holes are at the front or rear end of the muffler. Nor if the holes are placed in straight or curved lines; flush with the OD, or sunk into shallow grooves. As long as they look groovy; mission accomplished.
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About 5 years ago someone did a test with a series of different sized holes around the circumference of moderators. It was shown that somewhere at or below .015" diameter holes, (I can't find the write-up to quote actual size) which allowed the air to blow out but also deadened the sound report because it came out so slowly. It seems the required size of the holes was so small and so numerous it was not something that the manufacturers took up as a feature (those drill bits are expensive).
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You have to flow a lot of air in a tenth of a second from vent holes to offer any pressure or volume relief. If vent hole air takes a second to come out, most of the pressurized air in the moderator has already left via the front cap bore. So, slowing the air down from the vents prevents them from making the airgun louder on the side, but does very little for the noise coming out the front.
In other words, using 0.04" vent holes in place of 0.015" ones due to manufacturing constraints is like using someone else's credit card - it seems to work; providing you don't overdo it. You have to block the larger holes off from the inside to restrict their flow, else sound is not blocked. In the process, very little air comes out of the vents in the time frame that the bulk of the air leaves the front cap bore.
The replacement shrouds below are made by the same manufacturer. They have vents at the front and at the rear, respectively. Clearly it does not matter where vents are placed from a functional perspective; as long as they can be seen and admired. The extra grooves that have no vents makes it clear that this is about style; not substance. How else are you going to differentiate your product, when the competition is almost as good, and much cheaper?
In other words, using 0.04" vent holes in place of 0.015" ones due to manufacturing constraints is like using someone else's credit card - it seems to work; providing you don't overdo it. You have to block the larger holes off from the inside to restrict their flow, else sound is not blocked. In the process, very little air comes out of the vents in the time frame that the bulk of the air leaves the front cap bore.
The replacement shrouds below are made by the same manufacturer. They have vents at the front and at the rear, respectively. Clearly it does not matter where vents are placed from a functional perspective; as long as they can be seen and admired. The extra grooves that have no vents makes it clear that this is about style; not substance. How else are you going to differentiate your product, when the competition is almost as good, and much cheaper?
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This thread may be interesting to those looking for muffling nirvana:
www.airgunnation.com
Huggett ~ Shogun ~ Tatsu... sound level test
Just out of curiosity, today I mounted the following moderators on my Bantam Sniper .22. Sound level readings were taken several times with similar results each time. I used an app on my iPhone to measure the peak sound level, at 9' ahead and off 45 degrees to the side of the muzzle, with the...
www.airgunnation.com Upvote 0