Hello, I'd want to know what could be the real benefit of moving a classic front-firing reflex port (at half height of tower) to a down-firing position in terms of extremely low bass response.
I'm talking about a pair of brand towers designed to stay near a wall and instead constrained to stay approx in the center of the room, for which reason ultra low bass are a bit weak. I could move vent in the bottom panel but I'd want to know your opinion about.
Thank you very much.
I'm talking about a pair of brand towers designed to stay near a wall and instead constrained to stay approx in the center of the room, for which reason ultra low bass are a bit weak. I could move vent in the bottom panel but I'd want to know your opinion about.
Thank you very much.
Consider the port as the source of the low frequencies: those are mostly omni-directional because of the very long wavelenght compared to the size of the cabinet ( which isn't seen by those bass waves ). Theory says that when you change the radiation from full space ( 4 π ) to half space - 2π steradiants- there is a change in pressure of about +3 dB.
That is probably what floor gain refers to, when the port points downwards.
That is probably what floor gain refers to, when the port points downwards.
What do you mean by "extremely low bass"? <30Hz?
Consider that at 30Hz the wavelength is about (340m/s)/(30Hz) = 11.3metres. Unless your speaker box is huge (metres) these frequencies will therefore just diffract around it and it makes little difference which side the port is on. Similarly, moving the port to a different side of the box only moves the source of bass perhaps <1m so will do little to affect room reflections from the floor/walls/ceiling at those frequencies.
There however is one notable effect of a bottom exit and that is if the gap underneath the speaker is restrictive enough to function an extension of the TL/port. Therefore:
-Design the gap underneath the speaker to have a similar area to the TL/port opening and factor this into your TL/port length calculations.
-Design the gap underneath the speaker to have considerably larger area than the TL/port opening so it does not present a restriction and ignore it.
Consider that at 30Hz the wavelength is about (340m/s)/(30Hz) = 11.3metres. Unless your speaker box is huge (metres) these frequencies will therefore just diffract around it and it makes little difference which side the port is on. Similarly, moving the port to a different side of the box only moves the source of bass perhaps <1m so will do little to affect room reflections from the floor/walls/ceiling at those frequencies.
There however is one notable effect of a bottom exit and that is if the gap underneath the speaker is restrictive enough to function an extension of the TL/port. Therefore:
-Design the gap underneath the speaker to have a similar area to the TL/port opening and factor this into your TL/port length calculations.
-Design the gap underneath the speaker to have considerably larger area than the TL/port opening so it does not present a restriction and ignore it.
Having the port close to a rear wall, or close to the floor, can result in bass reinforcement. This may not be as positive as it sounds, as it can introduce bass boom.
Pay regard to what TMM has said. A downward firing port should really be designed taking its proximity to the floor into account. The simpler approach is to design the port as normal, but leave plenty of breathing space between the bottom of the cabinet and the floor.
..that's what I was expecting to listen to.. I'll give a try and if possible to make a measurement between the two stages, front and down firing vent and if reasonably good I'll publish.
Thank you in advance.
Generally the most variation will occur at upper bass frequencies. Very long wavelengths will experience room gain related to the size of the room. A 30 Hz wave is well over 30 feet long, and moving the speaker a few feet is not likely no make much difference overall. These waves will (in all but the largest rooms) encounter multiple room boundaries before one cycle is completed. Specific listening locations in the room may be affected by standing waves at some frequencies.
However, consider the situation at 100-120 Hz, where the wavelengths are near 10 feet long. Placing the radiating surface at a quarter-wavelength (2.5 feet or so) from the back wall will reflect that wave and that reflection will reach the speaker out of phase, and partial cancellation of the front wave will result. To avoid these situations you can place the speaker as close as possible to the wall, where the reflection is very nearly in phase. This will produce up to nearly 6dB of gain. Further gains can be attained by placing the woofer at the floor-wall intersection and corner (2 walls plus floor) locations. You can get too much gain and have to equalize the bass level to avoid "boomy" bass.
Depending on how solid the room walls (and floor and ceiling) are, some of the bass energy will pass through and some will be reflected. So the results from real rooms can vary considerably.
However, consider the situation at 100-120 Hz, where the wavelengths are near 10 feet long. Placing the radiating surface at a quarter-wavelength (2.5 feet or so) from the back wall will reflect that wave and that reflection will reach the speaker out of phase, and partial cancellation of the front wave will result. To avoid these situations you can place the speaker as close as possible to the wall, where the reflection is very nearly in phase. This will produce up to nearly 6dB of gain. Further gains can be attained by placing the woofer at the floor-wall intersection and corner (2 walls plus floor) locations. You can get too much gain and have to equalize the bass level to avoid "boomy" bass.
Depending on how solid the room walls (and floor and ceiling) are, some of the bass energy will pass through and some will be reflected. So the results from real rooms can vary considerably.
OP : The problem you'll have cannot be solved by moving the bass port.
Near-wall designed speakers ignore baffle step compensation within the crossover design.
If you want to turn them into mid-room speakers you would need to either use external EQ or re-work the crossover.
One BIG advantage of designing a speaker for wall reinforcement is efficiency. To make the same speaker work mid-room you have to trade a lot of efficiency for bass. 4-6 dB is very typical.
AFAIK, downward firing bass (ports and drivers) have fewer room modes. In other words the bass is smoother and will sound therefore bigger and tighter, but this won't alter your balance problems as mentioned above.
Best,
E
Near-wall designed speakers ignore baffle step compensation within the crossover design.
If you want to turn them into mid-room speakers you would need to either use external EQ or re-work the crossover.
One BIG advantage of designing a speaker for wall reinforcement is efficiency. To make the same speaker work mid-room you have to trade a lot of efficiency for bass. 4-6 dB is very typical.
AFAIK, downward firing bass (ports and drivers) have fewer room modes. In other words the bass is smoother and will sound therefore bigger and tighter, but this won't alter your balance problems as mentioned above.
Best,
E
a floor firing vent with no deflector is a bad plan IMO. Neither do you want the vent next to the floor, vent action will suffer from this orientation. You are simply placing your speakers where they were never meant to go. The roll off you are getting is not a bad think if you pair the speakers with a sub or two positioned near the walls so just make sure the sub yu choose have phase adjustment and all will be well and you will get more bass and better bass than the main speakers ever had.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.