Hi,
First of all. This NOT a thread with a Open baffle mid and Bass reflex bass. Now that we got that out of the way. Let me elaborate on it.
I was toying around with a concept that I thought off. For an OB woofer, one of the challenges quite often faced by the design is the gradual roll of at 100+ hz, unless you have a 2m wide baffle. So getting low end bass ~30Hz is a challenge. The benefit of OB baffle bass is there is no radial emittance therefore reducing room interactions. The common way to do it is to just boost it like crazy via a graphic equalizer or DSP or some other active means, or via the crossover. My proposal is to use a bass reflex system but in a wrong way.
In a bass reflex system, the port tuning is normally quite low, circa 30-50Hz for a large woofer, That is because the bass reflex design only works above the port tuning frequency. Below the port tuning frequency, the port output becomes antiphase with the woofer and cancels it instead of aiding it. To make it worse the back pressure on the cone becomes negative and the cone starts to go on extreme excursion with just a little power. This is the negative part of BR, but it could be used to our advantage in a OB.
The design calls for a normal practical OB, (circa 2 feet) or U/H frame. It will have a seriously undersized box for the woofer with a very large diameter short port to achieve of port tuning frequency of 150Hz or higher. Therefore the Woofer is actually in a negative backpressure region as compared to an OB which is a zero pressure region. This will be coupled to a midwoofer/full range WAW/FAST system crossing at about 150Hz. The port will be emitting a out of phase signal similar to the back of a woofer. But this has a added advantage of negative back pressure on the cone.
I have done some simulation on SBP softica software on using the SB Audience Bianco 150B350 Open baffle in a 20L box with an 8inch diameter 6 cm length port and this is what I got. There is an approximate 40% increase in excursion at 20Hz compared to a OB. I simulated OB excursion by using a ridiculously large box as a sealed system.
The file Hybrid Frequency response is what the simulated frequency response of the system as a bass reflex which looks ridiculous of course because there is no baffle consideration.
The file Hybrid excursion and OB excursion displays the excursion under same electrical conditions of 20W.
I would like your thoughs and feedback on this...
Thanks.
Oon
First of all. This NOT a thread with a Open baffle mid and Bass reflex bass. Now that we got that out of the way. Let me elaborate on it.
I was toying around with a concept that I thought off. For an OB woofer, one of the challenges quite often faced by the design is the gradual roll of at 100+ hz, unless you have a 2m wide baffle. So getting low end bass ~30Hz is a challenge. The benefit of OB baffle bass is there is no radial emittance therefore reducing room interactions. The common way to do it is to just boost it like crazy via a graphic equalizer or DSP or some other active means, or via the crossover. My proposal is to use a bass reflex system but in a wrong way.
In a bass reflex system, the port tuning is normally quite low, circa 30-50Hz for a large woofer, That is because the bass reflex design only works above the port tuning frequency. Below the port tuning frequency, the port output becomes antiphase with the woofer and cancels it instead of aiding it. To make it worse the back pressure on the cone becomes negative and the cone starts to go on extreme excursion with just a little power. This is the negative part of BR, but it could be used to our advantage in a OB.
The design calls for a normal practical OB, (circa 2 feet) or U/H frame. It will have a seriously undersized box for the woofer with a very large diameter short port to achieve of port tuning frequency of 150Hz or higher. Therefore the Woofer is actually in a negative backpressure region as compared to an OB which is a zero pressure region. This will be coupled to a midwoofer/full range WAW/FAST system crossing at about 150Hz. The port will be emitting a out of phase signal similar to the back of a woofer. But this has a added advantage of negative back pressure on the cone.
I have done some simulation on SBP softica software on using the SB Audience Bianco 150B350 Open baffle in a 20L box with an 8inch diameter 6 cm length port and this is what I got. There is an approximate 40% increase in excursion at 20Hz compared to a OB. I simulated OB excursion by using a ridiculously large box as a sealed system.
The file Hybrid Frequency response is what the simulated frequency response of the system as a bass reflex which looks ridiculous of course because there is no baffle consideration.
The file Hybrid excursion and OB excursion displays the excursion under same electrical conditions of 20W.
I would like your thoughs and feedback on this...
Thanks.
Oon
Attachments
2 amps and electronic Xover?
I'm doing something similar but using a B2 bass chamber and L/T filter with the diyA 6/24 Active filter kit and 2 amps.
I'm doing something similar but using a B2 bass chamber and L/T filter with the diyA 6/24 Active filter kit and 2 amps.
Sorry, B2 bass chamber is just shorthand for the B2 alignment which is the same as 'infinite baffle' or 'closed box' and vaious other names over the years - B4 (alignment) is the term for a 'ported box' (and not a 'transmission line') and so on - lots of varieties to get lost in.
L/T filter is again shorthand for the 'Linkwitz Transform' circuit that boosts/adds the low bass freq curve to compensate for the bass freq 'roll-off' when using the speakers in a sealed/closed box - there's a whole treatment of this here on 'diyA' and a rather good treatment on Rod Elliot's https://sound-au.com/linkwitz-transform.htm for the benefits/limitations
About 'Bass-in-a-Box', OB (Open Baffle) bass and Subs - I had a better read of your above post and realized that you have done much work on the bass driver options so I'll only add a comment about the Geddes approach see "Multiple Small Subs - Geddes Approach" on diyA also - this is the direction that I'm eventually going down
L/T filter is again shorthand for the 'Linkwitz Transform' circuit that boosts/adds the low bass freq curve to compensate for the bass freq 'roll-off' when using the speakers in a sealed/closed box - there's a whole treatment of this here on 'diyA' and a rather good treatment on Rod Elliot's https://sound-au.com/linkwitz-transform.htm for the benefits/limitations
About 'Bass-in-a-Box', OB (Open Baffle) bass and Subs - I had a better read of your above post and realized that you have done much work on the bass driver options so I'll only add a comment about the Geddes approach see "Multiple Small Subs - Geddes Approach" on diyA also - this is the direction that I'm eventually going down