Isobaric 2245

[gasfan]

You can build a pair of "push pull slot loaded" boxes. The theory is that because all drivers are assymetric the result will be symmetric since one driver is mounted with the magnet out. The slot also creates a tighter coupling of the drivers than traditional mounting.

On top of that you can do a closed enclosure and use a Linkwitz transform to get low bass from the box. Either an analog Linkwitz filter, or a digital one. You should design for a total Q=0.5 because this will have optimal cone damping.

If I had four 2245, this is what I would do :-).

Mårten

Thank you Marten. It's just that I want to see the drivers and I want to get punched in the chest. However, at 10cu. ft. with an effective volume of 20, does a linkwitz transformer really offer much benefit when I'm using active crossovers and separate amp for each driver?

[more10]

I made a simulation in WinISD. Two 2245 in a 688 litre box, that is 24 cubic feet. Q=0.5. The yellow curve is without Linkwitz transform, feeding 250W. The purple is with Linkwitz trasform feeding 75W.

[more10]

One can also go vented (8 cubic feet tuned to 26 Hz)

Quick and dirty simulation, vented in grey. 250W signal. 515 litre (18 cu ft). 4 dB parametric eq at 30 Hz.

[gasfan]

Quick and dirty simulation, vented in grey. 250W signal. 515 litre (18 cu ft). 4 dB parametric eq at 30 Hz.

Is that the best you can do?

[grumpy]

"Is that the best you can do?"

LOL, keep up that attitude and you may very well get punched in the chest.

[gasfan]

"Is that the best you can do?"

LOL, keep up that attitude and you may very well get punched in the chest.

No shit. I'm buckin'.

See what happens when you don't add the smiley face?

[gasfan]

Is that the best you can do?

I meant that purely technically since I've seen graphs with flat response to something like 25hz with eq in much smaller cabs? And not isobaric.

[more10]

Well gasfan, you shurely fit my european predjucides about americans :-). No insult meant to Canadians, Mexicans,...

Since you have not specified any requirements, I have made some assmptions. Here in Sweden an average listening room (called vardagsrum) is 20 square meters (215 sq feet). Plan is often 4 x 5 meters. The length of the room decides the frequency limit of wave propagation. Below this limit you have no propagation, but instead you will get room gain. A 5 meter (16 ft) long room will have room gain below 34 Hz. A box with the 3 dB point at 25 Hz will sound boomy. So I chose to put the knee at about 30 Hz.

When reading the thread from start I realize you have already built the boxes, and wonder if putting a second woofer inside will give any benefits. It will not since the benefit of building isobaricly is to get a smaller box.

I have not made the simulation isobaric. Since you have stated that size is not a problem, you could build 2 more boxes. Experiment with the placement, 4 cornes on the floor or 4 corners on a wall.

I am not that interested in vented enclosures so I didn't put any effort into the vented simulation, I just kept WinISD suggested alignment of a super-boom-box. Since my vented box is twice the size of yours, and I used 2 drivers in my simulation, and you have only one in your box, I believe you have built super-boom-boxes :-)

The limiting factor of all bass designs is x-max. The lower you tune the box, the lower output you can get. My simulations is applying power to reach xmax at some point above 20 Hz.

[more10]

Now with the isobaric (WinISD defailt) alignment (130 litre, 4.5 cu feet, vented super-boom-box) in brown:

[gasfan]

Well gasfan, you shurely fit my european predjucides about americans :-). No insult meant to Canadians, Mexicans,...

Since you have not specified any requirements, I have made some assmptions. Here in Sweden an average listening room (called vardagsrum) is 20 square meters (215 sq feet). Plan is often 4 x 5 meters. The length of the room decides the frequency limit of wave propagation. Below this limit you have no propagation, but instead you will get room gain. A 5 meter (16 ft) long room will have room gain below 34 Hz. A box with the 3 dB point at 25 Hz will sound boomy. So I chose to put the knee at about 30 Hz.

When reading the thread from start I realize you have already built the boxes, and wonder if putting a second woofer inside will give any benefits. It will not since the benefit of building isobaricly is to get a smaller box.

I have not made the simulation isobaric. Since you have stated that size is not a problem, you could build 2 more boxes. Experiment with the placement, 4 cornes on the floor or 4 corners on a wall.

I am not that interested in vented enclosures so I didn't put any effort into the vented simulation, I just kept WinISD suggested alignment of a super-boom-box. Since my vented box is twice the size of yours, and I used 2 drivers in my simulation, and you have only one in your box, I believe you have built super-boom-boxes :-)

The limiting factor of all bass designs is x-max. The lower you tune the box, the lower output you can get. My simulations is applying power to reach xmax at some point above 20 Hz.

Not quite sure what that means but I hope I'm not in trouble. I need all the friends I can get!

A few years ago, you, Pos, Ian, and a few others put together a recipe for me for the 2245, 2206, 2390, and 2405. I just haven't gotten around to starting the project yet. The cabs were for 10.3 cu. ft. which I want to follow through with. I was thinking to make them isobaric with dual 2245s since I have them. My listening room is approx 20ft.X20ft.

[more10]

Not quite sure what that means but I hope I'm not in trouble. I need all the friends I can get!

I guess you just can't help it :-) Im still here.

A few years ago, you, Pos, Ian, and a few others put together a recipe for me for the 2245, 2206, 2390, and 2405. I just haven't gotten around to starting the project yet. The cabs were for 10.3 cu. ft. which I want to follow through with. I was thinking to make them isobaric with dual 2245s since I have them. My listening room is approx 20ft.X20ft.

You will have room gain below 29 Hz. Any of the designs made with the 2245 will need eq, so if you can change it in the filter you can adjust after you have built the boxes.

Regarding the 2245 you have, there is plenty of good advice in this thread. You just have to decide what you want to implement. Isobaric is not a good solution. If quality is more important than output go for closed enclosure. If output is more important than quality go for vented.

If placing two 2245 together, mount one driver with the magnet facing out in order to get symmetri. If placing the boxes in different corners there is no point doing this.

Yet another alternative is to build Onken enclosures. Play around with the online calculator: http://www.mh-audio.nl/onken_br.asp. It will sound more like a horn or a closed box, than a vented.

[4313B]

If quality is more important than output go for closed enclosure.

I'd personally opt for the closed box linkwitz transform first. One can build an 8 cu ft to 9 cu ft box, add the transform and see if they like it. If not then they can vent the box as per the B460, apply the bump filter and go vented.

The linkwitz transform boxes for the 2245H can be much smaller than 8 cu ft but it will require a lot more amplifier power (risk burning out the VC) to achieve the same VLF response.

more10 is right in that one can use room gain to assist with the response. We have discussed this extensively over the years. The key is to get a real nice balance of transducer/enclosure response, room response and amplifier output without cooking the VC or breaking the VC off. The smaller boxes put more stress on the VC neck and they can pop apart. JBL went through that with the 121, 124/2203, 136/2231, 2235, 2245, etc. And that is exactly why J.M. reinforced the necks of transducers like the SUB1500 and W1500H. An 8 to 9 cu ft box for the 2245H should work just fine. I built many of them over the last thirty-some years.

[more10]

Now with the isobaric (WinISD defailt) alignment (130 litre, 4.5 cu feet, vented super-boom-box) in brown:

With a parametric EQ of 4 dB at 30 Hz.

[more10]

The smaller boxes put more stress on the VC neck and they can pop apart.

Go for the 12 cu feet box (per driver). Q=0.5 is called critically damped for a reason. If output is too low, put in vents as 4313B suggests.

Make 4 boxes. Then you can try different placements, as well as together and one magnet facing outwards.

[4313B]

HT BB6 Pro reports that an 8.757 cu ft box (net effective) with "typical" fiberglass fill yields a Qtc of 0.5

Oh well, the transform should "fix" any difference. Just build some boxes and let the transform sort them out.