So I still have two Dayton 15DVC sub drivers. I'm pretty limited on space, so I want to keep the enclosure somewhat small, but still be able to get some decent performance from 50Hz and below, with extension down a little below 20Hz, or at least very solid 20Hz output. The sub will be used for both music and movies, music being the most important.
This is what I'm thinking... And yes, I realise that you loose about -3dB of output doing this type of design.
I want to do a "front-to-back" isobarik sub with a total internal volume of about 4 cu.ft. sealed. That would be somewhat equal to 8 cu.ft for one driver. I figure that should get me pretty good output down to FS (19-20Hz), maybe a little lower.
Please remember, I'm not building this for movies, but mainly for music, am not concerned with total SPL output (my room is only 13x17 w/ 8' ceiling) but will be powering it with a 600W amp bridged to 8 ohms mono.
Whatcha think?
Thanks in advance!
This is what I'm thinking... And yes, I realise that you loose about -3dB of output doing this type of design.
I want to do a "front-to-back" isobarik sub with a total internal volume of about 4 cu.ft. sealed. That would be somewhat equal to 8 cu.ft for one driver. I figure that should get me pretty good output down to FS (19-20Hz), maybe a little lower.
Please remember, I'm not building this for movies, but mainly for music, am not concerned with total SPL output (my room is only 13x17 w/ 8' ceiling) but will be powering it with a 600W amp bridged to 8 ohms mono.
Whatcha think?
Thanks in advance!
The difference in output is 6dB, not 3dB.
With two 295-190 drivers isobaric in 4 cu ft net the Qtc=0.848 and is 3dB down at 25.78hz (Du-MAx data in BassBox v6.0).
With the same two drivers in the same 4 cu ft net box in a push-pull configuration like M&K uses you will have less distortion because of less cone motion. Qtc=1.259, F3=34.71hz, with a Linkwitz transform this would be my choice over isobaric any day.
With two 295-190 drivers isobaric in 4 cu ft net the Qtc=0.848 and is 3dB down at 25.78hz (Du-MAx data in BassBox v6.0).
With the same two drivers in the same 4 cu ft net box in a push-pull configuration like M&K uses you will have less distortion because of less cone motion. Qtc=1.259, F3=34.71hz, with a Linkwitz transform this would be my choice over isobaric any day.
djk said:
Ok, -6dB. I knew it was something like that. Thanks, I stand corrected.
As for the enclosure, I am not totally limited to 4 cu.ft. I can expand it out to about 6-6.5 cu.ft. net, if that would help lower the F3 some. (sorry, I didn't mean FS in my initial post)
Also, I have no clue, nor do I have the means to build a Linkwitz transform. I wouldn't even know where to begin. I think they have to be built specifically for the drivers and application, right? I would probably have to find someone to possibly build it for me.
Oh, and for the actual design, what would be the optimal driver positions? Would they have to be like the M&K style (1 below, 1 up front), or could they be opposing eachother like Sunfire and Earthquake SuperNova subs?
I only ask because I DO have a limit on the total height of 26" so it can fit under my projection screen.
Thanks again!
djk said:
According to WinISD Pro, running two 295-190 drivers isobarically (it doesn't have an option for push-pull), horizontally opposed (like the Carver Sunfire subs), in a 6.3 cu.ft. sealed enclosure (after displacement), I should have a Qtc of 0.630 and an F3 of 34.5Hz.
Being that WinISD Pro sees this as an isobaric design, I'm guess these #'s are way off.
But going from what you said about the push-pull design, and that I now have 2.3 cu.ft. more to go with, I'm certain my F3 will be somewhat lower than 34.71hz as you mentioned.
I'm getting ready to go buy the 0.75" MDF now and have it cut for me as I don't have the proper tools right now for the job. The enclosure is going to be a 24" cube. Both baffles on either side will be 22.5" square, as will be the center brace.
So once I get it all home, all I have to do is cut out 4 holes on the piece for the brace and cut out the two 15" holes for the drivers, then glue and screw it together.
BassBox says F3=30hz, Qtc=1.0 for 6.3 cu ft.
Try the drivers one on each side, one driver with its magnet out and its wiring reversed. If the back of the woofer is too noisey (some 'wheeze'), then you can flip it back in and re-wire.
With room gain and the lower Qtc you can probably get away without the Linkwitz transform.
Try the drivers one on each side, one driver with its magnet out and its wiring reversed. If the back of the woofer is too noisey (some 'wheeze'), then you can flip it back in and re-wire.
With room gain and the lower Qtc you can probably get away without the Linkwitz transform.
djk said:
Thanks djk! At least now I somewhat know the specs to my sub thanks to you.
As for driver mounting, I have them on either side of the enclosure, both facing out, all .75" MDF construction, center braced and plenty of screws and silicone! There is very very little vibration coming through the cabinet.
After listening to a couple of well known recordings (pipe organ), in my room I am easily getting solid bass down to 16Hz without a problem. And these subs are even reaching lower to where you just feel it. No joke!
In the movie "AEon Flux", towards the beginning where she gets captured and she's stuck in that cell with the vent in the ceiling, there's a really low and quiet rumble that sounds/feels much lower than 16Hz. You can actually hear/feel the individual beats. I wonder what freq that actually is.
Needless to say, I am very impressed with this sub. Dare I say it betters my old SVS PB12-ISD/2 tuned to 16Hz!
Again, thanks for the help djk.
GhettoSQ said:
Hey SQ!
I cut the squares in the brace and driver holes with my jig saw. Simple enough, and the drivers fit nice and snug.
Sound? Nice!
I pretty muched summed it up in my post above. One thing else I have noticed is how efficient these subs are in this configuration. Since I am running modified Klipsch Cornwalls with a matching center channel, most subs have to work harder than normal to keep up with their 100dB @ 1W efficiency, but this new sub does better than fine, barely moving at all. In fact, the drivers move very little but certainly pump out the bass with ease.
Everything bass intensive that I have tried so far, both music and movie, has only peaked the amp around 30-50 watts! And let me tell you, it's louder than heck in here when that's happening! Durring normal listening levels, the meter on the amp barely ever reaches 1 watt!!!
I wonder if djk can help me figure out how efficient these subs are in this configuration. I'm thinking maybe close the Cornwalls' 100dB.
The amp I'm using is an old Technics SU-8099 integrated that was bought back in 1979 with the Cornwalls new. It's rated at 115W @ 8 ohms per ch and 180W @ 4 ohms per. I have the drivers wired to a 4 ohm load to each channel of the amp and have the sub line-out on my receiver going into the "Main In" on the SU-8099 which bypasses ALL tone and volume controls. Right now, it is nothing more than just a two-channel amp. Plus its freq resp is rated down to DC (0Hz) for the first 5 watts or so!
I want to run in the new driver for a while longer before I play the ultimate test DVD, "War of the Worlds". That movie is pretty much considered the sub-distroyer. LOL We'll see how my new sub fairs.
BTW, here's a fw pics of the build...
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An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Very nice! what's the smaller sub?
So, is it OK to mount the drivers back-to-back and wire them out of phase? I seem to recall somewhere that that was less than ideal, but if it works I'm all for it since it will solve my space problems.
Thought you were getting the MCM amp? I'm going to buy that and run pre-out and pre-in with my NAD 3020. Luckily the NAD has a subsonic filter as I'll be going vented -- I don't need 16Hz just yet, 25Hz will be fine as it's a music-first system. Someday I will shoot for the real low stuff but I can't expect much more from an 8" woofer.
So, is it OK to mount the drivers back-to-back and wire them out of phase? I seem to recall somewhere that that was less than ideal, but if it works I'm all for it since it will solve my space problems.
Thought you were getting the MCM amp? I'm going to buy that and run pre-out and pre-in with my NAD 3020. Luckily the NAD has a subsonic filter as I'll be going vented -- I don't need 16Hz just yet, 25Hz will be fine as it's a music-first system. Someday I will shoot for the real low stuff but I can't expect much more from an 8" woofer.
If you mount the driver back to back on opposing sides of the box with both magnets facing each other, and then reverse the polarity of the wiring on one ... what you have is a dipole! Cancellation will occur and you will find it will be like driving with the brakes on!
Push pull mounting is where one driver has the magnet inside the box, and the other driver mounted so the magnet side is out of the box, and one has reversed polarity on the wiring. What this means is that while one driver VC moves out of the magnet gap, the other moves in. This reduces distortion. It is a remedy to the fact that the linearity of the drivers is different with the in and out stroke.
Mounting the drivers on opposite sides of the box, both with magnets in, is not push pull mounting. The force of the cones operate in opposite directions and this will prevent the sub from moving around at high excursion.
As far as simulations are concerned, push pull mounting is not relevant. It is no different to simply having two drivers. There is an isobarik option in WinISD as this is relevant.
Chops, can that screen come forward a little? Looks like room for a bass horn behind that screen to me! Move the screen 0.5m forward and make it say the width of the screen and floor to ceiling - 2 cabs with a driver in each.
Otherwise, what about some large vented EBS boxes? One driver per box set up like a stage, interrupted by the centre speaker. It would lift the mains up say 0.5m and could make up the volume by having a big footprint.
Push pull mounting is where one driver has the magnet inside the box, and the other driver mounted so the magnet side is out of the box, and one has reversed polarity on the wiring. What this means is that while one driver VC moves out of the magnet gap, the other moves in. This reduces distortion. It is a remedy to the fact that the linearity of the drivers is different with the in and out stroke.
Mounting the drivers on opposite sides of the box, both with magnets in, is not push pull mounting. The force of the cones operate in opposite directions and this will prevent the sub from moving around at high excursion.
As far as simulations are concerned, push pull mounting is not relevant. It is no different to simply having two drivers. There is an isobarik option in WinISD as this is relevant.
Chops, can that screen come forward a little? Looks like room for a bass horn behind that screen to me! Move the screen 0.5m forward and make it say the width of the screen and floor to ceiling - 2 cabs with a driver in each.
Otherwise, what about some large vented EBS boxes? One driver per box set up like a stage, interrupted by the centre speaker. It would lift the mains up say 0.5m and could make up the volume by having a big footprint.
paulspencer said:
As far as I'm concerned, push-pull refers to how the cones react with eachother (working together in the same direction), not which way the magnet faces. At the volume levels I listen at, I don't think I'll ever have to worry about the VCs going out of the magnet gap.
However, if I am wrong about that, please let me know. I am still kind of new to the whole push-pull theory. I always have room and time to experiment.
chops said:
As far as I'm concerned, push-pull refers to how the cones react with eachother (working together in the same direction), not which way the magnet faces. At the volume levels I listen at, I don't think I'll ever have to worry about the VCs going out of the magnet gap.
However, if I am wrong about that, please let me know. I am still kind of new to the whole push-pull theory. I always have room and time to experiment.
Push pull means one driver pushes, the other pulls! Lets say one driver pushes the cone out from the magnet, while at the same time the other drivers pulls the cone in towards the magnet. Hence, if you want a push pull monopole, yes it is about which way the magnet faces!
The main function of this type of mounting is the reduction of distortion!
Now if you merely place drivers on opposing sides of a cabinet, this would not be push pull mounting. Forces would cancel so that the box doesn't move around, but distortion is not reduced.
The way I understand it, if you do true isobaric (one driver directly behind the other, same polarity) you get half the needed Vb but -6db efficiency. If you do push-pull with the drivers in different spots, you get efficiency but double the Vb. So, if you do a "clamshell" mounting, do you get both reduced Vb AND harmonic cancellation? what about efficiency?
WinISD shows "isobaric" as clamshell-mounted but explains the trade-offs in the help. I can live with the ugly clamshell look if it will get me good efficiency, half Vb, and super-clean sound (maybe combat the traditional vented-box transient response?).
WinISD shows "isobaric" as clamshell-mounted but explains the trade-offs in the help. I can live with the ugly clamshell look if it will get me good efficiency, half Vb, and super-clean sound (maybe combat the traditional vented-box transient response?).
Here's the pics...
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An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Ghetto, unfortunately you can't get all that! In Isobarik clamshell loading, you get another driver to compress the air, but only one driver radiates directly to the room, hence there is no efficiency or output increase. The second driver merely allows a smaller box. Now, since they are push pull mounted, there will be some improvement in distortion level, but it won't be as much as you would get with both drivers radiating into the room. Simply adding a second driver will reduce distortion for a given SPL level, for each driver requires half the excursion to achieve that level, and the distortion will be quite a bit less with half excursion.
Also consider with isobarik that it will affect the power requirements. Suppose you have an 8 ohm driver in a 2 cu ft box. Your amp can put out 200w into 8 ohms and this is enough to reach xmax. Now you put in a 2nd driver and parallel wire them so that its a 4 ohm load. You amp can put out 300w into that load, however, half of that is going into a driver that contributes nothing to the output, hence you now have only 150w available to drive the original driver. This means in this case slightly reduced output, and the amp is working harder. This is only about 1.5db however, not much to worry about.
If it were me, I'd rather have two separate 1 cu ft subs and enough power to drive them both, or a single push pull corner sub - tall and with a small footprint, taking up no more floor space than the 1cu ft sub.
Chops, how does it sound? It's a pity you can't quickly get an AB comparison.
Also consider with isobarik that it will affect the power requirements. Suppose you have an 8 ohm driver in a 2 cu ft box. Your amp can put out 200w into 8 ohms and this is enough to reach xmax. Now you put in a 2nd driver and parallel wire them so that its a 4 ohm load. You amp can put out 300w into that load, however, half of that is going into a driver that contributes nothing to the output, hence you now have only 150w available to drive the original driver. This means in this case slightly reduced output, and the amp is working harder. This is only about 1.5db however, not much to worry about.
If it were me, I'd rather have two separate 1 cu ft subs and enough power to drive them both, or a single push pull corner sub - tall and with a small footprint, taking up no more floor space than the 1cu ft sub.
Chops, how does it sound? It's a pity you can't quickly get an AB comparison.
paulspencer said:
I can't really tell if there's less distorsion or not, but it does seem to be a little louder than before, and it also seems to be little tighter sounding.
BTW, could one of you guys possibly work out the numbers for me as to what this sub is doing in my room as far as room gain and F3 please? (when you have the time of course)
My room is 13' x 17' with an 8' ceiling and a large 3.5' x 8' opening in the right rear corner of the room for the hallway which is about 25' long.
One guy on another forum ran the numbers and says the sub is down -3dB @ 23hz. I also tried running the numbers and mine came out to be down -3dB @ 14.6Hz. Confusing...
I would suspect that in reality, it's probably somewhere in between those two since I am getting tremendous amounts of output below 20Hz on well known pipe organ recordings.
Thanks in advance!
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