Subs, what to do if you lack excursion?

Per Søvik

Per Søvik

Graduate Student
Jan 31, 2012
1,881
0
36
64
Norway
So, I've got a few dual 18 reflex cabs that take up too much space compared to what they are capable of. I'm thinking I could maybe rip them apart and build some boxes using four elements in each box, preferrably using the existing boxes (60x60x120cm, 2x2x4ft)
The elements, Eminence Omega Pro 18A have very little excursion available with an x-max around 5mm, so I'm thinking that I need to restrict excursion by providing resistance by doing some kind of 4th or 6th order configuration with small rear volume and at the same time effectively doubling low frequency capacity by compensating for lack of excursion by doubling the number of elements.
Am I totally insane in attempting something like this? Are there any designs out there that would fit? I have seen a few pro boxes that packs a lot of drivers into a small box, so there is obviously some merit to the notion, but I suspect all these are based on elements with far superiour xmax.
 
Re: Subs, what to do if you lack excursion?

I know, the cabinets work really well with maxxbass, but I wouldn't mind getting some real punch around the fundamental of the kick, and I don't seem to get that even when pushing 12KW into my current boxes, so I want to reduce the space they take up in transport even if I can't get an improved result.
 
Re: Subs, what to do if you lack excursion?

Per Søvik said:
So, I've got a few dual 18 reflex cabs that take up too much space compared to what they are capable of. I'm thinking I could maybe rip them apart and build some boxes using four elements in each box, preferrably using the existing boxes (60x60x120cm, 2x2x4ft)
The elements, Eminence Omega Pro 18A have very little excursion available with an x-max around 5mm, so I'm thinking that I need to restrict excursion by providing resistance by doing some kind of 4th or 6th order configuration with small rear volume and at the same time effectively doubling low frequency capacity by compensating for lack of excursion by doubling the number of elements.
Am I totally insane in attempting something like this? Are there any designs out there that would fit? I have seen a few pro boxes that packs a lot of drivers into a small box, so there is obviously some merit to the notion, but I suspect all these are based on elements with far superiour xmax.
Click to expand...
Per,

Not a fan of 4th or 6th order BP boxes.

You could retrofit a single one of the 2x2x4ft boxes using this design (slightly modified, it is 26.5 x 22.5 x 45 inches):

Tapped Horn Vs. Bass Reflex Case Study - diyAudio

It should do around the same output with one speaker as two in the BR cab, and only need half the amplification.

Then sell the extra pair of raw speakers and send the money to me :^)

Art
 
Re: Subs, what to do if you lack excursion?

Jay, offloading the subs to someone who wants them is always an option, and at some point I might go ahead and spend money on some real subs, but for now I've got a pile of boxes that I'd like to try and do something useful with. They are not bad the way they are, and with all six boxes I can set up a pretty useful cardio array. However I feel they lack some punch as well as leaving no space in the trailer when all the boxes are loaded in.

Art, I couldn't get the pictures, need to register at that forum first, but again, the object isn't to get the same with less power and the same amount of boxes, but to reduce the total volume of the boxes in any way I can without having to buy anything new.
So I'm basically thinking that I have 12 elements with xmax of 5mm and no real resale value that could combine to privide fairly high displacement and thermal limit, be it three boxes or maybe even two cardio boxes. I've been looking at the EV MH4 and even the F1 infrabass and contemplating small volume variants of those, or even trying to slot load into a short synergy type of horn, whatever might work by design or pure luck, but I don't really want to do a lot of woodwork either 8)~:cool:~:cool:
 
Per,

My first response was tongue in cheek but on a more serious note it is probably easier and more effective to design something to fit a set of needs, then to redesign around an existing product.

If a design is thought of as a set of parameters describing an end result, the more of those parameters that are unchangeable at the beginning of the process, the less flexibility you have been in the remaining parameters. Or the end result has to change.
 
Re: Subs, what to do if you lack excursion?

Jay Barracato said:
Per,

My first response was tongue in cheek but on a more serious note it is probably easier and more effective to design something to fit a set of needs, then to redesign around an existing product.

If a design is thought of as a set of parameters describing an end result, the more of those parameters that are unchangeable at the beginning of the process, the less flexibility you have been in the remaining parameters. Or the end result has to change.
Click to expand...

Definitely, but this is sort of "Got tofu, potatoes and chicken stock, how do I make a thanksgiving dinner?" and "Buy turkey!" doesn't qualify as an answer to the task at hand :razz:

What I'm asking maybe can't be done, and I'm fine with that, but I would like to try because if I could achieve it within the confines described, it would be convenient. Maybe what I'm thinking of is counter-productive, but there must be some merit to the notion of putting the maximum cone area into a box of confined size, or nobody (that should know better) would do it.
Maybe I should rename the topic "Scrapheap challenge, what to do with 12 drivers and limited space" :)~:)~:smile:
 
Re: Subs, what to do if you lack excursion?

Per Søvik said:
Definitely, but this is sort of "Got tofu, potatoes and chicken stock, how do I make a thanksgiving dinner?" and "Buy turkey!" doesn't qualify as an answer to the task at hand :razz:

What I'm asking maybe can't be done, and I'm fine with that, but I would like to try because if I could achieve it within the confines described, it would be convenient. Maybe what I'm thinking of is counter-productive, but there must be some merit to the notion of putting the maximum cone area into a box of confined size, or nobody (that should know better) would do it.
Maybe I should rename the topic "Scrapheap challenge, what to do with 12 drivers and limited space" :)~:)~:smile:
Click to expand...

Or you just have this desire to make sawdust... and sometimes that's a lot of fun, it's rewarding from the carpentry angle, and if the result is an audibly useful product so much the better. You get to decide the standards by which your work will be judged.... at least until you start posting about your build and then the armchair critics will come out. ;)

Go ahead, sacrifice a few Norwegian spruces and make some sawdust. :)
 
Re: Subs, what to do if you lack excursion?

Tim McCulloch said:
Or you just have this desire to make sawdust... and sometimes that's a lot of fun, it's rewarding from the carpentry angle, and if the result is an audibly useful product so much the better. You get to decide the standards by which your work will be judged.... at least until you start posting about your build and then the armchair critics will come out. ;)

Go ahead, sacrifice a few Norwegian spruces and make some sawdust. :)
Click to expand...

Unfortunately I'm not much of a sawdust lover, my last speaker projects was 36 years ago, and Norwegian spruce plywood is too expensive, even in Norway, so it will probably be Russian birch or larch :)~:)~:smile:

Maybe I'll just put all 12 drivers into a single horn and be done with it. Build it as a trailer and use the horn opening for transporting the rest of the equipment?
 
Re: Subs, what to do if you lack excursion?

Per Søvik said:
J
Art, I couldn't get the pictures, need to register at that forum first, but again, the object isn't to get the same with less power and the same amount of boxes, but to reduce the total volume of the boxes in any way I can without having to buy anything new.
So I'm basically thinking that I have 12 elements with xmax of 5mm and no real resale value that could combine to privide fairly high displacement and thermal limit, be it three boxes or maybe even two cardio boxes. I've been looking at the EV_MT4
Click to expand...
The Omega Pro 18A needs a big box to go low, but then runs out of excursion at low power and relatively little output.
I'd agree with your plan of putting four in each of your boxes, slot loaded, Fb around 44 Hz.
That is fairly similar to the MT4 frequency response, which was good enough for Rob Colby and Prince back in the day.
The slot should be very thin to avoid loss of cabinet volume.
Raising the level by 12 dB to account for four times the power and cone area, the sim says the quad should do around 133 dB with 1600 watts.

You should be able to reduce cabinet count by half, increase output, and use the empty cabinets for the wood needed for the slot plenums.

Art "save the trees" Welter
Art "the wood butcher" Welter
 

Attachments

  • Per Cab.png
    Per Cab.png
    780 KB · Views: 2
  • Small enclosure.png
    Small enclosure.png
    163.9 KB · Views: 2
Re: Subs, what to do if you lack excursion?

Art Welter said:
The Omega Pro 18A needs a big box to go low, but then runs out of excursion at low power and relatively little output.
I'd agree with your plan of putting four in each of your boxes, slot loaded, Fb around 44 Hz.
That is fairly similar to the MT4 frequency response, which was good enough for Rob Colby and Prince back in the day.
The slot should be very thin to avoid loss of cabinet volume.
Raising the level by 12 dB to account for four times the power and cone area, the sim says the quad should do around 133 dB with 1600 watts.

You should be able to reduce cabinet count by half, increase output, and use the empty cabinets for the wood needed for the slot plenums.

Art "save the trees" Welter
Art "the wood butcher" Welter
Click to expand...

There we go!!!!! I knew there would be someone with the answer I was looking for, I'll convert one box right away and do some measurements.

Are there any resources available for this kind of construction? You see, I haven't got the foggiest idea about calculating slots, calculating plenum chamber or how to place the ports or anything else that relates to this kind of construction. Then again, you must have already guessed that :)~:)~:smile:

EDIT: Maybe I'm misunderstanding something here. Is the plenum itself the "slot", and there are no slots in front of the individual driver cones?
 
Last edited:
Re: Subs, what to do if you lack excursion?

Per Søvik said:
So, I've got a few dual 18 reflex cabs that take up too much space compared to what they are capable of. I'm thinking I could maybe rip them apart and build some boxes using four elements in each box, preferrably using the existing boxes (60x60x120cm, 2x2x4ft)
The elements, Eminence Omega Pro 18A have very little excursion available with an x-max around 5mm, so I'm thinking that I need to restrict excursion by providing resistance by doing some kind of 4th or 6th order configuration with small rear volume and at the same time effectively doubling low frequency capacity by compensating for lack of excursion by doubling the number of elements.
Am I totally insane in attempting something like this? Are there any designs out there that would fit? I have seen a few pro boxes that packs a lot of drivers into a small box, so there is obviously some merit to the notion, but I suspect all these are based on elements with far superiour xmax.
Click to expand...

Art has a good plan here, but the simple answer to your question is to put them in a smaller box and tune it higher. That will control the cone movement better, but will push the Q higher also. Go too far this way and you end up with the kind of boom a mini-truck would be proud of.
 
Re: Subs, what to do if you lack excursion?

Tim Weaver said:
Art has a good plan here, but the simple answer to your question is to put them in a smaller box and tune it higher. That will control the cone movement better, but will push the Q higher also. Go too far this way and you end up with the kind of boom a mini-truck would be proud of.
Click to expand...

Yes, that was more or less what I had in mind, to tune them to have a peak around the kick fundamental and sacrifice sensitivity below that, and I know how to do that. The way I would have proceeded would have been to arrange the units similar to Art's drawing, leaving the plenum open in full length, and dividing the rear chambers in the middle so each driver would have a sealed chamber, and then maybe venting the rear chambers.
 
Re: Subs, what to do if you lack excursion?

Per Søvik said:
There we go!!!!! I knew there would be someone with the answer I was looking for, I'll convert one box right away and do some measurements.

Are there any resources available for this kind of construction? You see, I haven't got the foggiest idea about calculating slots, calculating plenum chamber or how to place the ports or anything else that relates to this kind of construction. Then again, you must have already guessed that :)~:)~:smile:

EDIT: Maybe I'm misunderstanding something here. Is the plenum itself the "slot", and there are no slots in front of the individual driver cones?
Click to expand...
Plenum is the fancy word for slot.
Make the plenum 3 inches wide, or 76 millimeters wide, whichever your preference ;^).
The depth of the port area should be as in the sim attached in post 13, the area should be four times for one cabinet of four times the volume with four speakers (approximately what you will have converting your existing cabinets).

If you divide the cabinet in four parts, each section would be ported as in the sim, using four 3 inch diameter tubes 9.4 inch long, or the rectangular equivalent in cross sectional area, about 28.26 square inches.
Making the plenum the full depth of the cabinet wastes a little bit of the valuable internal cabinet volume, which is already partially used up by speaker, plenum and port volume.
Ports closer to square than skinny will be more equivalent to round.

Rectangular ports will tune slightly lower than circular .
Round over the plenum and port exits to reduce chuffing noises

It is best to make the ports a bit long on the first cabinet, then cut them down until the desired Fb is reached.

You can determine Fb by running sine wave tones through the cabinet, the cones will move least at Fb. Put a white dot on the cone to make it easier to see the movement.

There are a number of on line port calculators you can use to determine the port size if you find that the internal cabinet volume differs much from the sim.
Since the small cabinet volume results in a non-flat alignment, you are free to choose the Fb, knowing the lower the Fb the less output at Fb the cabinet will have.
 
Re: Subs, what to do if you lack excursion?

Thank you Art, sorry for being such a dim-witted idiot about this, and I'm not done yet.

Art Welter said:
Plenum is the fancy word for slot.
Click to expand...
Gotcha, allthough I beg to differ from a general use perspective :)~:)~:smile:

Make the plenum 3 inches wide, or 76 millimeters wide, whichever your preference ;^).
The depth of the port area should be as in the sim attached in post 13, the area should be four times for one cabinet of four times the volume with four speakers (approximately what you will have converting your existing cabinets).
Click to expand...
This is the port from the plenum, the front port?

If you divide the cabinet in four parts, each section would be ported as in the sim, using four 3 inch diameter tubes 9.4 inch long, or the rectangular equivalent in cross sectional area, about 28.26 square inches..
Click to expand...
So the rear chambers are just ported as if the fronts were firing into open air, no compensation for the resistance when calculating, have I got that right?

Making the plenum the full depth of the cabinet wastes a little bit of the valuable internal cabinet volume, which is already partially used up by speaker, plenum and port volume.
Click to expand...
Got it, but I think I'll go for simplicity of construction at this point. Me lazy you know :blush:.

Ports closer to square than skinny will be more equivalent to round.

Rectangular ports will tune slightly lower than circular .
Round over the plenum and port exits to reduce chuffing noises

It is best to make the ports a bit long on the first cabinet, then cut them down until the desired Fb is reached.

You can determine Fb by running sine wave tones through the cabinet, the cones will move least at Fb. Put a white dot on the cone to make it easier to see the movement.

There are a number of on line port calculators you can use to determine the port size if you find that the internal cabinet volume differs much from the sim.
Since the small cabinet volume results in a non-flat alignment, you are free to choose the Fb, knowing the lower the Fb the less output at Fb the cabinet will have.
Click to expand...

OK, I guess I can just measure the current through the speaker while doing a sweep?
Thanks again for all your help, I've got an outdoor show in a week, maybe I'll have at least one cabinet converted by then.
 
Re: Subs, what to do if you lack excursion?

Per Søvik said:
1)This is the port from the plenum, the front port?

2) So the rear chambers are just ported as if the fronts were firing into open air, no compensation for the resistance when calculating, have I got that right?

3)OK, I guess I can just measure the current through the speaker while doing a sweep?
Click to expand...

1) The plenum slot volume will create a resonance up around 200 or 300 Hz. The plenum is not a port.
2) Yes.
3) I have never tried to do that, I find it easier to just look at the cone movement to find Fb.

The new Fb won't play very well with the old, you would be better off converting them all before the show, or do it after, unless you have dedicated DSP for both.
 
Re: Subs, what to do if you lack excursion?

Art Welter said:
1) The plenum slot volume will create a resonance up around 200 or 300 Hz. The plenum is not a port.
2) Yes.
3) I have never tried to do that, I find it easier to just look at the cone movement to find Fb.

The new Fb won't play very well with the old, you would be better off converting them all before the show, or do it after, unless you have dedicated DSP for both.
Click to expand...

OK, so I just leave the plenum open for the full length then?
 
Top Bottom