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Discussion Starter #1
In an attempt to make a subwoofer for my adult daughter and fiancé, I bought these two woofers for very cheap. I have a limited budget, no doubt. I originally was going to design a sealed enclosure, but after talking to my daughter and her intended, they like special effects and gamming. I shied away from the idea of ported orginally because I just hate the idea of building the enclosure and having male voice "boom". I ran the numbers on winISD on-line and the enclosures seem rather large. I've read about isobaric that will halve the space, but negate the efficiency advantage of having two speakers. Fourth order seems good, it help pull the response to the lower end, but I understand that it may require notch filter(s) and testing that I do not have the equipment to do. Sixth is even worse. T-line and horn appear they would make even larger cabinets, but I haven't run any of the calculations. I considered IB, but was told these speakers are not even close in specs to what would be needed. I like the idea of the speakers being mounted opposite of each other to cancel the box vibrations. Designing, drafting and building the cabinet is by far the easiest part of the project for me.

This will be used for LFE and "maybe" 100Hz and below from the other 7 speakers.
Specs: http://www.mcmelectronics.com/content/ProductData/Spec%20Sheets/55-2953.pdf

 

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Yikes, two 15" drivers rolling off below just 40Hz and <4mm of xmax... Those certainly are budget drivers. I would definitely go with the vented setup so the sub plays deep as possible. It's not for a PA application, so what's the point of a giant sub that's loud but doesn't get low? Play with the isobaric setup if it will keep the box size low, that driver is so sensitive you really don't need two anyways.

Boom of male voices when using a sub simply means the sub's LPF is set too high. Also, a "sub" without an LPF set below 100-200Hz isn't really a sub.
 

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Discussion Starter #3
Thank you Fusseli,
At this point, If I had the funds, I'd buy a better driver and use these for something else, but as it is, I still have to work on the material and an amp ($). With that in mind, I will most likely use the isobaric and when monies free up, I'll make them a stronger one. As a consolation, all they have to compare it to is a theater-in-a-box. This has been a very enjoyable learning experience and I will continue to study.
 

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Gotcha :T

This build will for sure be looouud for music with just a couple hundred watt amp, it will just be missing the deep rumbles in HT content. I don't picture an HT-in-a-box going any deeper than the 40Hz range, anyways. About any properly executed build will stomp all over those things.

Please post back with any questions or concerns along the way!
 

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Discussion Starter #5
I do have a question that may seem obvious to you with experience. The ratings for each speaker is 200W RMS max. They are 8 ohm speakers. If I wire in parallel to give 4 ohms total, then I would assume that the two together would be rated 400W rms max. If I were to drive these with a 200W-240W @ 4 ohm plate amp with a 6 DB boost at 30Hz-35Hz to make up for the near linear drop on the speaker frequency response curve, starting at 300hz. Would there be any problem with the cone not being loaded below the port tuning. I would be following the WinISD for ported with the port tuned to 31. My understanding is that the plate amps roll off at about 18Hz. (This is from reading, not experience). and that should prevent an un-dampened problem below 18 HZ.

One thing I haven't grasped is the chart of WinISD. Is it a predicted frequency response or does it have to be combined with the manufacture's frequency chart some way to get a predicted end result? My question about the boost is pretty much based on the manufactures chart showing a 20db drop by the time it reaches 20HZ.

Any base management, if used, will be 100Hz (lowest setting of their receiver) and the LFE signal.

Hopefully, I'll start my construction drawings next week.

Thanks!
 

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I do have a question that may seem obvious to you with experience. The ratings for each speaker is 200W RMS max. They are 8 ohm speakers. If I wire in parallel to give 4 ohms total, then I would assume that the two together would be rated 400W rms max. If I were to drive these with a 200W-240W @ 4 ohm plate amp with a 6 DB boost at 30Hz-35Hz to make up for the near linear drop on the speaker frequency response curve, starting at 300hz. Would there be any problem with the cone not being loaded below the port tuning. I would be following the WinISD for ported with the port tuned to 31. My understanding is that the plate amps roll off at about 18Hz. (This is from reading, not experience). and that should prevent an un-dampened problem below 18 HZ.

One thing I haven't grasped is the chart of WinISD. Is it a predicted frequency response or does it have to be combined with the manufacture's frequency chart some way to get a predicted end result? My question about the boost is pretty much based on the manufactures chart showing a 20db drop by the time it reaches 20HZ.

Any base management, if used, will be 100Hz (lowest setting of their receiver) and the LFE signal.

Hopefully, I'll start my construction drawings next week.

Thanks!
No, unfortunately actual power handling is not that simple. In a vented alignment especially, below tuning the drivers will handle nowhere near their thermal power limit without an HPF (aka infra- or sub- sonic filter). I will work up a sim for you in winISD tomorrow since an explanation is a lot easier with an example to learn from.

Do you have an amp picked out yet? What are your limitations on gross cab volume and/or dimensions?
 

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Discussion Starter #7
Remember that I am dealing with my daughter on this, as such, I'm offering reasonable alternatives to her as to size and style. The most likely design would be isoboric with the outside driver hung from underneath. I would be matching a TV table that is Depth: 18 1/2 " Height: 22 1/2 ". Height includes 4-1/2" tall legs. The width will be to match required volume (4.2 ft³) based on WinISD for a ported design tuned to it's recommendation. This would be next to the TV.

The second possibility is a square tower with the drivers opposing, mounted top and bottom, approximately 8' total height and the width and depth equal, and as required to match the WinISD volume (16.8 ft³) for ported. This would be off to the far left of the TV wall.

By the way, this wall does not meet in a corner on either side. Left is an entrance from the front door and right is a hall way for the bedrooms, etc.

The least likely would be two end tables - ported and wired in parallel from the same amp. Least likely because of exposed wiring to trip and be chewed.

They have animals so I am avoiding an exposed cone as well, that could get wet or scratched.

Other things that I have offered them is a sofa table or mounting the enclosure in their ceiling (one story slab house).

Amps: I was considering;

MCM Audio Select Part #: 50-6263 - 200 Watt Subwoofer Amplifier Module http://www.mcmelectronics.com/product/MCM-AUDIO-SELECT-50-6263-/50-6263

Yung SD200-6 200W Class D Subwoofer Amp Module with 6 dB @ 35 Hz http://www.parts-express.com/pe/showdetl.cfm?Partnumber=301-506

Or similar along those lines. They have a continuous adjustment for phase correction. I will not have very much leeway with location, and maybe I reaching for straws, but I hope to keep a bad dead spot away from their couch.

Thank you again for your patience with the inexperienced. I read the internet, but there always seems to be "assumed knowledge" that trips me up.
 

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Okay, I follow. Focus on the amps without the built in boost, which may do more harm than good for you. One last question: are you 100% settled on using this pair of drivers? I don't mean to beat a dead horse here I'm just trying to steer you down the best possible path.
 

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Okay, looks like no matter what you roll with 100W will be enough for the pair of subs. That will save you some $ over the 200W amp. You are right, having the continuous phase adjustment is an advantage for the Yung amps.

All three are vented isobarik setups: green is 4.2cuft tuned to 31Hz (2x 3" ports), red is 6cuft @ 25Hz (1x 4" port), and blue is 8cuft @ 20Hz (1x 4" port). All have 2nd-order LPFs applied at 80Hz, good for HT environment, and HPFs at 18Hz (typical built into sub plate amps).

The green would be better suited for a PA application than it would for HT. I'd recommend the red or blue over the green, the blue if possible. They both dig deeper and would have more impressive results. Unfortunately these drivers just can't handle more power to get much louder.



As you can see, 100W for the pair is still enough to push the subs a little over xmax in all three of those configurations. The ports are sized to keep the air velocity low.
 

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And just for comparison, a single15" Dayton DCS385 (~$100) in your "tower" option of 16cuft tuned to 18Hz with a 100W amp (purple), compared to the same 8cuft MCM as above (blue):



The Dayton DCS being a solid entry-level sub that's well suited for HT.
 

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Discussion Starter #11
You have me thinking. My daughter is out of town. I'm still trying to get them to decide on size restrictions.

For my education, with the driver you listed, you said a 100w would be fine, would it overdrive with the 200w (I'm still learning to read the graphs). I have ISD pro loaded, but I just recently started using it. I have been using the the on-line version.

Thanks!!!
 

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You have me thinking. My daughter is out of town. I'm still trying to get them to decide on size restrictions.

For my education, with the driver you listed, you said a 100w would be fine, would it overdrive with the 200w (I'm still learning to read the graphs). I have ISD pro loaded, but I just recently started using it. I have been using the the on-line version.

Thanks!!!
Yes. 100W is just right for a single Dayton driver I suggested in a large 16cuft box. 100W is also more than enough for the two MCM drivers you already have. On the cone excursion graph, you don't really want it to go higher than the xmax rating of the driver.
 

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Discussion Starter #13
Russ (and anyone else that wants to add opinions),
I'm going to take half your suggestion. Money dictates using what I have. I'm going to go with the blue (8cuft @ 20Hz), but unless there is a problem, I would like to use 4-2" ports. They have the same area, but with the square base I'm designing, they would fit in the corners better. This leads me to something that I been trying to understand about the limitation of ports. I understand that each port should have a minimum of the diameter of the port between each other (mine will be at the four corners). But I'm unsure of any other rules-of-thumb, such as the distance of the port from the driver (cone)?

Next week, I'll have a drawing to show, but, in words, this is what I'm planning;
Approximately 2'x2' base, height as required for the 8 ft³
Down firing
Isobaric
4-2" ports
The base will be about 7" from the floor, but the trim will start about 4" from the floor all the way around.

This is a very rough drawing of the bottom (my lunch time activity). I'm still thinking it through.

Thanks!
 

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Four 2" ports won't be nearly as effective, if possible be sure and flare the exits of the ports and consider using maybe six to avoid port noise issues all together. You might play with tuning frequencies in winISD a little to see what you like, just pick one maybe 20-23Hz or so. This big sub won't be super loud but it sould at least play low.

Ya, so allow one diameter of rear port clearance. Another rule for full-range speakers is to not position the ports behind the woofers such that you can see the back of the cone looking through the port tube. That shouldn't matter as much for a sub though. You should also group your ports tightly together and not have them spread out. Given your low tuning frequency that shouldn't be a big issue either though (even with the 24" spacing they'd be fine below the 150Hz range anyways).
 

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Discussion Starter #15
I’m having a problem getting the cone excursion graph to work. I entered all of the info from the data sheet and other graphs work. I notice that you were able to produce the graphs in earlier post. Is there some trick or fudge factor that I’m missing? It works fine when I input the info from the Dayton data sheet, which has more data.
By what you have said, cone excursion is my biggest enemy with these speakers. I’m deep into my layout, but the back of my mind keeps whispering “cone excursion”.
:dontknow:
 

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Good question! Usually what's missing is cone surface area, the rest of the parameters will auto-calculate in winISD provided that you have the basic T/S params including Re. Area is pretty safe to estimate just based on the size of the driver, adjusting a bit for the size of the driver's surround. I approximated about 850sqcm for your 15" MCM. You'll find that varying the area by a few tens of sqcm won't greatly effect your simulation.
 

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Sure is.

Just remember that it is a simulator that makes approximations. Furthermore, also realize that manufacturer's published driver parameters often aren't that accurate. It's best to have drivers in-hand and to test them with something like a Dayton WT3, and use those T/S params over the published ones. That's usually only a route for the serious enthusiast of the builder that makes lots of projects, though (especially useful for full-range speaker DIY). Published specs and winISD are plenty for the average Joe to get a nice sub put together! Sorry, I digress.
 

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Discussion Starter #19
And just for comparison, a single15" Dayton DCS385 (~$100) in your "tower" option of 16cuft tuned to 18Hz with a 100W amp (purple), compared to the same 8cuft MCM as above (blue):

The Dayton DCS being a solid entry-level sub that's well suited for HT.
Due to my Mother-in-law's illness, everything else went on hold. She entered her reward last Mother's Day week. We have just about caught up financially, so I'm going to work on the sub.
I was given a DATS V2 and tested the speakers. The Qts is greater than 0.707 so I'll use them in the garage. I was wanting to know if you think the same of the Dayton speaker or if you have a better recommendation now for the same price range.
I noticed that they also have a DCS380.
 

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Discussion Starter #20
I've noticed that 15" seems to be a sweet spot for low fs, Vas and price. I admit that I have not had much time to investigate in the last three years. Just when I could catch a break.
 
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