Infinity 1260W Media Cabinet Subwoofer - $250 build - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 33 Old 05-03-2015, 01:32 PM - Thread Starter
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Infinity 1260W Media Cabinet Subwoofer - $250 build

I have a pair of DIYSG 88 Specials (highly recommended) as my LR and am looking to add a subwoofer. I would like a high WAF and would like it to blend in like a piece of furniture. The 88 specials are mounted on the wall which gives enough space for a maximum cabinet of 23” wide by 28.5” tall, by 24” deep under them. I looked at the Marty variants, but they are too expensive at this time (max budget $250) and would require a new amplifier (old school Dolby Pro Logic amplifier right now). My amplifier doesn’t have LFE out so I settled on a plate amplifier that can take speaker level inputs. So for just under $200 dollars I got the Infinity 1260W ($55) and a Dayton Audio SPA250 250 Watt Subwoofer Plate Amplifier ($140). I have seen other posts that have driven the 1260 with more power, but at $195 bucks it leaves $55 dollars for MDF, etc. so it fits perfectly in budget. Also it has a high pass filter at 20 Hz which looks like a requirement based on WinISD modeling.

My original plan was to build a standard front-firing sub in the same style of the Martys (Mini-Marty?), but after playing around in WinISD and UniBox I started playing around with trying to make a down-firing Media cabinet.

I haven’t put it in Sketchup, but the idea would be to have a 22” wide X 22” deep X 28” high cabinet. The Infinity/subwoofer portion would be in the back part of the enclosure with the front part having a DVD section, and the port (outside of the internal volume of where the subwoofer is located). Then a cabinet door for the DVD section on the front. Basically from the front it would look just like a deep media cabinet.

Here is a sketch of the front with the front cabinet door cutaway:



Here is a sketch of the side with the side wall cutaway:



The relevant dimensions (internal dimensions when using .75” MDF) for the back section are 20.5” x 13” x 23” = 3.38 cubic feet (95.7 liters) after subtracting space for the braces and driver.
The port would be 4” x 4” running 15” in length tuned to 23 Hz. Not in the picture that this port area is outside of the subwoofer’s 3.38 cubic feet section.

Here is where things get interesting! Based on a post from @LTD02 (thread: Calculating Subwoofer Port Length - Not So Simple) and from users measuring some of the originally built Martys it looks like WinISD doesn’t properly model ports that are not in the center of the cabinet. The “k” value or end correction value in WinISD doesn’t look like it is used in the calculations. From the link by @LTD02 it looks like the port as I have it setup would need a 1.728 value for k, instead of .732 (default in WinISD). Based on this I entered all of the information into UniBox to determine what the proper length of the port should be since it allows a custom value for k. From UniBox I got a port length of 38 cm = 15 inches. For anyone following along in UniBox and WinISD, you will see that UniBox with a 300 watt input (max rms for the infinity) shows a peak port velocity of 32ms (high) vs WinISD showing a maximum of 23ms (ok). I think this is occurring because I have the High Pass filter configured in WinISD, but don’t have it setup in UniBox. I would plan to have a small round-over on both port ends so hopefully the port speed wouldn’t be an issue.

I don’t think the cabinet should be vibrating so much that it would be an issue with the DVDs/BluRays, especially with it down-firing. If it was an issue I thought just adding some of that spongy cabinet liner should keep the plastic from rattling against the wood. Or just buy enough DVDs/BluRays so they are smashed in there tight enough that they won’t rattle!

So… Am I crazy trying to build a cabinet like this? I originally modeled just a standard cabinet, but thought a media cabinet would be a little different and have a much higher WAF.
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post #2 of 33 Old 05-03-2015, 01:51 PM
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yours is a creative approach that should work fine in principal.


the net enclosure volume for the driver seems a little small. i'm calculating about 2.75 cu. ft. if that could be increased to 4 c.f. or so (by hogging the shelf space :-) ) that would help things (and lower the tuning).

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post #3 of 33 Old 05-03-2015, 04:14 PM
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Better be mightily braced if it's gonna have doors and dvds in it, as the dvds will be bouncing around making a racket..
I actually had something similar to this in mind for a project.

Why waste $ on more cheap stuff, it's like challenging a dragon with a pocket knife.
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post #4 of 33 Old 05-03-2015, 04:51 PM - Thread Starter
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Quote:
Originally Posted by LTD02 View Post
yours is a creative approach that should work fine in principal.


the net enclosure volume for the driver seems a little small. i'm calculating about 2.75 cu. ft. if that could be increased to 4 c.f. or so (by hogging the shelf space :-) ) that would help things (and lower the tuning).
Maybe I calculated the internal volume wrong, but I thought I had 3.38 cubic feet!

I got the depth by doing 22" (depth of cabinet) - 6.75" (depth of internal shelf) - 3 * .75 (MDF front, back, and middle divider)= 13"
For the width I did 22" (width of cabinet) - 1.5" (MDF sides) = 20.5"
For the height I did 28" (height of cabinet) - 3.5" (height of legs) - 1.5" (MDF top and bottom) = 23"

Which gives 6,129.5 cubic inches = 3.55 cubic feet. Then I subtracted .1 cubic feet for bracing. For 2 braces from top to bottom (1inch by 1inch), and 9 braces from front to back (1 inch by 1 inch) that totals .1 cubic feet total. If I used dowels it would be a little less area per brace and I could then add more dowels.
Then the driver I used .07 for its volume.
So my total was 3.38 cubic feet.

@muzz How does the bracing sound? With 2 top to bottom it would split the top and bottom into approximately 7" by 10" sections. With 9 front to back braces, it would be a 3 x 3 grid of braces front to back and would split it into approximately by 8" by 7" sections.
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post #5 of 33 Old 05-03-2015, 09:04 PM
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yeah, I missed the volume of the cab next to the port. ~3.4 c.f. is correct.

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post #6 of 33 Old 06-20-2015, 01:22 PM
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Update?
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post #7 of 33 Old 06-20-2015, 05:06 PM - Thread Starter
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I've got pictures queued up to post, but I've been super busy and haven't gotten them posted.

I have it completely built and just got done putting up a temporary spray booth in my garage to spray them. I hope to mount the infinity tomorrow and try it out!

Still have to make the legs since I want them to be removable. Since it is down firing I might just put it on some 2x4s to test it out!
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post #8 of 33 Old 07-11-2015, 06:18 PM - Thread Starter
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Quick Summary: I am VERY happy with such an inexpensive build. I have a 20 x 30 x 9 foot great room and even though this sub is little it still digs low enough to rattle stuff around the room!

Finally got some time to organize and upload some pictures as well as take some REW measurements and watch some movies. I haven't put the shelf or doors on the subwoofer cabinet yet, that can come later!

Here is the REW measurement with a umik from 1 foot away. I ran the sub-cal Pink Noise at 75 Hz and then ran the sweep from 19 to 120 Hz. No way I could do an outside measurement.



Since I am using a plate amplifier and an old receiver, I can't manage the crossover perfectly, but setting the plate amplifier to around 80 Hz blended ok with the 88 Specials (which are good down to 60 Hz).

Closeup showing the 88 Special on its custom shelf, with the subwoofer underneath. I built it to match the height of my existing media cabinet.



And an image with both speakers and TV. I chose the 88 Specials to give space for the subwoofer and so that I could wall mount them and leave space for the air vent on the left. I had considered the Fusion 4s, but wanted the larger waveguide of the 88 Specials. I've gotten a ton of compliments from my wife's friends on the 88 Specials, WAF goes way up when her friends are complimenting how they look!



Here are a few pictures of how the port is setup. In the second picture you can see the round cutout for the dowel. That was a recommendation from Bill Fitzmaurice and worked perfectly. A forstner bit just a little bit into the panel and the dowels sat in easily, then I added glue when I assembled them.




Here is all the bracing with sound deadening mattress topper.



Here is with the bottom attached. The 4 dowels line up with 4 of the mounting holes for the infinity subwoofer. Then I added the small braces (one is visible at the top of the picture) for the other 4 holes to give the screws something to grab into that was deeper than the 3/4" baffle. Since it is down firing I just did surface mount, nothing fancy.



Here is REW with everything on. I haven't done any sound deadening room treatments because this is the main family room, so there is some nastiness at 50 Hz, 120 Hz, and 250 Hz, but it sounds really good. A second sub should fix the 50 Hz issue, but not sure that will pass WAF. When I move the mic around and run more REW sweeps the 50 Hz dropout disappears so it seems to be a room null as opposed to a problem with the design.




Final Thoughts:

If you are on the fence for building either a kit speaker (i.e. DIYSoundGroup, etc.) or a custom subwoofer (i.e. WinISD, etc.) or "kit subwoofer" (i.e. Marty line) stop worrying and BUILD IT! You will not be disappointed. 6 months ago I couldn't spell crossover, and now I can sit and watch Edge Of Tomorrow with a huge grin. Everyone here is incredibly helpful!
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post #9 of 33 Old 07-11-2015, 06:53 PM
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Quote:
Originally Posted by bitmap42 View Post
Quick Summary: I am VERY happy with such an inexpensive build. I have a 20 x 30 x 9 foot great room and even though this sub is little it still digs low enough to rattle stuff around the room!

Finally got some time to organize and upload some pictures as well as take some REW measurements and watch some movies. I haven't put the shelf or doors on the subwoofer cabinet yet, that can come later!

Here is the REW measurement with a umik from 1 foot away. I ran the sub-cal Pink Noise at 75 Hz and then ran the sweep from 19 to 120 Hz. No way I could do an outside measurement.



Since I am using a plate amplifier and an old receiver, I can't manage the crossover perfectly, but setting the plate amplifier to around 80 Hz blended ok with the 88 Specials (which are good down to 60 Hz).

Closeup showing the 88 Special on its custom shelf, with the subwoofer underneath. I built it to match the height of my existing media cabinet.



And an image with both speakers and TV. I chose the 88 Specials to give space for the subwoofer and so that I could wall mount them and leave space for the air vent on the left. I had considered the Fusion 4s, but wanted the larger waveguide of the 88 Specials. I've gotten a ton of compliments from my wife's friends on the 88 Specials, WAF goes way up when her friends are complimenting how they look!



Here are a few pictures of how the port is setup. In the second picture you can see the round cutout for the dowel. That was a recommendation from Bill Fitzmaurice and worked perfectly. A forstner bit just a little bit into the panel and the dowels sat in easily, then I added glue when I assembled them.




Here is all the bracing with sound deadening mattress topper.



Here is with the bottom attached. The 4 dowels line up with 4 of the mounting holes for the infinity subwoofer. Then I added the small braces (one is visible at the top of the picture) for the other 4 holes to give the screws something to grab into that was deeper than the 3/4" baffle. Since it is down firing I just did surface mount, nothing fancy.



Here is REW with everything on. I haven't done any sound deadening room treatments because this is the main family room, so there is some nastiness at 50 Hz, 120 Hz, and 250 Hz, but it sounds really good. A second sub should fix the 50 Hz issue, but not sure that will pass WAF. When I move the mic around and run more REW sweeps the 50 Hz dropout disappears so it seems to be a room null as opposed to a problem with the design.




Final Thoughts:

If you are on the fence for building either a kit speaker (i.e. DIYSoundGroup, etc.) or a custom subwoofer (i.e. WinISD, etc.) or "kit subwoofer" (i.e. Marty line) stop worrying and BUILD IT! You will not be disappointed. 6 months ago I couldn't spell crossover, and now I can sit and watch Edge Of Tomorrow with a huge grin. Everyone here is incredibly helpful!
What your low pass filter set to? I like to cross my sub at 80hz. And low pass it filter it around 55.

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post #10 of 33 Old 07-11-2015, 06:55 PM
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Quote:
Originally Posted by bitmap42 View Post
Quick Summary: I am VERY happy with such an inexpensive build. I have a 20 x 30 x 9 foot great room and even though this sub is little it still digs low enough to rattle stuff around the room!

Finally got some time to organize and upload some pictures as well as take some REW measurements and watch some movies. I haven't put the shelf or doors on the subwoofer cabinet yet, that can come later!

Here is the REW measurement with a umik from 1 foot away. I ran the sub-cal Pink Noise at 75 Hz and then ran the sweep from 19 to 120 Hz. No way I could do an outside measurement.



Since I am using a plate amplifier and an old receiver, I can't manage the crossover perfectly, but setting the plate amplifier to around 80 Hz blended ok with the 88 Specials (which are good down to 60 Hz).

Closeup showing the 88 Special on its custom shelf, with the subwoofer underneath. I built it to match the height of my existing media cabinet.



And an image with both speakers and TV. I chose the 88 Specials to give space for the subwoofer and so that I could wall mount them and leave space for the air vent on the left. I had considered the Fusion 4s, but wanted the larger waveguide of the 88 Specials. I've gotten a ton of compliments from my wife's friends on the 88 Specials, WAF goes way up when her friends are complimenting how they look!



Here are a few pictures of how the port is setup. In the second picture you can see the round cutout for the dowel. That was a recommendation from Bill Fitzmaurice and worked perfectly. A forstner bit just a little bit into the panel and the dowels sat in easily, then I added glue when I assembled them.




Here is all the bracing with sound deadening mattress topper.



Here is with the bottom attached. The 4 dowels line up with 4 of the mounting holes for the infinity subwoofer. Then I added the small braces (one is visible at the top of the picture) for the other 4 holes to give the screws something to grab into that was deeper than the 3/4" baffle. Since it is down firing I just did surface mount, nothing fancy.



Here is REW with everything on. I haven't done any sound deadening room treatments because this is the main family room, so there is some nastiness at 50 Hz, 120 Hz, and 250 Hz, but it sounds really good. A second sub should fix the 50 Hz issue, but not sure that will pass WAF. When I move the mic around and run more REW sweeps the 50 Hz dropout disappears so it seems to be a room null as opposed to a problem with the design.




Final Thoughts:

If you are on the fence for building either a kit speaker (i.e. DIYSoundGroup, etc.) or a custom subwoofer (i.e. WinISD, etc.) or "kit subwoofer" (i.e. Marty line) stop worrying and BUILD IT! You will not be disappointed. 6 months ago I couldn't spell crossover, and now I can sit and watch Edge Of Tomorrow with a huge grin. Everyone here is incredibly helpful!
Also. I have a plan for a 1260w. In a 20Wx30Tx20D(5.5ft3) enclosure with a 19 hz tune. Sold be epic.



It's been dubbed the tiny marty.

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Vizio M501d-A2R(Calibrated), LG BD-330, Pioneer VSX-524-K, Custom DIY LCR Mains, DIY Sub ( Kicker 10c124, 2.25 ft3, 19 hz tune, powered by xm-sd46x(using only rear channel in bridge mode, 150watts), powered by 400w atx power supply.) Work in progress.
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post #11 of 33 Old 07-11-2015, 07:05 PM - Thread Starter
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That's a little bit of a problem. I ran speaker level outs to the plate amplifier. Then I tried hooking the speaker outs on the plate amplifier to the 88 specials, but the plate amp has a built in 120 Hz low pass filter to the speakers. This setup sounded terrible so I am running the 88s full range from the AVR. I split the speaker out from the receiver to the plate amp and the 88s. Basically all I can control is how high the subwoofer tries to play by adjusting the frequency on the plate amplifier. So above 80 Hz or so it was pretty easy to localize the sub and starting to sound bad.

If I had a receiver with LFE out It would have been a lot easier to buy a crown or inuke!
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post #12 of 33 Old 07-11-2015, 07:13 PM
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I really like the look of the 88s upside down. For some reason it looks more balanced or something.

Another one of those sub cabinets on the other side would look nice and symmetrical. The finish looks great.
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post #13 of 33 Old 07-11-2015, 07:15 PM
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Quote:
Originally Posted by bitmap42 View Post
That's a little bit of a problem. I ran speaker level outs to the plate amplifier. Then I tried hooking the speaker outs on the plate amplifier to the 88 specials, but the plate amp has a built in 120 Hz low pass filter to the speakers. This setup sounded terrible so I am running the 88s full range from the AVR. I split the speaker out from the receiver to the plate amp and the 88s. Basically all I can control is how high the subwoofer tries to play by adjusting the frequency on the plate amplifier. So above 80 Hz or so it was pretty easy to localize the sub and starting to sound bad.

If I had a receiver with LFE out It would have been a lot easier to buy a crown or inuke!
You have a stereo amplifier?

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post #14 of 33 Old 07-11-2015, 07:29 PM - Thread Starter
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It actually supports Dolby Pro Logic and a few other surround modes, but it was built before modern AVRs so it doesn't have LFE out, doesn't have Audyssey or similar, and does volume 1 to 10 instead of the new -X dB style. It's 100 Watts into each channel in stereo mode. I guess it would be considered a 5.0!
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What model is it?

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post #16 of 33 Old 07-12-2015, 12:27 PM
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bitmap,

I know the budget is tight here, but honestly, you should really upgrade your receiver to something with at least dolby digital/dts. This way you'll have an lfe out, and you'll have better sound with digital formats like Blu-ray.

Check craigslist and find yourself something. I've helped plenty of friends look for cheap basic digital receivers, over the years, and $50 bucks will get you one from any reputable manufacturer ( pioneer, sony, onkyo, yamaha...etc )

Do what I wrote above and then, down the road when you have a little more $, you can move your existing avr into the garage/bedroom/den/whatever, buy 2 inexpensive bookshelf speakers from Dayton audio, add a Bluetooth receiver via your rca jacks, and now you've also got a nice little setup somewhere else that you can use for pandora, spotify, etc.
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bitmap,

I know the budget is tight here, but honestly, you should really upgrade your receiver to something with at least dolby digital/dts. This way you'll have an lfe out, and you'll have better sound with digital formats like Blu-ray.

Check craigslist and find yourself something. I've helped plenty of friends look for cheap basic digital receivers, over the years, and $50 bucks will get you one from any reputable manufacturer ( pioneer, sony, onkyo, yamaha...etc )

Do what I wrote above and then, down the road when you have a little more $, you can move your existing avr into the garage/bedroom/den/whatever, buy 2 inexpensive bookshelf speakers from Dayton audio, add a Bluetooth receiver via your rca jacks, and now you've also got a nice little setup somewhere else that you can use for pandora, spotify, etc.
I couldn't agree with this more.

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I couldn't agree with this more.

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Also check your local bestbuy for open box recievers.

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post #19 of 33 Old 07-13-2015, 02:59 AM
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Quote:
Originally Posted by bitmap42 View Post
Maybe I calculated the internal volume wrong, but I thought I had 3.38 cubic feet!

I got the depth by doing 22" (depth of cabinet) - 6.75" (depth of internal shelf) - 3 * .75 (MDF front, back, and middle divider)= 13"
For the width I did 22" (width of cabinet) - 1.5" (MDF sides) = 20.5"
For the height I did 28" (height of cabinet) - 3.5" (height of legs) - 1.5" (MDF top and bottom) = 23"

Which gives 6,129.5 cubic inches = 3.55 cubic feet. Then I subtracted .1 cubic feet for bracing. For 2 braces from top to bottom (1inch by 1inch), and 9 braces from front to back (1 inch by 1 inch) that totals .1 cubic feet total. If I used dowels it would be a little less area per brace and I could then add more dowels.
Then the driver I used .07 for its volume.
So my total was 3.38 cubic feet.

@muzz How does the bracing sound? With 2 top to bottom it would split the top and bottom into approximately 7" by 10" sections. With 9 front to back braces, it would be a 3 x 3 grid of braces front to back and would split it into approximately by 8" by 7" sections.
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It actually supports Dolby Pro Logic and a few other surround modes, but it was built before modern AVRs so it doesn't have LFE out, doesn't have Audyssey or similar, and does volume 1 to 10 instead of the new -X dB style. It's 100 Watts into each channel in stereo mode. I guess it would be considered a 5.0!
I agree with the others. You definitely need to get a new AVR. You can find cheap Denon AVR 3310's or Yamaha RX-V663's for cheap. Heck, I have a Yamaha RX-V663 that does DolbyTrueHD, DTS-MA, and plain Dolby Digital and DTS with HDMI and it even has full 7.1 pre outs that I would sell you for a bill. Look around as you can get these slightly older models for cheap.
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post #20 of 33 Old 07-19-2015, 12:37 PM
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Just wanted to compliment Bitmap for a great job & a nice looking setup! Those 88's sound pretty good hanging on the wall? Did you have to adjust the crossovers for that type of mounting? Thanks.
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post #21 of 33 Old 07-19-2015, 09:40 PM - Thread Starter
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Just wanted to compliment Bitmap for a great job & a nice looking setup! ������������Those 88's sound pretty good hanging on the wall? Did you have to adjust the crossovers for that type of mounting? Thanks.
I can't find the link where I read this, but my understanding was these were designed for on wall or close to wall setups which makes sense since the 88s were designed as a center.

The reason the waveguide is on the bottom is to allow the waveguide to be at ear height with the shelves at a level that puts the speakers centered vertically next to the TV. I noticed a huge difference (both in REW and subjectively with voices in movies) when the 88s were "right side up" with the waveguide on top. The 88s sounded much worse when the waveguide was too high. I definitely recommend mounting them either with a lower shelf or "upside down" so that the waveguides are at ear height. That should to apply to all of the waveguide SEOS speakers.
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post #22 of 33 Old 08-04-2015, 08:33 PM - Thread Starter
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So I took everyone's advice and bought a new denon x2100w, good deal since it is last years model. This was a great purchase!

I need to rerun REW sweeps since I have used audyssey to dial everything in.

Watched Edge of Tomorrow and Transformers, very happy with the build, fits nicely in the room, didn't cost much, and sounds great.
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post #23 of 33 Old 08-04-2015, 09:20 PM
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Thanks for taking the time to document your build and post frequency response measurements. Great job and nice that the wife approves.
(I followed your post from another 1260W thread and will re-post your response if you don't mind.)
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post #24 of 33 Old 08-06-2015, 12:25 PM
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Nice build!

I'm really interested in both your speakers, the Infinity sub and the 88 Specials. In the coming years I'll be building new speakers but my long suffering wife won't put up with giants so looking at the 88's. The other part is running three subwoofers, one nearfield. The nearfield sub will be what I'm using now, a JBL 1214 with an 18" passive radiator tuned to 20Hz. Just pondering the last two subwoofers and the size they can be.

Knowing the efficiency of the 88 Specials, do you feel the need to add more Infinity subs at this point?
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post #25 of 33 Old 08-06-2015, 03:09 PM - Thread Starter
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I need to watch more movies, I've only watched 2 at -10 and -5 db so far, but I have some basic thoughts.

First, just to be clear, the 88s can be driven loud enough to be painful even in a large space, so the 88s are awesome!

For the subwoofer:

If you are going for a basic movie theater feel at just a bit less than reference then I think having the 1260 is plenty. For me this was what I was going for since it is my living room. It has plenty of output to make things rattle and it keeps up with the 88s at a pretty loud volume.

If you are going for full reference with a "pressurized room feel" (think standing in front of a stage at a concert or a good car subwoofer system) then the infinity just can't do that in a big room. So for my theater room that I am planning in the basement when you start to think about multiples the value proposition for the budget style build that I did starts to unravel. To build 2 of these you are at 500 or so and you are starting to get into making it worthwhile to add a little more to get 2 18s (Marty variant, etc.). That upgrade gives you a ton more output, gives you a single 2 channel amp, instead of 2 plate amps (which actually take up a surprising amount of space).

One other note, I would only build a ported infinity (I.e not sealed) for movies since you want the flat freq response to the lower frequencies. I don't think you could drive a sealed infinity with enough power before blowing it up when it is sealed.
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post #26 of 33 Old 08-06-2015, 03:38 PM
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Great job on the build. Looks like there's a perfect spot on the other side for another one.
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post #27 of 33 Old 08-06-2015, 07:42 PM
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Quote:
Originally Posted by bitmap42 View Post
First, just to be clear, the 88s can be driven loud enough to be painful even in a large space, so the 88s are awesome!

For the subwoofer:

If you are going for a basic movie theater feel at just a bit less than reference then I think having the 1260 is plenty. For me this was what I was going for since it is my living room. It has plenty of output to make things rattle and it keeps up with the 88s at a pretty loud volume.

If you are going for full reference with a "pressurized room feel" (think standing in front of a stage at a concert or a good car subwoofer system) then the infinity just can't do that in a big room. So for my theater room that I am planning in the basement when you start to think about multiples the value proposition for the budget style build that I did starts to unravel. To build 2 of these you are at 500 or so and you are starting to get into making it worthwhile to add a little more to get 2 18s (Marty variant, etc.). That upgrade gives you a ton more output, gives you a single 2 channel amp, instead of 2 plate amps (which actually take up a surprising amount of space).
Thanks for the information, nice to find someone that has basically what I have in a sub (JBL 1214 and Infinity 1260 are siblings) The 88 Special is my top contender for WAF speakers that can cause hearing damage with a typical AVR.

My plan is to build two Infinity 1262's ported to around 18 or 19Hz. I'll be using the dual voice coil versions so I can make them run 8 ohms with the voice coils in series. I'll power them with an iNuke 3000DSP so at 8 ohms, they will get around 300 watts each. The JBL 1214 will be my near field subwoofer and the plate amp adjusted to taste. If I need more output or more even bass response, I could build another pair of 8 ohm Infinity 1262 subs. The four subs running a pair each channel would be 4 ohms and 600 watts of power. Four 12" subwoofers running 300 watts each and a fifth sub next to the couch should be noticeable.

Should...this is AVS so all 5 of them might end up near field...
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post #28 of 33 Old 08-06-2015, 08:46 PM - Thread Starter
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One thing I really want to check with this build is whether WinISD was correct with the port length or Unibox was correct.

LTD02 created a thread about "k" and boundary loading based on where the port ends are located in comparison to the sides and back of the box. WinISD has a fixed k which is basically port in middle. Slot ports that end in a side would need a slightly different length to reach the correct tune (which has been seen by a lot of the Marty builds, k is a possible reason to why this happens).

I need to measure the final tune and see if the "calculating subwoofer port length" thread that has the k values in it works in real life. The k I used caused the port to be a lot shorter than WinISD said it should be.

That also might be why some builds don't get good low response as expected. If k really has such a dramatic effect it can change the tune close to 10hz which would be noticeable.

Hopefully I can check the tune this weekend and get a new REW sweep with audyssey.
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post #29 of 33 Old 08-07-2015, 06:46 AM
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Quote:
Originally Posted by bitmap42 View Post
LTD02 created a thread about "k" and boundary loading based on where the port ends are located in comparison to the sides and back of the box. WinISD has a fixed k which is basically port in middle. Slot ports that end in a side would need a slightly different length to reach the correct tune (which has been seen by a lot of the Marty builds, k is a possible reason to why this happens).

The k I used caused the port to be a lot shorter than WinISD said it should be.

That also might be why some builds don't get good low response as expected. If k really has such a dramatic effect it can change the tune close to 10hz which would be noticeable.

Hopefully I can check the tune this weekend and get a new REW sweep with audyssey.
Good information to know,

I've built 3 subs with WinISD, one with a passive radiator and the other two with round ports in the center of the box. It measures out accurately as I've used basic porting programs get get almost the same results.

I've never built a slot port although making one for the Infinity makes sense. Need to do some reading on "k" as this would make my build more accurate and I might be able to fit the single slot in the box size I plan on using.

It will be interesting to read about what WinISD predicted and the final results using slot ports, thanks for the information.
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post #30 of 33 Old 08-07-2015, 09:36 PM - Thread Starter
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Ok, I took some measurements. I didn't have a resistor on hand so I used the simplified method of measuring the tuning frequency. I simply measured current (multimeter connected in series) at different frequencies and looked for the peak in current draw.

Just for reference here is my SketchUp drawing of the sub (I made the top invisible so you can see the port detail). The port is down-firing and has a right angle bend into the inside of the subwoofer. The port opens freely on two sides and opens to an edge on the other two sides (the side of the box and the top of the box).



Original design was a 23Hz tune. WinISD said I needed a 23.86 inch long, 4.5 by 4.5 inch port as shown below. In the screenshot you can see that WinISD is using a value of .732 for the port end correction ("k"). Unfortunately in WinISD changing the value has no effect.



Based on the "Calculating Subwoofer Port Length - Not So Simple" thread that @LTD02 created I ran the same set of data through Unibox (which allows the value of k to be set). I chose k=1.7 based on it being the closest image, although the port in my build is a little bit different since it is actually at a right angle. Here is the original Unibox screenshot.



This gives a port length of 17.5 inches. The Unibox simulation with k=.732 (to match WinISD) gives a port length of 22.48 inches. So with the same value of k WinISD and Unibox are within 5% of each other. With a different value of k the Unibox simulation is 25% different!

For comparison if I adjust the tune inside of WinISD to a value that makes the port 17.5 inches, WinISD says the resulting tune would be 26 Hz. In other words Unibox says a 17.5 inch port will give a tune of 23 Hz, whereas WinISD says the same design will give a tune of 26 Hz.

---- BIG Question: Which was right! ----

Definitely Unibox was closer.

As measured it looks like the actual tune is closer to 21 Hz. To try to make my simulation match reality I tried adjusting the k value within Unibox to meet a 21 Hz tune and needed a k of 2.5. This value is pretty high. The only thought I have of why the tune is so low is because it is down-firing and is only 3.5 inches off the ground (3 inches after sinking into carpet). This might be affecting the tune. I might try turning the subwoofer front facing and see if that changes the tune.

At the end of the day there are a lot of posts within various slot ported build threads (ex. Marty subs) where the recommendation is to drop the port length a little bit to adjust for this mystery value. I saw the exact same thing from my build. It looks like WinISD's port length has to be shortened when a slot port on the edge of the box is used.
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