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Old 7th August 2010, 07:37 PM   #41
jbell is offline jbell  United States
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last 2 posts, hornresp input and fold. I think it works best
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Old 7th August 2010, 09:03 PM   #42
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Originally Posted by jbell View Post
what do you think don?
nice design JB very nice
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Old 7th August 2010, 11:23 PM   #43
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Quote:
Originally Posted by martinsson View Post
I recognize that folding type, I'we done something simillar in this design suitable for the 15TBX100 or eighteensound 15LW1401
It's a pretty nice folding - I copied it off the speakerplans site and modified it slightly for use in my stepped-horn POC. On the plus side, there's minimal bends = more effective path length in the same cross section, the horn is better braced around the mouth area by the internal sections, the design allows you to either top-mount or bottom mount the driver and if you leave the top removable, you've got access to the throat area to play around with its geometry if you want to post-build.

On the minus side, unlike the folds suggested by JBell, the section that's facing the floor is near the middle of the horn rather than at the end, and if it's not properly braced, box will start to "walk" when the volume is turned up and the bass will start to sound awful (ask me how I know this, LOL). Getting the bracing right is very important in sections one (top) and three (bottom).

I was able to finish my POC with plenty of ply left over (before I started playing around with the bracing), so it should be possible make a slightly larger one without having to use more than one 4x8 sheet.
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Old 7th August 2010, 11:39 PM   #44
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Default What if you can do this with a 12" driver?

Consider the Fi X12 - see https://ssl.perfora.net/www.ficaraud...iew.shopscript.

This driver is hand-built on order, and you can actually ask for variations in its design. The base model costs $119, and its powerhandling can be increased from 250W up to 500W via the $20 BPower option.

The specs as given suggest that you can get 100 dB/2.83V/1M from 40 Hz to above 100 Hz and over 125dB in the passband without exceeding Xmax (assuming you go with the BPower option), using a TH that works out to about 4.8 cu.ft. net. This should be achievable with one 4x8 piece of ply. I assumed Le of 2.30 mH - it's likely to be less than this, and can be adjusted upwards if necessary by an external inductor.

Of course, this is all in theory...
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Old 8th August 2010, 12:53 AM   #45
Xoc1 is offline Xoc1  United Kingdom
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Jbell
Your posted sim has a internal volume of 277.4 litres. This is bigger than the external volume of the 22 X 24 X 30 box - 15840cu in = 259.6 litres
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Old 8th August 2010, 03:20 AM   #46
soho54 is offline soho54  United States
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Originally Posted by Don Snyder View Post
Could you enlighten us?

I, for one, make every attempt to follow the HR sim. Of course I use CONICs and build Parabolics, but the error is small, and I know I'm off a few percent
in the corners.

When I can't follow the HR sim, I go back and update the sim with the as-built information. If the damage is too bad, I scrap the drawing.

Sims are sims, they are one dimensional equations simming a three dimensional world. We're lucky they even come close.
I am not really sure what you are after here. Neither were from you, so why get so out of shape?

If you look at the designs posted at that point, and go check out the threads, what was built and measured was not what was in the HR graphs posted here.

If you have a sub built, and then design a HR sim from it, and it turns out different then your sim is wrong. If you design a sim and then build a real sub around it, if the sub measures different from the sim you didn't build the simed horn. There is nothing else to it.

If you go back though these threads you can find many examples of this. Anytime there is a design that varies when built and measured from the HR sim, if you take the time to create a new HR sim from the blueprints you will find the error, and if done correctly the sim will match up to the measured response.

That said the amplitudes may vary a little (due to realities HR doesn't handle,) but the peaks and dips will match-up Hertz for Hertz on the FR and Impedance graphs.
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Old 8th August 2010, 05:46 AM   #47
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Default Why measuring impedance is important...

Quote:
Originally Posted by soho54 View Post
That said the amplitudes may vary a little (due to realities HR doesn't handle,) but the peaks and dips will match-up Hertz for Hertz on the FR and Impedance graphs.
It might not be an exact match, but it should be very close .

The impedance graphs will also indicate if there are other problems with your build.

For example:

Image 1 shows the impedance response of the TH I built a few days ago. Note that while the first two impedance peaks look like fairly close matches, some things stick out: (1) the actual impedance peaks are slightly higher in frequency than the predicted ones, suggesting that the path length may be slightly shorter (I predicted the possibility of it being off by around 3%~4%). This could also possibly be due to other things, like difference between HornResp's value for c and actual c in my location. However, more important though are the greatly reduced third peak and some ripples above 100 Hz, and the difference between predicted and actual impedance between 20 and 40 Hz is a bit higher than it appears to be elsewhere in the response graph. This suggests that the enclosure is not sufficiently braced and the panels are not properly damped.

Image 2 shows the same TH, this time with a bit of bracing added to the first segment. The upper impedance peak is easier to distinguish, but it's not very high, and there are still a few ripples in the response that are not predicted by HornResp.

Image 3 shows the same TH, this time with a lot more bracing added to the first segment (basically an additional layer of plywood was glued and screwed to the external panel at that point). Some bracing was also added to the third segment of the horn (found at the bottom of the box). The upper peak is now higher and very clearly defined and the ripple @200 Hz has disappeared.

Image 4 shows the same TH, this time with more bracing added to the third segment of the horn (two 5" x 20" strips of ply added to the bottom of the box). A small brace was also added internally to the second segment of the horn. Not much has changed, but it looks like there's now closer correlation between the predicted and actual impedance between 20 and 40 Hz. Further bracing is likely not going to make any significant difference, unless I manage to find what panel resonance is causing the little blip @ 100 Hz. I might spend some time on that later today.

Image 5 shows the same TH, with 185 Lbs of weight added to the enclosure (basically me sitting on top, LOL). All panel resonances are now sufficiently damped to the point of having little or no visible impact on the impedance curve.
Attached Images
File Type: jpg Dayton PA310-8 TH (13).jpg (32.4 KB, 1888 views)
File Type: jpg Dayton PA310-8 TH (14).jpg (32.4 KB, 1836 views)
File Type: jpg Dayton PA310-8 TH (15).jpg (32.5 KB, 1807 views)
File Type: jpg Dayton PA310-8 TH (16).jpg (32.6 KB, 1790 views)
File Type: jpg Dayton PA310-8 TH (17).jpg (32.5 KB, 1777 views)
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Old 9th August 2010, 04:19 AM   #48
jbell is offline jbell  United States
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I did a full size layout, just to make sure my cartoon drawing was going to work... I think it does. I brought S1 down to 450cm (3 1/2" x 21) but other than that, the full size drawing is almost identical to my scratch paper drawings.
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File Type: jpg singlesheet3.JPG (39.7 KB, 674 views)
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Old 10th August 2010, 07:24 AM   #49
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Any updates with this new design JBell?
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Old 15th August 2010, 02:09 AM   #50
jbell is offline jbell  United States
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Quote:
Originally Posted by CuttaBoi View Post
Any updates with this new design JBell?
Been busy with installs, no time to build the new single sheet design yet. I believe it will most likely be my favorite to date. I seem to end up with small things I don't like hearing out of a TH when there are too many dimensions that are too similar, and too many parallel walls. (The 150lb beast that had all dimensions of either 24" or 48" comes to mind.) This last design has none of that. I'm hopeful it will require zero reflector 'tuning.'

I just used up the last of my 'cubes.' Gymnasium theater with a 24' wide screen. One cube center court 27' in the air mounted tight to a solid concrete wall. AND as expected... my back likes me better than with the last 150lb beasts.

Iron man was silly fun... No it's not true HT low, but 40hz high pass still gets the job done, and xti amps make this kind of stuff brain dead easy.

Last edited by jbell; 15th August 2010 at 02:17 AM.
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