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-   -   Keystone Sub Using 18, 15, & 12 Inch Speakers (https://www.diyaudio.com/forums/subwoofers/185588-keystone-sub-using-18-15-12-inch-speakers.html)

weltersys 8th April 2011 11:11 PM

Quote:

Originally Posted by Josh Ricci (https://www.diyaudio.com/forums/subwoofers/185588-keystone-sub-using-18-15-12-inch-speakers-post2532177.html#post2532177)
Dang Art. Careful with the equipment man. Of course its just not a complete day of testing without frying a sound card or mechanically breaking an $800 driver. Both things I have done.

TH distortion is more variable than what you see with traditional direct radiator systems. Some areas are very very clean and others within the fr will have much higher thd than the equivalent direct radiator. The varying loading and pressures on the cone, the xmax variance and more importantly the acoustic boosting at certain freqs causes the thd profile to be highly range dependant unlike a traditional direct box that has a predictable but comparatively smooth thd profile. TH's have much greater swings in thd level through out the operational range.

Josh,
At least when a driver is destroyed while testing one finds the limits of it's potential. Computers riding on the wind just blows.
I do have a bit of an appetite for destruction, do you have pictures of the broken driver?
Did it make funny noises before coming apart?
Are your TH enclosures built yet?

Art

Josh Ricci 9th April 2011 04:53 PM

Quote:

Originally Posted by weltersys (https://www.diyaudio.com/forums/subwoofers/185588-keystone-sub-using-18-15-12-inch-speakers-post2532337.html#post2532337)
Josh,
At least when a driver is destroyed while testing one finds the limits of it's potential. Computers riding on the wind just blows.
I do have a bit of an appetite for destruction, do you have pictures of the broken driver?
Did it make funny noises before coming apart?
Are your TH enclosures built yet?

Art

TH enclosures are still in process. Not sure on an ETA. I will be sure to drop you a note when I get them in.

Picture of the failed driver, which had the triple joint break and ripped the spiders but the coil still never bottomed, a graph of the electrical signal FR and a brief synopsis of what happened are in paragraph 3 & 4 here...
Data-Bass

I had it reconed. User error on my part. The dangers of EQ. The driver has the most displacement available in a single mass produced unit that I am aware of. I have 5 and they have been incredibly rugged over the years but that much power below tune in a ported enclosure is too much for even one of those. 5" p2p excursion is scary looking even from 50+ ft away.

weltersys 12th April 2011 04:01 PM

Keystone Mouth compared to full width Exit
 
3 Attachment(s)
Quote:

Originally Posted by NEO Dan (https://www.diyaudio.com/forums/subwoofers/185588-keystone-sub-using-18-15-12-inch-speakers-post2531037.html#post2531037)
Hi Art,
It would be nice to see the difference in the keystone vs a normal box width terminated TH mouth.

My laptop is back, memory undamaged, screen replaced.

Below are screen shots of the Keystone exit (TH18 S glued), which is 6 inch wide at the top, 12.5 at the bottom, and 25 tall, 306.25 square inches, compared to the normal box width termination of 300 square inches, a 25 x 12inch exit. The Keystone shaped exit smooths out the response, and adds level over most of the pass band.

The next screen shows 200, 300,400 and 500 square inch exits compared to the TH18 S glued (Keystone exit). Although a bit harder to see with all the traces compared, the Keystone shape improves level and smoothness over any standard termination size.

Many (dozens) more shapes and sizes were tested, the 306 square inch Keystone exit size (which turned out to be within a few square inches of what a "normal" exit should be for this TH) had the most extended, smooth response of any.

Art Welter

NEO Dan 12th April 2011 07:14 PM

It looks like you've used the keystone to extend the mouth opening to the driver tap?
Do you think that a TH where the driver is not recessed into the horn would have a benefit from a keystone mouth?


Good to see you got your Mac back up and running.

weltersys 12th April 2011 08:02 PM

Quote:

Originally Posted by NEO Dan (https://www.diyaudio.com/forums/subwoofers/185588-keystone-sub-using-18-15-12-inch-speakers-post2536125.html#post2536125)
It looks like you've used the keystone to extend the mouth opening to the driver tap?
Do you think that a TH where the driver is not recessed into the horn would have a benefit from a keystone mouth?

Yes, the thinner portion of the Keystone mouth does extend nearly to the center of the driver.
Since heat rises, having the speaker's rear cooling vents near the upper portion of the Keystone exit also gives thermal advantages.

I think many upright fold TH which have the final exit making a roughly 90 degrees turn would benefit from the Keystone mouth, whether or not the driver is located at the very end (mouth) of the horn.

The Keystone shaped exit would probably offer no advantage in the type of tapped horns where the final segment is pointed forward with the driver located at the mouth.

Art Welter

Djim 12th April 2011 11:37 PM

1 Attachment(s)
Art, did you try a similar key opening (same mouth area) in different position in relation to your final one?

(Danley seems to use a similar approach and I'm curious about those results)

NEO Dan 13th April 2011 04:43 AM

The Danley TH mouths are not shaped for response, it's merely the expansion of the horn. I referring to the TH812, TH28, and TH50.

Djim 13th April 2011 05:05 AM

Maybe not Dan, maybe it's nothing more then a design solution in the TH28. I was just wondering about the results of the "Art-key-opening" in relation to its position. If it still works the way it suppose to and if it behaves perhaps a tiny little better in the lowest octave.

An externally hosted image should be here but it no longer works. Please upload images instead of linking to them to prevent this.

weltersys 13th April 2011 04:34 PM

3 Attachment(s)
Quote:

Originally Posted by Djim (https://www.diyaudio.com/forums/subwoofers/185588-keystone-sub-using-18-15-12-inch-speakers-post2536426.html#post2536426)
Art, did you try a similar key opening (same mouth area) in different position in relation to your final one?

(Danley seems to use a similar approach and I'm curious about those results)

Danley's unusual horn mouth shapes are whatever is "left over" after the folds are done.
The TH 28 exit shape is determined by the speaker baffle position, the same cover can be put on the “front” or the “side” of the cabinet to give location options.

The Keystone shape, with the horn's fold orientation, allows a compromise between a “too large” and “too small” opening.
Too large an opening provides more upper response with less low end, too small makes for a lower LF corner but less upper response.

I did not try asymmetrical openings.
The “sideways” keystone in your picture would work about the same as a 300 square inch opening at the bottom of the cabinet, as shown in the chart in post #23.

The sketches below show the various shapes tried before (and after) arriving at the Keystone shape.
The list of tests is actually only a fraction of the tests performed, many “in between” area tests were done and not saved.

Early in the testing one shape seemed promising, the extended upper response turned out to be a clamp resonating on a piece of wood.
After discovering that problem, each test required walking a 200 foot round trip twice, once to set the clamps and pieces of plywood in place, back to the shop to turn the pink noise on, then back outside to listen for any rattles and correct them if necessary. In retrospect I could have just unplugged the cabinet and saved half of those trips, but probably would have worn out the plugs from hot patching.

Of particular interest, the shapes in “E” and “N”, although similar in cross sectional area in relation to the horn path, did not smooth out the response, or increase SPL like the keystone shape.

NEO Dan 13th April 2011 04:45 PM

Quote:

Originally Posted by Djim (https://www.diyaudio.com/forums/subwoofers/185588-keystone-sub-using-18-15-12-inch-speakers-post2536697.html#post2536697)
Maybe not Dan, maybe it's nothing more then a design solution in the TH28.

Agreed ;)


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