TC 1000 sonosubs. - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 28 Old 04-25-09, 01:32 AM Thread Starter
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TC 1000 sonosubs.

I recently built a pair of sonosubs and here's the thread on them. From the outside, I was bent on designing a pair of subs to be used for music only, with the possibility of watching a movie once in a while. ( for second room )

Crossover <60 hz, closer to 50hz or less, depending on how the actual response was in room. Maximum enclosure volume possible with a large port for a few reasons. Large diameter port for low port velocity as well as linearity. I decided on 18 inch sonotube, and originally was set to build just under 9 cu ft net, 10cu ft before port and driver.

I estimated the outer diameter of a port, without having it on hand. DOH... as it was, I had to drive 75 miles to pick up sono and MDF, and a second trip was for a port and a few other odds and ends.

I had already cut the 18" sono ( actual inside measurement ) into two pieces 70 5/8" long, painted the outside of them with acrylic latex paint and cut endcaps before getting a chunk of 8" OD sono for the port. Never trust a label, measure it for yourself, lesson learned. And to think I was an aisle away from the tape measures...

It actually worked out maybe a tad better, the port velocity was a bit higher but the port resonance was pushed up a bit more than 2 octaves above the intended crossover point.... 250hz.
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post #2 of 28 Old 04-25-09, 01:38 AM Thread Starter
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Re: TC 1000 sonosubs.

Having issues in the past with T-nuts backing out at the most inappropriate time, I used baltic birch ply to mount the drivers, and MDF for the other endcap for the ports. Fasteners for the driver are the TC supplied hex head wood screws.

The inside port flare is two layers of baltic birch ply glued together ( the driver cut out at 13" and another 11" piece ) turned on a wood lathe. The outer flares are not yet attatched, I have to glue them on as well as figure out a base and legs for these.
Attached Thumbnails
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TC 1000 sonosubs.-port2.jpg  

TC 1000 sonosubs.-port3.jpg  

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post #3 of 28 Old 04-25-09, 01:42 AM Thread Starter
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Re: TC 1000 sonosubs.

I absolutely despise the smell of MDF outgassing from a vented enclosure during operation. I coated all of the MDF with Minwax urethane many times to seal it from outgassing, as well as the outside of the port. PL Premium construction adhesive was used in securing the port to the flare, as well as the endcaps. There are NO mechanical fasteners in the endcaps at all.

I don't have any pics of me turning the flares on the lathe or routering the endcaps for this build though. Note the big '8" OD' printing on the outside of the port tube, NOT. More like 7 3/8" ID and 7 5/8" OD. How is that close to 8" OD... home depot for ya...
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post #4 of 28 Old 04-25-09, 01:49 AM Thread Starter
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Re: TC 1000 sonosubs.

A few days ago, I threw in a driver and tested one while the adhesive was curing on the other. I drove it off the amplifier in the trunk of my car, and played some music through it, noting some resonances on higher frequency bass. I did not use any high or low pass filters at all, and it was plain there was issues.

OK, I pulled the driver out and it was obvious that speaking or shouting into the enclosure produced a resonance. Not good.
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post #5 of 28 Old 04-25-09, 01:52 AM Thread Starter
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Re: TC 1000 sonosubs.

I went down to my local store and bought 4 $ 6.00 pillows... returned, and installed them in the enclosure between the port flange and the endcap, it was a tight squeeze with a 13" OD flange and a 18" ID tube... about 2.5" to force the pillows down in there. I put all 4 pillows in the enclosure, re-installed the driver and did some rudimentary testing again. MUCH better, I was unable to get it to resonate, as well as when I tried the speak / shout test into it without the driver it was almost totally dead.
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post #6 of 28 Old 04-25-09, 02:00 AM Thread Starter
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Re: TC 1000 sonosubs.

In the interest of actually producing some good measurement data, I decided to test the unstuffed enclousre against the stuffed one. The enclosures were placed side by side, while testing one I would short the terminals of the other, to keep it from drastically affecting the measurement.

I tested GP outdoors, mic 1m from driver, and this is what I came up with. The unstuffed trace is red, the stuffed is blue. Tests were back to back, as close as possible, nothing was moved during the sweeps.
Attached Thumbnails
TC 1000 sonosubs.-unstuffed-sono.jpg  

TC 1000 sonosubs.-stuffed-sono.jpg  

TC 1000 sonosubs.-twins3.jpg  

TC 1000 sonosubs.-unstuffed-fr.jpg  

TC 1000 sonosubs.-stuffed-fr.jpg  

TC 1000 sonosubs.-unstuffed-waterfall.jpg  

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post #7 of 28 Old 04-25-09, 02:09 AM Thread Starter
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Re: TC 1000 sonosubs.

I measured tuning by watching for lowest excursion on each of the enclosures. This is where it got interesting. First I set REW up for a 15 hz sine wave at a low level, and increased it slowly until the driver was very close to maximum excursion, then moving the frequency up in 1/2 hz increments.

Unstuffed sonotube came in at 18.5 hz. The results of the stuffed enclosure were quite interesting to say the least. With the unstuffed enclosure, the tuning was easy to verify.... cone motion was almost stopped.

With the stuffed sonotube, it was much harder to determine the tuning point, but I was able to determine it was 17 hz. There was a lot more cone excursion at tuning on the stuffed enclosure vs the unstuffed one.

In conversation with a friend, he mentioned that PWK ( Paul Klipsch ) always talked about the rear volume of a sealed box being a capacitance. Adding ESR to the cap he mentioned changes the "Q" of the cap, widening it.

So, the tuning point effectively gets wider with a bit less boost at the tuning frequency, hence the excursion goes up at tuning, with a bit less above and below.
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post #8 of 28 Old 04-25-09, 02:12 AM Thread Starter
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Re: TC 1000 sonosubs.

Here's a graph of the two enclosures overlaid, I changed the scale a bit though. Interestingly enough HornResp predicted the resonances, when Mike Bentz modelled them, he sent me the picture through IM when we were talking about the enclosures.
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post #9 of 28 Old 04-25-09, 02:36 AM Thread Starter
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Re: TC 1000 sonosubs.

Rain cut my measurement time short, I had to hurry to get everything all packed up before it got soaked.

I had wanted to get a measurement at the port exit as well, however I might have to wait for better weather, we still have some snow here... and it's raining currently still.

Some graphs of the model:

Impedance is high in the 30-35 hz range, where *most* of the low bass in music is, of course there are exceptions to the rule. This means that power across the coil is low, contributing to less thermal compression. At around 35 hz, it's about 14 ohms, going up to 24 ohms at 30 hz.

I modelled cone excursion with a high pass filter at 17 hz, and 500 watts, with a bit of heat added to to the voice coil temp rise box.
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TC 1000 sonosubs.-tc1000-impedance.gif  

TC 1000 sonosubs.-tc1000-cone-excursion.gif  

TC 1000 sonosubs.-tc1000-vent-velocity.gif  

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post #10 of 28 Old 04-25-09, 01:30 PM
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Re: TC 1000 sonosubs.

Mike,
I consider your experiments and build an important revelation. Your enclosure, the usual sonotube, proves to have identifiable resonance issues with the ( open space surrounding the PORT ). Just as interesting is that the cure for the resonance is to stuff the open area surrounding the port with poly pillows. Simple.
But wait, does this resonance issue apply to ALL sonotube enclosures? If so, will the poly pillows cure any resonance issues in any sonotube?
It makes me wonder if square and/or rectangular ported enclosures also have a similar resonance issue surrounding the port tube as in the sonotube design?
I had always assumed that any resonances created within the enclosures would usually be below the hearing threshold. Obviously they are not as your charting shows and you also noticed immediately upon firing the units up.
This is interesting stuff.
Oh, by the way the tubes and drivers look neat. Are you gonna use them as rolls on the floor or install them vertically?
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