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Old 6th April 2010, 06:08 PM   #211
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Quote:
Originally Posted by tb46 View Post
Hi,

I have noted that there seem to be questions as to what is or isn't the throat chamber, and how to enter it into Hornresp. Maybe this example for a short L12 plus chambered driver helps:

Regards,
EXCELLENT explanation TB46! Unless you have the physical driver, you really can't calculate the volume inside the cone?
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Old 6th April 2010, 11:48 PM   #212
jbell is offline jbell  United States
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oliver:

update on my 24x24x48 box.
It was a little windy today, so I did 5.6, instead of 2.8v measurements. I did all kinds of baffle/no baffle trials, and still couldn't get rid of the NASTY 100hz null... I mean it falls off a cliff at 100.

I tried a shallow baffle at the bottom/back, and that really helped the 80-90hz....
Without a 45 degree baffle either top/front or top/back, I get a stuffy 70hz sound, and about 1.5db extra at 50hz. It's worth the trade off to lose a little 50hz to get a clean 70hz sound.

I don't really care that this sub falls off a cliff at 100 because of the way I plan on using it, but do you have any idea where I could try to change something to lessen it?

The following is with a shallow baffle at bottom/back, and a 45 degree top/back, no other bracing.

5.6v @1m

40 102.5
41 103
42 104.5
43 105.5
44 106
45 106
50 107.5
55 107.5
60 107.5
65 107
70 106
75 106.5
80 107
85 108.5
90 110
95 110
97 106
98 103
99 100
100 98
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Last edited by jbell; 6th April 2010 at 11:58 PM.
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Old 7th April 2010, 02:39 AM   #213
tb46 is offline tb46  United States
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Default jbell_24x24x48

Hi jbell,

Thanks for the additional information. Those are really very impressive measurements. Even without knowing the exact dimensions, when you have a 1:2 ratio for the side dimensions there will obviously be a few common length.

I had that shallow baffle in my drawing for the 24x30x48 box, did you use a similar angle/size?

It might help to shorten L12 as much as you can, that gets rid of one 23.5" section. Your experience with the top/front or top/back corners kind of matches what screamerusa experienced with his furybox, but he lost something when he filled in the top back, so maybe top front is the place. You could even try an oversized 45 degree baffle in that corner.

Did you brace the large back/duct area?

I would start with the S1-S2 area, according to the simulations: in most cases, the shorter the better.

Well, hope some of this helps.

Regards,
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Old 7th April 2010, 02:57 AM   #214
jbell is offline jbell  United States
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I expected some standing waves up around 150's, but not at 100.... that freq vs the dimensions I have intrigues me.

Here's some pics showing my shortened L12. I'll play around with it some more tomorrow. I didn't break in my 3015lf before measuring, and I know once done it changes things.

Right now I have a solid 102-104db from 45-95, and that's sufficient for my current need, however... that's a pretty narrow range... really need another half octave minimum.
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Old 7th April 2010, 06:18 AM   #215
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Default 5.6V @ 8Ohm ?

To convert to 1W/1m readings, should we subtract 3 dB?

Thanks for sharing your progress, this is fascinating. It seems like other areas, such as ported cabinets have been done to death, but there is so much more to be done here with tapped horns!

Ben

Last edited by salzburgsoundsystem; 7th April 2010 at 06:41 AM. Reason: typo
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Old 7th April 2010, 06:40 AM   #216
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Default High passing is important

Many equalizers offer a high pass.
My Peavey
(PEAVEY Q1311 PEAVEY Q1311 ) has a 40Hz high pass @ 12 dB per octave.

I have another Equalizer
(THE T.RACKS EQ 1215E THE T.RACKS EQ 2231E ) with a variable frequency high pass, but also only 12 dB per octave.

Power amplifiers now also sometimes offer high passes. E.g. Behringer offers a choice of 30Hz or 50 Hz (where 50Hz is too high for my subwoofer applications, and 30Hz is a little too low!). Does anyone know - the pdf manual does not state the dB per octave - how steep the behringer cut is?

Is it sensible or useful to combine the effect of two different high passes? (40Hz, 12 dB and 30 Hz unknown dB)

can I use the variable frequency equalizer, but start highpassing an octave higher, whilst boosting the frequencies down to 40Hz to recover the lost sound? Or will such levels of boosting sound terrible?

Ben
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Old 7th April 2010, 02:07 PM   #217
tb46 is offline tb46  United States
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Default Add to Post #213

Hi jbell,

I would add at least one back brace.

Regards,
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Old 7th April 2010, 04:13 PM   #218
jbell is offline jbell  United States
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absolutely I will put in braces oliver. However, for 'playing' purposes, I left them out.

Wind is lower today, I got to do a 28v test, 120-122db@1m from 45-95Hz. And yes panels were vibrating and leaks were happening, so it doesn't quite line up with my 5.6v tests. I think it's time to wrap this test up and get out the glue. I was really hoping for a quick one build day, 1.5 sheet cabinet that I could use for general purpose reasons.
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Old 7th April 2010, 07:54 PM   #219
tb46 is offline tb46  United States
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Default Bracing S1-S2

Hi jbell,

At least one of us is making progress. :-) How about some bracing in the S1-S2 area similar to the furybox?

Regards,
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Old 8th April 2010, 12:06 AM   #220
jbell is offline jbell  United States
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I put the 'wings' in, but it didn't make that big of a difference. Biggest difference was the small bottom/back reflector. Scott did a 11x6 opening, I did a 14x4, so I'm guessing the wider opening made the s1-s2 side reflectors less useful. (which was my guess, and why I did the wide slot in the first place)

glue tonight, paint tomorrow, install friday... these gotta go. At least I learned a little this time, instead of repeating what I've done before.
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