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Old 17th March 2011, 08:56 PM   #691
Djim is offline Djim  Netherlands
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Quote:
Originally Posted by tb46 View Post
Hi jbell,

Looking at your sketch in Post #683, I've done that one, and others, and it does not get you there within the 24"x30"x22" outside dimensions of the SS15. I'm very close to being convinced that you maxed that one out.

The other thing that I realized after just a few stumbles is, that you have to actually draw the path, and add some real dimensions, or you can talk yourself into all kinds of great solutions that will not work when you try to lay it out in wood.

Regards,
Oliver, although this post was meant for JBell, I'm sot sure if you have read my analyses about lowering it's design Fs and 1/3 wavelenght response at cost of overall SPL (except below 50Hz). Yes total efficiency above 50Hz will cost a few dB's but you can gain +5dB at 40Hz. This will make a huge difference in listening experience and provide the extra bottom. Also with four cabs the SPL difference above 50Hz gets smaller and around 40Hz the total gain will even rise from +5dB to +7dB (since compression around 40Hz will be lower than with the SS15 standard).

I have come up with my final drawing (used the best effort in "eye and hand" control to come as close as possible) and HornResp numbers.

I think this is the only way to reach 40Hz decently (and even below) but I need a little help to work it out more precise and to check my findings...
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Old 17th March 2011, 09:13 PM   #692
Djim is offline Djim  Netherlands
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SS15 Standard = 1/3 wavelenght = 47Hz

SS15 extended = 1/3 wavelenght = 40Hz

With Low cut filters used (SS15 standard: 38Hz/24dBoct / SS15 Extended:
32Hz/24dB oct)=

Above 50Hz is +2,5dB in favour of SS15 standard.

Below 50 Hz is +5dB at 40Hz in favour of SS15 extended.
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Old 17th March 2011, 09:57 PM   #693
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Quote:
Originally Posted by Djim View Post
SS15 Standard = 1/3 wavelenght = 47Hz

SS15 extended = 1/3 wavelenght = 40Hz

What's this "1/3 wavelength" thing all about?
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Old 17th March 2011, 10:37 PM   #694
Djim is offline Djim  Netherlands
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Quote:
Originally Posted by Brian Steele View Post
What's this "1/3 wavelength" thing all about?
Just the points where you see SPL is dropping in the THAM and in the SS15 in real measurements.

Last edited by Djim; 17th March 2011 at 10:44 PM.
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Old 17th March 2011, 11:36 PM   #695
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Quote:
Originally Posted by Brian Steele View Post
What's this "1/3 wavelength" thing all about?
Speed of sound (1128 feet per second) /47hz/3=8 feet
1128/40/8 =9.4 feet


Lower cutoff frequencies generally require a longer horn, or a reduced mouth dimension, both reduce SPL level.

Covering the front panel partially would be a good experiment that could be done in a few minutes with a piece of plywood and a few clamps.
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Old 18th March 2011, 12:10 AM   #696
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Quote:
I think art is confusing front loaded horns with tapped horns.

The ss15 driver is in the mouth -- no delay needed if tops are above subs.
Thanks Jim; Thats what I thought. Andy
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Old 18th March 2011, 05:36 AM   #697
Djim is offline Djim  Netherlands
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This is how the extended should (more or less) compare on your RTA
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Old 18th March 2011, 02:25 PM   #698
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Quote:
Originally Posted by 4pyros View Post
Thanks Jim; Thats what I thought. Andy
Most of the TH output is from the long path length.
Tapped horns need delay if you want to have time alignment with the top cabinet.
Many people confuse phase alignment with time alignment.

A tapped horn (or regular folded horn) crossed over at 100 Hz can phase align with a top without delay if the filters applied and the path length add up to 11.28 feet. It will sound "OK", but is lagging by one cycle from the top cabinet, which makes it seem less loud, as our ears tend to perceive whatever arrives first as louder.

My Keystone TH, longer than the SS15, judging by the Autosm delay finder function used in Smaart, will probably require about 10 to 12 milliseconds delay to align at 100 Hz.
That may be a few milliseconds longer than the DBX Driverack PA I have been using allows :^(.
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Old 18th March 2011, 02:37 PM   #699
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Quote:
Originally Posted by jbell View Post
I think art is confusing front loaded horns with tapped horns.

The ss15 driver is in the mouth -- no delay needed if tops are above subs.
Jim,

If you ever bother to use the Phase and Magnitude portion of Smaart, you will see that your SS15 output arrives later than a front loaded speaker at the same distance, as can easily be determined by deducting the measurement distance from each from Auto Sm.

You will find that tapped horns, just like any folded horn, need delay for time alignment.

Read my response to Pyros for a bit more explanation.

Note the delay time required below for the same 2 meter distance testing the BR cabinet compared to the Keystone TH, using the same BW 25 and 125 filters. The difference is the path length.

Art
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Last edited by weltersys; 18th March 2011 at 02:45 PM.
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Old 18th March 2011, 02:41 PM   #700
AndrewT is offline AndrewT  Scotland
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surely it's the faster responding (closer) drivers that need to be delayed??
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