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Old 3rd July 2013, 06:01 AM   #21
howardg is offline howardg  United States
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I tested a partly completed horn on the bench- without the front screwed down and laying on it's back. Made the mouth about 115 sq in.(about twice as big as the largest, closest section of the horn). Best bass seemed to be with about half of that mouth covered(so that what was left open was about the size of the inner passage near the mouth). Maybe it was more resonant, but in a way that seemed pleasing to me. Still going to need the walls nearby to bring the bass level up with the midrange and highs. Quality of bass is musical, less "pushed" or "mechanical" seeming than when coming from a big, powerful woofer. Resonant, I think, but in a different way than a big woofer in a BR cabinet. I wonder if the "waves" that come off a horn powered by a small driver are somehow different from those coming off a big woofer? I understand that a cone driver is typically about 1 percent efficient in coupling it's energy to the room air, and horns are much more efficient in that respect. Maybe we can somehow feel some of the pressure from a big woofer cone, but not hear it as sound. Or does the other, non audible energy, the 99%, just become heat?

When I play fairly uncompressed bass thru my 14" speakers, things in the room will rattle and vibrate. Hard to see that that would happen with these horns. Is there something other than frequency and amplitude at work? I understand that large bass horns can break windows-so it must have to do with the quantity of air being pushed around/vibrated.
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Old 3rd July 2013, 10:20 AM   #22
xrk971 is online now xrk971  United States
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Howard,
Great to hear that you built this! Please post some photos! Your question about quality of bass and its ability to rattle things: the simulation says that when you corner load this like you said you would, there is a +9dB boost compared to free space which is what you sort of have on a bench. SPL is SPL, and 103 dB at 1 watt at 40 Hz is a lot of sound energy for 1 watt. The comparison is how many watts does it take for your big woofer cone to get 103 dB at 40 Hz? I bet more than 1 watt. If the Fostex FE166EN excursion was not limiting, you could get even more - for example the case with the Alpair 10.3 - you could put 4 to 8 watts and I think it might shake things in the room too.
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Old 3rd July 2013, 10:49 AM   #23
sayrum is offline sayrum  Germany
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Quote:
Originally Posted by xrk971 View Post
Howard,
Great to hear that you built this! Please post some photos! ...

I second that !
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Old 3rd July 2013, 09:17 PM   #24
howardg is offline howardg  United States
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The speaker that I just built is the left channel, and will install horizontally in the wall above a set of wardrobe cabinets (that, strangely enough, will also extend into the wall cavity-to save room space) . The right channel will be in the wall vertically, like I suppose that most in the wall horns would end up being(this one going behind a bookshelf, up to 68” from the floor, like the wardrobes). A lot of design time has been consumed just getting the two driver/mouth combinations to look the same from the room, and to interact with their horns similarly enough. When I figure out how to scan in drawings, I will show all this for those who are interested.

I wonder what the truth is about making 180 degree turns near the comp chamber? Some think that it is too tight, while the Horneshop horns had a couple of tight bends there, apparently to help filter out higher frequencies from the horn.

One other thing that I wonder about is the effect of a rapidly expanding horn mouth at the end of otherwise gentle expansion? I kinda tried that here, sort of, and it didn't seem to work. Seems like if the horn expands all of a sudden that it would not load the driver much. Maybe the big expansion rates at the mouth of some small horns act like wave guides, but don't really acoustically couple/ load, the whole column of air in the horn so well.
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Old 3rd July 2013, 09:18 PM   #25
howardg is offline howardg  United States
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I do need to remember how to post photos----find the cord for my camera, how to get them attached to my post. You can see that I am better at making sawdust and wood things than at "technology". A hammer is technology, but I am not sure that the current lexicon acknowledges that! I am trying to get better at electronics too, but it is a slow uphill battle for me.
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Old 3rd July 2013, 11:23 PM   #26
xrk971 is online now xrk971  United States
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Howard,
The cell phone camera is the easiest way for me. Send myself email of photos, then upload the picture from computer. Use advanced mode to manage files. Good luck!
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Old 4th July 2013, 12:03 AM   #27
howardg is offline howardg  United States
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I screwed the horn together and sat it upright on the bench. The sound is much tighter. Without getting out my R.Shack meter to measure spl, I played pink noise 1/3 octave(?) test bands and listened. There is audible response in the 20-30hz region. There is a hump around 40 hz and another around 100-125hz. There is annoying resonance somewhere around 100 hz that I think could be tamed somewhat by bracing.
The 30 hz or so (must be a 5-string) electric bass notes on Lyle Lovett's “Road to Ensenada”(the song, specifically, rather than the whole album) come through with a sweet, sublime ease, though I suppose it must be down a few/several db.
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Old 4th July 2013, 12:08 AM   #28
xrk971 is online now xrk971  United States
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Awesome! 30 Hz is what we were aiming for. Can't wait to see the pics! Screwing the cover on does winders for the bass usually.
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Old 5th July 2013, 01:20 AM   #29
xrk971 is online now xrk971  United States
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Default In-Wall MLTL as Alternative to BLH

Using the constraint of 16 inch spacing between 2x4 studs in standard drywall interiors, I designed the following speaker that can be installed during the installation of framing, before drywall goes on. A 2x4 is really 1.75 in x 3.5 in. Thus the natural cavity in between walls in the US are 3.5 in deep x 14.25 in wide (internally). I decided to go with a TB W5-1611SAF as it has a moderate Qts that will allow deeper bass extension for a MLTL, and it has a nice smooth response with just enough sensitivity to match the bass from a MLTL port.

I actually used the Accidental MLTL technique to size the speaker prior to tweaking it in AkAbak. The AMLTL method assuming a length of 40 inches gave me a vent dia of 2 in x 3 in long. The driver will be mounted at 17 in from the closed end and the port will be 6 inches from the "bottom". In this case, I will flip the speaker upside down and put the port near the ceiling and the driver at about 32 in from the top of the ceiling. The following are the results of the simulation and they look pretty good: 40 Hz bass extension and 90 dB sensitivity. The impedance is pretty smooth and the cone excursion is well controlled.

So, if you are remodeling a room and have exposed joists/beams, tack some cross bars to make a cavity and seal with silicone. Silicone the drywall panels when they are installed for an airtight cavity that you prewire and stuff some polyfill or fiberglass in the top 2/3rds of the line. After drywall is done, cut out the driver hole and vent hole. Install drivers and enjoy! It will sound better than any store-bought ceiling or wall speaker.
Attached Images
File Type: png Wall-MLTL-W5-1611-Freq-1m.png (31.0 KB, 205 views)
File Type: png Wall-MLTL-W5-1611-Impedance.png (21.9 KB, 202 views)
File Type: png Wall-MLTL-W5-1611-Disl.png (21.7 KB, 195 views)
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Old 5th July 2013, 01:49 AM   #30
GM is offline GM  United States
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Try a BIB, seems one was done back in its early days with a small RS driver.

GM
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