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PostPosted: 16 Nov 2016, 07:13 
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Joined: 13 May 2016, 02:02
Posts: 91
Location: Javea, Spain
Hello All,
I'm just about to build a pair of back loaded horns using Fostex FE166En's and I want to use their cabinet design. I've just been looking at the diagram and it looks to me as though the throat of the horn narrows at one point instead of staying the same or getting larger.
Can anyone clarify this for me?
Attachment:
Speaker cabiet.png


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PostPosted: 16 Nov 2016, 07:20 
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Joined: 13 May 2016, 02:02
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Location: Javea, Spain
Okay, highly embarrassed now as I've just seen that the shaded area is a divider. Any tips before I start assembling the cabinets this weekend coming?


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PostPosted: 16 Nov 2016, 09:28 
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Joined: 05 Aug 2016, 14:35
Posts: 218
john55 wrote:
Okay, highly embarrassed now as I've just seen that the shaded area is a divider. Any tips before I start assembling the cabinets this weekend coming?


Not to worry, even I have been known to make the occasional mistake - never more than one per minute, however!

Only the usual:

Measure carefully.
Assemble to be plumb, level, square.
No gaps where they should not be.
Use the best possible glue you can find, in sufficient, but not sloppy quantity.
Give everything enough time to cure! If the package directions say 24 hours, allow 36.

Be patient with the results - tweaking may be required.


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PostPosted: 23 Nov 2016, 03:48 
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Joined: 13 May 2016, 02:02
Posts: 91
Location: Javea, Spain
Halfway through building the BLH cabinets and the drivers have arrived. Hoping to fire them up this weekend. Apart from wanting to compare them to the bass reflex cabinets that I'm using now, I'm wondering about how they would all sound together. I'm using the 6EM7 vertical amp and I'm not sure of the effect on the valves and OP transformers. What's better, 4 ohm or 16 ohm? Would appreciate any advice,


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PostPosted: 23 Nov 2016, 07:32 
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Joined: 05 Aug 2016, 14:35
Posts: 218
john55 wrote:
Halfway through building the BLH cabinets and the drivers have arrived. Hoping to fire them up this weekend. Apart from wanting to compare them to the bass reflex cabinets that I'm using now, I'm wondering about how they would all sound together. I'm using the 6EM7 vertical amp and I'm not sure of the effect on the valves and OP transformers. What's better, 4 ohm or 16 ohm? Would appreciate any advice,


WOW! there are as many answers to this question as there are worms in the proverbial can. Two schools of thought:

a) run at the tap up from the nominal impedance of the speaker in question. This reduces the stress on the power transformer (translates into heat) but also somewhat derates the output (in watts). Given the typical response curve of the typical speaker this is also the 'safe' option.

b) run at/below the nominal impedance of the speaker in question. This maximizes the power to the speaker, and purportedly gives the best frequency response - and the most bass.

There are infinite variations between.

Now, if you have a modern, well-designed, well made output transformer using good materials and in a well designed circuit, you should be at low risk running at the lower impedance tap. Otherwise, you are at some level of risk and should watch things closely, constantly checking for excess heat until you establish that the system is working safely.


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PostPosted: 24 Nov 2016, 02:25 
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Joined: 13 May 2016, 02:02
Posts: 91
Location: Javea, Spain
Thanks for your quick response Peter. Output transformers are Edcores so shouldn't be a problem there. The circuit is by Matt Renaud (6EM7 SET Vertical Amplifier) so no problem there either. I will only be playing around for a short time out of curiosity so I'll keep an eye on the OP transformers heat.


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PostPosted: 17 Feb 2017, 06:49 
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Joined: 13 May 2016, 02:02
Posts: 91
Location: Javea, Spain
It's taken some time but the back loaded horns are just about finished. I find that "earning a living" does steal time away from what's really important.
Once the assembly was done I filled the cavities below the drivers with sand in old socks (well washed to eliminate hum). I also used a wool damping material directly behind the drivers and some felt glued to the magnets and spokes if the drivers. The first sound test showed up a little harshness in the vocals which I had expected. Using the calculator on this site I built a pair of BSR circuits. The second sound test was very good. Clean, warm mids, crystal clear highs and a much improved bass over the Fostex bass reflex speakers I built last year. I've covered the cabinets to match the other equipment I've built. I decided to mount the BSR circuits outside the cabinets and make them switchable, just to give me the option for adjustments later. I'm running the BLHs in series with the bass reflex cabinets at the moment and the sound is really sweet. Although the bass is good, I am using an active subwoofer for that tiny little bit more.


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PostPosted: 17 Feb 2017, 07:03 
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Joined: 06 Jun 2008, 18:23
Posts: 4910
Location: Australia
Looks good.

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Projects: "Lagoon" - tube preamp with cathode follower | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
Website: retro-thermionic


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PostPosted: 17 Feb 2017, 08:32 
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Joined: 31 Dec 2008, 15:34
Posts: 441
congrats john, looks nice.

what are the smaller boxes on top of the horn ?


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PostPosted: 17 Feb 2017, 10:38 
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Joined: 13 May 2016, 02:02
Posts: 91
Location: Javea, Spain
The smaller cabinets are bass reflex using Fostex FF165WK's 6.5 inch full range drivers. They sound really nice but the horns have that extra "thud" to the bass.


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