Lack of Bass - Dallas II Horn

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Disabled Account
Joined 2019
Hello,

I have finished constructing a pair of the aforementioned horns and notice a lack of the low end.

I suspect it is due to one or several mistakes:

The front is angled while the back is straight (evident in the picture)
Perhaps, this directs sound from the speaker upwards and decreases the opening of the rear horn.

Fir instead of birch plywood

Terminals are duct taped, as I have lost the screws


P.S what is the ideal positioning of these speakers in a small room?



Thank you in advance,
 

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frugal-phile™
Joined 2001
Paid Member
The Advent woofers & the alignment are completely different beasts and the speaker a 2-way with a crossover. An 8” is not that much smaller than the 10” Advent and the Advent woofer is MIA above about 2k.

The enclosure is a major element in getting bass gain needed to deal with the low Q and small linear excursion. But it is still a small horn and low bass will be very room and room placement dependent.

A couple questions: 1/ How many hrs on the drivers? 2/ What amp are you using.

A leak in the horn can have significant impact.

And fir is probably not as stiff as good plywood, but likely better than MDF.

dave
 
frugal-phile™
Joined 2001
Paid Member
A few more hrs before you should start evaluating them. At least 100 hrs to get over the worst.

...a Raspberry Pi Digi Amp - 35 watts per channel...

Pi-DigiAMP+ - IQaudIO Limited

OK. That is very likely a problem. The FExx6 drivers prefer an amplifier with higher output impedance than your amp does. If used with a low output impedance (as i strongly suspect yours does — no specs here Pi-DigiAMP+ - IQaudIO Limited). It will over damp the LF with the net result of lean bass.

The typical target amp for these are single ended tube amplifiers, but there are some SS amps that your speakers would be happier with.

You can fake it somewhat by using very skinny highish R speaker cables. Start with a pair of wires (24g) pulled from a solid core CAT5/6 cable. If that is not enuff try 30g wirewrapwire (it is kinda fragile). Worst case you could add a series resistor.

At one CES Fostex was using a Luxman amp with something like your speakers (but one of the more exotic 8”). It had way too low an output impedance to match. They used tungsten speaker wires.

dave
 
frugal-phile™
Joined 2001
Paid Member
... a Elekit 8100 once it is built...

SE PCL86/ECL86. (likely UL or pentode) Even with a fair amount of feedback it should have a highish output impedance (not specified). If feedback is bringing the output impedance down too far one could consider reducing the size of the feedback resistor.

The key to the price of this amp is the switching mains supply. The B+ will have a big impact on the power output (rated 2w).

dave
 
The FE206En is an 8in drive unit. ;)

Assuming we're not going to go off into some twilight world and shall stick with fact, 'tight bass' depends on alignment with back horns in the same way as it does with any other enclosure. Dallas II is one of the better examples of the latter, although its acoustical high pass is a little higher than I personally prefer for keeping GD down.
 
Disabled Account
Joined 2019
Just one more question to ask: does the sloping front side and the straight back side make a notable difference to the sound?


I thought that angling the driver up would direct mid and highs away from the listener, and the straight back side does not increasing the opening of the back horn as much as if it were sloped


PS. This way a oversight and the angle is 4 degrees.
 
Vlad467,
Whats the driver you are using ?
FE166 or a FE206En
Keep a 1" piece of wood or a book at the back edge of speaker box to tilt it forward
So that the driver fires parallel to the floor.
Then you could check your doubt about its 4' angle of the box.
Sri.
 
Disabled Account
Joined 2019
Hello,

I am using a Fostex 206 En,

I am sure that the angle is 4 degrees.

Since the back side is straight, opening of the horn is not as profound as the schemes called for.

Thanks for the advice, I’m using spike feet so it may be difficult to rest a piece of wood or book.

Kind Regards,
 
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