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Old 10th January 2011, 04:19 PM   #91
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btw, i returned the Lapai amps... did not look good at all. never turned them on tho. Arrived with scratches and the knobs did not turn smoothly. the dayton t-amps look much better and sound very good to me. i love tubes as you already know. the beta 12lta does not need much power to get loud. my 30 watt cary amp sounds way too powerful with them connected.
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Old 10th January 2011, 08:46 PM   #92
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I cancelled my order as well after reading some comments on build, components & the delivery times were going to be ridiculous.
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Old 10th January 2011, 11:09 PM   #93
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Here you go, Beta 15 in closed cabinets. Looks like 7 - 9 cubic feet closed is the sweet spot. I simmed an 11cf vented box and it goes deeper but it's bigger, it's vented and it may sound boomy in a home environment. If you look at Eminence's suggested projects you will see they modeled a 6cf vented cabinet that's -3 @ 45hz. The slightly larger closed boxes also reach 45hz but measure flatter. Closed appears to be a good idea. Choose your size and dimensions and build away. They should provide visceral bass you will feel as well as hear.

Do the foster amps allow you to roll off the hi frequencies or will you be using a coil to do that?

Zilla
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Last edited by Godzilla; 10th January 2011 at 11:26 PM.
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Old 11th January 2011, 08:52 AM   #94
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Thanks for that Godzilla - Bigger looks flatter so let the build commence!

The Foster amp has a "4th order (24dB/octave) low pass adjustable from 50-200Hz. 0-180 degree phase switch, RCA and speaker level inputs, volume control. Unit has a 3rd order (18dB/octave) high pass filter at 29Hz with a Q of 0.707 built into the subwoofer section. Can easily be modified for any Q and cutoff frequency that you want by changing R615, R617, R618, C607, C608 and C609. The amplifier also has a spectral tilt control that is adjusted to give about 10dB of shelving. It can be manually adjusted with a pot on the PCB" according to the blurb

One thing I'm not sure on though is where to put the sub amps. I may build them into the mid cabinet and have that as a sort of control unit for the entire system. What do you think?
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Old 11th January 2011, 12:01 PM   #95
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OOF

I just received this http://cgi.ebay.co.uk/MINI-DAC-DIR90...ht_6357wt_1141 Previously I was just using an iPod headphone to phono cable (I know, I know thats rubbish!). The dac must have a pretty big output because I only need to turn the volume a few degrees from 0 to get a real blast
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Last edited by JRKO; 11th January 2011 at 12:21 PM. Reason: oops
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Old 11th January 2011, 02:56 PM   #96
GM is offline GM  United States
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Quote:
Originally Posted by Godzilla View Post
Here you go, Beta 15 in closed cabinets. Looks like 7 - 9 cubic feet closed is the sweet spot.
Greets!

I'm curious which specs did you use, published or some measured ones posted recently or........?

FWIW, for a 0.707 Qtc max flat alignment using the decades old, well proven Margolis/Small HP calculator program:

published specs:

~464.36 L/16.4 ft^3 lightly damped with fiberglass insulation.

~274.56 L/9.7 ft^3 stuffed at 1.5 lbs/ft^3 fiberglass insulation, so would theoretically need somewhat more for polyfil.

average measured:

~347.21 L/12.26 ft^3

~218.9 L/7.73 ft^3

Pretty big difference, though at least going in the right direction, a rarity.........

WinISD Pro:

~763.4 L/26.96 ft^3 lightly damped with ?

Couldn't find any Ql, Qa adjustment to come close to the fiberglass calc'd Vb WRT F3, Fb.

average measured:

~470.00 L/16.6 ft^3

Sealed is very tolerant of Vb errors, but this disparity between programs for a basic max flat alignment is a bit much!

GM
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Old 11th January 2011, 03:24 PM   #97
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Hi GM.

Lots of numbers but I'm afraid I'm a learner. Can you dumb the info down a bit? I do understand the the specs, measurements & calculations can vary but other than that I'm stumped
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Last edited by JRKO; 11th January 2011 at 03:25 PM. Reason: .
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Old 11th January 2011, 05:36 PM   #98
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Thanks for checking GM!

I used the specs from Parts Express here:

Eminence Beta-15A 15" Driver | Parts-Express.com

I used WinISD and noticed they had parameters for the Beta 15 already in their database that did not match the ones on the PE website so i input them again and generated the sim that way.

Zilla
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Old 11th January 2011, 07:32 PM   #99
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Snow day today so I thought I'd try some things and take a few measurements. First the disclaimers:

I don't know much nor have much experience. This is the first time I've used ARTA, but I used a tutorial I read on the PE board.
Measurements taken in my cluttered basement with 12lts in a 1.9 cu. ft. sealed box. Box stuffed with dacron pillow stuffing. Center of 12lta about 3" off the floor and mic about 30" from speaker.

First, the stock 12lta:

Click the image to open in full size.


Then I removed the dust cap:

Click the image to open in full size.

Next I made a quick and dirty phase plug. I used a deep well socket wrapped with foam and covered in electrical tape. It's about 3" long.

Click the image to open in full size.

Left the phase plug in, but cut off about 0.5" of the whizzer:

Click the image to open in full size.

Cut off another 0.5"

Click the image to open in full size.

Cut off all of the whizzer:

Click the image to open in full size.


I see some inconsistency below 1K that I attribute to my difficulty in deciding where to put the cut off point before the first reflection, but maybe some of you can gleam something useful from this - or tell me how to improve it. From listening I do know that I don't like the cupped sound and removing the whizzer did get rid of it. Most likely I'll build an econowave with my 12ltas.
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Old 11th January 2011, 08:47 PM   #100
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Quote:
Originally Posted by db6546 View Post
Snow day today so I thought I'd try some things and take a few measurements.
Thanks for doing that. With an untrained eye I would say that the greatest 'improvement' (smoothing it out) to the measurement line thingy came when you used a phase plug.

I'm definitely gonna get one made up to Planet10's measurements I noted a few posts back.
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