BillFitzmaurice.info

This is the continuation of a quadrilateral TLAH Pro build. Apparently the
forum software saw fit to purge ALL of my previous build thread ...including
the photos leading up to this point

To recap, I wanted a free standing TLAH Pro version. However this build
was started before BF released his rectangular version of the TLAH Pro.
So after some discussion on the forum, I had opted for a squared front
and back with tapered sides. The transmission line vents at the bottom.

The biggest errors I have made thus far is with the filling, sanding, priming
and finishing of the project. It came out much more rough looking than I
would have liked.

There were also some construction considerations related to the shapes
of both the tweeters and the midwoofers. The tweeters Dayton Audio ND20FB-4
are a tapering cone. Almost imperceptiably so, but it sure does become
noticable after trying to fit them into the holes you just finished boring
based on the diameter of their round face! By the way, NO I did not pay
the current price for those tweeters. They were less than $6 apiece back
when they were purchased. The midwoofers are of the recommended
pincushion style to facilitate close center to center placement. But the
underside of the face plate is not flat. The factory provided gasket conceals
a tapered bump that ruins a flat / flush mounting. So off the gaskets went.
The best solution to both problems seemed to be a quality silicone sealant
...and it worked rather well. The only issue is that the tweeters are not 'glued'
into place and may require something additional to make sure they are
secured in place.

The first photo was from when the midwoofers were individually tested to
make sure their polarity and +/- markings were correct ...they all were.

The second photo shows the approimately 3/8" - 1/2" bead of silicone used
to properly seal the midwoofers.

The third photo is with all the drivers mounted and most of the excess silicone
already trimmed away.

I wanted to repost the T/S parameters for both drivers as I will have some
questions concerning the wirring and cross-overs. I was not able to find any
graphs for the midwoofers.


Dayton Audio ND20FB-4 Rear-Mount 3/4" Neodymium Dome Tweeter

VCdia: 3/4"
Impedance: 4 ohms
Re: 3.2 ohms
Le (mh) @ 10Khz: 0.03
Fs: 2072 Hz
Qms: 2.08
Qes: 3.74
Qts: 1.33
Sd (cm2): 2.8
VC dia. (mm): 19
SPL: 93 dB 2.83V/1m, 90 dB 1W/1m
Frequency range: 3,500 - 25,000 Hz
Power handling: 15 watts RMS/30 watts max
Overall diameter: 1-9/16"
Cutout diameter: 1-7/16"
Depth: 1/2"


Samsung 10W72BRA / Atlantic Technology 350-3171 A309-28
4" Poly Cone Shielded Midbass
Poly cone w/rubber surround, Treated cloth dust cap
1" VC with aluminum former, Magnetically shielded

*Power handling: 40 watts RMS/80 watts max
*VCdia: 1.0"
*Le: 0.6 mH
*Impedance: 8 ohms
*Re: 5.3 ohms
*Frequency response: 100-8,000 Hz
*Fs: 105 Hz
*SPL: 88 dB 1W/1m
*Vas: 0.11 cu. ft. / 3.11 liter
*Qms: 4.16
*Qes: 1.03
*Qts: 0.826
*Xmax: 3 mm
*Efficiency bandwidth product (EBP) = 101.94
*Sd [Calculated]: 54.078 cm2
*Vd [Calculated]: 16.22 cm^3
*Dimensions: A: 4-1/4" (5-1/8" diagonally), B: 3-3/4", C: 2-5/8"
*Driver volume displacement (for 0.75" baffle thickness) = 166.43 cm3 / 10.16 in3
{speaker measurements: Dc 8.3cm, Md 5.8cm, Dm 7.8cm, Hm 3cm, Xmax 0.3cm}

They look damn good to me.

LelandCrooks wrote:They look damn good to me.

+1.

Chris

After thinking about it for some time, I've decided to use an active digital
cross-over and bi-amplification rather than a passive cross-over. My
current power amplifier, an OutLaw 7125, will power the midwoofers. And
perhaps a small 20 watt T-amp to power the tweeter line?

For the active digital cross-over, I was thinking some Behringer product?
Something that can accept inputs for 3 channels. This is needed because
a matching SLA center channel will be built next. The digital cross-over
should also be able to do equalization ...unless I am confused on that point?
A microphone and RTA software will be used to help equalize the speakers to
the room they are being used in.

So anyway, I wanted to ask for some help with the wiring schemes for the
tweeter and midwoofer lines.

The midwoofer lines are 12 drivers each. The tweeter lines are 24 drivers
each. There were two primary reasons for choosing this number of drivers
for each line. 1) The line heights allowed the listener to be in the "vertical
sound dispersion area" whether laying down on the living room couch or
standing up walking around in the adjoining kitchen. 2) I figured it would be
much easier to obtain the desired impedance for each driver line if they were
both based on the powers of numbers 2 & 3.

Yes, I have read the section in the plans that talks about using a specified
impedance ratio between the tweeter and midwoofer lines to help balance
differing sensitivities between the tweeter and midwoofer lines. However I
have also read elsewhere that when using biamplification that this is not
important ...if I am wrong on this point please explain why. Otherwise, I thought
it might be good to just try and place the impedance of both lines at 8 ohms?

There are 24 drivers in the tweeter line. Each tweeter has an impedance of: 4
ohms and SPL: 93 dB 2.83V/1m, 90 dB 1W/1m. There are 12 drivers in the
midwoofer line. Each midwoofer has an impedance of: 8 ohms and SPL: 88 dB
1W/1m.

Could someone please suggest series-parallel wiring schemes for the tweeter
and midwoofer lines using 8 ohms impedance as a goal...

Woofs
4 in parallel as a bank with 3 banks in series is 6 Ohm nominal for woofs or
3 in parallel as a bank with 4 banks in series is 10.67 Ohms.

Tweets
If you ran each pair in series and then treated them as one driver you could follow the same scheme above. Or just run
2 in parallel with 6 banks in series for 12 Ohms.
3 in parallel with 4 banks in series for 5.33 Ohms.

Oscillate,

I ran a quick check of the series combinations:

1) for 3 series banks of 4 parallel (8 ohm) woofers, the equivalent load is 6 ohms.
the system sensitivity (line height gain and sensitivity gain) is 100 dB.

2) for 4 series banks of 3 parallel (8 ohm) woofers, the equivalent load is 10.67 ohms.
the system sensitivity is 97.54 dB (because of the higher equivalent resistance).

3) for 6 series banks of 4 parallel (4 ohm) tweeters, the equivalent load is 6 ohms.
the system sensitivity is 102 dB.

4) for 8 series banks of 3 parallel (4 ohm) tweeters, the equivalent load is 10.67 ohms.
the system sensitivity is 99.5 dB.

So it looks like the best combinations would be the 6 ohm loads, provided that your amp(s) will be happy with that. If this is home audio, it should be right on the mark. And 100 dB sensitivity is a LOT of sound for a home stereo.

Also, my terminology may be confusing for you, so when I say, "6 series banks of 4 parallel", mean that there are 4 parallel banks each with 6 speakers connected in series. In the case of the tweeters, that's: 1/Req = 1/(6x4) + 1/(6x4) + 1/(6x4) + 1/(6/4) = 4/24 or Req = 24/4 = 6 ohms....get it?

Chris

Oh, and I just looked at that Outlaw amp too...125W per channel into a 8 ohm load, but it's also rated for loads as low as 4 ohms. So, I think the 4 parallel / 3 series woofers and the 4 parallel / 6 series tweeters would fit nicely with the amp.

What's the RMS rating for the drivers?

I suspect you'll have plenty of headroom in your amp for the system to get as loud as you can tolerate.

Chris