Multiple Tlahs using Apex jr tweet/Aurasound NS525-255-8A

[Bill Fitzmaurice]

it looks like 16 tweeters in 4 sets of 4 gives me 102dB sensitivity is that close enough?

math:
16 tweeters with a groupings of 4
Efficiency gain = 10 log 16 = 12dB
Total impedance = 1/(1/26.8+1/26.8+1/26.8+1/26.8 )= 6.7 ohm
Sensitivity gain = 10 log (6.7/6.7)= 0
System sensitivity = 90 + 12-0 = 102dB

Less than 2dB apart is fine.

[gene]

Long time without an update. Started a new demanding job last December. Anyway i had a bit of time to layout the TLAH speaker using cardboard and then drew it up in cad. Cnc machined in about 5 min a test front out of old plywood and everything fit up great.
I'll need to adjust the center to center spacing of the tweeters before I run the final version. Will be making 5 tlahs. First one will be put together active so I can play with it and get the crossover figured out using real world calibrated mic/REW testing.
I'm having some excellent half inch plywood picked up and everything will be ready for me to finish the build when I have time off the week of December 8th.

One thing I'm trying to remember is why I came up with 50" for the height of the speaker. It has something to do with keeping the dimensions correct to keep transmission line effect when using 5.25" woofers? Was size of speaker supposed to be half of FS? i can't remember. please correct me if sizing is wrong as it would be a lot easier to make it 48" when using plywood. FS of the Aura is 70hz

[ecut1]

Gene,

I'm using the same speakers as you and ended up at 54" for the height. That's with nine of the 5.25" aurasound speakers fit about as close as I felt comfortable with. The cages end up about 1/16 of an inch apart (mounted from the inside). For the top and bottom speaker I left about three inches between them and the top and bottom of the cabinet. I'm using 12 of the apex jr tweeters spaced 2.75" apart (per the input I received from Bill in my build thread).

My build is super low budget super low tech... $9.00 each pine baffles (imperfections will be fixed with spackling putty and filler primer), leftover MDF for the cabinet walls and back, home made circle jig for my router, ect. I also figured as long as I'm deviating from the plans so much I might as well make the backs removable instead of the baffles. With the larger cabinet I think I'll have more than enough room to solder in there. That way I can make the baffle completely smooth with no screws or bolts holding it in place. Here are some pics of the right channel. I started mounting the speakers in it but my build is going slow with birthdays and holidays approaching.

I actually read your entire thread when I was planning mine out. It's good to see you back! I'll keep an eye on your progress. We'll likely be building at the same time.

[miked]

Nice, ecut1. That's what this forum is all about; helping each other out.

[Fushie]

Hi there
I don't really want to hijack this thread but something got raised that in this thread that I don't understand. It's about calculating the sensitivty of each of the lines. Bill also mentioned

you don't want the HF line to have 4dB higher sensitivity than the woofer line

Since this came from Bill I'll be happy to believe him, but I don't know how to actually work this out. Equations where mentioned but i didn't see the actual formula. Could someone please help me by pointing me in the right direction so that I can work this out for my build.

Thanks in advance
Fushie

[Tom Smit]

Here is a quote from a few years ago on the forum that I had copied and saved, along with other tidbits of info:
If you mutual couple you get 3dB. Parallel wire you get 3dB. Series wire you lose 3dB. Therefore, coupled parallel wired is 6dB, coupled series wired is 0 dB.

[gene]

Formulas to figure out how many drivers to use was taken from the pdf paper of "Design guidelines for Practical Near Field Line Arrays". Specifically section "Overall Array Sound Pressure Level and Impedance"

What we are interested in:

Thus, the
acoustical improvement (efficiency gain) at 1 watts, 1 meter distance is given by:
Efficiency Gain = 10*log (Number of Drivers Driven)
while the sensitivity gain or loss at 2.83v, 1 meter is:
Sensitivity Gain/Loss = 10*log (Nominal Driver Impedance/Nominal Array Impedance)

If the nominal array impedance is less than the individual driver impedance, the array
sensitivity increases or is a gain. If the array impedance is greater than the individual
driver impedance, then the sensitivity decreases or becomes a loss.

Hence, for the overall system
System Efficiency = SPL + Efficiency Gain
System Sensitivity = SPL + Efficiency Gain + Sensitivity Gain/Loss

Example:
For example, consider a case wherein we have 12 drivers connected in parallel groups
of 2, 3, 3, and 4 in series. Each individual driver is 8 ohms impedance and has an SPL
of 85 dB. Hence, the efficiency gain, total impedance, and sensitivity gain are:

Efficiency Gain = 10 log 12 = 10.79 dB
Total Impedance of the Combination = 1 / (1/16 + 1/24 + 1/24 + 1/32) = 5.65 ohms
Sensitivity Gain = 10 log (8/5.65) = 1.51 dB
Hence, the sensitivity of the array is:
System Sensitivity = 85 + 10.79 + 1.51 = 97.3 dB.

So breaking down my usage of it with the apex jr tweeters:
16 tweeters with a groupings of 4 wired in parallel
Efficiency gain = 10 log 16 = 12dB (16 is the number of tweeters I'm using. Ecut would enter 12 here since he's using 12. You can input 10 log x ((x being number of tweeters)) into google if you don't know how to do logs on a calculator)

Total impedance = 1/(1/26.8+1/26.8+1/26.8+1/26.8 )= 6.7 ohm (you plug in each grouping of tweeters here. I'm using four tweeters per group wired in series and then wiring the four groups together in parallel. To get 26.8 I take the resistance of each speaker which is 6.5 to 6.7 ohm - I'm choosing to use 6.7 for each - from spec sheet and since I'm then wiring these four speakers in series you add it together 4 times for each group so it equals 26.8 )

Sensitivity gain = 10 log (6.7/6.7)= 0 (here you take the original resistance of the speaker and divide by the new impedance you got from the formula above. In our case it was the same. So 10 log 1 = 0)

System sensitivity = 90 + 12-0 = 102dB (90 spl is the base sensitivity of our speaker at 1watt @ 1 meter. Next we add our efficiency gain from the first formula. This is 12 spl. Finally you add in the sensitivity gain which in our case is 0. Total of 102db)

Hope this helps

[Tom Smit]

Well explained!

[gzc_stageTech]

Well explained!

+1.

I have a simple excel spreadsheet that does this work (math) for you. I built it using that same document as the reference. The spreadsheet allows me to compare multiple line heights and serrires/parallel combinations to match power source availability (amp power requirements). With it, I can model the best practical setup for the arrays. Ironically, sometimes fewer drivers is better for the balance of SPL to power ratings, especially when you consider circuit power sources.

Excellant discussion on this topic. Thanks

Chris

[gene]

Of course I managed to leave my tlah plans at home and they are not on my attached storage here. Anyway I'm going to route out a face today and build a single tlah for testing when I drag it back home. I've got cherry 1/2" ply on order to make the real ones out of but it won't be here for a few more days.

So for the tlah using the Aurasound mids that would give me a fs of 70. Using the formula for a transmission line it would be 1126/(.8 * fs)= x and then x/4 = final size in feet. So 1126 is the speed of sound in feet per second. The .8 is used because we are doing a transmission line with a 2:1 taper ratio or greater correct? Then divide by 4 to get the 1/4ths wavelength we want the enclosure to resonate at. So that puts me at 5.02ft aka round height to 5 feet or 60". Can I make it any shorter and still keep the transmission line aspects? All 8 of the aurasound speakers fit with a size of about 46" of height

I believe my width is 9" (may be 8") so that puts my dimensions at 60" height by 9" width. So to figure out depth I start with the distance to clear the 5.25" aurasound driver and that is the start depth of taper right? By the top of the speaker it then needs to be double that depth to get the 2:1 ratio correct? or am I missing something since the plans are not with me? PM me if needed

[ecut1]

Gene,

Did you get a TLAH built and tested yet? I'm curious to see what sort of numbers you came up with for a crossover. I've been busy with holidays and family, etc but I'm thinking I'll be able to get back to my build here very soon. Thanks!

[gene]

I just built my test TLAH last night. Got to the shop at 9pm, got home at 11pm. Seems like a cnc router speeds the process along. All the wood components of speaker box are finished. I'm going to add the speakers in and then wire it up.I'll test it as an active speaker to see how it does this weekend. I'll post results

Pics:

[gene]

Finally got the time to wire everything. Set the minidsp crossover to 5500/6000hz and ran the test speaker active. Sounds great. My father has already decided he wants a pair. Anyway I'll do some REW testing tomorrow to see what the signal response looks like and apply EQ to see how flat I can get it