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

[gene]

I thought I'd go ahead and start a build thread for the TLAHs I'm going to make. Woofers arrived yesterday and the tweeters today. I'll be doing the free standing rectangular tlah. Eventually there will be five behind an AT screen/AT wall. LCR and two wides in an 11.x system. Even though they will be behind the screen, I am going to make them look nice. For the face I think I'll make it out of a dark walnut and some kind of flat clear coat to be figured out later so they are not reflective or distracting with the projector and the at screen.


I'm going to go with 8 Aurasound NS525-255-8A 5.25" 8ohm woofers in a 4ohm load. This adds 12db to 89db/1watt sensitivity. Is there anything I should know about figuring out their C to C spacing? My current receiver, a yamaha rx-v667, indicates in the manual it can handle 4ohm loads. I'm not quite sure how many tweeters I should use, their c to c spacing and what ohm load to wire them for.From what I'm reading you should cross over the Apex jr tweets at 6Khz.

Once I get an idea of how I am going to arrange everything, I can go ahead and draw the cad files for routing out on my 4x8 cnc router.
On a side note I have a minidsp and a spare 20 watt x 2 channel amp for figuring out the crossover if needed. I don't really want to go active on all these speakers if I don't need to. That's a lot of minidsps to buy at $100 a pop.

I'll reread the tlah plans tonight to make sure I'm not missing anything.

[Tom Smit]

What I have done is put the drivers down on the baffle so see where they were going to end up in regards to rear depth, and to plans. Then I drew along the top and bottom of the driver (onto the baffle), measured and drew the centre line down the baffle, shifted the driver down/up so that the driver was at the new location where the top/bottom lines formed a curly 'X'. --> )( . If you desire, you can put them tight to each other, or leave a slight gap (1/8") between.

[gene]

What I have done is put the drivers down on the baffle so see where they were going to end up in regards to rear depth, and to plans. Then I drew along the top and bottom of the driver (onto the baffle), measured and drew the centre line down the baffle, shifted the driver down/up so that the driver was at the new location where the top/bottom lines formed a curly 'X'. --> )( . If you desire, you can put them tight to each other, or leave a slight gap (1/8") between.

Got it. I'll see if I have a piece of cardboard the right size to be a form for the front bezel or I could just use some tape to lay it out. I could actually 3d scan the tweeters/woofers and do it all in sketchup. hmm decisions, decisions

[wallywally]

You may want to reconsider the apex jr tweeter if the lowest it will go is 6k. The NS525 should be crossed @ about 4k due to cone breakup. With any speaker/tweeter the center to center spacing should be as close as you can make it for best results.

[gene]

hmm guess I'll have to see what it sounds like. I'll use an active crossover on the first tlah to try different crossover frequencies and settings. The lowest I read someone crossed the apex jrs at was 4.5k

[gene]

So what are the advantages of making the tlah speakers active? Better EQ across all the frequencies? Cost per speaker to do so would be about $70 (using cheap 15-20 watts a channel t amps and 2x4 minidsps) as opposed to $35ish plus shipping for the passive crossover components

My single active test speaker will be using a minidsp 2x4 and a Lepai LP-2020+ http://www.parts-express.com/pe/showdet ... er=310-300 - With 101 spl/1watt sensitivity of the woofers that would generate 108spl at 12 feet and 101.7spl at 24 feet (not including any sonic reinforcement) which seams like plenty to me. Amp puts at 15.9 watts rms per channel at 4ohm. With the sonic reinforcements included that spl reading goes to 115.5 and 109.5spl respectively

[Bill Fitzmaurice]

So what are the advantages of making the tlah speakers active?

Pretty much none.

[gene]

So what are the advantages of making the tlah speakers active?

Pretty much none.

Well that settles that then. Passive crossover it is

[LelandCrooks]

Yup. It's an inexpensive crossover and works really well.

[gene]

So I'm wanting to make some sawdust tonight. I made a cardboard form and laid out the woofers and tweets.

Center to center distance:
Woofers: 5.25"
Tweeter: 1.315" if directly touching each other

Using 8 woofers, it looks like I have to add 10" of height to the TLAH since I'm not using the goldwood woofers in the plans and these auroasounds are bigger. So total height of rectangular TLAH would be 50".
I'm not sure how many tweeters to use, but 20 seemed about right when positioned on the form and as close to each other as possible. How exactly do I determine how many apex jr tweets to use?

[Bill Fitzmaurice]

How exactly do I determine how many apex jr tweets to use?

As many as necessary to have the tweeter line impedance and sensitivity close to that of the woofer line. Caution: Math is required.

[gene]

not worried about math unless it gets into differential equations... hated that class ok well time to research how to go about getting/setting combined impedance and sensitivity

[gene]

So this is what I came up with after reading "Design guidelines for Practical Near Field Line Arrays" and using the formulas

Aura 5.25"
resistance meter reading = 7.2
Calculated nominal impedance (z) = 8.64 to 9 ohm
FS= 70hz
Sensitivity = 89db @ 1khz (1 watt at 1 meter)
using 8 woofers wired for a 4.5 ohm load
Efficiency gain = 10 log 8 = 9dB
total impedance = 1/(1/18+1/18+1/18+1/18) = 4.5 ohm
Sensitivity gain = 10 log (9/4.5) = 3dB
Combined sensitivity of 89db + 9db +3db = 101db

Apex jr (audax 10mm polymer)
resistance meter reading = 5.4
Calculated nominal impedance (z) = 6.5 to 6.7 ohm
FS=3000
Sensitivity = 90db/1watt @1 meter
Lowest crossover point used by others in a line array: 4300hz
24 tweeters with a grouping of 4 tweeters in parallel x 6
Efficiency gain = 10 log 24 = 13.8dB
Total impedance = 1/(1/27+1/27+1/27+1/27+1/27+1/27) = 4.5 ohm
Sensitivity gain = 10 log (6.75/4.5)= 1.76dB
System sensitivity = 90 + 13.8 + 1.76 = 105.56dB

That seem right to you guys?

[Bill Fitzmaurice]

So this is what I came up with after reading "Design guidelines for Practical Near Field Line Arrays" and using the formulas

Aura 5.25"

Combined sensitivity of 89db + 9db +3db = 101db

Apex jr (audax 10mm polymer)

System sensitivity = 90 + 13.8 + 1.76 = 105.56dB

That seem right to you guys?

I didn't check the math, but you don't want the HF line to have 4dB higher sensitivity than the woofer line. Since the tweeters and midbasses have roughly the same sensitivity you should be able to use the same number of drivers. You may use more tweeters if you wish, but if you do you want to wire them for a higher impedance to get their sensitivity closer to the midbasses.

[gene]

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