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Multi-Way Conventional loudspeakers with crossovers

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Old 3rd March 2013, 08:24 AM   #21
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Originally Posted by Hibernator View Post
Oddly I couldn't get any sound from the first amp. There's a label on the back about 1.5 mV sensitivity, so maybe that's not what I'm used to with non-pro gear. Will have to see about that.
Oh oh, brain fart. Sensitivity is 1.5 V, not mV.
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Old 3rd March 2013, 04:02 PM   #22
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I was under the impression that you decided to make a prototype of the full box, not following why there is the L shape to them.

You're moving fast!
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Old 3rd March 2013, 06:22 PM   #23
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Originally Posted by PB2 View Post
I was under the impression that you decided to make a prototype of the full box, not following why there is the L shape to them.

You're moving fast!
I didn't consider that at first because of just having one sub and because I assumed I would probably want a center and surrounds as well.

But now that you mention it, that would have made construction ten times easier. I had 32x49 MDF laying around in both 3/4 and 5/8. No matter what now I'll probably have to make a full tower version next time I pick up MDF.
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Old 3rd March 2013, 09:01 PM   #24
SY is offline SY  United States
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I have more drawings up on my website.

NHT M3.3 Cabinet Drawings

If anyone has more and would like me to host them, drop me an email.
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Old 10th March 2013, 10:14 PM   #25
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Default First sounds

Finally was able to find the time to complete the first prototype speaker. This is a satellite portion of the 3.3 or 2.9 with some minor modifications using 3/4" MDF instead of 1" MDF.

I have the top two drivers off to the wrong side due to late night SNAFU, but the cabinet is only screwed together right now anyway. There were also a few other lessons learned regarding cabinet construction that, so that I will definitely just rebuild when I'm ready to do something more final.

There are a few options for the subwoofer. I have one NHT 1259 in a 3.5 ft^3 sealed enclosure (pretty much just followed the standard builds posted on the net for almost 20 years). I have a NHT SW2 that I used for my quick demo connected through the Carver PM1.5 you can see in the picture below. The other amp is an Elan 12 channel amp I scored on Ebay (70-90W/ch). Really neat for quick hookup and testing of active speaker designs when combined with the Behringer Ultradrive Pro. I used the published XO settings and have the upper two drivers wired out of phase with the 6.5" woofer and subwoofer (or did I misunderstand the wiring issue?).

The enclosure is not 100% sealed as it is only screwed together, but its pretty decent. There is no stuffing yet either.

Despite all of that, it's pretty good. I haven't taken any measurements and all amp and gain settings are at best ballpark. I can't wait to (a) build the real XO and (b) dial in the correct gain and amp settings using measurement data.

One remaining question is whether to keep the sat/sub configuration or attempt to build a full range 3.3 clone. Since I only have one 1259 woofer it won't be 100%, but I am interested in several options:

- 1 10" npt-11-083-2 subwoofer in 2.3 ft^3 sealed enclosure per side. This could allow the cabinet to be a little less deep
- 1 10" npt-11-125-1 subwoofer per side. Need to measure and see how similar to the VT-3 sub driver above this woofer is. Supposedly it is used in the NHT B10.
- Some combination of all 4 10" woofers listed above, thus making the bass section similar to the VT-3. THis would require (assuming the B10 subwoofer is similar enough) adding at least 1.5 ft^3 to the overall enclosure. A rough 48x8x35 (32 on the short side) gives a 20.5 degree front and about 5 ft^3 total volume.
- 1 Sunfire True 10" subwoofer. I just bought this bare driver really cheap and am mostly just curious. I have a line on a second one and maybe these could be used in very small sealed enclosures allowing the overall tower size to be reduced.

Questions:

- Is the front baffle fully integrated into the rest of the speaker design? Or could I change the angle to say 10 or 35 degrees with only the following impact:
-- The sweet spot for listening presumably is found by the tip of the isosceles triangle formed by the ASA (angle/side/angle) relationship of the two main speakers. At 10 degrees you'd want to have a very long room and at 35 degrees you'd be sitting closer to the speakers.

If those particular choices are too extreme, how about more modest changes between say 18 and 25 degrees?

- How critical is the 7.5" baffle width? Can that be made up to 10" without significantly changing the sound?

- Can the height placement of the upper section be changed somewhat freely with the understanding that it should correspond to the listeners head position ? Let's say +/- no more than 10 inches over the 3.3 schematics.
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Old 10th March 2013, 10:26 PM   #26
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The baffle width is critical- there's some interesting subtlety to how they avoid the baffle step. Likewise, you'll want to use the original height- the interaction with the floor was taken into account, no "Allison dip" in any of my REW measurements. Use an open cell polyurethane foam strip on the outside edge- it makes a difference.
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Old 10th March 2013, 10:31 PM   #27
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Thanks Sy,

I wasn't aware the baffle width had that big of an impact. Likewise I never thought about floor interactions. I agree about the foam strip, but it's not necessary yet at this stage. I will have to dig up the e-mail from NHT suggesting where to buy the right kind of material (assuming it's the same used on the VT-2 and other speakers).
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Old 10th March 2013, 10:42 PM   #28
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That would be helpful- mine were pretty chewed from the get-go and my ex-wife's cats finished the job. Fortunately, I had some skived open-cell PUR foam in my junk-box which worked very nicely, but that's not an option for other cloners.

The other advantage you get from maintaining the front panel angle is that it reduces a notch in the midrange from the reflections off the back panel coming back through the cone.
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Old 10th March 2013, 11:39 PM   #29
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How close is that tweeter to the original?
Did you compare the DC resistance?

I have a pair of the original tweeters but they are the
chambered version - they were on sale when I got them.
I figure I can just plug the pole vent and check the Fs to
see if it is in the ball park of the original.

Those NHT 10" woofers are very inefficient from what I remember of
the numbers. I'd go with pairs, but even so, I think that there are
some auto sound 12" drivers that are close enough and under $100
each. I wouldn't be surprised if they are better than the 1259.
There's probably a parts express Dayton reference that would work
well, would have to check the numbers, but these are not cheap:
Dayton Audio RSS315HF-4 12" Reference HF Subwoofer 4 Ohm High Fidelity Reference Series 295-464

This looks closer based on cone mass and Fs, Qs are low but that allows
for higher DCR in the crossover inductor - one could ignore or use the
servo feature:
SW-12-04
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Old 22nd March 2013, 12:19 PM   #30
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Default NHT 2.9

Hi,

I've built the 2.9. If you send me your email address, I will send you pics ( step by step )

on how I built them; the hardest part being the cabinets of course. I'm now up for building the 3.3

2.9.jpg
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