Project with NHT drivers

[badman]

I thought this would make most sense as it's own thread here. If mods feel otherwise, please move it.

I have been working through the design of a basic speaker: a 3 way with the 10" sub2 (NPT-11-075-2), the peerless 5 1/4 (NPT-11-081-1), and a 2" tang band full range as a tweeter (take your pick, www.partsexpress.com has several)

I was thinking an XO between mid and woof (obviously) either first or second order at 2-300Hz and a first order XO at 1200Hz for the mid/tweeter (see why I wanted a 2" fullrange for a tweeter now?)

Basic box design is below. The design was simple- needed a good amount of output capability, and needed to be appropo for a variety of uses- modest stage monitors or recording monitors, celing/wall mounted for use in a school A/V setup, and as just plain hifi speakers. The wedge shape fits this multiple personality, as does the lack of large scale baffle step correction.

The drivers are well behaved around the chosen crossover points, so the crossover design should be fairly easy. It won't slay giants, but should be a pretty darn good speaker for a variety of purposes and placements. The price is right, too.

Any suggestions or comments are welcome. I'll attach the next file in a second post below this.

[badman]

Next up. These will be getting built by students in a school which is part of the not-for-profit where I work days, hence the relatively simple design.

[SY]

My first thought is that with a first order electrical crossover and the spacing between the midrange and the tweeter, not to mention the tweeter's inevitable funky dispersion, you'll have more lobes than a caterpillar. Bring them in tight, then bite the bullet and use something more like a 4th order LR. Those measures will help reduce the lobing and reduce the criticality of zero-delay-plane differences.

The front panel will need some attention. I take it that it's shown sideways and that the mid and tweet are in a vertical line? You'll want to play around with some diffraction modeling software to see where the optimum location of the drivers on that large baffle is found.You'll also want to really brace the heck out of it- that's a large surface flopping around.

[badman]

Hi Sy:

Those are all valid points, and have been considered, but there's only so difficult the cabinet can be, as it will be built by our disabled students at my job. Also notably missing are beveled or rounded baffle edges and driver flush-mounting, same reason. We'll try to get the mid and tweet as close as possible while retaining the divider to keep the backwave from the mid from interfering with the tweeter.

I don't foresee a funky dispersion pattern from that tweeter, looks to be clean on and off (30 deg) axis to 10k where it starts to break up. I think the low XO point and low order filters would work in this instance to help alleviate lobing, not exacerbate them: are you saying that higher order filters and a higher frequency would decrease lobing?

Here's some more driver information re: tang band driver and also a response curve for the peerless (kindly provided by Mr. Hidley @ NHT)



Tang Band tweeter

[SY]

A well-chosen higher order filter will definitely help reduce lobing- first order filters are notoriously bad about that. The low crossover point will help, not hurt- my main worry would be the polar pattern of that large tweeter at higher frequencies.

The effects of beveling and rounding are pretty minor. You can achieve more benefit from the intelligent use of stick-on felt.

[badman]

Looking at the response characteristics of the 5 1/4", above 2.5kHz we're going to have a pretty small amount of power response, which should relieve some of the lobing- less off-axis cancellation effects relating to the tweeter. But you may be right about using a steeper filter here. Good thing I have plenty of gear at my personal shop to test with before the XOs have to be nailed down.

Re: Bevels and roundovers: their efficacy is small compared to felt.... if the roundovers or bevels are small.

As things go I'll update, and we can perhaps see what the speaker does in the end.

[SY]

Oh, and the other thing is that high order crossovers will also minimize the sensitivity of the frequency response to ZDP offset- I mentioned it before, but in light of your desire for simplicity, I'll say it again. You don't want to have to step the drivers, you want them to just bolt in to a flat panel.

Fortunately, crossover parts for 1kHz+ tend to be compact and inexpensive, so shooting for a fourth order acoustic crossover is not unreasonable.