Opinions on driver arrangement of four ND90-8s plus tweeter please.

[crunchhardtack]

Re: Opinions on driver arrangement of four ND90-8s plus tweeter please.

Thanks Dan,

Good advice. I actually like John's Pencil tower design a lot (sorry John that I haven't responded to your suggestion on that design directly until now). I'm also seriously considering the 1.5 way direction too.

I was originally leaning toward a tower design (pun intended) in the first place. I would prefer a floor standing design that elevates the drivers closer to ear level.

My major question now is addressing the comb issue. My center to center measurement is 3.49". That equates to 3,888 hz. So, do I try to cross lower than that in either design?

[DanP]

Re: Opinions on driver arrangement of four ND90-8s plus tweeter please.

My major question now is addressing the comb issue. My center to center measurement is 3.49". That equates to 3,888 hz. So, do I try to cross lower than that in either design?

In the 1.5 design, you wouldn't really cross over per se, you'd just roll the bottom pair of woofers off as the baffle step kicked in while the upper pair ran full range. This would occur somewhere around 500Hz depending on the width of your cabinet. This would best be measured and modeled, but x.5 way designs usually use just a single inductor on the .5 section which means it wouldn't be hard to change values out until it sounded right.

If you want to use the tweeter you have and design your own crossover, don't get too hung up on that 3888 number. There are more variables to consider than just that one number. You could embark on this path, and you'd get plenty of help here, but it wouldn't be the quickest path to great sound. Coincidentally, John did cross his ND90s over at 3800Hz, and I'm sure he'd share his woofer measurements if you wanted to keep his baffle dimensions and layout.

Dan

[crunchhardtack]

Re: Opinions on driver arrangement of four ND90-8s plus tweeter please.

So, how about this,

I've got a preliminary box worked out with a baffle that's about 5.9" wide and 36" tall. What would you guys recommend that I roll off the bottom two drivers if I were to use a 1.5 way.

[Chris Roemer]

Re: Opinions on driver arrangement of four ND90-8s plus tweeter please.

You can model your BS loss using something like Tolvan's "Edge". Generally, the middle of a typical BSC range is roughly 300Hz.
I THINK (if you go the 1.5 route) you'd have to have your (top) FR range pair wired in series (16n), w/the bottom BSC pair (also in series) wired in parallel to get the +6dB gain for BSC. You'll end up back at a nominal 8ohms then.

[crunchhardtack]

Re: Opinions on driver arrangement of four ND90-8s plus tweeter please.

You can model your BS loss using something like Tolvan's "Edge". Generally, the middle of a typical BSC range is roughly 300Hz.
I THINK (if you go the 1.5 route) you'd have to have your (top) FR range pair wired in series (16n), w/the bottom BSC pair (also in series) wired in parallel to get the +6dB gain for BSC. You'll end up back at a nominal 8ohms then.

Thanks Chris, Tell me more.

Tolvan Edge software is new to me. I'm looking into downloading it if it will work with Windows 8. What do you mean by "the middle of a typical BSC range".

I'm not set on such a narrow baffle. Would I be better off with a wider one? Also, I am indeed thinking of the wiring you mentioned.

Cheers,
Matthew

[Chris Roemer]

Re: Opinions on driver arrangement of four ND90-8s plus tweeter please.

Virtually all baffles suffer baffle step loss. The width only affects the frequency.
The approx. -6dB "loss" typically occurs between about 100 and 1000Hz. You can model it in "Edge".

[crunchhardtack]

Re: Opinions on driver arrangement of four ND90-8s plus tweeter please.

Ok I,ll give it a try,

I downloaded it. Tomorrow I'll start learning how to use it. If you have any pointers, they will be greatly appreciated.

Thanks for your advice,
Matthew

[jhollander]

Re: Opinions on driver arrangement of four ND90-8s plus tweeter please.

Lots of baffle programs. Here's the edge

[crunchhardtack]

Re: Opinions on driver arrangement of four ND90-8s plus tweeter please.

Thanks for taking the time to plug my specs in this morning John,

That roller coaster wouldn't happen to be my response curve would it? I don't have too much time this morning to check out the program (day job), but does it have a good help section?

[Chris Roemer]

Re: Opinions on driver arrangement of four ND90-8s plus tweeter please.

That WOULD be your response curve IF you ran all 4 drivers the same, and had the "mic" (see the little red dot?) centered on the top speaker, AND took a measurement at whatever mic distance John used. Your "take away" from that graph to to basically see how the SPL level drops about -6dB from 1000Hz down to about 100Hz (as I had previously mentioned). Your top end will end up w/less "interference" (lobing) since you'll probably only use the bottom 2 woofs below 1k? (or maybe below 300). Also, as your distance from the "array" increases, it'll smooth out some.

[crunchhardtack]

Re: Opinions on driver arrangement of four ND90-8s plus tweeter please.

Chris,

Will Tolvan Edge software allow me to enter in the lower two driver's roll off?

Thanks,
Matthew

[jhollander]

Re: Opinions on driver arrangement of four ND90-8s plus tweeter please.

The graph posted is the baffle response that would get added to your driver's response. By playing with the driver location and your listening point you can get a feel for how lumpy your response might be. In this case this shows where you might want to roll off the lower two drivers.

Attached is one of my pencil tower FRDs, it's on a 6 inch wide baffle. I believe this is one of the outside drivers but don't know for sure

[Chris Roemer]

Re: Opinions on driver arrangement of four ND90-8s plus tweeter please.

A little more info.

The most common measurement method today (at least for the last 5-10yrs for us "hobbyists", and maybe 20yrs or more for "professionals") is NOT to measure a driver on a huge baffle in a large anechoic chamber (as was common previously), but rather to use a "windowed" impulse. The (time) window is quite short (like 3 milliseconds), and it's this short window during which the software will register a given frequency that's been generated (by software), amplified, reproduced by the driver(s), travelled through the air (the only part of the chain involving the s-l-o-w speed of sound), and captured by the mic. When the "window" closes (after about 3ms in THIS example), any more sound from that particular freq. is cut off (or ignored) by the windowing. That gets rid of almost all the reflections in the measuring environment (which, using that method, can be a fairly small untreated room, almost an 8' x 8' bedroom will do).

A 3ms window can only measure freqs. down to about 320 cycles per second. MOST graphs you look at showing driver response are only good down to about 300Hz. Below that point, you should be using ("splicing") the output modelling your bottom end rolloff from your favorite box program.

So . . . after you've added your own "box particular" bottom-end rolloff to your NS3s mfr. curve (near 300Hz), you should THEN adjust your response (from around 1kHz DOWN) by using your curve from the "Edge" software. If you subtract -6dB from Tolvan's scale (making his +6dB level = ZERO dB - which is really your "standard", and making 0 on his scale = -6dB), you can then use that baffle-step curve to sum with (actually subtracting from) your full-range response curve. So what SEEMs like a level ("0") dB line (say, in WinISD), actually will end up gently dropping from about 0dB near 1k, and ending up -6dB down around 100Hz, and THEN (if your NS3s show an F3 of 50Hz) dropping to -9dB at 50Hz.

When guys apply "baffle step compensation" (BSC) they're trying to flatten out that +6dB "rise" (it's a rise when you're going from low freqs. to high) to bring the mids (and highs) down (about -6dB) to get them more in line with the bottom end of that FR curve.

[jhollander]

Re: Opinions on driver arrangement of four ND90-8s plus tweeter please.

I was playing with a .5 crossover today and it looks like that would be the only filter required. However my sim used a damped second order to get the baffle step flat so that is not going to be cheaper than Paul's notch filter.

[crunchhardtack]

Re: Opinions on driver arrangement of four ND90-8s plus tweeter please.

Alright this is fun,

I'm immersed in wonderful info and advice. The more you guys tell me, the more questions I have. Though I must take it slow and only ask a few at a time.

John H. uploaded a screenshot this morning from T's Edge. The first thing I noticed was the substantial rise cresting at somewhere around 1300 hz. For a 1.5 way, is this where I should aim my filter on the bottom two ND90s?

I'm still very early in the design process and can easily sidestep things before they become problems. Would a wider baffle and/or some asymmetry like with the drivers closer to the left or right side help with the 6 db that Chris R. and most everything I read speaks of?

Cheers,
Matthew