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

[crunchhardtack]

I plan on making a pair of ported speakers using four ND90-8s in each enclosure, wired in series/parallel with tweeters for some improved top end response. I've got eight ND90-8s Plus two Tymphany D19TD-05s, two PE 5 Khz two-way crossovers, two 50 hz high pass filters, and the parts to make the contour filter from Paul Carmody's Sprite Boombox.

Here are three arrangements that I have come up with so far. Please give me some input. I need some baffle step help. I'm leaning towards the narrowest one that I call, "MMTMM" Please tell me if my images aren't showing up.

Thanks all,
Crunch

[Chris Roemer]

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

I think all 3 could have phasing (combing) issues if crossed at 5kHz.
The lower the Fc, the lower those issues.

[Face]

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

I believe the middle image would have the least issues. I also agree with Chris that a 5k crossover, especially a generic one, could be troublesome.

[superspeeder]

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

A bit of a novice opinion here, but wouldn't a 2.5 way setup be the way to go? It would mean starting over from a crossover standpoint, but the results might be worth it given the total cost of the project and the level of effort involved. Just throwing it out there.

This would likely require a MTMMM or MMTMM arrangement.

[isaeagle4031]

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

A bit of a novice opinion here, but wouldn't a 2.5 way setup be the way to go? It would mean starting over from a crossover standpoint, but the results might be worth it given the total cost of the project and the level of effort involved. Just throwing it out there.

This would likely require a MTMMM or MMTMM arrangement.

This. Either configuration would be better than 1 or 2. But will require a true crossover and not an off the shelf unit. Being 8 ohm drivers, the OP may need to run a series/parallel circuit for testing nd90s to avoid a very low imp in the bass region. The 4ohm units would be the better option.

[jhollander]

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

A bit of a novice opinion here, but wouldn't a 2.5 way setup be the way to go? It would mean starting over from a crossover standpoint, but the results might be worth it given the total cost of the project and the level of effort involved. Just throwing it out there.

This would likely require a MTMMM or MMTMM arrangement.

IMO the second pair of ND90's doesn't extend the bass frequency any deeper to be an advantage over picking up the additional sensitivity. The 4 ND90s will make for a 2-way that can reach 100 db at 47 Hz. Sensitivity is about 87 dB at 2.83v. I did a pencil tower design MMTMM (in my sig).

[crunchhardtack]

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

Hey Guys I'm back,

After looking at your responses, I'm wondering if maybe I should just eliminate the tweeters all together and just go full range with nothing but the contour filters and the 50 hz high pass. The Sprite Boomboxes seem to make people smile, even without a tweeter. They were the inspiration for this project in the first place; I just wanted to make bigger, louder, stationary versions that could be powered by something more like 80w.

Tell me what you guys think,
Crunch

[isaeagle4031]

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

Hey Guys I'm back,

After looking at your responses, I'm wondering if maybe I should just eliminate the tweeters all together and just go full range with nothing but the contour filters and the 50 hz high pass. The Sprite Boomboxes seem to make people smile, even without a tweeter. They were the inspiration for this project in the first place; I just wanted to make bigger, louder, stationary versions that could be powered by something more like 80w.

Tell me what you guys think,
Crunch

Nothing wrong with that. Paul's contour filter may not work as well though since your enclosure baffle will be vastly different (and therefore have a different diffraction signature) than yours. I would consider a 1.5 way to aid in baffle step and comb filtering. Yes you will have comb filtering in the upper registers.

[crunchhardtack]

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

I,m not clear on what a 1.5 way is.

[isaeagle4031]

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

Upper driver plays full range and lower driver plays up to the baffle step freq (200-300 is fairly typical).

[crunchhardtack]

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

Thanks,

I think I understand. I've got two high pass filters that work at 300 hz at 4 ohms. How would all of this be wired together with my series/parallel set-up?

[johnnail]

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

I'll tale a stab at it.... I had a 4 driver fullrange setup long time ago. 8 ohm drivers in series/parallel. Just the 4 drivers, top two pairs series, bottom two pairs series, then paralleled together with the lower pair having an inductor to lower/taper the top end...make them sound more authoritative....but finally, I put a tweeter off to the side at the top.....simple first order cap at probably 6-8k. I had to play with the polarity to get it right.....but after swapping the polarity and adding a few ohms series resistance, the whole thing sound much better....especially off-axis, as this was where it originally didn't sound quite right without the tweeter. Even with a minor amount of combing, the peaks and dips were so close together, my ears never really registered it when listening. I would use one of those ultra-small faceplate tweeters...to get it close as possible to the drivers....don't park it in between drivers....park it on top, or off to the side of the full range section. The .5 way section won't be an issue.

John

[crunchhardtack]

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

Ok, let me tell me if I'm understanding things correctly.

I've got four different drivers producing the same frequencies at the same time from four different points in space. At wavelengths shorter than the drivers' center to center distance (3.49" or 3,888 hz and up), I will get comb filtering due to the different arrival times to my ear from those different points of origin.
That makes me rethink why I'm using four small full range drivers only to hold back their full capability. This is one of the major arguments against line array speakers, isn't it?

[isaeagle4031]

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

Exactly.

[DanP]

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

Hey Matthew, glad to see you posting here. Welcome aboard!

There's a lot of good advice here but I'd break it down like this:

If you want to use your 8 ND90s to make a legit, great sounding speaker, just buy some ND20s and some caps and coils and make John's Pencil Towers that he referenced above. I'm sure you could modify some of the cabinet dimensions without too much detriment if that shape is not your cup of tea. This will get you a certified good speaker with all of the guesswork taken out of it.

On the other hand, the ND90 (or the Aura NS3 on which it was based) is one of the best balanced speakers for doing everything pretty good in a single driver. Pretty good bass, pretty good mid, pretty good treble, pretty good dispersion, pretty good output, etc. As such, putting 4 of them in a box to run full range probably wouldn't sound too bad. Yes, comb filtering will occur, but you may or may not notice it. Baffle step could be an issue too depending on where in your room they're placed, but again, it might be ok. I like Chuck's recommendation of the 1.5 way. You could use 2 ND90s for the 1 and the other 2 for the .5. This would minimize comb filtering (because only 2 of the woofers would be operating in the treble range) and take care of the baffle step.

Dan