[BoomieMCT]

I just bought four of the Aura NS3's on sale at PE and intend to make two ported full-range bipole speakers.

I can easily model a ported box in Unibox or WinISD however I'm having trouble deciding on a tune. Since only one driver will fire forward but both driver's port output will be coming out the front I'm not sure how to guesstimate the combined output. Does anyone have any tips?

Unibox shows output from the port and from the driver. I tried graphing the output in the same box using one and two drivers and interpolating what I might get by using a driver output halfway between the two. Is this valid?

 

[Anthony]

So let me get this straight:

A box. One forward firing driver. One rearward firing driver. One port on the front side.

Port output should just be 2x level of a single driver, since all the port "knows" is the pressure inside the box, which is essentially 2x single driver in a bipole speaker.

So for a combined response, I would put front + 2x port + rear*(shifted due to time/phase effects).

That's my first reaction. I'll have to think about it some more.

 

[BoomieMCT]

That's kind of what I did. I assumed the output would be the port (for both) and 1.5 x a single driver. I guessed only half of the rear-facing driver's output would make it to the listener. I took two Unibox graphs and drew on them to estimate - I'll post it when I get home.

Doing this seemed kind of odd - I could get an F3 of 45Hz. That seems low for two drivers with an Fs of 100 Hz. I guess some of this will become apparant when I acutally build and test.

 

[JCD]

I'll look forward to your results. I bought the same drivers for a line array I'm building.
If I don't like the results of the line array, besides crying, I was wondering what I'd do with all those drivers.

JCD

 

[BoomieMCT]

Here is my theory (see attached). The pink line (I had to use colors Unibox didn't) is a trace of the port SPL for both drivers. The purple line is a trace halfway between one and two drivers in the same enclosure. I am making the assumption that the reflected wave off the rear driver will roughly equal 1/2 of the front driver.

I'm also kind of assuming that these drivers, with an Fs of 100 Hz, actually can't make that hump at 42 Hz.

If anyone has experience with bipoles, especially ported ones, please share your experience with me.

JCD - I hope you post results about your line array foray. How many did you buy? If I recall from another post you were using the 8E's, not the 8A's (paper vs. aluminum cone). If I hadn't filled all the rooms in my house with other speakers I had thought of doing a line array with these same drivers as well. I don't mind getting them for less than 40% cost!

 

[JCD]

Your questions are way beyong my skill level -- I'm looking forward to seeing what the answers are. That being said, I think I'd assume 2x rather 1.5x. I'm not sure if anything would be lost with the rear wave.

and, as an aside, I have 12 drivers per side with a horn tweeter to handle the upper octave.
Here's a pic of the front baffle with the drivers "installed".

And yeah, I'm not sure where these guys are gonna end up either. :hide:

JCd

 

[mgboy]

Hey boomie, What do you think about this :

4 of those, inline, in a slot ported box, measuring (outside) 5.5*12*26, tuned to 60Hz?

Does even exceed excursion, according to the Aurasound T/S, which seem to differ from those.. =\ Are you sure those are the same drivers?

 

[BoomieMCT]

Hey boomie, What do you think about this :

4 of those, inline, in a slot ported box, measuring (outside) 5.5*12*26, tuned to 60Hz?

It sounds good. I'll be able to say better after I build these things.

Does even exceed excursion, according to the Aurasound T/S, which seem to differ from those.. = Are you sure those are the same drivers?

No, I'm not. I'm just going by what the reviews say. E

 

[mgboy]

It sounds good. I'll be able to say better after I build these things.



No, I'm not. I'm just going by what the reviews say. E

Alright, I'll be awaiting your build and/or "approval."


Ah, I see. When you modeled them, which T/S parameters did you use? Not that PE gives enough anyway.

 

[BoomieMCT]

No listening reports yet but I figured I'd post a pic to show how things are coming along. I made the front baffle double thick (so I could cut big chamfers in it) and now it is a PITA getting the rear of the driver holes chamferd out. I should have prototypes running in a week or so.

BTW, the ugly grey spots are slop from a two part wood filler I tried out. It got very messy so I think I'll stick with my traditional wood filler or stuff I make myself. After sanding / painting you'll never see those spots!

 

[BoomieMCT]

So I have the prototypes for these done and I'm breaking them in. No FRs yet (as I haven't tuned the port, stuffing or decided if the rear driver will have a lowpass filter) but I can give some listening impressions. Very diffuse sound, great for ambient / party music (with a sub). These fill the house very very well. I'll give more info in a few days after break-in and some tuning work.

mgboy: I haven't run these full power (i.e. 30 whole watts) yet but I have cranked my PsAudio2 up pretty high I've had no problems with the ported enclosure or excursion. Will report more with more testing.

 

[BoomieMCT]

These should be somewhat broken in now. Here is a quick FR. Since the amp in my testing room can't take a 4 ohm load I actually have both speakers in series stacked so their drivers are as close as possible. I'm not expert at reading these graphs but is the spike at 190 Hz possibly from driver resonance? The Fs should be lower - maybe I didn't chamfer the back enough (I thought I did). Any thoughts?

The first graph is with no stuffing, the second is with.

 

[BoomieMCT]

So after playing these for a while I was getting a very overly enegetic mid-bass that was causing electric guitars to be quite painful. I played around with changing stuffing and some notch filters but nothing seemed to fix this. So I took the whole thing apart and went crazy-go-nuts with a wood rasp to open up the chamfer behind the drivers as much as was physically possible. I also changed the tune of the box to something closer to the Fs of the driver (from 55Hz to 70Hz or a 4.5" port to 3").

I don't have a FR yet for these changes but these sound immensly better. I think that even with the chamfering done before these drivers were still way too constrained. Considering the small form factor of the motor it is too bad they couldn't have opened up the basket more to breathe better.

When I've played with the new sound a bit I'll experiment with the stuffing again and then do a new FR.

 

[mgboy]

Well atleast they look fantastic. ( As if anything you've made hasn't. )

But I'm glad to hear you've got them sounding decent, even if it took a bit of work.

 

[BoomieMCT]

Well atleast they look fantastic. ( As if anything you've made hasn't. )

But I'm glad to hear you've got them sounding decent, even if it took a bit of work.

Thanks! I added a BSC and I've been listening to radio over them all day. I think that is pretty close to dialed in. At the very least the screeching is gone. I'm going to solder in the BSC and experiment with changing the stuffing this weekend.

One thing I thought about was putting an inductor on the rear driver to limit the high frequency coming off the back wave. When the speakers were screeching I thought this might be a fix. Right now I'm leaning towards not doing this.

 

[JCD]

So, this is where I'm sure to show my extreme ignorance, but a random thought I had was to put some OC703 wedged betweent the two drivers. It'd absorb a good portion of the high frequencies that are coming off the back waves of the drivers.

JCD

 

[BoomieMCT]

So, this is where I'm sure to show my extreme ignorance, but a random thought I had was to put some OC703 wedged betweent the two drivers. It'd absorb a good portion of the high frequencies that are coming off the back waves of the drivers.

JCD

The problem (which is now solved) wasn't the interaction of the rear waves of each driver on each other. It was the fact that each driver did not have enough space behind itself to "breathe". It was almost like having the driver in a very very small box. This was raising the Fs of the driver and causing a lot of distortion. By liberally applying a wood rasp and opening up the chamfer to the rear chamber these problems went away.

After another day of listening with a moderate BSC (L = 0.7 mH, R = 2 ohms) I think I've just about got this where I want it. I'll try adding a little stuffing to remove any possible high frequency coming out of the port.

Someone had concerns over the excursion of this driver in a vented enclosure. I can say that with my 30 watt per channel PsAudio Number 2 this doesn't seem to be a problem.

 

[JCD]

The problem (which is now solved) wasn't the interaction of the rear waves of each driver on each other. It was the fact that each driver did not have enough space behind itself to "breathe". It was almost like having the driver in a very very small box. This was raising the Fs of the driver and causing a lot of distortion. By liberally applying a wood rasp and opening up the chamfer to the rear chamber these problems went away.

After another day of listening with a moderate BSC (L = 0.7 mH, R = 2 ohms) I think I've just about got this where I want it. I'll try adding a little stuffing to remove any possible high frequency coming out of the port.

Someone had concerns over the excursion of this driver in a vented enclosure. I can say that with my 30 watt per channel PsAudio Number 2 this doesn't seem to be a problem.

Ahh.. my bad.

Do you have a before and after pic of the chamfer? Since I've got a whole line of these, I'm worried about not having enough room myself now.

JCD

 

[BoomieMCT]

Ahh.. my bad.

Do you have a before and after pic of the chamfer? Since I've got a whole line of these, I'm worried about not having enough room myself now.

JCD

I don't. The rule I've always heard was to chamfer as close as you can at a 45 degree angle (no curves). One of my problems is that I changed my design mid-construction so the front baffle ended up being double thick (1.5"). That was very hard to get a 45 degree angle on so I initially did a more shallow angle. That was a mistake that had to be fixed with a lot of elbow grease (and a very aggressive rasp).

Generally when chamfering I don't get really agressive where the screws go in. The chamfer ends up looking like a rounded off plus sign from the back. I'm generally not a fan of pincushion frames but one advantage is they seem to keep the screws further away from the cutout hole.

 

[BoomieMCT]

I've had a few people ask me about making these. Since the drivers I used are discontinued, these are supposed to be a drop-in replacement;

http://www.parts-express.com/pe/showdetl.cfm?partnumber=290-210