DIY dipole to replace Apogee Diva?

[seaspeak]

hi LineSource and Scott,

Couple of questions.

First, what's most important in integrating a dipole woofer array with a line source ribbon? LS, you recommended the AES IB15 rather than the dipole 15. The IB driver has lower Fs, higher xmax, and higher mms. The dipole driver has much lower mms. Will high mms make integration harder, or does the high mms not really matter at ~150Hz? Is high xmax/low Fs more important for integration? Obviously those both extend the low frequency response.

Second, what simulation and CAD software should I be looking for? I have downloaded FEMM. I'll also need something to model the bass tower, plus baffle shapes on the MR/TW section. And then I'll need a CAD program to draw things. Any suggestions would be most appreciated. Ease of use would be my first priority re CAD programs.

Last, just curious what digital time alignment tool you are using, LS. I use Acourate (used to use TacT). I find that time alignment of the bass with the MR/TW makes quite a significant and positive improvement.

cheers,

Brandt

 

[seaspeak]

ps the IB15 also has a lower Qts than the dipole 15... curious how that plays into your thinking as well.

 

[Ang]

If you've got EQ, you can indeed get more bass out of the IB15. The issue with them is the impedance ripples vs how high you want to play them. Wouldn't take them past 200hz.

 

[seaspeak]

LineSource, you may get me on the slippery slope yet. I read valveitude's entire thread and started to think... 'I can do this.' Though in my case the work would be differently distributed -- I'd develop a CAD design and have it machined by a shop.

Not sure whether this is good or bad!!

 

[ScottG]

.. what's most important in integrating a dipole woofer array with a line source ribbon? LS, you recommended the AES IB15 rather than the dipole 15. The IB driver has lower Fs, higher xmax, and higher mms. The dipole driver has much lower mms. Will high mms make integration harder, or does the high mms not really matter at ~150Hz? Is high xmax/low Fs more important for integration? Obviously those both extend the low frequency response.

1. The ribbon should generally NOT extend very low - instead transition to the Neo 10's.

2. The mms generally makes a difference with respect to transients and subjective detail, (as does excursion). Of course it also makes a difference with respect to lower freq. extension and linear/non-linear behavior. At least with regard to the IB15 - linear decay is quite good up to about 300-400 Hz:


..and the impedance isn't showing any irregularities:


..nor are there any non-linear problems below 400 Hz:


http://sites.google.com/site/drivervault/driver-measurements/15/ae-speakers-ib15


3. You don't want any driver that could contribute to air "chuffing" near the ribbon. In other words keep most moving coil drivers away from ribbons (..of course the Neo 10 should do that).

 

[seaspeak]

I was thinking in terms of a dual-ribbon design. I figure if I build 1 ribbon per side, why not go all the way -- 1 midrange and 1 tweeter ribbon per side. I should be able to get the wider ribbon down to 200Hz.

Haven't simulated yet but other projects on the forum suggest this is not unreasonable (plus, the Apogee FR mid ribbon went down to ~400Hz and that was with ceramic magnets).

Let me know if not so.

Re the woofers -- just trying to get a sense for what the first order concerns are for ribbon integration. The IBs will obviously go lower than the dipole 15s. But will they integrate better with a ribbon, and if so, why.

cheers,

Brandt

 

[ScottG]

I was thinking in terms of a dual-ribbon design. I figure if I build 1 ribbon per side, why not go all the way -- 1 midrange and 1 tweeter ribbon per side. I should be able to get the wider ribbon down to 200Hz.

Haven't simulated yet but other projects on the forum suggest this is not unreasonable (plus, the Apogee FR mid ribbon went down to ~400Hz and that was with ceramic magnets).

Let me know if not so.

Re the woofers -- just trying to get a sense for what the first order concerns are for ribbon integration. The IBs will obviously go lower than the dipole 15s. But will they integrate better with a ribbon, and if so, why.

cheers,

Brandt

I honestly don't think a mid-range ribbon will provide you with anything better than a Neo 10 array, and in fact would likely be worse.

("worse" including: lower max spl for a given freq., much lower efficiency, much higher non-linear distortion, a much more limited low freq. use, etc..)


For better integration go with *2* bass lines, one a low mass with greater efficiency, the other the IB15. Seas is about to release a driver that should do nicely for the lower mass line.

 

[LineSource]

I was thinking in terms of a dual-ribbon design. I figure if I build 1 ribbon per side, why not go all the way -- 1 midrange and 1 tweeter ribbon per side. I should be able to get the wider ribbon down to 200Hz.

Haven't simulated yet but other projects on the forum suggest this is not unreasonable (plus, the Apogee FR mid ribbon went down to ~400Hz and that was with ceramic magnets).
Brandt

Hi Brandt,

I agree that it is worth exporing a two ribbon + woofers design if your goal is to surpass the Apogee Diva. The Apogee Full Range uses a 2" midrange ribbon with 6db Xover at 320Hz. I have Full Range and use a Krell Xover with 18db @160Hz. With modern N45 - N50 NdFeB magnets, 2" to 3" midrange ribbons with high efficiency can be constructed if you know how to emboss and strengthen aluminum ribbons. Study the RAAL "flatfoil" construction for ideas.

When integrating a dipole woofer array with a ribbon linesource I found it useful to: 1) use a (digital) delay to time align the woofers with the ribbons; 2) mechanically isolate the woofers to avoid vibrating the ribbons; 3) put the woofers on a separate base board that allows both butting up to the ribbons and pivoting toward the outside walls; 4) use wool felt spacers to block some of the woofer air from flopping the delicate ribbons.

I use Lambda TD15_dipoles and they sound excellent, but the AES IB15 is half the cost and is a good choice for low crossover frequencies. I do not know your budget, but suspect putting money into the ribbons is the best choice.

If you purchase strong NdFeB magnets you can get very good dipole motor field strengths with much less steel than valvitude's motor. FEMM and your wallet are all you need. Spaced rear steel braces are required to physically keep a fixed gap width against the super stong magnets. Valvitude's thread also warns about injury and death if you are not carefull assembling super magnets. The steel and magnets will last several lifetimes... ribbons are easy and cheap to replace. The Apogee Full Range speaker is in the Smithsonian.

 

[seaspeak]

LineSource, how do you think about the concerns Scott has raised about the midrange ribbon vs Neo 10?

Scott, how much distortion is 'much more' and is this based on experience, modeling, or something else? How far up in dB would this distortion be vs the Neo 10s, and how far down vs the signal?

You agree on the woofers and the tweeter, but the midrange ribbon is the bone of contention. It isn't clear to me that distortion is the primary concern (e.g. Bob Carver has indicated that distortion is not one of the things he targets in a design, and that if it's 50db down from the signal, we simply can't hear it.). So I'd like to explore this particular issue a bit more.

LineSource, have you heard or built a large midrange ribbon like this yourself? Has such a ribbon (ex the Apogee ribbon) been successfully implemented in the DIY community?

cheers,

Brandt

 

[ScottG]

Scott, how much distortion is 'much more' and is this based on experience, modeling, or something else? How far up in dB would this distortion be vs the Neo 10s, and how far down vs the signal?

"Much more" depends greatly on the operation bandwidth and spl, more particularly - how low in freq. it's operated and with what order of high-pass crossover, in conjunction with the average peak spl for that bandwidth.

IMO, (..and the opinions of others), you get a more detailed sound by operating a planar as low as practically possible - this requires uniform operation at excursion limits, which is something most ribbons won't "do".

The problem with a ribbon is uniform excursion, which practically speaking is something it doesn't have. The gap is already "wide", and increasing the surface area per driver runs into diminishing returns quickly - and actually is a detriment at some point, (also very quickly), due to the added mass of a larger diaphragm. (..and in fact the mid-bass "ribbons" of the Apogees weren't really ribbons at all, rather they were poorly driven, (edge driven), bending-wave planars.)

The only real solution to this is the use of multiple drivers (..and *many* at that). This then runs into other problems - like getting the multiple drivers close together, and even then it's a struggle to get much more than an additional octave of linear extension than what one driver can provide.

By contrast the Neo 10 planar is uniformly driven over it's entire surface area.

As far as the actual numbers on a non-linear comparison? I don't have that, but I'd bet that at a similar low freq. operation point.. say 150 Hz or less, of equal sd results in at least 10 times less non-linear distortion for the Neo 10 at that freq..

Here is the Neo10's non-linear profile again (which is better than most drivers regardless of design):

http://www.zaphaudio.com/temp/B&G-Neo10-HD-50-1.5k.gif

 

[seaspeak]

hi Scott,

If by 10x more distortion you mean 10x more power, then that should result in distortion artifacts about 10db higher than in the Neo 10, right?

Between 100-200Hz, the Neo 10's 3rd order distortion looks like it's about -50dB from the signal. So you'd expect a well implemented true ribbon to have distortion running about 10dB higher than that, say around -40dB?

Two questions: what in your view is the cutoff frequency for a wide ribbon (say 2" wide, plus or minus) below which the Neo 10s would be inarguably superior; and above what frequency will the Neo 10s in an array run into comb filtering problems?

I understand your reservations about the trad Apogee bass panels. I've never trusted that part of the design, for reasons similar to yours -- if the point is to move air with excursion, it's hard to see how a single-ended motor with a corrugated diaphragm clamped on all 4 sides is the right way to go about things. Fortunately this is also the hardest part of an Apogee to replicate. Anything not worth doing is worth not doing well.

thanks,

Brandt

 

[ScottG]

hi Scott,

If by 10x more distortion you mean 10x more power, then that should result in distortion artifacts about 10db higher than in the Neo 10, right?

Two questions: what in your view is the cutoff frequency for a wide ribbon (say 2" wide, plus or minus) below which the Neo 10s would be inarguably superior; and above what frequency will the Neo 10s in an array run into comb filtering problems?

At *least* 10 times more distortion..

2" is to wide IMO for a long line source. 1.5" should be about right. 4 of those as tall as the Neo 10 array should be comparable (..though having greater surface area). (..3 lines would be more similar in surface area, but I suspect inferior measurably at lower freq.s.) The magnetic "rails" spacing would determine crossover point.

Neo 10 cut-off freq.. as high as 1.5 kHz (depending on the crossover). (..you could probably go higher, but I don't think it would offer any advantage.)

 

[seaspeak]

Ok, I get the picture: using a midrange ribbon instead of the Neo 10 would be a bad idea.

I also see why, from the horizontal and vertical dispersion plots (as well as distortion plots), one wants to cross the Neo 10 over at around 1.5kHz.

I think arrays of AE dipole 12s would work in my room (room is fairly small, so a narrower baffle is good aesthetically, plus a dipole line isn't going to be able to pressurize the room, which has a relatively high fundamental resonance -- so trying to go very low with a dipole isn't my first priority). And I'm seeing your point on the Neo 10.

Will chase some tweeter options. Main ones at the moment would be the DIY ribbon vs a line of AMTs.

 

[audioandmusic]

@seaspeak Hi, as I´m pretty much a fan of AMTs, I´d like to share my ideas:
How about building a dipole according to Horbach-Keele with a small AMT (maybe made by Precide - they´re sold separetely, can be crossed low in OB and sound real nice - I have their big one "Kithara") and Neo10s?
With FIR you might even get the crossover low enough and avoid any lobing...