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-   -   Hybrid H-Frame, OB and nude driver (https://www.diyaudio.com/forums/multi-way/366380-hybrid-frame-ob-nude-driver.html)

iamvalheru 18th January 2021 08:01 PM

Hybrid H-Frame, OB and nude driver
 
Gents/Gals,

I am hopping for some recommendations on my first "serious" OB speaker project after playing around with a pair of Hawthorne Audio Silver Iris 15.




The room:

My dedicated audio room is 14' x 17' and acoustically treated; the first reflection points have floor to ceiling absorbers, the front wall (behind the speakers) has 9" deep broadband absorbers with a custom stepped diffuser face, the back wall (behind the listener) has bass traps and a huge custom stepped diffuser that's about H 3' x W 7' centered at ear level.




The equipment:

I have 2x miniDSP2x4 for crossover/EQ duty and for amplification a "couple" of Rotel power amplifiers at my disposal (i.e. RB-1090, RB-1080 and RB-985 Mk2). I am also looking at used Crown or QSC pro amps for the LF section if my RB-1090 isn't enough.




My wants:

After months of reading (e.g. diyAudio, Linkkwitz, MJK, Audiokarma, etc.) I am pretty certain of I want:

- As much as possible constant directivity across the full range;
- 91+ efficiency; and
- Either a 4-way multi-driver or a 3-way using an 8" full range:


4-way:

- For the LF (30 to 200 Hz): I am planning on using Fane 15-400LF in a H-frame, but I am uncertain of the dimensions;

- For the lower mids (200 to 800 Hz): I would like to use 12" woofer (I need recommendations) in a flat baffle that is isolated from the H-frame (i.e. Sorbothane hemispheres);

- For the upper mids (800 - 2500 Hz): I am planning on using a nude Peerless 830875 suspended by cables;

- For the highs (2500 Hz+): nude back to back RT-4001 ribbons, or GR Neo 3 or Aurum Cantus AST2560 suspended by cables.


3-way:

- For the LF (30 to 200 Hz): I am planning on using Fane 15-400LF in a H-frame, but I am uncertain of the dimensions;

- For the mids (200 to 2500 Hz): I would like to use a nude Tang Band W8-2145 suspended by cables;

- For the highs (2500 Hz+): nude back to back RT-4001 ribbons or GR Neo 3 or Aurum Cantus AST2560 suspended by cables.




Questions:

1. Is one Fane 15-400LF pro woofer (equivalent to a Eminence Beta-15A as per Basta simulations) in an H-frame sufficient to get me down to 30Hz +/- 3 dB?

2. What dimensions of H-frame should I been looking at to cross over between 150 and 250 Hz?

3. Are there any benefits in making the H-frame out of 1.5" thick MDF or sand filled walls versus 3/4 thick MDF?

4. For a 4-way, which 12" woofer and flat baffle sizes should I be looking at?

5. Is the Peerless 830875 a good choice for nude upper mids?

6. If the Peerless 830875 isn't a good choice, what is recommended for nude upper mids?

7. For a 3-way with a 8 FR should I sacrifice constant directivity for low-end output by placing the W8-2145 in a flat baffle?

8. Are back to back RT-4001 tweeters a viable option?



Thank you for your time and consideration.


Regards

Denis

Pano 18th January 2021 08:13 PM

That's quite an ambitious build. A 3 ways can be difficult enough, 4 ways much more so.
Do you have a lot of experience with crossovers? And with OB crossovers? They are different.

The Fane might not be the best choice for the low end, with it's Qts of 0.57 and Fs of 41 Hz. Not bad, but there might be better choices. I suspect you'll not get 91dB/1W out of it after baffle losses.

CharlieLaub 18th January 2021 08:32 PM

This sounds like a project with great potential.

One of the best drivers for your system as the "upper mid" is the SB Acoustics SB17CAC in the 4 Ohm version. It's better than the Peerless you are considering. I have measured it hanging, nude (the driver, not me) and it is one of the best I have come across.

The Aurum Cantus AST2560 would work very well above the SB17CAC. It's a great tweeter for a dipole system after you remove the faceplace and rear felt (easy to do). It is superior to the Neo3.

For the 12" woofer, keep the baffle width no wider than about 24", which is twice the width of the driver. You should be able to use the driver a little lower than you were planning, e.g. around 150Hz would be fine, and this will give you some flexibility with the crossover point to the H-frame.

An H-frame that is 24" x 20" x 20" (long, height, width) would work well. Thicker walls are not really necessary for an H-frame. If you can use a higher Qts driver that is helpful. I think the Fs of the Fane model is too high if Qts is around 0.5-0.6. Do you already own this driver or can you consider another one?

Even though you have two miniDSP 2x4 available you will still need to properly design the crossover and take measurements on the drivers. What is your plan for that?

iamvalheru 18th January 2021 08:33 PM

I upgraded the tweeter and made new passive crossovers for my B&W DM602 S3, otherwise I've been playing around with a pair of Hawthorne Audio Silver Iris 15 in a 24" x 38" flat baffle for the last month using a miniDSP2x4 as a digital crossover.

As for the 15-400LF, as per the tech I talked to at Solen.ca, where I plan on purchasing most if not all the components to make these since they are local to me, he said that they actually measure closer to Qts 0.64.

The simulations I ran in Basta using a the same baffle and a Qts of 0.57 for the 15-400LF predicts a near identical response to both the Eminence Beta-15A (Qts 0.58) or the Fane 15-250 (Qts 0.73).

To keep the package as small as possible, I am also considering using a single Goldwood GW-1858 in an H-frame, but this would probably max out the 24" overall width I don't want to exceed including the frame to support the nude drivers that will ride the H-frame without touching it.

iamvalheru 18th January 2021 10:47 PM

Quote:

Originally Posted by CharlieLaub (https://www.diyaudio.com/forums/multi-way/366380-hybrid-frame-ob-nude-driver-post6494509.html#post6494509)
This sounds like a project with great potential.

One of the best drivers for your system as the "upper mid" is the SB Acoustics SB17CAC in the 4 Ohm version. It's better than the Peerless you are considering. I have measured it hanging, nude (the driver, not me) and it is one of the best I have come across.

The Aurum Cantus AST2560 would work very well above the SB17CAC. It's a great tweeter for a dipole system after you remove the faceplace and rear felt (easy to do). It is superior to the Neo3.

For the 12" woofer, keep the baffle width no wider than about 24", which is twice the width of the driver. You should be able to use the driver a little lower than you were planning, e.g. around 150Hz would be fine, and this will give you some flexibility with the crossover point to the H-frame.

An H-frame that is 24" x 20" x 20" (long, height, width) would work well. Thicker walls are not really necessary for an H-frame. If you can use a higher Qts driver that is helpful. I think the Fs of the Fane model is too high if Qts is around 0.5-0.6. Do you already own this driver or can you consider another one?

Even though you have two miniDSP 2x4 available you will still need to properly design the crossover and take measurements on the drivers. What is your plan for that?


I’m already a user of REW with a UMIK-1, and I recently purchased a Dayton DATS V3 that I still need to unwrap and read on how to use it.

I am open to other 15” woofers for the H-frame, the Fane 15-400LF and the 15-250 were the recommended drivers by Solen, and I was planning on using the 15-400LF since the Fs was lower and has more Xmax Vs the 15-250, what are you recommending instead?

For the AST2560 and the SB17CAC, which 12” do you recommend to put in a flat baffle and crossover point?

Are there any advantages to go MTM with the AST2560 and the SB17CAC?


Thank you.

jjasniew 19th January 2021 12:04 AM

I see both your designs have a crossover point at 2.5k. I realize it's almost a "religious" belief, but some say to keep xover out of the "sacred" 1 - 8 kHz space. Seems easy enough to do.

Any particular reason to have a xover point at 2.5k? It's a pretty common area to cross and - if there's any actual merit to the belief - your new design might end up sounding like a lot of other more ordinary speakers in a particular way. FWIW,

iamvalheru 19th January 2021 01:51 AM

2500 Hz seems to be the sweet spot between most ribbon tweeters and mid range woofers.

I don't know of any 6-8" woofers that you can crossover at 8K+ other than full range drivers, and at that frequency what happens to constant directivity?

Pano 19th January 2021 03:48 AM

Eminence Beta-8 Super easy to use up to 5K and needs just a small inductor to flatten it. Take over with a ribbon or horn above 5K. Very clean driver. It's probably not fancy enough for most people, but it's a very clean driver and easy to use.

Pano 19th January 2021 03:56 AM

In my first successful OB speakers I ran Selenium 15s and was very happy with them. They are no longer made (and mine were crushed in a move) but the PRV Audio 15W700 is very close. Qts is similar to your Fane but with a lower Fs. Just another direction to look.

The Goldwood 18 is nice, especially if you use 2 per side. :)

iamvalheru 19th January 2021 01:55 PM

That PVR15W700 is really interesting, now to find someone that sells them in the frozen north without paying more for shipping, duties and fees than the actual product...


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