[danvprod]

Was asked on the low-wattage systems pics thread to provide a little more information about my latest build. Here she is. The system is:

JBL 2226J 16 Ohm woofers in a 3.9 cu ft. BR enclosure tuned to 45 Hz. Enclosure is made based on the plans from boxnotes/subwoofer builder. Pretty simple construction. 3/4" MDF all around, minimal external seams, 1x2 bracing inside, dual thickness baffle, PVC ports -- 2 x 5.5" 4" wide with a 1/4" radius in the front. One tube of latex sealant caulk around all the seams per speaker -- Loctite polyseamseal -- pretty solid stuff, and easy cleanup.

JBL 2445J Compression driver coupled with a 250 Hz Tractrix horn. 2405 Super tweeter with Alnico magnet. Passive 12 dB/octave crossover to the SuperTweeter at 16 kHz. Otherwise bi-amped with a miniDSP doing the dividing. X-over is a bit weird right now but sounds good.

The 2226J as is has a rising response in the midrange in a small enclosure like this one. So based on some advice on the Lansing Heritage DIY forum, I currently have a 80 Hz LP filter 6dB/octave, a couple dB boost at 50 Hz, and a 12 dB/octave HP filter at 40 Hz.

The JBL 2445J has a 24 dB/octave at 1 kHz. I am adding about 4 dB SHP at 6k to lift the HF response. Note, the super tweeter is not in a final location, and as-is is completely occluded by the midrange horn.

Not completely happy with the crossover, but am enjoying listening in the meantime. This is my first horn system, I've always dreamed about having one, so when I had the opportunity to purchase all of these components at a very good deal, I jumped at the opportunity and sold off all that I could, decommissioning my open baffle system in the process.

So still several things left to do:

• Finish the bass enclosure, still need to be sanded, rounded, sealed and painted. That will wait for spring.
• Mount binding posts on the bass cabinets, lined with R13 insulation. That should happen next week.
• Build a bracket for the 2" compression drivers. Book wedges are not a long term strategy.
• Build a super tweeter mount that will let him clear the midrange driver. Any ideas?
• Finalize miniDSP crossover settings.

Powering the speakers currently are a pair of Icon Audio 300B mono blocks for the CDs and Super Tweeters. A Rotel 1050B powers the LF Boxes. Decware preamp, miniDSP x-over rounds out the setup.

Here are measurements from my latest x-over settings (these are taken from an 8 position average around the listening position, in-room with 1/12 octave smoothing.) I'm not sure why the summed response has a lower HF response than the individual measurement, I may have had the SHP filter disabled for that measurement.

Anyways, thoughts and comments are more than welcome. I'd prob. say that I am 60% there on this setup, but it has amazing potential, more than any of the system's I've built in the past. I need someone to buy my H-Frame Alpha 15s now.

[danvprod]

Here is my idea for a mount for the super tweeter. This would be in two sections connected with bolts and rubber grommets between them for some vibration isolation. The 2" compression driver would be wedged in between the two sections, and then the super tweeter could be mounted from behind, and be in-line with the 2" driver's voice coil for time alignment. I'd also mount the super tweeter crossover behind to hide it from view. Using this setup, I'd also prob. wire up binding posts to the base of the mount.

Maybe I could make these out of some bamboo cutting boards or something.

[WireNut]

I like this build. Perhaps it’s due to owning a JBL 2245H in the past and knowing what those JBL’s can do.
Also, the large horn and super tweeter driver’s are very intriguing.

What I'm wondering about is driver time alinement. I've read over the years that driver voice coils need to be in-line or the drivers need to be offset to compensate for different efficiency's. Not sure how true or critical this is but seems to makes since. With a setup like yours it would be easy to move the top two drivers back and forth to your liking/room acoustics.

[WireNut]

and then the super tweeter could be mounted from behind, and be in-line with the 2" driver's voice coil for time alignment.

I see your also thinking about time-alinement  Good discussion topic.

[WireNut]

The 2" compression driver would be wedged in between the two sections, and then the super tweeter could be mounted from behind, and be in-line with the 2" driver's voice coil for time alignment.

I'm wondering if you could mount the top two drivers independently or at least be able to adjust them back and forth to suit your hearing/room conditions. Over the years due to room changes/your age/hearing/and equipment changes you might find that being able to move the top two drivers back and forth may be beneficial. At least that's what I've found in my 4 box system over the years.

If you plan on keeping this setup for a long time might be worth considering.
I think your setup has a lot of potential for years to come.
MY 2 cents.




 

[danvprod]

Yes, @Wirenut. My plan was to allow the driver units to be moved independently. Very good thoughts about time alignment, yes this is at the top of my mind currently. 

Did some more measurements this week and also tried to time-align the drivers. I did this by setting up a loop-back in REW and then measuring the individual drivers 1m from the box and looking for the peak in time without any delay. I did this with the crossover engaged in MiniDSP to account for the phase shift induced by the crossover. Woofer peak was 3.58 ms, tweeter 3.808 ms, delay set 0.3 on woofer to align.

2226:
80Hz 6 dB/oct LP
40Hz 12 dB/octave HP
0.3ms delay on woofer (matched IR peaks 1m from center of woofer/CD).

2445:
1000Hz 24 dB/oct HP

EQ:
2226:
60 Hz +4 dB Q2 Peak
160 Hz -6 dB to -8dB Q1 Peak

2445:
6000 Hz +8 dB High-Shelf.

In-room response from 8 position measurement per trace around listening position.

I still do not like the dip at the crossover frequency, I thought that would go away with the time alignment. I am also not taking into account the eventual contribution of the 2405s once I get them setup. That should extend my UHF response well past 20k.

[danvprod]

Some progress:

Following the guidance of a great thread on DIYAudio, I began experimenting with "Quasi-Optimal" crossovers, to better time-align the drivers given their physical offset.

Currently trying a La Cleach arrangement, which is:

3rd order Butterworth Low Pass, -3dB @ Fx*0.87 (+)
3rd order Butterworth High Pass, -3dB @ Fx*1.15 (-)
Offset = 0.22*c/Fx

I did end up having to add an additional 0.2ms delay to the woofer to get them into alignment, but as the measurements show, I am measuring good combination of the drivers in the crossover region:



Yesterday, I put together a simple bracket system to elevate the 2405 above the horns, and also to better align the voice coils of the CDs and the supertweeters, since they are being crossed over passively. I also flipped the polarity on the 2405 because of the 12 dB/octave phase shift. I'll have to confirm this with measurement.

I don't love the bracket, but it should work for now until I build something nicer.



My 300b amps are currently in for service, so I am running the CDs and STs with a ClassD amp, so I can't give an accurate impression of the improvements that the crossover and super tweeter bracket have brought to the final system, but I should have my amps back this week, so I will be able to judge then.

Open to ideas about improving the bracket.

[lokie]

Cool project. Thanks for sharing.

I 'm curious what the results would be if you turned the HF drivers and bracket upside down.... putting the tweeter below the Taxtrix horn.

Maybe too much reflection off the bass cab but you could raise it a little bit??? I'm thinking more coherency... but maybe not.

Are you using MiniDSP software and corresponding microphone. I'm awaiting a USB microphone to show up in the mailbox.

What are your general impression of the 2405?

[danvprod]

Hi, thanks @Lokie. Couple of thoughts.

You are right about the ideal placement of the 2405 under the 2445. But I'd have to change the bracket to take the weight of the CD, which is 40 lbs. The thin strips of wood aren't going to cut it. I know JBL makes some of those metal bolt brackets to hang the drivers, I need to see if I can find one of those, and then elevate the horn so that I can perhaps put the 2405 underneath.

The 2405 vertical dispersion is very narrow, so it should have no problem beaming through the horn and bass cab. My impression of the 2405 is that it adds quite a lot of detail to the system. More attack to drums, acoustical guitar cymbals. The system seems more dynamic and responsive now, but at the same time it is now a bit more taxing to listen too, and I may have to pad down the 2405 a few dBs. Will confirm with measurement.

I am using for measurement a Sencore microphone and either Room EQ Wizard, AudioTools IR (Studio Six Digital), Holmimpulse or ARTA. Holmimpulse is the easiest desktop program I've found to do the gated measurements and see the results visually, however I have some hardware issues with it (Mac system running it via parallels with a Apogee Duet). REW works on the Mac and I normally default to that. However, I like the GUI of Holmimpulse better.  The MiniDSP microphone should be pretty sweet, let me know your impressions of it.

[Russtafarian]

I have some of these parts in the garage.  Now you got me thinking...

[danvprod]

What do you have?

Seriously, I am amazed with what this system can do, reminds me of listening to big studio far-field monitors. Pretty cool what can be done with the MiniDSP, too.

[Russtafarian]

I have two 2225 woofers and two 2425 1" compression drivers rescued from an old church P.A speaker.  All drivers are still in great shape. 

Russ

[lokie]

The MiniDSP microphone should be pretty sweet, let me know your impressions of it.

I'm not getting the miniDSP microphone, I'm getting a Dayton Audio UMM-6

 I just finished version 1.0 of a new build utilizing an Altec 1" CD (802) in a 32b horn and a 15" Jensen Woofer.

The Altec is running out of gas around 9K so, I've been on the lookout for a 16 ohm 108db efficiency tweeter.

The overall sound is pretty darn good considering the room response is so ugly. So, my first step is to try to get some better measurements which you seem to have a pretty good handle on. I just slapped a xover together to get some sound going... trying to get more sophisticated going forward.

The MiniDSP looks like a fantastic tool to test different schemes. Which Mini DSP are you using/recomend for this purpose.

[danvprod]

I have the basic MinDSP-in-a-box the 2x4:

http://www.minidsp.com/products/minidsp-in-a-box/minidsp-2x4

Which is quite capable given the price. However the 4x10 HD may be the better buy if you want to keep it in your audio-chain full-time. I originally purchased the 2x4 so that I could prototype different crossover schemes without having to buy/build a lot of passive crossovers. It's paid for itself 10x over in component savings and time savings in the year that I have had it.

[lokie]

I have the basic MinDSP-in-a-box the 2x4:

Got it. Thanks

You're right...  that is reasonable.

[lokie]

Room EQ Wizard, AudioTools IR (Studio Six Digital), Holmimpulse or ARTA. Holmimpulse is the easiest desktop program I've found to do the gated measurements and see the results visually, however I have some hardware issues with it (Mac system running it via parallels with a Apogee Duet). REW works on the Mac and I normally default to that. However, I like the GUI of Holmimpulse better.

The Mic is in da house. Trying to decide where to start. Although I use Mac as a music server, I will be using my PC laptop for measurements.
I think I'll start with REW. Lots of online help including Youtube tutorials.

If you were me (meaning a complete neophyte), what would be the first measurement you would take?

Also, I'm a little confused as to room response software and speaker measurement software. My thought is to start w room response. Not even sure if I would need different mic for speaker measurements.

[versus rider]

Hi, that horn looks very much like a Jabo horn. I had  a pair of 400Hz Jabo's approx. 550mm diameter. looks like a pretty good frequency response you have there.

[danvprod]

Finally getting back to these after a few months. I sanded the bass cabs down, routed the edges, filled gaps with vinyl spackle and coated with duratex. The duratex is awesome. Goes on easily, creates a nice finish and no priming required. Very highly recommended.

[WireNut]

Hi Danvprod,

I remember commenting on this setup months ago. Haven't been able to read the whole thread lately, but I will asap. Not knowing your latest adventures until I have time to read the latest post, I'm glad to see them back here on AC and can't wait to read the latest comments. My first gut feeling was that you are on to something, I still feel that way. Can't wait to read these latest post asap.

   

[danvprod]

Here is how they look back up in my listening room. I still need to build a better mount for the 2" CDs and super tweeter. I want the midrange horn to be 10" or so higher and have the super tweeter mounted between the woofer and midrange. Next project...

Any ideas?