The best affordable DIY open baffle loudspeaker I've listened to so far.

JBspeakerman · « **Reply #20 on:** 10 Dec 2011, 04:40 pm »

OK, trying to post a few pictures of the Ultra to help fill out the project. The views are self explainatory.

panomaniac · « **Reply #21 on:** 11 Dec 2011, 05:53 pm »

Thanks for the photos. Can you review the crossover for us? It looks pretty simple.

Æ · « **Reply #22 on:** 11 Dec 2011, 10:09 pm »

Quote from: JBspeakerman on 10 Dec 2011, 04:40 pm

OK, trying to post a few pictures of the Ultra to help fill out the project. The views are self explanatory.

Any reason why the tweeter cannot be closer to the woofer?

JBspeakerman · « **Reply #23 on:** 12 Dec 2011, 03:24 pm »

The driver locations on the baffle are based on a combination of factors. The tweeter is offset from the center line to help with imaging, diffraction smoothing and proper OB loading. The position on the baffle provides part of the low end roll off slope and frequency knee. Also, I set it 38" off the floor to be on axis for a seated listener. The woofer location is just off center vertically to help minimise rear standing waves, maximise OB loading (lowest possible F= for the baffle - wing combo) and high enough off the floor to minimise floor bounce. One could move the woofer upward closer to the Vifa. You would want the final woofer position to remain off center vertically, above center if it is moved closer to the Vifa. There may be some modification required to the crossover if it is moved. The crossover is optimized for the current driver vertical separations. Hope this all helps.

Rudolf · « **Reply #24 on:** 12 Dec 2011, 08:50 pm »

Quote from: JBspeakerman on 12 Dec 2011, 03:24 pm

The woofer location is just off center vertically to help minimise rear standing waves, ... and high enough off the floor to minimise floor bounce. One could move the woofer upward closer to the Vifa.

Funny. Is moving the woofer to the floor no longer the best way to minimise floor bounce? Was Allison wrong?

Rudolf

JBspeakerman · « **Reply #25 on:** 12 Dec 2011, 09:53 pm »

There are many aspects to any given design. With the ultra's design, if the woofer were mounted as low on the baffle as possible, the woofer - tweeter vertical separation would become a major issue. Maintaining the Vifa at around 38" above the floor for me IS very important to the overall performance and power response of the system. There is a limit to crossover correction capability relative to vertical separation of the two drivers. Somewhere around 15" of center to center separation seems to be the limit. Otherwise major lobing issures begin to degrade the SQ. The accoustic crossover point is centered around 550 Hz, but the up woofer contribution reaches over 1 KHz, although it is down about 18 DB at that point. The Vifa is contributing down to about 175 Hz. (Down about 24 db at that point in overall power response).

Larger separation was not possible when maintaining a simple crossover topology - cost. So the best trade off was to mount the woofer up higher. With the woofer contributing well into the mid range, mounting it higher gets it's mid range output closer to the overall speaker axis. And with an OB woofer that is playing into the mid range, one has to deal with rear radiation issues including absorption than can occur with residential carpeted surfaces, front also.

Bottom line is the woofer is up where it is for a number of reasons. Mr. Allison is just fine when operating in a traditional monpole environment..

Æ · « **Reply #26 on:** 12 Dec 2011, 10:12 pm »

Quote from: JBspeakerman on 12 Dec 2011, 09:53 pm

There are many aspects to any given design. With the ultra's design, if the woofer were mounted as low on the baffle as possible, the woofer - tweeter vertical separation would become a major issue. Maintaining the Vifa at around 38" above the floor for me IS very important to the overall performance and power response of the system. There is a limit to crossover correction capability relative to vertical separation of the two drivers. Somewhere around 15" of center to center separation seems to be the limit. Otherwise major lobing issures begin to degrade the SQ. The accoustic crossover point is centered around 550 Hz, but the up woofer contribution reaches over 1 KHz, although it is down about 18 DB at that point. The Vifa is contributing down to about 175 Hz. (Down about 24 db at that point in overall power response).

Larger separation was not possible when maintaining a simple crossover topology - cost. So the best trade off was to mount the woofer up higher. With the woofer contributing well into the mid range, mounting it higher gets it's mid range output closer to the overall speaker axis. And with an OB woofer that is playing into the mid range, one has to deal with rear radiation issues including absorption than can occur with residential carpeted surfaces, front also.

Bottom line is the woofer is up where it is for a number of reasons. Mr. Allison is just fine when operating in a traditional monpole environment..

I still don't like the tweeter separated so far from the woofer.

Mudjock · « **Reply #27 on:** 12 Dec 2011, 10:30 pm »

At a crossover frequency of 550 Hz, the driver spacing looks manageable. While one might prefer closer, the impact of other factors would probably supercede that of the drivers being as close as possible.

JBspeakerman · « **Reply #28 on:** 12 Dec 2011, 10:41 pm »

You can move the woofer closer by around 2". Any more you will over lap into the Vifa counter bore on the rear of the baffle. You can barely see the dotted layout circle surounding the Vifa on the pic I posted a couple of days ago. The rear counterbore is 7" diameter IIRC. Not as much un unused baffle space as one would think!

scorpion · « **Reply #29 on:** 14 Dec 2011, 01:45 pm »

By introducing the GRS woofer the 'Manzanita' is approaching the normal 'MJK' type of OB speaker: http://www.quarter-wave.com/OBs/OB_Design.pdf
No more relying of 'Phantom' sounds in the deep hollow between bass and treble, and frankly I don't think the second version was really on target.
For bass quality I think it is a step down from the Peerless unit, for quantity it might be OK but you can't really approach any bass heaven with the GRS, 90 dB will not be attained at 40 Hz for instance in X-max limits.
No doubt the Vifa unit is a real find and it is also about 5 dB more efficient than the single GRS so two bass speakers might be more appropiate for matching.

I have been a bit famous for chasing MJK's Alpha15 recommendation for quality OBs. Judging from email and other support I may be right, So it is the question of the GRS sound quality. Not compared to quality units it will be OK but I certainly doubt that the real high quality will be there. For very little money anyway you certainly will be enjoying uncomparable OB sound.

/Erling

JBspeakerman · « **Reply #30 on:** 14 Dec 2011, 04:59 pm »

Interesting comments Scorpion. What, or should I ask which "second version" are you refering to?

As for comparing the Peerless to the GRS, today the Peerless is over 3 times the price and is still a bargain! However, the GRS is every bit the sleeper-performer for the money as are the Peerless or the Vifa. I think once a few of the Ultra's are built, most builders will be more than satisfied with the performance it provides, especially when one factors in the simplicity & cost. As for "channelling MJK" with the Ultra, that was not what is intended. When working up a viable low cost, bang for the buck OB capable of extened bass response, you are limited to large diameter, small motor woofers. Simply a cost reality. And the GRS can deliver around 93.5 db (96.5 FOR A STEREO PAIR) at 40 Hz in a typical 1/2 space residential setting. This is assuming 0.4 meter path difference, 860 sq cm cone area and a usable PP xmax of 9 MM. The 9 mm value is based on listening and test measurements. Not bad for $130 speaker! The Manzanita will play a couple of db louder at 40 Hz. It is capable of 18 mm p-p, but the 12" Peerless has less cone area on a way smaller baffle.

For most users and most music, a pair of GRS-15's will be very usable. And, you must remember the Vifa is pretty much reached it's clean peak output in the around 95 db or so on the lower end of it's operating range.

hoxuanduc · « **Reply #31 on:** 14 Dec 2011, 05:12 pm »

John,

Quick question. I did a quick check on the BOM and it appears PE 266-960 is a 20mH inductor, not 16mH. Can you clarify?

Also, can you connect 18ga inductors in series to arrive at the same inductance? Would the DCR matter much in this case? Maybe cheaper this way.

Thanks,

Duc

JBspeakerman · « **Reply #32 on:** 14 Dec 2011, 05:46 pm »

Thanks for noticing. Typo on my part. 20 Mh is correct. You can use an 18 Ga. if you wish. You may have to adjust the Vifa pad resistor to bring the Vifa output down to match. Difficult to predict exactly how much. I need to experiment a bit to see if it is enough to mater.

scorpion · « **Reply #33 on:** 14 Dec 2011, 06:59 pm »

I won't argue details about your speaker because I do think it very good value for money.
The second version I am referring to is with Peerless and Vifa and this I think had too far crossover values to really be able to sound anywhere what it really could have been with better crossover values !
Now with nothing presented, only 550 Hz hinted, most is in the air.

/Erling

JBspeakerman · « **Reply #34 on:** 14 Dec 2011, 07:27 pm »

Yes, the Manzanita Vifa version crossover values do look strange. However, after hundreds of hours of listening, measurements and god knows how many configurations, the current values are what work. Very flat on axis and power response. A lot of reasons for this. Do not have the time today to fully discuss. One reason I demo my creations at DIY and LSAF and similar venues is to get as many opinions as possible. Gut check if you will. Good & bad. Learn the most from the bad, what little there has been.

scorpion · « **Reply #35 on:** 14 Dec 2011, 07:55 pm »

Now this is OK !
If you believe my honest will I won't argue yours !
It works and that's it !

/Erling

JBspeakerman · « **Reply #36 on:** 15 Dec 2011, 12:11 am »

Trying to upload a couple of Ultra dimensional pencil drawings but not having much luck. Have reduced them to under 50K so size should not be the issue. Any suggestion?

panomaniac · « **Reply #37 on:** 15 Dec 2011, 12:52 am »

John emailed me the sketch, let's see if I can upload it here.

Mmaxed · « **Reply #38 on:** 15 Dec 2011, 04:19 am »

Did I miss the schematic for the cross over? I see the BOM but not the layout for the Ultra.

JBspeakerman · « **Reply #39 on:** 15 Dec 2011, 07:20 pm »

I am working on the final crossover diagram with notes. I hope to post by this weekend. John