Cheap and FAST OB, Literally - diyAudio
Go Back   Home > Forums > Loudspeakers > Full Range

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 26th January 2014, 01:36 AM   #1
xrk971 is offline xrk971  United States
diyAudio Member
 
xrk971's Avatar
 
Join Date: Oct 2012
Location: Virginia
Default Cheap and fast FAST bi-amped OB

Edit: latest results with 6 driver slot loaded woofer - see post 67.

Click the image to open in full size.

Click the image to open in full size.

Having a bunch of Vifa TC9FD's in hand from when they had the sale for $10 ea, and a few more of the PE 6.5 in polycone woofers (part 299-609) for $4.88 ea lying around... I thought I should try a FAST open baffle, that can be made in less than 1 hr. Having measured both of these drivers in a 24 in x 36 in cardboard baffle before, I knew they had very flat responses, and being high Qts drivers would lend themselves to an OB. I also happen to now have a miniDSP to handle the XO and EQ duties, and I planned to bi-amp them. I am convinced that messing with huge inductors, and huge poly film caps for a passive XO will end up costing just as much as a minDSP and a pair of class D amps.

I happened to have some double-wall corrugated cardboard on hand that measured 12 in x 18 in. Guess what, that is now my OB baffle size. I had some more cardboard that I used to make some wings and the stand for the baffles. These ended up as 8 in deep at the base and going to 3 in deep 15 in up. I gave a tilt backwards to add stability and aim it up. The 6.5 in woofer is mounted 5 in from the bottom at the middle. The Vifa fullrange is mounted 5 in from the top and 4.5 in from one of the edges. I made it asymmetric to reduce diffraction. I added a 2.75 in deep cross brace on the back that will also come in handy for the binding posts. Everything was cut and tacked with a few points of hot melt and glued with Titebond at all seams. Cutting and gluing took 30 minutes. Screwing the drivers in and adding crimped connectors took another 15 minutes. Waiting for the glue to dry took 3 hours.

I tried running both drivers in parallel and full range to see what it sounded like - just a terrible mess. I then connected the drivers in a bi-amp configuration and driven by the miniDSP with a 24 dB/oct XO at 300 Hz.

The miniDSP setup took 15 minutes. Taking a measurement with the mic showed that it was pretty good but had a few minor dips and peaks that were easily EQ'd out. The bass extension is natural - no EQ'ing needed - it really does go to 50 Hz with the modest wings.

Here is the frequency response and distortion - nice flat response and low THD from the Vifa above 300 Hz. Below 300 Hz, the 6.5 in driver's cone excursion is starting to get taxed and hence THD goes up. Adding more woofers will reduce excursion and reduce THD. If I had more drivers, I would have used two in series for 8 ohms.

Click the image to open in full size.

Here is the impulse response - doesn't get much better than this.

Click the image to open in full size.

So how does it sound? Fantastic! It has some very nice clean dynamics capable of reproducing fast transients and percussion. It doesn't go very loud as the Vifa is nominally 85 dB at 2.83V but perfect for near field or low level listening. The sound stage is what is perhaps the best part - very wide and I can close my eyes and pinpoint the location of the singer, the instruments, and where they are positioned on the stage.

Anyhow, not including glue drying time, all this was done in about 90 minutes. Cost is $20 per speaker including binding posts. Now that is a cheap and fast FAST that sounds great and measures well.
Attached Images
File Type: jpg Cardboard-OB-00.jpg (205.3 KB, 3726 views)
File Type: jpg Cardboard-OB-01.jpg (170.3 KB, 1679 views)
File Type: jpg Cardboard-OB-02.jpg (170.3 KB, 1325 views)
File Type: png Cardboard-OB-03.png (135.3 KB, 4045 views)
File Type: png Cardboard-OB-04.png (46.7 KB, 3385 views)

Last edited by xrk971; 6th March 2014 at 01:30 AM.
  Reply With Quote
Old 26th January 2014, 11:51 AM   #2
xrk971 is offline xrk971  United States
diyAudio Member
 
xrk971's Avatar
 
Join Date: Oct 2012
Location: Virginia
Default Sound Clip

Here is a recording of some blues for you to get an idea of the sound.
Let me know what you think.
Attached Files
File Type: zip Cardboard-OB-Clip-03.zip (878.6 KB, 223 views)
  Reply With Quote
Old 26th January 2014, 01:56 PM   #3
wesayso is offline wesayso  Netherlands
diyAudio Member
 
wesayso's Avatar
 
Join Date: Jul 2007
Good testimony for the Manzanita OB speaker!
Fast, fun, Inexpensive OB project - Page 46 - diyAudio
(and the later version with the GRS 15" woofer)
  Reply With Quote
Old 26th January 2014, 02:06 PM   #4
xrk971 is offline xrk971  United States
diyAudio Member
 
xrk971's Avatar
 
Join Date: Oct 2012
Location: Virginia
Quote:
Originally Posted by wesayso View Post
Good testimony for the Manzanita OB speaker!
Fast, fun, Inexpensive OB project - Page 46 - diyAudio
(and the later version with the GRS 15" woofer)
The Manzinita was the inspiration but I could never get over the hurdle of spending close to $200 on coils and caps for the cross over. The 15 in woofer also has a huge visual presence that makes the speaker a little too visible. I think qnty 6 x 6.5 in woofers have the same Sd as a single 15 in woofer and can have better dynamics and lower THD. I will start increasing the number of 6.5 in drivers to achieve the desired effect and I think I have a way to set them up in a push pull slot loading design that is modular.

More to come...
  Reply With Quote
Old 26th January 2014, 08:49 PM   #5
xrk971 is offline xrk971  United States
diyAudio Member
 
xrk971's Avatar
 
Join Date: Oct 2012
Location: Virginia
I am thinking of going with something along the lines of this aproach by Nelson Pass "The slot loaded Open Baffle": The Slot Loaded Open Baffle Project Article By Nelson Pass

But do it in modular 2-drive units that can be stacked as you need more surface area.

Click the image to open in full size.

Click the image to open in full size.
  Reply With Quote
Old 26th January 2014, 11:00 PM   #6
diyAudio Member
 
Join Date: Jul 2013
Quote:
Originally Posted by xrk971 View Post
Having a bunch of Vifa TC9FD's in hand from when they had the sale for $10 ea, and a few more of the PE 6.5 in polycone woofers (part 299-609) for $4.88 ea lying around... I thought I should try a FAST open baffle, that can be made in less than 1 hr. Having measured both of these drivers in a 24 in x 36 in cardboard baffle before, I knew they had very flat responses, and being high Qts drivers would lend themselves to an OB. I also happen to now have a miniDSP to handle the XO and EQ duties, and I planned to bi-amp them. I am convinced that messing with huge inductors, and huge poly film caps for a passive XO will end up costing just as much as a minDSP and a pair of class D amps.

I happened to have some double-wall corrugated cardboard on hand that measured 12 in x 18 in. Guess what, that is now my OB baffle size. I had some more cardboard that I used to make some wings and the stand for the baffles. These ended up as 8 in deep at the base and going to 3 in deep 15 in up. I gave a tilt backwards to add stability and aim it up. The 6.5 in woofer is mounted 5 in from the bottom at the middle. The Vifa fullrange is mounted 5 in from the top and 4.5 in from one of the edges. I made it asymmetric to reduce diffraction. I added a 2.75 in deep cross brace on the back that will also come in handy for the binding posts. Everything was cut and tacked with a few points of hot melt and glued with Titebond at all seams. Cutting and gluing took 30 minutes. Screwing the drivers in and adding crimped connectors took another 15 minutes. Waiting for the glue to dry took 3 hours.

I tried running both drivers in parallel and full range to see what it sounded like - just a terrible mess. I then connected the drivers in a bi-amp configuration and driven by the miniDSP with a 24 dB/oct XO at 300 Hz.

The miniDSP setup took 15 minutes. Taking a measurement with the mic showed that it was pretty good but had a few minor dips and peaks that were easily EQ'd out. The bass extension is natural - no EQ'ing needed - it really does go to 50 Hz with the modest wings.

Here is the frequency response and distortion - nice flat response and low THD from the Vifa above 300 Hz. Below 300 Hz, the 6.5 in driver's cone excursion is starting to get taxed and hence THD goes up. Adding more woofers will reduce excursion and reduce THD. If I had more drivers, I would have used two in series for 8 ohms.

Click the image to open in full size.

Here is the impulse response - doesn't get much better than this.

Click the image to open in full size.

So how does it sound? Fantastic! It has some very nice clean dynamics capable of reproducing fast transients and percussion. It doesn't go very loud as the Vifa is nominally 85 dB at 2.83V but perfect for near field or low level listening. The sound stage is what is perhaps the best part - very wide and I can close my eyes and pinpoint the location of the singer, the instruments, and where they are positioned on the stage.

Anyhow, not including glue drying time, all this was done in about 90 minutes. Cost is $20 per speaker including binding posts. Now that is a cheap and fast FAST that sounds great and measures well.
How much of a challenge would it be for you (assuming you were willing to take the time to do it) to design a passive crossover for this?

I'd love to try an OB, and the cost of the drivers is great (and I already have the Vifas), but I would need to go passive, at least for the time being. Is that something you could (or would be willing to) do?
  Reply With Quote
Old 27th January 2014, 12:23 AM   #7
xrk971 is offline xrk971  United States
diyAudio Member
 
xrk971's Avatar
 
Join Date: Oct 2012
Location: Virginia
I actually have the design for the passive line level XO (PLLXO) for bi amping with the tpa3116d2 (30k ohm input impedance). You do not want to go with passive speaker level XO as the price on that would be almost $200 dollars. Also, I would suggest you build the Manzanita OB if that is what you want to do. If you go with bi amping and PLLXO the amps cost $30 and the XO parts about $10. The XO has to be designed with the amp in mind as the input impedance sets the values of the resistors and capacitors in the XO.

Are you good with getting the two class D amps as part of the design? Seriously is cheaper than big coils and caps.
  Reply With Quote
Old 27th January 2014, 01:01 AM   #8
diyAudio Member
 
Join Date: Jul 2013
Well, I can probably figure it out (one way to learn). I just recently picked up a like new Behringer 2496 active crossover (for a price I could not refuse), so maybe that would be a good way to cut my teeth???

And, yes, I plan on picking up a couple of class D amps (probably two of the the little Lapai 2020 that most people speak highly of).

Your thoughts?

And, BTW, thank you.

Coincidentally, I spent a good portion of this afternoon reading the thread on the Manzanita OB. I am impressed.

Beau

Last edited by BeauB; 27th January 2014 at 01:03 AM.
  Reply With Quote
Old 27th January 2014, 01:23 AM   #9
xrk971 is offline xrk971  United States
diyAudio Member
 
xrk971's Avatar
 
Join Date: Oct 2012
Location: Virginia
Quote:
And, yes, I plan on picking up a couple of class D amps (probably two of the the little Lapai 2020 that most people speak highly of).

Your thoughts?
Don't get the Lepai 2020, the TPA3116D2 is a superior sounding state of the art class D amp. There is a huge thread on it in the class D forum. Do a search in Aliexpress for TPA3116D2 and you will see lots of choices. Pick the YJ red board for $15 (add your own laptop brick for PS). If you want a boxed amp with knobs that will cost you $50 ea. It is a true 40 watt/ch (<0.1% THD) into 4 ohms with 19 volt PS. Get two of them for $30 shipping included. It may take 3 weeks to arrive from China. It is important to get the amp with 26 dB gain as that will make the input impedance 30kohms for the PLLXO.

If you have the Behringer DEQ then you are all set for EQ but that doesn't handle the XO. I have heard people say the analog front and rear ends on the DEQ2496 is not very good... But many people don't seem to notice.
  Reply With Quote
Old 27th January 2014, 01:37 AM   #10
xrk971 is offline xrk971  United States
diyAudio Member
 
xrk971's Avatar
 
Join Date: Oct 2012
Location: Virginia
Default 300 Hz PLLXO Design for 30 kohm impedance amp

Here is the design for the PLLXO. There is a -12dB attenuation in the line level signal from the source through the XO so be sure you drive it with something that has some oomph - like a real RCA line out from a CD player deck or a receiver. An iPod won't cut it. Also, some 1/4 inch jack studio headphone monitor outputs from receivers or CD players can also work to drive this as they are low impedance (30 ohm drive) and have a built in volume knob if you are going straight from a CD player.

This design will only work correctly with an amp that has a 30kohm input impedance - the YJ red board TPA3116D2 amps.

Here is the PLLXO schematic:

Click the image to open in full size.

Here is the predicted transfer function and phase:

Click the image to open in full size.

For the PE 6.5 inch woofers, I suggest using six of them to get the equivalent of a 15 inch woofer. Wire them 3 in series x 2 in parallel for 6 ohms which this amp should have no problem driving. The efficiency of 6 drivers from an 88 dB driver should be about 92 or 93 dB - perfect match for an 85 dB full range to handle the baffle step losses and OB fall-off.

I will post the design for the slot-loaded woofers later but if you look at the Nelson Pass article above you will get the idea.
Attached Images
File Type: png PLLXO-300-HZ-V03-30KOHM.png (20.7 KB, 2835 views)
File Type: png 300-Hz-PLLXO-30kohm-v2.png (18.3 KB, 2821 views)
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Fast, fun, Inexpensive OB project Pano Multi-Way 1107 Today 03:05 AM
OB woofer (FAST) for tube amps dhieber Full Range 14 15th January 2009 03:44 AM
fast tight small OB sub inrank Subwoofers 3 31st July 2006 01:19 PM


New To Site? Need Help?

All times are GMT. The time now is 06:24 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2