DIY Audio Projects Forum

Here are some progress photos of the CommonSense Audio Monitor MkII bass reflex speaker enclosure that I am putting together to be used with the Audio Nirvana Classic 8 full range speaker driver.


The plywood is 3/4 inch (19 mm) thick multiplex (11 ply) birch. The price is $40 (Canadian) per 4' x 8' (1.2 x 2.4 m) sheet (purchased from Rona). The birch plywood is fairly void free, but the outer veneers are virtually paper thin. This birch plywood is not the superior quality of a true Baltic birch plywood, but it is good quality and a very good value at this price.


To construct the bass reflex speaker enclosure, the plywood pieces were simply butted together, glued and well clamped.


For the damping material an R12 insulation was used and is held in place using 12 mm staples at about 4 inch spacing. This seems like it will work really well as an acoustic dampening material.




And gluing the final piece of birch plywood to finish up the bass reflex speaker box.



I was pretty happy with the end result of the speaker box. There was a little excess to trim off with a flush trim router bit on one end. The speaker ports have a very small roundover. T-nuts are used for the driver.



For the finish I am planning on using a dark "Ebony" Minwax oil stain. I am thinking a dark finish will help to hide the plywood laminations on the edges. Before staining I'll apply Minwax prestain wood conditioner to prevent blotching. Two coats of ebony stain. Then I buff with ultra fine steel wool #0000. To finish I am thinking a coat of a polyurethane. I should get that done this weekend and I'll post photos.

Cheers

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The photo below shows the birch plywood enclosures after staining with Minwax Ebony. I think it turned out pretty good. When I opened up my can of polyurethane it had already hardened. At the store I picked up a tin of "Wipe on Poly". I'll try a coat or two of that before I finish up the speakers. The back panel will have insulation damping as well. None on the front baffle.

_________________
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excellent workmanship.

Merry Christmas everyone.

After having had to put this project (and others) on pause for some time in order to attend to some home repairs and renovations, I finally got a chance to resume work over this past week to finish up this speaker project. Stain was applied to the cabinets in the fall and for the final finish I used 2 coats of wipe-on poly. This product works real well with no streak so I don't imagine I will be using thick brush on poly anymore.

See the attached photo of the finished speakers in the workshop.

I used a dual binding post speaker plates on the lower rear of the speaker boxes. The top speaker binding posts are wired directly to the Audio Nirvana Classic 8" full range speaker driver. The bottom speaker binding posts lead to a passive BSC (Baffle Step Compensation) circuit. This way the listener has the option of hooking the fullrange speaker driver to the amp or to employ the use of the passive baffle step compensation circuit. This idea is from the Fostex FE127E bass reflex speaker project by Rabbitz. I'll post more details of the BSC once I've had a chance to crop the photos.

So far I have the speakers in the basement rec. room sitting inverted on my back loaded horn speakers. Not an ideal room or setup, but so far I'm liking what I am hearing. The "bookshelf" speakers are tall enough I think these may work best sitting right on the floor and tilted back aimed at the listening position.

I should get a chance to move these upstairs in the next day or so and a listening report will follow.

Cheers

_________________
[ DIY Mains AC Power Cable Cord ] - [ Gobo LM1875 Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]

Attached below is a photo of the baffle step compensation network. Using the dual binding post speaker plates
gives the listener the option of hooking the fullrange speaker driver to the amp or alternatively to use the passive baffle step compensation circuit.



Here are the speakers sitting inverted on a pair of back loaded horn speakers. Not the ideal setup, but ok to break in the drivers. Tonight they will be moving upstairs into the main listening room. I will try the bookshelf speakers on stands and also on the floor tilted back towards the listening position. I'll have comments about the sound after I get some good listening upstairs.

_________________
[ DIY Mains AC Power Cable Cord ] - [ Gobo LM1875 Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]

The speakers finally made it out of the basement and into the upstairs. Photo below shows a close up of the finished speakers. I'm really pleased with how they turned out, but would have preferred a matt finish over the semi-gloss.



So the open baffles only stayed connected for about a week and have now been displaced by the bass reflex speakers as I give them a good evaluation period. The timing is good as it allows me to pull apart my bi-amp set-up so I can check the bias on the F5 and I can reset the LED my nephew pushed into the enclosure. I appreciated that because when I was his age I was great at destroying things!

I started with the speakers on stands but prefer them on the floor and tilted back towards the listening position. See the photo for the setup.



Don't be fooled by the glorious rays of sunshine on the other side of the window. When that photo what taken is was about -34 Celsius! The only good news about that is it makes my class-A amplifiers 100% efficient as the waste heat is put to good use.

I really like how the AN drivers sound. Fostex drivers may initially sound more detailed but listener fatigue sets in rather quick. With the AN drivers, the higher frequencies are much more balanced and I find the drivers enjoyable to listen too for long periods of time. The bass is not where I expected it to be for an 8" driver but they are still in the break-in period. When I last measured, Fs was about 10Hz higher than spec but I'm thinking that may be due to the basement temp being a few degrees cooler than room temp. In the next week or so I will mic the in-room response and post a more detailed evaluation.

Amplification in the photo is a pair of OddWatt OddBlocks KT88 and the playback sources are a CDP and Raspberry Pi 3 with Rune Audio.

_________________
[ DIY Mains AC Power Cable Cord ] - [ Gobo LM1875 Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]

what no roundover on those box corners aren't you scared of the dreaded "diffraction monster"

are the blue pillows in the corners effective bass traps?

10+ gran for this speaker set, beautifull

Hi turk - I considered rounding over the edges, but only because I had the tools to do so. However, I opted against it because I didn't want to expose the plywood laminations. However, do note that I did do a slight roundover on both ends of the tuning port. A roundover of the port ends is actually an important detail in my experience.

The ugly shag pillows were on the way to the garbage but instead they ended up in the corner. I doubt they do much, but I figured something is better than nothing. I've been using an RTA to measure the speaker setups and the room is reasonably neutral, so while rooms treatments are on the to do list, they are currently a low priority. When I had more time I would tinker more, but now when I get free time, I tend to sit down and relax with some music.

Thanks for the compliment KochiyaYamato. Wood working is new to me and I am pleased with the results of this one.

Regarding the speakers, I have listened more and am enjoying the speakers, however, the bass is not where I would like it for this size of driver. My recommendation would be a larger cabinet and a lower tuning. Based on quick calcs of the enclosure dimensions, box tuning (not considering the damping material) is about 70Hz. Regarding the enclosure size, these bookshelf speakers essentially occupy the same footprint as a tower loudspeaker would and the increased volume would be beneficial. I also think this driver would be a good candidate for a double bass reflex cabinet, similar to the dimensions of that for the Fostex FE206En. This weekend I will get the RTA out and also sweep the impedance so I can compare my subjective comments to the measurements.

_________________
[ DIY Mains AC Power Cable Cord ] - [ Gobo LM1875 Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]

Gio:

A couple of questions for you after reading your post. Did you hear a noticeable difference with/without the BSC? Your last post mentioned changing the enclosure size to increase it, how much would you increase the dimensions? My reasons for asking is that I have the same drivers and plans that I got from David Dicks. Did you by chance dampen the driver baskets, similar to the Fostex 206 mods?

I too have a similar pair of BLH speakers using the 206 drivers, with the mods and have them positioned off center. I read these drivers can be fatiguing to listen to over a period of time. Anyway slightly off topic, I would like to get your thoughts on the MKII design as I am looking for my next enclosure project.

Thanks,
Patrick