Constructing soffit boxes for the Alesis Monitor Two

[Gash]

Hello everyone. My design thread can be found in this thread.

As of lately, for the most part, my build has been moving along at a somewhat slow but steady pace. I am nearing completion but there are still some things left to think about and take care of. Right now I am in the process of building soffit mounting boxes for my pair of Alesis Monitor Two speakers and after some consideration I decided it might be a good idea to ask the forum about a specific addition to the completed box design.

I have used the information supplied in the Alesis Monitor Two reference manual (Alesis website) to build my soffit boxes and I have attached some pictures of the results in this post.

My question is in regards to the rear vent of the Monitor Two. I know there have been a few posts on this subject in the forum but none that I felt answered the question of how the rear vent interacts with the soffit box. So my question is... when the speaker radiates, as in my feeble attempt at an illustration below, will this not create an undesired effect in the interaction with the speaker box. Even if the speaker box has an appropriate hole for venting.

In my case I have placed my box vent "perfectly" aligned/centered with the speaker vent and the monitor two's are "almost" (read: ~2mm) flush to the back of the box.

My immediate thought was to either extend the speaker vent into the box vent or place some kind of padding at the back of the soffit box to absorb the undesired effect (but I am sure this would create an even greater boost in low end response). If you where to soffit this type of speaker - what would you do?

Any comments on the subject would be great! Thank you.

[Soundman2020]

From the manual, that appears to be a rear-ported speaker. I'm not sure if you can soffit mount those successfully.

If Barefoot is around, maybe he can answer that.

- Stuart -

[Gash]

From the manual, that appears to be a rear-ported speaker. I'm not sure if you can soffit mount those successfully.

If Barefoot is around, maybe he can answer that.

- Stuart -

Hi Stuart,

Thank you for replying! Indeed they are rear-ported in the way I attempted to illustrate in my crude SketchUp image. I have seen a few topics on soffit mounting rear-ported speakers here on the forum and from what I can digest it is possible to do and still achieve a good result. Also, when I (very briefly) spoke to Mr. Gervais about a year and a half ago, he told me it would work well. If done properly, that is.

Maybe I should have added to the initial post that the main reason for my question is that Alesis recommends, at least, six inches of free space behind the speaker in order for it to vent properly. I have gone a bit further and allocated seven inches from the rear of the box to the wall in the soffit.

[gullfo]

if you leave enough space in the back and enough vent space (usually top and bottom of the box) and have a way t omake some adjustments for the change in bass response, i believe a number of folks have both said soffit mounting speakers with rear ports and/or passive radiators will work. you just want to make sure you do not clog up the rear port or dampen the rear radiator because it will significantly change the loading.

http://www.johnlsayers.com/phpBB2/viewt ... 380&p=2427
http://www.johnlsayers.com/phpBB2/viewt ... 05&p=93054

could could construct the box and mount a speaker in it and make some measurements to see what the differences are.

[Gash]

Glenn,
Thank you for your response! I have made sure to allocate enough room to allow the speakers rear port to vent properly. What makes me somewhat doubtful is whether or not a small (<2mm) air gap between the back of the speaker and the box will have adverse effects on the monitor performance.

Since my soffit construction is not based on a design that requires me to permanently (I will allow for some loose definitions of the word permanent here...) fix the speaker box in place, I can allow myself to experiment with the type of box and it's relation to the monitors (i.e. I can, with relative ease, remove the speaker box and test other types of configurations). I still have lots of 19mm MDF material so it is no problem to build additional boxes.

You mentioned the top and bottom vents... now this is something which I have been thinking a lot about lately. In my current design I have created the rear port hole which you can see in the images above. In addition to that hole I have also thought about creating a venting hole at the top of the box in order for the speaker to not accumulate heat. However... in most (all?) of the soffit constructions that I have seen, a port has also been placed in the bottom of the speaker box in order for it to vent/move air properly and also for it to share the volume below the monitor stand (pretty much John's well known model).

Now then... since the Monitor Two's are passive and do not heat up in the same manner that active speakers do... what additional function does the bottom vent in the speaker box serve? Is it to allow the speaker to move air more effectively by receiving air access to the room via the bottom "half" of the soffit?

I believe I have other thoughts as well... but I will try to work them out on my own first. Sorry about the Wall-o-Text.

Thank you again, for your response!

/Peter

[gullfo]

the top and bottom vents promote air flow. i'd say just do a before and after test with monitor on a stool or something to see if you get a noticeable increase in distortion due to loading from the box.

[Gash]

Way to go in keeping it simple and still functional. Thank you!

/Peter

[al-andrew]

Hello .... I am in the process of considering this method for a pair of Alesis Two monitors.... did this project get finished and what were the results sounding like ?

Regards

[Soundman2020]

I'm not sure if this ever was finished, but I have come to the conclusion that it is possible to soffit-mount rear-ported speakers, if some precautions are taken. So it should be possible to soffit-mount your Alesis Two's.

The results you will get would be the same as for soffit mounting in general: You would completely eliminate the undesirable artifacts that affect speakers that are located inside a room. No more SBIR, comb filtering, edge diffraction, or any of the other issues, plus much better, smoother bass response down to lower frequencies, etc. One of the things you'd need to do is to introduce a 6dB shelving filter in the low end, centered on the baffle step response center frequency for the width of the Alesis Two speaker cabinet, but that's very simple to do.

If the soffit is designed right and built right, then they would sound very good.


- Stuart -

[al-andrew]

Thanks for the input, I'll be bending you ear when I get to this stage.

[al-andrew]

Well here I have my first attempt at a sketch-up design for the practice room I am making.
I'm looking for some help with planning the soffit boxes for my Alesis Monitor Two speakers.So if anybody can help I would be very grateful.
As you can see I have drawn lines to where I plan to be sitting behind my console in an argosy 90 series desk.

sketchup file: https://www.dropbox.com/s/2rs4x67by7aa0 ... ~.skp?dl=0

[Soundman2020]

I'm looking for some help with planning the soffit boxes for my Alesis Monitor Two speakers.So if anybody can help I would be very grateful.

Take a look at John's design for soffits. That's a good place to start when designing your own. The basic concept is that you need to hold the speaker cabinet either very rigidly, or very resiliently, and have the front baffle of the soffit flush with the front baffle of the speaker itself. The baffle needs to be very massive (heavy), very rigid, and very firmly held in place. Most people build that up from a few layers of MDF, OSB, plywood, drywall, or something similar.

Then you need to have most of the internal volume of the soffit filled with insulation, to damp any resonances and sound transmission going on in there, but you do need to leave a path through that insulation for airflow past the back of the speaker, to keep it cool. Most people use chicken wire for that: forms a "chimney" out of the mesh, from the top of the speaker box to a vent slot in the soffit, and place the insulation around that.

You can use the space under the speaker shelf for bass trapping.

That's the basic concept.



- Stuart -

[davidjohnson789]

In manual, that appears to be a rear-ported speaker. it not sure if you can soffit mount those successfully.
There is chance to have success.

[Soundman2020]

In manual, that appears to be a rear-ported speaker. it not sure if you can soffit mount those successfully.
There is chance to have success.

Before plagiarizing other people's posts in your spam, you should at least try to read through the entire thread, so that you don't look to imbecilic. If you would have done that, you would have noticed that a few posts later the very same person who wrote the above (me!) also wrote the below:

I have come to the conclusion that it is possible to soffit-mount rear-ported speakers, if some precautions are taken. So it should be possible to soffit-mount.

- Stuart -

[PS: THE "DAVID JOHNSON" SPAMMER HAS NOW BEEN BLOCKED AND BANNED]

[kenedy]

I just wanna say that I like what you have shared here...very cool!!

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