Dual MCM FLH

[danielm]

Originally Posted by MartinQ

jbell, are you enclosing the MCM 8 with a removable baffle or is this a TH?

It's a FLH not a TH. I think Jim found this driver not well suited for a TH box.

[neddludd]

re: 8:1 compression ratio, id like to see a few different woofers on the same horn with a high powered sine input and see what lasts. Maybe these cheap cones which are plastic sound worse but are more durable for the high compression ratio -than the pro paper based stuff?

I wonder if you see ripples or rocking with laser interferometry on weak ones. I think b&w or kef have a nice r&d explanation of what the look at on cones.

[J. L.]

Jbell,

I thought you might like to see my adaptation of your bass-stick design.

I used the same MCM driver but made segment 2 and 3 slightly shorter, at 100 instead of 120. These will be used with four of the line arrays pictured. (It will result an 8 foot long line array on each side of the stage) The small change in height allows me to use the bass-stick cabinets as stands for the line-arrays in a room with 8 foot ceilings for smaller venues. I actually desired a response curve that extended upwards as I cross over at about 180Hz. I did not need response below 40Hz.

These will be used for PA use and to supply music for ballroom dancing. Their first public use will be in the ballroom at the local convention center for a black-tie formal dance. In my living room a single cabinet can easily supply enough volume. (I've been cautiously breaking in the drivers) With four cabinets I'm hoping I'll have sufficient bass to fill a gymnasium sized ballroom to 85+ dB levels.

I do not have the rear enclosure covers for the drivers in place yet to make them into true front-loaded-horns. I expect right now their frequency response is a bit ragged since their back-chamber cover is missing.

The bass-sticks easily exceeded my expectations in performance. I know what really low distortion high quality bass sounds like, as I have a pair of 18" Avalanche drivers in 12.5 cubic foot cabinets in my home theater. I did not expect an 8" driver to come close, but they really are impressive.

J. L.

[epa]

Originally Posted by J. L.

Jbell,

I thought you might like to see my adaptation of your bass-stick design.

I used the same MCM driver but made segment 2 and 3 slightly shorter, at 100 instead of 120. These will be used with four of the line arrays pictured. (It will result an 8 foot long line array on each side of the stage) The small change in height allows me to use the bass-stick cabinets as stands for the line-arrays in a room with 8 foot ceilings for smaller venues. I actually desired a response curve that extended upwards as I cross over at about 180Hz. I did not need response below 40Hz.

These will be used for PA use and to supply music for ballroom dancing. Their first public use will be in the ballroom at the local convention center for a black-tie formal dance. In my living room a single cabinet can easily supply enough volume. (I've been cautiously breaking in the drivers) With four cabinets I'm hoping I'll have sufficient bass to fill a gymnasium sized ballroom to 85+ dB levels.

I do not have the rear enclosure covers for the drivers in place yet to make them into true front-loaded-horns. I expect right now their frequency response is a bit ragged since their back-chamber cover is missing.

The bass-sticks easily exceeded my expectations in performance. I know what really low distortion high quality bass sounds like, as I have a pair of 18" Avalanche drivers in 12.5 cubic foot cabinets in my home theater. I did not expect an 8" driver to come close, but they really are impressive.

J. L.

nice
i bet they rattle the windows

[jbell]

Hey JL, I hadn't thought about this thread for a LONG time.... I thought I'd add a bit of info for you on these so you can have success with them.

First they are designed so that by themselves, they are not a complete cabinet. They were modeled in hornresp assuming they were 'v-plated' aka, put in the below configuration and a 3/4" plywood plate bolted to the top, so that the cabinets, floor and plywood plate extend the horn length / mouth size.

For a gymnasium setup, find the middle of a concrete wall, set up the 4 cabinets in a single 'V' so that you have a mouth that is basically 32"x60" Set it up so that the mouth is facing the wall and is about 32" away from the wall. This will effectively give you something close to 1pi cabinet loading.

On the driver cover, yes you definitely want it, and it needs to be as small as possible. I attached a pic so you could see what I did. I basically joined a couple boards at what I thought was a reasonable angle. Then taped a piece of cardboard over the back of the magnet to set a small gap so the cover wouldn't touch the driver, set the angled board down till I thought it was appropriate, and drew a line. The cleats you need to install for the cover to attach to are obviously 1/2" below that line. Use window gasket foam to make sure it's air tight.

In terms of standing them up and putting a line array over them, I think that only works if you have corners. If you have a small enough room that you can put a line array in each of the front 2 corners, then put a bass stick under each one facing into the corner, I think that will work well as the corner will 'finish' the cabinet, ala k-horn.

BTW -- nice looking cabinets.

[J. L.]

Originally Posted by jbell

Hey JL, I hadn't thought about this thread for a LONG time.... I thought I'd add a bit of info for you on these so you can have success with them.

First they are designed so that by themselves, they are not a complete cabinet. They were modeled in hornresp assuming they were 'v-plated' aka, put in the below configuration and a 3/4" plywood plate bolted to the top, so that the cabinets, floor and plywood plate extend the horn length / mouth size.

I understood that when I started the project. In my own hornresp simulations I deleted the final segment of the horn to predict the response without it. (It still looks good for my intended use)

I don't know if I'll ever need to generate that kind of SPL these things are capable of when stacked and configured as you described, but if I ever need to fill a gymnasium with sound for a younger audience, it is nice to know it can. I'm not sure I would have ever thought to face the mouth to the wall, but I can see how the wall would then act as the final reflector and horn segment.

For a gymnasium setup, find the middle of a concrete wall, set up the 4 cabinets in a single 'V' so that you have a mouth that is basically 32"x60" Set it up so that the mouth is facing the wall and is about 32" away from the wall. This will effectively give you something close to 1pi cabinet loading.

Actually, they do not do too badly as shown in my picture. The floor forms one side of the final horn, and the standing cabinets the other side at 90 degrees. The four cabinets side-by-side result in a horn width of 72 inches by 44 inches high.

I described the first venue I'd be using them in as gymnasium sized... Unfortunately, the wall I'm setting up against is a 20 foot high folding accordion style wall that separates their very huge ballroom into 6 smaller spaces. We'll be using two of those ballroom spaces for our dance. The folding wall is probably not a great reflector at bass frequencies. It is most definitely not concrete.

The up side is that I'm not trying to provide high SPL, in fact, the bass-sticks will probably be loafing along most of the evening. My sound equipment is being used to supplement the "house" sound system, as it has very poor bass response being designed more for speech than music.

I'm more constrained by appearance and stage placement then the need for as loud and deep and even a response as possible.

On the driver cover, yes you definitely want it, and it needs to be as small as possible. I attached a pic so you could see what I did. I basically joined a couple boards at what I thought was a reasonable angle. Then taped a piece of cardboard over the back of the magnet to set a small gap so the cover wouldn't touch the driver, set the angled board down till I thought it was appropriate, and drew a line. The cleats you need to install for the cover to attach to are obviously 1/2" below that line. Use window gasket foam to make sure it's air tight.

Thanks for the additional pictures and description of how you measured/fitted them.

In terms of standing them up and putting a line array over them, I think that only works if you have corners. If you have a small enough room that you can put a line array in each of the front 2 corners, then put a bass stick under each one facing into the corner, I think that will work well as the corner will 'finish' the cabinet, ala k-horn.

BTW -- nice looking cabinets.

Thanks. A bit of stain and a coat of polyurethane makes then fairly attractive as long as you do not look too close. It turned out my local Home Depot had the better plywood this time. It was equal to the auroco carried by Lowes down the street, with 5 equal size plys, one side cabinet grade, but on sale at $18 a sheet. Only issue is that it was 15/32 instead of 1/2 inch.

I've read posts from you were you've been hesitant to put more than 20v on them. Right now I've got one channel of a NADY 900 amplifier driving all four cabinets (wired in series/parallel to present a 4 ohm load) It can output 300 watts per channel into 4 ohms if turned up. 75 watts per driver is probably less than you've pushed them, and I've not turned it all the way up.

Believe me, it is far more than I need in my living room. My initial tests were with an amplifier that probably does not put out more than 30 watts per channel. It was pretty loud even with that.

Thanks again for a great concept.

J. L.

[jbell]

Well again -- congrats to you JL.

I did a quick hornresp, and for the way you are going to use them, just leave them without the cover. Looks like you are reasonably flat to 60hz, and can get about 120db@20v per cabinet. (just run a high pass at 40hz)

Putting the cover on, and making a FLH out of them only helps you if you lay them on their side and v-couple. Then you can get flat to 40hz.

Again, great job, looks like they will work well for you.

[J. L.]

Originally Posted by jbell

Well again -- congrats to you JL.

I did a quick hornresp, and for the way you are going to use them, just leave them without the cover. Looks like you are reasonably flat to 60hz, and can get about 120db@20v per cabinet. (just run a high pass at 40hz)

Putting the cover on, and making a FLH out of them only helps you if you lay them on their side and v-couple. Then you can get flat to 40hz.

Again, great job, looks like they will work well for you.

Wow... thanks for taking the time out to verify what I'm hearing. You really went out of your way. I know the response is not perfect, and I know my needs are different than yours. I did take the time to learn enough about hornresp to simulate the open rear chamber and altered segments before I started any cutting of wood. hornresp is a very nice program and I'm sure I've only touched on a small portion of its capabilities. About the only thing I've not figured out is how everybody gets all the windows open at the same time in their apparent screen captures. When I open the Edit screen the SPL window closes... There are so many posts with all the windows open at the same time. Are people just cutting and pasting into "paint" ?

As you might have guessed, the average 50 to 85 year old ballroom dancer does not expect chest pounding ear splitting bass. I have a much easier audience to please than you do when playing to high school kids in a gymnasium

Thanks so much again for your project's inspiration of mine.

J. L.