Re: RBR discussion thread

[Clearwave]

Ahh okay, thanks for the reply. So you do not advise using the .75cuft box I linked in the configuration above (or is there really no way of knowing, besides testing, how such a change would effect the sound quality)? Do you recommend this kit as a studio monitor or do you suggest that I buy something else such as a Mackie, Alesis, etc. brand name monitor.

Thanks!

-Chris

I recommend the cabinet that is closest to the original design because otherwise there will be more diffraction. The cabinet you have pictured doesn't really look deep enough to accommodate the port and the baffle is much wider than what the design calls for. For a studio monitor you might think that about maybe going with the sealed version and a subwoofer. That would be nice and compact for your application and give you a fullrange speaker. More than likely you'll be listening around 3ft or so so the drivers will sum well.

[Chrismoris]

I have thought about this but I would prefer to keep it all in one package. As far as compact I do not mind the extra size the MTM adds really. I would prefer it in a more sealed looking box, but if the MTM style box is a requirement that is fine. I would prefer not to use a subwoofer with this setup as I feel it would be more difficult to get a flat response and if so I would possibly be coloring the sound. I want to make sure that the low frequency response is fixed and close to zero with the mids and highs so I don't go down a long road of making a sound with too much or two little bass. Thank you for all your replies! If I did go with a sub + sealed route, what sub would you recommend?

-Chris

[Clearwave]

If you cross the sub around 50-70hz to the sealed RBR, you should not be able to locate it. I like the Seas L26ROY, but there a lot of good drivers out there that are reasonably priced.

[pop4richard]

Hi, I have noticed the shielding on the woofer has a ring when i tap it. Is this a problem and should I dampen the shielding or can the shield be removed? There does not seem to be much room for the sound to come out of the back of the woofer when a 25mm baffle is use. Is there something I should do to the baffle inside to held this? Many thanks for your design.
Richard C

[Clearwave]

Hi, I have noticed the shielding on the woofer has a ring when i tap it. Is this a problem and should I dampen the shielding or can the shield be removed?

When you play the speaker you won't notice any ringing from the driver.

There does not seem to be much room for the sound to come out of the back of the woofer when a 25mm baffle is use. Is there something I should do to the baffle inside to held this?

Yes, in my writeup in the website I mentioned doing a chamfer to open up the hole near the frame/magnet.

Many thanks for your design.

You're very welcome!

Regards,

Jed

[Clearwave]

Hi Jed,

Just ordered 3 of the kits from Mad and I need to make 1 into a low profile center channel.
It will sit on my entertainment center that is under my wall mount flat screen.
I will have no more than 10-12" for height so I'll need to make the cab wider than tall.

This will mean placing the drivers as close as possible, maybe even trimming the tweeter ring.
Any thought on how this will change the response? I can live with some small aberations.
Or I could tweek the xover too.

Thanks for any advice.

It won't be as designed for the baffle dimensions and as you deviate further away from the as designed box layout, the worse the response will be. You could have up to 2 dbs of difference in the mid/treble. It really would require me to measure your box to know how much.

As far as the left/right speakers I plan to make the vented boxes so that I could run stereo full range for some music, but will place them on top of subwoofer boxes which I will use for HT and louder music. Can I just use rear facing vent and stuff it with a tennis ball or some foam or something similar when using with subs?

Or you could build the sealed box design. But yes, you can stuff the ports for when you run the subs- a sock will do it.

Or will this larger volume of the vented box change the integration when used with the subs?

If you have an adjustable crossover that allows different crossover points, you can tune it that way for the best integration. Bass is so room dependent, I wouldn't lose sleep over a box qtc of .7 -. 6 when you have an adjustable electronic crossover in a plate amp.

[johnj]

"It won't be as designed for the baffle dimensions and as you deviate further away from the as designed box layout, the worse the response will be. You could have up to 2 dbs of difference in the mid/treble. It really would require me to measure your box to know how much. "

And I'm sure the iteraction with my entertainment center sitting directly below will affect it as well. Might act as basically an infinite baffle below.

I guess I'll just build it and try to come up with a way to measure it in place. Maybe the worst thing that could be required is a notch filter.

I could maybe plug in the measured response from the design baffle into Baffle Diffraction Simulator program and change the dimensions to see what generally happens. Is the response you posted on the buildRBR page an actual measured response of the designed baffle? I think I could trace it and import to BDS

Thanks again.

[Clearwave]

Yes, it's an actual measured response in the test box-- I only use sims as a preliminary precaution to optimize diffraction before I finalize box dimensions and driver layout. I also give values you could use to adjust the tweeter level a bit to voice it in the different environment for a center channel. It just won't be "perfect" because I didn't measure the RBR as a CC. Working with the baffle simulator will definitely get you closer to where you want to be.

[Bob in Tucson]

Hi Jed,

On your plan for the baffle layout, you note 3/4" offset. I assume that means 3/4" off the center line? Just wanted to make sure.

Thanks!

[Clearwave]

Hi Jed,

On your plan for the baffle layout, you note 3/4" offset. I assume that means 3/4" off the center line? Just wanted to make sure.

Thanks!

Correct.

[Bob in Tucson]

Hi Jed,

Hope I'm not being a pest!

In your description, you note that we should relieve the rear of the opening for the woofer, which makes perfect sense to me:

> Make sure you chamfer the front baffle opening (on the inside) for the woofer AT LEAST 1/2"

So if I have this right, you removed about 3/16" from the front of the baffle to recess that driver, then relieved 5/8" from the rear with a chamfer bit, which would leave about 1" - 3/16" - 5/8" = 3/16" at the thinnest point of the baffle surrounding the woofer. Does that seem right? (Seems thin!)

Anyway, I ask because I am using a 1.5" baffle; overkill, sure, but I wanted it to be thicker than 3/4", so I laminated two pieces of 3/4" MDF. Now I am wondering how much to relieve from the rear of the baffle around the woofer, and whether I should target 3/16" to match what you did.

Hope that's not too tough to follow.

[Clearwave]

I understand it is thin near the edge, but in order to get some breathing room around the driver the 1/2" chamfer is what I used. Since the baffle is so narrow it has plenty of strength from the sidewalls. You might go a bit less on recessing the driver than you mention. Part of the flange is rounded and on my baffle that is not recessed completely. This leaves another mm or 2 for overall thickness. Now for your baffle you can match mine or come very close. You could even do a fancy chamfer so when you are near the screw holes you leave more wood in that area.

Jed

[Bob in Tucson]

Thanks for the quick reply Jed.

I'm not worried about strength, I was just surprised -- I do plan to leave the baffle full thickness at the screw tunnels.

So far as recessing the woofer, it's too late as I cut those yesterday... Of course, mdf is cheap so I can make new baffles if need be. Anyway, on the speakers I own, the drivers are perfectly flush, so I cut the recess so the drivers would be close to flush after veneering. And to be clear, I mean flush with the edge of the flange before it starts to raise to go round... meaning the driver will be proud of the baffle everywhere but at the very edge.

One of the challenges in a first build of anything (this is my first speaker build) is not knowing where there's room for flexibility and where there's not, hence the detail questions.

Thanks again.

[Clearwave]

The woofer recess is 6.5mm if I recall correctly. No need to redo it if it is around that measurement.

[Bob in Tucson]

The flange is reported to be 5.5 mm which is 0.217" or about 7/32". I cut 3/16" (6/32") as the recess to allow for the thickness of the veneer.

So I haven't screwed up too much... yet.