A Speaker Dilemma, Please Help!

[MT Speakers]

I decided to build my own speakers. This is my frist time building speakers. First, I was set the Zaph|Audio SR-71 speakers. Then, I went to the Seas website and found the Mimir speakers. The woofer in the Mimir has a slightly different crossover than the woofer in the SR-71 speakers. Which one should I choose?

Zaph|Audio SR-71

Seas Mimir

[vinceb]

Do you have a subwoofer (or plan to build/buy one)? Are you looking for music primarily or home theater as well? I ask because to get the most out of this type of speaker you probably should plan on a sub to go with it to get full-range sound.

[Jed]

Of the two, I'd go with Zaph's design hands down. It has a smoother FR and he's a great designer.

[MT Speakers]

I have an SVS PB Ultra subwoofer. The speakers I build will be used for both music and home theater. I was thinking of building 5 speakers and using one as a center channel.

[Curt C]

Of the two, I'd go with Zaph's design hands down. It has a smoother FR and he's a great designer.

Not having heard either design, but based on other designs of John's I've heard, I concur with Jed.

C

[ThomasW]

+1..

[lunchmoney]

I haven't heard the Mimir's, but I just built the SR71's, and I'm absolutely thrilled with them... and +1 to Zaph being one of the best and well-known designers out there... you won't be disappointed.

In addition, the SR71's use the reed paper cone... which according to Zaph's driver tests are quite possibly the best Seas driver short of the Excel series... although I suppose that's a matter of opinion, as some prefer metal cones.

Here's my build thread for the SR71's...

http://www.htguide.com/forum/showthread.php4?t=32085

[MT Speakers]

Okay, I will stick to my plan of building the SR-71's. I plan to build my own speaker cabinets. It isn't clear according to Zaph's site how the boxes are damped. What is recommended for this design?

[MT Speakers]

I have a tight budget, not that much. My budget is about $160 per speaker. I'm going to try to assemble my own crossovers from materials that are available to me easily. Same thing with my 3.3 mH inductor. I found some funky torriods that might do the trick. Still testing to see if they will work. I also have some Owens Corning 705 fiberglass board and was wondering if it could be used for dampening on these speakers. Or do these speakers require some special stuffing like Acosti-Q? Thank for all of the help and as I develope this project, I'll post pictures and details.

[MT Speakers]

Today, I came out with another inductor design. Hope to be getting test results and pictures soon! For insulation, should I use the recommended Whispermat or is the Owens Corning 705 okay to use?

[ThomasW]

OC 705 is fine as long as it's not too thick.

[alias2]

It isn't clear according to Zaph's site how the boxes are damped.
What is recommended for this design?

As stated there are a lot of options for damping, take your pick.

Vented boxes are ideally lined with a quality acoustic absorbment.
They can be lightly stuffed with polyfill etc to adjust bass damping.

BTW another +1.

/alias2.

[MT Speakers]

Okay guys, I'm new at this. This might sound silly. According to Zaph's site, the woofer inductor should measure 3.3 mH and have a DCR of 0.185 ohms. I'm winding an inductor and when I get to 3.3 mH, my DCR measures 0.1 ohms. Is it okay to use an inductor with a DCR of 0.1 ohms in this speaker design?

[Finleyville]

I do not think you would hear a noticeable difference.

[MT Speakers]

Since it is rainy today, I decided to take a break from making my inductors. So, I went to Home Depot to buy a 4 X 8 sheet of MDF and had it ripped. Kudos to Home Depot in Crescent Springs, KY! :T :T The guy who ripped it was extremely professional and patient. The equipment was in excellent condition! All of my rips were within 1/32 of an inch. I have uploaded an attachment showing my cut plan.
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Note: Since I like to experiment, I decided to thicken the front baffle by gluing to the back of it a piece of 3/16 piece of fiberglass. This will be seperated by a 1/6 piece of felt impregneted with contact cement.

[MT Speakers]

I said that I was going to glue a piece of 1/4 fiberglass to the inside of the front baffle. So actually, I've had this material laying around for a long time. It is called GPO-3 Glass Polyester Laminate. I like it because it is free and makes a nice thud when I hit it. This makes me think speaker enclosures. So, I cut 5 sheets of 13.875" X 7.5". I sandblasted one side so that glue would stick better to it and the MDF. I'm thinking of adding an acoustic dampener between the MDF and the GPO-3. I will post a picture as soon as possible. Any comments would be greatly appreciated.

[MT Speakers]

Here are the pictures of the GPO-3.

[ThomasW]

If you want to attach pictures to your posts they need to be 70k in size. The pics on your site are larger than 2 megs each.

[MT Speakers]

I know. I have a camera that does not take small pictures. It is a 1080p camera.

[ThomasW]

Pictures from any digital camera can be resize and compressed with software.

[MT Speakers]

Thanks, I'll try that out and post them to HTGuide.

[MT Speakers]

I have tried 2 different 3.3 mH inductor designs. None of them seemed to work. So, I sell my pop cans to the local recycler. Since I am 12, it is an extra way for me to make some money. While I was selling my pop cans, I saw these devices lying on the floor. I thought, "There's some copper wire I could use." I asked the guy how much they were and he said just to take them. They had been laying there for ages. There was six of them scattered all around. I brought them home and measured their inductance with my LCR meter that I borrowed from my dad. They measured about 3.7 mH. I couldn't believe this; it was like a godsend. As you can see from the small picture, this is really 2 coils connected together. When I seperated the coils and measured them, each coil was about 4.65 mH and had a DCR of 0.2 ohms. I took about 6 turns of wire off of each coil and measured some more. Now I have a 3.3 mH inductor. My problem is, should I use both coils or just one coil? Any expert help would be appreciated!

[MT Speakers]

By the way ThomasW, thanks for the help. I figured out that I can reduce the picture size with Microsoft Office Picture Manager.

[ThomasW]

Looks like 2 inductors, and is if there are 4 wires?

[benchtester]

My problem is, should I use both coils or just one coil? Any expert help would be appreciated!

I am not an expert but I bet that is a "common mode choke".

http://www.butlerwinding.com/inductors/common_mode.html

It is basically two inductors on a common core. For fun (with the two coil assembly) you could measure the coils in series (connected end to end) then reverse one of the coils. In one case you will have more than 6.6 mH because the coils are working together to push the magnet field through the core. In the other case the inductance will be less than 3.3 mH because the coils are pushing against each other. Also you might try measuring one coil first with the second coil open (wires free in air) and then with the wires of the second coil connected to each other (second coil shorted).

For crossover use, you can use the single coil by itself.

[MT Speakers]

Thanks, I'll try that.

[ThomasW]

Might hacksaw them into single units for use in the crossover.

[MT Speakers]

I'll try that with a spare. I would want to test it first. It might just help.

[MT Speakers]

Okay benchtester and ThomasW, thanks for the help. This gave me a direction.
According to the Zaph|Audio site, the crossover circuit for the woofer uses a 3.3 mH with a DCR of 0.185 ohms.
Here is a picture of my woofer (L7) inductor. I have 5 of them. They all measure between 3.24 mH and 3.27 mH. They all have a DCR of about 0.17 ohms. These reading were taken with an AMPROBE LCR55A meter. Before I use this inductor, in our woofer crossovers, I'm going to do some plots for impedance versus frequency from say around 5 Hz to about 5 KHz. Also I have a 400 watt amplifier and I'm going to load test the inductor to see where the iron core saturates. If all seems acceptable, I'll use it.
I'm the apprentice, you guys are the experts. I'm really thankful for all of your help. Any input, ideas, or suggestions are greatly appreciated!

[MT Speakers]

To make things clear, my dad and I are working on this project.

[MT Speakers]

Okay guys, I was ready to glue up my boxes. I can tell by thunking the MDF panels that they needed something like mass loaded vinyl. I don't have the money for that. So I tried something different. I have this GPO-3 laying around, so I decided to use it to dampen the box panels. I have access to an old Brigeport. Thank you lunchmoney! You were the inspiration for this! ;x( So I hogged out the inside of the MDF 1/4 deep, 1 inch from all of the sides. Next, I cut out my 3/16 GPO -3 to fit in the cutouts. I created an airspace between the MDF and the GPO-3 with small pieces of 1-16 inch double sided tape. Next I sealed everything up with silicone caulk and inlaid the GPO-3. I tested on 1 panel. I am now going to do the other 19! :T

Any ideas and/or suggestions would be highly appreciated before I do the other 19 panels.

[Paul H]

... ( So I hogged out the inside of the MDF 1/4 deep, 1 inch from all of the sides. ...

Any ideas and/or suggestions would be highly appreciated before I do the other 19 panels.

I'm not familiar with this material you're using, but why remove any of the mdf, as oppposed to simply surface mounting the dampening material?

I know it would change the interior volume slightly, but I think not enough to worry about.

Paul

[lunchmoney]

I'm not familiar with this material you're using, but why remove any of the mdf, as oppposed to simply surface mounting the dampening material?

I know it would change the interior volume slightly, but I think not enough to worry about.

Paul

+1

Not sure why you think the mdf needed to be "mass-loaded"

Line the walls with acoustic foam, and add a couple of internal braces.

[MT Speakers]

Yeah, that's it. The volume was my concern. On the Seas website, there is a speaker design called the Mimir. I thought that it looked similar to John's SR-71. The Mimir design says not to change the baffle width or the internal volume. Also, after reading John's website, his designs seem to be very refined. Since speaker building is new to me, I don't have a feel for how much I can change things before I affect the sound.

[MT Speakers]

Okay guys, so I finally got my inductor GPO-3 inlays into the MDF bottoms of my speaker enclosures. The inductors are held in place with a little silicone caulk and clamped into place. All of the hardware that you see is stainless steel. Since there are only 2 components in the midrange speaker crossover. I think that I will glue the 12 mF capacitor to the top GPO-3 inductor plate. Any comments or tips will be appreciated. There will be a couple different replies of pictures.

[MT Speakers]

More pictues.

[MT Speakers]

Okay, I've had these 5-way binding posts laying around; had no idea where I got them. So, I decided to make my own speakers connection terminals. I had some scraps of fiberglass laying around also and I drilled holes 3/4 on center and installed the terminals. I isn't preatty but they are free. Right now I decided not to paint them or anything because with my skills, I don't think that I could make them look better. Any ideas on how I could label these and still have it look professional would be appreciated.

[MT Speakers]

Here is another picture.

[MT Speakers]

Here is the last picture.

[MT Speakers]

All righty then, today I had alot of time. I got the sides and tops and bottoms for my 5 speakers glued up. I think that they came out very excellent for my first time doing this type of stuff. I borrowed a biscuit my friend's dad. I put 2 biscuts in each joint. Each box that you see has a total of 8 biscuits. Do you think that I need inside corner braces too? Liking all of the feedback I'm getting here. I can tell that you are all experts.

[MT Speakers]

Howdy y'all! I've been going over my costs for the speakers. So far I've only spent about $12 per speaker and $60 total. This is below my budget. So, I'm thinking of doing something radical. I'm thinking of lining my enclosure with 1/8 inch mass loaded vinyl. Would this decrease in volume hurt the sound of the speakers? Would the money spent on this stuff make the a noticable sound improvement in the speakers? I still plan to line the insides of my speakers with OC 705 which I found out was actually 703; but it is not really 703 at all but a compatable product made by Johns-Manville. Thanks for your input.

[ThomasW]

I'm thinking of lining my enclosure with 1/8 inch mass loaded vinyl. Would this decrease in volume hurt the sound of the speakers? Would the money spent on this stuff make the a noticable sound improvement in the speakers?

Don't bother, in your situation it's a waste of money.

I still plan to line the insides of my speakers with OC 705 which I found out was actually 703; but it is not really 703 at all but a compatable product made by Johns-Manville.

If it's a form of compressed fiberglass it will work fine.

Do you think that I need inside corner braces too?

Corner braces are primarily used to keep the corners of the cabinet square during the glue-up process.

[fbov]

MT,
There are a lot of things you "can" do, and at your stage in the process (i.e. boundless enthusiasm), you want to do everything you can. That's understandable, and not uncommon (speaking only for myself). The trick is to find actual weaknesses and address them, since no possibility of payback if there's nothing to fix. It's the difference between good engineering and "design for marketing." Let me explain a bit, and see if I've absorbed the proper understanding.

There are two different topics involved in enclosure damping design:
- absorption of sound within the enclosure
- reduction in sound transmitted by the enclosure

The first involves use of acoustic absorbers like OC-703 and Acoustistuff. You're trying to damp the resonant sound field bouncing around inside the box caused by the woofer back wave. You're working with highly audible frequencies, 200-300Hz to the XO point around 2KHz and the goal is to damp the sound to the point where you will not hear the back wave transmitted through the cone. The flat stuff (703, Whispermat, etc.) goes on the rear and side walls of a ported box to damp the higher frequencies while allowing transmission of lower frequencies that feed the desired tuned port resonance. The fluffy stuff is added to sealed boxes to make them accoustically larger, as well as to damp higher frequencies.

Below 200-300 Hz, accoustic absorbers would need to be too thick for practical use, so you rely on mechanical means. This is also the frequency range that can excite sympathetic vibrations in the enclosure structure itself - the box vibrates. Increasing mass will lower a vibrating system's resonant frequency. Conversely, shortening a vibrating member will raise its resonant frequency.

This leads to the two approaches - mass loading and mechanical bracing - as well as a combination called constraint layer that adds a low-frequency absorber.

However, opportunity for improvement depends on you need, and needs depend on circumstances. Your working on a small box (9x10.5x15.4) with thick, accoustically dead sides (3/4" MDF). That gives you a 10:1 ratio of thickness to span in the shortest dimension (9" outside is 7.5" inside), and that will be an intrinsically very stiff structure. Next longest is 9" inside, a 12:1 ratio and again very stiff. Zaph's design specifies 2 cross braces between the 10.5x15.4" sides because that's all he feels you need, and you can see why. The longest dimension is approaching a 20:1 thickness-to-span ratio and the bracing drops that back to single digits. Bracing is also cheap, thus it's the most common approach.

In a large box intended for very low frequency output - subwoofer or large full-range - mechanical resonances become the primary concern (in a sub) or an additional concern (in full range). Here, double thickenss is common (adds mass and stiffness), as are wall-sized cross braces in place of dowels. I've heard of people literally coating the inside with tar, like a glass-lined tank, or make a box-in-a-box with deadening material in the gap between. This latter approach is actually a constraint layer system where a mecahnical absorber (i.e. not 703) is trapped between inner and outer layers.

It's a matter of degree; use what you need. In your case, that's just some cross braces and wall treatment, but no fiber fill so the port works. Anything more will not be audible, and may not even be measureable!

Have fun,
Frank

[MT Speakers]

Thank you very much for you responses ThomasW and fbov. fbov, what a clear statment.

It's the difference between good engineering and design for marketing.

I think I get it, but I am going to have to think about it alot more before I really get it.

Originally, I was going to stuff my box with alot of Acoustistuff I'm going to take your advice and at least start with nothing.

Thanks, and keep the comments coming!

[ThomasW]

I'm going to take your advice and at least start with nothing.

Line the walls of the enclosure with the fiberglass product you have.