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Multi-Way Conventional loudspeakers with crossovers

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Old 25th September 2001, 10:40 PM   #11
Wizard of Kelts
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Alex:

In an earlier post you wrote: "My setup will be PC soundcard -> audio receiver -> monitors.
Currently, I am using Yamaha YST-MS25 (R, L, and subwoofer)."

My question is: how is the audio signal sent? Does your receiver split it up into bands and send it to the subwoofer and the Left and Right satellites?

If so, forget about building ported boxes for the satellites. The bass signals will never reach them-they will be sent to the subwoofer instead.

The larger the box, the bigger the bass. No sense building large boxes with more bass if the bass signal never reaches these speakers.

Before I make a recommendation, please tell me how your subwoofer is set up in relation to the amp. We must know that the full signal, including bass, will reach the Left and Right channels.

Thank you.

PS: I have located a decent 8" subwoofer for $18.50 plus shipping in case you decide to do the whole thing-subwoofer and satellites-all at once. It should go down to 42 Hz in a 1 cu. ft. box.

[Edited by kelticwizard on 09-25-2001 at 08:08 PM]
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Old 27th September 2001, 05:43 AM   #12
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I'm not planning on using the PC subwoofer at all. If I can get 'good' sound from the MB Quarts and the passive crossover then I'll just go with that. So, the receiver will need to feed a full bandwidth signal to the monitors which I hope to build.

Thanks,
Alex
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Old 28th September 2001, 05:45 AM   #13
Wizard of Kelts
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Alex:

Okay. Then you do want the bass from the Left and Right speakers.

If I am envisioning your situation, you plan to put these on your work table while you mix or edit your music. Therefore, might I propose a workable design that is slightly smaller than .51 cu. ft?

The Thiele-Small numbers actually give you a whole range of enclosures, with the maximally flat among them. That is the one that Grey gave you.

The design I propose is .32 cu ft., tuned to 65 Hz and 3 db down at 60. There will be a slight 1.5 db hump in the response, which should not be a problem.

If Grey's design is not too big, then use his.

My proposal can be met by a box with internal dimensions of 12" X 7.75" X 6". The port would be a 2'' diameter plastic pipe, 4.75" long.

It should be pointed out that most PA speakers, such as what a DJ uses, cut of at 60 Hz. Many people make their livelihood playing music with speakers that have a 60 Hz cutoff. So it is pretty good for a small speaker.

Super's directions will build you one sturdy cabinet. A cabinet this small, however, is by nature stiff, so you can use plywood, .75", if you want to.

One more thing. You can retune the box lower if you can locate an equalizer on the web that will give you a boost at 45 or 40 or so. Since the speaker is nearfield, the amp can easily provide that boost without running out of power at crunch time.

Winamp's lowest equalizer frequency is 60 Hz. Drat!!

[Edited by kelticwizard on 09-28-2001 at 12:51 AM]
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Old 29th September 2001, 03:13 AM   #14
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Grey's enclosure of .51 cubic feet isn't too big for my environment. Actually, the more bass that I can 'get' the better. By the way I just measured the dimensions of my crossovers, each of which is enclosed in a box of 0.1536 liters or 2.5" x 1.5" x 2.5". So I guess I'll need to add this to the enclosure space of the monitors? How much bigger would the port be (or smaller) if I go with the bigger enclosure?

Anyway, I am ready to proceed. I guess that I need to decide on the following:

3/4" MDF or 3/4" plywood for the enclosure
how to brace the speaker enclosure
port pipe material (PVC??)
where to place the port relative to the speakers
buy acoustic foam, caulking, etc.

By the way has anyone used the Dow Corning caulking?

I'm sure I'm leaving out a lot. Please keep the posts coming.

Thanks again to kelticwizard, GRollins, Super, and tvi.
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Old 29th September 2001, 06:26 PM   #15
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I just remembered that I'm probably going to need to shield the individual drivers in the enclosure so that they don't interfere with my PC monitor. I'll search the archives for some recommendations. If you have any please let me know. I assume that this shouldn't affect the size or construction of the enclosure which I intend to build?

-Alex
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Old 29th September 2001, 07:14 PM   #16
Super is offline Super  United States
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I would go into detail, but I'm on my way out the door. In my opinion, 3/4" MDF is better than the plywood, and has better resonance characteristics. If you want to keep things simple, I would suggest mounting the crossover to the back of the cabinet. That way, you can change your speaker wire, and there's less to compensate for.

Before we discuss bracing, I need to know what shape enclosure you're going with. Different shapes require different amounts of bracing. Be sure to add this into your overall volume, too. I would suggest placing the port fairly close to the bass driver from the back of the cabinet. Porting from the rear can reduce the "whoosh" you hear coming from the port as air moves through it. PVC is fine for the port, but get the thinwall stuff. You can also buy ports online for less than 2 bucks a piece from numerous sources.

As for the shielding, well, ugh. It would be MUCH better if you didnt shield the speakers, rather, if you just placed them far enough away from your monitor. To shield it, you either have to increase the cabinet size and sheild the entire cabinet with thick metal, or you have to start attaching bucking magnets to the back of the drivers themselves. This not only changes the drivers parameters, but it rarely shields it 100% anyways, and also adds to the cost of your project, or adds a good deal of extra weight to your enclosures. What I would do is take the drivers and see just how close you can come to your monitor before needing to degauss it. If you can get withing a foot or two, you may want to reconsider shielding it. (The crossover doesn't compensate for the change in driver characteristics, thereby reducing the sound quality further)
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Old 1st October 2001, 06:22 AM   #17
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As far as the shape goes, I may just go with a rectangular box, although a pyramid (Wilson WATT-like) with the top and bottom parallel might be nice. Any suggestions on bracing each of these types?

I went to Home Depot today and found some 1"x12" x 8' feet MDF for around $6. I have to wonder if this is the 'right type' of wood. I seem to remember people stating that it was much more expensive?

For shielding..what if I covered the inside and outside of the enclosure with a thin sheet of aluminum. Would this help? It may add to the cost but I'd like to have it as an option if it doesn't affect the enclosure design.

-Alex
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Old 1st October 2001, 03:08 PM   #18
Super is offline Super  United States
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Ok, as far as a rectangular enclosure goes, the ideas of bracing it are fairly simple. Ideally, you want each wall coupled to that across from it, paying special attention to the front baffle, because its the weakest point. What many people do is couple the walls together using cylindrical wooden dowels, or closet poles. These can be found at the Home Depot for a nominal cost. Other methods include a "window pane" brace across the inside, coupling all 4 walls together. Some people do this, and then couple the top and bottom together with dowels. You have a lot of options in this category.

The pyramidal shaped enclosures are fairly easier to brace, and you'll have fewer problems in regards to controlling the resonances and standing waves. A heavy dowel or multiple smaller ones can be used to connect the top and bottom, and dowels or standard wooden braces can couple the side walls together. All thats required of this is to miter the braces at an angle, which is very simple to do. I'll give you a few links to some WW designs when I get home from school (I'm in study hall right now ).

It is possible to shield it with aluminum, although it will be very tough to work with, especially on the inside of the box. Also, thin aluminum isn't that good resonance wise, and it can even give off a "ring" from the inside and outside of the enclosure. Again, see how close you can get the drivers to the monitor without experiencing problems. You will save yourself a LOT of trouble.

By the way, I favor the pyramidal design, not only for favorable resonance characteristics, but also because it can help to time align the drivers. Feel free to ask more questions as needed. Good luck.

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Old 2nd October 2001, 05:03 PM   #19
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Super,

I look forward to the links you mentioned. This weekend
I hope to start building the monitors.

-Alex
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Old 2nd October 2001, 07:22 PM   #20
Super is offline Super  United States
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Sorry about that. Here are those links:

http://members.home.net/exquisiteaud...wattclones.htm <-- The easier of the two pyramids to construct, because it only uses a single layer of material.

http://www.users.nac.net/markowitzgd/david/david.htm <-- Little bit better cabinet, but requires over 3x the material.

Just remember, you'll have to adjust the internal volumes of the cabinet in accordance to your drivers. Good luck! Keep us posted on the progress
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