Need Help Getting Started - Nearfield Speakers

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I'd like to build some two-way nearfield monitors using some speakers and crossovers which I already have laying around.

The speakers are for automobiles however I'd like to utilize them in some low cost cabinets. For each cabinet I'd like to use:

1 MB Quart QM130TX (mid-bass)
1 MB Quart QM19HC (tweeters)

1 Passive MB Quart crossover, 3500Hz, 12dB/octave

This crossover came packaged with these 2 speakers when I bought them years ago.

I'm looking for some direction here - how to build some cabinets based on the speakers and crossover which I have.
Nothing too elaborate, just something that I can use as monitors to edit some recordings. Any help will be appreciated.

Alex Douglass
In order to build a proper cabinet, you'll need the Thiele-Small parameters for the mid-bass drivers. Once you have that information, it will be a simple matter of plugging the numbers into a program (any number of which are available--people tend to develop an emotional attachment to them and defend them against all comers) which will, in turn, give you the volume for the cabinet. Your next step will be the woodworking.
But first...the T-S numbers.

diyAudio Moderator Emeritus
Joined 2001

The tweeters and crossover came as unit, not much use monkeying around there.

The bass/mid will require the enclosure. I took the liberty of looking up the Thiele-Small specs at

Here they are:

Resonance Frequency [Fs]
80.90 Hz

Mechanical Q Factor [Qms]

Volume Equivalent of Air at Cas [Vas]
4.76 liters

Volume Equivalent of Air at Cas [Vas]
0.16 ft-3

X Linear [xmax]

Electrical Q Factor [Qes]

DC Resistance [Re]

Nominal Impedance [Z]

Total Q Factor [Qts]

Sensitivity [SPL 1W/1m]

86.0 dB

I have my own ideas for an enclosure for this speaker. But I will let Grey go first.
I'm hoping for some pyramids and cylinders this time around (pyramids in particular. I think we can assume that the crossover doesn't compensate for driver alignment.)

Also, with an efficiency of only 86db, looks like we're going to need a fairly powerful amp here. But I agree, lets listen to Grey first :)

[Edited by Super on 09-24-2001 at 07:13 AM]
And the three young men sat watching the flames of the dying fire, discussing the weighty matters of the day. Of boxes and ports and amplifiers strong they spoke, and methods of prying into the secrets of nature.
"Do you think he'll come?" one asked.
"I don't know," said another, shaking his head.
"Huh, I don't know if I even want the old buzzard to show up," muttered the third. "All he'll do is tell us we're up past our bedtimes."
And in truth, it was said by some that the one of whom they spoke was a fool, yet by others claimed to be wise. He was reputed to be everywhere--and nowhere.
In fact, he was...
...behind them.
Some small sound made one of them turn, and there, framed in the doorway against the dark of night, stood a cloaked figure, regarding them silently.
The young man gasped, causing his companions to turn also.
A gnarled, calloused finger raised, pointing at Alex. "I have consulted with the powers of the unseen world. The numbers have been returned on the wings of a white raven. You are seeking a ported enclosure of .51 cf volume, with a resonant frequency of 55.26 Hz." His eyes narrowed, flashing. "But I fear that you will not be entirely happy with your project."
"But, but...why?" Alex asked.
"It is not the destiny of a car driver to make a good monitor. For that, you need better drivers."
"Better?" the kelticwizard asked.
"He means it'll take eye of newt and toe of frog to make this come off properly," said Bryan. "And I went and left mine at home."
"I think I've got some in my pouch," the kelticwizard said, rummaging in the leather bag suspended from his belt.
"But one thing more will this take," whispered the shadowy figure in the doorway.
The three looked up in alarm, fearing that they might yet come up short in their efforts. "What's that?"
"Beer!" cried the old man, throwing back his hood, laughing. As he came towards the fire, he pulled off the latex prosthesis that had made his finger appear misshapen. "Everybody knows you can't build speakers without beer."
*****But seriously, folks*****
Actually, red wine or a good single malt Scotch will do just as well, if not better.
(Bryan, close your ears, lest I get arrested for contributing to the deliquency of minors...)
Jeez, fellas, you made it sound like I was supposed to arrive tap-dancing or something.
Honestly, Alex, I'm not sure that car speakers are the ticket to nirvana, here. But, if they're what you've got on hand and money is tight, then go ahead and build them. If you've got a little cash on hand, it might be better to look into other options. Just for giggles, I tossed those numbers into the program I use, and it said ported, which honestly surprised me, as I tend to think of car drivers as being in enclosed chambers. I mean, really, you just don't see ports in the rear decks of cars every day of the week.
That said, I couldn't seem to manipulate the box to give a truly flat response. It comes down to about 100Hz or so, shelves down a dB, goes to about 50Hz, and drops like a stone. If you think that a low end in that region will get you where you need to go, then get out your woodworking tools. It's up to you.


[Edited by GRollins on 09-24-2001 at 09:05 PM]
First, I'd like to think Grey for making my evening worth while. Nothing can quite compare to a combination of DIY audio and a good chuckle now and again. But anyways...

As Grey (sort of ;)) said, these drivers definitely aren't ideal, but if you have them on hand and don't need audiophile quality, then why let them go to waste?! So, lets start with the materials.

MDF: Material of choice for the DIYer. Heavy, fairly easy to work with, and better characteristics than hard wood in term of resonance. Depending where you're from, the cost for the MDF (medium density fiberboard) can be between 12-40 bucks, and can vary with your cabinet design. The thicker the better. 3/4 inch is widely available here, so I often double it up for 1 1/2 inch width. However, this stuff is MESSY. Its made from compressed sawdust, so its a good idea to work in a well ventilated area. And I STRONGLY suggest wearing a painters mask. It helps a lot. Also, its not a bad idea to have carbide bits, and a few of them for each tool. MDF is extremely hard, and wears bits down like none other.

Tools: Basically a must have: A router (though a dremel or Roto-zip with router attachment can be substituted), a table saw (unless you dont like straight cuts), plenty of clamps, and a drill or drill press. Again, carbide bits and replacement bits are strongly suggested to have on hand.

Putting it all together: There is some debate in this area. For attaching the driver, t-nuts and threaded screws seem to be the way to go. For laminating boards together, any strong wood glue or Liquid Nails will do, although I like to use "Rue glue". I get this from a nearby woodworking company. It dries slightly rubbery, giving it excellent damping, but once it dries, you're more likely to rip the face off of the MDF than you are to break the bond. If you are going to use screws to hold it together, I suggest drywall screws. They have a bigger thread, so they grip the MDF better. All vented cabinets must be sealed very well in all areas except the port. You can use your choice of materials for this, although I and many others use silicon caulk. Its a good idea to let this dry first, because the fumes can damage the driver. Also, you need to line the inside of the cabinet. A heavy felt can be used, but I prefer to use acoustic foam (the egg-crate stuff). It helps that I get this extremely dense foam for free from "Hi-Tech Packaging"; a company who my father, a UPS man delivers to.
Also, if you want to keep the cabinet from resonating, you're going to have to brace it. Be sure to compensate for all bracing when calculating the final volume.

Port tubes can be made of PVC, or there are several online sources to find them, for a neater look, and not much money. Now, we get to the shape...

If you want to keep things simple, you can make a box. Is this the best enclosure? In my opinion, no. Whenever you have a right angle, you have standing waves, and this we want to avoid. I can point you to a few pyramidal designs online, similar to the Wilson WATT appearance. For a small monitor speaker, I'd point you in the pyramid direction. If you have no woodworking skill or know how whatsoever, then come back and let us know, and we'll continue this further...
Thanks for the feeback!

You guys are outstanding! Thanks for all of the feedback. The epic yarn by GRollins still has me laughing.

Some of posts have me thinking a little more about this project. I expected to lose some bass but didn't quite think that I'd have as much dB loss from 50 - 100Hz. I guess I'll just have to sacrifice some bass. Also, I saw an estimated 86dBSPL W/m. Would this be the overall sensitivity for the speakers in the enclosure, or just the speakers by themselves? I don't plan to listen to the speakers very loudly. They will only be about 3 feet away from my head, played at modest levels.

I guess that I'd be losing some more sensitivity if I go with an outright sealed box. Any chance I can get something reasonable (better than regular Yamaha PC speakers) with a sealed box?

My setup will be PC soundcard -> audio receiver -> monitors.
Currently, I am using Yamaha YST-MS25 (R, L, and subwoofer). The subwoofer is OK but the two small L and R speakers are nothing to brag about. My goal is to construct these monitors to replace the R and L Yamaha speakers, and later on the sub. as well.

Thanks again,
Alex Douglass
Sensitivity, I believe, is almost always measured by itself, primarily because different boxes change the sensitivity (horns for example). The industry standard is to present an 8-ohm speaker with a 1 watt (2.83 volts) input signal and measure its output in an anechoic chamber with a microphone at a one-meter distance.

Being rather inefficient as they are, I wouldn't suggest placing them in a sealed box. It will take more amp power to reach the same output levels, and you'll lose even greater bass response. A sealed application doesn't seem to be the appropriate choice in this application, especially if they are only going to be played at moderate volumes.

Trust me on this one. Its not very hard to outdo almost ANY mass produced set of PC speakers on the market. Even with these drivers, I think you'll see a world of improvement.
Sorry...I guess I got rather carried away above...
Anyway, Alex, the T-S specs carry within them strong hints as to whether one should use a ported or sealed enclosure. The numbers for your drivers (assuming that the data from that site that kelticwizard found are correct) point towards a ported enclosure. That's not to say that you can't use a sealed enclosure, but be prepared to sacrifice a bit of performance in the process.
If you're going to use them nearfield and at 'moderate' volumes (moderate for some folks around here means that the trees in the back yard are swaying, but those out front are merely trembling) you need not worry about efficiency or sensitivity. A modest amp will drive them well enough.
Whether car speakers or PC speakers are better...oi! I think I'll go have another drink.

Your other option might be a <a href="">Tapered Quarter Wave Tube/Voigt Pipe</a>

Theres two excel spead sheets <a href="">here</a> for calculating the enclosue.

As to its suitability for near field?

diyAudio Moderator Emeritus
Joined 2001

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]
diyAudio Moderator Emeritus
Joined 2001

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]
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.
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?

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)
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.

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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