# Building a Simple Sealed Studio Monitor (1st project!)



## Signals (Mar 18, 2013)

Hello!

Well, I was doing some research and I've come to the conclusion that sealed monitors and a subwoofer would be a far better solution for my recording studio monitoring needs than my current 8 inch ported speakers (Inexpensive Mackie MR8's).

Apparently sealed speakers have far superior transient response/less smearing than ported speakers, which really appeals to me. I would actually prefer the gradual low end roll-off of a sealed cabinet over a ported speaker's sudden low end drop off. 

However, there seem to be very few sealed cabinet designs available as kits! I saw a few, but the cabinets they wanted were beyond my building ability - I'm more of a rectangular box sort of guy!

Anyway, I'm doing my research and trying to figure out how best to build a nice sealed monitor that is say, accurate around 100 hz - 20 khz +/- 3 db kinda thing - That's the goal anyway!

I have a book on loudspeakers I can use to calculate some rough cabinet sizes and whatnot. Should I be doing it this "old school" way, or is there software out there these days that will make designing these a breeze? I could definitely use some help with the software if there is.

Also would prefer to do this as inexpensively as possible, but willing to spend around $500 per speaker if necessary.

I'll post my progress as I go.

Thanks for the help!


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## fusseli (May 1, 2007)

Welcome to HTS!

I think your goals are very realistic, 100Hz-20kHz +/-3dB should be easily attainable. If you find the right design or are able to take the time to design and vett yourself, that could easily be more like 100Hz-20kHz +/-1.5dB with some decent drivers.

What are your size limitations? Did you have an ordinary 2-way in mind with a typical 5" or 6" woofer and dome tweet?

And yes, there is a lot of very good free software out there and not much of a reason to do any calculations by hand. If you have Microsoft Excel, these few spreadsheets by Jeff Bagby cover almost all of the design phase: http://audio.claub.net/software/jbabgy/jbagby.html


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## Signals (Mar 18, 2013)

5 or 6" woofer and dome tweeter would be a perfect. How would I know which would drivers will deliver a nice flat spectrum? Do I just pick a speaker and attempt to optimize the box size and all that as much as possible with those excel files, or is there a faster way to know what's going to be fairly accurate across the spectrum?

For size, it could be 14" x 14" x 14" at the most. Otherwise I don't think it'll fit on my desk, haha. 

I think it would be really cool to do a coaxial project, because of the superior phase relationship. Do you know of any coaxial speaker models that could give +/- 3 db accuracy in a sealed enclosure?


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## fusseli (May 1, 2007)

I have seen many many 2-ways of this design, as that's a pretty common format. I haven't seen any coaxial designs, but I have seen coaxial drivers around. I would suggest you start with a proven design (someone else's that's been built, measured, and verified) first, that iwll greatly improve your chances of success. Proper modeling and measurement is how you get a good, flat spectrum. It's not as simple as taking a raw driver that plays flat and sticking it in a cabinet. You'd want to pick a woofer and tweeter that overlap in theyir playable range, preferably with similar sensitivity and impedance.

Try browing around the gallery at PE TechTalk, there could be some coaxial designs there and/or you might get some ideas.


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## Signals (Mar 18, 2013)

Well, I took your advice on browsing those forums and I found something very appealing.

A single full range speaker:

JX92S (can't link to it since I don't have 5 posts, but just google it if you're interested). Distributed by Jordan-USA (it seems like EAD is distributing those drivers now though?).

It seems nice and easy, because they give instructions on how to mount it in a tiny box - auratone style. Plus it wouldn't require a crossover, but I guess that kind of defeats the purpose of learning!

I figured I'd try something like this with it:

Add a switch on the front that inserts a component that will highpass the driver at around 200 hz (to turn it into a more similar approximation of an auratone-esque device).

Possibly, if it's simple, add another switch on the front that inserts a lowpass around 5 khz.

Do you see any potential issues with doing something along these lines, or should it be fairly straight forward? 

Also, how difficult would it be to make these active/powered monitors that accept quarter inch jacks for input? Does the DIY community do much of that?


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## Jstslamd (Nov 30, 2010)

From what I understand and this is just my prospective and what I've gathered along my journey. It is no way shape or form factual. Full range designs are not 100% full range. If you want the flattest response with compromise of budget and size I would look for a solid two way design. Just my two cents. 

.... Not worth much.


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## fusseli (May 1, 2007)

If you saw someone's project that was just dropping a fullrange driver into a cabinet and calling it good, you should not take that as a proven design. Even fullrange single drivers need at least some contouring applied with a crossover in order to correct for baffle step. Baffle step is the frequency point, determined by baffle size, that sound shifts from omni-directional (low frequencies) to a point source (high frequencies). The simplest single driver design would be a single driver, a sealed box, and a few components for BSC. A speaker without any compensation would probably sound empty, and I can guarantee it would be nowhere near flat. It will be much more difficult (and perhaps require an expensive) to make a +/-1dB single driver fullrange than it would be to make a +/-1dB 2-way, that being said +/-3dB would be attainable I do believe.

I posted an initial crossover for a tiny 1.5-way fullrange that I may build for my own computer speakers one of these days in this thread. It may not be exactly what you're looking for but it might shed some more light!


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## fbov (Aug 28, 2008)

Signals said:


> ...However, there seem to be very few sealed cabinet designs available as kits! ...build a nice sealed monitor that is say, accurate around 100 hz - 20 khz +/- 3 db kinda thing - That's the goal anyway!


I have a personal favorite that fits your bill perfectly.
http://meniscusaudio.com/continuum-pair-p-1324.html

You'll note these are a Jeff Bagby design, the same guy whose name is on all that SW fusseli linked you to. He has a complementary subwoofer design. The trophy is 1st in Unlimited Class at MidWest Audio Fest. 
http://techtalk.parts-express.com/showthread.php?232854-The-Continuum-Subwoofer

I've built the Continuums and they are among my favorites from the first time I heard them at a DIY event. They disappear into the sound field, and blend nicely with a subwoofer, too. do some research and you'll find that Jeff was targetting the LS3/5a. BTW, no bad speakers at salksound; his was the other design that disappeared that day. 
http://salksound.com/continuum - home.htm

Have fun,
Frank


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## Signals (Mar 18, 2013)

Well, I guess I should clarify my interest in the JX92S. 

In recording studios, being able to monitor just mid-range from a single point source is EXTREMELY useful - even if not 100% accurate. It makes adjusting the level of vocals and other mid range instruments a snap. That's why Auratone style boxes are so popular. I figured the JX92s would be a great speaker for this specific type of application. I guess you could do a less flexible but flatter design using a mid-woofer just to cover the mid frequencies only. Obviously this is not the only monitor you would use for mixing, you'd want a nice legitimate full range set up as well.

I guess that leads me to another question, if I am trying to make an Auratone style monitor, if I used a nice mid frequency driver, say a 4" or something that goes from around 200 hz to 10 khz or something, would I need to add a highpass/lowpass to the circuit to protect the speaker if I'm running a full range signal to it? 

The 2 way Fbov mentioned looks perfect for my needs. I'm just not sure if my wood working skills are up to snuff to build those cabinets! And it looks like you can't get the speaker for his complimentary sub design anymore?

I guess I'm looking into building a more elaborate monitoring set up now, which involve a "mids only" auratone type small sealed box, and a full range set up (which preferably would be the 2 sealed speakers + sub).

So I guess I'm still looking for a few design ideas, especially for the small sealed auratone type box. Anyone got any good driver ideas for something that will just cover mid-range (somewhere within 200 - 10 khz) with excellent accuracy, in a small sealed enclosure?

Thanks for the help guys, appreciate it!


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## fbov (Aug 28, 2008)

Not sure where you looked, but "out of stock" is curable...
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=293-650

Plus there are a half dozen drivers in this class that would substitute well. 

But I forgot about the baffle recess... yes, that requires a router, common among those who cut circles a lot, but not a beginner tool. This is the one case where you can buy it in a box, too (salksound link). 

Have fun,
Frank


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## Signals (Mar 18, 2013)

Well, it's actually out of stock on that page too. Looks like they're planning on getting more in though, since you can still buy it.

I'm looking at hiring a woodworker in my city to help me build the boxes. At least that way I'll learn something over just purchasing the monitors pre-built. 

Cheers,

Alex


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## fusseli (May 1, 2007)

Signals said:


> Well, it's actually out of stock on that page too. Looks like they're planning on getting more in though, since you can still buy it.
> 
> I'm looking at hiring a woodworker in my city to help me build the boxes. At least that way I'll learn something over just purchasing the monitors pre-built.
> 
> ...


Hiring out the woodwork is fair game!  Git 'er done.


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## Signals (Mar 18, 2013)

Hey guys, quick question!

I want to create the Auratone single driver speaker shortly here - a Single driver in a small sealed box.

I want to enhance it's features over a regular Auratone speaker by adding two physical pots (rheostats) on the front of the speaker box. 

I want one rheostat/pot to control highpass, and the other to control lowpass. 

The speaker will likely be the E100 (JX92) HD. 

What would be a good reference book for designing circuits like this?

Any advice on the typical way that this kind of circuit is wired?

Are there different ways to do it in series/parallel?


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## Signals (Mar 18, 2013)

If someone gets a chance, could they please check that this sealed enclosure is in the ballpark for this driver?

Here's my plans:

https://dl.dropbox.com/u/6627888/Alex_Auratone.pdf

Here's the driver:

http://www.eadsweden.com/drive-units/ead/ead_e100hd

I'm still learning about the circuitry required to make the highpass and lowpass pots for this guy. I'll post up my design schematics when I've got something figured out.

Thanks in advance!

Alex


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## fusseli (May 1, 2007)

I've never seen trim pots for caps or coils with large enough values to be useful in a passive crossover. The best you could hope for would be a multi-throw dial or switch that could toggle between different crossovers inside the speaker.

I checked your box size in WinISD, you'll need that to be fully stuffed to get the Qtc down in the low .7 range.

I strongly recommend modeling your baffle in something like Response Modeler. You'd be best suited implementing a contour filter for BSC. Just tagging on an HPF to blend to other speakers is a sure recipe for phase effects and non-flat response.


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## Signals (Mar 18, 2013)

Excellent! Looks like I'm getting a hang of calculating the enclosure sizes.

Yeah, I forgot to mention that the enclosure was supposed to be fully stuffed to get that Q! Good catch.

I agree with you about the switches for the highpass/lowpass as opposed to some kind of elaborate rheostat device. I keep reading that highpass/lowpass filters affect phase in some kind of way, and I'm still reading up on that. I still can't wrap my head around how a single driver can have "phase" because "phase" the way I'm used to thinking about it in my recording studio isn't quite the same!

I'm going to give that BSC and Jeff Bagby excel stuff a shot here and see how else I can optimize these little speakers.

I've changed the design around a bit for the little Auratones.


These speakers.

http://www.eadsweden.com/drive-units/ead/ead_e60

Moved to a smaller size speaker (2") to roll off more lows and get a more detailed mid-range, which is really the whole point of the unit. This speaker isn't technically a full range speaker, so I hope I don't run into issues running a full range signal to it (at fairly low volumes, sub 5 watts kinda thing). 

This cabinet.

http://www.parts-express.com/pe/showdetl.cfm?partnumber=300-7040

This cabinet actually works well with that speaker. I think it comes out to having a Q of right around 7 with a bit of stuffing, I'll have to check my calculations again. I'll have to get a piece of 1/8th wood, and cut out the square shape of the speaker. That'll be glued to the front so the speaker can be flush mounted. Seems the easiest way. The F3 I think is around 130 hz, which is great because it's going to avoid a tonne of the bass issues.

And this little amp here looks like it'll do the trick!

http://www.parts-express.com/pe/showdetl.cfm?partnumber=310-310

So I'll keep looking into the circuit design for this. Maybe just a couple low pass switches, one at 8 kHz and one at 4 kHz would be pretty effective for it's intended use. 

Actually, can anyone predict what would happen if both switches were on at the same time? That would be useful to look into. I'm not sure if it works like this, but it'd be cool to say if you had a lowpass at 15 kHz and one at 10 kHz, and then with both on it low-passes at like 5 kHz or something. I doubt it's that simple though. 

Lots of stuff to look into! I'll be back with the results on that BSC.


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## fusseli (May 1, 2007)

To further muddy the water for you: for a speaker there is both electrical phase (crossover dependent) and acoustic phase (what comes out of the speaker). A speaker design needs to have both precisely modeled in order to be accurate.


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## Signals (Mar 18, 2013)

Yeah, I'm really familiar with acoustic phase, but the whole electrical phase thing just blind-sided me. Wasn't expecting that at all, had never even heard of it before haha.


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## Signals (Mar 18, 2013)

Okay, did a bit more research.

So, I figured out a pretty simple way to do the highpass and lowpassing.

I figured for convenience I'd combine the high passing and low passing onto one switch, which I'll label "focus" on the speaker.

I'll be using this switch, which is a 4 way single throw.

http://www.parts-express.com/pe/showdetl.cfm?partnumber=060-570

I figure'd I'd connect it like this. Simple first pass filters.

Position 1 - HP None LP None
Position 2 - HP 100 LP 15 Khz
Position 3 - HP 200 LP 8 Khz
Position 4 - HP 300 LP 4 khz

Hopefully I can cram all these capacitors and inductors into the boxes, haha.


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## Signals (Mar 18, 2013)

Well, I ended up building the continuums myself. Kinda tricky to do the circles! I tried it with a jig saw first, and it was nowhere near perfect enough, so I bought a fly cutter (circle cutter for drill press thingy) and did it that way. Much easier. In the future I would like to get a plunge router and a jasper jig, I think that would be the ideal way to do it.

Powering them with a little 8 watt (per channel) tube amp.

They are by far the best sounding monitors I have, no comparison (and those HR624's there would've been easily over $1000 new). No idea why people use ported speakers for mixing, it's so much easier on sealed units.

I'm not sure what I'll be building next in terms of speakers (well, besides a guitar cab I'm building next week), but I'll keep you guys posted.

Thanks for the help!

Alex


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## bbm (Oct 1, 2013)

nice build, love the result ! building myself a pair too !
also, can you give me a link to your amp ?


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