[swartzy.baby]

Okay, with all the vacation and time off I decided to try my hand at my first speaker build. I chose my drivers and components, got them, hooked them up outside of the box, and was absolutely thrilled. Granted, no real bass or anything (4" woofers; small build), but great definition and clarity. Cut the boxes out. slapped them together using some wood glue, flush-mounted the drivers, hooked it up to a receiver, and....was underwhelmed. Somehow, the clear, pleasant sounds had transformed into a muddy, poorly-defined mess. I then decided it had to be the closed enclosures' fault (HiVi M4N drivers are not recommended for closed enclosures, but thought I would try), so I cut out a 1 3/8" hole for a 1" port (to be delivered at a later date) in my 3/4" MDF, thinking that would at least improve things a bit. And it did, I think. But the definition still isn't there like it had been.


So, then I began reading up on forums, etc, trying to find out what I did/am doing wrong, and I have a couple possibilities to ask about. First, I believe what I'm hearing is cabinet resonance. It sounds like the cabinet itself is making noise/sound, though very unattractively. I did not believe I would need internal braces, since the scale of my build is relatively small...was I wrong? I'm also confused about lining the insides with a material of some sort. I currently have some Polyfill which I had been using, but in my recent readings discovered that will actually mess with the tuning frequency of my port.


Speaking of the port, there was music coming out of that as well (due to the "port" not really existing yet; it's only a 3/4" x 1 3/8" deep hole in the MDF wall?), is that normal? Of course you can't tell it's coming from the hole when sitting a few feet away, but the sound is muddy.


Something else I wondered about was the actual installation of the woofer (tweeter is external) itself. I just bought some black screws and put it in. I'm sure there's a more professional way of doing this, but is the method I used possibly a culprit?


And as for the enclosure, again, I used some wood glue/clamps to secure it together. Adequate? Not? I can feel the enclosure vibrating when in use...bad?


Apologies if these are really, really elementary questions but, well, I don't know the answers. I still have loads of MDF, so if I need to re-do the enclosures that shouldn't be a problem (frustrating yes) Thanks

 

[robertcharles]

Did you model the enclosure or just build a box?


How big is the box?


Pictures?

 

[Canadian_Dude]

You should have sound coming out of the hole that is normal. You have made a 1.375" port 3/4" long, so you will hear frequencies below the tuning frequency out of the hole there. Did you come up with the crossover and box design yourself or are you following someone else plan?


As for the box construction that is how most people do it.

 

[XanderMoser]

Speakers will always sound different in free air compared to an infinite baffle compared to a box. It's not just bass response. There are lots of diffractions occuring on the baffle that mess with your frequency response.


Creating a speaker from scratch without measurement equipment is hit or miss. Even simulations can only get you so far. What you really need is to measure the frequency response and adjust your crossover and box size and tuning.


And cutting a hole in the box is tuning to a very very high frequency...of course you're gonna hear music out of it. Get that tube in ASAP.

 

[Hades02]

You have to take the speaker parameters and model the enclosure to the

specs. It's not just about building a box and sticking a driver in it. Sometimes

the manufacturer will give their recommendation for an enclosure. Go to their

site and check. bassbox pro is a good piece of software for enclosure modeling.

 

[swartzy.baby]

Thanks for the replies. I did "think up" the design myself, though I had originally intended to use the box with a 3" full range speaker to make my first build simpler, but since I had the tweeters already (bought them when they were on sale a few months ago), I decided to give it a go. The box itself is small, outside dimensions of (HxWxD) 8"x6"x8". Barely enough room for the pre-made Dayton crossover to fit in. I'm pairing up the HiVi M4N with the TN28, attenuating the tweeter by ~6db to match the woofer, and the woofer/tweeter matching sounds pretty good.


I've been trying to do the math myself (should have known better

) based on calculations out of "Speaker Building 201", but failed to even attempt to make any sort of frequency response charts. Plugging in the T/S parameters into winISD, coupled with the rough volume of the box I'm using (~.15 ft3), the response chart is crazy under 100hz. There's a 4-5db hump in the 90's, then a rapid rolloff. I mean, I suppose there have been crazier responses, but still. And that's based on a port that has been tuned. I will wait to see what it's like after putting in the port before I throw the box against the wall and start over. WinISD's recommendations for sizes were pretty large compared to the driver - .7 ft3 for sealed, 3.8 for vented! I suppose if I were strictly using it for mid-range it might not matter so much, but I was trying to develop some nice (compact) computer speakers. I'm starting to think I chose the wrong drivers.

 

[cptomes]

Try high-passing it above the hump in response. A passive crossover (the one from Parts Express that's on sale this month would work) external to the speakers.


Most people advise to start speaker building with a known and proven design. Nothing wrong with starting off fresh, but expect to have some false starts...


I get different volume for those cabinets. For a 3/4" wall thickness and 8x6x8" external, internal is 6.5x4.5x6.5" for a volume of .11 ft^3. That would make the hump worse and raise its center frequency.


When I built similar (but a bit bigger...) cabinets, I used 1/2" instead of 3/4" MDF. With such small, low SPL drivers the strength of 3/4" isn't needed. If you're worried about panel resonance, put stiffening ribs off-center on each panel.


Given the size of the cabinets, you're not out much money.


I've never used pre-made crossovers. They never came in the right configuration. I'm pretty good at soldering so it's never been a problem.

 

[swartzy.baby]

Oh geez, you're absolutely right about the volume. I'm starting to build another box, larger (8x11x9) which (I'm pretty sure now) leads to an internal volume of roughly .268 cubic feet (7.5*9.5*6.5). I'm also trying my hand at inserting some braces (I think that's what they're called) running along the lengths of the sides, top and bottom, at 3/4" on the short sides. So, for instance, on the sides they would be 9.5"x.75"x.75". I'm also going to be buying (one to start with) the slightly larger M5N, which might make my tweeter adjustments off but I'll wait to hear how it sounds before ordering more parts. I will also be lining the interior with some 1" "acoustic foam" I have; something I did not do with the others. Putting the measurements into winISD (assuming an overall volume of .2 cubic feet after adding everything else in), that gives me a gradual decline starting around 90hz and hitting the -3db point at roughly 62.5hz, which is perfectly acceptable. The response chart is also much, much more solid, with no humps. And the driver's only $25.


So, we shall see.

 

[swartzy.baby]

An update for those that may be interested. I built an enclosure as outlined in my previous post, lined it with the foam, put in the braces, and threw in the same components that were in the previous attempt (4" M4N, TN28, Crossover), and the result is astonishing (for me and my first (well, second) attempt at this). I don't know if it was the acoustic foam (that's my guess), the bracing, or the larger cabinets, but these sound fantastic, and I could honestly not be happier with the results.

 

[oachalon]

If you probably spent a little more time with winisd you could design the proper enclosure for these speakers and a better crossover you would most likely blow the doors off what you have now even if you like them in their current state.