Parts Express Low Cost Home Theater Project

This project began as a desire to replace my KEF C1 bookshelf speakers and their sealed sibling the C6LCR center speaker. Since this its undergone three incarnations beginning with this:HT-1

In this incarnation I had the tweeter overlapping the woofer in an attempt to reduce the distance between them. While this worked it also created some odd sounds as air moved in and around the small pocket under the flange of the woofer. After creating a first crossover using Jeff Bagby’s PCD I realized I need to change the tweeter mount and cut the front off the boxes. This time I didn’t flush mount the driver and ended up with this incarnation:

new-baffle

In this incarnation all appears as it should be but it sounded like “SHIT”. Whoopee I can say shit here. I had more hills and valleys in the Frequency Response than grandmas have wrinkles.

phase questionWhile I was able to get a reasonable frequency response using only 11 components for a crossover I new I was fighting the baffle diffraction I had introduced since the previous design so I again decided to cut the front off the boxes and make new baffles which leads me to this:

New BaffleThis image only represents the driver placement. Two major things have changed. First the driver placement and second the tweeter. This version uses the Vifa XT25SC90 Neo Ring Radiator which is a small neo magnet version of the larger Ring Radiators sold by Vifa (Peerless), Scanspeak and others. I also realized that part of the issue I had before were all the large bumps and sharp edges on the baffle surfance. In this version both the woofer and tweeter are flush mounted. I like the asymmetric design better than the symmetric anyway. I still don’t know how this Visaton woofer really sounds when crossed correctly. It looks OK on paper. It has no huge breakup modes below 5K so if crossover can sufficiently reduce the level of the first large breakup mode around 4.5K it should sound very decent indeed.

Visaton W130S 8 Ohm frequency response and impedance.

Well, I had to completely re-measure and re-simulate the crossover several times before I was able to get usable results. Finally I got a usable crossover for this speaker and it sounds very nice. It has a bit of an edge to the tweeter but that might disappear with a stereo pair. I need to finish building both crossovers and listen to them as a pair for a while. Apparently the harshness comes from crossing this tweeter too low. It may have an fs below 1K but it does not cross low. I found 2.9K to be about the lowest reasonable crossover point. I initially tried at 2.7K and found it to be noticeably harsh. Changing caps moved the crossover point to 2.9K and it sounds very nice and smooth once it breaks in. It does seem to need a little time to loosen up cones in the tweeter before it smooths out. In all fairness I didn’t test it at 2.7K for very long so it might very well cross that low. In this design though it’s not necessary. Were I using a pair of woofers below this tweeter I’d be wanting the lowest XOP possible.

Update March 2nd 2013:

I finished these speakers about two weeks ago and have been listening to them as my front left and right home theater pair now for that long. At first they sounded a little harsh but now that I have a few hundred hours on them they sound perfect. I haven’t put any veneer on them yet because I wasn’t sure how to go about it but I purchased some Red Oak veneer for my next project and found it quite easy provided I prepare the surface first. I’ll probably get a darker wood for these and go ahead and veneer them. Rather than put a grill on them I’m going to remove the drivers and simply trim around them so the speaker will be completely covered in veneer. It will look like a solid block of mahogany which is probably what I’ll use. Below is the finished speaker with the riser I built to house the crossover components. I ended up with a fairly complex crossover consisting of a second order electric with an AL-1 notch filter for woofer and third order electric on the tweeter to align phase. Tweeter required some padding in the form of a 4 Ohm padding resistor between the first and second component in the crossover.

Finished with riser
Crossover schematic below shows the finished circuit. I have a little small step coil for a stand mounted woofer and it does sound a little thin in an open room on stands but blends very nicely with a sub woofer.

XO schematic-small

Will post finished project pictures when I do finally get the veneer on them and finished. It will certainly look unique with veneer trimmed right up against the raw driver frame.

In overall listening tests these speakers have a superb stereo image. I don’t know if it’s due to the offset tweeter which position I chose to reduce diffraction, or if if’s a good quality tweeter. This is not a woofer i would use again. It does work well in a sealed enclosure and goes down to 80hz easily but it lacks the transient response of a nice hard cone like aluminum, kevlar, carbon fiber or carbon/poly mix. However, it can also be built for at or near $100 per speaker making it an exceptional value. Below is a polar plot with 5 measurements to 90 deg on one speaker. This plot shows off axis response to 90 deg, meaning a full 90 degrees off to the side, and we still have some tweeter response. Best of all we get no nulls or dips due mostly to the crossover point and ring radiator combination. This Vifa XT25SC90 neo magnet ring radiator is one of the best tweeters around for dispersion. The stereo image it produces is astounding. On my home theater it’s difficult to tell whether sounds are coming from the HT or if there really is a police siren racing by outside. I also keep transient sounds like people walking around in the background or in the rear speaker field that sounds absolutely real. If you are looking for an excellent inexpensive speaker for home theater this might be exactly what you are looking for. All the parts can be ordered from Parts Express including the cabinet. The speaker baffle does require routing but if you want to build a pair send me an email and I’ll be happy to cut out a pair for you for a reasonable price. All other components are straight PE parts. See Parts Express dot com.

Tweet on Right turned to Right

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