Speekerz wot I maid

[Tenson]

Apologies to anyone who has already seen this, I have posted it in a few places.

This is based on the Seas T18RE/XFCTV2 (H1333) which is a coaxial 18cm driver. This driver is used in the Ascendo C7 & C5. there are a lot of other speakers out there which use some version of this driver but I don’t think they are this latest ‘TV2’ version, but they are out there and probably very good.

My aim was to build a very good speaker with the minimum of fuss. So it had to have a simple crossover and simple cabinet. …and that’s what I have done I think!

In terms of sound they are on par with speakers costing a few thousand. Nearly as good as my PMC AML1s. They image VERY well, as would be expected and have surprisingly deep tight bass for the size of the cone.

They cost me about £300 all together.

Oh, and I designed them originally to have a rear tweeter because the roll-off of the tweeter in the Seas is pretty early so they sound dull. But after playing with the Xover I decided I liked them more without the rear tweeter and simply using a resistor to compensate the early roll-off which seems to work perfectly. My point is, I built mine with a sloping back, but you really don’t need to and I have not drawn the plans that way.

So, some pictures! I do have a few of the build but I have to get them off my Dad’s camera and since I did mine with the sloping back and you probably won’t, it doesn’t mean a lot. But it is a very simple box and I’m sure anyone with a bit of woodworking skill and build it in their sleep.







I know, I know… not a living room friendly colour! I always wanted a pair of boy-racer, Ferrari red speakers with go-faster stripes but never thought I would be able to live with them for long. So I finally have my wish And actually they suit my room very well! The white lines are in fact grooves cut in to the wood. I painted the primer in to the grooves but just went over the top with the red. I wish I had Shinobiwan's skills at paint finishing but I think not only don't I have the skill, I don't have the patients either! I want to see them done and finished as soon as I can

Here are the plans – internal and external measurements as well as showing how the wood goes together. I used 18mm MDF. To the left there is a diagram of how you can get the wood for both speakers out of one sheet of MDF, so wood won’t cost more than £20-£30.

I stuffed the cabinet pretty well as I will show in the pictures I get from my Dad's camera. But the important thing is to put lots of absorption (I used Rockwool) around where the driver mounts. I was getting some colouration which was reflections from the internal sides of the cabinet coming back through the cone. Once I put rockwool to either side of the cone it cleared up completely. I used lighter stuffing, the more standard loft insulation wads (the sort that hold their shape but are floppy) for the rest of the cabinet.

The port is tuned about right for most rooms I expect but for mine I tuned them slightly lower by using a longer port. This is a good thing to do if you have a small room. I made my port 55cm. The speakers are tuned for use near room corners BTW. It makes no sense not to IMO.

There is also the crossover diagram. Very simple indeed The tweeter is marked as ‘-‘ because I think Seas already invert the terminals on it, so although it is a 1st order high-pass you have to wire it ‘out of phase’.

You can adjust the amount of treble by raising (more treble) or lowering (less treble) the value of R1. I am using 2.7 ohms but it is too bright and have some EQ in there, only because I don’t want to order just two resistors! I think 1.7 ohm will give about the same as I am hearing now. You might like to play though. 1 ohm in either direction should be ample adjustment.

You can also adjust the amount of bass and lower-mid via L1. A higher value will give you less bass, a lower value will give more. 0.3mH in either direction should give enough adjustment range.



Thank-you and enjoy

P.S. It does look a lot like the Ascendo C7 but apart from using the same driver it is completely my own. It would have been more similar wit the rear tweeter, admittedly.

[sreten]

Hi,

they look very nice but your crossover leaves a few things to be desired.

What is the point of the 1.7R tweeter resistor ?

It is not amplifier friendly with an ~ 1.5R treble impedance.

I cannot see the point of R3 either, and its not amplifier friendly either.



http://www.humblehomemadehifi.com/USB.html

Something like the above would be better or like :

http://www.madisound.com/pdf/seas/Se...nd%20Xover.pdf

/sreten.

[Tenson]

Sreten,

The Madisound Xover is too complex, I wanted something as simple as possible.

The HumbleHomeMadeHiFi one is probably quite good but I don't have experience of series crossovers and don't fully understand hy he chose to do it exactly that way, so again I'd rather not use it.

Oh, and both of those are for the older Seas driver, but it is about the same.

If you read what the designer said about the 'USB' speaker he said that it sounds a but dull, warm and soft. Thats because the tweeter rolls off pretty early - and thats what R1 is to compensate. If I didn't have that, I would need to use an L-pad to bring it down to the level of the woofer after the baffle step. But I want to boost the high-end anyway so I just have R1 rather than an L-pad.

R3 is part of a standard baffle step correction network such as that described in 'The Edge'.

It sounds fantastic. So my only worry is the amplifier load. I have some rather meaty studio amps (modified Alesis RA500) so frankly I don't care, and they don't complain!

The beauty of this Seas driver is how simple you can go in the Xover and still get great sound. Yes I could use impedance correction on the woofer and tweeter and a low pass on the woofer and... but it doesn't need it.

This is what SpeakerWorkshop thinks the impedance of the overall network will be. It is not particularly nice but it is not that bad I'd have thought. My Cyrus 3 does seem happy enough driving them.

[Pano]

I like 'em! The look really, really fast.

Funny little drivers. Thanks for the pix.

[Tenson]

Talking with Thorsten he pointed out that 4.7uF in to 1.3 ohm (the tweeter and parallel cap) is about the same as 1uF in to the tweeters own 6 ohm DCR. So I tried that and it is pretty close. After a bit of toying around I have found that 1.33uF with a 1.33 ohm resistor in series with the tweeter gets me the same response I was listening to before, but with a much more acceptable impedance plot. Thanks for the tip Thorsten! I would update the design plans above but for some reason DIY Audio won't let you edit after a few minutes?

So here is the new design, also with a slightly modified port length after reconsideration.



and the new impedance plot

[pjanda1]

Great looking speakers. You have a different definition of "living room friendly" than I. I love the color. The stripes remind me of Merlins.

pj

[Tenson]

Thanks.

The colour is 'Fire Cracker' from Dulux and I got it in Satinwood.

I think they suit a student pad more than your typical living room.

[pinkmouse]

Are you going to bring them along to the meet?

[Tenson]

Maybe. If I do I will need to get you to give me a lift

But I am also planning to make a nice small speaker soon so if that’s done I can take them on the train.

[sreten]

Hi,

Well the tweeter c/o section is now far more acceptable in terms
of loading, distortion measurements are the only sure way of
finding out if you can get away with a 6dB electrical section.

The bass section is still somwhat crude, probably omitting R2+R3
resistors and using around 2mH would give similar / better results,
noting as it stands all you have is BSC and no 6dB electrical roll-off.

/sreten.