The Small Bangs: plans for a little 2nd order MTM speaker

[fjhuerta]

Hi all, Merry Christmas!

Santa brought me (well, they are still on their way) four TB W4-1658SB drivers.

http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=264-878

http://www.parts-express.com/pdf/264-878s.pdf

It looks to me as a prime candidate for a second order filter. The break-up is at 10 KHz or so, and they look pretty smooth up to 4 KHz on both charts).

I already have a good subwoofer, so I'm not very worried about their bass extension.

Given that I want to build a speaker with a controlled vertical dispersion, an MTM seems to be a natural choice.

Given that my wife doesn't care about vertical dispersion, crossover topologies or other stuff, but loves small, unobtrusive speakers, an MTM with small woofers and a sub looks like the best compromise for us all. :rofl:

My plan is to build an ultra small MTM with a SEAS 27TBFC/G, crossed over second order at around 2.9 KHz, with the TB drivers.

Given the specs of the drivers involved, I'd assume the crossover would be extremely simple, and the sound quality pretty high.

The only thing I'm worried is that there are no distortion measurements of the TB woofers. That's the first thing I'll take when they get here. I'd assume they shouldn't have much problems at the frequencies I'll be using them, though.

I want to go 2nd order because I've heard many good things about their power response. Hopefully, I chose the correct drivers for this task (I know the SEAS tweeter is an excellent choice. I'm not sure as to how low I could cross the driver without damage).

Let's see if I understand this correctly - excursion requirements quadruple when you go an octave lower... is this right? If so, would a 4th order, 1450 Hz filter (the one used in Zaph's BAMTM) require the same excursion as a 2nd order, 2900 Hz one? If so, am I correct in choosing 2.9 KHz as the crossover point?

I'm also unsure about the behavior of an MTM using 2nd order filters. I believe there shouldn't be an issue, but I'm not completely sure.

Thanks for any help...

[Operandi]

Sounds like a nice look speaker.

Did you consider the W4-1720 though?

[fjhuerta]

Yeah, I did. As a matter of fact, I was very close to buying them. The reasons I didn't were various...

1) P/E had a sale on the W4-1658SB's - $44 each.
2) S/H on 4 W4-1720's costs $100 to Mexico - 4 W4-1658SBs were $66.
3) I am intrigued about the 1658SBs - nobody has tested them. Last time I did such a thing, I got lucky and bought 4 W4-1337s
4) Their frequency response seems to me to be easier to work into a 2nd order curve.
5) I like their looks.

Hopefully, their HD sweeps will look fine.

[fjhuerta]

Apparently, there's not much interest in this build.

I'll just try and find out if a 2nd order crossover can work on an MTM. Hopefully, it will

Santa brought me a plunge router and a circle jig, too!

[impala454]

Javier I am somewhat interested and watching the thread, I just have nothing to offer

[Xander]

Javier I am somewhat interested and watching the thread, I just have nothing to offer

x2

I like those small woofers...

And I like that Seas tweeter...

Just don't have the money right now for another pair of speakers

[fjhuerta]

Update.

MDF has been bought and cut.

Still waiting for the Tang Band little woofers.

[fjhuerta]

The Tang Bands arrived.

Strange little drivers. In my limited experience, I have never seen anything like them.

Here they are, next to a W3-1335 driver (another unit I have never seen tested).



Side view. Is this an under hung driver? I had never seen one.



Another shot of the driver. It's a complex basket. Nothing I had ever seen before in a Tang Band driver, that's for sure.



Top view.

[LING GOWA]

I don't see any off axis measurements.

[fjhuerta]

I don't see any off axis measurements.

Tang Band never does off-axis measurements, and I'm still on the "how on earth do I use a plunge router" phase of the project. :B

[Operandi]

Nice looking driver, looks like a underhung design to me. The frame seems to be new to TB, some others use similar looking frames though (Morel, Dynavox).

What do you have planned for the little Ti driver?

[fjhuerta]

The little Ti driver may go into any of two designs I've thought about:

1) a WMTMW with the RS150s and Seas 27TAFN, or
2) a WMT with an Usher 8137A and Seas 27TAFN.

It's quite possible I'll go for #1, though.

[fjhuerta]

Things are progressing slowly, but smoothly.

After quite some time, I managed to build the baffle.

Some observations:

1) The driver is NOT 5.5", no matter what Tang Band says. It's closer to 5.80". On the inside, it is 4.5". Even funnier - the driver's external diameter is bigger on the bottom than on the top. So, if you measure the driver on top, the driver won't fit on the baffle!

2) One of my drivers' cones is strangely misshapen. It's a very small thing, but I wonder if it'll affect performance.

3) I don't fully understand the raised faux-screws on the driver. I don't think they'll help diffraction.

I chamfered the underside of the baffle for better airflow.

I'll be doing distortion testing later this week.

[eyekode]

I have been wondering about those nipples on the flange. Don't have any idea what they were thinking...

[---k---]

3) I don't fully understand the raised faux-screws on the driver. I don't think they'll help diffraction.

I wonder if those are there to assist with alignment when installing the driver behind the baffle. I'm guessing there is a company somewhere using 1000's of these and they get to add whatever odd ball feature they want. That is all I can think of.

[fjhuerta]

I guess you could be right, Ryan. The flange is very thick - a bit more than 5/8".

And airflow looks pretty restricted from behind. I wonder if the chamfer will be enough.

A very strange driver, indeed.

[ThomasW]

In situations like this the drivers are typically mounted in a piece of 3/16" aluminum and that's mounted in the baffle. It's the only way for this type of design to 'breath'

[fjhuerta]

In situations like this the drivers are typically mounted in a piece of 3/16" aluminum and that's mounted in the baffle. It's the only way for this type of design to 'breath'

I was thinking about using this company to mount the W4-1337s, but shipping is prohibitively expensive to Mexico...

http://www.frontpanelexpress.com/

These drivers are even more restricted than the W4's. Actually, they are far more restricted... I think an aluminum panel would help, but the problem is the basket itself, IMHO!



Those little slits between the chrome Allen screws and the mounting frame (where you can barely see the drivers' surround) are the only thing that allows the cone's backwave to exit. The other holes (the big ones) are for the spider.

[---k---]

In situations like this the drivers are typically mounted in a piece of 3/16" aluminum and that's mounted in the baffle. It's the only way for this type of design to 'breath'

Ahhhh, so wise!


Javier,
Maybe consider doing a rear mount with the front of the baffle rounded over as a waveguide like Dan is doing in his Basslines. This would be easier than the aluminum and allow the driver to breath as much as the design allows. If I remember correctly, he stated that his measurements show no impact on the FR when the mid was mounted this way. You'll just have to make the baffle removable or some other way to install the drivers. Oh, and it looks nice too.

[fjhuerta]

That would mean routing a new set of baffles, but the suggestion is great Ryan... thanks!

I can still do such a thing, I believe. I need to see if one of the baffles I built could be used - all I did was cut the holes for the woofers, and the tweeter holes were never made. All I'd need to do is chamfer it and do the cut-outs for the tweeters on the other side...

[ThomasW]

If need be a adapter ring of 1/8" could be used. I find it hard to believe you need to go all the way to the US to find a small piece of alu. I buy the stuff at a local scrap/surplus store. Denver is a lot smaller than Mexico City, so I think you should be able to find local supplier.

Another option would be an adapter ring made from 1/8" Lexan/polycarbonate.

[fjhuerta]

You wouldn't believe it, Thomas. There's a brand of very high end audio built in Mexico (the owner just came back from the CES), and they can't find anyone to build the enclosures for their amps! They have to bring them from China..the hard part is finding a machining shop that will do the cut-outs with the needed precision.

[Eric89GXL]

I'll be doing distortion testing later this week.

Did you ever get around to doing this? I'm interested to see the results, especially for that W3-1335SB driver. Are you going to do frequency response measurements as well?

EDIT: If you do distortion measurements, could you check the W4-1337's as a reference?

[fjhuerta]

I decided to wait to do the distortion testing using the final enclosure. I may have them by next week (I cut the baffles and sent the boxes to be built with a local furniture maker).

I may not do distortion testing on the W3-1335 for a while, specially considering that I still don't know how to use ARTA. Today, though, I decided to give it a shot. Thanks (probably) to Windows 7, I couldn't do a thing (don't get me wrong, though - I love 7, and I think I may finally switch from XP), but I did do a FR comparison with my old laptop using LSPCad.

I didn't like what I saw at all. The enclosure I used to do the testing is old, and I had to do mounting rings for the drivers. Still, the W4 performed like a champ (as always), and the W3 struggled quite a bit.

They do sound good as full-ranges, though. I could definitely live with a pair of speakers for NF listening (say, PC speakers) with them. The break-up is so far high in frequency it may not be noticeable (I did notice a slight hint of "metallic" highs).

I'm not sure about using them as mids, though. I need to learn how to use ARTA!

Reference is the W4 driver.

[Eric89GXL]

I didn't like what I saw at all. The enclosure I used to do the testing is old, and I had to do mounting rings for the drivers. Still, the W4 performed like a champ (as always), and the W3 struggled quite a bit.

They do sound good as full-ranges, though. I could definitely live with a pair of speakers for NF listening (say, PC speakers) with them. The break-up is so far high in frequency it may not be noticeable (I did notice a slight hint of "metallic" highs).

I used the W4 fullrange with an LCR filter to tame the top octave, and it measured very flat. I don't remember if it was a series or parallel filter; my guess would be parallel.

ARTA shouldn't be too bad to use. If you track down the manual, it says:

ARTA can simultaneously estimate the frequency response and levels of harmonic distortions from the measured PIR. To apply this method, following measurement conditions have to be fulfilled:

1) The impulse response must be measured with a logarithmic swept-sine excitation (defined in section 5.2).

2) The length of the excitation sequence should be 64k or larger.

3) Measurements have to be done in a ‘Single channel mode’, with activated the check box ‘Center peak of impulse response’.

After obtaining impulse response in the PIR window the user have to:

1) put the cursor few samples in front of the peak of the impulse response (but less than 250 samples before the peak), and

2) press keys Shift+F12 or click menu command 'Analysis->Frequency response and distortion.

In any event, that W3 response is disappointing compared to the W4. Oddly, it doesn't look like the W3 matches the manufacturer's response curve as well as the W4. I hope it turns out just to be a problem with the enclosure or measurement, and not a reflection of the driver's performance. Unfortunately (for the W3), it sounds like you know what you're doing, so it might just be how the driver behaves...

[fjhuerta]

Hi Eric,

I'm not completely sure. I wonder if the mounting ring on the 3" was vibrating when the measurement was taken.

I still have hopes for the little guy, though. It really sounds very nice as a full range speaker. It has a lot more bass than what I was expecting. It definitely sounded "lighter" than the W4, but it wasn't bad at all.

As soon as I learn how to use ARTA, I'll try a new set of measurements.

[Dennis H]

STEPS (ARTA companion) is the one you want for distortion measurements.

[flacoman]

Great minds think alike !

I'm looking to build a 5.1 set for my living room with those 5 1/4 and the TB ceramic domes . I'm looking at 4-5 Khz as a crossover point, with a 4th order slope. Can they play that high without complaint?
Brouser burped , pardon the double post

TIA
Jorge

[mackintire]

You can do a 2nd order LR crossover, just remember to invert the polarity of the tweeters.

[flacoman]

Would anyone object to my posting crossover?

If I could i'd like to post my (weak) attempts at a crossover netwok for this
TIA
Jorge

[fjhuerta]

sure! Although 4~5 KHz is too high, IMHO. I haven't done any testing (the cabinets should be finished next week), but the CTC spacing may not be optimal.

I'm set on a 2.7~2.9 KHz crossover at 2nd order. The SEAS tweeter, though, is far sturdier than the little Tang Bands...

[flacoman]

Small difference here...

Small detail: I'm planning this as a simple 2-way , not MTM
Will this permit me to raise the x-over frequency?

[fjhuerta]

CTC spacing of an MT with the TB woofer would be around... 2.9" + 1.3" = 4.2"
Speed of sound: 13 397.2441 inches / second
Max CTC frequency: Speed of sound / CTC spacing = 3,189 Hz

I have heard conflicting opinions about CTC spacing using an MTM. Some people believe CTC is between woofers. Others say it's between woofer and tweeter. For my application, 2.7 KHz is the lower I'd take the 27TBFC using a 2nd order filter. But theoretically, if I used the CTC between woofers, I'd need a 1.488 KHz crossover...

[flacoman]

I should be able to get away with using the TB ceramic tweeter with a steeper slope and padded down to match the single woofer. What do you think of the new underhung motor driver (W4-1720)?

[fjhuerta]

I don't know much about it, but Zaph thinks it's a very good deal. I wanted to get the W4.1720, but since it was far heavier than the woofers I'm using, getting the 1658's instead was cheaper for me.

[flacoman]

Schematic rev b <fingers crossed>

Hopefully this is readable thinking of bobbing the flange down on the tweeter to get the spacing down .
TIA
Jorge

[fjhuerta]

You can do a 2nd order LR crossover, just remember to invert the polarity of the tweeters.

Trust me, inverting the polarity of the tweeter is the least of my worries. I need to find out whether the TB's can handle up to 2.9 KHz or so without too much distortion.

[fjhuerta]

Hopefully this is readable thinking of bobbing the flange down on the tweeter to get the spacing down .
TIA
Jorge

What acoustical order is the woofer? With a 4th order electrical, I'd assume it's close to 6th order acoustical.

Also... did you measure it? I'm curious - due to the woofers' behaviour, I'd have expected it to need at most a second order electrical for a 4th order acoustical.

[flacoman]

You're quite correct , back to the drawing board ooorrr I could go for one of those nifty metal coned drivers!

[fjhuerta]

This is crazy. 3 weeks have gone by, and the local furniture maker just called to come and see the speakers.

EVERYTHING about them is wrong. He got the size of the cabinet wrong, he didn't make a removable baffle, he installed the baffle backwards, and the finish isn't the one I asked for. The boxes aren't even parallel!

I returned them. I don't know if they'll build them all right next time. I can't understand it - these guys build any kind of furniture, and they can't get a simple box right? Incredible.

I thought building the baffle myself was enough. Now I'm slowly beginning to realize I'll have to learn to build the boxes myself.

[Eric89GXL]

What a disappointment. Sounds like you might be better off buying a table saw and router...

[fjhuerta]

Table saw... that's all I need. I already own the router.

For the price of a new set of cabinets, I could probably buy it.

It's worth considering.

[fjhuerta]

Time doesn't fly when you are having fun.

It has been... 6 weeks? I'm not keeping track of time anymore. But the furniture maker called today - the cabinets are ready!

I suppose small projects like these aren't worth his while. Still, he delivered. Oh, yeah.

The speakers are awesome. He used a brazilian wood laminate (can't remember it's name) with a dark red tint, and painted the baffle in a beautiful red hue. They are easily the best looking cabinets I've ever had. At $200, I really can't complain - they are really stunning. It was worth the wait.

I'll take pictures of them tomorrow. I already bought about 20 pounds of plastiline. I'll line the interior with it, and then add some foam on top. Overkill? Probably. So, to make it a sure thing, I'll also add some plastiline to the baskets of the drivers.

Hopefully, next week I'll be able to take the first measurements. I'll try to lift the speakers off the ground at least 1.7 meters, and take mesurement at 8 ms, just to be sure bass response is just right.

Hey, I started this project back in December, I want it to be perfect!

[Eric89GXL]

Can't wait to see the pictures and measurements.

[fjhuerta]

I've got it all...

First of all: distortion measurements on the woofers.



I'd assume this means I can use them as high as I'd like them to.

I had assumed I could use the woofers on a 2nd order filter without issues.

Apparently, the measurements aren't even nearly as friendly as I expected them to be. Maybe it has something to do with T-B's published specs being presented in such a way that any response curve will look flat.