DA175 MT design (Zaph, are you out there??)

[gonar]

during PE's xmas sale I bought 6 da175s, 4 to build a pair of Zaph's BAMTMs, and the other 2 to bring the price up to the free shipping minimum (was buying other stuff too...)

I would like to use the two spare da175s to build some 8ohm nominal MTs for my daughter's stereo. her current receiver can't drive 4Ohm speakers (klh r5001 el-cheapo receiver, probably wouldn't even drive 6Ohms.) originally, the BAMTM's were going to be for her, but I can't justify a better receiver for her, yet.

anyway, I haven't come across any MT designs for DA175s (yet) but given the bang/buck ratio of these drivers, it seems like a no-brainer.

is anybody aware of an existing design?

would anybody like to help me design one?

the things that attracted me to the BAMTM were the simplicity of the xover, and the overall cost-effectiveness of the design. I would like to try to keep this MT design in the same cost/complexity league.

eventually, when I can get her a new receiver, I would probably build her a set of BAMTMs and migrate these MTs to surround duty..

EDIT:
Man, it would be great if Zaph designed an BAMT to match the BAMTM

[Mudjock]

There are a couple designs around from people who hang around on the Parts Express board. The Silver Al (see www.retrieveraudiolabs.com) uses the DA175 with the Dayton silk dome tweeter. Pete Schumacher did an MT with the DA175 and the HiVi K1 tweeter (available at Madisound). I believe he brought those to DIY Iowa last year, so someone who heard them might be able to comment.

[gonar]

I found the Silver AI. looks interesting and prices out pretty cheap, although the tweeter crossover is a lot more complex than Zaphs for the BAMTM (I know, different tweeters, one driver instead of 2, different xovers...)

also he specs wire wound resistors and electrolytic caps (which is _great_ for cost, and I guess at this price point, it's probably not worth moving to the more expensive stuff)

he built his using clearance BR1 cabs, anybody know the measurements for driver positioning on the baffle (going to build my own cabs)?

[Mudjock]

I have some of the clearance BR-1 cabinets - so I can get the dimensions for you later tonight. If you want to use a better tweeter (like Zaph's design) it should be possible to model an MT version that will at least get you close. Pete Schumacher may have already done it...

I think there would be considerable benefit from using a tweeter like the Seas H1212 - since it would allow you to use a lower crossover point and get away from the higher distortion region of the DA175, which will somewhat limit the performance potential of the Silver Al's.

[gonar]

reading Zaph's BAMTM page, by upping the value of r6 to 9ohms, that attenuates the tweeter on the order of 3dB, approximately what I lose by cutting from 2 woofers to one (right?)
EDIT:
wrong, something I read tells me I lose 6dB does/can the baffle gve me +3?
/EDIT

, so if I could get a 1450 Hz LR4 low pass for a single DA 175, then I _should_ be able to just build "the bottom half" of the BAMTM baffle and have a fairly good starting point...

that would give me 8ohms nominal in the lower freq range, 6 ohms in the upper (where I understand it's less critical (wrong?))

given the same baffle width, and a desire to keep as simple a xover topology as possible, is a 2 component 1450 LR4 low pass even possible for a single da175?

[Mudjock]

I tried this in Passive Crossover Designer and found that simply doubling the inductance and halving the capacitance should work well for the low pass (about 3.5 mH inductor and 15 uF capacitor). The trick will be getting the H1212 to blend well. My first cut at it indicates that the 10 uF capacitor will work, but you will need a little smaller inductor (about 0.24 mH instead of 0.3 for the MTM) and a considerably bigger resistor (about 14 ohms). For this much attenuation of the tweeter, you might get better results by having a series resistor and a parallel resistor or by having a resistor before and after the crossover (those approaches will give you some flexibility in adjusting the slope of the tweeter response as well as the level).

[Mazeroth]

I had a chance to listen to the Silver Als at the DiY Dayton 2006 this year and they sounded pretty darn good for how much they cost (I think $80-$90 in parts). What really caught me by surprise was listening to Tool's newest album on these while they were playing at absurd levels. They never sounded harsh, by my standards, which is remarkable, considering the ho-hum reviews I've read on the silkie tweeter.

I'd say go for it! :T

[gonar]

ok, ordered the following:
tweeter circuit:
2x 0.25mH 19AWG Air Core Inductor $ 2.75 (each)
(couldn't find .24, how many turns should I take off?)
2x Bennic Poly 10 mfd $ 3.75 (each)
4x 7.5 ohm - 15 watt wirewound resistor $ 0.45 (each)
4x 6.5 ohm - 15 watt wirewound resistor $ 0.45 (each)
(with these I can make 13, 14 and 15 ohms for the tweet to find the right resistance, replace with better ones later)
2x 27TBFC/G (H1212) Aluminum/Magnesium dome $ 32.80 (each)

woofer circuit:
2x Sidewinder 3.5mH 16AWG $ 15.10 (each)
6x GE 5.0 mfd 40L Poly Cap 400V $ 0.75 (each)
(3 in parallel on each side will make 15uF)

for the boxes...
1x Acousta-stuf Fill 1# $ 9.5 (each)

[Mudjock]

You should be able to keep the high pass inductor at 0.25 mH. If you put 15 ohms on the amp side of the crossover (before the 10 uF cap), you should have a very similar response curve to the BAMTM (about 6 dB less efficient) and a very easy impedance load.

[jkrutke]

To answer the topic, yes, Zaph is "out there". :B

I could model this crossover with my data but one minor issue is that my tweeter data is taken in an MTM arrangement. That typically measures a little different due to the baffle and cavity effects.

The values you've selected are probably close enough.

[gonar]

Thanks to all for the help! Zaph, thanks for the vote of confidence.

Mudjock, thanks for the advice. I noticed you changed your mind from 14 to 15 ohms for the tweet, 14 modeled too bright?

I'm planning on building this on a 9x15 baffle, 10.5 deep (.75 mdf all around) for .527 cf gross, ~.5 cf net to line up with Zaph's BAMTM .5 cf per woofer sealed box.

I'm planning on keeping the same c2c distance between the woofer and tweeter and keep the tweeter offset. basically try and keep as clost to a BAMTM with one woofer lopped off as I can...

I will start on this this coming weekend or next.. (finishing up a nightstand sub for my daughter this week)

I suppose when I get this all done it would be cool to measure it and see if it came out worth a darn.

EDIT:
just got an email from madisound, tweeters are gonna be delayed 2 weeks, but I already have the woofers and I told them to send the rest of the stuff right away, so they should be all done, with the xover's all wired up by the time the tweeters get here.

[jkrutke]

EDIT:
just got an email from madisound, tweeters are gonna be delayed 2 weeks, but I already have the woofers and I told them to send the rest of the stuff right away, so they should be all done, with the xover's all wired up by the time the tweeters get here.

I've got a pair of 27TBFCG's on ebay for... 1 million dollars.

[fjhuerta]

I've got a pair of 27TBFCG's on ebay for... 1 million dollars.

Hopefully, they don't have that hexagrid cover... :T

[Mudjock]

Mudjock, thanks for the advice. I noticed you changed your mind from 14 to 15 ohms for the tweet, 14 modeled too bright?

I got a chance to play around with the design a little more, and 15 ohms seemed to match the response curve I modelled for Zaph's design better than 14 ohms. The primary difference was around 10 kHz and up - so depending on the room and personal preference, you might still want to experiment a little.

The other thing you will want to consider as you build this is the tweeter offset. In the BAMTM, the tweeter offset is 1 3/8 inches from center. In an MT cabinet, this might be a small problem if the spacing between the tweeter flange and the nearer side is about the same as the spacing between the flange and the top of the cabinet (in my experience with the H1212, it can lead to an on axis spike around 5 kHz). In that case, I would recommend either centering the tweeter horizontally on the baffle or reducing the offset to something like 1/2" or 3/4".

[gonar]

thanks for the advice about offset! I was trying to set my baffle dimensions so that the tweeter is a different aperiodic distance from each edge of the baffle, as I read somewhere that it can have a big effect.

I don't suppose you could post the modelled curves?

speaking of the hexagrid cover, is it removable, and if so, should I remove it?

[Nathan P]

Great thread, I am in the same position. I have two of those Dayton tweeters modified as here: http://www.partsexpress.com/projects...kdome/mod.html they are yet to be tuned (You adjust the position of the pvc on the back until they match what you want and each other), but they should sound even better than the stock ones. What changes in the crossover on the Silver Als would be needed?

[gonar]

my box-o-crossover-parts arrived yesterday (tweeters on backorder).

man that 3.5 mH inductor is HUUUGE.

I would like to mount my crossover on the bottom of he speaker in order to minimze stress on the hot glue holding the big coil in place, are there proximity issues with coils and woofers? (I was planning on mounting the coil as far towards the back of the speaker as possible oriented so the axis of the hole is perpendicular to the bottom)

should I use zip ties instead of/in addition to hot glue?