idea of a small monitor with 8" woofer/tractrix horn

[angeloitacare]

hi all

i've drawn a small monitor, using a 8" woofer and 12" diameter tractrix horn for mid/high. idea is to use a bms 4590 coax compression driver , crossed at 600hz,
and a precision devices woofer, http://www.precisiondevices.co.uk/showdetails.asp?id=74

any sugestions/comments ?

Angelo

[JonMarsh]

Nice looking design you've drawn up.

Be aware that Precision devices seems to be "fudging" on the Xmax- they rate it at 16 mm P-P, implyin a linear Xmax of 8 mm in one direction, BUT, the coil depth is 13 mm, while the gap depth is 6.5 mm, which works out to about 2.5 mm each way...- not long throw for a 8, though in a monitor application in small enclosure (they're talking 5-20 liters, whereas most 8" two way systems I've done have gone around 44-68 liters), so , consider it's really a midbass/midrange driver, which is kind of confirmed with a Qts of 0.279. The true sensitivity in the range you plan on using it is more like 90 dB, not shabby, but not the peak output of 93 in the upper midrange.

I'm inclined to think that a Dayton RS270 might be a better match, what with 90.5 dB/W sensitivity, and 6.6 mm of Xmax. Plus quite a bit more Sd. It would come closer to keeping up with the horn and BMS driver, and isn't all that dear price wise. Unless of course YOU are in the UK, then that's another matter.

Other woofers to think about for high efficiency with a 600 Hz crososver might include an Eighteen Sound 12ND930, 12NLW9300; Ciare 8.50NdW (if you insist on an 8" high efficiency), maybe the 10.5NdW or 12.00NdW1.

Just some ideas...

Are you planning on building the horn yourself? Why not an oblate spheriod, with it's lower HOM and generally nicely controlled dispersion?

[angeloitacare]

the dayton seems interesting

hi Jon

thanks for your reply. The bms drivers are very fast, high sensivity
(112db/wm) , so i need a mid/bass that catches up on them. i don't know if it makes even sense to use a 8" woofer. Probably a 10" is the better choice. In the drawing can be seen the size difference of the cab's, using a 8", and a 10" woofer. While the cab with the 10" is 32" x 17" x 24" ( not so small anymore ), with the 8" it gets 24" x 13" x 18".

The dayton seems interesting, however i dont know if aluminium cone sounds good. I like more paper cone. Sensivity is no problem, i would have to built in a attenuator anyway for the horn.
The german company AES :

http://www.aes-kassel.de/horn_bb/bd_design/oris_250.htm

uses the Beyma 10LW30/N in combination with bms4592nd driver and 250hz tractrix horn : http://www.beyma.de/seiten/framesets...t_beymapa.html
it seems to me to be a good match. What do u think ?

i dont know what is oblate spheriod, never heard. I live in brazil, and pretend to make the horns with two solid wood blocks, glued together, and than worked on a lathe.

What i want to accomplish, is small size, high-end performance, the woofer
very fast, and going as deep as possible. how abought to split between upper bass, and sub bass , adding a subwoofer , downfiring ? i've no one seen doing that. i dont know if i would have to shield in this case one woofer.

rds angelo

[Tommythecat]

I think some answers are in order...like are you building the horn? What's covering the bottom octaves (certainly not the 8")? Where would you cross that?

It just seems like: Why cock around at that point with a horn that big just to mate it crossed so low to an 8? And if you're willing to build a tractrix horn, just try an OS - otherwise (for less time/hassle/effort/tools) go with a properly terminated conical horn.

When designing around an 8" mid - I feel the real benefit is the fact that I can cross higher while maintaining a smooth polar response around the crossover point. This allows for the use of a 1" exit compression driver mated to a smaller horn - then the horn+mid can be squeezed together to minimize lobing problems.

The 4590+12" horn seems like a match for a 10/12" mid and 15/18" midbass.

edit:shoot, you responded before me...

[angeloitacare]

hi Tommy

i will built the horn. I want a small enclosure, that's why i want to use max a 10" woofer. As it is very difficult to have a woofer, witch is fast, and goes deep at the same time, it's why i think if it would be a solution/good idea to use a mid/bass front firing, and a sub woofer down firing. I do not want that someone has to buy a separate subwoofer. I want to cross as low as the horn alouds, as i want the horn to cover as much as possible. That alouds more phase coherence and to use the benefit of one point source. what is os ?

[Paul W]

Google for a program called "Hornresp". With it, you can model Tractrix, OS (Obulate Spheriod), Spherical, and many other profiles. After modeling an OS in Hornresp, you'll need to add a large radius (~1/4 wavelength) roundover at the mouth to minimize diffraction.

I also vote for a larger LF driver. The BMS will be still be coasting long after an 8" is overdriven.

[angeloitacare]

hi all

just wondering : to use a subwoofer for the lowest octaves, would i need to shield the volume of the driver? some manufactures do use subs in the backpannel, like zu. i think it would be a interesting solution, to put a sub, downfiring. but i dont know if it would give interferences internally, it i wont shield it. anyone can give me a answer on this ?

thanks Angelo

[Paul W]

If by shield you mean a separate partition or separate chamber for the subwoofer, the answer is yes it does need to be isolated from the midbass.

[angeloitacare]

sub downfiring

thanks, paul, for your info.
do u have any experience with sub's ? i want to use a 10" sub, witch does need only a small volume, working from 20hz - 50hz. i was thinking abought peerless, may dayton, ore adire.

Angelo

[Paul W]

Downfiring is fine, but 10" is small to me...it can be overpowered by BMS top end. I have BMS 4552ND, so I can guarantee BMS compression drivers in a waveguide will play LOUD with low distortion.

If you have small room 10" may be okay. Dayton aluminum cone RS subs should give you excellent performance. Sealed enclosure for midbass and sub will help minimize cabinet size. (By the way, I think you have excellent visual design.)
Paul

[angeloitacare]

may a atenuator resolves efficiency discrepance ?

hi Paul

i know , the BMS has a staggering 113db/wm, and a small, 8" woofer, does not have more than 93db, in the best case. i think to resolve this, there are two ways: bi amplification, ore use a atenuator. As i would have to seal a downfiring woofer, and i do not have enouth space, may the best will be just use one frontfiring woofer, with enough low octave output. Someone gave me a hint to try A Beyma 8BR40, it looks nice, is cheap, and has low fs, (31hz). That would be proably a good match.

thanks, rds Angelo

[Paul W]

Hi Angelo,
Yes, I agree single front woofer is a better way to go. However, I would do it with more than 8" with 5mm Xmax. Anyhow, have fun!
Paul

[angeloitacare]

pic's of the bigger enclosure at factory

hi Paul

here some pic's I made today of the first speaker I am building:

Images not available

rds Angelo

[Paul W]

Angelo,
Those will look very nice when you are done. Will you turn the horns on a lathe or build a mold?
Regards,
Paul

[angeloitacare]

they will be made on a lathe

hi Paul

the first pair, i will use Orphean Horns of BD-design, ABS plastic, red automotive color. But in the future i pretend to make wood horns, made on a lathe.

rds Angelo

[angeloitacare]

hi all

here some new ideas:

Images not available

[JoshK]

Muito Bem Angelo!

Can you buy the horns seperately or do you have to purchase their speaker kit? I have been curious about the BMS 4592 since I first saw it.

[angeloitacare]

you can buy only the drivers

hi,

you can buy the drivers and filter separetely.

[Paul W]

Josh,
If you're looking for tractrix, these are a decent price. They will drill the flange for BMS for free and even do custom colors for a small premium. As I recall, the shipping quote was about 50 euros.

Angelo,
The pictures you are posting are truly inspirational. Keep them coming!
Paul

[angeloitacare]

tractrix horns

hi josh

if you want wood tractrix horns, like cessaro and hornfabrik eder from germany make, with plywood , i will make the first pair ,starting next week. the pair withou flange shoul be around 700us. if you are interested, let me know.

more pictures

http://www.flickr.com/photos/7881544@N05/

rds Angelo

[JoshK]

Angelo,

Thanks but I'm not ready to play with tratrix yet, just a bit curious. I have too many things to finish up first. The thing I like about the BD Design horns, at least from sight, is they don't look as deep and a broader dispersion. The horns from german on ebay look quite narrow in their dispersion (and therefore deep).

I am still looking for someone to create a large OS waveguide like 15". At some point in the future I am going to buy a wood lathe and learn to spin. Now I have no room and no time.

[JoshK]

P.S. where in the North do you live? I've been to Salvador de Bahia (Carnaval '01).

[angeloitacare]

i live in aracaju

hi josh

aracaju is the next city north of salvador, abought 300km.

rds Angelo