[glt]

Hi, first time trying a diy speaker project. Currently using Newform645 speakers and want to experiment replacing the bass section with OB single or dual 15" woofer.

The Eminence alpha seems a good choice for the project. The crossover needs to be at 1KHz and I have not seen any project with such a high crossover point.

I also plan to use a miniDSP for active crossover

What would be the best choice?  Thanks in advance for any info

[jtwrace]

I also plan to use a miniDSP for active crossover

Let us know what you think of this...I've been eyeing one for a long time.  They look really cool.

Sorry I can't help on your question.

[derik736]

i don't know the eminence woofers but i used my woofers crossed at 1Khz. Mine were vintage tesla that lampizator uses in his projects. These are capable to play to 1,5Khz without any sweat. I also used the Altec 420Y and goodmans axiom 301 crossed so high. But these aren't typical woofers but fullrange speakers so the frequency response and overall characteristics might be different then Eminence. If you eminence can play so high on paper, it shouldn't be a problem.
If you can, find a pair of decent ALtec 420A or 420Y and use it as woofer crossed at 1000Hz. It is very very good speaker in this range.

[i4gotmyid]

AE Speakers Lambda TD15M, i run mine with no crossover they go up to about 3k ish

[panomaniac]

Ditto.  Not sure about the Alpha, but many 15s have no problem up at 1Khz.

[glt]

Wow, so much help. Thanks for all the responses.  Right now everything is just on paper. I like the miniDSP because you can have room EQ plus crossover. The 4th order crossover will come in handy because the eminence has a peak at 2K (on paper). Ah, yes, the AE speaker was another I was thinking about, but it is 5X the price of the eminence alpha...

[versus rider]

the eminence alpha may work up to 1KHz but when I adjusted the crossover point on my behringer to about 300Hz they didn't sound all that. My full range drivers sound far superior to the eminence at 300Hz. They may work but you may well be very disappointed with what you hear. Oh and mine are in open baffle by the way. Don't take my word on it, maybe others will have a different view.

[el`Ol]

Selenium even have 18"ers that can be used that high.

[Rudolf]

It's not about the on-axis response only. Look how a 15" driver on a 50 cm wide OB will radiate off axis:



The curves are 0°, 15°, 30° and 45°. Crossing at 250 Hz would be fine, 500 Hz acceptable. If you want to cross at 1 kHz, you need a driver with the same beaming character at that frequency. That has to be a horn or a waveguide.

[Angaria]

I've pushed the alpha up that high, and even with a deq, you really don't want to.

[Figo]

altec 416/515 sound fantastic at 1K, but they don't go very low and are unsuited for OB...

woofer of that size at that freq will either sacrifice response below 50hz to achieve the necessary sensitivity, or will sound like crap at 1K.  I'd go with an altec and then a sub, IMO

[glt]

Thanks for all the info. This is the best place to learn about OB

Would the AE lambda perform better at the 1K region?

Rudolf, the driver for >1K is the newform 4" ribbon driver (don't know the beaming pattern).

But listening position is about 15 degrees, so shouldn't be too concern about off-axis?

[Rudolf]

Rudolf, the driver for >1K is the newform 4" ribbon driver (don't know the beaming pattern).

Tried to do a radiation pattern 0-45° for a 2" line source (monopole) on a 4" wide baffle of 75 cm length:



At 1 kHz the loss from 0-45° is 3 dB for the ribbon, but 8 dB for the woofer. No good combination from my POV.
You can easily try it yourself with the free simulation program Edge from www.tolvan.com/edge

But listening position is about 15 degrees, so shouldn't be too concern about off-axis?

Even when listening on axis, more than 50° of what you hear is indirect sound. You need to be concerned about off-axis response too.

What I am really concerned about is how you are trying to connect a monopole line source with a dipole point source. If you want to look into OB bass for those ribbons your aim should be a dipole line source with 5-10 drivers of 5"-7" size stacked in a vertical line IMHO.

[glt]

Rudolf, since this is my first attempt at speaker building, I was mainly attracted at the simplicity of a single drive/OB. It seems that with a 15" driver there are many issues to consider. The ribbon I have is 4', not 4"

I would then trust your recommendation for a line array of 6" woofers. Would this be a reasonable choice: http://www.parts-express.com/pe/showdetl.cfm?Partnumber=299-250 ? or this: http://www.parts-express.com/pe/showdetl.cfm?Partnumber=299-908 ?
The only thing relevant to me is that the second driver has a much higher Qts

Thanks again for all your help.

[Rudolf]

Rudolf, since this is my first attempt at speaker building, I was mainly attracted at the simplicity of a single drive/OB.

Well, OB is as simple or complex as any other speaker principle. From my point of view it is even more dominated by the "housing" than a boxed speaker. For a first attempt I would stick to something better explored than the road you are trying to go.

It seems that with a 15" driver there are many issues to consider. The ribbon I have is 4', not 4"

A 15" woofer is perfect for OB - as long as you don't make it the midrange driver too. There are reasons why the woofer-fullrange combination is so popular for a first OB. You get a well integrated system without much complexity.
With 4' the line is even longer than I considered. I thought that 4" was for the width.

I would then trust your recommendation for a line array of 6" woofers. Would this be a reasonable choice: http://www.parts-express.com/pe/showdetl.cfm?Partnumber=299-250 ? or this: http://www.parts-express.com/pe/showdetl.cfm?Partnumber=299-908 ?
The only thing relevant to me is that the second driver has a much higher Qts

Both drivers would be reasonable. And the higher Qts would in fact make things easier. Sometimes I can't believe the great deals yo guys get from PE. The Peerless offer is amazing.
But -as said - I really can't recommend such a system as a first venture into OB.
Would be nice if some of the other contributors to this thread could comment my reservations.

Rudolf

[scorpion]

I tend to agree with Rudolf and especially with LA souces they are not so easy to get right. But going DSP and wanting not to spend a fortune why not investigate in 3-way OBs. Like the MJK H-dipoles for Alpha15 and Goldwood 18" (http://www.quarter-wave.com/ - look at Open Baffle theory and Projects) and then putting a single Peerless SDS above on a say 12x28" baffle side by side of the 4' ribbon. Crossing at 200 and 1000 Hz the Peerless might use some EQ low but it will put up with it graciously. As Rudolf said the Peerless at this price is a real bargain and if later you would go for an even better unit the option is there. OK, you might have to spend some more on amplification but that you would have discovered yourself trying to press a 15" speaker up this high.

In fact I am a bit surprised about Earl Gedde's SUMMA speakers to evidently perform extremly well within your first proposed limits, so one option would be to get one of the same bassunits and design a closed enclosure from information available. But then you will not escape putting subs for the bottom.

My Alpha15s do not play over 200 Hz nowadays for reasons others have given above. It will not compete with the smaller good bass-mid or mid speakers in tone and quality.

/Erling

[panomaniac]

Just as a point of reference, here's measurements of 2 different 18" drivers on OB.  In room, at listening position.  So maybe ~30-45 degs. off axis.

Also pics of the speakers.  You can see what a difference there is in the drivers and also what a difference crossover slope makes.  The Eminence is a super clean driver.  The Goldwood, not so much. But it's not meant to be.  More intended for M.I. use than subwoofer.  The Goldwood is a hi-Q driver, the Eminence, very low.






One cheat with the Emmy.  I took out the 34Hz room bump with active EQ. No EQ on the Goldwoods.

So crossover is essential, especially with cheap drivers.  With cheap drivers you often have to trap out resonances to get good bandwidth.  This is true of 18",15" - right up to dome tweeters.

[glt]

Thanks so much for all the info. I've decided to follow the advice here and do a 3 way: 200Hz, 1KHz, which means getting two more amps and a miniDSP at a minimum. I did purchase 20 of the $10 Peerless drivers to experiment with OB Line Array. I'll do 9 per side in a 3 parallel/3 groups series configuration to keep the impedance at 4 ohm.

BTW what is a "good" (and cheap ) microphone to measure in-room response?

Also, panomaniac, what are the models of the speakers?. When you say say "the Eminence is a super clean driver.  The Goldwood, not so much" do you mean flatness of the response?...Thanks.

[panomaniac]

For a mic this is a very good choice:
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=390-801
Just remember that in room measurements are difficult because of reflections.  You have to use your best judgment there.

The Eminence 18" is not longer made, too bad.  It had very little cone break-up or other noise above its usable range.  The Goldy is not in the same league.  But it is not meant to be nor priced to be.  It's probably meant as a bass guitar driver, where you want extra noise for harmonic richness.

The Goldwood has more noise above its useful bandwidth.  That can be taken care of in the crossover, however. Yo just have to be aware of it.

[rick57]

Just saw this interesting thread . .

“Even when listening on axis, more than 50° of what you hear is indirect sound”
Hi Rudolf
50% 
I know off-axis response is important, but didn’t feel it could be that much ~ without ever seeing a figure.
Where did you see or calculate that figure?
Would it be a little room dependent, ie with closer side walls, that figure would it be higher?

Fyi I have a pair of Lambda TD15M, and cut the 46 cm (18”) baffles  last weekend. Progress will be slow, as the only wood workshop I can access is 4 hours return drive 
But I will over time try these:
 - crossing about 250 Hz to an 8” full range, as a 2 way. I thought that’d be both the easy and good answer . . until I considered the beaming above about 1500 Hz
 - As TD15M's can go so high: a 2 way, crossing about 1500 Hz to back to back tweeters. Be "interesting" to hear the drop in off-axis response, over say 500 Hz . .
 - Later as a 3 way, crossing about 350 Hz to a 6.5” mid, then about 1500 Hz to back to back tweeters