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Old 2nd June 2004, 08:41 PM   #1
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Question "fixing" a speaker project, going from 2 way to 3 way

Hi all, I've been reading this forum for a while, but I haven't posted here yet. This post is kind of long; it starts out with some background on my DIY speakers.

I recently designed a set of speakers based on Martin King's mathcad worksheets. I didn't want to just do a project somebody had already done (half the fun designing and learning), but his software was a big help. Here's a picture:

Click the image to open in full size.

They are the large towers (solid birch front, the rest is birch ply). The B&Ws on top aren't mine, and aren't here anymore.

The main driver is an Eminence Beta 8, operating from about 35 to 4,000 hz. Before anyone tells me that you can't make the driver do 35 hz, I'd just like to say that you can. There is a fairly stable shelf in the output where 35-400hz is about 5 db below the output from 400-4k.

Here's the simulated FR- I forget why I thought that this would be good enough to go ahead and build the speaker. I guess I'm young and dumb. (didn't think a recessed bass response would be a big deal)

Click the image to open in full size.

The observed drop matches with the models based on the driver FR and the mathcad worksheets. I'm using a digital equalizer to correct this shelf, and the sound is fairly even and balanced now. The bass is there, and at low listening levels it goes nice and low, and gives good detail on different bass guitars, strings, and synthesizers.

The problem is when I listen at louder volumes, the beta 8 just can't produce enough bass- it starts to visibly move. 90% of the time it's "good enough", but sometimes I want to feel the kick drums in my chest. Also, I'm 22 and I want to impress my friends!

This cabinet is 44 inches high, 10.5 wide, and 16 deep (internal). There are two rear firing ports near the bottom. Stuffing occupies the top two thirds to three quarters of the box. I don't want to get into an argument about quarter wave resonance- I say that this is how I hit 35 hz, yet people in other forums have said that the performance I've got should not exist, and that this is merely a tall bass reflex.

Now here's the part I'm looking for opinions on. I'm looking at taking the eminence beta 8 off of bass duty, and crossing it over to a side firing 12, or perhaps a front firing 10 or two.

The first option I can think of is constructing a sealed compartment of 1.75 cu ft behind the 8 (vas is 1.25, winisd shows this to look a lot like an infinite baffle). This would leave 2.5 cu ft for the woofer, and the option to have the woofer ported or not.

The second option I can think of is creating a ported enclosure behind the 8". This would be a 0.7 cu ft vented enclosure for mids, tuned to 70 hz. This would leave 3.5 cu ft for the woofer, again- ported or not.

The tweeter is a Morel MDT-20. The crossover is first order at about 4khz, with a capacitor in series with the tweeter, and an inductor in series with the woofer. Their sensitivities seem to be well matched, with the difference being made up with another digital EQ shelf.

It really boils down to three questions. Ported or closed for the mid? Side firing 12/15 woofer, or front 10(s)? and the third question- is this crossover going to be a nightmare?

Oh yeah, and the amp I'm using is a Hafler DH-500 I just brough back from the dead
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Old 4th June 2004, 03:01 AM   #2
Ap is offline Ap
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First off if it works then dont mess with it,
than again if you are unhappy then re-design.
The Beta8 is designed as mid fs of 58hz & low xmax means as you have mentioned when you turn it up you can see the drivers move!
I dont think side-fired woofers 12 or 15 will give you that kick (which is in the range 100-200) you are looking for.
A front firing 10, Deltalite 2510? (or pair of 8s) will
- how about a pair of the Dayton 8 series 2 (re is high so paralleling is fine, S=90db single so you should get 96db for two!)

.ps sealed for mid in 3way is much easier.
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Old 4th June 2004, 03:58 AM   #3
azira is offline azira  United States
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Interesting... I have a pair of 8" woofers with a Fs ~55Hz that I put into a TL also. I actually noticed exactly the same results you have. I thought that it would go down to 40Hz but not with as much volume as I had hoped. Nice to know I didn't screw up that much.
I think I'd cross it with a sub down around 150 Hz but it would seem like a waste to build a big TL cab and not get to run it low.
I know this isn't exactly in your choices but what I would (will?) do is create a standalone sub using dual 10's or 12's.
--
Danny
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Old 4th June 2004, 05:03 AM   #4
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Quote:
Originally posted by Ap
...
I dont think side-fired woofers 12 or 15 will give you that kick (which is in the range 100-200) you are looking for.
A front firing 10, Deltalite 2510? (or pair of 8s) will
- how about a pair of the Dayton 8 series 2 (re is high so paralleling is fine, S=90db single so you should get 96db for two!)

.ps sealed for mid in 3way is much easier.
From what I've been reading, I think I'm going to have to agree with you about going with a sealed midrange. Clarity in the vocal range is one of the things I notice.

Also, I've got to agree with the suggestion for a front firing woofer. I've heard people talk about how you've really got to cross below 100hz for side firing because of directionality and for imaging stability. I've examined some electronic kick drums, and they all have initial transients (not counting the slap) with fundamentals around 250hz.

Thanks for the suggestions on the drivers; but I'm not sure if they'll go quite low enough. I'm looking to get to 30hz; lower if possible. I listen to some electronic music (and occasionally classical) that goes that low.

Right now I'm looking for a front firing 10, and considering these peerless 8's:

http://www.partsexpress.com/pe/showd...number=297-614

One thing that I've decided is that I definitely want the bass to be sealed, for the sake of transient response. I'm finding it difficult to find a driver that will go to 30 hz in a sealed box.

I've got 4.25 cubic feet (internal) to work with, and I only need 0.5 cubic feet to give the beta 8 a Q of 0.7. That means I have some 3.5 cubic feet to work with. It would be a shame to have to start all over; these cabinets are very large, and in person they also look good. I'm convinced that this can go to a 3-way, and give good performance all around.


Quote:
Originally posted by azira
Interesting... I have a pair of 8" woofers with a Fs ~55Hz that I put into a TL also. I actually noticed exactly the same results you have. I thought that it would go down to 40Hz but not with as much volume as I had hoped. Nice to know I didn't screw up that much.
I think I'd cross it with a sub down around 150 Hz but it would seem like a waste to build a big TL cab and not get to run it low.
I know this isn't exactly in your choices but what I would (will?) do is create a standalone sub using dual 10's or 12's.
--
Danny
Danny, I'm not sure if it's the Fs or the Qts that has the worst effect on these. Honestly, if I had a huge house I would consider the standalone subs. As it is, I have no idea how I'm going to move across country with these things. (and I'm moving any month now- just graduated)

The bottom line is that I love the TL bass and mids, but this wasn't the right driver, and the design is too compromised. I don't have trouble with holes in the bass; just that it's too recessed overall.

Ok, so it sounds like my next step will be finding a woofer that will go from 20-400hz within 3.5 cubic feet. (optimistic, but that's what to look for). I think I'll cross it over above 200 hz; maybe as high as 300 hz. I'll position the driver(s) below the tweeter, but high enough that the woofers can play high without messing up imaging.

Joe


PS-
Ignoring the rest of the spectrum, you should hear a 35 hz sine wave!! This isn't a good thing, but you can walk around my room and find the nodes and antinodes of standing waves by ear. That would bug a lot of people, but it seems really cool to me that I can demonstrate to friends that sound has an observable wavelength. It always impresses them when I tell them how the TL relies on quarter waves (they're nodding and saying "ok" the whole time), and then it REALLY sinks in when they can walk around and see what waves are like.
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Old 4th June 2004, 07:05 PM   #5
azira is offline azira  United States
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Quote:
Originally posted by joe carrow

Thanks for the suggestions on the drivers; but I'm not sure if they'll go quite low enough. I'm looking to get to 30hz; lower if possible. I listen to some electronic music (and occasionally classical) that goes that low.

One thing that I've decided is that I definitely want the bass to be sealed, for the sake of transient response. I'm finding it difficult to find a driver that will go to 30 hz in a sealed box.

I've got 4.25 cubic feet (internal) to work with, and I only need 0.5 cubic feet to give the beta 8 a Q of 0.7. That means I have some 3.5 cubic feet to work with. It would be a shame to have to start all over; these cabinets are very large, and in person they also look good. I'm convinced that this can go to a 3-way, and give good performance all around.

I've been thinking about using 2 Peerless XLS10's in a sealed box for my own sub. But given your volumn numbers, WinISD says you can only get to about 50 Hz (-6db). That's nearly an octave off of what you want... Those have Fs's of 19Hz too.
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Old 4th June 2004, 09:07 PM   #6
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I wish I'd made the front baffle half an inch wider... the Adire Shiva would be down 3db at 38 hz, and down 6db at 28 hz, and down 10db at 20 hz.

It would look a little silly trying to fit the Shiva on the front of this baffle... its overall diameter is 12.25", and the baffle is only 12" across. It's cutout is 11".

I'd love to put it on the side, but in order to get all of the "kick" in those drums, it's got to crossover around 300hz+ !

If only the Shiva came in a 10" model...

Does anyone know any other botique brands to look at?
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