DiyMobileAudio.com Car Stereo Forum banner

1 - 20 of 48 Posts

·
Registered
Joined
·
731 Posts
Discussion Starter #1
Since I am a bit of an attention whote. Ahem...

Well, I have been doing lots of experiments with all kinds of drivers I had laying around. My favorite was 15 inch drivers and compression horns from a 1960s Magnavox in a simple baffle. Sounded phenomenal for what is was. Second favorite was my line arrays, which were a mistake (way to big).

So on that note, going to do a serious project this time around. This is an attempt at a fairly low distortion, 20hz(30?)-20khz tower at moderate listening levels. Ill post some pictures when I'm done in a couple weeks. They consist of modified Fostex FF85KeN:

planet_10 hifi

Covering from 250hz-20khz. The midbass/subbass will be handled with four Pyle Pro PPA15 15 inch drivers in U-baffles. These have been used with great success over on diyaudio.com with very low extension for an open baffle system. Since this is on a budget, I will be using twin Audiosource Amp100s, actively powering the system.

Here are my first drafts. Key here is a simple build. if I had time, I would use multiply ply and add some more curvature. But alas, Im limited with time.





Im sure most of this is way some of your heads, but thats ok. Hope someone will appreciate it :) If anyone has any questions about dipoles, feel free to ask. And experiment!
 

·
Registered
Joined
·
731 Posts
Discussion Starter #4
These two websites will provide you with pretty much all the basics on the theory and implementation:

Linkwitz Lab - Loudspeaker Design

OB Theory

I saw this over in the full range forum. I'm interested to see how you end up with it!
Thanks! Still working on the baffle geometry. Two 15s per side is a bit of overkill but I want to have some headroom for EQ on the lower octaves. Plus I am a bit of a bass head.
 

·
Registered
Joined
·
731 Posts
Discussion Starter #6
I want to design a system this summer, but I don't know if I can get the project approved.

Phil
If I were you, I would search ebay for some old vintage drivers. If you can find large diameter woofers with compression horns that would be perfect.

These vintage drivers generally have a higher total Q and work well in open baffle alignments. What I am trying to say is, you don't need to spend a bunch of money to get good sound. Open baffles are very forgiving alignments. As long as you give the baffle at least a meter of space from the back wall, and make it nice and stiff, the sound will be great :)
 

·
Registered
Joined
·
293 Posts
What are measured specs on the FF85en from p10?

Why go for the U-frame over the H-frame? Was it simply an aesthetics thing? From simply looking at martin j king's page it seems the H-frame gives slightly lower extension than the U-frame at with about the same loss in efficiency. Now having said that I haven't played around with OB yet has you have, so what have you found out in your own experiments regarding baffle designs for dipole bass?
 

·
Registered
Joined
·
731 Posts
Discussion Starter #8
What are measured specs on the FF85en from p10?

Why go for the U-frame over the H-frame? Was it simply an aesthetics thing? From simply looking at martin j king's page it seems the H-frame gives slightly lower extension than the U-frame at with about the same loss in efficiency. Now having said that I haven't played around with OB yet has you have, so what have you found out in your own experiments regarding baffle designs for dipole bass?
Mostly aesthetics...and I want to keep the full range driver on the same flat plane as the woofers. I feel that the transition will be smoother without a 5-7 inch wall extending outward, from the FRs perspective. I can solve that by pushing the H baffle front edge back so its flat to the upper baffle. Ala the Orion+ by linkwitz. Problem with that is, since I am crossing over the woofers pretty high, there will be a time alignment issue with the mid-tweet. The Orion uses a larger midwoofer for lower extention, so this offset is not a problem. Besides, it uses a much more sophisticated external processor. At $5000, its got a lot of bells and whistles.

The extention gained fro a H-baffle isn't all that important to me. I will be using some EQ, but in all honesty, if I can get these things to dig down to 40hz with a bit of output below that, I will be VERY satisfied for just an open baffle setup woofer setup.

As far as what I have learned from my experience, flat baffles simply do not cut it for bass in my opinion. U-baffles are a much better option. When I constructed the U-baffles for my girlfriend using the vintage drivers, I ensured that the wings did not extend too much (4 inches) and used foam on the inside of the wings in attempt to reduce the ripple.

What I found was that short wings do wonders for bass response, and the actual heard ripple really isn't all that bad for the midrange, as long as the wings are kept relatively short. Its also important to note that extending the wings doesn't really add to the extension like you would think. Best way for more output is to increase the area of the baffle.

With that in mind, since the FF85K will not be playing bass, higher QTS wasn't really a concern. In addition, the baffle will be kept flat and its width will be relatively small for a smoother response.

Hope that answers some questions. I would also like to add that I have modified the design per suggestions at diyaudio. I simplified the upper portion of the baffle, made it wider, and moved the driver up slightly to remove some nulls and peaks caused by the irregular shape of the baffle. I am also going to move the full range and woofer crossover points to around 325hz and 200hz, respectively, for better power handling. Its not as pretty, but I'll try my best to make it nice :)



 

·
Registered
Joined
·
731 Posts
Discussion Starter #9
The project has changed yet again, after considering the peaks the decision was made to go ahead and try widening the baffle to spread out the dip originally present in the midrange. It also simplifies the build even more. All thanks to the help and simulations by another member...

The wings are 1 inch at the top and 7.5 inches at the very bottom. This was done to keep the width of the wings relatively short at the top near the full range driver. Plus its aesthetically more pleasing. The driver is at 38 inch height but offset, 8 inches from one side. Baffle is also wider now at 20 inches versus 16.

Just got the wood today. The front baffle will be 1.5 inches thick (two slabs of birch glued together) and the FR hole will be rounded over so it can breathe. I got my crossover in, amplifiers should be here tomorrow, and speakers should be here tomorrow or next week. Not sure when I am actually going to build it. Probably this weekend since it will only take a couple hours.


 

·
Registered
Joined
·
731 Posts
Discussion Starter #11
I think it looks better than the original.
yes I agree, thank you.

Got some drivers in today. Still waiting on two more 15s. These things are pretty average quality. But for 35 bucks, they are an absolute steal...
 

·
Registered
Joined
·
524 Posts
I just wanted to make a quick comment.

I will admit I do not know much about open baffle speaker designs. However, from what I've seen, all seem to implement a sealed chamber at the bottom of the tower. The purpose of this chamber is to increase low-end efficiency by using the front baffle vibrations as a transducer, and using the chamber to control the "rear wave" of the baffle, increasing output. Frequencies affected depend on enclosure volume.

Also, do not forget about BSC: boost in frequencies above baffle width.

And consider changing the design to an MTM design, or design the crossover so the lower woofer is used in a 2.5-way manor (only playing up to certain frequencies to boost low-end output) while moving the tweeter as close to the top woofer as possible.

Using the two woofers in this configuration playing the same frequencies could cause some issues around the crossover point.
 

·
Registered
Joined
·
731 Posts
Discussion Starter #14 (Edited)
I just wanted to make a quick comment.

I will admit I do not know much about open baffle speaker designs. However, from what I've seen, all seem to implement a sealed chamber at the bottom of the tower. The purpose of this chamber is to increase low-end efficiency by using the front baffle vibrations as a transducer, and using the chamber to control the "rear wave" of the baffle, increasing output. Frequencies affected depend on enclosure volume.

Also, do not forget about BSC: boost in frequencies above baffle width.

And consider changing the design to an MTM design, or design the crossover so the lower woofer is used in a 2.5-way manor (only playing up to certain frequencies to boost low-end output) while moving the tweeter as close to the top woofer as possible.

Using the two woofers in this configuration playing the same frequencies could cause some issues around the crossover point.
Using this chamber that you speak of would reduce the benefits of an open baffle design. These are outlined in depth at linkwitz' website. You want to keep the front wave and back wave fairly similar, hence the relatively short wings, for an ideal dipole radiation. Otherwise you start approaching a monopole response. For ultra low frequencies (40hz and under) this isn't as vital, hence you see many designs using a subwoofer for home theater reinforcement.

As far as the placement of the drivers, I have considered an MTM type arrangement but decided against it because of the increased baffle size to raise the full range driver to an acceptable listening level. Goal is simplicity, relatively small size, and easy to build. Having said that, I am fully aware of your concerns of the placement. My concern is the image moving down in the lower frequencies with the lower woofer playing, especially with the introduction of floor bounce. I have some inductors laying around, so if it comes down to it I will apply a simple 6db/octave filter for the lower driver to make it a 2.5 way.

The response with the final configuration has been modeled with a starting point for the crossovers. The FR is crossed over at 400hz while the bass drivers have been crossed over at 200hz. Since the drivers will exhibit a rising response due to the open baffle, the acoustic crossover is actually at 300hz as shown. Keep in mind these are starting points, and I will likely increase the gain for the woofers and cross them over lower as preference. Also note that the bass response should be better slightly better in room. The woofers have a lot of headroom left mechanically, so I will likely use a linkwitz transform cirtuit or something similar to lower the response to a reasonable level (40-50hz is great for my purposes). Depends on how it actually plays out in real life. The high Q notch at ~3khz looks a lot worse then it really is. Thats the only real problem that I can see, and much improved over my original design.



Finally, I will also add a bass horn of some sort, likely posing as a big TV stand, in the future for home theater goodness.
 

·
Registered
Joined
·
731 Posts
Discussion Starter #15
Much too expensive. I have spent a total of ~$450 for everything, including amplification to date. Yes, this is relatively low efficient, but with my experience 50 watts or so has faired well for drivers of this sensitivity range with decent dynamics and headroom.

I come from line arrays, so nothing will really match the impact and dynamics of that setup. That is not what I am trying to replicate. I want a great sounding, affordable open baffle project that employs full range drivers and open baffle bass support. This is for a college student who is simply getting older, and I feel that this is my most mature build to date. Hopefully, I will actually keep this one (though the projects will never end :) )

 

·
Registered
Joined
·
293 Posts
Is there anyway you measure the the 1w/1m sensitivity and the in-room response of the pyle woofers in the U frame? or measure the t/s parameters of the pyle's after a break-in period?
 

·
Registered
Joined
·
731 Posts
Discussion Starter #17
Is there anyway you measure the the 1w/1m sensitivity and the in-room response of the pyle woofers in the U frame? or measure the t/s parameters of the pyle's after a break-in period?
unfortunately no... I don't have a woofer tester or an RTA setup. Do everything the old fashion way :D
 

·
Registered
Joined
·
731 Posts
Discussion Starter #18
I suppose I can update this thread now lol. I have spent most of my time updating diyaudio.com. Here are my recent posts:

Fast1one said:
I went ahead and got everything hooked up...

First of all, the FF85KeNs sound absolutely phenomenal. I haven't been listening for long, but one thing is for sure that these things are VERY revealing. I was expecting them to have this characteristic, but not at this level. I'm not completely sure if I want to keep them yet simply because they have brought out the worst of mediocre recordings in my collection. I am not quite ready to simply abandon half of my music :eek:

They have an incredible sound stage. Also very good micro and macro dynamics for such a tiny speaker. In addition, they are not fatiguing or do they have the imfamous fostex "shout" that I have heard about. Extremely smooth sounding, and I suspect its because of Dave's treatment. Also, suprisingly they handle genres like rock very well.

He wasn't kidding when he said they can rival quality tweeters. They definitely have wonderful sparkle to them, and nothing seems to be missing on the top end.

As far as the woofers go. I definitely need more power in the future. Currently they are each receiving only 30 watts each. I will be upgrading eventually to 100 watts each for head room. The FRs don't seem to be straining at all at higher levels with the 400hz crossover point. The woofers have great bass with a little EQ, enough for my tastes. Cone movement is controlled with music, only reaching about 2-3mm P-P with heavy bass passages.

However, they do leave a bit to be desired on the top end. Crossing them over above ~150hz simply doesn't sound very good. So right now I have a small gap in the frequency response. Not too big of a deal for my tastes. Over all the performance of the woofers is very good for the price, with great impact. The higher crossover point doesn't really steer the sound stage down as many led me to believe.

One more thing I forgot to mention. They are currently operating WITHOUT the wings because of a mistake I made when cutting. Being a college student, I only had access to a circular saw and router. I got a little careless with the circular saw and screwed up on one of my cuts. Needless to say I didn't have any more wood. However, I like the configuration very much and will likely keep them wingless for now.

Fast1one said:
I am currently listening to the self titled album Nouvelle Vague. Bossa Nova music...Her voice is absolutely beautiful.

Here are some quick pictures I took. They are currently in my bedroom until I make room in the living room



Fast1one said:
These woofers are definitely sounding better by the hour. I gave them a little exercise while I was at the library studying for about 6 hours with a 15hz test tone at low volume.

I don't think the crossover point is going to budge for now. Currently its set at ~140hz and I am enjoying the blend they have with the FRs. I don't really feel like I am missing much from the recording in that range. After all, its a crossover not a brick wall :smash:

Also, the bass is really nice even with no EQ. I am not in a terrible rush to get more power either. I haven't played anything that really made me miss deep bass yet. Even playing Pink Floyd's "Dark Side of the Moon" album was quite satisfying from beginning to end. The track with the clocks going off (Time?) is eerily life like. "Money" also has that same quality with all the registers going off in the beginning.

I think I may have some wiggle room as far as the FF85s go. They don't really move at all even with heavy music crossed over at ~350hz now. I will slowly bring the crossover point lower once I am confident that I they have the mechanical head room.

One final note for now. I think I am going to end up keeping the Fostex and just listen to good recordings with them :D After all, I have other rigs for the rest of my collection ( *cough* car).
Cheers!!!
 
1 - 20 of 48 Posts
Top