Fast, fun, Inexpensive OB project

Sujat: I need to make way too many assumptions to provide a meaningful answer. Ultimate system efficiency and effective low frequency cut off for an O.B. system are largely determined by the baffle dimensions and configuration. So.... can you advise what you have in mind in those two areas? Once that is known, you can start to look for your 8" driver. This assumes of course there is a driver available that can work within your design goals. J


Thank you Mr. Busch. I greatly appreciate your considerateness.

I am on a very modest budget - a passive 2-way with a 3" paper cone tweeter crossed over at 6,880 hz (i.e. at least 2 octaves above fs = 1,600 hz with a 1st order highpass - single 2.2 mf capacitor) & an 8" midbass driver run direct and full range without any crossover component at all. I can go up to an open baffle sized H x W = 38" x 18". I would be ok with a low end useable response down to 80 hz.

And if this too is not going to be practical, then i would be prepared to abort OB and resort to a large sealed enclosure (with a resistive pressure release vent) with Vb = up to 4 times Vas, retaining the same configuration. The baffle width will then be 11".

I am aware that neither of these will be high fidelity even in linearity of frequency response, but yet something better and cheaper than the market ever offers, with the added satisfaction of having done diy. Provided it can take upto 20 watts for effective 99-100 dB at 1 metre, which will still be a reasonable concern even if i opt for the large leaky monopole.... due to the 8" remaining very lightly loaded.

I hope this information should be adequate.

Thanks and regards,
Sujat.
 
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Since with OB, EQ is a given, so I would have gone for an active minidsp based setup, it is so flexible. With OB amplifier power is trivial, anyway.
Also, the baffle has trade offs, it may be tempting to choose a wider baffle in favour of extension but that gives a wider figure 8 radiation, it defeats the purpose of OB.
 
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Also, the baffle has trade offs, it may be tempting to choose a wider baffle in favour of extension but that gives a wider figure 8 radiation, it defeats the purpose of OB.


I appreciate your input on this dilemma, wonderful audio.

What i tend to think is.... a wider baffle (say 18"-24") may not end up being a totally defeated OB; but an OB compromised to a degree. And compromises either this side or that side, are inherent to speaker design, if i understand well! It is simply a matter of design target as to what one's design priorities and criteria are. :)
 
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I think we're getting off topic here, there may be a better thread for these questions... But... I doubt you'll have any success at all with an 8 inch driver on an open baffle.

And open baffle is entirely possible without eq. Martin Kings work has been all about modelling this sort of thing and with the right driver selection eq doesn't come into the picture. In fact too much reliance on dsp manipulation is likely to lead to decisions on drivers etc that are less than optimal.

I suggest Sujat that you join Martin Kings Facebook group where you may get specific guidance on what you are proposing.
 
I think we're getting off topic here, there may be a better thread for these questions... But... I doubt you'll have any success at all with an 8 inch driver on an open baffle.

And open baffle is entirely possible without eq. Martin Kings work has been all about modelling this sort of thing and with the right driver selection eq doesn't come into the picture. In fact too much reliance on dsp manipulation is likely to lead to decisions on drivers etc that are less than optimal.

I suggest Sujat that you join Martin Kings Facebook group where you may get specific guidance on what you are proposing.



Thanks a lot for your suggestion, Gazzagazza. That should be of great help.

I too found it a bit strange believing that OB cannot be done without eq. There are a few quite workable examples, not to forget Martin King's own very well documented design as you mentioned using the alpha 15a if i remember correctly.

I came across gainphile's successful S11 OB design which is a 2-way using an 8" driver for bass down to useful 45 hz or so. I am not sure if he used it flat or with eq.
 
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I built the vifa/GRS standard Manzanita a while back and have enjoyed them at lower volumes but get a sorta flutter or buzzing out of the woofer when playing louder with heavy bass. The amp is a Folsom DIY7297 with a B1 in front. I used this crossover as I was kinda confused when ordering parts, although I believe I read somewhere in the thread that this crossover would work. The speakers are about 5 feet from the wall/sliding glass doors. Other deviations from the design are- I used 1/2" phenolic for the baffle and I mounted the woofer on the back of the baffle (with a generous chamfer on the front).
Any suggestions to help me listen louder are appreciated!
 

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I built the vifa/GRS standard Manzanita a while back and have enjoyed them at lower volumes but get a sorta flutter or buzzing out of the woofer when playing louder with heavy bass. The amp is a Folsom DIY7297 with a B1 in front. I used this crossover as I was kinda confused when ordering parts, although I believe I read somewhere in the thread that this crossover would work. The speakers are about 5 feet from the wall/sliding glass doors. Other deviations from the design are- I used 1/2" phenolic for the baffle and I mounted the woofer on the back of the baffle (with a generous chamfer on the front).
Any suggestions to help me listen louder are appreciated!


I am a student here, so all I can offer is speculated response. :)

1. I hope you have made sure the flutter/buzz is the GRS 15" contributing its song, and not the glass in your sliding doors at the back resonating with the rear energy of the GRSs.

2. If it is indeed the GRSs over-excursing due to playing so much low frequency energy unloaded, a way to remedy it just might be using a 2nd-order high-pass filter a little below its Fs, subject to what the experts have to say.

Regards,
sujat.
 
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Well your baffles look solid and the woofers appear to be well attached. Of course seeing them up on the table like that leads to the obvious questions. :) Can we assume that you have the same flutter/buzz when they speakers are on the ground? And what happens if you disconnect the Vifa? Still there? How much power does your amp have?

Those are the first things I would check.
 
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I played around with placement of the speakers and it seems there was some interaction with the turntable, separating the two seemed to solve the problem. Speakers sounded pretty good on the floor at max. volume!
The DIY7297 has 15w/ch., I believe the PS is 24v but it's been a little while since the build and my head is like a sieve. I realize this is below the recommended wattage for these speakers but to my mid-fi ears they sound pretty good. Have a F5 build planned for this winter, looking forward to hearing them with more power.
Thanks for all the input, as I have little technical knowledge of what I'm doing this forum is invaluable!
 
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Good to hear, thanks for trying that. :up:

The TDA7297 chip is rated at 18V max working voltage, so you are probably running 12-15 volts. Having rum the 12" Manzie on a 24V chip amp, I can tell you it just enough - I wanted more. The 15" is a little more efficient which helps you. If you want to play loud with good headroom you'll need 80-100 watts. Meaning about 30 volts on your power supply. More wouldn't hurt. That's Open Baffle for you.
 
sffrhd Thanks for sharing your Manzanita build! Look very nice. As Pano said, additional power can improve the Manzanita overall performance. 75 watts each is a good practical power handling value, and with certain music, up to 100 watts each is a good max value. You know when you are at the systems limit when you notice dynamics starting to compress. Look forward to hearing your future conclusions once you have your larger amplifier up and running. J
 
For such big speaker, like 15", you need about 200W minimum amplifier with +-50V supply, which has to be super fast (min 50V/uSec), with dumping factor about 200 or more, that mean paralleling more output transistors, actually the lowest possible output impedance. When you send the signal peak into coil, you will became in answer similar return signal, inducted from speaker coil via inertia. So amplifier has to be capable to fighting with direct signal and forwarded signal too in real time.
If the baffle is from wood, normally not enough stiff, you also will be limited with some peak driven SPL, if you want to go over this point, became baffle noisy and unstable, ringing from wood is present and uncontrolled. Help exist, change material of baffle from wood to something heavier, with lower resonance, like concrete or granite stone. Such a big diameter of membrane (15") allow to go up to max 100Hz, higher frequencies are reserved for mid/tweeter, in your case 6-8" fullrange, which are also finished with proper sound widening on about 1500Hz. In any case, for excellent 3D spatial sound, you absolute need the tweeter and 3-way x-over. In any case, have you OB or not, the low frequency driver are not linear from about 22Hz (Fs is the lower usable frequency) to 50Hz. You need to shelf it minimum +16dB on 22Hz to became linear bass. In this case signal input in amplifier would be about 3V or more, thats mean with ampifying 26x, to have enough headroom for driving it with 100V peak to peak. In opposite case you became clipping and frying the woofer.
 
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Thanks, John, for the design and support. As someone who drooled over the last of the Heathkit catalogs as a kid, these diy projects have been something of a kid's dream come true. Apart from the main goal of listening to great sounding music, I've been intrigued with improving my listening and understanding the correlation between components (even if my understanding of the circuits involved is limited). That being said, and understanding that answers to this question could be contentious, are there recommendations for low cost amps that would sufficiently drive these speakers? In the meantime, I'll keep building!
Doug