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audiomik View Drop Down
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    Posted: 24 May 2015 at 10:28am
Am trying to design a Speaker system with associated Amplification including as near as I can get to a flat and coherent phase and frequency response.
The 'target' is for very good transparency of sound, so as not to hear the 'Speakers themselves but the actual sound being played through them!

So far it seems from much study that an isobaric Bass section would be most suitable, in an infinite baffle enclosure with phase corrected Linquitz Transform correction filters to provide a coherent response.

The High section to be some form of Lens or constant directivity Horn using a top quality compression driver well under it's rated power capacity.

However, I'm having a problem with the Mid frequency section.
There are a number of options from direct radiating Drivers to different types of Horn,
The exponential design of horn possibly with it's plane wave-front but restricted dispersion I've looked at; but will not really meet the wide dispersion I would like.

What are other members ideas on this please?

The design is for a sort of multi-use Full range cabinet suitable for high quality Hi-Fi or small acoustic gigs etc...... Possibly also Disco systems even!

Thanks in advance

Mik

Edit - schpellnig!

Edited by audiomik - 24 May 2015 at 10:32am
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Elliot Thompson View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 25 May 2015 at 9:58am
Six months ago I focused primarily on full-range speakers. It is something that many of us that are old enough to remember experienced when we were lads in our households. With column speakers back in the forefront, there are many manufactures designing speakers aimed for columns that can produce a relatively flat response from 200 Hz – 10 kHz.


As we know, the least amount frequency breakdown using various components in the chain will offer the least amount of phase cancellations. So using one speaker to cover Mid-High to High Frequencies and one speaker to cover Mid-Low to Low Frequencies would offer best results to minimise phase issues.

Your biggest obstacle will be the horn. The majority of horns available on the market tend not to offer a flat response but, more to wards a jagged frequency response from 1 kHz on up. Diffraction from the sound waves bouncing about in the horn cylinder is the culprit. The end result is lots of dips and peaks which leave the impression of being dynamic.

Interesting enough, conical horns offer the smoothest response out of all Mid/High frequency horns yet, is the least popular. The lens were considered great for high frequencies, however if you remember, they were always mated with a tweeter.

The graphs below illustrate a comparison of a 3-inch full-range speaker to a compression driver on a conical horn. The frequency steps began at 5 kHz and ended at 32 kHz. There are 200 steps from 5 kHz – 50 kHz

3-inch Full-Range Loudspeaker In Free Air



Compression Driver On A Conical Horn




Best Regards,
Elliot Thompson
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audiomik View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote audiomik Quote  Post ReplyReply Direct Link To This Post Posted: 25 May 2015 at 10:18am
Elliot
thanks, a few things to think about!
Mik
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 25 May 2015 at 4:24pm
Here is a short video on how full-range speakers handle high frequencies if you decide to go that route.



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Elliot Thompson
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Post Options Post Options   Thanks (0) Thanks(0)   Quote darkmatter Quote  Post ReplyReply Direct Link To This Post Posted: 26 May 2015 at 12:18pm
What sort of dispersion are you aiming for and how high will your bass section play?

I doubt I'll be able to help, just being nosy ha.

Have you considered a sealed push-pull design for bass? Or something like the Beyma TPL 150 for HF?

I was going to suggest an array of smaller drivers for mid, as Elliot has said. 

Don't know whether these are relevant but potential food for thought, OS waveguide for HF: http://www.metaacoustics.com/Oblectroid.html and a sealed MTM design that minimises distances between acoustic centres: http://barefootsound.com/micromain27/




Edited by darkmatter - 26 May 2015 at 12:19pm
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audiomik View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote audiomik Quote  Post ReplyReply Direct Link To This Post Posted: 26 May 2015 at 12:45pm
Tom
thanks for the suggestions. Interesting designs!

The prototype Bass section will use two ATC 12" drivers clamshell mounted in an IB enclosure with phase and frequency correction, so as yet I don't know what might be a suitable crossover frequency for them.
Looking at getting a prototype bass section box built when I can, so I can adjust internal panel angles etc to look for best results.

This thread is to try to collect some ideas at an early stage......

Mik

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Post Options Post Options   Thanks (0) Thanks(0)   Quote darkmatter Quote  Post ReplyReply Direct Link To This Post Posted: 26 May 2015 at 12:58pm
"or small acoustic gigs etc"

Curious to see how an IB design would be portable in this scenario and I'm not sure on your reasoning for going isobaric (probably just my lack of knowledge), so will be interested to see how this pans out :)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote audiomik Quote  Post ReplyReply Direct Link To This Post Posted: 26 May 2015 at 1:21pm
Tom
a pair of say BMS or perhaps similar 12" drivers isobaric loaded should be capable of sufficient SPL given their power handling?

The ATCs? - well because I happen to already have 4 of them

Mik

Edit: schpllinmg

Edited by audiomik - 26 May 2015 at 1:22pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote darkmatter Quote  Post ReplyReply Direct Link To This Post Posted: 26 May 2015 at 1:42pm
Might just be my misunderstanding of the terms to be honest. When you say infinite baffle, are you referring to 

1 a 'free air' design, where the drivers are mounted on an open baffle (rather than in an enclosure) and both the front and rear output from the driver are free to radiate in to the room?

2 does the back of the driver see a different 'room' to the front (that's the scenario where I don't understand how it'd be portable)?

3 a sealed box, that is sufficiently large that the sealed volume behind does not impact driver behaviour significantly

I guess this is just semantics, because I'd call 1 "open baffle", 2 "infinite baffle" and 3 "low-tuned sealed box" but I realize that might just be a personal thing.

No real qualms about going isobaric and I'm sure you'll get the output you need, but I think I would tend to favour standard push-pull to get the extra 3db efficiency (at the cost of a marginally larger box). I've seen really interesting and detailed posts from you about amp analysis though so I've got no doubt you have your reasons :)

Sorry for going off on a tangent by the way!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote audiomik Quote  Post ReplyReply Direct Link To This Post Posted: 26 May 2015 at 2:49pm

not a 'tangent' at all, might depend upon who's books you've read but I'm referring to a sealed box design...... tis easier for me to build.

Should be able to get two of the finished 'Speakers and most of the rest of the kit for a small gig into an estate car plus not completely fill the living room - well that's the design 'target'.

Mik
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 26 May 2015 at 3:22pm
how low do you want your bass to go before crossing to a sub? do you fancy a look at one of my unity horns?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote darkmatter Quote  Post ReplyReply Direct Link To This Post Posted: 26 May 2015 at 4:20pm
Ah ok it's all slotting in to place now, I can see why you're going isobaric in that case, lower Vas = fits in the car! My only thought is that a dual 12" push pull design where one driver is reversed and wired with reverse polarity might do better at cancelling cabinet vibrations and might have slightly less tendency to want to walk around the floor (though maybe 2 x 12" ATCs are heavy enough to avoid that being a major concern!).

Seeing as that's the bass design, I guess there's no particular need for the efficiency that a horn would get you in the mid range, and that multiple direct radiating drivers in a sealed box would fulfil the aims of minimal distortion (due to hardly using the available excursion) and good behaviour in the time domain. I think a mid range horn would add a fair bit of R&D time/cost and may not be the ideal considering that for this application the listening position may often be fairly close to the speaker itself and presents a number of challenges in terms of dispersion / beaming.
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