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-   -   Full range driver in a small speaker system (http://www.diyaudio.com/forums/full-range/209978-full-range-driver-small-speaker-system.html)

exeric 1st April 2012 09:59 PM

Full range driver in a small speaker system
 
I've recently gotten interested in getting my feet wet in speaker building. What got me interested was Morgan Jones' article on designing a small sealed box speaker for flea power single-ended amps - the Arpeggio. Everything was nicely demonstrated as to the design principles and the Small equations that must be used to get your target results. The whole article really appealed to my "less is more" sensibility of using correct engineering principles to simplify the final product.

When I got into audio as a young fart, (now i'm an old fart), my first good sounding speakers were Spica TC-50s. They imaged like crazy, and were built from the start with one of the first computer designed crossovers ever designed. I never liked them on stands set 2 to 4 feet from the front wall. Just too thin sounding with no bass. So they were a very convenient speaker to have sitting on top of furniture where they disappeared into the room. I hate speakers that define a room because for a guy like me house real estate is just too precious to waste with big speakers that stand out several feet from the walls. So I'm really big on small speakers with smooth, but lower than usual bass response. I use bass traps to smooth out any boominess created by that speaker placement.

For equivalent speakers a sealed enclosure will be the smallest volume, another thing that appealed to me about MJ's article. So I'm thinking about building a speaker using a full range driver and using that article as a baseline. Thirty years after acquiring those original Spicas I'm only now appreciating one part of the design element that made made them so special. Apart from the time aligned nature of the woofer and tweeter what also contributed to their special appeal (I think) was the fact that the tonal balance didn't shift much as one moved away from the sweet spot. This was due to the slanted baffle.

In most normal speakers there is a certain amount of beaming in the high frequencies, even worse in many full range drivers. If you move from the listening sweet spot most speakers tonal balance changes. I think that is part of the reason the TC-50s were good. They used a rising response tweeter and but then directed it about 30 degrees up so one just got a smoother response high frequency response as one moved in the room. Think of an analogy where the speakers were directed straight up but with a FR designed for that. As long as you are moving in the horizontal plane FR will not change. Some people advise using a rectangular box speaker with a rising response driver and then just use toe in or out to correct for that at the listening spot. That is an inferior way of building a speaker because as you move laterally you will
decrease the high frequency response on one speaker but increase it on the other - terrible idea if you like to boogie to the music.

So I'm planning on building a small bookshelf speaker using MJ's ideas. But I'm going to select a driver with a rising response on the high end. Then tilt the baffle, ala Spica. With any luck it should image even better than the old TC 50s because i won't be using two drivers.

exeric 2nd April 2012 01:50 AM

Since one would be dissipating most of the high frequency energy if the driver was point straight up it is not practical to have a full-ranger pointed straight up. But I think 30 degrees up baffle angle is practical. I've seen lots of full range drivers with FR charts going up around 2000 hz. But the beaming characteristics start as low as 500 hz at about 1db and from some charts I've seen can peak around 15k hz at over 15 db difference on axis vs 30 degrees off axis. That's huge.

I think full range driver designers should start thinking about designing in a high frequency tilt starting about 500hz and increasing to around maybe 15 db at 15k Hz. That would be the baseline flat frequency response with the baffle tilted up 30 degrees. If you were looking to more closely align with a B&K response curve then a single driver designer could modify it so the final 30 degree baffle tilt curve would match that modified frequency response.

It makes no sense at all to engineer high frequency lift when listening to a traditional vertically aligned baffle. In that condition, especially in a small
room, any change in lateral position of the listener with respect to the speakers will maximize the frequency response change as one moves from the center position. If the speakers were towed in originally to compensate for the rising response then as you move "right" the left speaker would peak 15 db at 15k hz at a 30 degree lateral angle while the right would dip say 5 to 10 db at that freq. If the speakers were towed out originally then then as you move right at some point the right speaker would increase 15db at 15k Hz at 30 degee angle while the left would further dip 5 to 10 db at that freq. So at a particular listener position you could have a maximum change in high frequency content of 20 to 25 db. That ain't the way to design a
system.:headbash:

While just tilting the baffle up won't get rid of all lateral off axis frequency change it is a good happy medium between beaming loss versus efficiency loss.

DYNABLASTERTUNERS 2nd April 2012 06:02 AM

no beaming with TB w3-1797, but you need bass helpers, because TB is a midhigh unit for use from about 600Hz (12dB), or 1000-1500Hz (6dB)... btw. it's a magical driver :)

exeric 2nd April 2012 07:10 AM

Quote:

Originally Posted by DYNABLASTERTUNERS (Post 2969471)
no beaming with TB w3-1797, but you need bass helpers, because TB is a midhigh unit for use from about 600Hz (12dB), or 1000-1500Hz (6dB)... btw. it's a magical driver :)

Well, I looked at the response charts for it, and you're right that it looks like what I'm looking for. Unfortunately I'm looking for a little more efficiency so I can dip my foot into the single ended pond. The Alpair 12 mk2 looked real good but they don't seem to be available anymore.:o

DYNABLASTERTUNERS 2nd April 2012 07:26 AM

then take two per side :D
6moons audio reviews: Boenicke Audio SLS
Boenicke Audiomanufacture SLS ))) Raindrop Audio (((
AUDIOMANUFACTURE ULTIMATE GRADE MUSICAL PLAYBACK INSTRUMENTS AND RECORDINGS
6moons audio reviews: Boenicke Audio B10

here is my opinion about those little gems
http://www.diyaudio.com/forums/full-...d-sound-2.html

zman01 2nd April 2012 08:22 AM

I heard the Boenicke Audiomanfacture SLS once. The shop owner played the live version of "Calling Elvis" by Dire Straits. Sound was very live and the sound stage was created beautifully. It sounded like a proper performance vs his small showroom. But that was not only the TB W3-1797 playing, the whole speaker and electronics playing together. :)

But Dynablastertuners, you sound very impressed and have made me very curious. The FAST thing is bit of an inconvenience though... more stuff to put together.

Driver seems to be out of stock from PE (discontinued?) - are they coming out with a ferrite magnet version at lower cost?

zman01 2nd April 2012 08:47 AM

Quote:

Originally Posted by exeric (Post 2969505)
The Alpair 12 mk2 looked real good but they don't seem to be available anymore.:o

Madisound are out of stock - have you tried CSS?

DYNABLASTERTUNERS 2nd April 2012 09:56 AM

FAST is the way to go, active crossover with DSP and two amps is all you need, and today that stuff is cheap, and you are very flexible with such a solution ;)

on TB site there are still those flatcones, nothing seems to be discontinued

I must say it again, for electronic music I claim there is nothing better in the universe, period. I think that same for home theater setup


PS: after listening to flatcone 3", all fullrangers that I have sounds flat in dimensionality, flat cone has flattened them all lol :D

exeric 2nd April 2012 09:15 PM

Dynablaster, I think perhaps you have a different philosophy than me. I hate adding new amplifiers, additional speaker drivers to a system if not required. More expense that seems to often just be the bill of goods the merchant is trying to sell you. Plus, how many diyers have access to CNC machines for carving horns. Sure, there are backloaded horn kits available but the whole premise of my original post was to use MJ's original Arpeggio project and perhaps update it and improve it.

The way I was trying to do it was to increase structural rigidity by creating a scalene triangle front to back box instead of a rectangular box. Plus that eliminates parallel front and back that reinforce standing waves. Simultaneously that angled front eliminates one of the biggest drawbacks of full range drivers - excessive beaming. There are a million projects out there where someone says "well the old one was good so let's just add this to it". It takes a lot more thinking to reorder things so you not only accomplish the original goal with less parts and complexity, but actually the improve the original in the process. I'm not saying my idea accomplishes that goal since I haven't built it to see, but it has a chance to. Plus its a lot more fun thinking about simple, but neat ideas. Of course YMMV :D

DYNABLASTERTUNERS 2nd April 2012 09:21 PM

T-Amp 50$
mini DSP 100$

and thats it! for good passive crossovers you have to pay about 100$


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