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Old 16th February 2009, 10:08 PM   #1
tinitus is offline tinitus  Europe
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Default 100db, AMT and 4x BETA-8 +sub

This is my latest idea

I have been through lots of considerations with various horns/compression drivers and 12" woofers and more

But I think I like this one better...its simple and quite cheap

It consists of Beyma AMT ribbon and 4x Eminence BETA-8

2.5way...300/1khz...natural rolloff at around 100hz in closed
May be a combination of passive and active

"Subwoofer" will be something 18" with digital XO/EQ with "gain"

Do you like it or not, or have other options in line with this

any comments are welcome
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Old 16th February 2009, 10:46 PM   #2
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I like the form factor you chose because i recently built a pair of H-Frames using Alpha 15's and use towers behind (soon to be beside similar to your sketch).

I know they are more money but check out these 8" Eminence drivers.


Two per side to make 8ohm or they have another one...


The second one is 8ohm so you can use 4 like your sketch but i don't like how it doesn't go as high as the 16ohm driver.

Overall, i do like your idea and think it could be pretty much ideal as far as achieving overall performance from top to bottom.

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Old 16th February 2009, 10:47 PM   #3
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I would be highly tempted to try 2 modded Fostex 206/207s (removed whizzer cone and phase plug) as dedicated midrange drivers with Beyma AMT's.

Btw, have you noticed the impedance of the AMT's? Although they're specified as 8Ohms drivers, the impendance is basically a flat line at the nominal 4.93 Ohm dc resistance. And only goes over 5 Ohms (to 5.1 Ohms) once in the audible range, so it'll be much more precise to name them 5 Ohm drivers.
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Old 17th February 2009, 05:15 AM   #4
CLS is offline CLS  Taiwan
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For 1kHz xover, I'd like to have a bigger midbass -- 12" or even 15", and one is more than enough (instead of 3). Also, this can be a 'clean' 2 way instead of 2.5way.

I'm very interested in the Beyma, too. If anything is really built around it, please share.
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Old 17th February 2009, 08:38 AM   #5
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Default the crossover

I would aim for midrange drivers that are good up to 3khz rather then down at 1khz, and with what size ofdrivers you are using a hybrid 3 way crossover would be a better choice.
at 750 and 3khz would be my choice and you only need 2 midway and I would use them in parallel with a load stablizing resitor in the circuitry and separate tuned boxes. Aim for 92 or 93 db smooth.
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Old 18th February 2009, 11:42 AM   #6
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I know this is a bass guitar speaker, but I have thought about crossing it at 3khz to make some vocal/guitar PA speakers as it looks pretty good on the graph, and could be used sealed to cross to a sub:


Would the whizzer help with beaming?
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Old 21st February 2009, 01:34 AM   #7
tinitus is offline tinitus  Europe
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Thanks fore interest

All suggestions are good and valid

I have been through them all of them, and some more, before I came to this one
Due to the low cost of the BETA-8 its almost cost effective
I could continue about my design criteria, but it will only be very long and boring

Well, it will take a while before Im able to make the saw dust, so things may change before that, and no price of the waveguide AMT yet

The last few days have been awfull
I began to simplify my 3way crossover, and sound did improve significantly with each component removed
Unfortunately I experienced severe and ear hurting phase issues
I almost gave up completely, until I began to experiment with driver polarity
And magic happened
Tweeter xo is still 12db with a Fs-notch and zobel, the whole shabang
But woofers and mid are scaringly simple
Pure "6db" with notches
No zobels or other paralel components, apart from the notches
Sounds so smooth and natural as ever, no artefacts what so ever

Man, do I fell lucky...I thought my days were over

With such simple xo with only series components its quite interesting and funny to experience how the woofer change when mounting any component on the mid, and vice versa
Interaction between the drivers and related xo is clearly audible
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Old 5th March 2009, 05:18 PM   #8
mige0 is offline mige0  Austria
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Thumbs up - for your early testing - not that much about the Beyma AMT available yet!

If you find your tweeter to be stressed too much by the 1 kHz XO - and are willing to throw in some more money - I'd suggest you to try Troels JA8008 - its smooth all way up.

Crossover would become more complicated though to avoid excesive beaming (too many drivers for higher XO).

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Old 5th March 2009, 05:49 PM   #9
tinitus is offline tinitus  Europe
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Originally posted by mige0
Thumbs up - for your early testing - not that much about the Beyma AMT available yet!


Thanks Michael

When you write "early testing" I may have confused you a bit

The crossover trouble I descibe is with my present speaker, and not with the AMT project I suggest here

Im still strugling with xo phase issues, though it seems Im very close to a good result

Regarding the 2.5way WWWTW, AMT with BETA-8, I have second thoughts
The AMT is quite big(height), and based on that Im in doubt about about the WTW top section...the two Beta-8 may be too far apart from each other

I am considering a simpler WWT 2.5way, and I am searching fore a good mid/midwoofer
Beta-8 may still be a good option
I have looked closely on Beymas, but all the 8" rated at 95db all seems to be more like 90db with "hickups"

I have contacted ECOnoline about their 8" Afficionade, but no reply, but it will probably be too expencive anyway
Also looking at Supravox 215GMF, but also expencive

All very far from the cheap and good looking Beta-8
I actually at first didnt choose the Beta-8 solely on its price, but think it looks pretty good quality
Hard to see what justifies the much higher price on the other drivers
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Old 5th March 2009, 07:39 PM   #10
mige0 is offline mige0  Austria
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Ahh, so I misunderstood - but anyway let us know about any of your impressions with the AMT.

Don't worry about the heavy spacing of the 8" speakers - just give it a try - especially if you use e'm all in (series-) parallel.

I use the 8" JA8008 - and before that the 6.5" B&C also - above and below an AMT roughly with the same spacing as yours. No problem whatsoever to my ears.

I do it in power split technique though - hence no additional SPL gain at the XO crossing over to the AMT - but less load per speaker towards lower frequencies.

You could try this trick in passive as well - and as you have 4 speakers each side you could do it twice:

One is the "top" speaker (crossing to the AMT at 1000Hz) getting paralled by another one at slightly lower frequencies (lets say at about 7-800Hz ) and that two paralleld by the other two (lets say at about 4-500Hz ).

This way you get two times a (very) roughly half cut in excursion from 1000Hz down to 300Hz .

Just a little experiment if you already did your setup.

Again the Beta's are a bargain - you won't loose much if you don't look any further and just give it a try.

The JA8008 I suggest (as almost nobody seems to have posted about it) present music with a really beautiful personality, high resolution for details emphasizing not compromizing the sound experience as a whole, vivid, great tonality, room filling, easing to fall into the flow of beat and harmonics.

Just read the interview with Troels Gravesen - I'd say he luckily was able to transferr a considerable amount of his own friendly personality into the JA8008 speaker he developed.


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