B200 and Eminence Alpha-15A report ~

scorpion · « **Reply #100 on:** 7 Jul 2008, 10:56 pm »

Mark,

I think you have a good point. Here is the measurement 2.5 m distance and 90 cm above floor for the mic. Also it is with high 1/24 octave resolution so it looks a bit ragged and exaggerated. The resolution is just to prove that the 50 Hz roomresonance in my measurements is very narrow and probably not heard at all on normal music. You are not that sensistive to bass-variations anyhow. This is the plot:

Now we are seeing a build up around 2 kHz so it is there, but it just a bit more prominent than other buildups. However the Alpha fullrange is not bad at all soundwise. I think one could refer to Hawthorne's Silver Iris which is an Alpha15 adapted to Eminence's American Standard Coaxial magnet assembly. If I remember correctly its crossover to the treble takes the form of a notch filter around 2 - 2.5 kHz and then using the normal roll-off of the unit. I think the Iris proves that Alpha15 can be used well up in the midrange with success.

/Erling

scorpion · « **Reply #101 on:** 7 Jul 2008, 11:06 pm »

DerrO,

In fact it might help with the rising B200 by letting the Alpha complement it to above 1 kHz making the combined response more in line with B200's response from 2 kHz and upwards all the way to 10 Khz. The combination should be experienced as better balanced.

/Erling

opnly bafld · « **Reply #102 on:** 8 Jul 2008, 12:22 am »

DerrO,

Your baffles are very nice.

How about trying a single Alpha 15 or a 15" Hawthorne Augie in a small H baffle with a plate amp to augment the other 2 15" drivers?

http://www.hawthorneaudio.com/catalog/index.php?main_page=product_info&products_id=19&zenid=rri4nbao4h17d2jhptmue7brg0

Lin

MJK · « **Reply #103 on:** 8 Jul 2008, 01:37 am »

DerrO,

Lin's idea is a good one, that would in effect be like adding a second Alpha 15A to your baffle without having to rebuild. The speakers look so nice I would hate to see you start over.

Erling's idea to add some temporary wings is also a good thought. This would in effect simulate a wider baffle. Don't be afraid of adding 12" or 18" deep wings. Wings do not generate resonances as is often reported. See if the bass or tone changes and adjust the temporary wings to optimize the result.

The other thought I had concerned how close you set up the speaker to the rear wall. Maybe moving the speakers a bit further into the room might help bring out some more bass. The rear wave bouncing off the rear wall and adding destructively to the front wave might be part of your problem.

Martin

panomaniac · « **Reply #104 on:** 8 Jul 2008, 07:52 am »

Those are super nice looking baffles! Great work.

I can understand why you would not like to add side wings - the baffles are so pretty, the wings could only hurt.
Sooo.... Maybe glass or plexiglass wings.

Just try some cheaper materials first, to see if it works for you.

The hot mids and highs from the B200 are probably what is causing the subjective lack of bass. Get them down and it's going to sound a lot more balanced.

Very nice work, I'm jealous!

scorpion · « **Reply #105 on:** 8 Jul 2008, 09:56 am »

I think Martin and I talk about wings 90 degrees to the main baffle. They will be almost invisible from the front if placed just to make room for the Alpha. We had a discussion about this kind of back-wings. Martin argued the theory and I have complemented with measurement of two different bass-baffles to prove the point. There will be no resonances.

/Erling

DerrO · « **Reply #106 on:** 8 Jul 2008, 11:22 am »

Many thanks to all for your kind words and thoughts on this.. Yes, I will try wings and the idea of clear perspex would seem to be a great solution as I would not loose the overall appearance. That said, over the next few days I think that I will just have to throw together some kind of baffle and mount the Alpha right at floor to determine just how much that is effecting things.

That said, given that I am using MacBook/iTunes/Apogee DUET DAC, means that I can dial in a certain amount of bass with the iTunes equalizer without detrimental effect. and I may be able to recover the missing bottom with this.

Thanks agin....

DerrO

tubamark · « **Reply #107 on:** 8 Jul 2008, 01:36 pm »

DerrO:

Gorgeous. After finishing your next baffles, please auction those pictured. Make it a silent auction. Notify only me to bid.

Lowering the Alpha to the floor + small wings will buy you maybe 3 db - still worth trying, of course. I would suggest triangular or curved rather than rectangular wings - more stealth.
I think that right now the sensitivity mismatch is going to obscure other factors, but still think that some Alpha filtering is warranted due to significant beaming that will be occuring where the 2 KHz bump is . . .

Before going to all the expense and time for new baffles and more drivers, why not "try before you buy"? : Put a test L-pad on the B-200, and set it to attenuate 6 db. That will give you a very good idea of the relative balance that will result from adding an additional Alpha 15. Then tinker with inductors.

It is also possible (gasp) to install a permanent L-pad on the B200 and leave it at that. I know that purists (often self-titled) will poo-poo this, but c'mon guys - the tradeoff here is certainly no worse than the "sins" already commited: all drivers run in their beamy range, etc . . . We're already playing outside the box here (pun intended).

Another free experiment: Hook the B200 to the right channel amp, Alpha + inductor to the left, play a mono source, and use balance control to experiment with driver balancing. Quick, dirty, and free experiment that can only lead to enlightenment

. I think you will be surprised.

Try & let us know what you discover.

-- Mark

MJK · « **Reply #108 on:** 8 Jul 2008, 04:39 pm »

DerrO,

Add Mark's suggestions to your list of things to try and you have an excellent set of options that will undoubtedly improve the performance of your B200/Alpha 15A open baffle system. Try them all and let us know which is most effective and what combination provides the highest level of performance.

Martin

panomaniac · « **Reply #109 on:** 8 Jul 2008, 05:41 pm »

Mark is right - as Martin points out. Some very good options there for you to try.
Bringing that B200 down a few dB is the 1st step.

OT: Mark, how did my cat get into your speaker box???

scorpion · « **Reply #110 on:** 8 Jul 2008, 07:52 pm »

Or, indeed, my cat ! I do like that picture !

/Erling

scorpion · « **Reply #111 on:** 8 Jul 2008, 08:18 pm »

I have studied the Silver Iris crossover, it is centered at around 3.1 kHz. If you instead try .5 mh, 10 uF and a 10 ohm/10Watt MOX resistor in parallel all in series with the Alpha15 plus connection, I think you might hit just the right frequency to cross between the Alpha and the B200. Then it is just the matter of matching levels.

/Erling

DerrO · « **Reply #112 on:** 11 Jul 2008, 11:40 pm »

DerrO

fergs1 · « **Reply #113 on:** 12 Jul 2008, 04:29 am »

Greetings Derro, really enjoyed reading your website, thanks for sharing.I think its already been echoed but if you can bring the baffles out further to about 1 meter you will be richly rewarded

.what inductor did you end up using on the alpha(mH?).The baffles look fabulous, mini 909's. one thing to keep in mind is that cenral rear brace is the perfect opertunity to magnet mount the drivers which has a huge effect on reducing baffle vibrations especcially if you place soft rubber srtips under where the speaker is recessed into the baffle(you'll have to increase the countersink by the thickness of the rubber strip.Surpringly this has a very marked effect of stabilizing and improving imaging and sound stage. I have heard the difference with my mag mounted b200 on Mr Content baffles as developed on the decwaree open baffle thread. Look forward to any other developments with you baffles.
peace and goodwill fergs(been openly baffled for nigh on 3 years now,no turning back)

SAC · « **Reply #114 on:** 15 Jul 2008, 01:13 pm »

DerrO and others, would substituting a 4ohm alpha version for the 8ohm version I assume you are using increase the alphas sensitivity thereby making it a better match for the B200 as I see you are trying to achieve.

Thought I'd suggest this since I have the 4ohm versions on order to go with my B200s, last two I can find in the UK due "lack of demand" as the supplier told me.

Michael V · « **Reply #115 on:** 15 Jul 2008, 07:25 pm »

I've never seen a 4R Eminence Alpha 15. I'll have to look around at US distributors, because if this is available I would definitely order a couple pairs.

Regards
Michael

Maxdd_nj · « **Reply #116 on:** 15 Jul 2008, 09:02 pm »

DerrO, I really enjoyed reading your page. What happened to the link?
Were you running both B200 and Alpha off your 300B amp?
Max

DerrO · « **Reply #117 on:** 16 Jul 2008, 12:43 am »

Hi,

I removed the link as it was deemed to be a breach of forum rules. Yes, i am running the Visaton and the Alpha directly from the 300B amp. Still working on it and the Visaton requires a lot more burn in time - leastways I hope that it what it is as it has a bit of an "edge" - a bit "spitchy"!. Also I have not settled upon the value of the inductor for the bass unit as running this too high up the frequency range is causing smearing of the image as it is giving me some of the midrange like I have from the Visaton and the result is somewhat disjointed.

Actually tonight I tried the Eminence Beta 12 LTA in place of the Visaton with an added temporary baffle piece on top of the present one and the sound was glorious. Prior to this I was using the Beta 12 LTA/Fostex FT17H in a reflex cab. and I loved everything about that. So I can see myself at the very least making a proper baffle to test this setup. Actually I am more impressed with the Eminence Alpha than I am with the Visaton!

DerrO

scorpion · « **Reply #118 on:** 16 Jul 2008, 08:03 am »

DerrO,

The Visaton is as it is, thats why many people go far to cure its rising response. The thing you should try first is the simple BSC-LR circuit consisting of a 1 mH (air-wound) inductor and a 10 ohm, MOX or any other non-inductive, resistor connected in parallel in the Visaton's plus lead. This will gradually shelve the response from a bit under 1 kHz reaching a full effect at about 2 kHz. Have a look at the Visaton NoBox filter: http://www.visaton.de/bilder/weichen/gross/noboxbb_w.gif. This will definitely give a more balanced response in the combination with the Alpha15. If you read through some of the threads here about the B200 (and there are some !) you will see more tricks to come on speaking terms with it, but the BSC-LR is the simplest and should be tried first to see how you like it.

/Erling

FullRangeMan · « **Reply #119 on:** 4 Sep 2009, 03:14 am »

Dear OB guys,
Iam very impressed with this old thread, seems the ALPHA15A and the B200 are a perfect pair through ?? I do not listen no one of them yet.
One thing caught my attention, all OB projects here are one ALPHA and one B200 only.
So, I wonder if two ALPHAS and one B200 could work fine?? Or even better than just one ALPHA and one B200 ??
An poster in this thread was using just a simple 4,7mH coil as ''xover'', but now in 2009 do you think this is a good sound option??
Is there any better filter option?
Someone has made an OB with two ALPHAs and one B200??
Thankyou for your comments or sound impressions about his OB set.
Regards, Gustavo