A6A VOTT's Mid-bass problem - to all who replied...

[Manta-Ray]

To: Dave Fitts-
Dave suggested switching the + and - wires (but not both)... Isn't this called "phasing".
The N1285-8B crossovers have multiple connection points. One connection (soldered) leads directly to the 2 15" woofers. The woofers are either wired in "parallel" or in "series" to maintain the 8 Ohm load rating. The woofers remain wired exactly as I received them. Perhaps the A6A's may have been "re-wired" by the theater for some electronic "up-grade"..I don't know.
The 288-8K HF Compression driver is connected to the x-over separately via its own wire to a different connection point on the x-over (also soldered).
I have switched the wiring in the exact manner you suggested. I am unable to distinguish any audible difference. There seems to be no change. It would be most helpful to acquire a "factory" wiring diagram from Altec...but...Like Telex-EV, Altec Pro has no "archival" data to refer to. I cannot tell you if these speakers are "factory wired" correctly or incorrectly.

To: Dwight St
Dwight: Thank you for the informative Frequency Range Fefinitions explanation. I must elaborate. These A6A's (150 watts max -per factory spec sheet) are being driven by a McIntosh 200 watt/channel integrated amp. Because of A6A's prodigious output, I built a pair of subwoofers capable of matching the A6A's SPL's. Each subwoofer is a 15" speaker with it's own 1000 watt "plate amp" power supply. Each subwoofer is connected to the MAC amp by a "line level" input. Now to your suggestion of "attenuation" or turning down the the HF Compression driver...I have no clue how to accomplish this. It appears to be impossible using the x-over networks as they are currently wired. The volume control on the MAC reduces the volume of the entire system. Again, I am faced with the uncertainty of the wiring and/or the x-over networks malfunctioning. Again.. a "factory" wiring diagram showing X-over network to speaker diagram would prove most usefull.

To:Cal Weldon
Cal, I am gratified someone else had a similar reaction to the "all-inclusive" solution provided on the other forum. If I follow your suggestion by the addition of an equalizer...How do I "integrate" it? Are the x-overs bypassed? Is this equalizer active or passive? My assumption is the output of the McIntosh amp would be fed into the equalizer which, in turn, would be connected to the woofers, the HF compression driver and to the subwoofer? I have not explored this alternative approach. The MAC amp provides ample power at very low distortion levels. Can an equalizer be introduced without causing other "downstream" problems? Can you suggest a specific brand of equalizer?

Thank you gentlemen... I really appreciate information that I can both understand and use. Continued thoughts and ideas greatly appreciated.

Sincerely,
Manta-Ray

[Todd W. White]

Put the equalizer just ahead of the power amps.

I may be able to loacate a schematic of that crossover, but it will take a few days - I'm already behind getting some other documents to people.

[Fitts]

Manta Ray, sorry that switching the wires didn't yield any results. You are right, it is called phasing.

I have a formula somewhere that lets you calculate a desired level of HF attenuation while holding the impedance seen by the crossover constant. I will find it and post it for you.

Regards,

[dstamand]

The following url goes to one of 21 different models of L-pads from PartsExpress -

http://www.partsexpress.com/pe/showd..._ID=5647&DID=7

Does anyone know if this is the sort of thing that Manta Ray might need?

[ckp]

Manta Ray,
You have your PM's turned off.
While I do not have 288 HF drivers, I have 909-8a, the other components have the same number. Your Mac is probably of better quality than my Onkyo 787. I can't imagine having to go through all that equalizing, L-padding and whatever else. (This is like the problem I was having with my A7's) Back to the A6's. I hooked mine up and that's it......done. They only need a sub for the really low frequencies. When listening to music, a sub isn't really even needed if you crank it. Mine is a cheap Cambridge Soundworks I bought about 10 years ago at Best Buy and it does an adequate job.
The knob on my crossover is between 10 and 11 O'clock. The button is out. I can probably take some pictures of the crossover and the wiring or draw a diagram or something. What would help you out? Mine have always worked fine , so I never had to do any research to try and figure them out.

[Fitts]

Hi, me again. The formula for an attenuator network that keeps the impedance for the tweeter (or woofer) constant is as follows:

A=attenuation in db

Rp=resistance in parallel with the tweeter (or woofer)

Rs=resistance in series with the tweeter (or woofer)

Rt=the tweeters (or woofers) operating resistance

Do these calculations:

Rp=10^A/20*Rt/(1-10^A/20)

Rs=Rt-(1/Rp+1/Rt)^-1

I would start with three DB attenuation and see if that helps bring out the mid bass. For an 8 ohm tweeter, the formulas yield an Rp of 8 and an Rs of 4. You can use half watt resistors for testing just don't push them too hard.

Regards,

[Cal Weldon]

Hi Manta-Ray,

An equalizer is just a bunch of tone controls that allows you to adjust the highs, mids and lows to your taste.

All "equalizers" will be active, basically meaning you plug it in to the wall.

They are connected to your pre-in and pre-out plugs in the back of your amp. These are the ones that have short connectors going between them now. If you don't have those connectors then you run it through your tape monitor circuit. The instructions that come with it will explain it all. It's really quite easy to do.

As far as quality, I suggest you go to your local HiFi outlet and describe your system to them. They will help you decide. Equalizers are not that expensive.

Back before I could afford to build good speakers, many of my systems were OK speakers and an equalizer.

Hope this wasn't too simplistic, just trying to go easy on you.

Cal