Lowering the crossover point.

[aditya]

...........I don't understand why these speakers seem all over the place? one day they sound good the next day they don't. And it's been that way since the day I got them.

:/

hahhahhah lol

This means that you are missing something ( response-wise ) in your setup. When they sound good, it means that the number being played was not that dependant on the missing portion of the spectrum, and the other way around for the bad sounding days. Assuming that everything about the drivers & the enclosure are standard, it has to do with the xover only. I had suffered similarly for nearly 2 yrs. with my A7-500, and it was finally over for me recently. Ofcourse it ended up with me having kind of a refresher-course in xover designing.

[VolvoHeretic]

Cradeldrof, what other gear are you running? Personally, I could never listen to my Altec speakers without a graphic equalizer and while alternatly listening to CD's, Youtube videos, and Movie DVD's, am constantly adjusting the EQ not only for each different format, but each different CD, or video. They are all recorded differently and each has to be individually adjusted to taste. It is a time consume task, but is a necessary requirement for listening nirvana. Altec, more than any other speaker brings out all of the flaws in recording engineering.

[VolvoHeretic]

I don't really know because I don't have one, but I thought that unless you have true 5.1 with a center channel speaker, you will never be able to balance the voices vs soundtrack vs special effects from a video source. I would worry more about how the system plays audio music rather than video. When are they going to split soundtrack voices from the rest of the audio and give us control over how loud those damn special affects and music are on video?

[aditya]

I'm kinda confused as to what OG is trying to say about the horn not loading the phram? I would thing the metal Phase plug with the hair width circular slots in it would do the phram loading? I am running the loading caps right now.

Yes, OG is absolutely right.

For such a small horn, trying to xover it too low may damage the phram, as the air-mass (volume of air inside the horn) will be too less to prevent it from being over-excursed. On the other hand, the phase-plug as the name suggests, only prevents any phase cancellation from occuring within the prescribed bandwidth, which otherwise can happen as the phram is not a flat surface, and hence the path length from the periphery & the center of it to a point in front of it in space will be unequal. This difference will cause frequency cancellations at different spots throughout the bandwidth. The loading-caps when 'ON' will also prevent the phrams to some extent from being over-excursed, but it usually is the happiest when the pressure/loading on both the sides are similar (linear excursion), which will not happen here for this horn if the xover was too low, even though the caps were on.

[aditya]

Don't take this as a negative attitude but are you saying that the phram can push enough air through those tiny slots to actually create a back pressure against the air that's in the horn tube which has a much larger volume than the slots? It just sounds as if physics would say that it would take a lot of air movement through the slots before you could build up pressure against whats in the tube. Or maybe I just don't understand enough yet. 604B's had a 1000hz crossover point? other than the horn mouth being slightly different, the throat I believe was the same size.
Altec 604 Duplex Speakers and related

There is no need to worry about negative attitude etc. We all are beyond that.

Coming to the subject.....yes the air thru the phase-plug slots is enough to find resistance in the horn pipe. It is also to do with frequency. Actually these drivers are very much like a rugged-ized microphone. Forget about this, think of a 515 in a 825/828, and think of the cone movement...and how little it is !
Yes you are right by saying that you have not yet got the feel of this subject.

[bowtie427ss]

It's the unwritten audio law of compromise Cradeldorf. It exists in some form in every step of the audio chain.

Everything we know in our tangible world is confined by basic laws of general physics. Speakers are no exception. In fact, speakers are in some ways a "bridge between worlds" where the laws of electricity meet the laws of kinetics.

[VolvoHeretic]

Get a 418 guitar speaker run full range and use it as your center channel. Don't you have a left over OB?

[Cal Weldon]

Hi cradeldorf,

I know just what you are thinking. I had the same thoughts come back and bite me. Aditya has done a nice job helping to explain the pressurizing thing.

I had made a little boombox with some small Jordan speakers along with vented woofer all in the same box. I didn't worry about the Jordans because there was a vent so how could the woofer cause excess cone movement in the Jordans when there was a great big port in there to relieve the pressure.

Well, long story short, bye bye Jordans, hello new project.

I am now wiser.

[aditya]

I guess my argument isn't that I think the HF needs to be down to 1000 but that the LF doesn't have the ability to stay at 98-100db efficiency up to 1600. sounds like it's down to about 70-80db by the time it gets there and is leaving a huge gap in the loudness between about 1000 and 1600. Also going by 515 specs just because they have the same cone and voice coil I think isn't a very good decision either since about half the cone is robbed by a giant 6 inch felt dust cap behind the horn which coincidentally is also blocking the sound path as opposed to a normal 515 which has a much less restricted cone and 3 inch dust cap. It would be nice to have the ability to measure the actual response of the LF side of these things to get a grasp on how they are performing.

Yes you are quite right here about the differences between the standard 515 and the one in the 604. Yes, in the case of the 604, it will have a drooping o/p post 1K Hz compared to a standard 515. All the points that you have mentioned will have their influence. But I don't have any actual 'db' figures with me. But i think the combination that the 604 has with the Hf horn, it should be able to match it up. I have listened to them for nearly 2 years, and I am yet to find a substitute to be sounding so good and so full !

[aditya]

Which model of 604's do you have? Mine are 1954 604C's.

I was actually talking about a pair of 604-8Gs at my friend's place. We both were put up together there for 2yrs, and everyday we used to listen to them in the late evenings. The cabs were BR, approx 12 cu.ft.

Just read about your plans to go for a db meter. I am sure you are going to make those 604s rock. I love their resolving abilities. Good wishes in advance.