605 TIME DELAY CROSSOVER

[Seadweller]

I'm very wet behind the ears when it comes to speaker design, so of course I didn't model the system myself....I guess it would be nice to have some measurements taken in my room!!!

The enclosures are based on the specifications that Jay Fisher kindly provided me...I bought the drivers and crossovers brand spanking new from Great Plains Audio...My pre-amp does not have tone controls, so everything is set flat by default, and the Great Plains crossovers I bought along with the drivers do not have L-Pads...

I wish I knew at what frequencies this anomaly was occuring, but I don't have the tools to make these measurements, and I wouldn't know how to use them if I did!

As I mentioned, I don't believe I'm the only one that has experienced this phenonema, and many have reported better results using different crossovers, many of which have indicated that this excessive midrange energy was tamed with a different crossover design (the Markwart crossover for example)....

I don't know if upgrading the standard Great Plains crossover to higher quality components would tame this midrange energy or not, and honestly, I don't know what components Great Plains used to begin with....I was so excited to get the cabinets home that I didn't give the crossovers a second look before I installed them....

Any advice would be graciously accepted!!!

[donaldpatten]

Seadweller
Did you note the time delay on your response?
Nov 23, 2006 to Nov 28 2007; a year!
The math : all my work was on factory ( GPA re built ) spec: 8 to 16 Ohm LF . I think that means 12 , and is close too the DCR I have measured.
The BESSEL low pass filter?s time delay , is very sensitive to load impedances.
Hence the Zobel network flattens the LF to 13 Ohms. The delay time offsets the mechanical spacing of the two drivers. To change either or both of these changes all the low pass parts.
I do have a design for a stock 604E that is 8-16 Ohm and with a Alnico magnet ; but no 604E to try it on.
Both waitinonthebuss and I have 605As.
Don

[selmerdave]

Seadweller,

I think most comments about improvements to the stock crossovers are in reference to the N1500A's from years ago. I don't recall reading many negative comments about the GPA crossovers, which I'm pretty sure are a significant improvement on the N1500A. I'm not sure what the issue you are describing would be though, and I can't say I've experienced it either with my current active setup or my prior passive setup using simple 2nd order networks with a fixed 4-db pad.

Dave

[Todd W. White]

As I said, Jerry Hubbard did the design on the GPA crossover, and I've listened to the combination in the Stonehenge V (9 cubic ft tuned) enclosure and not heard what you're describing.

Questions:

1. Are your electronics tube type, transistor, or other?

2. What source material are you using (CD, LP, cassette, R2R, etc.)?

3. What size box volume does your box have, and what frequency is it tuned to?

[bfish]

Turntable/preamp sans RIAA EQ?

[Seadweller]

I'm using a SS amplifier with a hybrid tube/SS preamplifier, with CD as the primary source....

I calculate the boxes at around 10.5 cubic feet, but what they are tuned to, I have no idea...I simply used the dimensions provided to me, along with the port size/location and length, distance from the floor, etc.

[Todd W. White]

Observations:

1. Some of what you're hearing could be distortion from the solid state (ie, transistor) amplifier and/or the SS side of the preamp, as we all know that SS electronics produces more odd-order harmonic distortion than does properly designed and operating tube stuff.

2. Some of what you're hearing is probably caused by improper box size, and/or tuning.

3. Distance of the 604's from the floor could have a bearing too.

4. Standing waves and unwanted reflections, in addition to the reverberant field, all of these could be combining to negate the bass response, thus making them sound like their midrange heavy.

5. Distance of the cabinet to the walls can have positive or negative effects, too. If you had a TEF analyzer, you could see what is going on and know for sure.

6. I also think hearing is different for each person, and some people have LF hearing loss due to damage from various sources of noise (note: rock music is included as a source of noise in my book :-) ).

I have played the same speakers in various environments, both small (demo rooms, small listening rooms) and large (our church auditorium), and found the perform well in all environments, but your room may be interfering with their performance. I know that there is a famous recording studio in NYC that has them and LOVES them, and they're a pretty picky group.

My ears tell me that "real", aka live, recordings - not ones that have been "sweetened" sound really really nice on these speakers, as do recording made on older (pre-K) 604's and UREI's (with OEM'd 604's) in them. Other recordings, where the mixdown is eq'd to compensate for the crummy speakers, don't fare so well..

That said, my guess is the box has something to do with the overall problem you're experiencing - what is the vent shape & size? These dimensions, plus knowing the location of the 604 from the floor, will help us figure out what's going on (maybe). It would also be good to know what wattage your amp is, and your room dimensions and speaker locations (or did you already mention that - I'll look again and see).

[Seadweller]

Thanks for taking the time to diagnose my problem!!!

Regarding your specific questions, the vent size is 6" round, in the center of the bottom of the cabinet...The cabinet is approximately 10" from the floor...The cabinet is meant to be an MLTL configuration...

The driver is around 34" from the floor, and the speakers are on the short wall of a 12x16 room..I have them placed about 2' in from the side walls, and 2' from the back wall...

The amplifier (200/wpc) is greatly oversized for this system, as my previous speakers were hideously inefficient, however it does operate in class A up to 20/wpc..

The excessive energy I'm referring to seems to be in the range of voices, so from 300HZ to 3500HZ maybe?

[zelgall]

I was under the impression that those cabinets were meant to be placed against a wall for low end reinforcement. The Six Moons write up of a similar box and driver indicated that the speaker was very well balanced and even a little laid back.

[Todd W. White]

How deep is the vent? I'm guessing it's a ducted port, right?

You may not have it tuned properly - one of the math geniuses here will have probably already have the duct area figured out by the time I can get my HP 41CV Programmable Calculator (yes, I still have it, and sometimes use it. Along with my thermal printed and card reader - at one time many of we Altec Engineering Sound Contractors had to have them.) and figure it out...it will be interesting to find out.

Also - I thought MLTL cabinets are usually designed to have some pretty hefty amounts of acoustic damping material (aka fiberglas). It may be that you're sucking the LF right out of the 604's and are left with mostly midrange and up.

The crossover really crosses around 1,500 to 1,800, as I recall. I can't see the LF cone getting annoyingly harsh, and the rolloff is such that you're really not getting into the horn by itself.

I think it's the box and/or box placement.