Improve upon this old Genz Benz cab...

[barebones]

Here's the story: I got this old GB115B cab for free. Added some damping material to the interior and loaded it with my current favorite speaker, the Eminence 3015. It sounds good, and it's extremely efficient, delivering plenty of volume with the 200 watt tube head you see on top there.

Only a couple things I would try to address about it if at all possible.

1) Low end roll-off. As it is now, I get strong fundamentals down to my A string. I'm wondering if I can extend that down to at least my low G, perhaps by modifying the existing ports. Interior volume is about 727.5 cubic inches. The cab has only minimal interior bracing in the corners, which I have not accounted for in my volume estimate. Jeff Genzler says this particular cab was indeed designed with the two 3 inch port holes, no tubes. Could I get lower fundamentals by adding proper port tubes for this driver? If so, would anyone be able to tell me what length to use?

2) Bracing. Of course addressing this alters potential solutions to the above issue. The cab vibrates quite a bit. Enough that it rattles the tubes in my head, which is why I put the head on the amp stand you see there. If I wanted to stiffen this cab up, how would I go about it? What bracing configurations work best in a cab like this?

Obviously, I'm open to plenty of experimentation with these issues, since I've got nothing into the cab. Just your basic salvage job. It sounds fairly acceptable to me as is, but it would be nice if I could improve in the aforementioned areas.

On a related note, if anyone has another of these for sale, I'd be interested. Also interested in the GB215B model.

Thanks!

Matt

EDIT: Interior volume is about 8421.8 cubic inches. Darn math!

[greenboy]

I think you should check it again. 727³" would be so shallow you couldn't mount a 6" midrange driver on the baffle.

And do you have WINISD?

[barebones]

Yikes! Math was never my strong subject. In addition to incorrectly calculating my volume, I also started with two incorrect interior dimensions. Should have realized I had a problem when I unsuccessfully tried to calculate for cubic feet. Measure once, cut twice, right?

So... Let's try again. With corrected L, W, and H figures, and calculating L x W x H, I'm getting approximately 8421.8 cubic inches. (Again, not accounting for minimal bracing strips in the interior corners of the cab.)

I do not have WINISD, although I have seen it mentioned many times here. Is it a free download I can get?

Thanks again.

[kosmicwizard]

Why don't you search for it in google? Cheers.

[Muckaluck]

Hey, if its the LS 115B pictured here: http://www.genzbenz.com/?fa=detail&m...id=631&cid=118 then I have one. I actually really like it and it is my go-to cab at the moment.

If you were really looking for another one you could PM me and we could work something out. Otherwise I'm really curious about your modifications to this, especially with the Eminence being dropped in.

Subscribed!

[barebones]

Originally Posted by kosmicwizard

Why don't you search for it in google? Cheers.

Thanks, Whiz. Anything else to add? Cheers!

To those in the know, will my port questions be answered if I simply get this WINISD program? If so, I'll get it, and I'll figure it out. I enjoy this stuff, but it simply isn't my area of expertise, so I guess there's a little trepidation here. That's why I'm attempting to consult with some trusted resources here at TB. I can learn; I just want to make sure I'm not headed in some ridiculous direction.

Regarding my second issue above, does anyone have any suggestions for bracing this cab? It makes sense to me that I'll need to address this first, so that I can calculate a more accurate box volume before working on the porting. I have no idea how to go about bracing an already fully built cab, though. Does anyone have any ideas?

Thanks again, everyone.

[barebones]

Originally Posted by Muckaluck

Hey, if its the LS 115B pictured here: http://www.genzbenz.com/?fa=detail&m...id=631&cid=118 then I have one. I actually really like it and it is my go-to cab at the moment.

If you were really looking for another one you could PM me and we could work something out. Otherwise I'm really curious about your modifications to this, especially with the Eminence being dropped in.

Subscribed!

From my correspondence with Jeff, I believe that is the second generation cab. Mine, the GB115B, is nearly identical. The porting is different, but I believe everything else is the same. Yours has port tubes; mine never did. I'm guessing that was due to the use of a slightly different driver, or there was a different outcome desired when my cab was designed.

[MuzikMan]

If you are interested in learning from this experience then I highly recommend that you work with a program like WinISD. It's a free download. You will get the answers to your port questions with it. Adding internal bracing to an existing cab can be a pain; I would suggest that you place 1" square strips on as many panels as you can leaving no more than a 12" square surface of unbraced panel. You then might be able to add front to back strips to it if there is room.

[MuzikMan]

On second thought check this thread out. If Bill says it I believe it. Bracing a Peavey TNT 115

[barebones]

Originally Posted by MuzikMan

On second thought check this thread out. If Bill says it I believe it. Bracing a Peavey TNT 115

Thank you! Dowels? I never would have guessed it could be as simple as that!

Sounds like I should be able to achieve my goals in the bracing realm, and I'll just have to run WINISD to figure out my porting.

A couple other questions, knowing that cab design is all about trade-offs:

First, does it make sense to any of the audio engineers here that I'm hearing the fundamental disappear below A with my current configuration of driver and cabinet?

And, second, if I manage to get the tuning I want (maybe as low as a strong fundamental on my E string, but, I hope, at the very least, a nice, strong G and F) is there going to be a big sacrifice of efficiency, or apparent "loudness" at the gig. I do enjoy the fact that I currently can fill a dive bar with one cab and my tube head. My gig on Saturday, I was not mic'ed or run to the board at all. This was in about a 150 person venue. The sound guy, whom I've worked with before and trust, said the bass was plenty loud out front. I'd like to maintain the ability to do that but get the fullness I'm looking for on standard 4-string bass.

Am I even making sense here? Jeesh, I'm out of my depth!

Additional information: Saturday's gig was with a three-piece rock band, and the 150 person venue probably had about 50 people in it. Hey, don't tell me you haven't played that kind of gig before!

[agedhorse]

Before assuming that the cabinet needs additional bracing, I would suggest that you work on tuning first. That's a relatively small cabinet with 3/4" stock and reasonably small panel spans.

I suspect that optimizing tuning will be far more meaningful in the big picture.

[barebones]

Originally Posted by agedhorse

Before assuming that the cabinet needs additional bracing, I would suggest that you work on tuning first. That's a relatively small cabinet with 3/4" stock and reasonably small panel spans.

I suspect that optimizing tuning will be far more meaningful in the big picture.

Thanks, agedhorse. Obviously, you have more experience in this area than I do. The problem I'm experiencing is lots of vibration to my head as it sits on top of the cab. Is it incorrect to assume that additional bracing would cure this? Like I said, I like everything else about the cab; if I can address these two points it will be pretty much perfect for me.

[agedhorse]

Originally Posted by barebones

Thanks, agedhorse. Obviously, you have more experience in this area than I do. The problem I'm experiencing is lots of vibration to my head as it sits on top of the cab. Is it incorrect to assume that additional bracing would cure this? Like I said, I like everything else about the cab; if I can address these two points it will be pretty much perfect for me.

If you like the sound of the cabinet, I would just put a small piece of plank foam (closed cell) under the head before jumping through all the work of adding bracing that may not help.

Again, if the tuning is off on the cabinet, that will change the way the cabinet interacts with the driver and I would suggest that as the first thing I would look at to "improve". It will also help in the reliability of the driver if the tuning is poor as is.

[barebones]

Originally Posted by agedhorse

If you like the sound of the cabinet, I would just put a small piece of plank foam (closed cell) under the head before jumping through all the work of adding bracing that may not help.

Again, if the tuning is off on the cabinet, that will change the way the cabinet interacts with the driver and I would suggest that as the first thing I would look at to "improve". It will also help in the reliability of the driver if the tuning is poor as is.

I think I see what you're saying. Are you suggesting that improper tuning for this driver could actually be contributing factor in the vibration I'm experiencing? If so, then it makes complete sense to address the tuning before anything else.

Thanks for your insight.

[agedhorse]

Originally Posted by barebones

I think I see what you're saying. Are you suggesting that improper tuning for this driver could actually be contributing factor in the vibration I'm experiencing? If so, then it makes complete sense to address the tuning before anything else.

Thanks for your insight.

Yes, this is possible. Resolve any tuning problems yu have first then re-evaluate to see if you need to address anything else.

Any thine you have several spring-mass systems working together, there exists the possibility of unexpected results from negative interactions. The driver is one, the air is another and the cabinet is a third system all worken together and against each other.

[barebones]

Originally Posted by agedhorse

Yes, this is possible. Resolve any tuning problems yu have first then re-evaluate to see if you need to address anything else.

Any thine you have several spring-mass systems working together, there exists the possibility of unexpected results from negative interactions. The driver is one, the air is another and the cabinet is a third system all worken together and against each other.

Thanks for your help. I'll start there then and post my results.

[barebones]

Well, I haven't done any mods to the cab yet, but I have been learning a lot messing around with WinISD Pro Alpha. Pretty fascinating program. Just playing around with various speaker/driver combinations has been instructive. I'm finally truly seeing (in the form of SPL charts) what all the more learned folks here have been talking about in terms of the various trade-offs when constructing speakers. By that, I'm referring to the interplay between box size, port tuning, number and type of driver/s, etc. I'm really enjoying comparing drivers in sealed vs. ported boxes, as well as watching how changing box size and tuning frequencies effects the SPL modeling.

Anyway, I do have a couple of questions maybe somebody can help me out with. First of all, I attempted to enter parameters for the 3015, since this program does not have it pre-loaded. (It has the 2515 but not the 3015.) I read in some other threads that there are basically nine parameters that should be entered, and I did enter those. However, I know I'm doing something wrong, as the SPL results I get when I attempt to "reverse engineer" the Genz Benz cab with the 3015 show a steep curve from around the high-mids to the high frequencies, with no mid or low content whatsoever. In fact, I get similar results no matter what box volume I enter. Is there something I'm overlooking here? Other parameters besides the nine I read about in the other thread? I went through the WinISD tutorial on entering driver parameters, and I'm still in the dark here.

Also, just a general question about how the program functions. As I mentioned, I am able to play around with box size and tuning and observe how that effects port length. I'm not seeing the reverse, however; when I alter port length and leave box volume the same, the program does not respond by showing the cab tuning. Not a big issue, really, but I thought I might be able to enter the volume and port dimensions of the Genz cab as they currently are and see what the program says the cab's tuning would be with various drivers. Does it just not work in reverse like this? Just curious.

[barebones]

Little bump for the day crew.

[MuzikMan]

Your wacky spl chart on the 3015 sounds like a result of user error on the parameters. Check to make sure your units are correct (in. vs mm. for instance) on everything you entered.

The program IS able to output the correct tuning when you change the port dimensions. I can't imagine why that isn't working for you. One thought is to run it in compatibility mode for windows xp. I know my version was unstable on windows 7 until I did that.

[barebones]

Originally Posted by MuzikMan

Your wacky spl chart on the 3015 sounds like a result of user error on the parameters. Check to make sure your units are correct (in. vs mm. for instance) on everything you entered.

The program IS able to output the correct tuning when you change the port dimensions. I can't imagine why that isn't working for you. One thought is to run it in compatibility mode for windows xp. I know my version was unstable on windows 7 until I did that.

Thanks for your thoughts. I'll have to see if I can figure out the whole compatibility mode thing. I'm experiencing a couple other occasional glitches that I've been able to work around--certain parameters clearing out unexpectedly, for example.

I'm sure I have to have entered something incorrectly on the 3015. I just have to figure out what. This is all completely new to me. I've had some fun designing various cabs, and I was just to the point of thinking, "Hey, this isn't that hard." Then I read about something called "port velocity." Guess where all my cab ideas failed epically? I have a lot to learn!

By the way, what should I be looking at for acceptable port velocity? I've run across a couple different figures bounced around. I also gather that at least some of it is dependent upon how the cab will be used--wattage, 4 or 5 string bass, that sort of thing. Any general guidelines here?