New Dual 8" Tower Design

Rick Craig · « **on:** 25 Feb 2013, 02:29 pm »

Recently I had a local audiophile contact me about building a floorstander on a limited budget. We went over different options that fit within his constraints for cabinet size and performance objectives. He had listened to the Tempesta Extreme and really liked the driver combination but the cost was beyond his budget. The idea of separate powered subwoofers with a pair of monitors came up but the montitor driver choices were restricted due to budget. At that point I looked at other alternatives and suggested using dual 8" woofers with an Accuton C90 mid and RAAL tweeter. With high-excursion / low distortion aluminum cone woofers he's going to be able to have a $8-10K/pr. speaker for far less than that. I'll post more as we progress...

AvFan · « **Reply #1 on:** 6 Mar 2013, 03:34 am »

Any pictures of this design?

Rick Craig · « **Reply #2 on:** 6 Mar 2013, 04:05 am »

Quote from: AvFan on 6 Mar 2013, 03:34 am

Any pictures of this design?

No pictures at this time. The builder is using a composite material and it hasn't arrived yet.

AvFan · « **Reply #3 on:** 6 Mar 2013, 06:08 am »

Thanks for the update. I'm curious to know what kind of "composite" is being used. By chance is it Panzerholz? Panzerholz is being used for turntables and is truly bullet proof. It would be interesting to use it for a speaker cabinet.

navin · « **Reply #4 on:** 12 Mar 2013, 06:33 am »

Which RAAL? The 70-20XR?

vanderstephen · « **Reply #5 on:** 12 Mar 2013, 02:52 pm »

AVFan,
I am using a 3/4 phenolic resin for the cabinet structure. The baffle will be 3/4 mdf (total 1.5" thick front). I will also have an additional layer of mdf on the outside of the phenolic resin bonded with 2 part epoxy so that I will have a surface that can be veneered. I am finally finishing up my flooring project so will soon be starting on the speakers- i only have a few panels cut so far.
Navin,
Rick will need to comment on the drivers. I do not remember off hand.

This is my first time to use 2 part epoxy and I haven't done much veneering so this will be a slow process for me.

nickd · « **Reply #6 on:** 12 Mar 2013, 04:06 pm »

I'm a bit jealous

Always wanted to try a build with phenolic.

The downsides are expense, and it cuts more like steel than MDF.

Cant wait to see pics!

Rick Craig · « **Reply #7 on:** 13 Mar 2013, 12:24 am »

Quote from: navin on 12 Mar 2013, 06:33 am

Which RAAL? The 70-20XR?

Sorry for my late reply due to the Axpona show. The 70-10D is the tweeter.

navin · « **Reply #8 on:** 13 Mar 2013, 07:36 am »

Quote from: vanderstephen on 12 Mar 2013, 02:52 pm

AVFan,
I am using a 3/4 phenolic resin for the cabinet structure. The baffle will be 3/4 mdf (total 1.5" thick front). I will also have an additional layer of mdf on the outside of the phenolic resin bonded with 2 part epoxy so that I will have a surface that can be veneered. I am finally finishing up my flooring project so will soon be starting on the speakers- i only have a few panels cut so far.
Navin,
Rick will need to comment on the drivers. I do not remember off hand.

This is my first time to use 2 part epoxy and I haven't done much veneering so this will be a slow process for me.

I wont get ito the phenolic resin box as I dont know enough about this resin but some resins tend to resonate so a rap test might be required to ensure that the resin you are using does not.

With very thick baffles you can get some echo due to the cavity caused b the woofer cutout. With Woofers that have NdFeB magnets like ScanSpeak's Illuminator this is less pronounced but with larger ferrite magnets you need to be more careful. I suspect the Aluminum cone 8" woofers you are using have a ferrite magnet.

The C90-6-078 (I assume) has a slight hump post 1k but I believe Rick will solve that in this XO. It makes a nice partner to the 70-10D and goes low enough (200hz) for the 8".

vanderstephen · « **Reply #9 on:** 13 Mar 2013, 12:26 pm »

Navin,
The cut out in the B baffle will be oversized to account for this.
I did a rap test a while back- much less resonant than MDF. This is basically the same material as Wilson uses.
I enjoyed reading your thread before for your speaker construction and hope to hear them one day if I'm ever in your area.

AvFan · « **Reply #10 on:** 14 Mar 2013, 02:56 am »

I'm looking forward to reading about your progress on your speakers. I built a kit Rick designed for my particular needs and it has been terrific plus doing the woodworking made them sound all the sweeter. Please post pictures when you can so we can check out how the phenolic resin works. Enjoy!

navin · « **Reply #11 on:** 14 Mar 2013, 04:38 am »

Quote from: vanderstephen on 13 Mar 2013, 12:26 pm

Navin,
The cut out in the B baffle will be oversized to account for this.
I did a rap test a while back- much less resonant than MDF. This is basically the same material as Wilson uses.
I enjoyed reading your thread before for your speaker construction and hope to hear them one day if I'm ever in your area.

You are always welcome to Mumbai. You will be even more welcome if you bring your speakers along! LOL.

vanderstephen · « **Reply #12 on:** 27 Mar 2013, 02:46 am »

Hey guys,
I am starting to make some real progress. Here are a couple of quick snapshots of what's done so far. This is just a dry fit of one of the cabinets so I can double check dimensions for bracing etc. I will post more updates when I have something worthwhile to take a picture of. Thanks for looking.

navin · « **Reply #13 on:** 28 Mar 2013, 06:23 am »

Quote from: vanderstephen on 27 Mar 2013, 02:46 am

Hey guys, I am starting to make some real progress.

Nice work. I would have tapered the cabinets front to back too to comply more with WAF.

vanderstephen · « **Reply #14 on:** 29 Mar 2013, 03:58 am »

I was very close to doing that, but that would just add to potential complications or issues for me. Maybe if I was using a less expensive and easier to handle material than phenolic resin. Regardless, they go in the bonus room, which is my room so there are no WAF issues. She is more ready for me to spend time inside and get it over with instead of spending my free time in the garage. I looked a lot at the shape of the Verity speakers and wanted to do something like that, but it was too complex.
On an unrelated note, have you been to Tewari Brothers in Juhu? I love that place. My wife's aunt is bringing me some kaju katli from there next week.

navin · « **Reply #15 on:** 1 Apr 2013, 04:31 am »

Quote from: vanderstephen on 29 Mar 2013, 03:58 am

I was very close to doing that, but that would just add to potential complications or issues for me. Maybe if I was using a less expensive and easier to handle material than phenolic resin.

On an unrelated note, have you been to Tewari Brothers in Juhu? I love that place. My wife's aunt is bringing me some kaju katli from there next week.

If Pheonilc resin is like the Epoxy resins I have used it is a pain to work with especially shape.

I rarely venture north of Worli where my office is so no I have not been to Tewari, but I have driven through Juhu a few times and gone to JW Marriott there once.

AvFan · « **Reply #16 on:** 13 Jun 2013, 03:43 am »

Ahhhh, now we see in the other thread how these turned out. Do you have any additional photos you can share on this build?

vanderstephen · « **Reply #17 on:** 15 Jun 2013, 02:38 am »

Partial view of internal construction.

Basking in the sunlight.

My wife didn't like this stage so much as I had stolen the garage from her.

Front and back views prior to driver and crossover installation.

Photos of the speakers in the installed position to follow. They sound incredible, by the way.

AvFan · « **Reply #18 on:** 15 Jun 2013, 02:50 pm »

Thanks for sharing some more photos. Your speakers look fantastic.

I did a quick search on phenolic resins and came up with many different products; what did you use and were you able to eliminate some internal bracing by using the phenolic? Does in cut using standard carbide tipped saw blades and router bits? Lastly, I noticed the refrigerator dolly in the background; just how heavy are your speakers?

vanderstephen · « **Reply #19 on:** 15 Jun 2013, 07:36 pm »

AvFan, Thanks for the compliment. Specifically, I used Trespa TopLab which is one of the two main countertop work surfaces that you find in laboratories. I work for a company that sells it, so was able to get a good deal on the raw material. I did use less bracing than if I were to have used MDF since the phenolic is much stiffer. I used Smooth-On two part epoxy to bond panels together and then pre-drilled and used type F thread cutting screws for extra good measure. Carbide tip blades are all that is needed. I had much better luck with setting up a straight edge and using a circular saw than using a table saw- the table saw was quick to bind if the blade wasn't perfectly parallel to the fence. The speakers are in the 120 pound range without drivers and 150# range with drivers (each).