• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Box question

Tube Radio

Tube Radio

Super Member
I have a speaker enclosure and I need some ideas on what damping material to put inside.

Internal box dimensions are as follows.

16 1/2" wide
29" high
16" deep

slot port in the speaker baffle

10" wide
4" high

With the 12" Rola speaker I have installed there is a peak in response around 80 Hz. Also there is only minimal damping material installed which consists of some stuff on the bottom, left side and rear panel of the cabinet.

Not sure what this damping material is.

IMAG0207.jpg
 
Last edited:
Register to hide this ad
Hey Tube.

Usually, in a ported box, the material to use is poly batting. You don't want fiberglass pumping out of the port. The stuff you show in the pic looks like old insulation called rockwool. Like fiberglass, but not. Health-wise, kinda, dangerous (if it is). Bag it and dump it. Vacuum out the box to be safe.

If it were me, I'd take all that out and get poly batting. Any fabric store carries it. Walmart also has it cheap. Cut to size and staple on. As for placement, I cover all interior surfaces except the baffle board. If it still sounds peaky, I'll put some poly fill in 'till it sounds about right. If the bass is thin, I'll take a side wall off and try again. Just play with it 'till it sounds good to you. That's all I can tell you.
 
I had thought about the polyfill, but the acoustical foam will be a little easier for me to work with.

What I had thought about doing is possibly using a 31 channel EQ if using proper damping material doesn't work. That way I can somewhat tune the amp to work best with the speaker.

I do plan on getting rid of the original material ASAP as it seems to shed fine particles when messed with.

I can block the port and the peak is gone, but the low bass is not as present. Also the peak is stronger or weaker depending on how the speaker is wired to the amp. The peak is most noticeable with music such as rock that use a lot of kick drum.

Box. The crossover has since been reworked and properly mounted. I am wondering if that Rola speaker was designed for an open back, ported or sealed enclosure. I bought it off Ebay, but all I know is it came from a Hammond organ.

IMAG0033.jpg
 
Last edited:
Is the foam the "egg crate type"? That would also work.

When you say it depends on the amp hookup, are you talking about impedance taps on the amp? Is it a tube amp? Have you taken a meter to the driver to see what the ohms are on the driver?

I see the port in the pic. Have you tried to block some of it off? It looks big. That should load the woofer more, and maybe get rid of the peak you are getting. Worth a shot.
 
For the crossover I just did what sounds best to my ears.

Zenithschematic.jpg


What I mean by amp hookup is the speaker polarity.

The amp is a tube amp.

I'll play around with the damping material.
 
Last edited:
Many organ and instrument speakers have a high QTS. They played best in an infite baffle arrangement aka, open back cabinet. From just looking at the back of the cone of the Rola, I bet this is the case, hence the hump around 80 hz.. Since you're in there and messing around with the damping material, maybe you could try placing just a restrictive piece over the port. Maybe a piece of netting or thin polyfill may get the bass right for you.
 
Rockwool is dangerous like fiberglass?? First time I've heard someone say that. Not saying it's not true, I'm simply-saying this is the first time I've heard that. My W60E's are filled with rockwool (Not sure about the W90's... Somebody had already recapped them... They ARE ported though, unlike my W60E's).
 
How would that affect the crossover frequency? Also would a 5 uF capacitor work? If so I have one I can try now. I also have a 3.9 uF cap I can try.

With the back off the speaker the lower bass seems to be lacking somewhat although the bass seems to sound slightly better. Wondering if I should look for another woofer?

I wonder if that cabinet was tuned for 80 Hz whether on purpose or quite simply as a result of the way the cabinet was done? I could see it possibly being done to enhance the bass of the music back then and with the original speaker it was probably rather good sounding, but the original speaker had a vibration I couldn't get rid of so out it went.

Maybe I could get a new Dayton woofer from Parts Express then seal the port and ensure the rest of the cabinet is sealed?

EDIT: I found a Dayton 12 db/octave 2,500 Hz crossover and that seems to have helped, although I am not exactly sure why. I had intended for the Rola speaker to play much higher since it has a whizzer cone, but it seems like the 2,500 Hz crossover does integrate the woofer and tweeter better. Another option would be to build a smaller speaker cabinet and install a fairly efficient 12" or 15" woofer and build a 12 db/octave 150 Hz crossover. or I could even use a two way active crossover and integrate a powered sub. That is not the way I really want to go, but if it will be best I'm not opposed to it.
 
Last edited:
Tube Radio said:
How would that affect the crossover frequency? Also would a 5 uF capacitor work? If so I have one I can try now. I also have a 3.9 uF cap I can try.

With the back off the speaker the lower bass seems to be lacking somewhat although the bass seems to sound slightly better. Wondering if I should look for another woofer?

I wonder if that cabinet was tuned for 80 Hz whether on purpose or quite simply as a result of the way the cabinet was done? I could see it possibly being done to enhance the bass of the music back then and with the original speaker it was probably rather good sounding, but the original speaker had a vibration I couldn't get rid of so out it went.

Maybe I could get a new Dayton woofer from Parts Express then seal the port and ensure the rest of the cabinet is sealed?

EDIT: I found a Dayton 12 db/octave 2,500 Hz crossover and that seems to have helped, although I am not exactly sure why. I had intended for the Rola speaker to play much higher since it has a whizzer cone, but it seems like the 2,500 Hz crossover does integrate the woofer and tweeter better. Another option would be to build a smaller speaker cabinet and install a fairly efficient 12" or 15" woofer and build a 12 db/octave 150 Hz crossover. or I could even use a two way active crossover and integrate a powered sub. That is not the way I really want to go, but if it will be best I'm not opposed to it.
Click to expand...

Hey Tube.

Yea, a 5uf would be fine. It's about the same x-over point, but maybe the sharper dropp-off would tame the peak. The 3.9uf would raise it too much, and there would be a hole in the mids. Do you have any way to measure the VC inductance or the fs of the driver? That would help alot.
 
Hey Tube. Good Morning.

So your meter doesn't do inductance. Too bad.

Thinking about this last night, maybe it's box induced resonance. That's a big box with no bracing anywhere. I might try a brace width-wise, in the middle of the side panels, just above the woofer. A 2x4 should do it.
 
Last edited:
I may try a different woofer

http://www.parts-express.com/pe/showdetl.cfm?partnumber=295-320

That was the only 12" woofer I could find that would possibly work although I'd have to either add a midrange driver or lower the tweeter crossover frequency.

I could always just install an eminence delta pro 12A midbass driver then get a two way crossover and run a powered sub. That might be the best option as I wouldn't have to dick around with the cabinet as much., but if I did that I wonder if I will loose the character of the sound? Also how well would at setup work when listening to the AM tuner in the console?
 
Last edited:
It sounds as if your speaker and box were not made for each other.

The woofer wants a smaller port. That is why it sounds better with the port blocked. You can tri k the driver by restricting the port with some foam, or you could try and lengthen the port about 6-8 inches.
 
Tube.
The woofer at PE is a good quality driver. It has a "middle of the road" Qts, so it'll work in a sealed or vented box. Your box is about 4cu.', too big for sealed. You're going to have to cover the slot up. My calc's say a 3"d port would be a starting point. At about 5" long, box tuning would be 28hz. Leave everything the way it is, just cut some ply to cover the slot and put the PVC in that. You can always change back if it don't work. You can experiment from there.

Look at this tweeter: http://www.parts-express.com/pe/showdetl.cfm?partnumber=279-102

If you cross it over at 2khz, it just might sound good. I would go with a 2nd order x-over for both drivers.

That's all I have for you. Good Luck
 
With the port blocked the bass peak is gone, but the low bass suffers. Sound is actually best with the back removed yet again low bass suffers.

I wish Radio Shack still sold speakers. Their 12" they once sold would have worked great in this cabinet provided I blocked the port. I used a pair in a couple fisher speakers and they to this day still sound great and were a near perfect match to the fisher midrange and tweeters.

Now I could use a sealed back midrange driver which would allow for more choices as to using a better woofer.

I tried the 12" woofer I had laying around from a Magnavox console that was in a styrofoam enclosure and I still have that same peak so it is the box causing it.

What I may do is purchase that woofer I posted then get a small two way active crossover and use a second smaller vacuum tube amp for the tweeter with the Console's amp for the woofer provided that Isophon tweeter can play well down to 2,000 Hz.

I do somewhat still like the idea of a powered sub though. That way I don't have to touch the speaker box at all except to add some damping material. I could more than likely pick up a good used powered sub for what I would pay to get the cabinet + speakers right. Problem is I don't know if I really want a powered sub as I would like the console to reproduce the deep bass on its own. One benefit of a powered sub is the main amp can then go a little louder since it is not having to reproduce the low bass any more.
 
Last edited:
What I may do is just purchase a single channel 31 band eq and use that to remove the 80 Hz peak then it should sound ok I think. The port seems to help the low bass somewhat.
 
Good news. I remembered that I had an Oxford 12" speaker. I tried it and the speaker so far seems to work good in the cabinet. I think the main problem is I am expecting the 12" woofer on 20 watts to hit like a subwoofer. One reason why I am contemplating adding a powered subwoofer.

All I need is a Rolls SX-21 crossover, and a powered sub with the ability to defeat the internal crossover. The input impedance of the Rolls is 10K and the output impedance of the Browning tuner is either 10K or 15K so should drive the Rolls with ease.

One benefit is if I do use a powered sub I won't have to dick around with the original amp to get more power out of it. I still may try to seal off that port and see how the bass sounds. I am wondering if that Oxford speaker was meant for a sealed or ported enclosure as I had it in an open baffle speaker box for awhile and it didn't sound very good in the bass. I will try first using cabinet damping material then closing off the port if the damping material is not enough. For some reason it sounds like the 80 Hz peak is much reduced or not there at all.

I held something in front of the port and the sound didn't change much unlike it did with the Rola so it seems like I can just close the port off, seal the hole where the speaker wires pass through then seal the speaker back. I will more than likely use some of that speaker sealing stuff. Which is the best to use while permitting removal of the back if necessary?

I may just keep using the 12 db/octave crossover as it sounds pretty good.

Thing is I had originally thought about trying that Oxford speaker before buying the Rola, but was hesitant based on how it sounded on an open baffle. I am pretty sure it was designed for a sealed or ported cabinet as unlike the Rola the Oxford's bass sounded weak with the back of the console off.

Now I have a good 12" Rola speaker I can put in an open back box and use with a communications receiver :D
 
Last edited:
You must log in or register to reply here.
Back
Top Bottom