Modifying/Improving Cerwin Vega HED U-123 Cabinets

[ScooterMcTav]

While I wait for my new woofer and surrounds to arrive for my CVs, I was wondering if anyone had any suggested cabinet mods for the pair.

When I look in the boxes, I see a big empty rectangle with batting stapled to the sides. Any value in adding a brace to the inside, and making an enclosure for the mid so it's not getting pushed in and out by the woofer's excursion? How about doing some mass loading, or adding some polyfill?

Curious if anyone else has modded these old beasts and what sort of results they had.

 

[gdmoore28]

I can't find any links to the HED-123, so my remarks will be general.

An acre of unbraced cabinet panel is never the best idea. The speaker-building manuals all suggest breaking up a large panel into smaller areas by adding bracing. The general technique is to add braces that break up the panel into smaller ones. A good rule of thumb is 3/4"X1" mdf or plywood with the 3/4" side glued to the panel. The most common pattern is a window-frame style with braces irregularly spaced so that you end up with several differently-sized panels which will cause each panel to vibrate at different frequencies. Or, you can simply create an "X" pattern. Most of the time, bracing the long sides and the back panel will suffice. Some people add a brace that connects side to side and front to back.

Adding polyfill will simply be a matter of experimentation and personal taste. I wouldn't do any mass loading inside the cabinet, as that will change the cabinet volume and the tuning.

Are you sure your midrange is open in the back or never had its own enclosure? If it is completely open to the cabinet, a small enclosure would definitely be a benefit.

GeeDeeEmm

 

[turboyam]

What GDM said. And if the mid is really not closed-back, it is mandatory that it should be. Some use cardboard tubing, with a wood cover. The idea is to make the mid, airtight to the main enclosure but in this case, you want a small (not ideal) sub-enclosure as it's volume is going to mess-up the woofer's volume.

 

[ScooterMcTav]

Sorry GDM, I was sloppy on my posting - the speaker is a HED U-123, not a HED-123.

The U-123 looks a lot like the A-123, except that the A-123 had the dhorm tweeter, while the U-123 has the D series bullet tweeter.

Here's a photo of my old A-123s.

They had a sealed mid - but between age and vibration the seal was lost, and the air moved by the woofer excursion actually caused the outside edge of the mid cone to fray and tear.

Here's a photo of the U-123 with the covers on. Drivers have a similar configuration - the mid and tweeter switch places:

Now the port for the woofer is on the bottom of the cab - it occured to me that I could make a solid 3/4 - 1" piece of MDF to insert internally that creates two separate chambers - one for the woofer and one for the mid/tweeter. However, I imagine it would affect the Q, making the port size incorrect.

Of course, I could always then make the woofer compartment acoustic suspension......

 

[turboyam]

Humm, don't change the woofer's loading, have a comparable size sub-chamber for the mid.

 

[ScooterMcTav]

So to chamber the mid, are we looking for dampening vibration isolation, or something rigid to protect from excursion in the cabinet?

If it was the former, I could silicone on a yogurt tub with batting in it - seems to me it would provide excellent vibration isolation, and some pressure relief. Or do I need something more rigid (like the wood/tube idea)?

I wouldn't want to put too large a chamber into the cabinet, as not to affect the woofer's loading.

 

[turboyam]

A yougurt thub is too flexible, will transmit pulsations to the mid. I would use a rigid cardboard tube with a snug fitting, glued in place, wood round cover. Fill it loosely with fiberglass or else.

 

[Fiddleboy]

While I wait for my new woofer and surrounds to arrive for my CVs, I was wondering if anyone had any suggested cabinet mods for the pair.

When I look in the boxes, I see a big empty rectangle with batting stapled to the sides. Any value in adding a brace to the inside, and making an enclosure for the mid so it's not getting pushed in and out by the woofer's excursion? How about doing some mass loading, or adding some polyfill?

Curious if anyone else has modded these old beasts and what sort of results they had.

Back in 1977 a friend of mine had some CerwinVega hard rockers that sounded incredible.
Well one day we blew one of the drivers.
We replaced it with a driver that came out of a Marantz speaker. We both thought the speaker would not sound near as good but it sounded great. I just got through building some car speakers, so why not build some speakers like these Vegas and copy them as close as possible. When looking inside the cabinets, the port that was in it was called a base reflex port. It wasn’t a tube or a hole in it with a tube going about halfway down inside,i It was more like a shelf at the bottom of the speaker, vented out the back of the speaker.
About 2” from the bottom. Also had a soft dome mid range on the backside of the speaker wall reflecting setup. They put out bottom end that pretty well shakes everything. Maybe some of this will give you some ideas on some mods for your speakers.