New speaker type? OB-RLH

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Is it just my 'puter, or are the pictures not loading? I'm having a little difficulty picturing the design in my mind's eye.

This sounds interesting as I have a pair of old Goodmans, for which I cannot find any information. They have small magnets, so I'm assuming high Q and thus suitable for OB. I just don't have the space for a regular OBs in my apartment.

PS, anyone got any info on Goodmans twinax 220c?

Max
 
A drawing will give you a better idea:

Here's what I've built and is working well, just a bit big since I'm using a 15" driver.

An externally hosted image should be here but it was not working when we last tested it.



I'll have some B200's to try in a couple of weeks. It will be drastically smaller and should have satisfying bass, but not the forget-a-sub bass like I'm getting with the 15" . The small one should compete or beat the extension of any reasonable sized RLH, but retain the natural OB sound.
 
jdybnis said:
Interesting. How much output are you getting out of the lower opening relative to the back of the cone?


Good question. I would think that the driver's backwave would just take the path of least acoustic resistance (straight out the back) and the folded transmission line/horn wouldn't even come into play.

So, just what is going on here to create deep bass response?

Max
 
maxro said:
Hmm.. I did a little looking. It seems the TL part is acting as an acoustic high pass filter. although the proportions seem out of whack. Maybe I should try a gesstimate of measurements with the formulae from here:

http://en.wikibooks.org/wiki/Engineering_Acoustics/Filter_Design_&_Implementation

Very interesting, indeed. More research is needed.

Max

I believe the slot is the low pass filter which combined with the airspace in the horn shape determines what low frequencies go into the horn. I also believe the proximatey to the driver is important because that is where the highest pressure occurs, causing a portion of the low frequency content to see the slot as an acoutical shortcut. I looked to the forumla for Helholtz panel bass absorbers to guestimate an initial slot size.

I got a pair of B200's in today, so we'll see if I can get similar results with a smaller driver. It moves much more than my 15" driver at similar volumes, which tells me I'll have a higher pressure and velocity for loading the slot despite having a shorter open back chamber. I hope that will help make it able to load a wider bandwidth into the expanding pathway.
 
jdybnis said:
Obvious question, can you measure the impedance of the driver in the box? It should be informative.

You've got me confused with someone who care's about measurements. I believe our ears are the most sensitive instruments we could ever own as long as they're trained well. I occasionally will use my SPL meter to double check what I'm hearing and it's been so long I can't locate it after a recent move. My most used non-bodily tool is a tone generator that I use to home in on problems my ears detect. I'm strictly an OB guy, so measurements become even more meaningless.

That being said, if you explain how measuring the impedance could benefit optimizing the design for another driver, I'll dig the stuff up to measure the impedance and share the results. Just please don't convert me to a numbers guy. I really enjoy designing by ear and visualization of wave flow using just enough science to generate new ideas. I'm currently on the right track to coming up with a single driver OB speaker that really doesn't need a sub and has nothing but speaker wire between the driver and the amp, and has a domestically acceptable size.
 
Well. I'm curious if the driver is seeing higher acoustic impedance at the pipe's resonant frequency or lower acoustic impedance. You've addressed the question of what it sounds like in the postings above. This is more of a question of how the parts of this enclosure interact to affect the driver.

If the impedance goes down with frequency that supports the acoustic low pass theory. But what happens to the energy that goes down the pipe? Maybe the pipe is providing a longer path length for the low frequency sound and thereby lowering the dipole cutoff?
 
jdybnis said:
Maybe the pipe is providing a longer path length for the low frequency sound and thereby lowering the dipole cutoff?

That is definitely at least part of it and one of the few things I can say with some certainty about the cab. The extra 2.2m down the pathway and around to the front of the cab is enough distance, so whatever goes through the pathway provides reinforcement of the front wave down to 26hz before cancellation starts. There's not a lot of output coming out of the mouth, but it's only very low frequency stuff.

I'm sure that is part of the equation, because at say 35hz, whatever goes thru the pipe changes from 6db of dipole cancellation to a couple of db of reinforcement. 2 things that make me believe that not all that's happening is the increase in LF power handling and the quite peaky bottom octave response with the speaker out in the room.
 
Hi Chris,

I went through a few prototypes and came up with an OB-RLH that I'm reasonably happy with. That uptilted response is a real bear to try to overcome. All the guys raving about the B200 on OB must have a very limited range of music they listen to, because they are still quite forward sounding, despite my extreme attenuation of the HF in the rear wave. I still want to try one more shot at the RLH portion in an attempt to round out the bass a bit more. I'm getting solid low 40's now, but I really want to get rid of remaining tilt in the response, if possible.

The pair in the center are the B200 version which is 13" deep, making it quite compact.

An externally hosted image should be here but it was not working when we last tested it.
 
Hmm... I found the B200's to be a grade "A" pain to set up room position. I found that toeing out worked better than toeing in. Also mine are at a 24" off the ground at a 10 deg tilt. I must be listening to them more off axis than most.

I listem to mostly acustical, jazz, and orcesteral. But the still do very well with some Iron Maiden, Ministry, or the wife's Billy Joel.

Also, I just lined the back of the u-baffel with siill plate insolation for houses. It's pink packing material with 1/4" high ridges down the back, and it's about 5 1/2" wide and comes in sheets of 50' for $6.

That stuff really tighened up the imageing and made the pressentation more balanced.
 
el' Ol,

I'm a hard core minimalist by necessity and I'm sold on the point source sound. If I can get my B200 cab as easy to listen to as my FE108ez's on OB with bass augmenter, then I'll have it made. I'm just not there yet.

Corloc,
I'm not saying they don't sound really good. If they were a 10" driver with at least 4mm of Xmax instead of the measely 2mm (which Visaton tries to hide), then I think I could get to where I want much easier. That is a single driver compact OB with an F3 in the low 30's.
 
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