Hi guys, I'm trying to troubleshoot bass issues with one of my speakers. Here's a picture of one of them. What I'm trying to do is figure out if this is a room/placement issue and if not, if it is an issue with the speakers themselves.
This is a 1m farfield measurement of two speakers in the same room. Room placement is similar. The better looking curve is from a small two way 6.5" bookshelf speaker I made. The red curve is from the transmission line floorstander I fixed up (recapped, but mostly a cosmetic makeover). The floorstanders have a somewhat odd design. The best I can describe them as is that they're a 2.5 way speaker. One 6.5 woofer with coaxial tweeter on the inner baffle, and another 8" woofer with coax tweeter on the outer baffle. They are ported on the front.
I've moved them along the wall they are placed on, but the bass response doesn't seem to change to my ear. (i.e kick drums are anemic due to the bass nulls, I don't need my mic to tell me that much.) I've moved around the room and the only places where the bass picks up to my ear are along the walls of the room and in the corners.
I have the baby brother speakers of the floorstanders (with a similar design but slightly smaller) and they do not appear to have this problem in this room.
Any suggestions?
An externally hosted image should be here but it was not working when we last tested it.
This is a 1m farfield measurement of two speakers in the same room. Room placement is similar. The better looking curve is from a small two way 6.5" bookshelf speaker I made. The red curve is from the transmission line floorstander I fixed up (recapped, but mostly a cosmetic makeover). The floorstanders have a somewhat odd design. The best I can describe them as is that they're a 2.5 way speaker. One 6.5 woofer with coaxial tweeter on the inner baffle, and another 8" woofer with coax tweeter on the outer baffle. They are ported on the front.
An externally hosted image should be here but it was not working when we last tested it.
I've moved them along the wall they are placed on, but the bass response doesn't seem to change to my ear. (i.e kick drums are anemic due to the bass nulls, I don't need my mic to tell me that much.) I've moved around the room and the only places where the bass picks up to my ear are along the walls of the room and in the corners.
I have the baby brother speakers of the floorstanders (with a similar design but slightly smaller) and they do not appear to have this problem in this room.
Any suggestions?
Cant be room modes when another speaker doesnt suffer from the same problem at the same location. I am not too familiar with TL speakers, but since they have some common ground with tapped horns, those nulls could be the speaker.
Apart from that i am amazed by the smooth bass response of the small speaker. My room is +/- 15 dB without EQ and multiple sub approach.
Apart from that i am amazed by the smooth bass response of the small speaker. My room is +/- 15 dB without EQ and multiple sub approach.
That's interesting to know. So it might actually be characteristic of the speaker's design. Why is that? Does increased stuffing density move the nulls or does it actually lessen them?
Is it normal for the nulls to be octaves at a time though? Seems excessive to me.
mav, the bookshelf speakers were measured, modeled, and designed in this very room. Maybe that's why they integrate so well?
Is it normal for the nulls to be octaves at a time though? Seems excessive to me.
mav, the bookshelf speakers were measured, modeled, and designed in this very room. Maybe that's why they integrate so well?
So can anything be done to alleviate the standing waves?
The speaker features a folded transmission line. It travels from the chamber behind the woofers down to the bottom of the speaker and then back up to the ports. The only damping material in the speaker is located in the chamber behind the woofers and down the transmission line until the point where it begins to fold back up. From that point on, there is no damping material. This is a good half of the TL without stuffing.
Would added damping material here help with the standing waves?
The speaker features a folded transmission line. It travels from the chamber behind the woofers down to the bottom of the speaker and then back up to the ports. The only damping material in the speaker is located in the chamber behind the woofers and down the transmission line until the point where it begins to fold back up. From that point on, there is no damping material. This is a good half of the TL without stuffing.
Would added damping material here help with the standing waves?
With respect, I'm not sure I'd agree that nulls are always present in TLs. Badly designed ones, certainly.
Anyway, as Earl points out, what you've got there are classic line harmonic modes. The problem with TLs is that the term itself has become a millstone -very few cabinets that are called TLs actually are transmission lines, and many of the characteristics claimed for them are incorrect.
In this case, you can increase the stuffing density to help absorb the unwanted line harmonics, but unfortunately, it will also start to absorb the cabinet 1st mode (fundamental resonance) too, weaking the LF gain. Technically, this will move it closer to actually being an acoustic transmission line, which are essentially extremely well damped, non-resonant cabinets, designed to provide the flattest possible impedance to the amplifier (the electrical TL is where the name comes from). But that's at odds with what many people think are TLs and therefore their reasons for using them. Definitions -they've always caused problems. If you want a compromise solution, I'd try stuffing the first half or 2/3 of the line with ~0.75lbs ft^3 of dacron or similar, which won't affect the fundamental as much & then adjust to suit yourself from there.
Anyway, as Earl points out, what you've got there are classic line harmonic modes. The problem with TLs is that the term itself has become a millstone -very few cabinets that are called TLs actually are transmission lines, and many of the characteristics claimed for them are incorrect.
In this case, you can increase the stuffing density to help absorb the unwanted line harmonics, but unfortunately, it will also start to absorb the cabinet 1st mode (fundamental resonance) too, weaking the LF gain. Technically, this will move it closer to actually being an acoustic transmission line, which are essentially extremely well damped, non-resonant cabinets, designed to provide the flattest possible impedance to the amplifier (the electrical TL is where the name comes from). But that's at odds with what many people think are TLs and therefore their reasons for using them. Definitions -they've always caused problems.
If you want a compromise solution, I'd try stuffing the first half or 2/3 of the line with ~0.75lbs ft^3 of dacron or similar, which won't affect the fundamental as much & then adjust to suit yourself from there.Well I opened one of the speakers and applied some damping material in it. All I had on hand was about 1/2 lb. of 'acousta-stuf' and 2 old sweaters.
Here's a plot of the same speaker with and without the added damping. The black line is the speaker with the added damping. The higher frequency differences are due to the mic not being at exactly the same angle relative to the tweeter.
Doesn't seem like much changed.
I suppose there's not much else that can be done?
Here's a plot of the same speaker with and without the added damping. The black line is the speaker with the added damping. The higher frequency differences are due to the mic not being at exactly the same angle relative to the tweeter.
Doesn't seem like much changed.
An externally hosted image should be here but it was not working when we last tested it.
I suppose there's not much else that can be done?
Even though it made it worse, here's a plot with a ton of stuffing added just for kicks.
I'll have to consider if I want to spend any more money on literal fluff. Are there cheap options for damping material? For reference 5lb's of acousta-stuf runs $35 + shipping at partsexpress. Haven't checked what madisound has yet.
An externally hosted image should be here but it was not working when we last tested it.
I'll have to consider if I want to spend any more money on literal fluff. Are there cheap options for damping material? For reference 5lb's of acousta-stuf runs $35 + shipping at partsexpress. Haven't checked what madisound has yet.
Get thee down to the craft shop or a place that sells cheap bedding & buy some hollow-fiber pillow stuffing, or some cheap pillows with the same & rip out what you require.
Looks to me like a duff design with too small a Vp. Still, worth trying. Without knowing the driver specs., & exact cabinet / line dimensions, we're flying blind anyway.
Looks to me like a duff design with too small a Vp. Still, worth trying. Without knowing the driver specs., & exact cabinet / line dimensions, we're flying blind anyway.
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