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Author Topic: TOPS FOR LABS  (Read 44959 times)

Wayne Parham

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Actual verses expected performance
« Reply #20 on: November 17, 2006, 11:28:11 am »


Mike {AB} Butler wrote on Fri, 17 November 2006 07:29

My own issue is that many of the folded bass horn designs of today seem to violate all of the traditional wisdom of the mouth size equating with the lowest frequency the horn will reproduce.. before the driver unloads from the horn and turns into a direct radiator.. and Fitz' designs seem to do this all the time.. so I'm left wondering just what the benefit is to all the labyrinthine mazes created. Sure, you can put a nozzle on a hose to get more pressure.. but at some point, it has to unload.
Anyway, we are hardly in disagreement. I just find it amazing that so many people are building and using these things..
Best Regards,


I have never seen a traditional folded basshorn that couldn't be modeled very accurately with Hornresp, including Fitzmaurice's Tubas.  Under 1/4λ, the horn rapidly unloads, and this can be seen in the distortion chart.  If the mouth is too small, the horn loading is peaky, so excursion and efficiency, and similarly amplitude response, phase response and distortion are peaky too.  See the measurements from the 2005 Prosound Shootout, for example.

The smaller a basshorn mouth is made, the more the horn acts like a transmission line, just like one might expect.  The driver will be loaded at 1/4λ of the length of the horn, so if long enough, it will load down to low frequency.  But if the mouth is small, there will be ripples in response as loading is only in narrow bands at multiples of 1/4λ.  This is transmisison line behavior, and can be modeled with Hornresp or Martin King's spreadsheets.

As an aside, Martin King has done great work analyzing systems like these, and can predict where in the line a driver should be placed to take advantage of the 1/4λ boost while minimizing notches from standing wave harmonics higher up.  That's why driver placement in a transmission line is important, and why it is rarely placed at the end of the pipe.  This is the underlying philosophy that Danley has used in his recent "tapped" basshorns, which are really transmission lines designed using the same approach.

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Wayne Parham
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peter.golde

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Re: TOPS FOR LABS
« Reply #21 on: November 17, 2006, 12:04:51 pm »

The "labyrinthine mazes created" have a few advantages in an undersized bass horn, the load on the load on the driver lowers it Fs allowing deeper bass response, also the box acts as a tuned pipe reinforcing bass response, and the path doesn't allow distortion created by the driver to be heard. Danley's horns suffer the same problems, though he has figured out how to load the driver better by moving it down the throat chamber and tapping into the horn further down. The closer you come to the true required mouth area to support the frequencies, the better the horns perform. Compare spl of Fitz Titan-48 vs the Danley TH-115 and you will see the Danley sub is louder down lower due to the tapped configuration, but the more subs you pile on, the less of an advantage that is. Listening test are another thing altogether, but a lot of Fitz builders are hearing what their bass guitar is actually capable of sounding like for the first time, thats why all the smiles and "labyrinthine mazes created".  


"But you do have to admit, this site has done more to bring business to his site than we as purists would like to admit."

I don't agree with this statement, for a lot of reasons. His site is more grass roots, from the musicians (tired of getting ripped off, and showing an interest in building their own stuff) on up. 99% of the folks on this forum wouldn't take his designs if you built them and handed them for free, due to the fact they are DIY and as of yet still to be proven in the industry I don't think anyone at PSW, other than a musicians building and running their own PA will even consider this stuff.

Reading forums at speakerplans, it seems Jens has had a hard on for BF for a while, he is entitled to his opinion, he is probably a purist as well.
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Dave Rickard

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Re: TOPS FOR LABS
« Reply #22 on: November 17, 2006, 12:05:53 pm »

Jens Droessler wrote on Fri, 17 November 2006 08:33

But good mids, THAT'S what a top is about. The music comes from the mids, not from some trickery to fool the ear into hearing them. OF COURSE the 'fake' mids seem somehow to sound good, the hearing does a good job on that, but it is not the real deal.

Jens, I intend this post without antagonism.  I say this because it's hard to know on a web page. Smile

I agree that it's all about the sound.  Wouldn't "fake mids" show up as some sort of anomaly when measured?  Do you see that anomaly in the graphs?  IMO, this is what good measurements should show.  What are your thoughts?

On the other hand, if it really is all about the sound, why does it matter if the ear is fooled or not.  "If it sounds good, it is good" (Bob Lee's sig).  Is there a situation where a user would be failed by this trickery?

So you know where I'm coming from, I have not heard Bill's tops, but I have a pair of Tuba30 slims, and intend to build more.

Dave
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Dave
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peter.golde

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Re: TOPS FOR LABS
« Reply #23 on: November 17, 2006, 01:53:52 pm »

DAVID_L_PERRY wrote on Fri, 17 November 2006 05:04


Regarding the DR cab, all I can say is that I did what I feel to be a pretty detailed assesment of the DR with the tools at hand before putting anymore time building another box.  Myself and two other PA providers where present during all the tests.  I was not willing to put tha vast amount of time into another build if the cab sounded just ok.

Cheers, Dave


Perhaps you were experiencing a mass auditory hallucination induced through trickery waves from across the pond emanating from a small town in New Hampshire Laughing
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Antone Atmarama Bajor

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Re: TOPS FOR LABS
« Reply #24 on: November 17, 2006, 07:24:59 pm »

     I think Jens is concerned that there maybe time domain smearing due to the reflection/diffraction of the upper range of the mid bass horn.

     I think he is concerned about the wavelength to bend relationship at the high cut of the horn.

    There will be smearing and resonance of some sort in that range.  Though there is smearing introduced in any HF horn at the High end of its response due to Radical Diffraction slots (in attempt to improve coverage) and, multiple path lengths around the phase plug.

    In my thoughts Its midband smearing is probably about as bad as most of the compression driver horn hi end smearing.  But I could be wrong.

    In my opinion less smear is always better.

    The one thing that I dislike the most about the DR's is that the HF horn configurations are not conducive to good polar response.  The Higher in frequency they go the wilder the lobing will be.  I'm sure you could really hear some comb filtering if you play some pink through them and walk the horizontal.

    I've noticed that some people still think if you simply take a bunch of drivers and close couple them that they will receive extra gain.  That is only partially true,  and is fairly spacing, frequency and frequency range dependant.

Antone-
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peter.golde

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Re: TOPS FOR LABS
« Reply #25 on: November 17, 2006, 07:42:28 pm »

Antone Atmarama Bajor wrote on Fri, 17 November 2006 19:24

     The one thing that I dislike the most about the DR's is that the HF horn configurations are not conducive to good polar response.  The Higher in frequency they go the wilder the lobing will be.  I'm sure you could really hear some comb filtering if you play some pink through them and walk the horizontal.
Antone-


I agree that with the cross firing tweeter array, the hf response will be wider than mf, and polars will not be perfect.
I think Jens is holding these speakers to a standard that a lot of commercial designs won't hold up to, and do not even provide a response curve let alone 3d waterfall charts.
I will try the pink walk and listen carefully.
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Jens Droessler

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Re: TOPS FOR LABS
« Reply #26 on: November 17, 2006, 11:23:56 pm »

@ Dave Rickard: GOOD measurement a.k.a. useful measurements will show that, I'm sure about that. A simple frequency response plot won't show it. A such measurement can only show energy and nothing about the time domain integrity.

The problem about the trickery is that the original signal is not played back as supposed. The ear might not as easily be fooled with room reflections of the tops output for example.  You could compare it with me-too-products in the snack industry (you know, they look a it like the original brand stuff, taste a bit like the original...): It's simply not the real deal.

@ peter.golde:
Quote:

and the path doesn't allow distortion created by the driver to be heard

And that is why? Simple, because the path and its folds/bends create a lowpass filtering out distortions above the usable range (as well as signal!). I didn't calculate this to the finest details but I think that BF puts in speakers with a 'natural' output increase towards higher frequencies, so it almost equals out frequency response-wise. That won't help on the time domain....

It has nothing to do with comparison. Most things the professional manufacturers throw at the market has at least the 'potential' to work like intended (sometimes it actually does, sometimes the drivers don't do what they should, sometimes the crossover is bad... but the enclosure itself could do it). And that is what's basically missing with the DRs. If I see for example a straight horn with a 10" or a 12", see that the throat and mouth are of appropriate size, there is no reason for me to believe that this horn won't play quite good up to 800 or 1000Hz (without phaseplug). If I see bass horn folded two or three times with a path length >2m I know it won't play nice above ~100Hz. In other words I, like every designer who did his homework, can tell by the enclosure design if the physical properties of the enclosure actually allow what the designer intended. That's not arrogant or ignorant, it's simply the basic knowledge a speaker designers should have about physics. And noone can do 'magic' beyond physics. You can argue and discuss with ME, but not with physics.

So if I had to decide for a manufactured or a DIY speaker, I would never go for the DRs in their original form. I think most professionally manufactured speakers (from a real brand, not chinese cheapo cabs or lowest MI grade stuff) are a much better choice than the BF designs. But you are right that I would buy or build most of them either for myself. OTOH I have no problems to recommend a design which would work for some requested applications even if I wouldn't build them myself. The DRs in their original design are simply a no-go for me.


With a tightly packed piezo crossfire array you will barely hear lobes/combfiltering, because the distance between the drivers is too small. This doesn't change the fact that these lobes/combfiltering issues are present. They always are if you use multiple drivers in a freq range >> lambda half of the drivers distance to each other (unless you can make them stop overlapping in coverage). Physics again.
But with bigger horns the distance from center to center is bigger, so combfiltering will be an issue. Of course if the HF drivers are on top of each other you won't notice anything in the horizontal plane, so you'd have to move to the top and away from it to get it.

Antone Atmarama Bajor wrote on Sat, 18 November 2006 00:24

     I think Jens is concerned that there maybe time domain smearing due to the reflection/diffraction of the upper range of the mid bass horn.

     I think he is concerned about the wavelength to bend relationship at the high cut of the horn.
That's definitely part of the problem.

   
Quote:

Though there is smearing introduced in any HF horn at the High end of its response due to Radical Diffraction slots (in attempt to improve coverage)
That's why I like HF horns without or with 'a little bit of' diffraction slot. I know they tend to beam on HF, but that's in most cases not as bad as it sounds...

   
Quote:

 In my thoughts Its midband smearing is probably about as bad as most of the compression driver horn hi end smearing.  But I could be wrong.
It's worse, because there is less precision in building them and there is no sound at all going straight through the horn. Every bit of sound has to be 'bent around the corner'.

 
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Dave Rickard

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Re: TOPS FOR LABS
« Reply #27 on: November 18, 2006, 11:01:38 am »

Interesting thoughts, Jens.

Thanks.

Dave
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Dave
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"If you don't have good stuff at each end of the signal chain, (mics and speakers) what you use in between is just turd polish."--Dave Dermont

peter.golde

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Re: TOPS FOR LABS
« Reply #28 on: November 18, 2006, 01:03:52 pm »

I am not sure what physical laws you are referring to but the DR250 does actually have good output in the midrange, pretty clean and non offensive to my ears. It works, even though you claim it is impossible, oh well, can't can't please all the pysicists all the time. Razz
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Jens Droessler

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Re: TOPS FOR LABS
« Reply #29 on: November 18, 2006, 03:13:33 pm »

@ peter.golde: Have you tried shutting off the HF drivers or lowpass the DR (to get rid of the masking effects of the HF) and compared the output with another good hornloaded top lowpassed equally? I guess not...

@ Dave Rickard: Another thought would be about the masking effects. Imagine sweeping with a noth filter through the range, searching for a nasty peak of a specific instrument for example. You stop right above where the HF driver starts working and you notice that the sound changes more than you'd expect. Why? Because the masking breaks down...

Same thing goes for MP3s for example. They work with masking too to save bandwidth (but the big difference is that this happens dynamically, so if the encoder decides that masking frequency range X won't work, it won't mask it...). Now especially people with some 'problematic' hearing (like being deaf to a specific frequency range, say 7-9kHz for example) could tell MP3s from the original by nearly 100% precision, whereas NOONE with 'fully working ears' could even get close to these results (a public test of a German magazine)...
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