DIY Waveguide loudspeaker kit

[poseidonsvoice]

A visit with Earl Geddes - Review of Summa 15's

Hi fellas,

Wife and kids were out the door visiting friends down south so I called up Earl and asked if I could audition his speakers yesterday. For what its worth, here are some speakers I have heard and respect:

Linkwitz Orions++, right at Siegfried's house near San Francisco
NaO II dipoles designed by John Kreskovsky
GR Research OB5's and OB7's

Earl was an excellent host, brought me down to his well treated home theatre room (about 15 feet wide and 30 feet deep with a 10 ft ceiling) where the Summa 15's were in the corners behind curtains and turned in 45 degrees to avoid the side walls. There were also 3 subwoofers setup in the room (all bandpass design!). The Summa's are about 98dB/2.83V/m efficient in full space. His electronics are extremely simple and plain by audiophile standards. A PC and Toshiba CD player as sources, a Pioneer Digital Receiver (100 watts/channel), zip cord wire and zip cord interconnects. Nothing amazing here at all.

First CD we played were various tracks from Bela Fleck & Flecktones, a Live CD.

Wow! We were playing at peaks of 100 dB from my listening position (roughly centered about 10 feet away from the speakers). No compression. Tight clean bass. Performers were in the room. Imaging was very stable over a horizontal axis of an entire sofa. Music appeared from a complete black void.

The most open midrange I have ever heard. This includes the dipole systems I have listed above. There was no real part of the frequency response that was drawing attention, although I was continuously amazed by how clean the bass was and how delineated it was. Treble was just there, never drawing attention to itself but never lacking either.

Image body, intensity were all there. Small instruments sounded small. Close miked, sounded close miked.

Neutral is a great way to describe it.

Next we listened to some cuts from Diana Krall. Her voice was so compelling that she really sounded she was right up there on stage, playing for you. A personal treat if you will.

Next, Geddes played a cut from a DVD from Phantom of the Opera. Dynamics in spades. Everything was released unshackled. And just when you thought the music may lose control, it doesn't. How quickly the Summas start and stop is uncanny. I believe this is as much a product of speaker design as it is the room. The final cut was my favorite. Eagles DVD Live! The guitar solos were electrifying, even soul searching.

I am beginning to understand why some audiophiles say they listen at 80 or 85dB. I think its because of compression. When I auditioned the Orions and NaO II's, I was a little hesitant to crank it up. With the Summas, the music just gets louder but never, ever loses control.

In any case I suggest anybody within a spitting distance of Michigan to call up Earl and give these an audition. Even if you own fancy schmancy loudspeakers, I mean TAD 3 ways, Avante Garde, etc...give it a listen. It will challenge every audiophile belief you have had. Earl was kind enough to let me have one of his books, "Premium Home Theater." I have been leafing through the book and found one paragraph regarding 'subjectivism' that I found quite eye opening (page 249):

"When dealing with subjectively oriented AV issues,I prefer to deal with the science (facts), whenever possible, and not Audio Tarot. My wife coined this wonderful phrase after she first came into contact with the audio community that I work in. She has a background in experimental psychology and knows how easily subjective opinions can be swayed by external factors. She noted that a large amount of audio folklore is accepted by its practitioners purely on faith,i.e. there is no way to either prove or disprove these beliefs. Basically, audio,in these aspects, is a religion. Mankind has always had trouble reconciling facts with their fundamental belief system when the two come into conflict (to wit Galileo). The facts are often suppressed in order to perpetuate the established belief system. The practitioners of Audio Tarot will always prefer to suppress those facts that contradict their established beliefs."

Trust me just like many of you, I am part of the (gulp) Audio Tarot as well. Will I give up some of my fancy schmancy equipment? Probably not terribly soon. But boy was this system an awakening.

What did it teach me? The speaker/room equation is the achilles heal to audiophile aural enlightenment. Until you've solved that issue, you (I mean me) will be in this perpetual audiophile merry-go-round of exchanging equipment, spending thousands of dollars, etc...

Fix that problem first. For if a loudspeaker/room with Pioneer electronics can blast me into an eargasmic orbit, what more do I want? Better question is what more can I have? Will better electronics make a better listening experience? Perhaps. However, the Summa 15's really take you 90% there, so I'm not surprised that a simple receiver can take you so far ahead of everybody else.

A few pictures to follow tomorrow.

Till then,

Anand.

 

[tinitus]

Nice read!

But dont let Earls amp fool you
He has written a lot about it ... its very carefully selected

 

[gedlee]

Anand

Thank you for your kind review. I should point out that we have never met before and that all I asked of you was that you post your impressions. I had no doubt what they would be.

And yes, the loudspeaker room interface is the key, To ignore this is to ignore the essence of audio.

(Well not zip cord interconnects, Radio Shack )

Thanks again. It was a pleasure meeting you.

 

[publius]

What a FANTASTIC review.

Thanks Anand!

Do you know what frequency the Summas were crossed to the subs?

 

[publius]

Congrats E.G. These Summas MUST be something very special.

 

[gedlee]

What a FANTASTIC review.

Thanks Anand!

Do you know what frequency the Summas were crossed to the subs?

I don't "cross" to the subs. The subs all overlap with various frequency responses.

 

[poseidonsvoice]

As Gedde said, he has 3 subs, all bandpass design, with different frequency response overlap. First time I have ever heard a bandpass system done right.

In due time, I think Gedde will reveal the details of these bandpass subwoofers as future kits perhaps.

In the meantime, I figure let the Nathan10 run full range and have a low pass set for your sub. Best to do it with measurements. Most subs nowadays whether DIY or commercial are either sealed, ported or dipole based anyway.

Anand.

 

[publius]

I don't "cross" to the subs. The subs all overlap with various frequency responses.

So, the rolloff on the mains is sufficiently steep (>=12db/octave)to protect them from any sub-bass in the L-R channels? Then you send a combined L-R channel sum to each subwoofer where you have high and low pass filters and you use each of the three subwoofers to cover a different frequency range? Do you do this to reduce the burden on each subwoofer or to "shuffle" the room modes (or some other reason)?

How would this work for people who are running a home theater? THX assumes second order rolloff at 80hz in the mains to which it adds an additional second order filter to create a net fourth order rolloff. THX rolls off the subwoofer channel at fourth order at 80hz for a smooth transition.

 

[gedlee]

So, the rolloff on the mains is sufficiently steep (>=12db/octave)to protect them from any sub-bass in the L-R channels? Then you send a combined L-R channel sum to each subwoofer where you have high and low pass filters and you use each of the three subwoofers to cover a different frequency range? Do you do this to reduce the burden on each subwoofer or to "shuffle" the room modes (or some other reason)?

How would this work for people who are running a home theater? THX assumes second order rolloff at 80hz in the mains to which it adds an additional second order filter to create a net fourth order rolloff. THX rolls off the subwoofer channel at fourth order at 80hz for a smooth transition.

Each sub does not cover a different frequency range. One does, in my case, but that not necessary. The 15's go down to about 50 Hz, monopoles with a natural rolloff. There is one very LF sub 25 - 50 Hz. one broadband sub 50-100 and another 50 - 150. So at about 50 Hz there are five sources, one below that, four to about 100 Hz, three to 150 Hz and then just the mains.

The subs feed from the LFE channel on the receiver.

My room is a home theater.

THX is not the gospel in audio.

 

[Salas]

Congrats E.G. These Summas MUST be something very special.

Bravo Dr. Geddes. Congrats from me too.

 

[publius]

Each sub does not cover a different frequency range. One does, in my case, but that not necessary. The 15's go down to about 50 Hz, monopoles with a natural rolloff. There is one very LF sub 25 - 50 Hz. one broadband sub 50-100 and another 50 - 150. So at about 50 Hz there are five sources, one below that, four to about 100 Hz, three to 150 Hz and then just the mains.

The subs feed from the LFE channel on the receiver.

My room is a home theater.

THX is not the gospel in audio.

This is the most screwed up system that I have ever heard, but you are E.G. and I am nobody, so I feel compelled to try to understand why you have put it together this way.

Question 1: If you are not crossing any content to your subs and your mains roll off at 50hz, how do you hear content below 50hz that is in the music? I know there is not much content below 50hz, but still, your system would appear to be incapable of reproducing the bottom octave on a piano and I am guessing that is not right.

Question 2: The Dolby LFE channel spec has a brickwall at 120hz, so there is no content above 120hz for the sub that is crossed at 150hz. What is the purpose of the low pass filter on this sub?

Question 3: Given that deep bass requires much more power and displaced air than upper bass, why do you have two subs (and two speakers) covering the upper bass and only one unit covering the deep bass? Seems like the sub that is not playing any content in the LFE channel from 120hz and up could be better deployed assisting below 50 hz.

I am completely baffled by your configuration, I admit that I don't understand your approach, and I apologize if my questions are poor questions.

 

[gedlee]

Question 1: You do misunderstand, there is a sub specifically tuned to do 25-50 Hz. Reread my post.

Question 2: This is not true. The LP filter in the LFE is tunable and on my receiver it can go up to 150 Hz.

Question 3: I use multiple subs to smooth out the LF mode problems in a small room. I have more than enough SPL capability for any situation and in fact the biggest problem with this approach is getting too much low end. Balancing all this out correctly is not trivial and I posted that point elsewhere when we talked about multuiple subs in the "cardiod bass" thread. You should go read that one.

There is no "one right way" to set the subs paramters (gain, filters, phase). You take the subs that you have and set them up in the room with measurements. If you have enough subs you will usually get something satisfactory. Too few subs and you will always be disappointed.

 

[poseidonsvoice]

There is no "one right way" to set the subs paramters (gain, filters, phase). You take the subs that you have and set them up in the room with measurements. If you have enough subs you will usually get something satisfactory. Too few subs and you will always be disappointed.

Thank you. I wholeheartedly agree.

Anand.

 

[limono]

Seems like this going to be SOTA speaker kit and I only wished dear DR provided plans for proper woofer to compliment satelites.
Somehow I'm not convinced in matching some Costco Booomer to
Summas 80-100 Hz.
Regards, L

 

[Patrick Bateman]

Question 3: I use multiple subs to smooth out the LF mode problems in a small room. I have more than enough SPL capability for any situation and in fact the biggest problem with this approach is getting too much low end. Balancing all this out correctly is not trivial and I posted that point elsewhere when we talked about multuiple subs in the "cardiod bass" thread. You should go read that one.

Here's the thread: http://www.diyaudio.com/forums/showthread.php?s=&threadid=121590&perpage=25&pagenumber=1

 

[gedlee]

Seems like this going to be SOTA speaker kit and I only wished dear DR provided plans for proper woofer to compliment satelites.
Somehow I'm not convinced in matching some Costco Booomer to
Summas 80-100 Hz.
Regards, L

Summas are 50Hz and up. I will supply plans for my subs thats not a problem, but I won't make them as kits since thats just a waste of my time considering the economics.

 

[Patrick Bateman]

Seems like this going to be SOTA speaker kit and I only wished dear DR provided plans for proper woofer to compliment satelites.
Somehow I'm not convinced in matching some Costco Booomer to
Summas 80-100 Hz.
Regards, L

Could someone explain to me the advantage of using a boutique subwoofer instead of a Costco subwoofer?

You might argue that the Costco sub will have lousy power handling. If that's the case, buy four of them. That increases your SPL limit by 12db.

You might argue the Costco sub isn't as handsome as an audiophile sub. That may be true, so hide it! No one wants to look at three subs anyways.

You might argue that the Costco sub has lousy frequency response. While some cheap subs are designed with a hump in the midbass, there are plenty of inexpensive powered subs that measure well and have predictable crossovers and EQ built in.

Last but not least is price. Spending $750 on three Costco subs and pairing them with a $1200 kit seams reasonable. Spending $3000 on three boutique subs seems unnecessary with $1200 mains.

I've always been mystified by the use of exotic subwoofers in the home. In car audio, they make a lot of sense, because box size is king in mobile audio. Also, car subs function in "pressure mode" due to the small dimensions of the cabin. Exotic subs also make sense in pro audio, where dozens of subs are in play and each is being fed thousands of watts.

In the home, not so much.

 

[limono]

Well , sorry but by Summa I meant 10" dIY version which is 80-100 Hz and needs a woofer not subwoofer to be a regular full range speaker. Maybe it's time to name the kit ??I agree that for HT the quality of subwoofer is of no importance and most everything will do. Sorry to add a confusion to already confused thread .
Regards, L

 

[publius]

Question 1: You do misunderstand, there is a sub specifically tuned to do 25-50 Hz. Reread my post.

I have read and re-read your posts in this thread. You have a sub tuned to do 25-50hz. BUT, you said that this sub is receiving the LFE channel source. The *LFE channel* is different from the *subwoofer channel*.

Since you have said in a previous post that you "do not cross to the subs", then the only content that your subwoofer array is receiving is that which is contained in the LFE channel. If you are listening to a two-channel source, such as a piano recording, there will be no content in the LFE channel and in your system you will hear not hear the bottom octave of the piano (~27-51hz).

Question 2: This is not true. The LP filter in the LFE is tunable and on my receiver it can go up to 150 Hz.

I think that you are confused. The LFE channel and the subwoofer channel are two separate sources of content though they are summed and fed through the same cable to the subwoofer. In a previous post you said that you "do not cross to subs". This indicates that you are running your main speakers full range and that no content is being shifted from the main channels to the subwoofers. In such a system, the subwoofer(s) will receive only the LFE (aka ".1") content. Dolby has a low-pass filter for LFE content at 120hz. There is no slope. All content above 120hz is just filtered out. So nothing is gained by setting the LFE LP filter on your receiver to 150hz.

Question 3: I use multiple subs to smooth out the LF mode problems in a small room. I have more than enough SPL capability for any situation and in fact the biggest problem with this approach is getting too much low end. Balancing all this out correctly is not trivial and I posted that point elsewhere when we talked about multuiple subs in the "cardiod bass" thread. You should go read that one.

Thank you for pointing out the cardiod bass thread. I will be sure to read through.

It remains an open question though how you can have "too much lowend" when you are only powering your subs with the LFE content channel.

Perhaps what you are really doing is:

1. running your main speakers full range (and letting their natural rolloff below 50hz protect them from overdrive)
2. using your receiver to SUM content from your main speaker channels below 150hz to the LFE channel, creating what is called a subwoofer channel (which is distinct from an LFE channel).
3. using this subwoofer channel as the input for each of your subwoofers, which you then adjust for frequency and level.

If this is the case, then it would all seem to make some sense.

There is no "one right way" to set the subs paramters (gain, filters, phase). You take the subs that you have and set them up in the room with measurements. If you have enough subs you will usually get something satisfactory. Too few subs and you will always be disappointed.

Yes. Parametric EQ can also help as well. Do you have parametric EQ in your subwoofers? If not, how do you deal with room modes?

[EDIT: I see (in another thread) that structural methods are used to tame modes. Nice.]

 

[MJL21193]

I agree that for HT the quality of subwoofer is of no importance and most everything will do. Sorry to add a confusion to already confused thread .
Regards, L

HT is the ONLY place a subwoofer matters. You don't need one for music, providing you have real main speakers.

Good quality subs beat one note boom boxes and over eq'ed, over driven poop producers any day.